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SOILS
SOILS
THEIR
FORMATION, PROPERTIES, COMPOSITION, AND
RELATIONS TO CLIMATE AND PLANT GROWTH
IN THE
HUMID AND ARID REGIONS
BY
E. W. HILGARD, Ph.D., LL.D.,
PROFESSOR OF AGRICULTURE IN THE UNIVERSITY OF CALIFORNIA, AND DIRECTOR
OF THE CALIFORNIA AGRICULTURAL EXPERIMENT STATION
gtew
THE MACMILLAN COMPANY
LONDON: MACMILLAN & CO., Ltd.
1921
Copyright, 1906,
By THE MACMILLAN COMPANY.
Set up and electrotyped. Published July, 1906.
Norfajoob breast
Berwick & Smith Co., Norwood, Mass., U.S.A.
SUMMARY OF CHAPTERS.
i. Origin and Formation or Soils.
Introduction.
Chapter
I.
««
II.
<<
III.
««
IV.
V.
Physical Processes of Soil Formation.
Chemical Processes of Soil Formation.
Chief Soil-forming Minerals.
The Various Rocks as Soil-Formers.
Minor Mineral Ingredients of Soils. Mineral Fertilizers.
Minerals Injurious to Agriculture.
2. Physics of Soils.
Chapter
VI.
<«
VII.
tt
VIII.
«
IX.
a
X.
a
XI.
u
XII.
a
XIII.
a
XIV.
a
XV.
a
XVI.
a
XVII.
Physical Composition of Soils.
Density, Pore Space, and Volume-Weight of Soils.
Soil and Subsoil ; Causes and Processes of Differen¬
tiation ; Humus.
Soil and Subsoil ; Organisms Influencing Soil-Con¬
ditions. Bacteria.
Soil and Subsoil in their Relations to Vegetation.
Water of Soils ; Hygroscopic and Capillary Moisture.
Water of Soils ; Surface, Hydrostatic, and Ground-
water ; Percolation.
Water of Soils ; Conservation and Regulation of Soil
Moisture. Irrigation.
Absorption by Soils of Solids from Solutions. Absorp¬
tion of Gases. The Air of Soils.
Colors of Soils.
Climate.
Relations of Soils and Plant-Growth to Heat.
3-
Chemistry of Soils.
Chapter XVIII.
“ XIX.
“ XX.
“ XXI.
“ XXII.
“ XXIII.
Physico-Chemical Investigation of Soils in Relation
to Crop Production.
Analysis of Virgin Soils by Extraction with Strong
Acids, and its Interpretation.
Soils of Arid and Humid Regions.
Soils of Arid and Humid Regions continued.
Alkali Soils, their Nature and Composition.
Utilization and Reclamation of Alkali Lands.
iii
IV
SUMMARY OF CHAPTERS.
4. Soies and Native Vegetation.
Chapter XXIV. Recognition of the Character of Soils from their
Native Vegetation. Mississippi.
44 XXV. Recognition of the Character of Soils from their
Native Vegetation. United States at large, Europe.
14 XXVI. Vegetation of Saline and Alkali Lands.
TABLE OF CONTENTS.
Preface . xxiii
Introduction, xxix. — Definition of Soils, xxix. — Elements Constituting the
Earth’s Crust, xxix. — Average Quantitative Composition of the Earth's
Crust, xxix. — Clarke’s Table, xxx. — Oxids Constitute Earth’s Crust, xxx.
— Elements Important to Agriculture ; Table, xxxi. — The Volatile Part
of Plants, xxxii.
CHAPTER I.
Agencies of Soie Formation, i. — i. Physical Agencies , i.— Effects of
Heat and Cold on Rocks, i. — Unequal Expansion of Crystals, 2. — Cleav¬
age of Rocks, 3. — Effects of Freezing Water, 3. — Glaciers ; Figure, 3. —
Glacier Pdour and Mud, 4. — “ Green” and “White” Rivers, 4. —
Moraines, 5. — Action of Flowing Water, 5. — Enormous Result of Cor-
rasion and Denudation, 6. — Effects of Winds, 8. — Dunes, 8. — Sand and
Dust Storms in Deserts, Continental Plateaus and Plains, 8. — Loess of
China, 9. — Migration of Gobi Lakes, 9. — Classification of Soils , 10. —
Their Physical Constituents, 10. — Sedentary or Residual Soils, 11.—
Colluvial Soils, 12. — Alluvial Soils. Diagram, 12. — Character of these
Soil Classes, 13. — Richness of Flood-plain and Delta Lands, 14. — Low¬
ering of the Land Surface by Soil Formation, 15.
CHAPTER II.
Chemicae Processes of Soie Formation, 16. — 2. Chemical Disintegra¬
tions or Decomposition, 16. — Ingredients of the Atmosphere, 16. — Effects
of Water ; of Carbonic Acid, 17. — Carbonated water a universal solvent,
17. — Amnionic carbonate, effect on silicates, 18. — Action of oxygen ; on
ferrous compounds, 18. — Action of Plants and their Remnants , 19. — A.
Mechanical ; Force of Root Penetration, 19. — B. Chemical ; Action of
Root Secretions, 19. — Bacterial Action, 20. — Humification, 20. — Causes
Influencing Chemical Action and Decomposition , 21. — Heat and Mois¬
ture, 21. — Influence of Rainfall on Soil-Formation, 22.— Leaching of the
Land, 22. — Residual Soils, 22. — Drain Waters ; River Waters. Tables
of Solid Contents, 22. — Amount of Dissolved Matters Carried into the
Sea ; Amount of Sediment, 24. — Sea Water, Composition of ; Waters of
Land-locked Lakes, 25. — Results of Insufficient Rainfall ; Alkali
Lands, 28.
v
VI
CONTENTS.
CHAPTER III.
Rock- and Soil-Forming Minerals, 29. — Quartz, quartzite, jasper, horn-
stone, flint, 29.— Solubility of silica in water ; absorption by plants, 30.
— Silicate Minerals, 31. — Feldspars, tlieir Kaolinization, 31. — Formation
of Clays, 33. — Hornblende or Amphibole, Pyroxene or Augite, 33. —
Their Weathering and its Products, 33. — Mica, Muscovite and Biotite,
35. — Hydromica, Chlorite, 35. — Talc and Serpentine ; “ Soapstone ”, 36.
The Zeolites ; Exchange of Bases in Solutions, 36. — Importance in
Soils, in Rocks, 38. — Calcite, Marble, Limestones ; their Origin, 39. —
Impure Limestones as Soil-Formers, 40. — Caves, Sinkholes, Stalactites,
Tufa, 41. — Dolomite ; Magnesian Limestones as Soil-Formers, 42. —
Selenite, Gypsum, Land Plaster ; Agricultural Uses, 42. — Iron Spar,
Limonite, Hematite, Magnetite, 44. — Reduction of Ferric Hydrate in
Ill-drained Soils, 45.
CHAPTER IV.
The Various Rocks as Soil-Formers, 47.— General Classification, 47. —
Sedimentary, Metamorphic, Eruptive, 47. — Sedimentary Rocks ; Lime¬
stones, Sandstones, Clays, Claystones, Shales, 47. — Metamorphic Rocks :
Formed from Sedimentary, 48. — Igneous or Eruptive Rocks, Basic and
Acidic, 49. — Generalities Regarding Soils Derived from Various Rocks ,
49. — Variations in Rocks themselves. Accessory Minerals, 50. —
Granites ; not always True to Name ; Sierra Granites, 51. — Gneiss. Mica-
schist, 51. — Diorites, 51. — Diabases, 51. — Eruptive Rocks ; Glassy ones
Weather Slowly ; Basaltic Oxidize Rapidly, 52. — Red Soils of Hawaii,
Pacific Northwest, 52. — Trachyte Soils ; Light-colored, rich in Potash.
Rhyolites generally make Poor Soils, 53. — Sedimentary Rocks , 53. —
Limestones, 53. — “ A Limestone Country is a Rich Country,” 53. —
Residual Limestone Soils; from ‘‘Rotten Limestone” of Mississippi;
Table, 54. — Shrinkage of Surface, 55. — Sandstone Soils, 55. — Vary
According to Cement, and Nature of Sand, 55. — Calcareous, Dolomitic,
Ferruginous, Zeolitic, 56 — Clay-sandstones, Claystones, 57. — Natural
Clays , 57. — Great Variety, Enumeration and Definition, 58. — Colors of
Clays, 58, — Colloidal Clay , Nature and Properties, 59. — Plasticity ;
Kaolinite Non-plastic, 59. — Causes of Plasticity, 60. — Separation of
Colloidal Clay, its Properties, 61. — Effects of Alkali Carbonates on
Clay, 62.
CHAPTER V.
The Minor Mineral Ingredients of Soils ; Mineral Fertilizers, 63.
— Minerals Injurious to Agriculture, 63. — Minerals used as Fertilizers ,
63. — Apatite; Phosphorites of the U. S., Antilles, Africa, Europe, 63. —
Phosphatic Iron Ores, “ Thomas Slag,” 64. — Animal Bones ; Composi¬
tion and ’Agricultural Use, 64 — Vivianite, Dufrenite, 65. — Chile Salt¬
peter, 66. Occurrence in Nevada, California, 66. — Origin of Nitrate
Deposits, 67. — Intensity of Nitrification in Arid Climates, 68. — Potash
Minerals, 68. — Feldspars not Available, 68. — Depletion of Lands by
Manufacture of Potashes, 69. — Discovery of Stassfurt Salts, 69. — Origin
CONTENTS.
Vll
of these Deposits, 70. — Nature of the Salts, 71. — Kainit, 71. — Potash
Salts in Alkali Soils, 72. — Farmyard or Stable Manure ; Chemical
Composition, Table, 72. — Efficacy largely due to Physical Effects in
Soils, 73. — Green-manuring a Substitute for Stable Manure, 74. — Ap¬
plication of Stable Manure in Humid and Arid Climates, 74. — Mine¬
rals Unessential or Injurious to Soils , 75. — Iron Pyrites, Sulphur Balls,
75. Occurrence and Recognition. Remedies 75. — Halite or Common
Salt, 76. — Recognition of Common Salt, 76. — Mirabilite or Glauber’s
Salt ; in Alkali Rands ; not very Injurious, 77 — Trona or Urao ; Car¬
bonate of Soda, “Black Alkali,” 77. Injury Caused in Soils, 78. —
Epsomite or Epsom Salt, 78. — Borax, 79. — Soluble Salts in Irrigation
Waters, 79.
CHAPTER VI.
Physical Composition of Soils, 83.— Clay as a Soil Ingredient, 83. —
Amounts of Colloidal Clay in Soils, 84. — Influence of Fine Powders on
Plasticity, 85. — Rock Powder; Sand, Silt and Dust, 86. — Weathering
in Humid and Arid Regions , 86. — Sands of the Humid Regions, 86. —
Sands of Arid Regions not Sterile, 86. — Physical Analysis of Soils , 88.
— Use of Sieves. Limits, 88. — Use of Water for Separating Finest Grain-
Sizes, 89. — Elimination of Clay by Subsidence and Centrifugal Method,
Hydraulic Elutriation, 90. — Schbne’s Instrument, 90. — Churn Elutriator
with Cylindrical Tube, 91. — Figures of Same, 91. — Yoder’s Centrifugal
Elutriator, 92. — Number of Grain-sizes Desirable, 93, — Results of such
Analyses, 93. — Physical Composition Corresponding to Popular Desig¬
nations of Soil-Quality. Table, 96. — Number of soil-grains per Gram,
99. — Surface Offered by various Grain-sizes ,99. — Influence of the several
Grain-sizes on Soil Texture, 100. — Ferric Hydrate, its Effects on Clay,
100. — Other Substances, 101. — Aluminic Hydrate, 101. — Influence of
Granular Sediments upon the Tilling Qualities of Soils, 102. — “ Phy¬
sical ” Hardpan, 103. — Putty Soils, 103. — Dust Soils of Washington ;
Table, Physical Analyses of Fine Earth, 104. — Slow Penetration of
Water, 105. — Effects of Coarse Sand, 105.
CHAPTER VII.
Density, Pore-space and Volume-weight of Soils, 107. — Density of
Soil Minerals, 107. — No Great Variation, 107. — Volume-weight most Im¬
portant, 107. — Weight per Acre-foot, 107. — Air-space in Dry Natural
Soils. Figure, 108. — May be Filled with Water, 108. — Effects of Tillage.
Figures, 109. — Crumb or Flocculated Structure ; Cements, 109. — How
Nature Tills, 111. — Soils of the Arid Regions; do not Crust, 112. —
Changes of Soil-Volume in Wetting and Drying, 112. — Extent of
Shrinkage, 113. — Expansion and Contraction of Heavy Clay Soils.
Figure, 113. — Contraction of Alkali Soils on Wetting, 114. — “Hog
Wallows,” 114. — Physical Analyses of such Soils. Table, 115. — Crumb¬
ling of Calcareous Clay Soils on Drying, 116. — Yazoo Bottom, Port
Hudson Bluff, 116. — Loamy and Sandy Soils, 117. — Formation of Sur¬
face Crusts, Physical Analyses, 117. — Effects of Frost on the Soil ;
Heaving; Ice-flowers, 118.
Vlll
CONTENTS.
CHAPTER VIII.
Soil, AND SUBSOIL ; CAUSES AND PROCESSES OF DiEFERENTATIATION
Humus, 120.— Soil and Subsoil ill-defined, 120. — The Organic and Or*
ganized Constituents of Soils , 120. — Humus in the Surface Soil, 120. —
Soil and Subsoil ; Causes of their Differentiation, 121. — Ulmin Sub¬
stances or Sour Humus, 122. — Sour Soils, 122. — Cultivation Induces
Acidity, 123. — Humin Substances, 123. — Porosity of Humus, 124. — -
Physical and Chemical Nature of the Humus Substances. Table, 124.
— Chemical Nature, 125. — Progressive Changes and Effect on Soils, 126.
— The Phases of Humification, Wood to Anthracite ; Table, 127. —
Amounts of Humus and Coal formed from Vegetable Matter, 128. —
Figure, From Port Hudson Bluff, 128. — Conditions of Normal Humifi¬
cation, 129. — Eremacausis in the Arid Regions, 129. — Black Earth of
Russia ; Kosticheff’s Table, 130. — Fosses of Humus from Cultivation
and Fallowing, 131. — Estimation of Humus in Soils; Unreliability of
Combustion Methods, 132. — Grandeau Method, “ Mature Noire,” 132. —
Amounts of Humus in Soils, 133. — Humates and Ulmates, 134. — Mineral
Ingredients in the Humus, 134. — Functions of the Unhumified Organic
Matter, 135. — The Nitrogen Content of Humus, 135. — Table for Arid
and Humid Soils, 136. — Decrease of Nitrogen Content in Humus with
Depth, 138. — Table, Russian River Soils, 139. — Influence of the Original
Material upon the Composition of Humus, 139. — Table of Snyder, 139. —
Effect of Humus in rendering Mineral Plant Food Available, 140.
CHAPTER IX.
Soil and Subsoil Continued ) , 142. — Organisms Influencing Soil-Condi¬
tions. Bacteria, 142. — Micro-organisms of the Soil. Bacteria, Moulds,
Ferments, 142. — Numbers at Various Depths, given by Early Observers,
142. — Investigations of Hohl ; Mayo and Kinsley. Tables, 143. — Multi¬
plication of the Bacteria, 144. — Aerobic and Anaerobic Bacteria, 144. —
Food Materials required, 145. — Functions of the Bacteria, 145. — Nitrify¬
ing Bacteria. Figures, 146. — Conditions of their Activity. Table, 146.
— Effects of Aeration and Reduction, 147. — Unhumified Organic Matter
does not Nitrify, 148 — Unhumified Vegetable Matter, Functionsin Soils,
148. — Denitrifying Bacteria. Figures, 148. — Ammonia-forming Bacte¬
ria. Figures, 149. — Alinit, 149. — Effects of Bacterial Life on Physical
Soil Conditions, 149. — Root-bacteria, or Rhizobia of Legumes, 150. —
Figures of Root Excrescences and Corresponding Bacteroids, 152. —
Varieties of Forms, 154. — Mode of Infection, 154. — Cultural Results,
155. — Table Showing Increased Production by Soil Inoculation, 155. —
Other Nitrogen-absorbing Bacteria, 156. — Distribution of Plumus in the
Surface Soil, 157. — Fungi, Moulds and Algae, 157. — Animal Agencies —
Earthworms, Insects, Burrowing Quadrupeds, 158.
CHAPTER X.
Soil and Subsoil in their Relations to Vegetation, 161. — Physical
Effects of the Percolation of Surface Waters, 161. — Chemical Effects ;
Calcareous Subsoils and Hardpans, 161. — “Rawness” of Subsoils in
CONTENTS.
IX
Humid Climates, 162. — Subsoils in the Arid Region, 163. — Deep Plow¬
ing and Subsoiling in the Arid Region ; examples of Plant growth
on Subsoils, 164. — Resistance to Drought, 167. — Root System in the
Humid Region, 168. Figures of the Root System of an Eastern (Wis¬
consin) Fruit Tree, 168. — Comparison of Root Develop)nent in the
Arid and Hamid Regions , 169. — Prune on Peach Root, 169. — Adapta¬
tion of Humid Species to Arid Conditions, 169. — Grapes, 170. — Ken¬
tucky and California Maize, 175, 176. — Hops, 172. — Deep Rooting in the
Arid Region, 174. — Goose Foot and Figwort, 174. — Importance oj
Proper Substrata in the Arid Region , 175. — Injury from Impervious
Substrata. Figure, 177. — Faulty Lands of California. Figure, 178. —
Shattering of Dense Substrata by Dynamite, 181. — Leachy Substrata,
182. — “Going-back” of Orchards, 182. — Hardpan, Formation and
Varieties, 183. — Nature of the Hardpan Cements, 184. — Bog Ore, Moor-
bedpan and Ortstein ; Calcareous and Alkali Hardpan, 184. — The Causes
of Hardpan, 185. — “ Plowsole,” 186. — Marly Substrata, 186.
CHAPTER XI.
The Water of Soies. Hygroscopic and Capillary Moisture, 188. —
General Properties, 188.— Physical Factors of Water compared with
other Substances. Table, 188. — Capillarity or Surface Tension, 189.—
Heat Relations, 190. — Density, 190. —Specific Heat and its Effects, 190.
Ice, 191. — Vaporization, 191. — Solvent Power, 191. — Water-requirements
of Growing Plants, 192. — Evaporation from Plants in Different Climates,
192. — Relations between Evaporation and Plant Growth. Table, 193. — ■
Fortier’s Experiments. Figure, 194. — Different Conditions of Soil
Water, 196. — Hygroscopic Water in Soils ; Table , 196. — Influence of
Temperature and Air-Saturation, 197. — Utility of Hygroscopic Water
to Plant Growth, 199. — Mayer’s Experiments, 200. — Summary, 200.—
Capillary Water , 201. — Ascent of Water in Soil-Columns. Table, 202.
— Ascent in Uniform Sediments. Figure, 204. — Maximum and Minimum
Water-holding Power, 207. — Capillary Water held at different Heights
in a Soil Column. Table, 208. — Capillary Action in Moist Soils, 210. —
Proportion of Soil Moisture Available to Plants, 21 1. — Moisture Require¬
ments of Crops in the Arid Region, 21 1. — Tables of Observations in
California, 214.
CHAPTER XII.
Surface, Hydrostatic and Ground Water. Percolation, 215. —
Amount of Rainfall, 215. — Natural Disposition of Rain Water, 216. —
The Surface Runoff, 216. — Wasliing-away and Gullying in the Cotton
States, 217. — Injury in the Arid Regions, 219. — Deforestation, 219. —
Prevention of Injury to Cultivated Lands from Excessive Runoff, 220.
Absorption and Movements of Water in Soils, 221. — Determination of
Rate of Percolation. Diagram, 221. — Summary, 224. — Influence of Var¬
iety of Grain-sizes, 224. — Table of King’s Experiments, 224. — Percola¬
tion in Natural Soils. Figure, 225. — Ground or Bottom Water, 227. —
Lysimeters, Surface of Ground Water ; Variations, 227. — Depth of
X
CONTENTS.
Ground Water most Favorable to Crops, 228. — Moisture Supplied by Tap
Roots, 229. — Reserve of Capillary Water, 229. — Injurious Rise of Bottom
Water from Irrigation, 230. — Consequences of the Swamping of Irrigated
Lands ; Prevention, 231. — Permanent Injury to certain Lands, 231. —
Reduction of Sulfates, 232. — Ferruginous or Red Lands, 233.
CHAPTER XIII.
Water of Soils ; The Regulation and Conservation of Soil Moist¬
ure ; Irrigation, 234. — Loosening of the Surface, 234. — Effects of
Underdrains ; Rain on Clay Soils, 235. — Winter Irrigation, 236. —
Methods of Irrigation, 236. — Surface Sprinkling, 237. — Flooding, 237.
— Check Flooding. Furrow Irrigation, 237, 238. — Figure Showing Pen¬
etration, 239. — Figure Showing Faulty Irrigation in Sandy Lands, 239.
— Distance between Furrows and Ditches, 241. — Irrigation by Lateral
Seepage, 242. — Basin Irrigation of Trees and Vines ; Advantages and
Objections, 243. — Irrigation from Underground Pipes, 245. — Quality of
Irrigation Waters, 246. — Saline Waters; Figures of Effects on Orange
Trees, 246. — Limits of Salinity, 246. — Mode of Using Saline Irrigation
Waters ; Apparent Paradox, 249. — Use of Drainage Waters for Irrig¬
ation, 250. — “ Black Alkali ” Waters, 250. — Variations in the Salinity
of Deep and Shallow Wells, 250. — Muddy Waters, 251. — The Duty of
Irrigation Waters, 251. — Causes of Losses, 252. — Loss by Percolation.
Figure, 252. — Evaporation, 253. — Tables Showing same at California
Stations, 255. — Evaporation in Different Climates ; Table, 255. — Evapo¬
ration from Reservoirs and Ditches, 257. — Prevention of Evaporation ;
Protective Surface Layer, 257. — Illustrations of Effects of Tillage ;
Table, 258. — Evaporation through Roots and Leaves, 262. — Weeds
waste Moisture, 264. — Distribution of Moisture in Soils as Affected by
Vegetation, 264. — Forests and Steppes, 265. — Eucalyptus for Drying
Wet Lands, 265. — Mulching; Effects on Temperature and Moisture, 266.
CHAPTER XIV.
Absorption by Soils of Solids from Solutions. Absorption of Gases,
Air of Soils, 267. — Absorption of Solids, 267. — Desalation, 267. — Deco-
lorization, 267. — Complexity of Soil-Action, Physical and Chemical,
268. — “ Purifying” Action of Soils on Gases and Liquids, 269. — Waste
of Fertilizers, 269. — Variation of Absorptive Power, 270. — Generalities
Regarding Chemical Action and Exchange, 270. — Drain Waters, 271. —
Distinctions not Absolute, 272. — Absorption or Condensatioyi of Gases
by the Soil, 272. — Proof of Presence of Carbonic and Ammonia Gases in
Soils, 273. — Absorption of Gases by Dry Soils. P'igure, 274. — Composi¬
tion of Gases Absorbed by Various Bodies from the Air. Table, 275.
— Discussion of Table, 277. — The Air of Soils , 279. — Empty Space in
Dry Soils, 279. — Functions of Air in Soils, 279. — Insufficient and Ex¬
cessive Aeration, 280. — Composition of the Free Air of Soils, 280. — Car¬
bonic Dioxid vs. Oxygen, 281. — Relation to Bacterial and Fungous
Activity, 281. — Putrefactive Processes, 282.
CONTENTS.
xi
CHAPTER XV.
Conors of Soils, 283. — Black Soils, 283. — “ Red ” Soils, 284. — Origin of
Red Tints, 285. — White Soils, 285. — Differences in Arid and Humid
Regions, 286. — White Alkali Spots, 286.
CHAPTER XVI.
Climate, 287. — Heat and Moisture Control Climates, 287. — Climatic Con¬
ditions, 287. — Ascertainment and Presentation of Temperature Condi¬
tions , 288. — Annual Mean not a Good Criterion, 289.— Extremes of
Temperature are most Important, 289. — Seasonal and Monthly Means,
289. — Daily Variations, 290. — Rainfall , 290. — Annual Rainfall not
a Good Criterion, 290. Distribution most Important, 290. — Winds, 291.
— Heat the Cause of Winds, 291. — Trade Winds, 291. — Cyclones, 292.
Influence of the Topography on Winds ; Rains to Windward of
Mountains, Arid Climates to Leeward, 293.— General Distribution of
Rainfall on the Globe. Figure, 294. — Ocean Currents, 295. — The Gulf
Stream, 295. — The Japan Stream, 296. — Contrast of Climates of N. W.
America, 297. — Continental, Coast and Insular Climates, 297. — Subtropic.
Arid Belts, 298. — Utilization of the Arid Belts, 299.
CHAPTER XVII.
Relations of Soils and Plant Growth to Heat, 301.— Temperature of
Soils, 301. — Water Exerts Controlling Influence, 301. — Cold and Warm
Rains, 302. — Solar Radiation, 302. — Penetration of the Sun’s Heat into
the Soil, 302. — Change of Temperature with Depth, 303. — Surface Con¬
ditions that Influence Soil Temperature, 303. — Heat of High and Low
Intensity, 304. — Reflection vs. Dispersion of Heat, 304. — Influence of
Vegetation, and of Mulches, 305. — Influence of the Nature of the Soil-
Material, 306. — Influence of Evaporation, 307. — Formation of Dew, 307.
— Dew rarely adds Moisture, 308. — Dew within the Soil, 308. — Plant
Development under Different Temperature-Conditions, 309. — Germin¬
ation of Seeds ; Optimum Temperature for each Kind, 309. — Artificial
Heating of Soils ; by Steam Pipes or Water, 310.
CHAPTER XVIII.
Physico-chemical Investigation of Soils in Relation to Crop
Production, 313. — Historical Review of Soil Investigation, 313. —
Popular Forecasts of Soil Values, 313. — Cogency of Conclusions Based
upon Native Growth, 314. — Ecological Studies, 315. — Early Soil Surveys
of Kentucky, Arkansas and Mississippi, 316. — Investigation of Cultivated
Soils, 316. — Change of Views, 317. — Advantages for Soil Study offered
by Virgin Lands, 318. — Practical Utility of Soil Analysis ; Permanent
Value vs. Immediate Productiveness, 319. — Physical and Chemical
Conditions of Plant Growth, 319. — Condition of Plant-food Ingredients,
in the Soil, 319. — Water-soluble, Reserve, and Insoluble Part, 320. —
Hydrous or “ Zeolitic ” Silicates, 321. — Recognition of the Prominent
Chemical Character of Soils, 322. — Acidity, Neutrality and Alkalinity,
xii
CONTENTS.
322. — Chemical Analysis, 323. — Water-Soluble and Acid-Soluble Por¬
tions most Important, 324. — We cannot Imitate Plant-root Action, 324
Cultural Experience the Final Test, 324. — Analysis of Cultivated Soils,
325. — Methods of Analysis, 325. — The Solvent Action of Water upon
Soils, 327. — Extraction of Soils with Pure Water, 327. — Continuous
Solubility of Soil Ingredients. Tables, 328. — King’s Results. Table,
329. — Composition and Analysis of Janesville Roam, 331. — Solubility of
Soil Phosphates in Water, 332. — Practical Conclusions from Water
Extraction, 332. — Ascertainment of the Immediate Plant-food Require¬
ments of Cultivated Soils by Physiological Tests, 333. — Plot Tests ;
their uncertainties. Diagram, 334. — Crop Analysis as a Test of Soil
Character, 337. — Chemical Tests of immediately Available Plant Food ;
Dyer’s Method, 338.
CHAPTER XIX.
Analysis of Virgin Soils by Extraction with Strong Acids and its
Interpretation, 340. — Loughridge’s Investigation on Strength of Acid
and Time of Digestion, 340. — Writer's Method , 342. — Virgin Soils with
High Plant-food Percentages are always Productive. Table, 343. — Dis¬
cussion of Table, 343. — Low Plant-food Percentages not always Indica¬
tion of Sterility, 346. — What are “Adequate” Percentages of Potash,
Lime, Phosphoric Acid and Nitrogen, 347. — Soil-Dilution Experiments,
347. — Table of Compositions, 350. — Figures of Plants and their Root-
Development, 351. — Limitation of Root Action, 351. — Lowest Limits of
Plant-food Percentages and Productiveness Found in Virgin Soils, 353.
Limits of Adequacy of the Several Plant-food Percentages in Virgin
Soils, 353. — Lime a Dominant Factor in Interpretation, 353. — Potash,
354. — Phosphoric Acid, 355. — Action of Lime and Ferric Oxid, 355. —
Table of Hawaiian Ferruginous Soils, 356. — Unavailability of Ferric
Phosphate, 356. — Nitrogen, 357. — Nitrification of the Organic Matter
of the Soil, 358. — Analysis of Soil from the Ten-Acre Tract at Chino,
Cal., 358. — Experiments and Results; Matiere Noire the Only Guide,
360. — What are Adequate Nitrogen Percentages in the Humus ? 360. —
Table of Humus and Nitrogen-Content of Californian and Hawaiian
Soils, 361. — Confirmatory Experiment. Figure, 362. — Data for Nitrogen-
Adequacy. Table, 363. — Influence of Lime upon Soil Fertility, 365. —
“ A Lime Country is a Rich Country,” 365. — Effects of High Lime-Con¬
tent in Soils, 365. — Table of Soils showing Low Phosphoric Acid with
High and Low Lime-Content, 366. — What are Adequate Lime-percent¬
ages ? Differ for Light and Heavy Soils, 367. — Table Showing Need of
High Lime Percentages in Heavy Clay Soils, 368. — European Standards
for Land Estimates, 369. — Maercker’s Table, 369.
CHAPTER XX.
Soils of the Arid and Humid Regions, 371. — Composition of Good
Medium Soils ; Table, 371. — Criteria of Lands of the Two Regions, 371.
— Tables of Soil-Composition in Both Regions, 372. — Soils of the Humid
Region governed by Time, 374. — Soils of the Arid Region Governed
CONTENTS.
xiii
by Moisture, 374. — Lime and Magnesia Uniformly High in Arid Soils,
Despite Scarcity of Limestone Formations ; Potash also High, 374. —
General Comparison of the Soils of the Arid and Temperate Humid
Regions , 375. — Basis of Same, 376. — New Mexico and Analysis of Soil,
376. — General Table, 377. — Discussion of the Table, 378. — Lime ; Sum¬
mary of Physical and Chemical Effects of Lime Carbonate in Soils, 378.
Discussion of Summary, 379. — Magnesia : Its role in Plant Nutrition,
381. — Manganese : Its Stimulant Action, 383. — The “ Insoluble Res¬
idue” ox Silicates, 384. — Soluble Silica and Alumina , 384. — Analysis
of Clay from Soil, 385. — Difference in Sand of Arid and Humid Regions.
Table, 386. — Soluble Silica or Hydrous Silicates more Abundant in Arid
than in Humid Soils, 388. — Aluminic Hydrate. Table, 389. — Retention
of Soluble Silica in Alkali Soils, 391. — Ferric Hydrate, 392. — Phosphoric
Acid , 392. — Sulfuric Acid, 394. — Potash and Soda, Retained more in
Arid Soils, 394. — Arid Soils Rich in Potash, 395. — Humus, Low in Arid
Soils, but Rich in Nitrogen, 396. — The Transition Region, 397.
CHAPTER XXI.
SoiivS of Arid and Humid Regions Continued, 398. — Soils of the Tropics,
398. — Humus in Tropical Soils, 399. — Investigations of Tropical Soils,
401. — Soils of Samoa and Kamerun, 402.— Soils of the Samoan Islands,
403. — Soils of Kamerun, 404. — Soils of Madagascar , 405. — Soils of
India, 410. — The Indo-Gangetic Plain, 41 1. — The Brahmaputra Al¬
luvium in Assam, 413. — Black Soils of Deccan, 414. — Red Soils of the
Madras Region, 415. — Laterite Soils, 416. — Influence of Aridity upon
Civilization, 417. — Preference of Ancient Civilizations for Arid Coun¬
tries, 417. — Irrigation Necessitates Co-operation, 419. — High and Per¬
manent Productiveness of Arid Soils Induces Permanence of Civil
Organization, 419.
CHAPTER XXII.
Aekali Soies, their Nature and Composition, 422. — Alkali Lands vs.
Seashore Lands, 422. — Origin, 422. — Deficient Rainfall, 423. — Predom¬
inant Salts, 423. — Geographical Distribution, 424. — Their Utilization of
World-wide Importance, 424. — Repellent Aspect, Plate, 424. — Effects of
Alkali upon Culture Plants. Figures of Apricot Trees, 426. — Nature of
the Injury, External and Internal, 426. — Effects of Irrigation, 428. —
Leaky Irrigation Ditches, 429. — Surface and Substrata of Alkali Lands,
429. — Vertical Distribution of the Salts in Alkali Soils, 429. — How
Native Plants Live, 430. — Figures of various Phases of Reclamation,
431. — Upward Translocation from Irrigation, 433. — Distribution of Al¬
kali in Sandy Lands, 433. In Heavier Lands, 436. — Salton Basin or
Colorado Delta, 436. — Diagram of Alkali Distribution in Same, 438. —
Horizontal Distribution of Alkali Salts in Arid Lands, 439. — Alkali in
Hill Lands, 439. — Usar Lands of India, 440. — “ Szek ” Lands of Hungary,
440. — Alkali Lands of Turkestan, 441. — Composition and Quantity of
Salts Present, 441. — Nutritive Salts, 441. — Black and White Alkali.
Tables, 442. — Estimation of Total Alkali in Land, 444. — Composition of
XIV
CONTENTS.
Alkali Soils as a whole. Tables, 445. — Presence of much Carbonate of
Soda, 448. — Cross Section of an Alkali Spot. Table, 448. — Reactions
between the Carbonates and Sulfates of Earths and Alkalies. Figure of
Curve, 449. — Inverse Ratios of Alkali Sulfates and Carbonates. Dia¬
grams, 451. — Exceptional Conditions, 453. — Summary of Conclusions,
453.
CHAPTER XXIII.
Utilization and Reclamation of Alkali Land, 455. — Alkali-resistant
Crops, 455. — Counteracting Evaporation, 455. — Turning-under of Sur¬
face Alkali, 456. — Shading, 457. — Neutralizing Black Alkali, 457. —
Removing the Salts from the Soils, 458. — Scraping off, 458. — Teaching-
Down. Figure, 459. — Underdrainage, the Final and Universal Remedy
for Alkali, 460. — Possible Injury to Land by Excessive Leaching, 462.
— Difficulty in Draining “ Black ” Alkali Land, 462. — Swamping of Al¬
kali Land, 463. — Removal of Alkali Salts by Certain Crops, 463. —
Tolerance of Alkali by Culture Plants, 463. — Relative Injuriousness of
the several Salts. Effects on Sugar Beets, 464. — Table of Tolerances ;
Comments on same, 467. — Saltbushes and Native Grasses. Australian
Saltbushes, 469. — Modiola ; Native and Cultivated Grasses, 469. — Other
Herbaceous Crops, 472. — Legumes, 472. — Mustard Family, 473. — Sun¬
flower Family, 473. — Root Crops, 474. — Stem Crops, 475. — Textile Plants,
475. — Shrubs and Trees, 475. — Vine, Olive, Date, Citrus Trees. Deci¬
duous Orchard Trees. Timber and Shade Trees, 475. — Inducements
toward the Reclamation of Alkali Lands, 481. — Wheat on Reclaimed
Land at Tulare ; Figure, 482. — Need of Constant Vigilance, 484.
CHAPTER XXIV.
The Recognition of Soil Character from the Native Vegetation ;
Mississippi, 487. — Climatic and Soil Conditions, 487. — Natural Vegeta¬
tion the Basis of Land Values in the United States, 488. — Investigation
of Causes Governing Distribution of Native Vegetation, 488. — Investiga¬
tions in Mississippi, 489. — Vegetative Belts in Northern Mississippi,
490. — Sketch Map of Same, with Tabulation of Lime Content and
Native Vegetation, 490. — Lime Apparently a Governing Factor, 492. —
Soil Belts in Southern Mississippi, 493. — Vegetative and Soil Features
of Coast Belts. Diagram, 495. — Table of Plant-Food percentages and
Native Growth, 496. — Definition of Calcareous Soils, 496. — Differences
in the Form and Development of Trees, 498. — Forms of the Post Oak.
Figures, 498. — F'orms of the Black Jack Oak. Figures, 500. — Charac¬
teristic Forms of other Oaks, 502. — Sturdy Growth on Calcareous Lauds,
502. — Growth of Cotton, 503. — Lime Favors Fruiting, and compact
Growth, 504. — Physical vs. Chemical Causes of Vegetative Features,
505. — Lowland Tree Growth, 506. — Contrast between “ First” and
“Second” Bottoms, 506. — Tree Growth of the First Bottoms. The
Cypress, 507. — Figures of Swamp and Upland Cypress, 508. — Other
Lowland Trees, 509. — General Forecasts of Soil Quality in Forest Lands,
509-
CONTENTS.
xv
CHAPTER XXV.
Recognition of the Character of Soies from their Native Vege¬
tation. United States at Large, Europe, 51 i. — Forest Growths
outside of Mississippi ; Alabama, Louisiana, Western Tennessee, and
Western Kentucky, 511. — North Central States East of the Mississippi
River, 513. — Upland and Lowland Vegetation in the Arid and Humid
Region, 515. — Forms of Deciduous Trees in the Arid Region, 516.—-
Tall Growth of Conifers, 517. — Herbaceous Plants as Soil Indicators,
517. — Leguminous Plants Usually Indicate Rich or Calcareous Lands,
518. — European Observations and Views on Plant. Distribution and its
Controlling Causes, 519. — Composition of Pine Ashes on Calcareous and
Noil-calcareous Lands. Table, 520.— Calciphile, Calcifuge, and Indifferent
Plants, 521. — Silicopliile vs. Calciphile Flora, 523. — What is a Calcareous
Soil ? 524. — Predominance of Calcareous P'ormations in Europe, 525.
CHAPTER XXVI.
The Vegetation of Saeine and Aekaei Lands, 527.— Marine Saline
Lands , 527. — General Character of Saline Vegetation, 527. — Structural
and Functional Differences Caused by Saline Solutions, 528. — Absorp¬
tion of the Salts. Table, 529. — Injury from the Various Salts, 531. —
Reclamation of Marine Saline Lands for Culture, 533. — The Vegetation
of Alkali Lands , 534. — Reclaimable and Irreclaimable Alkali Lands
as Distinguished by their Natural Vegetation, 534. — Plants Indicating
Irreclaimable Lands, 535. — Tussock Grass ; Bushy Samphire ; Dwarf
Samphire ; Saltwort ; Greasewood ; Alkali Heath ; Cressa ; Salt Grass,
536. — Relative Tolerances of the different Species ; Table, 549.
APPENDICES.
A. — Directions for taking Soil Samples, issued by the California Experiment
Station, 553.
B. — Summary Directions for Soil-Examination in the Field or Farm, 556.
C. — Short Approximate Methods of Chemical Soil-Examination Used at the
California Experiment Station, 560.
General Index, 565.
Index of Authors referred to, 591.
PREFACE.
This volume was originally designed to serve as a text-
and reference book for the students attending the writer’s
course on soils, given annually at the University of California,
who complained of their inability to find in any connected treat¬
ise a large portion of the subject matter brought before them.
As all these students had preliminary training in physics, chem¬
istry and botany, no introductory chapters on these general
subjects were necessary or contemplated; the more so as good
elementary treatises embracing the needful preparation are
now numerous.
As time progressed, however, outside demands for a book
embodying the writer’s soil studies in the humid and arid
regions, especially the latter, became so numerous and pressing
that the scope of the work has gradually been much enlarged
to conform to these demands; and this, rather than com¬
pleteness of detail, when such detail can be found well given
elsewhere, has been the guide in the necessary condensa¬
tion of the whole. To give the entire subject matter full eluci¬
dation, would require several more volumes.
It may not be unnecessary to explain at the outset why and
how this treatise deviates in many respects from previous pub¬
lications on the same general topic. From boyhood up it has
fallen to the writer’s lot to be almost continuously in more or
less direct contact with the conditions and requirements of
newly settled regions, as well as with those hardly yet invaded
even by the pioneer farmer; where the question of cultural
adaptation was yet undetermined or wholly in the dark. Being
during his active life constantly called upon in his official capa¬
city to give information and advice to pioneer farmers or in¬
tending settlers in regard to the merits and adaptations of virgin
soils, the writer’s attention was naturally and forcibly directed
toward soil investigation as a possible means of determining,
beforehand, the general prospects and special features of agri-
XVI 1
PREFACE.
xviii
culture in regions where actual experience was either non-exis¬
tent or very brief and partial. In the pursuit of these studies
he has been favored by exceptional opportunities, extending
over a varied climatic area reaching on the south from the Gulf
of Mexico to the Ohio, across to the Pacific coast, and to
British Columbia on the north. That a systematic investiga¬
tion of soils over so large an area, covering both humid and
arid regions, should lead to some unexpected and novel re¬
sults, is but natural ; and it is the discussion of these results in
connection with those obtained elsewhere, and with some of
the prevailing views based thereon, that must serve as the
justification for the present addition to an already well-
stocked branch of literature.
From the very beginning of the scientific study of agricul¬
ture, the investigation of soils with a view to the a priori de¬
termination of their adaptation, permanent value, and best
means of cultural improvement, has formed the subject of
continuous effort. It is not easy to imagine a subject of
higher direct importance to the physical welfare of mankind,
whose very existence depends on the yearly returns drawn by
cultural labor from the soil.
It is certainly remarkable that after all this long-continued
effort, even the fundamental principles, and still more the
methods by which the object in view is to be attained, are
still so far in dispute that a unification of opinion in this re¬
spect is not yet in view ; and a return to pure empiricism is from
time to time brought forward to cut the Gordian knot.
While this state of things is primarily due to the intrinsic
complexity and difficulty of the subject itself, it has unquestion¬
ably been materially aggravated by accidental, partly historic
conditions. Foremost among these is the fact that until within
recent times, soil studies have borne almost entirely on lands
long cultivated and in most cases fertilized : thus changing
them from their natural condition to a more or less artificial
one, which obscures the natural relations of each soil to vege¬
tation.
The importance of these relations is obvious, both from the
theoretical and from the practical standpoint. From the
former, it is clear that the native vegetation represents, within
the climatic limits of the regional flora, the result of a secular
PREFACE.
xix
process of adaptation of plants to climates and soils, by nat¬
ural selection and the survival of the fittest. The natural
floras and sylvas are thus the expression of secular, or rather,
millennial experience, which if rightly interpreted must convey
to the cultivator of the soil the same information that other¬
wise he must acquire by long and costly personal experience.
The general correctness of this axiom is almost self-evi¬
dent ; it is explicitly recognized in the universal practice of
settlers in new regions, of selecting lands in accordance with
the character of the forest growth thereon ; it is even legally
recognized by the valuation of lands upon the same basis, for
purposes of assessment, as is practiced in a number of States.
The accuracy with which experienced farmers judge of the
quality of timbered lands by their forest growth, has justly
excited the wonder and envy of agricultural investigators,
whose researches, based upon incomplete theoretical assump¬
tions, failed to convey to them any such practical insight. It
was doubtless this state of the case that led a distinguished
writer on agriculture to remark, nearly half a century ago,
that he “ would rather trust an old farmer for his judgment
of land than the best chemist alive.” 1
It is certainly true that mere physico-chemical analyses, un¬
assisted by other data, will frequently lead to a wholly errone¬
ous estimate of a soil’s agricultural value, when applied to cul¬
tivated lands. But the matter assumes a very different as¬
pect when, with the natural vegetation and the corresponding
cultural experience as guides, we seek for the factors upon
which the observed natural selection of plants depends, by
the physical and chemical examination of the respective soils.
It is further obvious that, these factors being once known,
we shall be justified in applying them to those cases in which
the guiding mark of native vegetation is absent, as the result
of causes that have not materially altered the natural condition
of the soil.
It is probable that, had agricultural science been first de¬
veloped in regions where the external conditions permitted
the carrying-out of such a course of investigation, instead of
in the abnormally temperate, even and humid climate of middle
1 “ The Soil Analyses of the Geological Surveys of Kentucky and Arkansas.”
S. W. Johnson in AM. JOUR. SCI., Sept. 1861.
XX
PREFACE.
Europe, with its long-cropped, worn fields, and very predomi¬
nantly calcareous soils, the present condition of this science
might differ not immaterially from that actually existing. As
a matter of fact, it has attained its present state under very
disadvantageous external conditions, which frequently necessi¬
tated a recourse to highly complex and laborious methods and
artificial appliances, for the establishment and maintenance
of the conditions which elsewhere might have been found
abundantly realized in nature; thus permitting, by the multi¬
plication of observations over extended and widely varied areas,
the elimination and control of accidental errors of experiment
and observation.
Just as in historical geology the subdivisions of formations
observed and accepted in Europe formed for many years a pro-
crustean bed upon which the facts observed elsewhere had to
be stretched, so in the domain of soil physics and chemistry,
and even in vegetable physiology, the observations made in the
really exceptional climates and soils of middle Western
Europe, have often erroneously been construed as constituting
a general basis for unalterable deductions.
The rapid extension of civilization and the carrying of
minute scientific research into other regions, now rendered
possible by the improved means of communication, has shown
the one-sidedness of some of the views prevailing heretofore,
inasmuch as they are really applicable only to accidental and
rather exceptional conditions.
It is therefore one object of this volume to present and
discuss summarily the facts of physical and chemical soil con¬
stitution and functions with reference to the additional light
afforded on the wider basis, embracing both the humid and the
arid regions ; of which the latter has, as such, received but scant
and desultory attention thus far, to the detriment of both the
work of the agricultural experiment stations and of agricul¬
tural practice. The book therefore includes the discussion
both of the methods and results of direct physical, chemical and
botanical soil investigation, as well as the subject matter relat¬
ing to the origin, formation, classification and physical as well
as chemical nature of soil, usually included in works on scien¬
tific agriculture.
In the presentation of these subjects, it has been the writer’s
PREFACE.
xxi
aim to reach both the students in his own classes and in the
agricultural colleges generally, as well as the fast increasing
class of farmers of both regions who are willing and even
anxious to avail themselves of the results and principles of
scientific investigation, without “ shying off ” from the new
or unfamiliar words necessary to embody new ideas. It
would seem to be time that the latter class, and more especially
those constituting farmers’ clubs, should learn to understand
and appreciate both the terms and methods of scientific reason¬
ing, which are likely to form, increasingly, the subjects of in¬
struction in the public schools. But in order to segregate to
some extent the generally intelligible matter from that which
requires more scientific preparation than can now be generally
expected, it has been thought best to use in the text two kinds
of type ; the larger one embodying the matter presumed to be
interesting and intelligible to the general reader, while the
smaller type carries the illustrative detail and discussion which
will be sought chiefly by the student.
As regards the chemical nomenclature used in this volume,
the writer has not thought it advisable to follow the example
set by some late authors in substituting for the well-known
names of the bases and acids, those of the elements, and still
less, those of the intangible ions. Any one who has taught
classes in agricultural chemistry will have experienced the
difficulty and loss of time unnecessarily incurred in the inces¬
santly recurring transposition of terms, and complication of
formulae, serving no useful purpose save that of academic con¬
sistency. It is of at least doubtful utility to present to the
farmer, e. g., the inflammable and dangerous elements phos¬
phorus and potassium as prime factors in the success of his
crops, and of healthy nutrition.
Inasmuch as all the elements are presented to and con¬
tained in the plant in compounds only, and these compounds are
themselves, in the dilute solutions used by plants, known to be
largely dissociated into their basic and acid groups, it seems to
be most natural to present them under the corresponding, even
if not absolutely theoretically correct names of acids and bases,
to which the farmer and the trade have been accustomed for
half a century. Upon these considerations the long-used
designations of potash, soda, lime, phosphoric, sulfuric, nitric
XXII
PREFACE.
and other acids and bases have been retained in this volume,
adding the chemical formula where, as in analytical statements,
a doubt as to their meaning might arise. Assuredly, the diffu¬
sion of scientific knowledge should not be needlessly hindered
by the adoption of a pedantic mode of presentation.
The great breadth of the subject of this volume has ren¬
dered inadvisable any extended bibliography, such as it has of
late become customary to add to works of this kind. References
have therefore been restricted to publications specially discussed,
and to such as are not widely known on account of limited
circulation.
The author’s warmest acknowledgments are due to Professor
R. H. Loughridge, of the University of California, for effi¬
cient and sympathetic assistance, both in the revision of the
manuscript, and active personal help in the preparation of the
illustrations. Without his cooperation the preparation and
publication of the volume would have been much longer de¬
layed.
Acknowledgments are also due for helpful suggestions and
criticism to Professors L. H. Bailey, of Cornell University,
F. H. King, of Wisconsin, and Jacques Loeb of the University
of California.
E. W. HILGARD.
Berkeley, California,
November 15, 1905.
INTRODUCTION.
Definition of Soils. — In the most general meaning of the
term, a soil is the more or less loose and friable material in
which, by means of their roots, plants may or do find a foot¬
hold and nourishment, as well as other conditions of growth.
Soils form the uppermost layer of the earth’s crust ; but the
term does not indicate any such definite average texture as is
sometimes implied by its popular use to designate certain loose,
loamy materials found in older geological formations. We do
find in these, not unfrequently, layers that in the past have
served to support vegetation, as evidenced by remains of plants
found therein. But as a rule, such ancient soils are much
compacted and otherwise changed, and would not now be
capable of performing the office of plant nutrition without
previous, long-continued exposure to the same agencies by
which all soils were originally formed from pre-existing rocks.
Within the latter category must be included, in scientific par¬
lance, not only the hard rocks known as such in daily life, but
also such soft materials as clay, sand, marls, etc., which often
compose, partially or wholly, the bodies of wide-spread geo¬
logical formations.
Elements Constituting the Earth's Crust. — More than
seventy elementary substances have been found within the
portion of the earth accessible to man ; most of these are present
only in very minute proportions ; of those occurring in relatively
considerable quantities, a list showing their approximate pro¬
portions is given below.
Average quantitative composition of the Earth's Crust. —
The total thickness of the outer shell of the earth, thus far
known to us, does not exceed about 95,000 feet, as observed
in the accessible rock deposits. Estimates of the proportions
in which the more abundant elements contribute to the com¬
position of these constituent rocks, have repeatedly been made.
The latest and most widely accepted of these, by F. W. Clarke,
of the U. S. Geological Survey, is given herewith. It in-
xxiii
XXIV
INTRODUCTION.
eludes the constituents of the sea and atmosphere as well;
these two constitute about 7 per cent of the whole, 93 per cent
being solid rocks.
RELATIVE ABUNDANCE OF THE ELEMENTS TO A DEPTH OF TEN KILOMETERS.
Oxygen . . . .
Silicon ....
Aluminum .
Iron .
Calcium . . .
Magnesium
Sodium
Potassium . ,
Hydrogen .
Titanium . . ,
Carbon. . . .
Chlorin
Phosphorus
Manganese
Sulphur . .
Barium. . . .
Nitrogen . . ,
Fluorin. . . .
Chromium .
Solid Crust
Ocean
Mean,
(93 Per Cent).
(7 Per Cent).
Including
47.29
85-79
49.98
27.21
25-30
7.81
7.26
5-46
5.08
3-77
0.05
3- 51
2.68
0. 14
2.50
2.36
1 . 14
2.28
2.40
0.04
2.23
0.21
10.67
0.94
o-33
0.30
0.22
0.002
0.21
0.01
2.07
0.15
0. 10
0.09
0.08
0.07
0.03
0.09
0.04
0.03
0.03
0.02
0.02
0.02
0.01
0.01
It will be noted that one-half of the total consists of oxygen,
and that nearly 86% (or 47.29% of the 49.98%) of this
amount is contained in the solid rocks; nearly 2.50% of the
remainder in sea and other water; and .41% in the atmosphere,
in the free condition, in which it serves for the respiration of
animals and plants, and for the various processes of slow and
rapid combustion, or “ oxidation.” This relatively small pro¬
portion of the whole, is, nevertheless, the most directly im¬
portant for the maintenance of organic life.
Oxids Constitute Earth's Crust. — The vast predominance
of oxygen in the above list suggests at once that most of the
other elements must exist in combination with it, i. e., as
“ oxids.” H. S. Washington 1 has lately revised the esti¬
mates heretofore made, on the basis of a very large number of
analyses made by him and others, of rocks within the United
States, and gives the following table; alongside of which is
placed a revised estimate by Clarke, which also includes rocks
from abroad; both being given in terms of oxids of the several
elements.
1 U. S. Geol. Survey, Professional Paper No. 14, p. 108.
INTRODUCTION.
XXV
Silica .
Alumina .
Peroxid of Iron....
Protoxid of Iron...
Magnesia .
Lime .
Soda .
Potash .
Water, basic .
Water, acid .
Ferric Sulphid .
Phosphoric acid
Manganese Protoxid
Washington.
Clarke.
SiO,
57-78
59-89
ai3o3
i5-67
15-45
Fe203
3-31
2.64
FeO
3-84
3-53
MgO
3.81
4-37
CaO
5-lS
4-91
Na2Oi
3.88
3-56
k2o
3-I3
2.81
h2o+
1.42
L52
PI2O—
•36
.40
FeS2
1.03
.60
P2O5
•37
.22
MnO
.22
.10
The salient point which at once attracts attention in these
tables is the great predominance of the oxid of silicon — silica,
silicic acid, quartz, etc., — over all other substances. While
quartz occurs alone in enormous masses, as will be shown
later, probably the greater proportion is found in combina¬
tion with other oxids, notably those of aluminum, calcium,
iron, magnesium, and the alkali metals potassium and sodium.
Chlorin and fluorin, however, do not occur as oxids.1
The Chemical Elements Important to Agriculture. — Of the
numerous elements known to chemists, only eighteen require
mention in connection with either soil formation or plant
growth ; and of these only thirteen or fourteen participate in
normal plant growth. They are the following :
METALLIC ELEMENTS. NON-METALLIC ELEMENTS.
Potassium
Carbon
Sodium
Hydrogen
Calcium
Oxygen
Magnesium
Nitrogen
Iron
Phosphorus
Manganese
Sulphur
Aluminum
Chlorin
Titanium
Fluorin
Iodin
Silicon.
Of this list, titanium, though a very constant ingredient of
1 A trifling amount of chlorin is found oxidized in the form of sodium perchlor¬
ate, in the nitre deposits of Chile.
XXVI
INTRODUCTION.
soils in the form of titanic dioxid, is not known as performing
any important function in soils, and is not, so far as known
at present, ever taken up by plants. Aluminum, in the form
of its compounds with oxygen and silicon, is a very prominent
and physically very important soil ingredient, but does not,
apparently, perform any direct function in plant nutrition, and
is absent from their ash, except in the case of some of the
lower plants (horsetails and ferns).
Iodin appears to be normally present in all seaweeds, and
occurs in traces in some land plants. Fluorin is a normal in¬
gredient of animal bones, and its presence in plant ashes is
often easily shown. The remaining fourteen, however, are
always present in plants ; carbon, hydrogen, oxygen and nitro¬
gen forming the volatile or combustible part, while the rest
occur in the ashes.
It is true that other elements, or rather their compounds, are
sometimes found in plants, being taken up by them from solu¬
tions existing in the soil. Thus the alkalies caesium and rubi¬
dium, also barium, strontium, zinc, copper, boron and some
others, may be absorbed when present in soluble form. But
they are neither necessary nor beneficial to plant economy, and
when in considerable amounts are harmful. Thus fifteen ele¬
ments, ommiting iodin and titanium, alone require discussion.
The Volatile Part of Plants, as already stated, consists
of carbon, hydrogen, oxygen and nitrogen. Of these, car¬
bon is obtained by the plant exclusively from the carbonic
(dioxid) gas of the air; hydrogen and oxygen, from the soil
in the form of water; nitrogen, directly from the soil but in¬
directly also from the air, through the agency of certain
bacteria. The ash ingredients of course are all derived from
the soil through the roots, and must all be present in the lat¬
ter in an available form, to a sufficient extent to supply the
demands of vegetation.
The Agencies of Soil Formation . — With respect to their
mode of formation, soils may be defined as the residual product
of the physical disintegration and chemical decomposition of
rocks; with, ordinarily, a small proportion of the remnants of
organic life. The agencies producing these changes are those
classed under the general term “ atmospheric ” or “ meteoro-
INTRODUCTION.
XXVll
logical ; ” they include therefore the action of temperature —
heat and cold — that of water , and that of air and its ingre¬
dients. In popular parlance, it includes the processes of
weathering; nearly the same processes are involved in the
“ fallowing ” of soils.
PART I.
THE ORIGIN AND FORMATION OF SOILS.
CHAPTER I.
THE PHYSICAL PROCESSES OF SOIL FORMATION.
Since the physical and mechanical effects of the agencies
mentioned above usually precede, in time, the chemical changes,
which are materially facilitated by the previous pulverization of
the rocks, the former should be first considered.
Effects of heat and cold on rocks. — Most rocks are aggre¬
gates of several simple minerals; a few only (limestone,
quartzite and a few others) expand or contract alike in all their
parts. Of the minerals composing the compound rocks,
scarcely any expand to exactly the same extent under the in¬
fluence of the sun’s heat, especially when their colors differ;
nor, in the great majority of cases, does one and the same
mineral expand alike in all three directions. It follows that at
each change of temperature there is a tendency to the forma¬
tion of minute fissures between adjacent crystals or masses of
different simple minerals ; and especially in the case of large
crystals of certain kinds, this action alone will gradually result
in the disruption of the rock surface, so that individual crystals
may be detached with little difficulty. In any case, the cracks so
formed are gradually widened by a frequent repetition of the
changes of temperature, coupled wih access of air, water, dust,
and the rootlets of plants ; all of which brings about a gradu¬
ally increasing rate of surface crumbling. This is especially
conspicuous at the higher elevations of mountains, where the
temperature changes are very great and abrupt ; and also in the
clear atmosphere of deserts, where owing to the extent and
suddenness of temperature- changes between day and night,
caused by the free radiation of heat into the clear sky, even
homogeneous pebbles are known to be almost explosively dis¬
rupted in the mornings and evenings of clear days.
2
SOILS.
Such effects may often be strikingly observed on small sur¬
faces of compound crystalline rocks, such as granite, exposed
on glaciers, where the daily changes of temperature are often
extreme, viz., from below the freezing point to as much as
130 degrees Fahr. (54.4 degrees C.). In such cases one may
sometimes scoop off the disintegrated rock by the handful,
while yet the mineral surfaces are almost perfectly fresh.
On a larger scale, the disruption and scaling off of huge
slabs of granite, and rocks of similar structure, may be observed
in southern California on the southwestern side of rock ex¬
posures, where slabs from a few inches to ten and more feet
in length and eight or ten inches thick, have slid off, perhaps
still leaning against the parent rock, which has been rounded
off by a succession of such events into the domelike form so
characteristic of granite mountains. Merrill 1 reports similar
exfoliations to occur especially on the peninsula of California,
on Stone Mountain in Georgia, and elsewhere.
A striking exemplification of the effects of frequent and
rapid changes of temperature on rocks, and of humid and dry
climates as well, is seen in the case of the great monoliths of
Egypt, one of which now stands in the Central Park, New
York. In the quarries of Syene in Upper Egypt, where most
of these monoliths were obtained, the rough blocks that were in
progress of quarrying when the work was abandoned, quite
two thousand years ago, still show an almost perfectly fresh
surface; and the same is true of the finished obelisks in Lower
Egypt, where both the changes of temperature and the rain¬
fall are somewhat greater. It is a matter of public note that
one of “ Cleopatra's Needles ” which was set up in Central
Park nearly thirty years ago, but originally erected at Helio¬
polis on the Nile, is in great danger of destruction from the
influence of a totally different climate, in which both the
temperature changes and the rainfall are much more frequent
and severe than in Egypt. The large crystals of feldspar and
quartz which compose the (syenite) rock material have had
fine fissures formed between them by often-repeated expansion
and contraction ; which when filled with water and subsequently
1 See Rocks, Rock-weathering, and Soils, page 246 ; also paper on Domes and
Dome Structure, by G. K. Gilbert, in Bulletins of the Geol. Society Am., Vol. 15,
pp. 29-36.
THE PHYSICAL PROCESSES OF SOIL FORMATION.
3
changed to ice, the latter's expansion in freezing (see below)
has still farther enlarged them and caused a scaling-off, which
threatens to obliterate the hieroglyphic inscriptions. Thus
temperature-changes and a rain followed by freezing may
in a few days produce a greater effect than a thousand years
of Egyptian climate.
Cleavage of rocks. — Many kinds of rocks have definite direc¬
tions of ready cleavage. The most common and obvious cases
of this kind are schists, slates and shales, cleaving readily into
plates or irregular flat or lens-shaped fragments. Such struc¬
ture greatly favors disintegration, especially when the layers
are on edge at steep angles. But there are other apparently
structureless, massive rocks, particularly basalts and other
eruptive rocks related to them, as well as many sandstones and
claystones, that have a strong tendency to cleave into more or
less definite forms when struck; such as columns or prisms,
square, six-sided or diamond-shaped blocks, etc. Similar forms
are naturally produced in them under the influence of changes
of temperature ; by the formation of minute cracks at first, then
enlargement of these by the several agencies already mentioned.
Effects of freezing water. — The irresistible force exerted
by the expansion of water in freezing, amounting to about 9
per cent of its bulk, is a powerful factor in widening and deep¬
ening fissures and cracks of rocks ; not uncommonly, whole
masses of rock are rent into fragments by this agency, which
is one of the most common causes of “ rock falls ” on the
brink of precipices. By the freezing process cracks and crevices
are enlarged, and the surfaces exposed to weathering are still
farther increased; and the rock fragments or soil particles are
loosened and rendered more liable to be removed from the
original site, whether by gravity, wind or water.
Glaciers. — Ice in the form of the glaciers that descend from
mountain chains (see figure 1), and of the moving ice sheets
that have covered large portions of North America and Europe
in past ages and now cover Greenland and the South Polar con¬
tinent, exerts a most potent action in abrading and grinding
even the hardest rocks ; not so much by the direct friction of
the moving ice itself, as by the cutting, scoring, grinding and
crushing action which the stones imbedded in the ice, or carried
4
SOILS.
and shoved by it, exert upon the rocky channels in which the
ice stream moves, as well as upon each other. The product
of this grinding process is largely very fine (hence “ glacier
flour”), so that it remains suspended in the water of the
glacier-streams until their velocity is permanently checked
when reaching a plain or lake. This suspended stone-flour
imparts to the glacier streams their distinctive character of
“ white rivers,” as contradistinguished from the clear, dark
“green rivers” that have their origin outside of glaciated
Fig. i. — Zermatt Glacier (Agassiz).
areas. This difference can be readily observed in traveling
along any of the glacier-bearing mountain chains of the world,
and is frequently expressed in the names of the streams.
The physical analysis of mud from the foot of Muir glacier,1
Alaska, at its sea front, made by Professor Loughridge, shows
the prevalent fineness of the materials brought down by the
glacier waters.
1 Collected by Dr. W. E. Ritter of the University of California.
THE PHYSICAL PROCESSES OF SOIL FORMATION.
5
PHYSICAL COMPOSITION OF GLACIER MUD.
Material.
Diameter.
Per Cent.
Clay . . . . .
?
i6-57 ) 7n 7I
Pine silt .
.0023 — .016 mm.
C7.74 ( 70-31
Fine silt . . . .
.016 to .025 mm.
4-38
Medium silt .
.025 to .036 mm.
7.06
Coarse silt .
.036 to .047 mm.
5-91
Coarse silt .
.047 to .072 mm.j
3-76
Fine sand .
.072 to .12 mm.
1. 14
Medium sand . . .
.12 to .16 mm.
1.56
Total .
94.12
It will be noted that over 70 per cent of this mud consists
of extremely fine, wholly impalpable materials; but little of
which is true clay.
The fineness of the glacier-flour renders it peculiarly suitable
for the rapid conversion into soil, and such soils are usually
excellent and remarkably durable. The great and lasting
fertility of the soils of southern Sweden is traced directly to
this mode of origin, and doubtless the great American ice
sheet of glacier times is similarly concerned in the high cpiality
of the soil of our “ north central ” states, from the Ohio to
the Great Lakes and the Missouri.
The accumulations of rocks and debris of all sizes in the
“ moraines " or detrital deposits of glaciers and ice-sheets form
another class of glacier-made lands which cover extensive and
important agricultural areas (drift areas), both in the old and
new worlds. Such lands are undulating or slightly hilly, and
the soil usually contains imbedded in it stones of a great
variety of kinds and sizes, partly angular, partly rounded and
polished by friction. Of course the frequent and violent
changes of temperature occurring on the surface of a glacier,
aid materially in reducing the rocks carried by it to the con¬
dition in which we find the material of the moraines ; which
commonly form lateral or cross ridges in valleys formerly
occupied by glaciers.
Action of flowing zvatcr. — The action of flowing water is
doubtless at this time the most potent mechanical agency of
soil formation. From the sculpturing of the original simple
forms in which geological agencies left the earth's surface
6
SOILS.
into the complex ones of modern mountain chains, to the
formation of valleys, plains, and basins out of the materials so
carried away, its effects are prodigious. The torrents and
streams in carrying silt, sand, gravel and bowlders, according
to velocity and volume, do not merely displace these materials ;
the rock fragments of all sizes not only score and abrade the
bed of the rill or stream, but by their mutual attrition produce
more or less of fine powder similar to that formed by glacier
action ; usually more mixed in its ingredients than the former,
because derived from a wider range of drainage surface. In
Fig. 2. — Erosion of Hawaiian Hills, near Honolulu. (Phot, by H. C Myers.)
the glacier stream itself, it is easy to trace the gradual transi¬
tion from the sharp stone fragments lying in the water as it
issues from the terminal ice cave at the lower end of the
glacier, to the rounded shingle found a few miles below.
On slopes where water flows only during rain or the melting
of snow, the same erosive effects may be seen as between the
heads of ravines and their outlets. (See figure 2,) It is
there too that the surprisingly rapid cutting-out of channels by
the aid of water charged with rock fragments or gravel, can
readily be observed, and the enormous power of water
erosion convincingly shown. In the United States the stu¬
pendous gorges of the Columbia and Colorado rivers, the
THE PHYSICAL PROCESSES OF SOIL FORMATION.
7
former cut to a depth of over 2000 feet into hard basalt rock,
the latter to over 5,000 feet, partly into softer materials, partly
into granite, are perhaps the most striking examples of this
power; the manifestations of which can, however, be as con¬
vincingly seen in thousands of minor rivers and streams.
All the materials so carried off from the higher slopes are
finally deposited on a lower level ; whether only a short distance
away on a lower slope (colluvial soils), or farther away in the
flood plain of streams, rivers, or lakes (alluvial soils). Other
things being equal, the finest materials are of course, carried
farthest, and often into the sea : in which, however, they can¬
not long remain suspended, but are quickly thrown down,
forming river bars, flood plains, and deltas. The fineness of
the material of delta soils, like that of those made from glacier
flour, insures them the same advantage, viz. great fertility and
durability.
It is calculated that the Mississippi River carries into the
Gulf of Mexico annually some 7469 millions of cubic feet of
earthy deposits, which would fill one square mile of surface
to the height of 268 feet, or would cover that number of square
miles to the depth of one foot.
Fig. 3. — Cliffs and caves on sea-beach at La Jolla, Calif, showing effects of Wave action.
Wave-Action. — The powerful effects of the beating of waves
upon abrupt shores of seas or lakes are in evidence all over
the world, and these effects are so characteristic that they can be
recognized even where no sea or lake exists at present. Gravel
and sand are carried in the surf and serve as grinding ma¬
terials, wearing even the hardest rocks into grooves, rills, chan-
8
SOILS.
nels and caves, defining sharply the varying degrees of hard¬
ness or tough resistance in different parts of rocky cliffs;
frequently undermining them and causing extensive rock-falls.
The latter then serve for a time to break the violence of the
waves' onset, and may even cause permanent shore deposits to
be formed under their lee.
Such deposits are very generally formed on gently sloping
beaches, and as the water gradually recedes, sometimes by
elevation of the ground, beach lines or beach-terraces are left,
which indicate the successive levels of the lake or sea. Such old
beach lines or terraces and level-surfaced “ buttes " in the Great
Basin country, and “ bench lands " elsewhere, show in their
structure the characteristic lines of wave-deposition.
Effects of f Finds. — The action of winds in transporting soil
particles (dust and sand) is familiar; and the accumulations
that may be formed under the influence of regular, continuous
winds are sufficiently obvious on lee shores having sandy
beaches, inland of which the formation of sand dunes at times
assumes a threatening magnitude. Where winds are irregular,
frequently reversing their direction, of course the local effects
will be less obvious, and the transportation of material actually
occurring will often not be noticed. Yet there can be no doubt
of the importance of wind action in soil formation, and there
are cases in which no other agency can explain the facts ob¬
served over widely extended areas. This is especially true with
regard to the soil masses of the high plains or plateaus of the
dry continental interiors, where not only the regularity of the
prevailing winds, but also the structure (or absence of struc¬
ture) and pulverulent character of the soil itself, renders this
the only rational mode of accounting for its presence where we
find it.
The effects that may be exerted by regular winds are well illustrated
in the plains and deserts of Africa as well as those of central Asia.
Here we find a distinct subdivision of the desert (rainless) areas into the
stony , from which the wind has swept all but the bedrock and gravel and
where scarcely any natural growth, and certainly no cultivation is pos¬
sible in the almost total absence of soil. The next subdivision is the
sandy desert, to leeward of the stony area, where the winds are less
violent and regular, and where, therefore, the sand has been dropped
THE PHYSICAL PROCESSES OF SOIL FORMATION.
9
and is wafted back and forth by “ sand storms,” the surface being covered
with moving sand dunes. Still farther to leeward we find the region in
which the finer portions of the desert surface has been deposited ; here
we have “ dust storms” so long as the land is not irrigated; but the
application of water renders the soil abundantly fruitful. Such is the
case of the Oases and fertile border-lands of the Sahara and Libyan
deserts.
In the cultivated portions of the Mojave and Colorado
deserts in Caliiornia. plowing of the land during a dry time is
not uncommonly followed by a bodily removal of the loosened
soil to neighboring fields, sometimes leaving a gravel surface
behind. Such “ blown-out lands “ exist naturally at numerous
points in the Colorado desert.
Sven Hedin ( Central Asia and Tibet. Yol. II.) shows that
from the effects of the violent storms that prevail in the Gobi
or Takla Makan desert, Lop-nor lake, the sink of the Tarim
river, has in the course of time shifted its bed as much as
fifty miles in consequence of the excavation of the southern
part of the desert by the wind : while the sand so blown out,
together with the deposits from the rivers, now tends to fill
up the present (southern) lake, which is gradually returning
northward toward its original site, now a desert, but around
which formerly a dense population existed.
The great plains of North America, the pampas of South
America, the plateaus of Mongolia and especially the fertile
loess region of northwestern China, are also cases in point.
The dense dust storms of these regions are familiar and un¬
pleasant phenomena, which are often observed even by vessels
at sea off the east coast of South America, where the dust-laden
“pamperos " at times compel them to proceed with the same
precautions as in a fog; and the same is true of the northeast
winds blowing oft the Sahara desert on the west coast of
Africa.
The effects of windstorms carrying sand in the erosion of
rocks are very obvious and striking in many parts of the world :
nowhere probably as much so as on the great plains of western
North America, where the geological composition of the “ bad
lands " is frequently impressed upon the rock surfaces very
prominently. The strikingly grotesque forms are frequently
10
SOILS.
brought out in this way, especially in the case of “ mush¬
room ” rocks, where a hard stratum has remained as a covering
while softer layers underneath have been worn away. The
illustration annexed shows such a case on the plains of Wyom¬
ing as figured in the Report of the U. S. Geological Survey,
on the Central Great Plains, by N. H. Darton. Striking ex¬
amples of the same effects are seen on the shores of Lake
Michigan in the Grand Traverse region, where the rocky cliffs
are visibly worn away and carved under the influence of the
regular “ sand-blasts ” of northwest winds. On a smaller
scale the effects of these sand-blasts mav be noted in the cob-
Fig. 4. — “ Mushroom rocks,” produced by Wind action, Wyoming. (I)arton.)
ble-deserts, where we frequently find the cobbles worn awav
on the windward side in a very characteristic manner; the lee
side remaining rounded and smooth, while the structure of the
rock is strongly outlined on the windward side.
CLASSIFICATION OF SOILS.
The physical Constituents of soils are thus, in the most gen¬
eral terms, first, rock powder (“ sand ” ) ‘more or less changed
THE PHYSICAL PROCESSES OF SOIL FORMATION.
II
by weathering; second, clay, as one of the chief results of the
weathering process of silicate minerals; and thirdly, humus, the
dar^-colored remnant of vegetable decay. According to the
obvious predominance of one or the other of these primary
ingredients, soils are popularly, in the most general sense,
classed as “heavy” and “light"; the former term corre¬
sponding as a rule to those in which clay forms a prominent
ingredient, while sandy and humous or “ mold ’’ soils usually
fall under the latter designation, because of their easy tillage.
For practical purposes these subdivisions are both convenient
and important, and they form the ordinary basis of land class¬
ification. Beyond these, the degree of fineness of the rock de¬
bris, and their physical and chemical constitution, determine
distinctions such as gravelly, sandy, silty, loamy, calcareous,
siliceous, magnesian, ferruginous, and others of less general
application, though locally often of considerable importance.
For the purposes of discussion and definition, however, an¬
other basis of classification is needed, which essentially con¬
cerns both the origin and the adaptations of lands.
UPLAND
Plateau
I Se den Iciry Soil
LOWLAND
Alluvial
Flood Plains
Fig. 5. — Diagram illustrating the genetie relation of different soil classes to each other.
i. Sedentary Soils. — When soils have been formed without
removal from the site of the original rock, by simple weather¬
ing, they are designated as sedentary, or residual soils, or
“ soils in place." In the case of these, the original rock under¬
lies the soil or subsoil at a greater or less depth, according to
the intensity and duration of the weathering process, and is
usually more or less softened and decomposed at the surface
where it meets the soil layer. The latter of course bears some
of the distinctive characters of the parent rock, and its composi¬
tion and adaptations may, in a measure, be directly inferred
from that origin. Such soils usually contain, especially in their
lower portions, some angular fragments of the parent rock. In
12
SOILS.
some cases sedentary soils may have been partially derived
from rocks that have been removed from above the present
country rock by erosion, and in that case fragments of such
vanished rock may also be present.
Sedentary soils are most commonly found on rock plateaus
and on slopes or plains underlaid by rock strata of but slight
inclination, where the velocity of the “ run-off ” rainfall is not
sufficient to dislodge the rock debris. Extended areas of such
soils exist in the granitic areas of the southern Alleghanies, in
the “ black prairies ” of the Cotton States, and on the “ basal¬
tic ” plateaus of the Pacific Northwest.
2. Colluvial Soils. — When the soil mass formed by weath¬
ering has been removed from the original site to such a degree
as to cause it to intermingle with the materials of other rocks
or layers, as is usually the case on hillsides, and in undulating
uplands generally, as the result of rolling or sliding down,
washing of rains, sweeping of wind, etc., the mixed soil, which
will usually be found to contain angular fragments of various
rocks, and is destitute of any definite structure, is designated
as a colluvial 1 one. Colluvial soil masses are frequently sub¬
ject to disturbance from landslides, which are usually the result
of water penetrating underneath, between the soil mass and
the underlying rock, or sometimes simply of complete satur¬
ation of the former with water. Aside from such catastrophic
action, they commonly have a slow downward movement in
mass (creep), which ordinarily becomes perceptible only in
the course of years ; most quickly where there are heavy frosts
in winter, which act both by direct expansion, and by the state
of extreme looseness in which the soil mass is left on thawing.
Colluvial soils form a large portion of rolling and hilly up¬
lands, and are of very varying degrees of productiveness.
3. Alluvial Soils. — When soils are the result of deposition
by streams, the material having been gathered along the course
1 The term “overplaced,” used for such soils in late memoirs of the U. S. Geo¬
logical Survey, is at least superfluous, in view of the perfectly understood term
already in general use, and does not seem to commend itself for adoption by any
special or superior fitness; nor does the suggestion of Shaler (The Origin and
Nature of Soils, 12th Rep. U. S. Geol. Survey) to include the colluvial soils within
the alluvial class, commend itself either from a theoretical or practical point of
of view, since but few useful generalizations can apply to both classes.
THE PHYSICAL PROCESSES OF SOIL FORMATION.
13
of the stream from various sources and carried to a distance
before being deposited, the soil is designated as alluvial.
These are the soils of the valleys, flood-plains, and sea- and
lake-borders, past and present. Being of mixed origin, their
general character may vary from one extreme to the other,
both as regards physical and chemical composition. Since,
moreover, they represent the finer portions of the soils of the
regions drained by the watercourses, alluvial soils are as a rule
of a fine texture ; and as representing the most advanced de¬
composition products of the parent rocks, they are usually
preeminently fertile. This is proverbially true of the flood-
plains of rivers, and still more of their deltas — the bodies of
lands formed near their outlets into seas or lakes.
Character of these soil-classes. — Sedentary soils are as a
matter of course, other things being equal, dependent entirely
on the parent rock for their specific character ; and taking into
consideration the various rocks (usually one or few) from
which they may have been derived, nearly the same is true of
colluvial soils, except that a portion of the clay and finest pul¬
verulent matters may in their case be carried down on the
lower slopes and into the valleys and streams, by the hillside
rills.
According to the calculation of Merrill (Rocks, Rock-weathering, and
Soils, p. 188) granite when transformed into soil without loss would
increase in weight by 88 °j0 ; more than doubling its bulk. More
usually, the leaching process diminishes their volume as compared with
the parent rock.
Alluvial soils are also of course to a certain extent de¬
pendent upon the character of the rocks and surface deposits
occurring within the drainage area of the depositing stream.
As a rule their composition is much more generalized ; but their
character as to the relative proportions of sand and clay is
essentially dependent upon the velocity of the water current.
Thus in the upper portions of valleys, where the slope is
relatively steep and the velocity therefore high, a large pro¬
portion of cobbles and gravel is often present in the deposits,
sometimes to the extent of rendering cultivation impracti¬
cable, or at least unprofitable. As the slope and velocity de-
H
SOILS.
crease, first coarse and then fine sand will be the prominent
component of the deposited soil ; while still lower down, in
the region of slack water, the finest sand or silt, together
with clay, will predominate. According to Hopkins,1 flowing
water will, at a velocity of three inches per second, carry in
suspension only fine clay (and silt) ; at eight inches it will
carry sand as large as linseed. At one and one-third inches,
it will move pebbles one inch in diameter; and at a velocity of
two inches per second, pebbles of egg size are moved along the
stream bed. Since the velocity of streams subject to freshets
will vary greatly from time to time, deposits of very different
grain will in such cases be found alternating with one another
in the soil stratum of the flood plain. In fact, this alternation
and the more or less stratified structure resulting therefrom,
is the distinguishing mark of alluvial soils as such. It is true
that this peculiarity is also sometimes found in the case of
lands now lying far above the flood-plains of present rivers :
but this is due to the elevation of the land or the depression
of the river channels at a former period, prior to which such
lands (commonly known as river terraces, benches or second
bottoms) were formed. The same is true of lake terraces
(“ mesas v), which cover enormous areas in some parts of the
world, more particularly in western North America. It must
nevertheless be remembered that such alluvial terrace or bench
soils differ in some respects from the modern alluvials, on
account of their long exposure to atmospheric action alone;
one result of which is that they are usually much poorer in
humus, and therefore of lighter tints, than the more modern
soils of alluvial origin. Other differences will be adverted
to hereafter.
As a matter of course the above distinctions, especially
between colluvial and alluvial soils, cannot be rigorously
maintained in all cases. There are transitions from one
class to the other, so that it is sometimes optional with the
observer to which of the two classes a particular soil may
be considered as belonging. On the lower slopes of the hills
bordering alluvial valleys the colluvial slope-soil may often
be found alternating with the alluvial deposits, or bodily
1 Geikie, “Text-book of Geology, 3d ed.
THE PHYSICAL PROCESSES OF SOIL FORMATION.
15
washed away to be redeposited as alluvium at a greater or less
distance.
One characteristic of the flood-plain lands of all the larger
rivers, and more or less of all streams subject to periodic
overflows, is that the land immediately adjoining the banks
is both higher and more sandy than are the lands farther back
from the stream. The cause of this phenomenon is that as
lateral overflow diminishes the velocity of that flow, its coarser
portions are deposited near the river banks, while the finer
particles are carried farther away, until finally only the finest
— clay-substance — reach the lagoons or lakes filled with the
overflow or back-water, and are there in the course of time
deposited as heavy clay “ swamp ” soils. The same occurs
where rivers empty into lakes or the sea ; and these slack-water
or delta lands are, as a rule, the most productive on the river’s
course. The continued productiveness of alluvial soils is more¬
over in many cases assured by the deposition, during overflows,
of fresh soil-material brought down from the head waters of
the streams. The Nile, and the Colorado river of the West,
illustrate this point.
Lowering of the land-surface by soil formation. — It is
evident that the soil-forming agencies must in the course of
time materially affect both the surface conformation and the
absolute level of the land. The sharp pinnacles and crests of
rock are abraded into the rounded forms now characterizing
our uplands and lower ranges of hills and mountains ; and
it is estimated that, e. g., the general level of the drainage basin
of the Mississippi river is lowered about one foot in 7.000
years, the material being carried into the lowlands and the sea.
CHAPTER II.
THE CHEMICAL PROCESSES OF SOIL FORMATION.
Chemical Disintegration, or Decomposition.
It may be said that in general, the physical agencies of dis¬
integration are most intensely active in the dry or arid regions
of the globe, while chemical processes of decomposition are
most active in humid climates.
The chemical decomposition of rocks is primarily due to the
action of the atmosphere, the average composition of which
may be stated as follows :
Volume Per Cent.
Weight Per Cent.
Nitrogen .
78.00
75-55
Oxygen . . .
21.00
23.22
Carbonic dioxid .
Ammonia .
Water vapor . . .
°3-.°4
1 to 4 millionths
Variable ; 48 to 83 grams per
cubic meter, when satu¬
rated between O® and
5o0C.
.045-.060
In addition to the above, air contains minute amounts of the
very indifferent and therefore practically negligible elements,
argon, krypton, neon, xenon and helium, the aggregate amount
of which in air is somewhat less than one per cent, of which the
greater part is argon. So far as known these elements take
no part whatever in vegetable or animal life, and possess no
known chemical action or affinity.
The primary active agents in effecting chemical changes
in rocks by which soils are formed, are water, carbonic acid,* 1
and oxygen; all therefore ingredients of the atmosphere.
Hence the chemical changes so brought about are in the most
general sense comprehended within the term weathering, as
1 Owing to the universal presence of water (H20) in air as well as in soils, it is
usual and convenient to speak of carbonic dioxid (C02) gas when so occurring as
carbonic acid (H2C03), of which it produces the effects (C03+H20 = H2C03).
16
THE CHEMICAL PROCESSES OF SOIL FORMATION.
17
applied to rocks; while the corresponding but more complex
action within the soil itself is usually termed fallowing.
Effects of Water. — Since but few substances, particularly
among those forming rocks, are totally insoluble even in pure
water,1 and some (such as gypsum) may be considered easily
soluble in the same, the rain water must exert solvent action
wherever it penetrates. In nature, however, strictly pure water
does not occur, it being difficult to obtain it even artificially.
Among the “ impurities ” almost always contained in natural
water, there are several that materially increase its solvent
power. Foremost among these, both because almost univer¬
sally present and on account of its great ultimate efficacy, is
Carbonic dioxid, in contact with water forming carbonic
acid, the acidulous ingredient of all effervescent waters, the
gas which is produced in nature by innumerable processes,
such as decay, putrefaction, fermentation, the slow or rapid
combustion of vegetable and animal substances, such as wood,
charcoal and all other fuels; by the respiration of animals;
m the burning of limestone, etc. It is therefore of necessity
contained in air, on an average to the extent of about 1-3000 of
its bulk in the general atmosphere, but locally in considerably
higher proportions because of proximity to sources of forma¬
tion, and of its greater density as compared with air ( 1 ^ as
against 1 ) . It may thus accumulate in inhabited buildings, in
cellars, wells, mines, caves; and it is contained in considerable
proportion in the air of the soil. Moreover, being easily soluble
in water (to the extent of an equal volume at the ordinary
temperature and barometric pressure) it is contained in all
natural water, whether of rains, rivers, springs or wells, and
largely of course in that percolating the soil. Such waters
may therefore be considered as being acid solvents ; and as
such, they exercise a far more energetic and far-reaching effect
than would pure water.
Carbonated zvater a universal solvent. — While limestones
are the rocks most obviously acted upon by carbonated water,
few if any resist it altogether. Even quartz rocks of the ordi¬
nary kinds are attacked by it ; only the purest white crystalline
quartzite may be considered as sensibly proof against it.
2
1 See Chapter 18.
i8
SOILS.
Granite and the rocks related to it are rather quickly acted upon,
because of the presence of the feldspar minerals containing
potash, soda and lime as bases 1 together with alumina.
The results of this action are highly important; one being
the formation of clay, so essential as a physical ingredient of
soils; the other the setting-free of potash, one of the most
essential nutrients of plants. Hornblende and the related
minerals are similarly acted upon so far as they contain the
same substances. In all cases, of course, the silica (silicic acid)
set free by the carbonic acid remains partially or wholly in the
resulting soils, as such. Lime also at first mostly remains
behind in the form of the carbonate ; but potash and especially
soda compounds, being mostly readily soluble in water, are
largely carried away by the latter.
The effect of carbonated water upon silicate minerals is
greatly increased by the presence of ammonia (ammonic car¬
bonate), which always exists in atmospheric water to a greater
or less extent. This effect may readily be noted on the win¬
dows of stables, or other places where animal offal decays,
by the dimming of the glass surfaces; also in glass bottles
containing solution of ammonic carbonate.
Action of Oxygen. — The effects of atmospheric oxygen on
rocks are of course confined to those containing substances
capable of farther oxidation. Chief among these are ferrous
(iron monoxid) and ferroso-ferric oxid the latter imparting
bottle-green, bluish and black tints to so many minerals and
rocks that these colors may usually be taken as indicating its
presence. By taking up more oxygen the ferrous and ferroso-
ferric oxids are converted into ferric oxid or its hydrate (rust),
the tints mentioned passing thereby into brick-red or rust color,
according as the former or the latter (or sometimes their in¬
termixtures) is formed. In either case there is an increase in
bulk; and this when taking place in the cracks or crevices of
minerals or rocks, tends, dike the freezing of water, to widen
■>
1 The increase of solvent power on feldspar when carbonated instead of distilled
water is used, was well exemplified in an experiment made by Headden (Bull.
, 65, Color. Exp’t Sta., p. 29), who allowed pure distilled and carbonated water
respectively to act on fresh but finely pulverized feldspar, with frequent shaking,
for five days. The distilled water disol ved .0081 gram, the carbonated water,
.0723 gram of solids, or nearly nine times as much as the distilled water. Both
residues gave strong reactions for potash with platinic chlorid.
THE CHEMICAL PROCESSES OF SOIL FORMATION.
l9
the cracks and thus to increase the surface exposed to attack.
Since ferrous compounds, when soluble in water, are injurious
to plant growth, this oxidation is of no little importance, and
in soils must be carefully maintained against a possible reversal.
It is hardly necessary to insist that the action of all these
chemical agents continues in the soils themselves, and that
owing to the fineness of the material, resulting in an enor¬
mously increased surface exposed to attack, such action ac¬
quires increased intensity. This is the more true as in soils
bearing vegetation there are always superadded the effects
of the humus-acids resulting from the decay of vegetable
matter, as well as of the acid secretions of the living plants.
Action of Plants and their Remnants in Soil Formation.
(a) Mechanical action. — The direct action of plants in forc¬
ing their roots into the crevices of rocks and minerals and thus
both widening them by wedging, and by exposing new sur¬
faces to weathering, has already been alluded to. That the
mechanical force exerted by root growth is very great, may
readily be judged from their effects in forcing apart, even to
rupture, the walls of rock crevices ; but actual measurement has
shown the force with which the root, e. g., of the garden pea
penetrates, to be equal to from seven to ten atmospheres, say
from 200 to over 300 pounds per square inch. Such a force,
exerted under the protection of the corky layer protecting the
root tips, often produces surprising effects.
( b ) Chemical action. — Vegetation takes a most important
part, from a chemical point of view, both in the first formation
of soils and in their subsequent relations to vegetable life. The
lower forms of vegetation are usually the first to take posses¬
sion of rock surfaces ; foremost among these are the lichens.
In humid climates we find these crust-like plants incrusting
more or less all exposed rock surfaces, sometimes with a solid
mantle “that can be peeled off in wet weather, showing the
corroded rock-surface, and the beginnings of soil clustering
amid the root-fibrils beneath. A microscopic examination of
the substance of these lichens often shows as a prominent in¬
gredient, crystals of oxalate of lime, the lime having of course
been derived from the rock, while the oxalic acid has been
20
SOILS.
formed by the plant and used in the corrosion of the rock
minerals. When it is remembered that this acid is comparable
in strength to hydrochloric and nitric acids, the energy of the
attack of the lichens is explained. Its progress can often be
traced, even beyond the visible root fibers, by a change in the
color of the rock; e. g., from rust-color to brick red.
When by the action of the lichens a certain depth of loosened
rock or half-formed soil has been produced, the next step is
usually the advent of various mosses, which gradually shade
out the crust-like lichens, while the erect kinds persist for some
time. Eventually the mosses, after having increased still
farther the soil layer on the rock surface, are themselves par¬
tially or wholly displaced by the hardier species of ferns ; and
with these the higher flowering plants, such as the stonecrops
and saxifrages (the latter deriving their name from their
“ rock-breaking ” effect), the heather, and many other or
shallow-rooted plants, gradually take possession. The roots
of all plants secrete carbonic acid; and many of them, much
stronger vegetable acids, such as oxalic and citric. In the
crevices of rocks we commonly find the roots forming a dense
network over the surfaces, the marks of which show plainly the
solvent effect produced on the rock by the root secretions.
This is most readily observable on a polished marble surface,
or on feldspathic rocks. Of course the progress of soil-forma¬
tion is very much more rapid when, as in the case of powdered
lava (volcanic ash) and rock debris resulting from the effects
of frost etc., the surface is very much increased. In tropical
climates, where both vegetative and chemical action is most
intense, it takes some of the higher plants only a few years
after a volcanic eruption to take possession of portions of the
“ ash ” surfaces; thus helping to form a soil on which after a
few more years agricultural plants such as the vine and olive
yield paying returns.
To this direct action of the higher plants is always added,
to a greater or less extent, that of innumerable bacteria, as
well as molds; whose vegetative and secretory action mater¬
ially assists that of the roots, and the weathering process in
general.
Humification. — While the mechanical action of the roots and
the chemical effect of the acids of their root secretions are very
THE CHEMICAL PROCESSES OF SOIL FORMATION, 2I
efficient in promoting the transformation of mere rock powder
into soil material proper, the efficacy does not end with the
life of the plant. In the natural process of decay to which the
roots are subject after death, and which also affects the
leaves, twigs and trunks falling on the surface, the vegetable
matter suffers a transformation which must be considered more
in detail hereafter, and results in the formation of the com¬
plex mixture of dark-tinted substances known as vegetable
mold or humus; the remnant of vegetation that imparts to
surface soils their distinctive dark tint. Its functions in soils
are both numerous, and important to vegetable growth; as re¬
gards soil formation, it assists disintegration of the rock min¬
erals both by the formation of certain fixed, soluble acids ca¬
pable of acting on them with considerable energy, and by the
slow but continuous evolution* of carbonic acid under the in¬
fluence of atmospheric oxygen, which has been alluded to
above.
Causes influencing chemical action and decomposition. — The
chemical processes causing rock decomposition are of course
continued in the soil, and there also are materially influenced
by climatic and seasonal conditions, which bring about great
differences in the kind and intensity of chemical action.
Within the ordinary limits of solar temperatures it may be
said that, other things being equal, the higher the temperature
the more intense will be chemical action in soil formation.
Since, however, water is a potent factor in the majority of
these processes, the presence or absence of moisture at the same
time with heat will cause material differences in the kind and
intensity of chemical action. In view of the importance
of carbonic acid as a chemical agent, the presence or absence
of vegetable matter or humus, from which by oxidation or
decay carbonic and humus-acids are formed, will likewise be
of material influence.
The presumption that climatic and seasonal conditions must
greatly influence both the kind and rapidity of the soil-form¬
ing processes, is fully borne out by observation and practice.
Especially is the amount and distribution of rainfall of great
importance in this respect, and should therefore be first con¬
sidered.
22
SOILS.
INFLUENCE OF RAINFALL ON SOIL FORMATION; LEACHING OF
THE LAND.
In the general consideration of the soil-forming processes,
it has been stated that soils formed by the disintegration of
rocks “ in place/’ i. e., without removal from the original
locality, are also designated as “ residual ” ; meaning thereby
that only a portion of the original rock remains to form the
soil mass, while another portion has been removed. To a slight
extent this removal occurs by the partial washing-away of the
finest clay and silt particles; but the most important action
from the agricultural point of view is the removal by leaching
with the carbonated water of the atmosphere and soil, of cer¬
tain easily-soluble compounds formed in the process of chemical
decomposition of rocks and resultant soils. The nature of these
compounds is exemplified in the subjoined table giving the
composition of some waters flowing from drains in unmanured
fields, laid at depths of from two to three feet ; and for compari¬
son with these, the composition of the water of some of the
world’s large rivers, showing what these largest drains carry
into the ocean.
The analyses have in all cases, where necessary, been re¬
calculated to parts per million, and to oxids, from the published
data.
The letter “ c ” indicates that the preceding figure has in the
absence of a direct determination been stoichiometrically cal¬
culated from the data given, in order to complete the com¬
parison.
COMPOSITION OF DRAINAGE WATERS FROM UNMANURED GROUND.
PARTS PER MILLION.
Rotham-
sted.
(VOELKER.)
Proskau.
(Krocker.)
Mockkrn.
(0. Wolff.)
Farnham.
(Way.)
Munich.
(Zoller.)
Rye
Field.
Mead*
ow.
Wheat
Field.
Hop
Field.
Lysemeter
Drainage.
Aver¬
age.
Potash, K20 .
*•7
5-4
2.0
2.0
8.5
3-4
Trace.
Trace.
6.5
2-4
3-2
Soda, Na.20 . .
6.0
11. 7
15 1
*3 7
23-3
8.2
*4-3
45-7
7-1
5-6
15. 1
Lime, CaO .
98.1
124 3
*33-°
1 18. 1
122.6
22.5
693
185.0
145.8
57.6
107.6
Magnesia, MgO .
5- 1
6.4
33-3
22.4
*4-9
6.7
9-7
35 1
20.5
8.9
16.3
Iron Oxid, Fe203 .
5-7
4-4
6.6
6.6
) 0
)
6-3
Alumina, Al203 .
•
j- 8.0
6.0
J 5-9
| 7- 1
Silica, Si02 .
IO. O
I C.a
7.0
7.0
i-35
12. 1
IO.4
”•3
Carbonic Acid, C02.. .
48. 1
44 4
75.8
82.6
12 1.3
Phos* Acid, P205 .
• 63
9.1
Trace
Trace
Trace.
19.0
Trace.
1.7
2.2
Trace.
O.C
Sulfuric Acid, S03 ....
24.7
66.30
122.7
67-3
.
.
23-5
*358
*7-5
27. 1
60.8
Chlorin, Cl .
10.7
1 1. 1
4-3
4.2
14.0
Trace.
10.0
37-4
57-5
9 5
>7-7
Nitrogenas, N205 .
3 00
K. 10
102.4
Nitrogenas, NH3 .
.12
•'3
•25
•03
Total Mineral Matter..
215.9
295 5
400.3
322.9
198.3
191. I
248.8
623.5
267.6
128.7
Less O : Cl .
2.35
2.4
I . I
• Q
2 . I
8 2
Corrected Total .
213-3
293- «
399-2
322.0
1952
191. I
246.6
6i5-3
2 54-9
126.6
285.7
Organic Matter .
22.9
19-3
25.0
16.0
26.0
26.0
100.0
'05-7
20.5
12.6
Total Solids .
2352
312.4
424.2
338-0
221.2
217. 1
346.6 j
721.0
275 4
‘39-2 j
352.6
THE CHEMICAL PROCESSES OF SOIL FORMATION
23
Total Solids .
Total Mineral Matter...
Less O : Cl .
Corrected Totals .
Organic Matter .
- - - - - 1 'A U
Sulfuric Acid, S03 .
Chlorin Cl .
Ammonia. NH» .
*:
ti
SL
z\
hi
K
O
TJO tp >
3- V EC £-
3 -1 rr- c
3 0 “ 3-
n- § 1
5 > « >
>2. : .r-
2> : 0
/-s • K
? : : :
^‘0
2.
?
?“
4
2 2 f
? w 5‘ Eg. 2.
iq 3 ™ S - <«
U ft - Ky
= S£. 0
S? ??"o
? 0 : ; ; :
• • • •
• • • •
, • • . .
, • • • •
• • • • •
• • • • •
F. W. Clarke,
Jour. Am.
Chem. Soc.
Feb. 1905, p.
1 12.
O
S
0
0
O
S
b
0
sO
M
M M
0 0
00
Cn
O O
04
04 V4 M
0 O' bo
000
04 • l_3
va O • 00
04 • xi
0 0 : 0 s
Yukon,
Alaska.
C. Schmidt,
Jahresb. d.
Chemie,
>873.
M
W
04
O
00
W
04
V4 M
04 04
04 M
04 K4
04 O
b O'
O K>
cn
O) • m
4w 0 0 • O'
0 « cn • 04
04 04 • *4 m
O' N • 04 |4
K) 04 • 04 cn
cn 0 • 00 00
Dwina,
above
Archangel.
T. S. Hunt,
Geol. of Can¬
ada, 1863.
k>
u
00
in
Is)
04
00
in
s
4**
cn
cn 0
i. v*
O
32.60
68. 40
Trace
I.40
6.90
45-30
9.70
St. Lawrence,
Pointe des
Cascades.
Traphagen,
Bull. Mont.
Expt. Sta.
No. 190.
K)
14
**
fc)
M
N>
14
M
04
M
M
14
4^ cn
- 4^
0
•x K)
00 x
s *
x
Cn 00 04
WOO 0
0
1.90
30. IO
58.00
18. 10
Missouri,
Montana.
i
Porter, I
Sewera
Board.
Ln
O'
X
cn
K>
O'
04
cn
K) 4*
- ^4
0 04
vO O'
O' M X
0 0 04
• • ♦ •
*4* m4^**m*
I in 00 K) M 0 I | vO !
• m xi 4*> 00 * I bo I
00 000 | ) 0 i
* . . 0 .
Mississippi near Carrol
Average of one year.
<» n
a ns
*> z
a 0
CL j!
£- 0
^ b
stE-t-
in ^ ^4 •
0 N* .
• &
• x-n M •
• pj •
• *1 . •
• n •
: :
49-75
Dec.
16.39
March
g
p
H
Orleans
Water
0=
rt> 0
p b
• •
8.18
Jan.
6.90
Dec.
• •
: > :
: ^cn :
• ^0 *
l 4k *
-T] M ’ • •
<t 0 n 0- ; ; :
o',- cr • . . .
w • • .
§
5*
Stone, U. S.
R e c lama-
tion Serv¬
ice.
M
4*
O'
00
O
M
4*-
O'
bo
'O
M
Cn
04 0
O' in
04 14
M D 04 M 4*. • M
O' 04 04V4 mm04K)
x x O K> 04 x 4l. x x m 04 K) * Cn 00
O' 0 0 04 04 O' 0 ^l*-«0' 0 0 *00
O I
2
p
sO
0
cn
*-r-
O
P
r
p
O. Loew, U. S.
Geogr. Sur¬
vey W of
100th Merid.
Vol. 3.
M
in
04
0
Cn
04
0
O'
00 14
O 04
cn cn
04 4*
O' ^
8 8
M • •
O *
Is) •
in • •
• Is) • -4*.
• Is) Is) • 04
. M 00 • 4k- 00
• 0 0*00
• •
• •
• •
• •
Rio Grande,
Ft. Craig,
N. M.
1
Letheby,
of the
Agr. S
M
O' **
4>- -
O' 00
00 O'
04
cn
M
00
hi
04.
cn
m 4^
4w N)
0
04
O' 00
0 w 04
4w 00 ^4
04
4k xi *
K4 M
SPi :
M * M
• 0 4k. * Cn cn
I 04 14 * 00 b
I 04 14 . V4 X
05 ^ Bt
CTQ <2.
Nile near Cairo.
Jour.
Khediv.
ociety.
8 m
cn K)
O O
4»-
O'
sO
04
0
•K
M
•K 04
x
04 04
4»-
M N»
^4 nO
0 04 04
x x
4^
0 :
<> ^ •
M M a
x« Cn ’ «
: 0 x. • 04 4k.
: i4 ^ : b b
. O 00 . XI 4k*
-
00 &) Q
on m <
* 04 *
1
O'
K)
M
S'
O'
K)
^4
04 04
cn —
0 N>
M M 04 X • M 4k • N
Cn O' 000 m • 04 04 • 004^-
Cn O *■« 14 x OO CO x Cn • 14 00
O O C«4^ 0 0 0*0 0*0 0
Average
of these
7 Rivers.
John Mur¬
ray, Scot¬
tish Geogr.
Mag., Vol.
3, 1887.
M
O'
00
O'
In
n in
O' N
in
X
Cn
fc>
vj vO
K) vj
4»- h
04 0004 OsO'04K>«x4w 04 Nl (4
0 **4 O 0004 0 4^ H OOM N K> M m 4.
vjo OOOOOOOOO OOOO
(Average
of 19 Great
Rivers of
(the World.
COMPOSITION OF RIVER WATERS. PARTS PER MILLION
24
SOILS.
It will be noted that in all the drain waters, lime is the in¬
gredient most abundantly leached out, and as reference to the
acids shows, mainly in the form of carbonate, also in that of
sulfate. Magnesia is next in amount among the bases; next
in amount is soda, largely in the form of sodium chlorid or
common salt. Potash is present only in small but rather uni¬
form amounts. Of the acids the carbonic is the most abundant,
sulfuric next; chlorin and silicic acid come next, in about
equal amounts. Nitric acid passes off in small, but still rela¬
tively considerable amounts.
Comparison of the drain waters with the river waters, while
showing a general qualitative agreement, also shows a marked
diminution of total solids (from 285.7 to 188.7; hence “ soft
river water”), and especially of lime (from 107.6 to 43.2),
together with the carbonic acid with which it is mostly com¬
bined ; indicating a deposition of lime carbonate in the river
deposits or alluvial lands. There is, on the other hand, little
if any general difference in the magnesia content of the two
classes of waters; nearly the same is true of soda, so that these
two bases really show a considerable relative increase when
the diminished total is considered. Potash remains about the
same all through, viz. two parts or a little more; phosphoric
acid shows a fraction of one millionth ; nitric acid varies greatly
but is usually higher in the drain waters, sometimes showing
a heavy depletion of the land by the leaching-out of this im¬
portant plant food.
It has been computed by John Murray, as quoted by Rus¬
sell,1 that the volume of water flowing into the sea in one
year, including all the land areas of the earth, is about 6524
cubic miles. From the average composition of river waters
as given above, it would follow that nearly five billions (4,975,-
117,588) of tons of mineral matter are annually carried away
in solution from the land into the sea. The amount of sedi¬
ment carried at the same time is many times greater; in the
case of the Mississippi river, it is more than five times the
amount of the matter carried in solution.
Comparison of the river waters among themselves shows
less of any consistent relation to climatic conditions than might
have been anticipated. The waters of the arctic streams
1 Rivers of North America, p. 80.
THE CHEMICAL PROCESSES OF SOIL FORMATION.
25
Yukon and Dwina show wider differences than any two other
waters in the list, unless it be the St. Lawrence, another
northern stream. The Missouri and Rio Grande show by
their high content of soda, chlorin and sulfuric acid their
origin in arid climates, where alkali lands prevail. The water
of the Nile is here represented by two analyses,1 one showing
the season when the water is “ red ” and of high fertilizing
quality because of the sediment it brings down from the
mountains of Abyssinia ; the other the “ green ” and relatively
clear water which comes from the great lakes and through the
“ sudd ” or grassy swamp region near the junction of the
Gazelle river with the Nile. Of the analyses given of the
Mississippi river water, the first represents the average of a
full year’s observations made weekly under the auspices of the
New Orleans Commission on Sewerage and Drainage, by J.
L. Porter. The fourth is an analysis made of water taken at
the same point in May, 1905 ; the analysis having been made in
full by Mr. Stone, of the Reclamation Service of the U. S.
Geol. Survey, the direct determination of potash and soda
being in this case included. As will be seen, and might be ex¬
pected, the average of the Mississippi water corresponds quite
nearly to that of nineteen of the world’s great rivers as given
by Murray. The very great variation in the content of sul¬
fates is evidently due to the occasional heavy influx of the
gypseous waters of the Washita and Red rivers when in flood;
while the minimum content (in January) agrees almost pre¬
cisely with the general average. Murray’s table would hardly
be changed if these analyses of Mississippi water were incor¬
porated therein, owing doubtless to the large and varied
drainage area of the great river.
Sea Water. — The nature of the substances permanently
1 The correctness of Letheby’s analyses has been disputed, partly because of their
disagreement with former analyses in the very high amount of lime, partly because
of the high potash-content in the Low-Nile water. The lime content is, however,
confirmed by the partial analyses made by Matheyin 1887, which gives an average
of 44. 1 for the year, while the older analyses, made in Europe, of transported water
gave only half as much. Letheby working on the spot was doubtless more nearly
right in this respect. His figure for potash in the “ Low-Nile ” water agrees with
former determinations, but that in the “ High-Nile ” is approached only by that in
the Dwina water. It may be suspected that the soda is too low and potash too
high in this analysis.
26
SOILS.
leached out is also seen by considering the composition of sea
water, since the ocean is the final reservoir for all the leachings
of the land. It might be objected that the ocean may have
received its salts from other sources; but this objection is over¬
borne by the fact that substantially the same salts are found in
landlocked lakes, in which, as they have no outflow, the leach¬
ings of the adjacent regions are perforce, as a rule, the only
possible source of the salts. It is true that the nature of the
salts differs somewhat in different lakes, as might be expected ;
but a general statement of that nature will, after all, be the
same as that made in regard to sea-water. The following
table of the average composition of sea-water, according to
Regnault, illustrates these facts.
MEAN COMPOSITION OF SEA-WATER.
Sodium Chlorid (common salt) . 2.700
Potassium chlorid . 070
Calcium sulfate (gypsum) ■. . 140
Magnesium sulfate (Epsom salt) . 230
Magnesium chlorid (bittern) . 360
Magnesium bromid . 002
Calcium carbonate (limestone) . 003
Water (and loss in analysis) . 96.495
100.000
The average saline contents of sea-water would thus be
3.505 per cent. In twenty-one determinations of the saline
contents of the Atlantic Ocean, the percentage ranged from
3.506 to 3.710 per cent. Of this mineral residue, common
salt constitutes from about 75 to over 80 per cent.
We see that most prominent among the ingredients mentioned here
is common salt (sodium chlorid), which forms nearly four- fifths of the
total solid contents. Next in quantity are the compounds of magnesium,
viz. Epsom salt and bittern, with a very small amount of the bromin
compound. Next come the compounds of calcium (lime), of which
gypsum is the more abundant, while the carbonate, so abundant on the
land surface in the various forms of limestone, is present in minute
amounts only, yet enough to supply the substance needed for the shells
THE CHEMICAL PROCESSES OF SOIL FORMATION.
2;
of shellfish, corals, etc. Least in amount of the metallic elements
mentioned is potassium. Calculating the total amounts of chlorin, we
find that it exceeds in weight any one other element present in the salts
of sea-water, being two-sevenths of the whole solids.
Substantially the same result, with variations due to local causes, as
exemplified in the varying composition of river and drain waters, is
obtained when we consider the saline ingredients of lakes having no
outlet, and in which therefore, the leachings of the tributary land area
have accumulated for ages. The Great Salt Lake of Utah, the land¬
locked lakes of the Nevada basin, of California, Oregon, and of the
deserts of Asia, Africa, and Australia, all tell the same tale, which may
be summarized in the statement that the chlorids of sodium and
magnesium, and the sulfates of sodium, magnesium and calcium con¬
stitute the bulk of the leachings of the land ; while of other substances
potassium alone is present in relatively considerable amount.
While the above analysis shows the ingredients of sea-water so far as
they can at present be directly determined by chemical analysis, yet the
presence of many others is demonstrable, directly or indirectly, from
various sources. One is, the mother- waters from the making of sea-salt,
in which such substances accumulate so as to become ascertainable by
chemical means, and even become industrially available in the cases of
potash and bromin. Another is the ash of seaweeds, which is in¬
disputably derived from the sea-water, and contains, among other sub¬
stances not directly demonstrable in the original water, notable quantities
of iodin (of which this ash is a commercial source), iron, manganese,
and phosphoric acid. Again, the copper sheathing of vessels, as it is
gradually corroded, becomes more or less rich in silver, manifestly
thrown down from the sea-water, and the silver so obtained is associated
with minute amounts of gold. Copper, lithium, and fluorin likewise
have been found in sea water ; and it is probable that close search
would detect very many of the other chemical elements as ordinary in¬
gredients in minute amounts. This is what must be expected from the
fact that few mineral substances known to us are entirely insoluble in
pure water, and still fewer in water charged with carbonic acid. The
latter is always present in sea-water and holds the lime carbonate in
solution ; on evaporation or boiling, this substance is the first to be
precipitated ; and thin sheets of limestone from this source are com¬
monly found at the base of rock-salt beds, which, themselves, are
evidently the result of the evaporation of segregated bodies of sea-water
in past geological ages.
28
SOILS.
Summing up the facts concerning the water of the sea and
of landlocked lakes, with reference to the ingredients of soils
needful for the nutrition of plants, it appears that the rock-in¬
gredients leached out in the largest amounts (lime alone ex¬
cepted) are those of which the smallest quantities only are re¬
quired by most plants; while of those specially needful for
plant nutrition, only potash is removed in practically apprecia¬
ble amounts by the stream drainage.
Result of insufficient Rainfall; Alkali Soils. — When the rain¬
fall is either in total quantity, or in consequence of its distribu¬
tion in time, insufficient to effect this leaching, the substances
that otherwise would have passed into the drainage and the
sea are wholly or partially retained in the soil; and when the
rainfall deficiency exceeds a certain point, the salts thus re¬
tained may become apparent on the surface in the form of
saline efflorescences, or as it is usually termed in North Amer¬
ica, “ alkali. ” 1 Their continued presence modifies in various
ways the process of soil formation and the nature of the soils
as compared with those of regions of abundant rainfall (“ hu¬
mid climates ”) ; one of the most prominent and important re¬
sults being that, besides the easily soluble salts mentioned
above, the carbonate of lime formed in the process of decom¬
position is also retained, and imparts to the soils of regions of
deficient rainfall (“arid climates ”) the almost invariable
character of calcareous lands. There is thus in the United
States a marked and practically very important contrast be¬
tween the soils of the arid region west of the Rocky Moun¬
tains and those of the “ humid ’’ region between the immediate
valley of the Mississippi and the Atlantic coast. These differ¬
ences and their practical bearings can be best discussed after
first considering more in detail the chemical decomposition of
the several soil-forming minerals.
1 In some cases the soluble salts originate in rocks impregnated with salts from
marine lagoons or landlocked lakes, or directly from their evaporation residues.
But this is the exception rather than the rule.
CHAPTER III.
THE MAJOR SOIL-FORMING MINERALS.
Since the several stratified rocks, such as sandstones,
shales, claystones, clays, limestones, etc., are themselves
but the outcome of the same disintegrating and decom¬
posing influences upon the crystalline rocks by which
soils are now formed, we must study the action of these influ¬
ences upon the minerals composing the latter rocks in order to
gain a comprehensive understanding of the subject. While
the number of different minerals known to science is very
large, such study need not go beyond a small number of the
chiefly important, rock-forming species which are so generally
distributed as to require consideration in this connection.
These minerals are the following: Quartz and its varieties;
the several feldspars ; hornblende and augite ; the micas ; talc
and serpentine. Calcite, gypsum and dolomite, though not
contained in the older rocks, must be considered because of
their forming large rock deposits by themselves; and zeolites
require mention because, though rarely forming a large pro¬
portion of rocks, they are of special importance as soil ingre¬
dients.
Quartz and the minerals allied to it consist essentially of
dioxid of silicon, usually without (quartz proper) but partly
also with water in combination (opal and its varieties). Sili¬
con is next to oxygen the most abundant element found on the
earth’s surface. It occurs largely in the various forms of
quartz, alone, or as one ingredient of compound rock-masses;
the rest, in combination (as silica) with various metallic oxids,
forms the important group of silicate minerals, constituting
the bulk of most rocks.
Quartz occurs frequently in crystals (rock crystal; six-sided
prisms terminated by six-sided pyramids), clear or variously
colored ; but more abundantly as quartz rock or quartzite, read¬
ily known by its hardness, so as to strike fire with steel, and
29
30
SOILS.
by its glass-like, irregular fracture. Besides the crystalline
quartz rock we find close-grained and at least partly non-crys¬
talline varieties, such as hornstone and flint. Sandstones most
commonly consist of grains of quartz cemented by some other
mineral, or by silica itself ; in the latter case the siliceous sand¬
stone frequently passes insensibly into true quartzite. The
loose sand so well known to common life is prevalently com¬
posed of quartz grains, whose hardness and resistance to
weathering enables them to survive longest the soil-forming
agencies.
Quartz and its allied rocks — jasper, hornstone, siliceous
schist, etc., are all, as already stated, acted on with difficulty
by the “ weathering ” agencies. Crystalline quartz rock may
be considered as practically refractory against all but the
mechanical agencies, and hence remains in the form of sand
and gravel, more or less rounded by attrition, as a prominent
component of most soils; sometimes to the extent of over 92
per cent, even in soils highly esteemed in cultivation, especially
in the arid region. Such soils are mostly the result of the dis¬
integration of sandstones, the cement of which has been dis¬
solved out in the course of weathering; or they may be derived
directly from geological deposits of more or less loose and un¬
consolidated sand. Among crystalline rocks, granites, gneiss
and mica-schists are those most usually concerned in the form¬
ation of sandy soils; since in common parlance, quartz is un¬
derstood to be the substance of the sand unless otherwise stated.
The exceptions are especially important in the regions of de¬
ficient rainfall.
But while crystalline quartz is practically insoluble in all
natural solvents, the same is not true of the jaspers and horn-
stones. These consist of a mixture of crystalline and amor¬
phous (non-crystalline) silica, which is more readily soluble
than the crystalline, and is attacked by many natural waters,
especially by those containing even very small amounts of the
carbonates of potash or soda. We thus often find that horn¬
stone and jasper pebbles buried in the soil, while still hard in¬
ternally, have externally been converted into a friable, almost
chalky substance, consisting of crystalline quartz from which
the cementing amorphous silex has been removed by the soil
water. In the course of time such pebbles may be completely
THE MAJOR SOIL-FORMING MINERALS.
31
destroyed by this process, so as to be light and chalky through¬
out, and readily crushed in tillage. The change is the more
striking when, as frequently happens, the hornstone pebble is
traversed by small veins of crystalline quartz, which remain as
a skeleton.
Solubility of Silica in Water. — It is easily shown experimen¬
tally that the compound of silica with water (hydrate) is under
certain conditions readily soluble not only in pure water, but
also in such as contains carbonic acid. It thus occurs in nearly
all spring and well waters; some hot springs deposit large
masses of it (sinter) ; and geological evidence clearly demon¬
strates that quartz veins have as rule been formed from water-
solutions of silica.
That silica in its soluble form circulates freely in the soil
water, is abundantly evident from the large amounts of it
which are secreted on the outside of the stems of grasses, horse¬
tail rushes and other plants, imparting a gritty roughness to
their outer surface. In the case of the giant bamboo grass of
Asia, the silica accumulated on the outside of the joints forms
a hard sheath of considerable thickness, known to commerce
as tabashir.
That among the first products of rock decomposition we
often find small amounts of the silicates of the alkalies (potash
and soda) has already been mentioned. It cannot be doubted
that the same continues to be formed in soil containing the
proper minerals ; and there they also take part in the formation
of the easily decomposable hydrous silicates designated as
zeolites, which are largely instrumental in retaining the “ re¬
serve ” of mineral plant-food in soils.
SILICATE MINERALS.
Silica occurs in nature combined with the oxids of most
metals, forming silicates ; but most abundantly with the earths
(lime, magnesia, alumina) and alkalies (potash and soda).
These compounds are the most important in soil formation;
and among them the following are the chief :
The Feldspars, which may be defined as compounds of
silicates of potash, soda or lime (either or all) with silicate of
alumina. They are prominent ingredients of most crystalline
32
SOILS.
rocks; potash feldspar (orthoclase) with quartz and mica forms
granite and gneiss; feldspars containing soda and lime (either
or both) form part of many other crystalline rocks, such as
basalt, diabase, diorite, gabbro and most lavas. The feldspars
are decomposed by weathering rather readily, and are import¬
ant in being the chief source of clays as well as of potash in
soils. When acted upon by carbonated water, the bases
potash, soda, and lime or carbonates, the silica being mostly
displaced; while the silicate of alumina takes up water and
forms kaolinite, the essential basis of clays, and one of the
most important constituents of soils; imparting to them the
necessary firmness and cohesion, together with other important
physical properties, discussed more in detail hereafter.
While thus on the one hand feldspars are the source of clay,
on the other they supply one of the most essential ingredients
of plant food, viz. potash ; which is first dissolved by the water
in the forms of carbonate and silicate, but in most cases soon
becomes fixed in the soil by forming more complex (zeolitic)
combinations. The soda not being retained by the soil as
strongly as is potash is washed through into the country drain¬
age; while if lime is present, it mostly remains in the form of
the carbonate.
Orthoclase feldspar contains nearly 17% of potash;
Leucite, a related mineral occurring in some lavas, contains
21.5%. The other feldspars contain only a few per cent,
sometimes none.
Other silicate minerals, so far as they contain the same
bases, are acted upon similarly to the feldspars.
In the decomposition of the feldspars by carbonated water, the com¬
pounds of potash and soda so formed are soluble in water, those of
lime and magnesia are insoluble or nearly so. Hence pure clays can
be formed only in the decomposition of the potash- and soda-feldspars
(orthoclase, albite) while in the case of lime feldspar (labradorite) and
the mixed feldspars (plagioclase, anorthite) calcareous clays (marls)
are the result. Lime feldspar resists decomposition more tenaciously
than do those containing large proportions of the strong bases potash
and soda ; potash feldspar especially is attacked most readily, and is
the main source of the formation of the valuable deposits of porcelain
earth or kaolin, which is essentially a mixture of kaolinite with fine silex
and more or less of undecomposed feldspar, and is of a chalky texture.
THE MAJOR SOIL-FORMING MINERALS.
33
Formation of Clays. — When instead of remaining in place,
this kaolin is washed away and triturated in the transportation
by water, it is partially changed from its original chalky con¬
dition to that plastic and adhesive form which is the character¬
istic ingredient of all clays. The remarkable properties of this
substance and the part it plays in the physical constitution of
soils, will be discussed in another chapter. Its lightness and
extreme fineness of grain (if grain it can be called) cause it to
be carried farther on by the streams than any other portion of
the products of rock-decomposition save those actually in
solution ; it can therefore be deposited only in water that is
almost or quite still (as in swamps) so long as the latter is
fresh. So soon however as brackish or salt water is en¬
countered, clay promptly gathers into floccules (“ floccu¬
lates”), and thus enveloping the finest-grained silts that may
have been carried along with it, it quickly settles down, form¬
ing the “ mud banks ” and heavy clay soils that are so char¬
acteristic of the lower deltas of rivers, as well as of swamps
formed by the backwater or overflow of the same.
When instead of potash feldspar alone, the lime- or soda-
lime feldspars are also concerned in the decomposition process,
the resulting clay soils will be more or less calcareous, while
the soda, as stated above, is for the greater part leached out
permanently.
Hornblende (Amphibole) and Pyroxene (Augite). These
are two very widely diffused minerals, differing but little in
composition though somewhat differently crystallized, mostly
i/n short columnar forms. The typical and most abundant
varieties of these minerals appear black to the eye, though in
thin sections they are bottle-green; they form the black in¬
gredient of most rocks.
The color is due to ferroso-ferric (magnetic) oxid of iron ; the mineral
as a whole may be considered as a silicate of lime, magnesia, alumina
and iron, varying greatly in their absolute proportions ; alumina and
iron being sometimes almost absent. When iron is lacking the mineral
may be almost white (tremolite, asbestos), and its weathering is then
much retarded, since the oxygen of the air cannot take part in the pro¬
cess of disintegration.
The black variety of hornblende is not only the most abun-
3
34
SOILS.
dant as a rock-ingredient, but it also the one most easily de¬
composed and therefore most commonly concerned in soil
formation. The black hornblende owes its easy decomposi¬
tion under the atmospheric influences to two properties; one,
its easy cleavage, whereby cracks are readily formed and ex¬
tended by the agencies already mentioned (pp. 1-3). The other
is its large content of ferrous silicate (silicate of iron pro¬
toxide), whereby it is liable to attack from atmospheric oxy¬
gen; the latter forms ferric hydrate (iron rust) out of the pro¬
toxide, thus causing an increase of bulk which tends to split the
masses of the mineral in several directions, while the silex is
set free. At the same time the carbonic acid of the air con¬
verts the silicate of lime and magnesia, which forms the rest
of the mineral, into carbonates; and the alumina present forms
kaolinite, as in the case of the feldspars. There is thus
formed from this mineral, when alone, a strongly rust-colored,
more or less calcareous and magnesian clay, constituting the
material for rather light-textured “ red ” soils. In most
cases however the hornblende is associated in the rock itself
with the several feldspars, (mostly lime- and soda-lime feld¬
spars) as well as with more or less quartz. The rust-colored
soils are therefore most commonly the joint result of the
weathering of these several minerals. This is well exempli¬
fied in the case of the “ red ” soils formed from the so-called
granites and slates of the western slope of the Sierra Nevada
of California.
Pyroxene or Augite so nearly resembles hornblende in its
chemical composition and crystalline form, that what is said of
the latter may be considered as applying to augite also. Owing
however to the absence of any prominent tendency to cleavage,
the smooth crystals of this mineral are attacked much less
readily than is hornblende, so that we often find them as
“ black gravel ” in the soils formed from rocks containing
it. Such soils are particularly abundant and important in the
region covered by the great sheet of eruptive rocks (basalts,
so-called) in the Pacific Northwest, and on the plateau of
South Central India (the Deccan), and result likewise from
the decomposition of the black lavas of volcanoes; thus in the
Hawaiian islands, and in the Andes of Peru and Chile.
Both hornblende and augite being either free from, or de-
THE MAJOR SOIL-FORMING MINERALS.
35
ficient in potash, of course the soils formed from them are apt
to lack an adequate supply of this substance for plant use.
This is markedly true of hornblende schist or amphibolite
rocks.
Mica, commonly known as isinglass, is so conspicuous
wherever it occurs that it is more readily recognized than any
other mineral. It occurs in glittering scales in soils and
sands, and in rocks it sometimes forms sheets of sufficient size
to supply the small panes for the doors of stoves, lamp
chimneys, etc., which being flexible are not liable to break, bur
only gradually scale into very thin films, into which it can also
be split by hand. When white, (muscovite, phlogopite) its
scales are sometimes mistaken for silver by mine prospectors ;
when yellow, for gold ; but their extreme lightness should
soon remove these delusions. The composition of mica is not
widely different from that of the two preceding minerals ; like
these it sometimes contains much iron, and is then dark bottle-
green (biotite) ; this variety in weathering becomes bright
yellow, and soon disintegrates.
This mineral is so abundant an ingredient of many rocks and
soils, that one naturally looks for it to play some definite or im¬
portant part in soil formation. By its ready cleavage it favors
the disintegration of rocks ; but it seems that owing to the ex¬
tremely slow weathering of its smooth, shining cleavage sur¬
faces, it exerts no notable effect upon the chemical composi¬
tion of the soil, although, owing to its peculiar character of
fine scales, it sometimes adds not immaterially to the facility
of tillage in otherwise somewhat intractable soils. So far as
is known at present, its presence or absence does not constitute,
in itself, any definite cause or indication of the quality of any
soil. It may nevertheless be said that the rock in which it
usually occurs most abundantly — mica-schist, a mixture of
mica and quartz — is known to form, as a rule, lands of poor
quality. On the other hand, the soils derived from granites
and gneisses, even when rich in mica, are usually excellent, on
account of their content of feldspars, and frequently of other
associated minerals.
Hydomica differs from the preceding mainly in containing
a larger proportion of combined water; but it hardly de-
36
SOILS,
composes more readily, and the rocks in which it mainly occurs
(hydromica schists) are refractory to weathering, and in any
case do not yield soils of any fertility, the mineral being as¬
sociated simply with quartz.
Chlorite , essentially a silicate of alumina and iron, somewhat
resembles mica but is deep green or black, in small scales. It
forms part of certain rocks (chlorite schists), which greatly
resemble the hornblende schists, but are usually inferior to the
latter as soil-formers, containing but little of any direct value to
plant life.
Talc and Serpentine, Hydrous silicates of magnesia, are
extensive rock-materials in some regions, and as such require
mention as soil-formers also. Serpentine usually forms black¬
ish-green rock-masses, that although soft disintegrate very
slowly in the absence of definite structure, and are attacked
with some energy only when charged — as is frequently the
case — with ferrous oxide. The conversion of this into ferric
hydrate, so common in nature, here also serves as the point of
attack on a rock otherwise very stable; causing it to crumble,
even though slowly.
Talc (the true “soapstone") being usually free from iron,
would be even more slow than serpentine to yield to weather¬
ing, but that its extreme softness and ready cleavage greatly
facilitate its abrasion. Thus talc schist, which is usually a
mixture of talc with more or less quartz, undergoes mechanical
disintegration quite readily.
But the soils formed from either serpentine or talcose rocks
are almost always very poor in plant food, and sometimes
totally sterile. Magnesia, though an indispensable ingredient
of plant food, is rarely deficient in soils and unlike lime does
not influence in any sensible degree the process of soil forma¬
tion. Magnesian rocks as a whole are practically found to be
not specially desirable soil-formers, even in the form of
magnesian limestones. They do not even, as a rule, contain
as many useful accessory minerals as are commonly found in
limestones. Moreover, an excess of magnesia over lime is
injurious to most crops, as is shown later (chapt. 18).
The Zeolites. — Zeolites may be defined as hydro-silicates
containing as bases chiefly lime and alumina, commonly to-
THE MAJOR SOIL-FORMING MINERALS.
37
gether with more or less of potash and soda, more rarely
magnesia and baryta. The water is easily expelled by heat¬
ing, but is present in the basic form, not merely as water of
crystallization. All zeolites are readily decomposed by chlor-
hydric and other stronger acids.
The zeolites proper are not original rock ingredients, but are formed
in the course of rock decomposition by atmospheric agencies, heated
water, and other processes not fully understood. They are therefore
usually found in the cavities and crevices of rocks that have been sub¬
ject to the influence of atmospheric or thermal waters, most frequently
in eruptive rocks, particularly in the vesicular cavities characterizing
what is known as amygdaloids. They are also found in the crevices of
sandstones and shales percolated by water, as well as in nodules of
infiltration (geodes), in which they are frequently associated with quartz.
Those found in the cavities of rocks are usually well crystallized wherever
room is afforded, and are readily recognized by their crystalline form;
they are mostly colorless, sometimes yellow or reddish.
Exchange of bases in Zeolites. — Although zeolites rarely
form a large proportion of rock masses and therefore do not
enter directly into the soil minerals to any great extent, their
interest in connection with soil-formation is very great, because
of the continuation, within the soil, of the same processes that
bring about their formation in rocks. Under the conditions
existing in soils they will naturally rarely form crystals, but
will appear in the pulverulent or gelatinous form, leaving the
zeolitic nature of the material to be inferred from its chemical
behavior. Among these characters the ready decomposability
by acids has already been mentioned ; another of special import¬
ance in the economy of soils is the fact that when a pulverized
zeolite is subjected to the action of a solution containing either
of the stronger bases usually present (potash, soda or lime),
such base or bases will be partially or wholly taken up by the
zeolitic powder, while corresponding amounts of the bases
originally present will pass into solution.
Thus when a hydrosilicate of soda and alumina is digested with a
solution of potassic chlorid or sulphate, the soda may be partially or
wholly replaced by potash, while the corresponding sodium salt passes
into solution. In the case of zeolites containing lime or magnesia or
38
SOILS.
both, the action of potassic or sodic chlorid will be to partially replace
the lime, while calcic and magnesic chlorids pass into solution, result¬
ing in the partial or complete replacement of the lime by one or the
other, or by both bases. It is important to note that, other things
being equal, potash is usually absorbed in greater amounts and is held
more tenaciously than soda. The process may frequently be partially
or wholly reversed again, by subsequent treatment with large amounts
of solutions of the displaced base or bases. Thus while a solution of
potassic chlorid may be made to expel almost completely the sodium
present in analcite, subsequent treatment with sodic chlorid solution
will again almost completely displace the potash before taken up. The
same happens when the natural mineral potash leucite, (see p. 32) of fre¬
quent occurrence in certain lavas, is pulverized and treated with a sodic
solution ; resulting finally in the production of a mass corresponding to
natural analcite, the sodium mineral corresponding to leucite.
In other words, in any zeolitic powder the alkaline or alkaline
earth bases present may be partially or wholly displaced by
digestion with an excess of solution of any of these, varying
according to the amount of solution employed, and the length
of time and temperature of action.
This characteristic behavior of zeolites is exactly reproduced
in soils. Few soils permit any saline solution to pass through
them unchanged ; solutions of alkaline chlorids filtered through
soils almost invariably cause the passing through of calcium
and magnesium chlorids, while a part of the alkaline base is re¬
tained ; and as a matter of fact, we find that this absorbing
power of soils for alkaline bases is more or less directly pro¬
portional to the amount of matter which may be dissolved or
decomposed with elimination of silica, by means of acids.
This absorption of bases from solutions by chemical fixation will be
farther discussed later on ; but it should be mentioned here that both
naturally and artificially, rock-masses are very commonly cemented,
wholly or in part, by zeolitic material. Hydraulic concretes may be
considered as sandstones or conglomerates whose grains are cemented by
a zeolitic cement consisting of silica, lime and alumina, with usually some
potash or soda, and of course containing the basic water ; hence unaf¬
fected by the farther action of the latter substance after the time of setting
has expired, which varies somewhat according to the nature of the material
used. That similar cements should occur in natural sandstones is to be
THE MAJOR SOIL-FORMING MINERALS.
39
expected ; thus we find not unfrequently that certain sandstones are
materially softened, and their resistance destroyed, by treatment with
even moderately dilute acid, while silica and the usual zeolite bases pass
into solution. It is not often, however, that zeolitic material alone
cements the sandstone ; it is most frequently associated with siliceous,
calcareous and sometimes even with ferruginous cementing material.1
CALCITE AND LIMESTONES.
Calcite or calcareous spar is one of the minerals most com¬
monly known in the crystallized form, and is readily recognized
by its perfect cleavage in three directions, producing cleavage
forms with smooth, rhomb-shaped faces (rhombohedrons) ;
these are sometimes colorless and perfectly transparent, and
laid on printed paper show the letters double. But it may be
whitish-opaque, and of various colors, which may also be im¬
parted to the limestones formed from it. It is readily dis¬
tinguished from quartz, which it sometimes resembles, by its
cleavage, its inferior hardness, being easily scratched with a
knife; and by its effervescence with acids, the latter being the
crucial test when other marks are unavailable, as when it forms
soft granular masses or “ marls.” In all cases it can be recog¬
nized by its crystalline form under the microscope, even when
the substance containing it has been pulverized in a mortar.
The great importance of this compound — calcic carbonate —
from the agricultural point of view renders it desirable that
it, as well as limestones as such, should be recognized, when
seen, by every farmer.
In mass the pure mineral constitutes white marble ; colored or vari¬
egated marbles are more or less impure from the presence of other
minerals. Some compact limestones also are nearly pure ; and as sup¬
plying only a single ingredient of plant food these would not be much
better soil-formers than quartz or serpentine. But it is quite otherwise
with common limestones ; the mass of which, it is true, is formed of
calc-spar, but owing to its origin, is in the great majority of cases so far
commingled with other matters of various character, that limestones are
1 A zeolitic mass, at first gelatinous and then becoming granular-crystalline is
frequently observed oozing from the lower surface of newly made concrete reservoir
dams : just as we find similar oozes consolidated into natrolite crusts in ths
crevices of natural sandstones.
40
SOILS.
popularly reputed to form the very best soils. “ A limestone country
is a rich country ” is a popular axiom to which there are, on the whole,
but few exceptions.
Origin. — Actual observation of what is happening at the
present time, as well as the examination of the rock as anciently
formed, prove conclusively that with insignificant exceptions,
all limestones have been formed from the framework and
shells, and to some extent from the bones, of marine and
fresh-water organisms, ranging in size from the extinct giants
of the lizard relationship to those recognizable only by the
microscope. Owing to the solubility of lime carbonate in car¬
bonated water, the organic forms have often (in crystalline
limestones) been almost completely obliterated in some por¬
tions, but in others are so preserved as to prove undeniably
the similarity of origin of the whole, and that they have been
formed in relatively shallow water, as they are to-day.
Impure Limestones as Soil-formers. — From what has been
said regarding the composition of sea-water, it will readily be
inferred that a pure deposit of any one kind cannot easily be
formed in it; moreover, the matter held in mechanical sus¬
pension everywhere near the coasts must very commonly be
included within the calcareous deposits formed off-shore.
Hence few limestones dissolve in acids without leaving a
residue of sand, clay and various other substances, usually
even some organic matter not fully decomposed ; sometimes
less than half of the mass is really lime carbonate. It is
obvious that when the solvent action of carbonated water is
exerted upon such impure limestones, a loose residue of earthy
matters will remain behind. It is by this process that a con¬
siderable proportion of the richest soils in the world have been
formed, which have given rise to the popular maxim above
quoted. They are emphatically “ residual ” soils ; sometimes,
it is true, somewhat removed, by washing-away, from their
point of origin, but in many cases forming a compact soil-
layer on top of the unchanged rock, into which there exists
every shade of transition. Striking examples of such residual
soils in place are seen in the black prairies of the southwestern
United States; they are mostly rather “stiff” (clayey), and
hence has arisen a local popular error, to the effect that clay
THE MAJOR SOIL-FORMING MINERALS,
41
or “ heavy ” soils are always calcareous. On the other hand,
the blue-grass region of Kentucky, and most of the lands of the
arid regions are prominent examples of “ light ” calcareous
soils.
CaveSy Sinkholes , Stalactites . — Perhaps the most striking exempli¬
fication of the solvent power of carbonated water is seen in the form¬
ation of limestone caves. As a matter of fact, the vast majority of all
existing caves is found in limestone formations ; and such formations,
as will be more fully discussed hereafter, nearly always bear a luxuriant
vegetation. The water filtering through the vegetable mold, in which
carbonic acid is constantly being formed, becomes charged with it, and
on reaching the underlying rock, dissolves to a corresponding extent
the lime carbonate of which this rock wholly or chiefly consists. When
penetrating crevices it soon enlarges these, to an extent proportioned
to the length of time and the strength of the solvent ; and thus gradually
subterranean passages or caves are formed, which at first are almost
always the bed of a stream, the mechanical action of which accelerates
the process of enlargement, until after some time the water is perhaps
drained off through some crevice to a lower level, where the same pro¬
cess is repeated.
Sometimes the ceiling gives way, forming the funnel-shaped “ sink¬
holes ” or “ lime-sinks ” so familiar in some of the Mississippi Valley
States. Sometimes the lime solution on reaching the ceiling of the
cave, instead of dropping down, evaporates there and eventually forms
icicle-like “ stalactites ” out of the dissolved substance ; while when
dropping on the floor and thus growing upwards, the corresponding
formation is called “ stalagtnite.” These caves, subterranean rivers,
sinkholes, natural bridges and tunnels, etc., mostly owe their origin to
this solvent action of carbonated water on limestone formations.1
The same occurs on a small scale, when calcareous land is
underdrained ; the lime carbonate dissolved from the soil is
partially deposited in the drain pipes, which it frequently ob¬
structs. Similarly, an impure, porous deposit of calcareous
tufa is frequently formed on the surface, at the foot or in rills
1 T. M. Reade (in his treatise on Chemical Denudation in Relation to Geological
Time) calculates that 143.5 tons °f fime carbonate are annually removed by solu¬
tion from each square mile of land in England and Wales, and that the average
amount thus removed annually from each square mile of the earth’s surface
is about fifty tons.
42
SOILS.
of calcareous hills. When “ hard ” water, being usually such
as contains lime carbonate dissolved in carbonic acid, is boiled,
or long exposed to the air, carbonic gas escapes and the lime
salt is deposited partly on the walls of the kettle, partly form¬
ing a pellicle on the surface of the water.
Dolomite, or bitter spar, greatly resembles calcite in its as¬
pect and properties, although containing nearly half its weight
(47.6%) of magnesic, together with calcic carbonate. It is,
however, nearly always whitish-opaque; its crystalline and
cleavage surfaces are usually somewhat curved; and its effer¬
vescence with acids is much less lively than in the case of
calcite. Like the latter it often forms pure granular rock de¬
posits, frequently used instead of marble and limestone, and
under that designation. The dolomite rocks, however, are
much more subject to weathering than the non-magnesian lime¬
stones, and it is a curious fact that in contradistinction to the
limestone regions proper, those having strongly magnesian
limestones or dolomites as their country rock are frequently
remarkably sterile. In some portions of Europe dolomite
areas are sandy deserts, whose sand consists of weathered do¬
lomite, so pure as to offer no adequate supply of mineral food
to plants. In the United States, magnesian limestones under¬
lie the “ barrens ” of several States and thus seem to justify
their European reputation of being poor soil-formers. The
exact cause of this difference is not fully understood, for at
first sight it is not clear why the presence of the magnesian
carbonate should interfere with the well-known beneficial ef¬
fects of the lime compound. O. Loew and May 1 and others
have, however, shown that a certain excess of lime over mag¬
nesia in the soil is necessary to prevent the injurious effects
exerted by magnesic compounds on plant nutrition, in the ab¬
sence of an adequate supply of lime. This point will be dis¬
cussed more in detail farther on.
Selenite or Gypsum, sulfate of lime with about 14 per cent
of water, though not as abundant in nature as the carbonate or
limestone, is a very widely disseminated mineral and often
occurs in large masses over considerable areas. These are un¬
doubtedly in most cases the result of evaporation of sea water
1 Bull. No. 1, U. S. Dept. Agr. Veg. Path, and Physiol. Investig.
THE MAJOR SOIL-FORMING MINERALS.
43
(see p. 26), more rarely of the transformation of limestone.
In mass it frequently resembles the latter, but is readily dis¬
tinguished by its softness; it does not grit between the teeth,
is readily cut with a knife and does not effervesce with acids.
Very commonly it occurs in crystals, which are easily split into
thin plates. The crystals are very frequently found imbedded
in gray or bluish, tough clays, in rosettes, or flat sheets which
mostly show characteristic incurrent angles (caused by twin¬
ning), and are hence known as “ swallowtail ” crystals. Such
sheets of selenite are popularly called “ isinglass/’ which name
however is equally applied to the mineral mica (see p. 35).
Gypsum is only exceptionally an abundant ingredient of
soils; yet such soils prevail quite extensively on the upper Rio
Grande, in New Mexico and adjacent portions of Chihuahua,
Coahuila, and on the Staked Plains of Texas. Here whole
ranges of hills are sometimes composed of gypseous sand, bear
a scanty, peculiar vegetation, and are ill adapted to agricultural
use. It may be said in general that few naturally gypseous
soils are very productive. This is largely because of the very
heavy clays which commonly accompany it, as the compound it¬
self is not only not hostile to plant life but is in extended use as
a valuable fertilizer (‘Hand plaster”) for special purposes.
From causes not fully understood as yet, it particularly pro¬
motes the growth of leguminous plants, notably the clovers;
and as stated in chapter 9, it also specially favors nitrification in
soils. In the arid region it renders important service in the
neutralization of “ black alkali ” or carbonate of soda in alkali
soils. Being soluble in 400 parts of water, it easily penetrates
downward in most soils, and in doing so effects changes in the
zeolitic portions, setting free potash from silicates and thus in¬
directly supplying plants with this essential ingredient in a
soluble form. About 200 pounds per acre is an ordinary dose.
For agricultural use the rock gypsum is ground in mills
so as to be easily distributed, and dissolved by the soil water.
Frequently, however, it occurs in the soft granular form
(gypseous marl) requiring only light crushing; thus in the
hills bordering the Great Valley of California, and in parts of
New Mexico and Texas.
Iron Minerals. — In connection with calcite and dolomite, the
44
SOILS.
several minerals constituting the common iron ores require
mention. One of these is :
Iron Spar or siderite; carbonate of iron, corresponds in com¬
position to calcite and dolomite and crystallizes in the same
form. It sometimes occurs in large masses and is an import¬
ant iron ore, brownish-white in color, and when compact re¬
sists the attack of atmospheric oxygen remarkably well. Like
the carbonates of lime and magnesia, it is soluble in carbonated
water, and its deposits are undoubtedly formed from such
solutions. The latter are copiously formed wherever ferment¬
ing or decaying organic matter is in contact with iron-bearing
materials, such as rust-colored sands or clays; and if the
solution so formed can percolate without coming in contact
with air, iron-spar is formed. But whenever the solution
comes in contact with air, it absorbs oxygen and the ferrous
carbonate is converted into ferric hydrate or rust, mineralogi-
cally known as :
Limonite or brown iron ore. This ore is frequently found
deposited on the upper surface of clay layers traversing sandy
strata, the clay having arrested the carbonate solution and thus
given time to the air to effect the change. Sometimes such
deposits form great masses in rock-caves, fissure-veins, or
crevices; and like siderite, it is an important iron ore, though
frequently quite impure, as in the case of bog ore , which is
formed in ill-drained subsoils. It is also sometimes found as
the residue from the weathering of rocks rich in hornblende
or pyroxene, and in this, as well as in other cases, is pulveru¬
lent, constituting yellozv ochre. It makes a rust-colored streak
on biscuit porcelain or unglazed queens ware. It is the coloring
material of all yellozv or “ red ” soils and clays , as well as of
brown sandstones, which are cemented by it.
As is well known, such clays and sandstones become dark
red by heating or “ burning/’ as in the case of common brick
clays; the brown or yellow ferric hydrate losing its water and
becoming red ferric oxid. The latter sometimes occurs in
nature in the impure, pulverulent condition, constituting “ red
ochre ”; but more commonly and abundantly it is found in the
form of
Hematite or red iron ore, which is sometimes formed in
THE MAJOR SOIL-FORMING MINERALS.
45
nature by limonite losing its water, but more commonly in
different ways. It is but rarely found in soils and is of no
special interest in that connection.
A fourth form of iron ore, quite common in the soils of some
regions, is
Magnetite or magnetic iron ore, also known as lodestone.
This mineral, the oxygen-compound of iron corresponding to
“ blacksmith’s scale,” also occurs in large masses and is an
important and usually a very pure iron ore. It occurs very
commonly disseminated through certain rocks, and in their
weathering it remains unattacked and thus passes unchanged
into the soils and sands, constituting the “ black sand ” so well
known to gold miners and almost universally present in the
alluvial soils of the Pacific coast. These black grains are of
course attracted by the magnet and can thus be easily recog¬
nized and extracted. In soils they are simply inert, like quartz
sand.
But while the ore is of little interest to the farmer, it is quite
otherwise with the compound of this oxid with water, the
ferroso-ferric hydrate; intermediate in composition between
the white ferrous and the brown ferric hydrates. As men¬
tioned above, the black silicate minerals, such as hornblende
and pyroxene, are bottle-green when seen in thin sections.
Nearly the same color, with modifications running toward blue
and bright green, is often seen in natural clays and rocks,
and is almost always caused by the ferroso-ferric hydrate.
Such materials always become red or reddish when heated by
the formation of red ferric oxid ; while when exposed to damp
air, they assume the rust color of ferric hydrate.
Reduction of ferric hydrate in ill-drained soils. — When such
oxidized, rust-colored clays or soils are exposed to the action
of fermenting organic matter, the first effect observed is the
change of color from rusty to bluish or greenish, by the reduc¬
tion of the ferric to ferroso-ferric hydrate. Afterward, if the
action is continued, the solution of ferrous carbonate (see
above) may be formed, and the greenish or bluish color may
disappear.
The importance of this reaction to farming practice lies in
the fact that the blue or green tint, wherever it occurs, indi¬
cates a lack of aeration, usually by the stagnation of water, in
46
SOILS.
consequence of imperfect drainage. Such a condition, always
injurious to plants, becomes doubly so when it is associated
with the formation of a metallic solution, such as ferrous
carbonate, and promptly results in the languishing or death of
plants in consequence of the poisoning of their roots. In the
presence of sulfates such as gypsum, the formation of iron
pyrites (ferric bisulfid) and sulfuretted hydrogen, is likely to
take place. Moreover, under the same conditions the phos¬
phoric acid of the soil may be concentrated into ferrous or
ferric phosphate, which pass into deposits of bog ore in the
subsoil.
CHAPTER IV.
THE VARIOUS ROCKS AS SOIL-FORMERS.
Rock-weathering in arid and humid Climates. — From what
has been said in the preceding chapters of the physical and
chemical agencies concerned in rock-weathering, it is obvious
that climatic differences may materially influence the character
of the soils formed from one and the same kind of rock. Since
kaolinization is also a process of hydration, the presence of
water must greatly influence its intensity, and especially the
subsequent formation of colloidal clay ; so that rocks forming
clay soils in the region of summer rains may in the arid regions
form merely pulverulent soil materials. Many striking ex¬
amples of these differences may be observed, e. g., in comparing
the outcome of the weathering of granitic rocks in the southern
Alleghenies with that of the same rocks in the Rocky Moun¬
tains and westward, especially in California and Arizona. The
sharpness of the ridges of the Sierra Madre, and the roughness
of the hard granitic surfaces, contrasts sharply with the
rounded ranges formed by the “ rotten ” granites of the At¬
lantic slope, where sound, unaltered rock can sometimes not
be found at a less depth than forty feet ; while at the foot of
the Sierra Madre ridges, thick beds of sharp, fresh granitic
sand, too open and pervious to serve as soils, cover the upper
slopes and the “ washes ” of the streams, causing the latter to
sink out of sight. A general discussion of the kinds of soils
formed from the various rocks must, therefore, take these
differences into due consideration.
GENERAL CLASSIFICATION OF ROCKS.
Rocks may be broadly classified into three categories, viz:
1. Sedimentary rocks, formed by deposition in water and
hence more or less distinctly stratified.
2. Metamorpliic rocks, formed from rocks originally sedi¬
mentary, by subterranean heat in presence of water. Usually
47
43
SOILS.
crystalline, that is, composed of more or less distinct (large or
minute) crystals of one or several of the minerals mentioned
above.
3. Eruptive rocks, ejected in the molten state from vol¬
canoes or fissures; crystalline or not, according to slow or
rapid cooling.
Sedimentary Rocks. — Sedimentary rocks are forming to-day
by deposition from either sea or fresh water, precisely as they
were in the most remote geological times; the oldest clearly
sedimentary rocks being sometimes undistinguishable in their
nature and composition from the very latest immediately pre¬
ceding our present time. They may for the purposes of the
present work be simply classified as follows :
1. Limestones, formed in comparatively shallow seas, or
fresh water basins, from the calcareous shells or skeletons of
various organisms.
2. Sandstones, and conglomerates (sometimes called pud¬
ding-stones) formed from the debris of pre-existing rocks dis¬
integrated by the agencies described above, (chap. 1-2), re¬
cemented by means of solutions of one or several substances,
such as silex, carbonate of lime, ferric hydrate and others.
Loose sands and gravels are the initial stages of such rock for¬
mation as well as the results of their disintegration.
3. Clays, Claystones and Clay shales, consisting of clay sub¬
stance with more or less sand, and soft or hard according to
the nature of the waters or solutions that may have acted upon
them, with or without the aid of heat. These rocks can only
be formed in comparatively quiet or “ back ” waters, since
clay would not ordinarily be deposited in moving water.
Metamorphic Rocks. — The effects of subterranean heat or
metamorphism upon the sedimentary rocks may be roughly
stated as follows:
Limestones are transformed into marbles of various degrees
of purity, according to the nature of the original rocks.
Sandstones when cemented by silex are transformed into
quartzite, of greater or less purity according to the nature of
the “ sand ” entering into its composition. When cemented
by materials other than quartz, these also will be segregated
in the form of various minerals in the body of the rock.
THE VARIOUS ROCKS AS SOIL-FORMERS.
49
The clay rocks form the most varied products under the in¬
fluence of (aqueo-igneous) metamorphism; granites, gneiss,
syenite and hornblendic schist are among the most common.
The great variations in the composition of clayey materials
account for the correspondingly great variations in the nature
of the resultant metamorphic rocks.
Igneous or Eruptive Rocks. — These are usually divided into
two groups ; the one characterized by a large proportion of free
quartz (silicic acid), and hence designated as acidic, and usu¬
ally of a light tint; the other the basic, containing little or no
free quartz, and commonly of a dark tint caused by the pres¬
ence of a large amount of iron (contained in pyroxene, more
rarely in hornblende).
Of the latter class are the dark “ basaltic ” rocks constituting the
mass of the enormous eruptive sheet of the Pacific Northwest, covering
the greater part of Washington, Oregon and northeastern California.
The lavas of the Hawaiian islands are of the same class and even more
basic; while the eruptives of Nevada, middle and southern California,
and eastward to the Rocky Mountains, are mostly of the light-colored,
acidic type. The same is largely true of the rocks of the Andes of
Central and South America, the gray “ Andesites,” also represented in
the Caucasus.
As one and the same eruptive material may, according to
the greater or less rapidity of cooling, appear as a glassy mass
(obsidian, pumice, volcanic ash, tuff, etc.,) or as a crystalline
rock resembling coarse granite in structure, it is not easy to
identify them in all their various forms. This can frequently
be done only by ascertaining their component minerals by the
microscope, or by chemical analysis. The same is sometimes
true of metamorphic rocks; and as in the latter, the several
feldspars and quartz, with pyroxene instead of hornblende, con¬
stitute the predominant soil-forming minerals. More rarely,
garnet, chrysolite, leucite and other silicates require considera¬
tion.
Generalities regarding the Soils derived from various Rocks.
It is hardly necessary to insist that as in the case of the
rocks composed of single minerals, already referred to above,
4
50
SOILS.
the predominant mineral or minerals of compound rocks de¬
termine the facility of weathering-, as well as the quality of the
soil resulting therefrom. Since rocks are named essentially
in accordance with the kinds of minerals that constitute their
regular mass, the proportion in which the several constituents
stand to each other may vary greatly. Thus a granite may
consist, over considerable areas, mainly of a mixture of potash
feldspar and quartz ; in others, mainly of quartz and mica with
little feldspar. Very frequently, hornblende replaces mica par¬
tially or wholly. The latter will weather much more slowly
than feldspar or hornblende, and will produce an inferior soil
when decomposed. Allowing for such variations, a fairly ap¬
proximate general estimate of the quality and peculiarities of
soils from crystalline rocks may nevertheless be made. To
some extent such estimates must make allowance not only for
the chief ingredients, but also for those which are called “ ac¬
cessory ” or characteristic, and which while not present in
large amount, may nevertheless exert a considerable influence
upon the quality of the soil.
Soils from granitic and crystalline rocks. — In the case of
the (potash-feldspar) granite soils it is generally admissible
to expect that they will be fairly supplied with phosphoric
acid, because in the great majority of cases, minute crystals of
apatite (phosphate of lime) are more or less abundantly scat¬
tered through it. From the potash feldspar present, granite
soils may always be relied on for a good supply of potash for
plant use ; on the other hand, unless hornblende be present,
they are pretty certain to be deficient in lime, since neither
lime, feldspar nor calcite are probable accessory ingredients
of this rock.
Granite is exceedingly apt to weather by mechanical disin¬
tegration far in advance of its chemical decomposition. It is
therefore common to find in sedentary soils overlying granite,
a gradual increase of grains of its component crystalline min¬
erals as we descend in the subsoil ; until finally the latter grades
off into rock almost unchanged save in lacking coherence.
This is seen strikingly in the southern Appalachians, as well as
in the Sierra Nevada and Sierra Madre of California; at Cin-
tra in Portugal, at Heidelberg in Germany, and elsewhere.
But of the rocks that resemble granite and are popularly so
THE VARIOUS ROCKS AS SOIL-FORMERS.
51
called, a good many are not “ true to name ” and therefore
form soils differing materially from the type just mentioned.
Thus the so-called granite areas of the Sierra Nevada of California
are largely occupied by a rock containing, besides quartz, chiefly soda-
lime feldspar and some hornblende, and scarcely any mica. It is more
properly a diorite (grano-diorite) ; the soils formed from it are rather
poor in potash, not strongly calcareous, and quite poor in phosphoric
acid. On account of the small proportion of hornblende (unusual in
diorites), these soils are light-colored (not “ red ” ), and bear a growth
of small pine instead of the usual oak growth of the lower Sierra
slopes.
What is said of granite soils is also generally true of those
formed from
Gneiss , which is composed of the same minerals as granite,
but has a slaty cleavage and on that account when upturned on
edge, weathers rather more rapidly than most granites.
Owing to the frequent occurrence of lenticular masses of quartz
in gneiss, its soils are more commonly of a siliceous nature
than are those of the true granite regions, and not as “ strong ”
as the latter. This is the more true since gneiss often passes
gradually into mica schist , which, being a mixture of quartz
and mica only, not only weathers very slowly but also supplies
but little of any importance to plants, to the soils formed
from it. Such soils would mostly be absolutely barren but for
the frequent occurrence in the rock, of accessory minerals that
yield some substance to the soil. Yet it remains true that in¬
asmuch as gneiss and mica-schists are among the rocks in
which mineral veins most commonly occur, the proverbial
barrenness of mining districts is very frequently traceable to
these rocks. The same may be said of some of the related
rocks, such as gabbro, minette and others.
Normal diorite consists of hornblende and soda-feldspar,
with more or less quartz.
The soils derived from certain diorites of the Sierra Nevada
of California have just been referred to. But these granite¬
like diorites are on the whole exceptional ; it should be added
that the (diabasic) “ greenstones ” of the Eastern United
States and of the Old World, which are usually much finer-
52
SOILS.
grained, do not form the mass of fine, angular debris consti¬
tuting the subsoil in the Sierra Nevada, but weather into
rounded masses and fine-grained soils possessing, on the whole,
a fair fertility, though liable to contain an excessive proportion
of silex in various forms.
Of the eruptive rocks as a class it is often said that they form
very productive soils; yet, as these rocks differ widely from
each other in composition, this statement must be taken with a
great deal of allowance. Very many of them decompose with
extreme slowness on account of their glassy nature ; this is par¬
ticularly true of obsidian, pumice stone, and the “ volcanic ash ”
derived from its pulverization, and which is found unchanged,
in sharp scales, among the decayed minerals of other rocks in
complex soils. Other volcanic ash, however, being formed by
the pulverization of crystalline or of basic lavas, weathers
rather readily, as already stated ; so that certain plants take
possession in the course of a few years. The general classifi¬
cation into basic and acidic rocks, given above, is of importance
in connection with soil formation from eruptive masses; for
the basic rocks are much more easily attacked by the atmos¬
pheric agencies than the acidic class.
A broad distinction must, however, be made between the basic rocks
of the basaltic class, which contain black pyroxene as a prominent
ingredient, and those which, like many trachytes, are rich in feldspathic
minerals. The latter are naturally rich in alkalies (potash and soda)
which they impart to the corresponding light-colored soils ; while the
black basaltic rocks and lavas weather into “ red ” soils, sometimes
containing extraordinary amounts of iron (ferric hydrate) and (from the
lime-feldspars they contain) a fair supply of lime, but oftentimes very
little potash. Experience seems to prove that the red basalt soils are
mostly rather rich in phosphoric acid ; this is especially true of the
country covered by the great eruptive sheet of the Pacific Northwest,
in the rocks of which the microscope readily detects the presence of
numerous needles of apatite (lime phosphate). The same is true of
the highly iron-bearing soils from the black basaltic lavas of the Hawaiian
islands, even though they have been leached of all but traces of lime
and potash. All these soils are physically “ light ” and easily workable,
since the rocks in question contain but little alumina from which to
form clay ; they are sometimes extremely rich in iron, even to the
extent of being capable of serving as iron ores.
THE VARIOUS ROCKS AS SOIL-FORMERS.
53
The soils derived from trachytes and trachytic lavas are
generally light-colored and light in texture; the latter from
the presence of a large proportion of volcanic glass, together
with undecomposed crystalline minerals. These are usually
rich in potash, but poor in lime and phosphates. The high
quality of the wines of the lower Rhine has been ascribed to
these soils, which however vary greatly within the areal limits
of the production of the high-grade wines, not only from gray
trachytes to dark colored, highly augitic basalt, but also to
acidic quartz porphyries or rhyolites, and clay-slates.
The rhyolites on the whole yield the poorest soils among the
eruptive rocks; they are slow to weather at best, and the soils
produced are poor and unsubstantial, largely from the predom¬
inance of quartz and undecomposable, glassy material ; of which
the phonolites are the extreme type, resisting* the influence of
the atmospheric agencies just as would so much artificial glass.
Soils consisting largely of volcanic glass may be found cover¬
ing considerable areas in the Sierra Nevada of California.
Such “ volcanic ash ” soils are usually very unthrifty, and bear
a growth of small pines.
Soils from sedimentary rocks. — Limestones, when pure and
hard, are very slow to disintegrate, and are also very slowly
attacked by carbonated water (see chap. 3, page 41). Soft
impure and vesicular limestones are, however, very rapidly at¬
tacked, especially when underlying a surface clothed with the
luxuriant vegetation that usually flourishes on soils rich in
lime. The popular adage that “ a limestone country is a rich
country,” is of almost universal application and stamps lime,
from the purely practical standpoint, as one of the most im¬
portant soil ingredients.
Residual Limestone Soils. — Striking examples of the forma¬
tion of large, fertile soil areas by the leaching out of limestones
are found in the States of Alabama, Mississippi, Louisiana and
Texas, where the fertile black prairies have been largely thus
formed. The “ blue-grass ” country of Central Kentucky is
another case in point.
The following table shows a representative example of the
relative composition of the (cretaceous) “ Rotten Limestone ”
of Mississippi, and the “ residual ” soil-stratum derived from
it. The average thickness of the layer of residual clay above
54
SOILS.
the limestone is about eight feet, but ranges from seven to ten ;
the upper layers of the limestone are somewhat softened, but
the rock is always fresh at twelve feet, from which depth the
sample analyzed was taken, in a cistern adjoining the field from
which the soil and subsoil were procured. The black soil
varies in depth from 8 to 15 inches; then there is a change to
a brownish subsoil, reaching down to about two feet, and in
drying cleaving into prismatic fragments. The black soil has
here in the highest degree the peculiarity of crumbling in dry¬
ing from its water-soaked condition, so that it may be plowed
when wet without injury, although in the roads it works up
into the toughest kind of mud. The prairie is sparsely tim¬
bered with compact, fair-sized black-jack oak, accompanied
originally by red cedar.
The limestone derives its popular name of “ rotten ” from
its being usually soft enough to be cut with a knife or hatchet,
and is therefore somewhat used for building, and for burning
lime.
COMPOSITION OF LIMESTONE, AND RESIDUAL SOIL AND SUB-SOIL, FROM BLACK
PRAIRIE, MONROE CO., MISSISSIPPI.
“ Rotten
Limestone.”
Subsoil
(yellow).
Soil
(black).
Fine Earth.
Chemical analysis of fine earth.
Depth . . 12 ft.
2-3 ft.
15 ins.
Insoluble matter .
10.90
71-54
78.29
Soluble silica .
Potash (K00) .
•25
•32
4579
.88
•54
23
1.08
•77
•°5
5-42
1315
•05
O A
•33
.08
B37
•36
.14
)
Soda (Na26)! .
Lime (CaO) .
Magnesia (MgO) .
Br. Ox., of Manganese (Mn304) .
Peroxide of Iron (FeO) .
1.42
1 96
Alumina (A1203) .
\ 14.22
Phosphoric Acid (P90.) .
)
.IO
.cn
Sulfuric Acid (SOU .
Carbonic Acid (C02) .
35 73
2.84
•'-'J
Waterand Organic matter .
6.99
575
Total .
TOO 09
99.86
100.67
Humus .
I O'*
“ Ash .
x-yj
4-38
1 2. S'’
Hygroscopic moisture .
IO TC
absorbed at °C .
IQ°
IQ°
xy
THE VARIOUS ROCKS AS SOIL-FORMERS.
55
It appears from the above table that in the change from the
original limestone to the soil mass as found at three feet depth,
81.5% of the lime carbonate has been eliminated by leaching,
leaving behind somewhat less than one fifth of the original
mass. Taking the average depth of the soil mass at 8 feet,
this thickness of material has required about 45 feet of the
rotten limestone. Considering that notwithstanding the ten¬
acity of the clay soil, some of it must in the course of time
have been washed away, we may safely assume that the orig¬
inal rock surface was from 50 to 60 feet higher than at
present.
Sandstone Soils. — The indefiniteness of the nature of “ sand¬
stones ” as such renders generalizations in regard to the soils
formed from them rather difficult, save as to their physical
qualities, which in the nature of the case are always “ light.”
In the Old World and in the humid region generally, sandstone
and sandy soils are usually spoken of as being poor, because
there the sand almost always consists of quartz grains only, and
hence the fine portions alone can be looked to for plant nutri¬
tion. Consequently, the more sand is seen in a soil, the poorer
it is usually presumed to be. But this presumption would be
wholly erroneous in the arid regions. (See chapt. 6, p. 86).
Clearly, the nature of the soils produced by the weathering
of sandstones depends upon two points : first, the nature of the
cement binding the sand grains, and second the character of
the latter themselves.
Varieties of Sandstones. — As has been stated above, the
cements may be roughly classified into five kinds, and their
intermixtures, to wit: quartzose or siliceous,, calcareous , fer¬
ruginous, aluminous or clayey, and zeolitic. As regards the
first, it is obvious that siliceous sandstones will disintegrate
with great difficulty, since neither the cement nor the grains
are susceptible of material change by weathering. Such sand¬
stones frequently pass insensibly into quartz rock, and the
light, unsubstantial soils they produce are of the poorest, con¬
taining often mere traces of the plant-food ingredients. This
of course, is true, not only of the soils formed by the actual
weathering of sandstones, but equally of those consisting of
quartz-sand deposited bv water or drifted by winds.
56
SOILS.
Of this character are the pine-forest soils of the coast region of the
Gulf of Mexico, particularly the “ Sand hammocks ” of the immediate
Gulf border, from Mississippi Sound to Charlotte Harbor, Florida; the
sandy lands of the Grand Traverse region of Michigan, and many other
minor areas in the United States, usually characterized by a pine growth,
often more or less stunted, according to the nature of the sand grains.
Calcareous sandstones usually form a very much better
class of soils, partly for the intrinsic reason given above as
regards limestones as soil-formers. The calcareous cement is
very rarely pure calcite; in most cases it is very impure, as,
most commonly, is also the “ sand ” itself. This is explained
from the fact that such rocks (mostly soft and often quite un¬
consolidated) are, like limestones themselves, the result of de¬
position in shallow seas or lakes, receiving deposits from the
land drainage, and enriched by the animal and vegetable life
of such waters. Not uncommonly they contain, disseminated
through them, grains of the mineral glauconite (a hydrous
silicate of iron and potash), which readily supplies available
potash; while the remnants of animals and plants furnish
more or less of available phosphates. Thus the general pre¬
sumption regarding calcareous sandstones is that the derived
soils are of good quality, frequently of the very best. The
same, however, does not appear to be true of sandstones cem¬
ented by dolomite; the soils derived from magnesian sand¬
stones are in many cases noted for their unproductiveness.
(See chapt. 3, p. 42).
Ferruginous Sandstones manifestly derive no important soil
ingredients from their cement when the latter is measurably
pure ferric hydrate; and when in addition the sand itself is
purely siliceous, the soils resulting from the disintegration of
the rocks are very poor.
Such are, e.g.? the soils derived from the ferruginous sandstones of the
Lafayette formation in a part of northern Mississippi and adjacent por¬
tions of Tennessee and Alabama, characterized by small scrubby oak or
dwarfed pine. On the whole, however, such purely ferruginous quartz
sandstones are exceptional, and should not detract from the favorable
inferences usually to be drawn from the iron-rust tint of soils (see
chapter. 15
THE VARIOUS ROCKS AS SOIL-FORMERS.
57
Sandstones with purely zeolitic cement are on the whole not
of frequent occurrence, the zeolites forming, more commonly,
the hard portion of a clay-sandstone cement, which disinte-
grates by their weathering-out.
In regions where the tufaceous rocks of eruptives prevail, we not
uncommonly find the “volcanic ash” solidly cemented by a zeolitic
mass, which is then usually apparent in cavities or crevices in the form
of crusts or crystals. Such tuffs are commonly rich in alkalies and
lime, but mostly poor in phosphates, and in disintegration form soils of
a corresponding nature. They are largely represented in the valleys
off Puget Sound, as well as in portions of central Montana, and north¬
ward.
Clay-Sandstones (argillaceous sandstones) when soft, as is
mostly the case, form as a rule desirable loam soils, of a gener¬
alized composition, difficult to predict. It is here that the com¬
position of the sand grains themselves most frequently comes
into play in modifying the soil quality. From clay-sandstones
to claystones of various degrees of sandiness there is, of course,
every grade of transition, the soils ranging correspondingly
in the scale of lightness or clayeyness. As a general rule, the
potash contents of such soils are sensibly proportioned to the
clayey ingredient, at least in the humid regions.
Claystones (i. e., clays hardened by some one or more of
the cements mentioned in connection with sandstones), will
in the nature of the case, when disintegrated from the condi¬
tion in which they lie in the geological formations, make cor¬
respondingly clayey, heavy soils, which as experience shows
are usually rich in the ingredients of plant food, but frequently
too heavy and intractable in tillage to be readily utilized.
There are, of course, exceptions; such as soils formed from pipe¬
clays, in which little if any mineral plant-food remains, and which are
best used for other purposes than agriculture, unless under special con¬
ditions it may be worth while to reclaim them by fertilization.
Natural Clays. — Clays occur in nature in a great variety of
modifications that have received designations known in com¬
mon life. Such are porcelain clay, pipe-clay, fire-clay, potters’
53
SOILS.
clay, brick-clay, and many others of more or less local use
only. As these materials practically concern the farmer in
very many cases, they may properly find a brief discussion
here.
The variety-names enumerated above in the order of the
actual contents of the materials in true clay substance (“ col¬
loidal clay ”), are partly based upon that fact, partly upon the
degree of plasticity attained by that substance, and essentially
upon the nature and amount of foreign admixtures associated
with it. Thus, porcelain clay is chalky kaolinite, sometimes
associated with enough of pure white plastic clay to render it
workable in the potter’s lathe, but more commonly requiring
to be molded in porous molds; it is very refractory to heat.
Pipe-clay is also white, but more plastic and usually less re¬
factory. Fire-clay is a refractory pipe-clay commingled with
some coarse infusible material, such as quartz sand (or the
same clay burnt and crushed), in order to prevent excessive
contraction and change of shape in drying and burning. Pot¬
ters’ clay is a much less pure, and from that cause more fusible
clay, which when burnt forms at a moderate heat a semi-fused,
more or less hard mass, such as crockery and pottery ware.
Brick-clay is a still more impure clay, or loam, containing con¬
siderable sand and usually iron oxid, and largely falls already
within the limits of tillable soils or subsoils, rendered fusible
by the presence of relatively considerable amounts of iron,
magnesia and lime.
Iron colors natural clays either red, yellow, green or blue ; the latter
two colors turning to yellow or red on exposure to the air, and to red
on burning. Black color is usually due to carbon, such clays often
turning white on heating.
Clays containing much lime are usually of a gray or whitish tint, and
like the soft crumbly limestones are often called marls, and are used as
such for land improvement. But it should be understood that the
colors of clays, mostly derived from some iron compound, have little to
do with their uses in the arts, except that no deeply colored clay (black
excepted) is refractory in the fire.
THE VARIOUS ROCKS AS SOIL-FORMERS.
59
“ Colloidal ” Clay }
In connection with soils, clay may be defined, in the most
general terms, as being the substance which imparts plasticity
and adhesiveness to soils when wetted and kneaded, and
which, when heated to redness, loses this property completely
and permanently, becoming hard and coherent in proportion
to the degree of heat to which it is exposed.
In common life, however, the name is applied to the whole
of any naturally occurring earth which on wetting and knead¬
ing assumes a reasonable degree of plasticity and adhesiveness.
When the latter property becomes nearly or quite insensible,
the earth is designated as a “ loam,” more or less “ clayey ”
according to the amount of the pure, plastic and adhesive ma¬
terial associated with the mineral powders and sand that form
the bulk of most soils.
Chemically, the pure clay substance 2 probably consists (as
has been stated above) of silica and alumina in the proportion
of nearly 46 to 40, the rest (14%) being water of hydration,
which is lost on burning the clayey material. But while it is
true that such is the composition of the plastic substance of
clays, plasticity and adhesiveness are by no means invariable
properties of this compound. In its purest state, as kaolinite,
it is readily mistaken for chalk, (and is sometimes used as
such), being powdery to the touch and entirely devoid of plas¬
ticity 3 when wetted and kneaded. The microscope shows this
1 This term was first employed by Th. Schloesing, in communications to the
French Academy of Sciences, and reported in the Comptes Rendus of that body ;
first in 1870. Unaware of Schloesing’s work, the writer began a full investiga¬
tion of the subject of mechanical soil analysis in 1871, and published the results
in 1873 (Am. Jour. Sci., Oct. 1873). Up to that time the limited resources of the
library of the University of Mississippi had not given him an opportunity to see
Schloesing’s publication. The two independent investigations, chough conducted
on somewhat different lines, gave of course practically the same results, and com¬
plement each other.
2 There is still some discussion as to the chemical identity of colloidal clay with
Kaolinite; but the objections are not convincing.
3 It has of late been attempted to extend the meaning of this word to the be¬
havior of all powders when wetted with water. But the adhesive plasticity of
clay stands almost alone, in that (aside from contraction) it preserves in drying
the form into which it may have been molded while wet, even when struck>
whereas other powdery substances similarly treated at once collapse back into the
original powder. The exclusive use of clay in modeling offers the typical example
of plasticity as generally understood. The addition of any powdery substance,
however fine, diminishes the plasticity of clay.
Go
SOILS.
chalky kaolinite to consist of minute, mostly rounded, origin¬
ally six-sided, thin plates, which when pure resemble to the
touch powdered talc (soapstone) or even black-lead, rather
than any clay known to common life. But being exceedingly
soft, the kaolinite substance is easily ground or triturated into
an extremely fine powder; and Johnson and Blake 1 succeeded
in producing sensible plasticity and adhesiveness by long-con¬
tinued trituration of kaolinite with water in a mortar. A
similar process, but continued much longer by the mechanical
agencies concerned in soil-formation (see chapt. i), is un¬
questionably the chief factor concerned in the formation of
natural plastic clays; but whether this is the only process by
which the powdery kaolinite may be transformed into plastic
clay, is a question not definitely settled. It is at least possible
that repeated freezing and thawing, as well as the action of
hot water, may take a part in the transformation, beyond that
by which they destroy the crumbly (flocculated) structure of
soils and clays, and render them plastic ; as is done in the ma¬
turing of clays by potters.
Causes of Plasticity. — In any case the property of plasticity
and adhesiveness is restricted to the particles so fine that they
fail to settle, in the course of 24 hours, through a column of
pure water eight inches (200 m) high, while some are so ex¬
tremely minute that they will not settle for many months, and
even for several years.2 Such turbid “ clay water” may
1 American Journal of Science, 2d Ser., Vol. 43, p. 357.
2 Williams (Forsch. Agr. Phys. Vol. 18, p. 225 ff.) claims that the diameter of
the minutest clay particles is one-thousandth of a millimeter, their form being that
of scales showing continual (Brownian) motion in water. He maintains that the
plasticity of clay is due to this minute size, and this view has gained wide accept¬
ance in late works on the subject. But this assumption cannot be maintained in
the face of the fact that nothing like the adhesive plasticity of clay can be attained
even by the finest powders of other substances, least of all by those having the
closest mineralogical resemblance to kaolinite, such as graphite and talc. Above
all, the most persistent trituration with water utterly falls to restore plasticity to
clay once baked so as to expel its water of hydration, although, the fineness of the
particles is thereby not only not diminished, but actually increased, by contraction
in heating. No powders however fine can replace the functions of clay in soils,
viz. the maintenance of floccules, and tilth dependent thereupon ; and they dis¬
tinctly impair the plasticity of clay. The fine “ slickens ” of quartz mills merely
render soils containing them more close and impervious, and more difficult to
flocculate. Even gelatinous masses like hydrated ferric and aluminic oxids fail to
replace clay in its adhesive functions.
THE VARIOUS ROCKS AS SOIL-FORMERS.
6l
sometimes be found existing in nature, in moist, secluded
places, for weeks after the subsidence of the overflows of
rivers whose water is exceptionally free from dissolved mineral
matter.
Separation of Colloidal Clay. — This property of the plastic clay
substance, of diffusing in pure water, furnishes the means of separating
from it the coarser, sandy and silty portions of soils and natural clays,
and observing its characteristic properties, so far as the almost un¬
avoidable admixture of some other substances, presently to be considered,
permits.
In natural soils the clay particles usually incrust the powdery ingredi¬
ents, cementing them together ; or themselves form complex aggregates
(floccules) of large numbers of individual particles. These may be
loosened from their adhesion or cohesion either by prolonged, gentle
kneading of the wet clay, or by more or less prolonged digestion (soak¬
ing) in hot water, or more expeditiously, by lively boiling with water.
The boiling should not, however, be prolonged beyond the time actually
required for disintegration, since (as Osborne 1 has shown) long-pro¬
tracted boiling tends to render the clay permanently less diffusible.
From the turbid clay-water the diffused clay may be obtained either
by evaporating the water (which as the bulk is very large, is usually
inconvenient), or, more conveniently, by throwing it down from its
suspension by the action of certain substances which possess the prop¬
erty of curdling (coagulating) the clay substance into flocculent masses
that settle quickly. Of all known substances, lime, in the form of
lime-water, acts most energetically in producing this change ; but other
solutions of lime, as well as most salts and mineral acids, produce the
same effects when used in sufficient quantity. Common salt is among
the most convenient, because it can most readily be leached out of the
clay precipitate thus thrown down. This when white, resembles boiled
starch, but being usually colored by iron might be easily mistaken for
the mixed precipitate of ferric hydrate and alumina so commonly
obtained by chemists in soil analysis. When separated from the water
and dried, the jelly-like substance ( “ colloidal clay ” ) shrinks as
extravagantly as would so much boiled starch, into hard, shiny crusts or
flakes, which when struck in mass are sometimes even resonant, and
bear more resemblance to glue than to the clay of everyday life. Like
glue, too, but much more quickly and tenaciously, the dried colloidal
1 Rep. Conn. Agr. Expt. Stn., 1SS6, 1887.
62
SOILS.
clay adheres to the tongue, so as to render the separation painful • when
wetted it quickly bulges with great energy, and in a short time resumes
its former jelly-like condition. When moistened with less water it
assumes a highly plastic and adhesive condition, so that it is difficult to
handle and almost as sure to soil the operator’s hands as so much
Ditch.
a
Effects of Alkali Carbonates upon Clay. — The carbonate of
potash and soda, when in very dilute solution (.01 to .05%)
exert upon diffused clay an effect the reverse of the acids and
neutral salts. They destroy the flocculent aggregates formed
by precipitation with these, or naturally existing in the soil,
and tend to puddle the clay so as to render it impervious to
water. It is thus that in the alkali lands of the arid regions
we often find the soil or subsoil consolidated into a very re¬
fractory “ hardpan,” difficult to break even with a sledge ham¬
mer and impossible to reduce to tilth until the alkali carbonate
is destroyed by means of a lime salt, such as gypsum. (See
chapt. 23). Ammonia water also helps to cause the diffu¬
sion of clay in water, but its effect of course disappears upon
drying. It is probable that this property of sodic carbonate
can be utilized in rendering earth dams firmer and more secure
against the penetration of water.
CHAPTER V.
THE MINOR MINERAL INGREDIMENTS OF SOILS; MINERAL
FERTILIZERS ; MINERALS INJURIOUS TO AGRICULTURE.
(a.) minerals used as fertilizers.
Of minerals important in soil-formation, not usually present
in large amounts in rocks, but extensively used in fertilization,
the following require mention :
Apatite ; phosphate of lime containing more or less of the
chlorids and fluorids of the same metal; the mineral from
which the phosphoric acid of the soil is mostly derived. In
the crystallized condition when perfectly pure it is colorless;
but it is mostly of a greenish tint (hence “ asparagus stone ”).
The pure crystalline mineral rarely occurs in large masses (as
in Canada) ; but small to minute crystals are found widely dis¬
seminated in many rocks (granites, “basalts” of the Pacific
Northwest), thus passing into the soils formed from these
rocks. These crystals are readily recognized, being regular
six-sided prisms with a flat or obtusely pyramidal termination
(distinction from quartz), and do not effervesce with acids
(distinction from calcite). By far the largest deposits of
this mineral occur in connection with carbonate of lime, in the
rock materials known as phosphorites. Lime phosphate be¬
ing, like the carbonate, soluble in carbonated water, the two
naturally frequently pass into solution, and are subsequently
deposited together. Most limestones contain a small propor¬
tion of lime phosphate, being, as already stated, formed from
the shells and the framework of animal organisms usually
containing also phosphates. But the content of phosphates
in limestones is not readily apparent to the eye, and the richest
deposits, save such as contain animal bones, have long
passed unsuspected as to their being anything else but lime¬
stone. Systematic search has now revealed the presence of
phosphate rock in numerous localities, chiefly where limestone
63
64
SOILS.
formations occur. In the United States, in South Carolina,
Florida, Alabama, Tennessee, Kentucky, Nevada; in South
America, on Curagoa island, Venezuela ; in the Antilles on Som¬
brero, St. Martins and Navassa islands. In Africa, in Algiers
and Tunisia; in Europe, in Spain (Estremadura, one of the
first deposits known), France, Belgium and the adjacent parts
of Germany; in Bohemia and Galicia in Austria; and very ex-
tendedly in European Russia. Many islands of Oceanica sup¬
ply phosphorites derived from the decomposition of bird guano
by the coral limestone.
Unfortunately the percentage of phosphate in a large proportion of
these materials is not sufficiently high to make their conversion into
water-soluble superphosphate economically possible at the present time ;
since all the calcic carbonate present must also be converted into com¬
paratively worthless sulphate (gypsum ) by the use of sulfuric acid ;
and as yet no practicable method for avoiding this difficulty has been
found.
“ Thomas Stag .”- — Probably the nearest approach to such a method
is indicated by the fact that a compound containing four instead of
three molecules of lime to one of P/)5, such as is contained in the
“Thomas slag” of the basic process of steel manufacture, is nearly or
in some cases ( “ sour ” soils) quite as effective for the nutrition of
plants as the water-soluble superphosphate. This discovery has rendered
available for agricultural use the phosphoric acid contained in the
enormous deposits of limonite iron ore known as bog ore, which con¬
tains a large proportion of ferric phosphate and from that cause has
until lately been excluded from the manufacture of wrought iron and
steel. It is reasonable to hope that by some analogous process the
low-grade phosphorites, such as those of Nevada and the plains of
Russia, will also in the course of time become available for agricultural
use. Extremely fine grinding and washing (producing “ floats ” ) has
been resorted to for the purpose of rendering the raw phosphorites
effective in fertilization. But while this is successful on some soils, on
others the “floats” remain almost inert; so that this method has found
only limited acceptance.
Animal bones , which consist of from 24 to 30% of animal
substance and 70 to 76,% of “bone earth,” (or when fossil
are free from the former), are largely used for the manufac-
MINERALS USED AS FERTILIZERS.
65
ture of superphosphate. The bone-earth consists in the main
of tri-calcic phosphate with from one to two per cent, of cal¬
cium fluorid (much as in natural apatite), a small amount of
magnesic phosphate, and about 4 to 6,% of calcic carbonate.
Bone meal can therefore supply to plants both phosphoric acid
and nitrogen, and the presence of the latter has been largely
the cause of a material overestimate of its efficacy as a fertil¬
izer in the past. Wagner’s and Maerker’s experiments have
shown that at least in sandy soils poor in humus, it cannot be
considered an adequate source of phosphoric acid for annual
crops, and that in these soils its immediate effects are almost
wholly due to its nitrogen-content. The slow availability of
the phosphoric acid renders it unprofitable as a source of the
latter, outside of the heavier lands with abundance of humus;
in “sour” lands (notably on meadows) bone meal produces
its best results. In soils naturally calcareous, or in such as
have received heavy dressings of lime either as carbonate or in
the caustic condition, the manurial effects of bone meal are
seriously diminished. Nagaoka (Bull. Coll. Agr. Tokyo, Vol.
6, No. 3) shows that the crop of rice fertilized with bone meal
was reduced to less than half when limed, and that the phos¬
phoric acid taken up by the crop was reduced to one-sixth. In
any case it is most important that bone meal should be as finely
ground as possible, as in the case of the phosphorites ; and this
can best be done when it has first been freed from fats by boil¬
ing with water, and then steamed under pressure. It can then
also be most readily converted into superphosphate.
The phosphate minerals and the fertilizers manufactured
therefrom are of primary importance to agriculture. The
phosphoric-acid content of soils is mostly very small, and only
a fraction of it is usually in an immediately available form.
Hence for permanent productiveness, and especially for in¬
tensive farming or gardening, a cheap supply of phosphate
fertilizers is of first importance in all soils and climates.
Other phosphate minerals occur frequently, but as a rule
only in small amounts, in connection with the ores of most
metals. The only ones of these of interest to agriculture are
Vivianite and Dufrenite, the phosphates respectively of the
protoxid and peroxid of iron. The former occurs in mineral
deposits as small blue crystals, or more frequently as blue
5
66
SOILS.
earthy masses or streaks, in the substrata of rich alluvial
ground (Louisiana, California). Dufrenite sometimes results
directly from the oxidation of the protoxid mineral, which then
turns greenish and finally brown. Unfortunately these miner¬
als, rich as they are in phosphoric acid, cannot readily be util¬
ized as sources of phosphate fertilizers, because of the difficulty
of getting rid of the iron. Their occurrence usually suggests
the presence of abundance of phosphoric acid in the soil. But
that which is actually combined with the iron oxids is prac¬
tically unavailable to plants ; especially so in the case of the
peroxid compound, the formation of which is a common
source of loss of phosphoric acid when soils rich in iron are
submerged for any length of time; a point which is discussed
below (chapt. 13).
Among the iron phosphate minerals, may also be mentioned
“ bog ore,” which results from the reductive maceration of
swamped ferruginous soils, and accumulates in the subsoils
and in the bottom of swamps or moors, forming “ moorbed-
pan ” ; a dark brown, rather soft mass, which is sometimes used
as an iron ore, especially since the invention of the “ basic
process ” of iron smelting, one of the products of which is
the phosphate or Thomas slag. (See above).
Nitrate of Soda or Chile saltpeter. — This mineral being
(like all nitrates) easily soluble in water, can only occur in
regions nearly or quite destitute of rainfall. Such is the case
in the Plateau of Tarapaca in Northern Chile, where it occurs
in large quantities; it is likewise found, but to much smaller
extent, in Nevada, southern California, Egypt and India. By
far its most extended occurrence is that in Chile, where, to¬
gether with common salt, it fills cavities and crevices in a
gravelly clay that forms the surface of a plateau from three to
six thousand feet above the sea. It is never pure, but always
mingled with a large proportion (up to 50% and over) of
common salt; also some Glauber’s salt (sulfate of soda) and
some sodic perchlorate and iodid ; hence it forms an important
commercial source of iodine.
The mixed mineral mass, called “ Caliche,” when taken out of the
ground is dissolved in water ; and the solution boiled down, during
which process the common salt is first deposited and is raked out of
MINERALS USED AS FERTILIZERS.
67
the pans ; the nitrate is afterward farther purified by crystallization.
As brought into commerce for agricultural purposes it constitutes a
moist gray saline mass, somewhat resembling common salt, of which
substance it usually contains a few per cent ; occasionally also a small
amount of sodic perchlorate (which acts injuriously on vegetation).
Aside from its use as a fertilizer, Chile saltpeter serves for the man¬
ufacture of nitric acid ; and either directly, or after previous transform¬
ation into potassic nitrate, for that of gunpowder.
The Chilean locality is the only one from which the commercial
article is derived ; the deposits elsewhere are too limited in extent to
compete commercially with the South American product. Caliche
ranging as high as 80% of nitrate of soda has been sent to the writer
from the Colorado Desert in Southern California, but the exact locality
of occurrence has not been divulged. Extended areas of clay hills
impregnated with nitrates exist in the Death Valley region of California,
but in the absence or extreme scarcity of water in that region, it is
doubtful whether these impregnations can be made practically available.
Another locality is that near White Plains, Nevada, where Caliche
averaging about 50 °J0 purity is found in cavities and crevices of a reddish
volcanic rock. The rainfall in this region is so slight that the greater
part of the dust or sand blown about by the wind consists of Glauber’s
salt. Here also, as in Chile, the niter deposits appear to be restricted to
within a short distance from the surface, and the total amount thus
far observed appears to be insufficient to encourage large-scale ex¬
ploitation.
Origin of Nitrate Deposits. — The probable origin of these niter
deposits has given rise to a great deal of discussion, and a wide differ¬
ence of opinion exists as to the source from which the nitrogen may
reasonably be supposed to have been derived. According to the
present state of our knowledge, it must be presumed that its sources
have been organic, and that the niter has been produced by the activity
of the same bacteria which now produce nitrates in our soils, rendering
the nitrogen of humus available to plants. But it is by no means clear
what that organic material could have been ; for at the present time
the plateau of Tarapack is almost wholly destitute of vegetation, if not
of animal life. The latest and apparently most reasonable suggestion
is that of Kuntze , who calls attention to the fact that the vicunas and
llamas which are at home in this portion of the Andes, and are known
to have roamed over that region in countless herds, have the curious
habit of always depositing their manure in one and the same place
68
SOILS.
whenever at liberty. Each herd of these animals has its definite dung¬
ing place at some convenient point. That such herds have existed in
the region from time immemorial is obvious from historical as well as
collateral evidence ; and as their manure accumulated, its nitrification
would progress rapidly under the prevailing arid conditions. The conv
mon salt would naturally be derived from the urine and excrements,
and the alkaline salts which exist throughout this region as the products
of soil decomposition, would be quite sufficient to account for the
alkaline bases in the caliche. On the other hand, the presence of
iodine points to seaweeds as the organic source.
Intensity of Nitrification in Arid Climates. — Of the efficacy
of nitrification under arid conditions abundant evidence may
be found within the State of California. In the alkali lands
of southern California the nitrates of soda, lime and magnesia
are almost universally present; they form at times as much as
one-fifth and even more of the entire mass of alkali salts, and
in one case the total amount in the soil has been found to reach
two tons per acre, with an average of twelve hundred pounds
over ten acres. In the plains of the San Joaquin Valley, spots
strongly impregnated with niter are found, especially under the
shadows of isolated oak trees, where the cattle have been in the
habit of congregating for a long time ; a case quite analogous
to that supposed by Kuntze to exist in the Chilean locality.
Of course it is only in arid climates that the accumulation of
nitrates can usually occur; for in the region of summer rains
the nitrates formed during the warm season will inevitably be
washed into the subdrainage, unless restrained by absorption
by the roots of vegetation. The heavy losses occasionally
occurring from this cause in the course of a rainy winter on
summer-fallowed land have been amply demonstrated by many
investigations.
Potash Minerals. — By far the most abundant occurrence
of potash in the earth’s crust is that in silicates and notably in
orthoclase or potash feldspar, which contributes so largely to
soil-formation. But in the absence of any economically suc¬
cessful artificial method for producing potash compounds from
feldspars on a commercial scale, almost the entire supply of
potash salts was, until a comparatively late period, derived from
plant ashes, viz., the “ potashes ” of commerce. At the same
MINERALS USED AS FERTILIZERS.
69
time, almost the entire demand for alkalies for industrial uses
bore upon the same product, until the invention, toward the end
of the last century, or LeBlcinc’s process for the manufacture
of soda from common salt; for until that time, soda in the
various forms in which it was imported from the Orient or
prepared from seaweed ashes, was a comparatively costly pro¬
duct. LeBlanc’s invention was most timely in that it very
quickly diminished materially the production of potashes
which, in view of the increased demand for alkalies for in¬
dustrial uses, seriously threatened the depletion of agricultural
lands, and of woodlands as well, of one of its most essential
ingredients. Yet as there are many industrial uses in which
soda cannot replace potash, the manufacture of potashes con¬
tinued to a greater or less extent, as no other available source
except the ashes of land plants, was then known. The pro¬
duction of potassic chlorid from the mother-waters of sea salt
in the spontaneous evaporation of sea water for the manu¬
facture of common salt, was on too small a scale to influence
materially the manufacture of potashes.
Discovery of Stassfurt Salts. — The depletion of potash had
become so serious a matter in the agricultural lands of Europe,
that for a time much research was bestowed, and prizes offered
for an economical method of producing potash salts from feld¬
spar, on a commercial scale. But the problem had not been
satisfactory solved when, in the year i860, attention was called
to the fact that the saline deposits overlying certain large
rock-salt beds that had been developed by borings near Stass¬
furt in Prussia, contained so large a proportion of potash salts,
as to render their purification and conversion into fairly pure
sulphate and chlorid technically feasible. The impulse having
been given, the potash industry developed rapidly in that
region as well as in the adjacent portions of Saxony, where the
same formation underlies; the production of “Stassfurt
Salts ” rapidly assumed a greater development than that of the
rock-salt which had originally prompted the enterprise, and
numerous additional boreholes demonstrated an unexpectedly
wide extension of the same beds. At the present time, in con¬
sequence of such development, the manufacture of potashes
from plant ash has almost ceased, outside of Canada and
Hungary; and the production of potash salts in the Stassfurt
;o
SOILS.
region now supplies the demand of the entire world, both for
industrial and agricultural purposes.
The cheapening of potash as a fertilizer has rendered pos¬
sible the profitable cultivation of large areas of land which
were naturally too poor in that substance for ordinary cul¬
tures; and has likewise rendered possible the restoration to
general culture of lands that had ceased to produce adequately,
on account of the depletion caused by long-continued cropping.
It has likewise served to intensify agricultural production
wherever desired; and between this supply and that of phos¬
phoric acid from the phosphorites (see above), and the dis¬
covery of the nitrogen-absorbing power of leguminous plants,
which can be used for green-manuring, farmers have been
enabled to dispense, in many regions, with the production and
use of stable-manure, which until then had been considered an
indispensable adjunct to agriculture everywhere. Even
within the last fifty years it was proclaimed by high authority
in Germany that stable-manure constituted, as it were, the
farmer’s raw material, from which he manufactured the var¬
ious products of the field through the intervention of the
plant-producing power of the soil.
Origin of the Potash Deposits. — The manner in which this accumu¬
lation of potash salts has been formed deserves explanation. It is
abundantly evident that nearly all deposits of rock-salt thus far known
have been formed by the evaporation of sea-water at times when bays
or arms of the sea were cut off from open communication with the
ocean. The composition of sea-water has already been given and
discussed (chap. 2, p.26) ; and by the slow evaporation of sea-water on
a small scale we can quite successfully imitate the phenomena observed
in natural rock-salt deposits. When sea-water is heated a slight deposit
of lime carbonate (usually containing a little ferric oxid and silica) is
soon formed ; and a corresponding thin deposit of ferruginous limestone
is commonly found at the base of rock-salt -bearing deposits. Next
above this we almost invariably find a deposit of gypsum, sometimes of
great thickness ; in the artificial evaporation of sea-water the same thing
occurs so soon as the brine has reached a certain degree of concen¬
tration. It constitutes the major portion of the “ panstone ” of salt-
boilers. Next above follows a deposit of rock-salt, at base somewhat
mixed with gypsum ; its thickness varies greatly according to circum¬
stances. Above it lie the potash salts.
MINERALS. USED AS FERTILIZERS
71
In the manufacture of sea-salt by evaporation in shore lagoons 01
“ saltpans,” the solution remaining after the salt has been deposited
(known as “mother-waters,” or “bittern” ), of course remains on the
surface of the salt unless allowed to drain off, as is done in the process
of manufacture. When not drained off, the water gradually evaporates,
and there remains a saline crust of a composition exactly resembling
that of the upper layers at Stassfurt, containing a large proportion of
potash salts.
If it be asked why the Stassfurt salts are not found overlying every
rock-salt deposit in the world, the answer is that in a great many cases
the concentrated mother-waters have had an opportunity to flow off
from the surface of the rock-salt by the action of tides, the inflow of
fresh water from the land or from other causes. Their presence
therefore depends upon the fulfilment of accidental conditions not
nearly always realized in the natural evaporation of sea-water, but
which happened to occur on a very large scale in that portion of the
North-European continent.
Nature of the Salts. — The potash is present in the Stassfurt salts in
the form of complex sulfates and chlorids containing, besides, sodium,
calcium and magnesium in various proportions and modes of com¬
bination. The most abundant of the potassic chlorid minerals is car-
nallite, a hydrous chlorid of potassium and magnesium. The chlorids
characterize chiefly the upper portions of the deposit, the sulfates
the lower.
Kainit. — Of the products derived from the Stassfurt salt
industry for agricultural use, the two requiring special con¬
sideration are “ kainit,” a natural mixture of the several chlo¬
rid minerals in varying proportions; and “ high-grade sul¬
fate.” Being a natural product, “ kainit ” is the cheapest
source of potash available to the farmer; but on account of
its variability in composition it must be sold and purchased on
guaranteed assay. On account of its large content of chlorin
it is not desirable in the production of certain crops, especially
in the arid region, where alkali soils, and even those not visi¬
bly alkaline, often contain already large amounts of chlorin.
Moreover, kainit usually contains a considerable proportion
of common salt. For the arid region therefore the sulfate
is generally preferable, although it is somewhat higher in
price for the same amount of potash. The potash content of
72
SOILS.
commercial kainit (calculated as K2O) ranges from 16 to
35%, while the sulphate frequently ranges from 80 up to
95% of the pure sulfate; thus costing materially less in
freight charges than the lower-grade kainit. Its potash com
tent ranges from 43 to over 50% of K2O.
Potash Salts in Alkali Soils. — The sulfates and chlorids of
potassium, however, occur not only in connection with rock-
salt deposits, but are also found in the alkali soils of the arid
region. They are, in fact, never absent where such salts
occur at all, and their percentage in the total of salts ranges all
the way from about 4 to as much as 20% of potash sulphate.
In numerous cases it has been found that the content of this
salt to the depth of four feet amounts to from 1200 to 1500
pounds per acre. In such lands, of course, additional fertiliza¬
tion with potash salts is totally uncalled for, the more as such
soils invariably contain, besides the water-soluble potash, an
unusually large percentage of the same in the form of easily
decomposable silicates, or zeolites.
Farmyard or Stable Manure. — In connection with the sub¬
ject of mineral fertilizers, it will be proper to discuss briefly
the uses and special merits of stable manure, composts, etc.
Up to within the last century, these were practically the only
fertilizers known and used, and the exclusive use of this
manure might have continued indefinitely but for the dis¬
covery that as time progressed, stable manure and with it
grain crops, for the production of which it was necessary, be¬
came less and less in amount, so as to threaten bread famines.
The cause of this diminution was, of course, the incomplete¬
ness of the return of the soil-ingredients taken off by the crops,
when these were exported to feed the cities or foreign coun¬
tries. Thus the attention of chemists, and notably that of
Liebig, was attracted to the solution of the problem of keeping
up production even with an insufficient supply of stable ma¬
nure; and the discovery of the use of mineral fertilizers was
the result of their activity.
The chemical composition of stable manure does not, alone,
suffice to explain its remarkable efficacy and the difficulty
of replacing it by any other material. The composition of
manure of course differs not only with different animals but
MINERALS USED AS FERTILIZERS.
7 3
also with the different feeds consumed by them ; but the aver¬
age composition of farmyard manure is approximately given
thus by Wolff and others:
ANALYSES OF VARIOUS FARMYARD MANURES.
1.
2.
3.
4.
5.
Water .
71.00
75.00
79.00
79-95
72-33
Dry Matter .
29-00
25.00
2 1 00
20.05
2767
Ash ingredients . . .
4.40
580
6.50
• • * •
5’87
Potash .
0.52
0.63
0.50
0.84 1
0-69
Lime .
0.57
0.70
0.88
• • • •
0-85
Magnesia .
0.14
0.18
0.18
• • • •
o‘i4
Phosphoric acid .
0.21
0.26
0.30
0.40
0*30
Ammonia .
• • • •
• • • •
• • • •
• • • •
002
Total Nitrogen .
o-45
0.50
0.58
00
d
046
1. Average composition of fresh farm manure (Wolff).
2. Average composition of moderately rotted farm manure (Wolff).
3. Average composition of very thoroughly rotted farm manure (Wolff).
4. Mixed cow and horse manure from a bed two feet thick, accumulated during
the winter in a large covered yard, and packed solid by the tramping of cattle (The
analysis by F. E. Furry).
5. “ Box Manure,” consisting of mixed manure of bullocks, horses, and pigs
(Way, Royal Agric. Soc. Journ., 1850, II., 769).
It is thus seen that the percentage of the important plant-
foods in stable manure are minute when compared with those
commonly found in “ commercial ” fertilizers. Nor are they
so much more available for plant absorption than the latter;
a very large proportion is not utilized at all the first year, and
unless the amount applied is very large it hardly carries the
supply needed for the usual crops.
It is now well understood that its efficacy is largely due to
the important physical effects it produces in the soil. It helps
directly to render heavy clay soils more loose and readily till¬
able. If well “ rotted ” or cured it also serves to render
sandy, leachy soils more retentive of moisture ; and the humus
formed in its progressive decay imparts to all soils the highly
important qualities discussed later on (chapt. 8). More than
this, the later researches have shown that stable manure acts
perhaps most immediately upon the bacterial activity in the
soil, greatly increasing it not only directly by the vast numbers
of these organisms it brings with it, but also in supplying ap¬
propriate food for those normally existing in the soil (see
1 And soda.
7 4
SOILS.
chapt. 9). In so doing it serves indirectly to render the soil
ingredients more available, and to impart to the soil the loose
condition required in a good seed-bed — a “ tilth ” which can¬
not be brought about by the operations of tillage alone.
The only possible substitute for the use of stable manure is
found in green-manuring with leguminous crops conjointly
with the use of commercial or mineral fertilizers. Unless this
is done the use of the latter, alone, ultimately leads to a deple¬
tion of humus substances, which renders the acquisition of
proper tilth by the seed-bed impossible, and causes a com¬
pacting of the surface soil which no tillage can remedy.
Proper method of using stable manure in humid and arid
climates. — In the humid region it is a common practice to
spread the stable manure on the surface of the fields and leave
it there without any special operation to put it. into the soil;
trusting to the rains, earthworms and subsequent tillage for
its being brought into adequate contact with the roots; it is
rarely plowed in. In the arid region this mode of using it is
impracticable; it would remain on the surface indefinitely with¬
out advancing in its decay because of the dryness, and unless
plowed in very deep the ordinary, strawy manure would ruin
the seed-bed by rendering it too pervious to the dry air, thus
preventing germination. Much of this valuable material has
therefore been, and to some extent is still being burnt, thus
causing a severe depletion of the land, both of humus and of
mineral plant-food. The best way to deal with stable manure
in the arid regions is to thoroughly rot or cure it before putting
it on the land, and then plowing it in. To do this of course it
must be put in piles and wetted regularly; a procedure which
at the high prices of labor is thought to be too expensive, but
which in the end would be found eminently profitable, unless
green-manuring is regularly done. The very small proportion
of humus generally present in arid soils renders this precaution
indispensable, if production and proper tilth is to be main¬
tained. The saving of stable manure and of all composting
material, even if less needful as a means of supplying plant-
food in the rich soils of the arid regions, is fully as essential
in order to maintain the humus supply.
MINERALS UNESSENTIAL OR INJURIOUS TO SOILS. 75
(B.) MINERALS UNESSENTIAL OR INJURIOUS TO SOILS.
The minerals heretofore mentioned contribute to soil forma¬
tion either one or several ingredients, important to plant growth
either by their mechanical or chemical action. It remains to
consider some not intrinsically desirable, but frequently pres¬
ent in certain soils, which should be known to the farmer in
order that he may be enabled to counteract or remove their
injurious effects. Leaving aside such as are of only casual or
rare occurrence, the following may be mentioned as among
those which not unfrequently affect soils desirable for culture
to such extent as to make them unavailable for general farming
purposes :
Iron Pyrites; sulphid of iron containing two molecules of
sulphur to one of iron; a mineral exceedingly common in de¬
posits of metallic ores, and whose deceptive gold-like color has
caused it to be mistaken for gold so often as to cause it to be
designated as “ fool’s gold ” among miners. While it fre¬
quently does contain some gold and is often associated with
valuable ores, it is practically valueless when occurring outside
of mineral veins, in rock masses; and more especially in sedi¬
mentary rocks, such as sandstones, limestones, shales and clays.
When present in soils it sometimes becomes a source of
trouble to the farmer, because in contact with air it is soon
transformed into ferrous sulfate or copperas, which, like the
carbonate referred to above, is injurious to plants. Sometimes
indeed iron pyrites is actually formed in badly-drained soils
alongside of the carbonate of iron, when much sulfate (such
as gypsum) is present; and then its injurious effects subside
more slowly than do those of the carbonate (see above, p. 46).
Recognition of Iron pyrites. — The mineral is easily recognized by its
golden or brass-yellow tint ; the latter color being the one most com¬
monly shown in the “ sulphur balls ” occurring in marls or soft lime¬
stones. A very easy test is to pulverize it and then heat it on a shovel
over a fire, when it will soon itself take fire, burning with a blue sulphur
flame, and upon more complete roasting, leaving behind a red powder,
viz., “ Venetian red” or red ochre; that is, ferric oxid. In clays it
commonly occurs in large, well-defined cubes, which do not readily
form copperas but rather become covered with a crust of limonite
or brown iron ore.
;6
SOILS.
When a subsoil is found to contain pyrites, or when “sulfur
balls ” have been accidentally introduced with dressings of
marl, the remedy is thorough and persistent aeration of the
material. In the case of marls nothing more need be done; but
in that of ill-drained subsoils it is best to add lime in moderate
dressings, to accelerate the transformation into ferric hydrate
or iron rust, and gypsum ; whereby the copperas becomes not
only innocuous but adds two beneficial ingredients to the soil.
The same policy will render available manure or other materials
which have been disinfected by means of solution of copperas.
Halite (rock-salt), or common salt, has already been men¬
tioned as to its occurrence in connection with the Stassfurt
potash salts (see above, page 71); but as rock-salt it rarely
exerts any injurious influence upon lands. It is, however, a
common ingredient of seashore lands, and is also present to a
certain extent in the alkali lands of the arid countries. While
it is true that occasionally small quantities of common salt are
used as an ingredient in fertilization, its usefulness in that
direction is exceedingly subordinate; and it is far more gener¬
ally to be considered as an injurious ingredient of all culti-
vatable soils whenever present to a larger extent than a few
hundredths of one per cent. It is usually considered that one-
fourth of one per cent of common salt renders lands unfit for
most culture plants. Only a few, such as asparagus, the beet,
the saltbushes and some others, succeed when it is present in
this or in larger amounts. In the case of sea water it is usually
accompanied by a still more injurious ingredient, magnesic
chlorid or bittern ; which is detrimental to plant growth in
much smaller quantities than the common salt itself.
Recognition of Common Salt . — The presence of common salt may,
as a rule, be detected by the taste, well-known to every one ; when this
taste is very intense or somewhat bitterish, it indicates the presence of
bittern. The presence of salt, however, is easily verified without the
use of chemical reagents, by slowly evaporating some of the clear water
leached from the soil in a clean silver spoon. If the last few drops are
allowed to evaporate spontaneously, it will be easy to distinguish, even
with the unaided eye, the square, cubical crystals, sometimes combined
into cross-shape, which are characteristic of common salt. It is always
an unwelcome addition to the land, and as its action cannot be neu-
MINERALS UNESSENTIAL OR INJURIOUS TO SOILS. 77
tralized in any way, it can be gotten rid of only by leaching-out. This
process is usually accomplished in seashore lands by the action of rain,
or by the overflow of fresh-water streams, after the tide has been ex¬
cluded by means of drains provided with check-valves to prevent the
inflow of tidewater ; or else by underdrainage, and flooding when
possible.
Mirabxlite, (Glauber’s salt) or sulfate of soda, exists not
un frequently in the soils of the arid region and sometimes en¬
crusts extended areas of lowlands during the dry season.
When present in the soil it will commonly be seen blooming
out on the surface after a rain, in light, feathery, needle-shaped
crystals, sometimes to such an extent that it can be collected by
the handful. Subsequently, when wafted by the wind, it is
reduced to a fine white dust, which constitutes a goodly pro¬
portion and sometimes the entire mass of the “ alkali dust ”
that is so annoying on the plains of Nevada, and in the desert
regions generally, during the hot summer. Near White Plains,
Nevada, it forms a thick layer of “ white sand," in which the
foot sinks deeply, and which is carried about by the wind with
great ease.
Glauber’s salt is never a desirable soil-ingredient. It is
largely produced as a by-product in several industries, but
cannot be utilized for agricultural purposes to any extent. It
is, however, much less injurious to plant growth than common
salt; according to experience in California it may be considered
about three times less so. It constitutes the major portion
of what is commonly known as “ white alkali,” which is well
known to be much less injurious to crops than the “ black ”
kind, which contains carbonate of soda.
Trona and Urao are natural forms of carbonate of soda or
salsoda. Like Glauber’s salt, it commonly occurs as a surface
efflorescence or crust in dry or desert regions ; either from the
evaporation of standing water, as in the case of the soda lakes
of Nevada, Hungary and Egypt, or as an efflorescence on the
surface of the soil, as in the western United States, Mexico
(“urao”), North Africa (“trona”), and at many points in
the Old Continent. In the United States it is commonly
known as “ black alkali,” because of the black spots formed on
the surface by evaporation ; practically the same name
73
SOILS.
(“ kara ”) is given it in Arabia and Asia Minor, whence im¬
pure soda has long been imported into Europe ; while in north
India it forms part of the “ reh ” salts that incrust large areas
(usar lands) in the Indo-Gangetic plain.
The natural mineral always contains an excess of carbonic acid over
the “ normal ” salt, nearly in the proportion of four parts of carbonic
dioxid to three of soda; it is sometimes designated as sesqui-carbonate.
In hot sunshine it may lose most of this excess for a time ; while within
the soil itself it may, in presence of abundant carbonic acid, become
temporarily converted wholly into hydrocarbonate or “ bicarbonate,”
which is less corrosive than the monocarbonate or common salsoda.
hi jury caused in soils. — Like common and Glauber’s salt,
carbonate of soda is always an unwelcome soil ingredient ;
more so, in fact, than either of the other two, since less than a
tenth of one per cent is sufficient to render certain soils
wholly untillable, by the deflocculation or puddling of the clay ;
at the same time rendering it impervious to water. It is by
far the most injurious ingredient that ordinarily occurs in
otherwise good, arable soils; for in addition to the physical
effect just mentioned, it dissolves the humus-substance of the
soil, forming an inky-black solution which, especially when
evaporating on the surface and forming black spots, has given
rise to the popular name of “ black alkali.” As will be more
fully explained hereafter, wherever such is the case, the first
step necessary toward reclamation is the transformation of the
carbonate of soda, at least in part, into the relatively innocu¬
ous sulfate, by means of gypsum in the presence of water;
while carbonate of lime remains in the soil.
In its direct action on the plants themselves, soda is also
most injurious; as when accumulated to any extent near the
surface by evaporation it will corrode the root-crown or stem,
and sometimes completely girdle the same, destroying the
bark. Farther details on this subject are given in chap¬
ter 22.
Epsomite , or Epsom salt, or sulfate of magnesia, is another
one of the water-soluble minerals frequently found efflorescent
on the surface of the ground ; more commonly in saline sea¬
shore lands than in the alkali region proper, although it is
MINERALS UNESSENTIAL OR INJURIOUS TO SOILS. 79
rather common in the northeastern portion of the arid region
of the United States. Whether on the soil surface or in the
crevices of rocks, its needle-shaped, feathery crystals greatly
resemble those of Glauber’s salt, but are readily distinguished
by the more intensely bitter taste. Epsom salt is frequently
the last remnant of sea-salts left in the soil after reclamation.
Though probably somewhat more injurious to plant growth
than Glauber’s salt, the mineral Kieserite, one of the Stassfurt
salts and consisting essentially of Epsom salt, is sometimes
used as an application to calcareous lands instead of gypsum,
and with good results. Yet gypsum is usually the safer, and
equally effective.
Borax (bi-borate of soda) occurs much more rarely than
the salts just described; most frequently in certain portions of
California, forming part of the “ alkali ” in the soil. It is
injurious to plant growth, but is as readily dealt with as is the
carbonate of soda, by dressings of gypsum, whereby inert
borate of lime is produced.
It is hardly necessary to say that saline waters containing
any of the above salts in notable amounts must be used for
irrigation very cautiously. The measures to be observed in this
respect will be discussed later.
PART SECOND,
PHYSICS OF SOILS.
CHAPTER VI.
PHYSICAL COMPOSITION OF THE SOILS.
As has already been stated (chapt. i, p. io), the general
physical constituents of soils are rock powder or sand and silt,
more or less decomposed according to the nature of the orig¬
inal rocks ; clay, the product of the decomposition of feldspars
and some other silicates ; humus, the complex product of the
decomposition of vegetable and animal matters on and in the
soil mass ; as well as vegetable matter not yet humified. Each
of these several constituents must now be considered more in
detail. Since clay is the substance whose functions and
quantitative proportions influence most strikingly the agri¬
cultural qualities of land, it should be first discussed.
Clay as a Soil Ingredient.
The plasticity and adhesiveness of clay, together with the
extreme fineness of its ultimate particles (said to reach the
1-25000 of an inch), explains its great importance as a
ph ysical soil ingredient. It serves to hold together and im¬
part stability to the flocculent aggregates of soil particles that
compose a well-tilled soil ; for without clay the sand would
collapse into close-packed single grains so soon as dried, and
loose tilth would be impossible. Sand drifts illustrate this
condition.
On the other hand, the fineness of the particles serves to
render clay very retentive of moisture as well as of gases and
of solids dissolved in water, imparting these important prop¬
erties to soils containing it ; while coarse sandy soils are often¬
times so deficient in them as to render them unadapted to any
useful culture, despite the presence of an adequate supply of
plant-food.
When to these essential physical properties of clay, there is
added the fact that usually the clay-substance as it exists in
83
84
SOILS.
soils contains the most finely pulverized and most highly de«
composed portions of the other soil-minerals, and therefore the
main part of the available mineral plant-food, it is easy to
understand why soils containing a good supply of clay should
be called and considered “ strong ” land by the farmers of all
countries. “ Poor" clay soils are exceptional; but sometimes
the clay content reaches such a figure that the difficulties of
tillage render them too uncertain of production for profitable
occupation.
Amount of Colloidal Clay in Soils. — Any and all of the kinds
of clay mentioned (p. 57) as occurring naturally may, of
course, enter into and form part of soils. But as the amount
of true, plastic clay substance contained in them is very in¬
definite, it becomes necessary, in order to classify soils in re¬
spect to their tillableness, to ascertain more definitely the
amount of pure, or nearly pure, colloidal clay substance con¬
tained in the several classes of soils ordinarily recognized and
mentioned in farming practice. That this determination can
at best be only approximate, is obvious from the fact mentioned
above (chapt. 4, p. 59), that pure kaolinite itself is not plastic,
and only becomes so by the indefinite comminution and hydra¬
tion it experiences in the processes of soil-formation. As the
progress of this process is also indefinite, the same soil con¬
taining particles ranging from the finest to the chalky scales
of pure kaolinite, the drawing of a line must be more or less
arbitrary and empirical.
From numerous experiments and comparisons made, the writer has
been led to place the limits of “ plastic clay ” at and below such grain
sizes as will remain suspended (afloat) in a water column eight inches
high, during 24 hours. To go beyond this point in the examination of
soils for practical purposes, would render such examinations so labor¬
ious and hence so rare, that this kind of work would be practically ex¬
cluded from ordinary practice. According to this view the following
percentages of such “ clay ” correspond approximately to the designa¬
tions placed opposite :
Very sandy soils
Ordinary sandy lands .
Sandy loams.
Clay loams ....
Clay soils. .
Heavy clay soils
.5 to 3% clay
3.0 to 10%
1 0.0 to 15 %
15.0 to 25%
25-° ^ 35%
35.0 to 45% and over.
it
tt
tt
it
PHYSICAL COMPOSITION OF SOILS.
85
It must be distinctly understood, however, that these figures make no
claim to accuracy or invariability. For, the tilling qualities of a soil
containing one and the same amount of such “ clay ” may be very
materially modified according to the kind and amount of each of the
several grain- sizes of rock powder or sand they contain.
Influence of fine powders on plasticity and adhesiveness. — An
admixture of a large amount of fine powders diminishes mater¬
ially the adhesiveness of a clay soil, even though it may render
it even more “ heavy ” in tillage; while the admixture of coarse
sand, even in very considerable proportions, does not greatly
influence the adhesiveness of the clav. The latter alone can-
not therefore serve as a proper guide or basis for the classifica¬
tion of soils in respect to tillage; we must also take into con¬
sideration the nature and amount of the several granular sedi¬
ments mixed with it.
Moreover, the nature and especially the adhesiveness of the
clay substance as obtained by analysis may vary considerably
in the presence of a very large amount of the finest grain-sizes ;
among which ferric hydrate or iron rust is especially apt to
accumulate predominantly in the clay, considerably increasing
its apparent weight and greatly diminishing its adhesiveness.1
In strongly ferruginous soils, therefore, it becomes necessary
to take into special consideration the amount of the ferric
hydrate or rust which accumulates in the clay substance. The
presence of large amounts of humus or vegetable mold also
influences materially the adhesiveness and physical properties
of the clay obtained by the method described, although most of
it remains with the finer powdery sediments or grain-sizes.
There are, besides, other colloidal or at least amorphous sub¬
stances present in all soils, such as silicic, aluminic and zeolitic
hydrates, which are all non-plastic, and yet sufficiently fine to
form part of the “ clay ” obtained as above specified.
Despite these imperfections, (which however can in a meas¬
ure be taken into consideration in judging of a soil’s tilling
qualities by its clay content), the figures given in the above
table approximate much more nearly to a tangible basis for
such estimate, than the utterly indefinite mixtures which under
the older methods of analysis have been, and still are to some
extent, used as a basis for soil classification by writers on
agriculture.
1 This fact emphasizes the impossibility of explaining the plasticity and adhesive*
ness of clay simply as a function of fineness of grain.
86
SOILS.
Rock Powder ; Sand , Silt and Dust.
The powdery (sandy and silty) constituents of soils usually
constitute the greater part of their mass ; and the proportions
present of the several grades of fineness exert a most decisive
influence upon their cultural qualities, and very commonly
upon their agricultural value also. It is needless to add that
the kind of mineral of which they consist or from which they
were formed, is also of great importance in determining the
quality of soils from the standpoint of the chemist, with respect
to their content of mineral plant-food.
WEATHERING IN HUMID AND ARID REGIONS.
Sands of the Humid Regions. — As has already been stated,
“ sand ” is usually understood to be, in the main, quartz more
or less finely pulverized, generally intermingled with a few
grains of other minerals. With this understanding, since
quartz is practically inert with respect to plant nutrition, it
follows that soils consisting mainly of this substance contain
but little plant-food ; hence the common expression “ poor,
sandy land,” the outcome of the experience had in Europe and
in the Eastern United States, and which until recently has been
held to be of general application. The “ sands of the desert ”
have, both in ordinary life and in poetry, always stood as the
symbol of sterility.
Thus the sandy lands (“sand hammocks”) of Florida, the (long-
leaf) pine lands of the Gulf States, the “ pine barrens ” of New Jersey
and of Michigan, are noted both for their sandy soils and their sterility
after brief cultivation ; necessitating fertilization within a few years
from the time of occupation. In Europe, the “ Heide ” (heather)
soils of northeastern Germany are of the same cultural character.
Sands of the Arid Regions. — The experience of arid coun¬
tries however, has long ago shown that some very sandy lands
— e. g., such as form the oases of the north African deserts — -
may be extremely productive when irrigated, and also of con¬
siderable durability. Actual experience and close investiga¬
tion given this subject in the arid regions of the United States
has fully demonstrated that lands appearing to the casual ob-
PHYSICAL COMPOSITION OF SOILS.
3/
server to be hopelessly sterile sandy deserts, very commonly
prove to be even more productive than the more clayey lands of
the same regions. Examination of the sand shows, in these
cases, that instead of mere grains of quartz, the minerals of the
parent rock, partially decomposed, themselves constitute a
large proportion of the sandy mass. But in the regions of
deficient rainfall, as has already been stated, (p. 47) the
formation of clay (kaolinization) is exceedingly slow; hence
the decomposition of the rock powder results in the production
of predominantly pulverulent instead of clayey soils. But the
mineral plant-food is not on that account less available, pro¬
vided other physical conditions necessary for the success of
plant growth are fulfilled. Among these moisture stands
foremost; hence the relative proportions of the several grain-
sizes are of vital importance, since upon this depends to a great
extent the proper supply and distribution of moisture, without
which no amount of plant-food will avail. Moreover, the
finest and most highly decomposed powder is the portion from
which the roots draw their chief food-supplies.
The point last mentioned is well shown in the results obtained by
Dr. R. H. Loughridge, from the analysis of each of the several grain-
sizes into which he had resolved a very generalized soil of the State of
Mississippi, representing a very large land area in that State as well as
in Tennessee and Louisiana. The details of this investigation are
given farther on ; but summarily it may be stated that he found prac¬
tically the whole' of the acid-soluble mineral plant-food accumulated
within the portion of the soil the fineness of whose grains was below
.025 millimeters (one-thousandth of an inch) ; ingredients so fine as
to be wholly impalpable between the fingers. Moreover, two-thirds of
the total amount was found in the portion described above as “clay.”
It is thus readily understood why clay soils are in the regions of summer
rains commonly designated as “strong” lands.
The corresponding later investigations of Rudzinski (Ann. Agr. Inst.
Moscow, Vol. 9, No. 2, pp. 172-234; Exp. Sta. Record, Dec. 1904,
p. 245) and of Mazurenko (Jour. Exp. Landw. 1904, pp. 73-75 ; Exp’t
Stn. Record, Dec. 1904, p. 344) fully corroborate Loughridge’s con¬
clusions, for typical soils of European Russia.
In the arid or irrigation regions, however, the case is dif¬
ferent, for the reason that much of the decomposed rock-
88
SOILS.
substance remains adherent to the surface of the larger grains,
and plastic clay is formed to a much less extent. Much avail¬
able plant-food may therefore, in arid lands, be present even in
rather coarsely sandy soils almost devoid of clay ; such as in
humid climates would he likely to be found wholly barren.
(See chapt. 19).
PHYSICAL ANALYSIS OF SOILS.
Use of Sieves. — Down to a certain point the separation of
the soil into its several grain-sizes may be accomplished by
means of sieves. We may thus separate coarse gravel from
fine gravel and from sand; and the latter may itself be sepa¬
rated into several sizes by the same means. This presupposes,
of course, that the soil has been previously prepared for the
purpose by crushing the lumps consisting of aggregates of
finer particles, that in the operation of tillage would again be
resolved into their fine constituents, or be penetrated by roots.
But this preparation of the soil for sifting must not be carried
beyond the point mentioned, for a grain consisting of particles
somewhat firmly cemented together will under ordinary con¬
ditions play in the soil precisely the same part as a solid sand-
grain, and must not therefore be broken up, if the soil is to be
examined in its natural condition. The pressure of the fingers
or of a rubber pestle is as far as trituration should go. The
disintegration of these compound particles by means of acids,
as prescribed and practiced by the French soil chemists, may
wholly change the physical nature of the soil by the breaking-
up of mechanical aggregations which in the usual course of
tillage would remain intact. This is especially true of
strongly calcareous soils, and particularly those containing
calcareous sand.
The sieves used for this purpose should not be ordinary wire sieves,
but should have bottoms of sheet brass perforated by round holes of
the various diameters desired, of fractions of inches, or preferably of
millimeters. For the finer grain sizes, silk bolting cloth is used by the
U. S. Bureau of Soils.
In the sifting process it will be found that so soon as the finer grain-
sizes of the sand are approached, the sieve fails to act satisfactorily ;
the more so, the more clay was originally contained in the material.
PHYSICAL COMPOSITION OF SOILS.
89
The fine particles flock together, forming little pellets, which refuse to
be separated by the sieve. This difficulty can, of course, be partly
overcome by previously separating the clay from the sand by means of
water, as detailed above ; but even then it will be found that so
soon as the grain-sizes fall much below A_. of an inch (|- millimeter)
the same difficulty is experienced, so long as the sand is dry. By
playing a small stream of water upon the sieve, however, all the parti¬
cles beyond the of an inch may be successfully separated from the
coarser portion ; and for many practical purposes the separation need
be carried no farther.
Use of Water for Separating Finest Grain-Sizes. — The scientific
investigator, however, must of necessity proceed to separate the finer
grain-sizes from each other, since, as will presently be shown, they
influence the tilling qualities of the soil to a much greater degree than
do the coarser particles. Such farther separation can be accomplished
only by the aid of water.
Subsidence Method. — When a small amount of soil is
stirred up in water, and is afterward allowed to stand for some
time, the different grain-sizes will settle consecutively in ac¬
cordance with their sizes (or weights) ; the smallest ones
settling latest, and the clay only remaining suspended, as
stated above. So long, however, as any considerable amount
remains suspended in the water, the latter is not only denser
but especially more viscid than if the clay were absent. In
order therefore to obtain correct results by any method in¬
volving the use of water, it is necessary to remove the clay be¬
fore proceeding to the separation of the granular sediments.
This, as has been already stated, is approximately accom¬
plished by allowing the soil, when diffused in water after
proper disintegration, to settle for 24 hours from a column of
water 200 mm. high, whereby all grain-sizes, of and above .01
mm. diameter are removed from the turbid liquid. This
sedimentation is then repeated until after 24 hours the water
becomes clear. The clay is then determined in the “ clay
water” by evaporation or precipitation; the granular sedi¬
ments may then be successfully separated by sedimentation.
The U. S. Bureau of Soils uses for the separation of clay,
instead of subsidence for 24 hours, the more expeditious pro¬
cess; of contrifuging the turbid soil water in appropriate glass
cylinders, by the aid of an electric motor; and thus in a rel-
9o
SOILS.
atively short time obtains “ clay ” in which the upper limit of
size is one-half of that mentioned above, viz., .005 mm. But
for the costliness of the appliances required, including the
entire time of an operator, this method of separating the clay
would undoubtedly be preferable to the elimination by sub¬
sidence; the more as a more minute grain-size for the clay
group is thus secured.
The separation of the clay having been accomplished, the
various sizes of silt and sand may be separated by again sus¬
pending them in water; and interrupting the settling process at
stated times, the grain-sizes corresponding to definite velocities
in settling may be segregated and weighed. When this process
of settling and decanting is carefully and repeatedly carried
out, very good results are obtained.
Tcp
/
Hydraulic Elutriatiou. — The sedimentation (or
‘‘beaker”) method, long practiced in the arts is,
however, quite tedious, requiring the constant
close attention of a skilled observer. The desired
results may, in the writer’s judgment, be more
conveniently obtained by the hydraulic method,
whenever no very large volume of work of this
kind is required to be done at once.
When instead of allowing the soil to settle in
quiet water, the latter is used as an ascending cur¬
rent of regularly graded velocities, it is clear that
the soil particles will be carried off by this current
in exact conformity with their several sizes (or
strictly speaking, volume-weights) ; and when
maintained in such a current for a sufficient length
of time, the entire quantity of the sediment cor¬
responding to the prevailing velocity will be car¬
ried away. It is of course easv to ascertain to
£ what grain-sizes certain velocities of the upward
Eiutriltor.10116 S current (regulated by a stopcock with arm moving
on a graduated scale) correspond, and to regulate accordingly
the intervals between the different velocities to greater or less
detail, as may be desired. A number of instruments have been
devised for this purpose.
Schone’s Elutriator is the one commonly used in Europe;
PHYSICAL COMPOSITION OF SOILS.
91
in it the upward current ascends in a conical glass tube, (see
figure 6) entering through a narrow, curved inlet tube, in which
the soil sample is kept agitated by the current itself. The
objection to this plan is twofold: first, the narrow, curved
inlet-tube is readily clogged by the soil mass at the lower
velocities, which are thereby changed, so that, unless a very
small amount of soil only is employed, the whole mass is not
kept properly stirred ; second, the circulating currents brought
about by the conical shape of the tube cause the sediment-par-
Fig. 7. — The Churn Elutriator (Hilgard’s) for the physical analysis of soils.
tides to coalesce into complex, larger ones (floccules), which
will then settle down and fail to pass over at the current-
velocity corresponding to their individual component parts.
Churn Elutriator with Cylindrical Tube. — The errors just
alluded to are obviated by an arrangement devised by the
writer, in which a rapidly-revolving stirrer, placed at the base
of a cylindrical tube in which the washing process is conducted
92
SOILS.
and which eliminates counter-currents, continually disintegrates
these compound particles, and thus enables the entire quantity
of the sediment corresponding to the prevailing current-velo¬
city to pass off with a comparatively slight expenditure of time
on the part of the operator (see figure 7). A wire screen in¬
terposed between the churn and cylindrical glass tube prevents
communication of the whirling motion to the column. As the
apparatus works automatically, the analyst has only to observe
from time to time whether or not the turbidity near the top of
the tube has disappeared ; and as the sediment accumulates at
the bottom of the tall receiver bottle,1 no harm is done if the
attendant should neglect to change the velocity in time, except
that water will run to waste.
The conical relay glass below the churn serves to retain the
coarser grades of sediments which are not concerned in the
velocities employed in the elutriator tube, and thus prevents
injurious attrition. But these sediments can at any time be
stirred up by the incoming current and brought into the wash¬
ing tube if desired. In the same manner the passing-off of
the finer sediments can be materially accelerated by running
off rapidly about two-thirds of the turbid column of water
every twenty minutes.
It should be fully understood that prior to attempting such
separation, the “ colloidal clay ” must first be removed by the
subsidence or centrifugal method, since otherwise much larger
grain-sizes may be carried off at a given velocity.
Yoder s Centrifugal Elutriator . — A very ingenious instru¬
ment which combines the elutriation and sedimentation pro¬
cesses into one, has been devised by P. A. Yoder, of the Utah
Expt. Station. The elutriator bottle is placed in a centrifuge
driven by an electric motor; it is closed by a glass stopper
carrying a delivery tube to a short distance above the bottom
of the elutriator bottle, as well as an outflow tube ending at the
base of the stopper; the latter also carries a funnel coinciding
with the center of rotation. Into this funnel flows gradually
1 The figure given of this elutriator in Bulletin No. 24, on physical soil analysis,
published by the U. S. Bureau of Soils, shows as the receiver a bottle entirely too
low to insure the complete retention of the sediments by settling. The receiving
bottle should not be less than twelve inches high and five inches wide.
PHYSICAL COMPOSITION OF SOILS.
93
the muddy water containing the soil in suspension ; and the rate
of its flow, together with the velocity of rotation, determines
the size of the sediment-granules that will be deposited in the
slack-water below the mouth of the delivery tube. The muddy
soil-water is kept agitated in a funnel-shaped reservoir by air-
bubbles from a constant-pressure chamber.
While the principle of this instrument is good, it is quite
complicated and the results obtainable from it in practice have
not as yet been made public. The inventor claims that an
analysis may by its means be completed in less than three
hours.
In all hydraulic elutriators a provision for constant press¬
ure in the reservoir supplying the current of water is needed ;
although in Schone’s and some other instruments a gradually
decreasing pressure in a plain reservoir is employed. A large
glass bottle or carboy fitted with the proper tubes so as to con¬
stitute a Mariotte’s bottle (in which the air enters near the
bottom of the vessel), is a very convenient arrangement.
Number of Sediments. — The number of grain-sizes or sedi¬
ments into which the soil mass is to be segregated is of course
entirely within the option of the operator. Experience has
shown that it is unnecessary to discriminate very closely be¬
tween the several sizes of the coarser portion of the sand, such
as those lying between one-fourth and one-half of a millimeter.
But below this point, and especially between one-tenth of a
millimeter and the clay, a proper discrimination becomes very
important. The series first devised by the writer in 1872 is
based upon a consecutive doubling of the velocities of the cur¬
rent from a quarter of a millimeter per second to thirty-two
millimeters per second ; the sediment of sixty-four millimeter-
velocity corresponding to a diameter of one-half of a milli¬
meter, will remain in the elutriator. Above this, as before
remarked, the sieve (especially when aided by a jet of water)
effects a satisfactory segregation.
The table below shows the elements of these series both as
regards current-velocities and maximum quartz-grain diame¬
ters carried off by each. In a great many cases, however, it is
altogether unnecessary to go into such detail, and a subdivision
into six or seven divisions is quite sufficient. Such a sub-
94
SOILS.
division, based upon the doubling of grain-sizes instead of
current-velocities, has been adopted by Prof. Milton Whitney,
of the U. S. Department of Agriculture, and others.
TABLE OF DIAMETERS AND HYDRAULIC VALUES OF SEDIMENTS.
Designation of materials.
Velocity per sec¬
ond, or hydraulic
value.
- \
Maximum dia¬
meter of quartz
grains.
Mm .
Mm.
Grit .
(?)
i-3
(?)
•5-i
32-(H
.50
Sand . ■{
16-32
•3°
8-16
.16
4- 8
.12
2- 4
.072
1 .0— 2
.047
•5- 1
.036
.25-0.5
.025
0.25
.016
< 0.25
.010
Clay .
<1 0.00->5
Results of such analyses. — A tabular presentation of the re¬
sults of analyses made in accordance with the above plan will
give a good idea of the differences between the various grades
of soils recognized in farm practice, to any one accustomed to
the study of figures. But a much more satisfactory showing
is made by placing the several grain-sizes segregated, into
small vials or tubes of identical diameter and placing them in
parallel series alongside of each other.1 The curves formed
by the surfaces of the several sediment-columns in each series
show to the eye very strikingly the relations of the several
grades of soils to each other, and suggest at once that while
gentle slopes or gently undulating curves belong to soils of
intermediate, loamy character, steep grades and zigzags show
soils of extreme types. This is exemplified in the subjoined
Figures :
1 Convenient stands for this purpose, used by the writer since 1872, may be cut
from L-shaped moldings of wood, such as can be readily ordered from any
planing mill. The vials can be cemented, wired or tied.
PHYSICAL COMPOSITION OF SOILS.
95
Riverside
Cal ifo m « a
Sandy Soil
San Joaquin Plains
Cali f orni a
Slack Adobe S
Berkeley
California
Soil
■
g-~~
Clay;
* f •
Silts
D iaffleters '
'< Sands
{in Mf 11 i me ters)
!
*
•
?
I
0
h.oifi
.0i^.O25F7056
~.C2 *1*036 h 047
1 0471.072
KC72 |-J20
.12
<*.16
—.30
.30
-.50
Fig. 8- — Illustration of Results of Hydraulic Elutriation, showing extremes of soil texture, and
intermediate loam.
96
SOILS.
Alluvial Lq o iJi,
Sacramento Valley
Cal J f a raC»
Sandy i_oain Soil
San Bernardino Valley
Cal iforma
Leant Soil
Long- leaf Pine Woods
Mississippi
{ in Millimeters
)
I .0471 .072]
.12 1,
.16 1
.30 |
|..072Ul20j.
-16 |»
.30
50 |
f ig. 9. — Illustration of Results of Hydraulic Elutriation, showing Alluvial Silts and Pine-Woods
Soil.
Physical composition corresponding to popular designations
of Soil quality. — The subjoined table illustrates the physical
composition of a number of soils from the State of Mississippi,
PHYSICAL COMPOSITION OF SOILS.
97
selected for their representative character, in order to deduce
therefrom approximate definitions of physical character corre¬
sponding to popular designations. This table, published in
1873 in accordance with results obtained during the two pre¬
ceding years, does not require any material modification on
account of subsequent investigations. It lacks, however, a
characteristic representative of the predominant soils of the arid
region, viz., the silty soils so prevalent in dry climates, only
approximately represented by No. 165 of the table; hence two
such, from California, exemplifying respectively the valley
deposits of the Sacramento and Colorado rivers, have been
added to the list.
It must not, however, be understood that these typical soils
necessarily represent correctly the physical constitution of all
soils falling under the same popular designation; for we are
far from being able as yet to predict accurately in every case the
tilling qualities of a soil material from its physical composi¬
tion. To do this it would be necessary not only to know with
some degree of precision the several physical coefficients of each
of the several grain-sizes, and perhaps of many more inter¬
mediate ones; but we would also have to construct a formula
according to which each could be given its proper weight when
present in varying proportions, and of varying shapes, surface
condition, and material. For this our present knowledge is
wholly inadequate, if indeed the problem is not beyond the
limits of mathematical computation. We must for the pres¬
ent at least be satisfied with the empirical approximations
afforded us by the constantly increasing number of such
analyses, correlated with farming experience.
Since the finest grain-sizes above those classed as “ clay ” do not
tend to “ lighten ” soils, but even to render them more intractable
(“ putty soils”), while coarser ones gradually change the dense clay-
texture into the “ loamy,” it is clear that in between there must be a
neutral point, some grain sizes which by themselves do not influence
soil texture either way. Discussion of numerous physical analyses, and
some direct experiments, have led the writer to conclude that this theo¬
retically neutral grain-size lies at or near the diameter of .025 mm., or
.5 mm. hydraulic value. In correlating the results of analysis with the
tilling qualities of the soil as to “ heaviness and lightness,” therefore,
that grain-size may usually be left out of consideration.
7
PHYSICAL ANALYSES OF SOILS AND SUBSOILS.
SOILS.
Mississippi Uplands. Mississippi River Bottom. California.
! - - l
River Deposit.
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• • • .
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8
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m m vO ro m rooo m m
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I
PHYSICAL COMPOSITION OF SOILS.
99
Number of soil grains per gram . — It is of some interest to
consider the number of grains of different sizes that may be
contained in, e. g., a gram of soil. If for this purpose we as¬
sume all the soil grains to be spherical, we shall obtain the
minimum figures, for most other shapes will pack more closely.
King (Physics of Agriculture, p. 117) calculates such figures
for different grain-sizes, assuming the density to be that of
quartz (2.65), with the result that while with a diameter of one
millimeter (1-25 inch) the number of grains would be 720,
and with one-tenth of a mm. 720,000; if made of the finest
particles only, viz., one thousandth of a mm., the number
would be 720,000 billions. Probably few of the clayey soils
we ordinarily deal with are of this order; it is doubtless
approached in certain fine plastic clays.
Surface afforded by various grain-sizes. — The amount of
surface afforded by a similar amount of soil must naturally be
considered in this connection, since upon it depends not only the
amount of moisture which the soil may hold in the form of
superficial films, but also the extent of surface upon which the
weathering agencies as well as the root hairs of plants may act.
Quoting again from King’s work, we find on the same premises
given above for the number of grains, that their surface would
in the case of grains of one mm. diameter be eleven square feet
per pound (about half a pint) of material; while in the case of
the finest grade we should have 110,538 square feet, or more
than two and a half acres.
From actual experiments made with the flow of air through
various soils, King calculates that while in ordinary loam soils
the total surface is about an acre per cubic foot, in fine clay
soils it rises to as much as four acres. If we imagine this
large surface to be covered with even a very thin film of water,
it is readily seen how large an amount may be present in a cubic
foot of moist soil.
E. A. Mitscherlich (Bodenkunds fur Land-und-Forstwirthe ; Berlin,
1905) attributes to the surface offered by the soil particles supreme
importance in determining the productiveness of soils. According to
him the internal soil-surface determines directly the ease with which
roots can penetrate the soil ; and he proposes the determination of this
factor by means of the heat produced in wetting the soil ( “ Benet-
IOO
SOILS.
zungswarme ” ), measured in a calorimeter, as a substitute for all methods
of physical soil analysis, which are vitiated by the varying shapes and
densities of the particles ; while his method gives directly the actual
surface. To the consumption of energy required by difficult penetra^
tion he attributes most of the differences in production, and hence re¬
fers to the internal soil-surface as governing nearly all the other physi¬
cal factors. The introduction of many arbitrary assumptions, and the
failure to show that the admitted inaccuracy of the ordinary mechanical
soil analyses are of any practical importance, greatly detract from the
cogency of the rigorous mathematical discussion carried through his
work by Mitscherlich.
Influence of the several grain-sizes on soil texture. — Un¬
doubtedly the most potent of all the sediments appearing- in the
above table in influencing soil texture, is the “ clay.” That
the materials included under this empirical designation may
vary considerably in different soils, has already been sufficiently
insisted on ; and it is doubtful that in the present imperfect state
of our knowledge of the functions of the several physical grain-
sizes, we would be much wiser were we to go to the extreme
advocated by Williams (Forsch. Agr. Phys., vol. 18, p. 22 5, ff),
of determining with precision the actual amount of such ex¬
tremely fine clay particles as cease altogether to obey the law
of gravity when once suspended in water. It is at least doubt¬
ful that the essential property of adhesive plasticity belongs
only to these, for this property doubtless increases gradually
as the size diminishes, although unquestionably not a mere
function of the latter, since it belongs only to the hydrated
silicate of alumina.
Ferric Hydrate. — Probably the body which most commonly modifies
materially the adhesive and contractile properties of the clay substance,
is ferric hydrate ; the more as on account of its high density it tends
to exaggerate materially, in many cases, the apparent content of true
clay, and the estimate of the soil’s plasticity based upon it. A good
example in point is the case of soil No. 246 (Miss.) of the above table.
This is a heavy clay soil, yet not excessively adhesive ; scarcely as
much so as No. 230 (Miss.), the heavy gray “ flatwoods ” soil, and
not nearly as “ sticky” when wet as No. 173 (Miss.), the prairie sub¬
soil, although containing apparently 15 °J0 more clay than the former,
PHYSICAL COMPOSITION OF SOILS.
IOI
and 7 °Jo more than the latter. But No. 246 is a highly ferruginous
clay, in which the ferric hydrate is in a very finely divided condition,
and materially influences the physical qualities of the clay substance.
Were it all accumulated in the “ clay,” it would diminish the percen¬
tage of true clay by 1 1.75 %, reducing the clay-percentage to 28.5%
which accords more nearly with the soil’s only moderate adhesiveness,
and not excessively heavy tillage.
But it must be remembered that the iron oxid shown in the
analysis is not nearly always in this finely diffused condition.
Frequently it incrusts the sand grains; quite commonly it forms
small concretions of limonite, which themselves act as sand
grains ; and again, it may be present in the form of “ black
sand ” or magnetic oxid, as is commonly the case in California
and on the Pacific slope generally. To take this point properly
into account, therefore, it would be necessary to determine the
amount of ferric hydrate actually present in the “ clay ” as
separated by subsidence of the granular constituents.
Other substances. — This circumstance as well as the inevi¬
table presence of other modifying substances, clearly shows the
desirability of being enabled to examine the physical properties
of this “ clay ” directly, by collecting its entire amount as ob¬
tained in analysis, instead of merely determining it by weighing
fractional portions. When this is done the analysis is much
more valuable as indicating the true tilling qualities of the
land. The increase of bulk suffered by this substance after
wetting, is a very fair index of its content of true clay, and is
preferable to the chemical analysis proposed by some investi¬
gators. For it is quite impossible to distinguish the silica and
alumina derived from the kaolinitic substance proper, from that
which is due to the decomposition of zeolites.
It is possible, however, to determine the possible maximum
of the kaolinite ingredient by taking into consideration the
quantitative ratio according to which silica and alumina com¬
bine to form it, viz., approximately 46% of the former to 40 of
the latter, the rest being water. By using this calculation we
can often demonstrate clearly the presence in the “ clay ” of
considerable amounts (up to 33%) of aluminic hydrate; since
no zeolitic mass can contain as much alumina as does kaolinite,
Whether the aluminic hydrate be in the form of gibbsite,
102
SOILS.
bauxite, disapore,1 or in the gelatinous state, the nature of the
soils containing it proves that it is totally destitute of plasticity
and adhesiveness; and this consideration will often serve to
explain the fact that soils showing in their chemical analysis
high percentages of alumina, nevertheless show quite low de¬
grees of plasticity, adhesiveness and water absorption. What
part it may take in modifying the physical properties of the
soil we can thus far only conjecture.
Influence of the granular sediments 'upon the tilling qualities
of Soils. — Considering the granular sediments by themselves,
in the absence of clay, it may be stated in a general way that
while in a moist condition they flocculate sufficiently to pro¬
duce a fair tilth, they will nevertheless on drying collapse into
a close arrangement resulting from the single-grain structure.
The form of the grains being angular instead of rounded, they
are apt to form a very closely packed mass far from suitable
to vegetable growth ; as will be seen by an example taken
from one of the culture stations of the University of California,
from a piece of land which on the surface would be called a
very sandy loam, but after we descend increases in its content
of fine grains until at a depth varying from eighteen inches to
three feet we find what appears to be a hardpan, which is
equally impervious to roots and water and causes the water to
stagnate to such an extent that after heavy rains the land
becomes so boggy as to render plowing almost impossible with¬
out endangering the team. A close examination of this hard-
pan shows that, unlike others, it is devoid of any cement, and
when taken out can be readily crushed between the fingers, and
softens in water, but does not become plastic. Its impervious¬
ness is therefore due solely .to the close packing of the sand
grains, for it contains practically no plastic clay, and under
the microscope the grains are seen to be angular-wedge-shaped
and composed of the remnants of granite. The physical
analysis shows the following result :
1 Bauxite is not only the most abundant of the three hydrates of alumina
known to occur naturally, but also stands nearly midway between the two others
in its water content, viz., a little over 25° 0 ; that of diaspo re being nearly 15°/^
gibbsite about 35 °/0.
PHYSICAL COMPOSITION OF SOILS.
103
MECHANICAL ANALYSIS OF HARDPAN.
Designation.
Diameter.
Percentage.
’
.50 mm.
io-93
Sand . \
•3° u
21.23
.16 “
7.58
_
.12 “
7.27
.072 “
9-63
.047 “
12.00
Silt . j
.036 “
7.19
.025 “
1.25
.016 “
14.20
“Clay” .
?
8.64
It is doubtful whether this condition of things can be
remedied by the usual measure of breaking up the hardpan
either by hand or by means of giant-powder blasting. Ex¬
perience seems to show that the effect is only temporary, and
that in the course of time, by the action of the percolating
waters, the particles settle back into their original impervious
condition. It is just possible, however, that if once penetrated
by roots, the intervention of these would permanently destroy
the close structure, so as to make this a fair subsoil for the
growth of trees and other plants. The writer is not aware that
this kind of purely physical hardpan without cement has ever
been observed elsewhere.
This physical condition is doubtless responsible for two other
phenomena, viz., the “ putty soils,” and also certain difficulties
experienced in irrigation.
“ Putty Soils ” is the name popularly given in the Cotton
States, and probably elsewhere, to soils usually occurring in low
ground and also known as “ cray-fishy.” They consist of very
uniform, powdery sediment, with little or no coarse sand and
still less of clay to render them coherent. When wet these
soils behave precisely as would glazier’s putty, adhering to the
surface of even the best-polished plowshare, so that no furrow-
slice can be turned and the plow is soon dragged out of the
ground. At a very closely limited condition of moisture such
lands may plow fairly well ; but when this limit is passed in
the least (as sometimes happens in the course of a single day),
it turns up only hard clods, which in a few hours of sunshine
become so hard that no instrument of tillage short of a sledge-
104
SOILS.
hammer will make any impression upon them. The physical
analysis of these usually gray soils shows that they contain only
a trifling amount of clay; perhaps i or 2%, playing the part
of linseed oil in making putty out of whiting. Even the addi¬
tion of lime does not help such soils much, because there is
little or no clay to flocculate. They are, as a matter of fact,
among the most refractory lands the farmer has to deal with.
A soil showing similar behavior, though not quite as extreme
as in the case of the Gulf or Cotton States' soils in question,
occurs at the culture substation at Paso Robles, California,
and is probably closely correlated to the physical hardpan re¬
ferred to above. The physical analysis of this soil yielded the
following result :
Designation.
Sand
Silt... .
“ Clay
MECHANICAL ANALYSIS OF SOIL.
Diameter.
Percentage.
.50 mm.
14.24
.30 “
15-17
.16 “
8.88
.12 “
5.60
.072 “
6.75
.047 “
8-35
.036 “
8.55
.025 “
6.03
.016 “
17-77
?
7-5°
It would seem the best and almost only remedy to be ap¬
plied to such soils as these is the introduction of vegetable
matter or green-manuring, by which their texture is loosened :
for the hauling of mere clay upon the land would hardly ac¬
complish the purpose intended, within the limits of farm
economy.
Dust Soils , which during the dry season are even in their
natural condition so loose as to rise in clouds and render travel
very uncomfortable, are not uncommon in arid countries, e. g.,
in Washington and adjacent parts of Oregon, on the uplands
bordering the Columbia, Yakima and Snake rivers. The
physical analyses of three of such soils, given in the table be¬
low, will convey some idea of their peculiarities in this respect.
PHYSICAL COMPOSITION OF SOILS.
105
PHYSICAL ANALYSIS OF DUST SOILS.
Hydr. Value.
Diameter.
No 17.
No. 37.
No. 79.
Clay .
Silt . '.. \
Sand .
Total .
^.0023. mm.
<.25 mm.
.25 to .5
.5 to 2.0
2.0 to 8.0
8.0 to 64.0
<.IO — ?
.010
.016
.025— .047
.047.— .120
.12 — .50
•93
30-93
3.20
7.18
21.88
32-39
3-59
1 3.06
5.82
27-37
43-78
49-57
1.27
32.29
12.75
37oi
10.92
3-97
96-57
08.18
08.72
Slow penetration of Water. — Soils of this class are wetted
with extreme slowness by irrigation water ; so that when first
taken under cultivation it sometimes takes twenty-four hours to
soak the land for twelve inches in each direction. Irrigation
furrows must be placed very close together and in large num¬
bers, in order to ensure the wetting of the soil so that the crop
shall not suffer from lack of moisture at a distance of two or
not more than three feet. Where the irrigation furrows are
drawn farther apart a fine stand of grain may be seen within
eighteen inches of the same, while farther away the crops may
be dying from lack of moisture. This difficulty is by no means
infrequent in the arid region, and is difficult to overcome except
by frequent and thorough tillage, which gradually increases the
rapidity of water-penetration; as has been shown in the soils
of the alluvial prairies of the Yakima country in the State of
Washington. It is necessary, however, to take care that they
shall always contain an adequate amount of humus or vege¬
table matter, in order to prevent re-consolidation by the burn¬
ing-out of the humus during the warm, rainless season.
There is an unmistakable resemblance between these dust
soils of the Northwest and the “ putty ” soils mentioned above;
both showing a very low percentage of clay with a relatively
large amount of the finest sediments, with a sudden downward
break of the curve before the coarser grain-sizes are reached.
It would seem as though the absence of these intermediate
grains favors the close packing of the fine sediments in the
interstices of the coarse ones, thus bringing about the imper¬
viousness, which is the chief obstacle to their cultivation.
Effects of coarse Sand. — Coarse sand intermingled with
heavy clay soils has but little effect in improving the tilling
qualities, unless carried to such excess as renders it financially
io6
SOILS.
impracticable. In actual practice it is frequently possible to
improve such soils by properly distributing upon them the
washings of the adjacent hills, which will always carry sands
of many grades; and when it is intended to improve garden
land by hauling sand it is important to choose the latter so as to
complement the deficient grain-sizes of the soil. The sand of
wind drifts or dunes is generally well adapted to such improve¬
ment, being, as Udden 1 has shown, of a fairly definite com¬
position of sufficiently wide range of grain-sizes for the pur¬
pose.
The effects of humus in modifying soil texture are discussed
farther on.
1 The Mechanical Composition of Wind Deposits, Bull. No. t, Augustana Library
Publications; 1898.
CHAPTER VII.
THE DENSITY AND VOLUME-WEIGHT OF SOILS.
Aside from the humus-substances the specific gravity of the
common soil constituents, taken individually, do not vary
widely; kaolinite being the lightest (2.60), feldspar next
(2.62); then quartz (2.65), calcite (2.72). Mica and horn¬
blende range (according to their iron contents) from 2.72
to over 3.0. The average specific gravity of soils of ordinary
humus content only will thus range between 2.55 and 2.75;
sandy soils approaching very closely to that of quartz alone.
Volume -Weight. — The specific gravity of the soil is, how¬
ever, of little practical consequence compared with the “ volume-
weight ” i. e., the weight of the natural soil as compared with
an equal bulk of water. A cubic foot of water weighs 62 p 2
pounds; a similar volume of soil usually weighs more, but in
the case of peaty lands may actually (when dry) weigh less.
The extreme range is from no pounds for calcareous, and
somewhat less for siliceous sand, to as little as 30 to 50 pounds
in the case of peaty and swamp soils. It may be conveniently
remembered that while average arable loams range from 80 to
^about 95 pounds per cubic foot, “ heavy ” clay soils range from
75 pounds down to 69, observed by the writer in the case of
certain alluvial soils, poor in humus,1 of the Sacramento river,
California. Manured garden soils, and the mold surface soil of
deciduous forests, generally contain so much humus as to
depress their weight considerably, varying according to their
state of tilth from 66 to 70 pounds per cubic foot.
Weight per acre-foot. — As for practical purposes and calcu¬
lations it is often desirable to know approximately the weight in
pounds of an acre (43,560 square feet) one foot deep, it is
convenient to remember that in the case of sandy land, this
weight (per “ acre-foot ”) may be assumed at four millions
of pounds; for loams, at 3 ^ millions; for clay lands, 3*4
1 This remarkable soil seems to have been derived from the finest “slickens ” of
the hydraulic gold mines.
107
io8
SOILS.
millions; for humus or garden land and woods earth, about 3
millions of pounds; for reedy swamp and peaty lands, 2 to 2^4
millions.
The loose tilth and humus-content of the surface soil will in general
cause it to weigh less, bulk for bulk, than the underlying subsoil, even
when the latter is more clayey; moreover, the continuous pressure
from above will tend to consolidate the subsoil and substrata. Waring-
ton (Phys. Properties of Soils, pp. 46, 47) gives interesting data on
this point from the Rothamstead fields, as follows :
Old pasture, first nine inches . 71.3 pounds per cub. ft.
Same, fourth do.
do. .
. 102.3 “
U it
U
Arable land, first do.
do. . .
. . . 89.4 “
t( u
it
Same, fourth do.
do. .
. . . 101.4 “
u a
U
Fig. 10. — Various possible
arrangements of soil particles.
The influence of humus and unhumified organic
matter, as well as of tillage, in diminishing the
volume-weight of soils is here strikingly shown.
Air-space in Natural Soils. — The differ¬
ence between the specific gravity as usually
determined, and the volume-weight of soils,
is of course caused by the large amount of
air contained in them when dry, but which
in wetting them is partially or wholly re¬
placed by water.
Theoretically, assuming all soil grains
to be globular, and packed as closely as
possible (in oblique order), the space not
filled by them would be the same for all
sizes, whether that of marbles, or so min¬
ute as to be hardly felt between the fingers ;
and would be 25.95 per cent of the soil
volume.1 If the same globular particles
were packed as loosely as possible, i. e ., in
square instead of oblique order (see figures
10 and 11), the vacant space would be
47.64 per cent. If however we imagine
each sphere to be itself composed of a num¬
ber of smaller ones, the empty space will
obviously be greatly increased, to an ex-
1 King, Physics of Agriculture, p. 116, ff.
THE DENSITY AND VOLUME-WEIGHT OF SOILS. 109
tent proportionate to the diminution of solid mass thus brought
about. The pore-space might in that case, with the oblique
arrangement of the globules as shown in Fig. 10, be as high as
74.05 per cent. But since the soil particles may be of all
shapes and sizes within the same soil, and usually fit much
more closely than would globular grains, the empty space rarely
approaches (only in certain alluvial soils and in loose mulches)
to the figure last named. In sandy soils it may fall as low as
20%, and in coarse gravelly soils even as low as 10%. Most
cultivated soils range between 35 and 50% of empty space.
Effects of Tillage. — That these figures can be only approxi¬
mations is obvious from the consideration that one and the
same soil will vary materially in its volume-weight according
to its temporary condition of greater or less compactness.
After land has been beaten by winter rains, its volume-weight
will be found to have materially increased from the well-tilled
condition brought about by thorough cultivation. This differ¬
ence is strikingly seen when, in plowing, the height of the
ground on the land side is compared with that of the turned
furrow-slice in well conditioned loamy land. This loose con¬
dition is called tilth , and it results from the formation of
relatively large, complex crumbs 1 or floccules, between which
there are large air spaces that were wholly absent in the un¬
tilled land ; the floccules themselves being also more loosely
aggregated than was the case before tillage.
Crumb or Flocculated structure. — Figure 1 1 illustrates the
difference between the unplowed land, consolidated especially
on the surface by winter rains, and in its upper portion con¬
sisting largely of single grains; while the plowed land, toward
which the furrow-slices have been turned, is greatly increased
in height and volume and consists almost wholly of variously-
shaped and-sized aggregates or floccules, loosely piled upon
one another and separated by large interspaces. The increase
1 The word crumbs, which is generally understood as meaning a relatively large,
loose aggregate, seems preferable to the word kernels, suggested for the same by
King (Physics of the Soil, p. no). Kernels are understood to be bodies rather
more solid than the surrounding mass, and do not convey the idea of loose aggre¬
gates. The word “ Kriimelstructur ” (crumb-structure), adopted by Wollny for
this phenomenon, has both fitness and priority in its favor.
iio
SOILS.
in volume from consolidated clay to crumb-structure is given by
Fig. ii. — Land before and after plowing. The compactness of the soil is indicated by the density
of dotting. Before plowing there is a compact surface crust (s), below which the soil becomes less
and less compact as we go deeper. After plowing we find the soil (fs, furrow-slice) converted into a
loose mass of crumbs (floccules), with increase of bulk. Compacted plow-sole at pi
-Wollny (Forsch., vol. 20, p. 13, 1897) at 41.9%, to powder as
33%. On moistening dry clay
increased 36.9%, quartz powder
8.01%. When land is plowed
in the proper moisture-condition
the crumbs of floccules are held
together by the surface tension of
the capillary films (menisci) of
water at the points of contact. In
the case of sands, the crumbs will
collapse into single grains when-
F,G ,,"-A soi'-crumb, magnified ,0 , water_films evap0rate, UI1-
show the particles of which it is com- i
posed. The paniciesare held together by less some cementing substance was
... ,, *, rpi ... dissolved or suspended in the
a brush when wetted. I he white spaces. r
between the particles represent air. Water. (See figure 12). Lime
carbonate is one of the substances most commonly found per¬
manently cementing the floccules ; hence the ready tillage of
most calcareous soils, and especially the loose texture of the
“ loess ” of the western United States, and of Europe and
Asia. In these deposits we find sandy and silt aggregates or
concretions ranging from ten or more inches in length (loess
puppets) to microscopic size, held together by lime carbonate,
but collapsing into silt and sand when the material is treated
with acid so as to dissolve the cement. The rough surfaces
of these aggregates, gripping into each other, explain the
stability of the steep loess cliffs in the United States, as well
as in northeastern China, as observed by Von Richthofen and
Pumpelly.
Clay is most frequently the substance which imparts at least
temporary stability to the crumbs and crumb-structure; this is
THE DENSITY AND VOLUME-WEIGHT OF SOILS. m
one of its most important functions in soils, as it serves to
maintain tilth once imparted by cultivation, even after the land
dries out. Beating rains, and cultivation while too wet, will
in this case of course destroy the crumbs and the loose tilth.
Other substances which greatly aid the maintenance of tilth
are the several humates (of lime, magnesia, iron), which when
fresh are colloidal (jelly-like) like clay itself, but unlike the
latter, when once dried do not resume their plastic form by
wetting (Schloesing). The crumbs thus formed are there¬
fore quite permanent and contribute to the looseness of soils
rich in humus. One part of lime humate is said by Schloesing
to be equal in cementing power to eleven parts of clay.
Silica, silicates and ferric hydrate are sometimes found
cementing soil crumbs, wholly or in part.
The importance of the ready penetration of air, water and
roots thus rendered possible is obvious; and the question arises
how it happens that wild plants are able to do without tillage.
How Nature Tills. — When we examine the undisturbed soil
of woods or prairie in the humid region, we will as a rule find
the natural surface soil in a very good condition of tilth ; the
obvious cause being the presence in it of an abundant network
of surface roots and rootlets of grasses and herbs, which in
connection with the fallen foliage prevent the beating and com¬
pacting of the soil surface; which can be seen to happen before
the observer’s eyes whenever a heavy rain falls on a bare land
surface, however well tilled.
Crusting of Soils. — In some soils, especially of the Gulf
States, the beating of rain followed by warm sunshine so
effectually compacts the surface that in the case of taprooted
plants like cotton, it becomes necessary to cultivate after each
rain, so as to break the crust that would otherwise not only
prevent the proper circulation of air, but would also serve to
waste the moisture of the land. The same land in the wild
condition suffered no such change, being protected by the
native vegetation, and by fallen leaves. (See chapt. 8).
Soils of the arid region. — In the regions of deficient rain¬
fall the conditions are modified in several respects. Grass
sward rarely exists, nearly all grasses assuming the habit grow¬
ing in tufts or bunches some distance (a foot or two) apart;
I 12
SOILS.
hence the name of “ bunch grass ” commonly used, which how^
ever means not any one definite kind of grass, but serves to
distinguish the grasses of the uplands from those of the moist
lowlands, where true sward may be found. Between these
bunches of grass the soil is fully exposed, and being free from
roots and leaf-covering is compacted, unless its nature is such
that the usually gentle rains do not produce a serious crusting
of the surface.
That such is actually the predominant nature of the soils
formed under arid influences has already been stated; and
thus the hard-baked soil-surface so often seen in the Eastern
United States in unplowed bare land, or during the prevalence
of a drought, is rarely seen in the arid region. The clay lands
that do exist are usually sufficiently calcareous to possess the
property of “ slaking ” into crumbs whenever wetted after dry¬
ing. But where this is not the case, the stony hardness brought
about by the long dry and warm season is long in being re¬
moved by the winter rains.
Charges of soil-volume on wetting and drying. — The be¬
havior of colloidal clay in the above respects has already been
described above (see chapt. 4, page 59). It is obvious that
whenever soils contain a large proportion of such clay, their
behavior on wetting and drying will approximate to those of
the pure clay. This is exemplified in the heavy clay, or so-
called “ prairie soils ” of the United States, which when
thoroughly wetted in spring will, during a dry summer, form
wide, gaping cracks. These in the long summers of the arid
region may extend to the depth of several feet, with a width of
as much as three and more inches at the surface of the ground.
This, of course, contributes greatly to the drying-out of the
soil to the same depth, and results as well in the mechanical
tearing of the root-system of growing plants; sometimes
causing the total destruction of vegetation. In some clay soils
it happens that after a rain or irrigation, the shrinkage occur¬
ring upon the advent of warm sunshine will cause the surface
crust to so contract around the stem, e. g., of grain, as to con¬
strict and injure the hark, causing serious injury to the crop.
In soils of this character very thorough tillage in preparing
for a crop, and the maintenance of a loose surface during its
growth, are of course extremely essential.
THE DENSITY AND VOLUME-WEIGHT OF SOILS.
1 13
In the arid region it will frequently happen that such soils
when not tilled to a sufficient depth, will during the later part
of the summer so shrink and crack beneath the shallow-tilled
surface layer that the latter will bodily fall into the cracks, ex¬
posing the roots to all the deleterious influences of mechanical
lesion and drying-out. It is thus obvious that the cultivation
of such soils should not be undertaken at all by those not nat¬
urally able and willing to bestow upon them, to the fullest ex¬
tent, the deep and thorough tillage which is absolutely essential
in the utilization of their usually high productive power.
Extent of Shrinkage. — The extent of this shrinkage in drying, and
.subsequent expansion in wetting, have been measured by the writer by
the use of the sieve cylinder described below (chapt. 11, p. 209), as
serving for the determination of the water capacity of soils. When a
soil of the kind above referred to is placed in the sieve cylinder in the
tilled (flocculated) condition, then allowed to absorb its maximum of
water and then dried at 100 degrees C., the contraction in drying can
be very strikingly seen, and its amount measured by filling up the
empty space with mercury ; then measuring the latter after expelling
the surplus by means of a ground glass plate laid on top. The con¬
traction of several heavy clay soils, thus measured, has been found by
the writer to range from 28 to as much as 40 per cent, of the original
bulk.1 The soil thus contracted, when again wetted, does not return
altogether to its original bulk, but remains in a more or less compacted
condition, like that of a soil which has been rained upon.
The expansion and contraction of a heavy clay soil on wet¬
ting and drying are well illustrated in the figure below, in which
the soils are shown in the shallow cylinder which serves for the
determination of water-holding power (see chapt. 11, p. 209).
The middle figure shows in profile the expansion of a dry,
pulverized “ black adobe,” struck level, when allowed to absorb
its maximum of water; it rises above the rim of the sieve-box
to nearly the half height of the latter. The outside figure to
the right shows the same soil after drying; that to the left, a
red clay soil similarly treated. It is easily seen that these
variations in volume may bring about very marked results in
1 Wollny (Forsch. Vol. 20, p. 13 ff, 1897) records similarly high shrinkages in
his experiments.
8
SOILS.
1 14
the fields; the surface of which, apart from the cracks usually
formed, may be several inches lower in the dry season than
during wet weather.
Red Clay Soil. Black “ Adobe ” Clay Soil.
Fig. 13 — Expansion on Wetting and Contraction on Drying ot heavy clay soils.
Contraction on Wetting. — In the case of alkali soils contain¬
ing much carbonate of soda, a very notable contraction occurs
in wetting the loose, dry soil. The cause is here obviously the
collapse of the crumbs, formed in dry tillage or crushing, into
single grains, closely packed. The same result is observed in
the naturally depressed ‘‘alkali spots” (see chapt. 22).
“ Hog-wall ozvs." — In the field the wetting of cracked clay
soils produces some very curious effects. The effect of the
first light rains usually is to crumble off the edges or angles
near, the surface, the materials thus loosened falling into the
lower portion of the cracks. This is repeated at each success¬
ive shower followed bv sunshine, the crevices thus becoming
partly filled with surface soil. When, subsequently, the heavier
and more continuous rains wet the land fully, also causing the
consolidated mass in the crevices to expand, the latter cannot
close on account of the surplus material having fallen into
them; the result being that the intermediate portions of the soil
are compelled to bulge upward, sometimes for six or more
inches, creating a very uneven, humpy surface, well-known in
the southwestern United States as “ hog-wallows,” 1
1 A totally different kind of “hog-wallows,** occurring in California and the arid
region generally, have been described in a previous chapter under the head of
Aeolian soils (See chapt. I, p. 9).
THE DENSITY AND VOLUME-WEIGHT OF SOILS.
115
Such a surface is always therefore an indication of an ex¬
tremely heavy soil , difficult to cultivate; yet embracing” some
of the most highly and permanently productive lands known in
the United States, and in India, where the “ regur ” lands of
the Deccan are of this character; they have been cultivated
without fertilization for thousands of years. The subjoined
physical analyses of lands pi such extreme character as to be
almost uncultivatable will serve to exemplify their physical
composition.
PHYSICAL ANALYSES OF HEAVIEST CLAY SOILS.
Weight of gravel over 1.2 mm. diameter
“ “ between 1.2 and 1 mm.
“ “ between 1 and 0.6 mm.
Fine earth .
Hydr. Value.
FINE EARTH.
Diameter.
Clay
Silt
Sand
. <.0023 mm
<0.25 mm
0.25 mm.
0.5 mm . .
1.0 mm . .
2.0 mm . .
4.0 mm. . .
8.0 mm. . .
16.0 mm. . .
32.0 mm. .
64.0 mm.. .
.010
.016
.02 1:
.036
.047
.072
.120
.160
•30
•5°
No 242 Miss.
No. 643 Cal.
Hog-wallows
Black Adobe.
soil.
Contra Costa
Jasper Co.
Co.
Mississippi.
California.
•83
1. 19
97.98
100.00
100.00
100.00
48.00
45-96
00
37-64
5-50
2.74
3-74
3-31
2-54
2-95
.20
2-39
.27
1.68
.90
•79
1.67
2.36
2.00
100.00
100.00
It will be noted that in both these extremely heavy soils the sum of
the clay and finest sediments is a little over 83%.
It should be stated that both these soils after being thoroughly
wetted become so adhesive that it is almost impossible to travel
over the tracts occupied by them, and that they are practically
almost untillable, being too adhesive when wet; yet if allowed
to dry to a certain extent (varying within very narrow
limits) they turn up by the plow in large clods, which after a
SOILS.
1 16
few hours of sunshine become of stony hardness and will resist
all efforts at pulverization or the production of tilth.1
Calcareous Clay Soils crumble on drying. — The heavy clay
soils of some of the calcareous prairies of the Southwest, in¬
stead of contracting into a stony mass on drying, on the con¬
trary resolve into a mass of crumbs, thus producing excellent
tilth. This occurs even though, the land may have been
plowed when wet, and of course is a great advantage. The
most striking exemplification of this peculiarity occurs in the
heavy but profusely fertile “ buckshot ” clay lands of the
Yazoo bottom, in Mississippi, where it is usual to plant corn
and sweet potatoes in the semi-fluid mud left after an over¬
flow, after turning a shallow furrow, then covering by turn¬
ing another. To the onlooker it seems impossible that such
plantings could be successful ; but within a short time the
muddy surface becomes a bed of crumbs (“buckshot”),
forming a seedbed not readily excelled by any made by arti¬
ficial means. Hence, largely, the almost invariable success of
crops in the Yazoo region.
Port Hudson Bluff. — The same clay produces a most un¬
pleasant result at the foot of the Port Hudson bluff, where it
crops out some feet above low water. When after a freshet the
water level falls below this stratum, on drying the clay dis¬
integrates into crumbs just as does the Yazoo buckshot soil;
with the result that at the next rise, the loose mass subsides into
the river as a flood of mud. Thus the foot of the bluff is
being constantly undermined, and the falling of the bluff scarp
has obliged the town above to recede many hundreds of feet
from its original historic site.
The exact proportions of lime carbonate necessary to produce
this phenomenon, and its necessary relations to clay substance
and other physical soil ingredients, yet remain to be investi¬
gated.2
1 In driving a light carriage over the land represented by No. 643 above, after a
light rain, the wheels gathered up so much soil within a hundred yards as to
render it necessary to stop and chop it off the tires by means of a hatchet. This
is a common experience in the black prairie lands of Texas.
2 Schiibler (Grandsatze d.Agrikulturchemie, 183S) ascribes the crumbling of
calcareous clay soils to the difference in the contraction of calcareous sand and
the clay substance. But it is doubtless more directly connected with the floc¬
culation of the latter by lime.
THE DENSITY AND VOLUME-WEIGHT OF SOILS.
1 17
Loamy and Sandy Soils. — It is largely the absence of these
extreme changes of volume that renders the cultivation of
loamy or even sandy lands so much more easy, and the success
of crops so much more safe, than is the case in clay soils.
Whenever the content of colloidal clay diminishes below 15%,
the shrinkage in drying from the wet condition becomes so
slight as to cause no inconvenience ; while in sandy soils prop¬
erly speaking, no perceptible change in volume occurs.
Peaty soils, however, and all those containing a relatively
large amount of humus, are also liable to visible shrinkage
when passing from the wet to the dry condition. But on ac¬
count of their looseness and porosity such shrinkage does not
usually result in the formation of cracks or rupture of the
roots, as is the case in heavy clay lands. The entire mass of
the soil then shrinks downwards, but rarely forms cracks on the
surface. Hence the introduction of humus into “ heavy ” soils
is among the best means of improving their tilling qualities.
Formation of Surface Crusts. — Some soils, especially those
of a clay-loam character, are very liable to the formation of
hard surface crusts from the beating of rains, and from sur¬
face irrigation ; owing, doubtless, to the ready deflocculation
of their clay substance. It is not easy to define the precise
physical composition conducive to this crust formation ; but
the subjoined physical analyses show examples of soils in
which this tendency is very prominent and is frequently an¬
noying, in that when they occur in the regions of frequent
summer rains, it becomes necessary after each one to till the
surface in hoed crops ( e . g., in cotton-fields) in order to pre¬
vent the injurious effects of such consolidation of the surface.
It may, of course, be prevented by mulching, or on the large
scale by green-manuring, to such extent as to prevent con¬
traction.
The subjoined physical analyses of two soils from the Brown-Loam
region of Northern Mississippi (see chap. 24), shows the composi¬
tion of lands excellent in every respect other than the tendency to
crust after each rain :
1 18
SOILS.
PHYSICAL ANALYSES OF CRUST-FORMING SOILS.
Diameter.
Hydr. Value.
No. 219.
No. 197.
fnarup materials .
1 — mm.
)
•5— 1 “
\ -2 3
•5°
64 mm.
1.47
Sand . -
•3°
32 “
2-33
79
.16
16 “
1. 17
.12
8 “
.78
.18
.072
4 “
.76
.78
.047
2 “
979
3-56
Silt . -1
.036
1 “
7.20
13. 12
.025
•50
13.H
16.64
.016
•25
1 5-°7
27.28
.010
<25
26.36
18.87
Clay .
?
<.0023
19.10
17-23
These soils agree in having a sufficient amount of clay (17 to 19 %)
to characterize them as clayey loams, associated with a very large pro¬
portion of the grain-sizes of less than .025 mm., or .5 mm. hydraulic
value. A higher proportion of clay, even though associated with a
similarly high or even larger proportion of these fine sediments, seems
to prevent crusting, probably because the swelling of the clayey ingre¬
dient on wetting and its extravagant contraction in drying breaks up
the continuity of the surface. The heaviest clay soils, such as those
shown on a preceding page, neither crust nor crumble on drying after
wetting, but contract into lumps of stony hardness, as a whole.
The burning-out of the humus from well-tilled surface soils
during the extended heat and dryness of rainless summers,
brings about such a contraction or packing of the surface soil
of orchards in California as to greatly reduce their productive¬
ness, and to render necessary diligent green-manuring as the
only practical remedy. In many cases, liming of the surface
also serves well to prevent this injurious effect, which to some
extent of course follows surface irrigation as well as rains.
In most soils, repeated alternate wetting and drying in place
produces a loose, flocculated texture, so long as no defloccula¬
tion is brought about by mechanical causes, such as beating
rains or running water.
Effects of Frost on the Soil. — The expansion suffered by
water in freezing necessarily tends to separate the soil par¬
ticles previously held together by the surface tension of the
THE DENSITY AND VOLUME-WEIGHT OF SOILS,
119
capillary water, or otherwise flocculated or cemented. Freez¬
ing of the soil is therefore of material assistance in disintegrat¬
ing cloddy, ill-conditioned soils, leaving them in loose, crumbly
condition after the ice has melted and the surplus water drained
off; so as to materially facilitate tillage and root penetration.
When, however, soils thus circumstanced are tilled or trodden
while too wet, they quickly become puddled, being practically
reduced to single-grain structure. (See this chapt. p. no).
Hence the injury caused by allowing cattle to range in winter
on cultivated land subject to freezing and thawing, which it
sometimes takes years to correct.
A disagreeable effect often produced by the freezing and
thawing of wet lands is the “ heaving-cut ” of grain, result¬
ing from the upward expansion of the surface soil in freezing,
that may readily rupture the roots; while on thawing, the soil
surrounding the upheaved stool is apt to settle down, especially
in case of a rain, leaving the stool and roots exposed either to
drying or freezing, as the case may be. Hence the desire of
grain farmers in northern climates, for a sufficient covering of
snow to protect the fall-sown grain, rather than an “ open
winter,” during which the grain is exposed to alternate freezes
and thaws, or extreme cold.
In certain soils, notably in those liable to crusting (p. 117),
instead of heaving the soil, the water in freezing emerges bodily
from small cracks, in foliated or wire-like forms (“ice-
flowers”) resembling those of native silver, and formed sub¬
stantially in the same way, by a kind of “ wire-drawing ” pro¬
cess, aided by crystallization.
Small ice-crystals formed on the surface of small crevices filled with
water cause others to be formed at their lower ends, and the expansion
occurring in freezing, forces the ice upward ; the process repeating
itself under favorable conditions, until the stalks or sheets of ribbed ice
grow to a height of several inches. This phenomenon is especially
frequent in the middle cotton States — Arkansas, Tennessee, northern
Mississippi, etc., where frequent changes from rainstorms or thaws to
cold northwest winds occur in winter.
CHAPTER VIII.
SOIL AND SUBSOIL.
CAUSES AND PROCESS OF DIFFERENTIATION. HUMUS.
Soil and Subsoil Ill-defined. — While the general mass of rock
debris formed by the action of the agencies heretofore dis¬
cussed as soil-material, may under proper conditions be¬
come soil capable of supporting useful plant growth, universal
experience has long ago recognized and established the dis¬
tinction between soil and subsoil : by which are ordinarily
meant, respectively, the portion of the soil-material usually
subjected to tillage, and what lies beneath. There can be no
question about the practical importance of this distinction; but
the definition of the two terms, as commonly given in some
works of agriculture, is both incomplete and, in its application
to many cases, partly misleading.
The differentiation of soil and subsoil is due partly to the
action of organic matter and micro-organisms, partly to
physico-chemical causes, now to be discussed in detail.
THE ORGANIC AND ORGANIZED CONSTITUENTS OF SOILS.
Humus in the Surface soil. — The most obvious mark of dis¬
tinction between soil and subsoil is, usually, the darker tint
of the former, due to the presence of humus or vegetable mold,
which becomes most apparent by darkening of the tint when
the soil is moistened. Thus soils having a gray tint when dry,
may become almost black when wetted.. When no such deepen¬
ing of color occurs in wetting, the absence or great deficiency
of humus may safely be inferred. The only other substance
whose presence may invalidate the conclusions based upon the
darkening of the soil tint, is ferric hydrate (iron rust), which
itself possesses the property of darkening on wetting, and may
effectually cover either the presence or the absence of humus.
Since the formation of the humus depends upon the decom-
120
SOIL AND SUBSOIL.
1 2 1
position of organic matter (mostly of the cellulose group)
derived partly from the roots, partly from the leaves and
stems of plants growing and dying on the soil, its accumulation
near the surface is natural. But since the depth to which roots
penetrate varies greatly not only with different plants, but very
essentially in conformity with the greater or less penetrability
of the soil and susoil, the depth to which the dark humus tint
may reach vertically varies correspondingly, from two or three
inches to several feet. In the case of soils that have been
formed by the gradual filling-up of swamps or marshes, the
humus-tint may reach to several yards depth.
Surface Soil, and Subsoil. — It is thus apparent that the term
“ surface soil,” while commonly confined by the farmer to the
portion turned by the plow or usually reached in cultivation by
any implements, may or may not belong, functionally, to layers
of greatly varying thickness. Similarly the term subsoil may
or may not refer, in individual cases, to parts of the soil mass
materially different from the surface soil. Yet this distinction
is of no mean practical importance, because the efficacy of one
of the most common measures of soil improvement, viz., sub¬
soil plowing or “ subsoiling depends materially upon the
differences between soil and subsoil in each particular case.
Most of the diversity of opinion regarding the merits of this
operation is simply the result of a corresponding diversity in
the natural facts and cultural practice of each case.
Causes of the Differentiation of Soil and Subsoil. — One of
the prominent points of difference between surface soils and
subsoils has already been mentioned in the usual predominance
of root-mass in the upper layers; to which is added a part at
least of the substance of fallen leaves and stems of its vegeta¬
tion. How much of this vegetable mass ultimately becomes
converted into humus, as well as the nature of the product
formed, depends upon a great variety of circumstances ; some
of which have already been mentioned in connection with the
general discussion of humification (chapt. 2, p. 20). Briefly
stated, the main controlling conditions are : the amount of
water or moisture present, the access of air (oxygen), a proper
temperature, and the presence of the several organisms which
in the course of time take part in the process of soil-formation.
122
SOILS.
Ulmin Substances; Sour Humus (Germ. Rohhumus). — In
the presence of so much moisture or liquid water as will mater¬
ially impede the access of air, and with the concurrence of
reasonably low temperatures, the organisms that at first take
the chief role in the transformation of the vegetable tissues into
humus-like substances are bacteria. But the antiseptic nature
of the compounds thus formed 1 soon puts an end to their ac¬
tivity, and thereafter the process seems to be a purely chemical
one, and very slow. In peat bogs, the transition from the fresh,
dead stems and roots to brown peat is easily followed down¬
ward, white cellulose fibers remaining apparently unchanged
to some depth ; so that such fiber has been used for tissues and
paper. The solid decomposition-products are brown substances,
partly soluble in water and imparting to it a brown or coffee
color (frequently seen in the drains of marshes) and an acid
reaction; the latter due to ulmic (as well as apocrenic) acid,
readily soluble in caustic and carbonated alkalies, and forming
insoluble salts with the earths and metals; while another por¬
tion, ulmin, is insoluble in the same, but gradually becomes
soluble by oxidation.
The gaseous products formed under these conditions are
carbonic dioxid and “marsh gas” (methan, CH4), the
former predominating in the early stages ; while later, the car-
buretted hydrogen predominates, rendering the gas readily in¬
flammable.
Sour Soils. — The “ sour ” soils thus produced in nature in
presence of excess of water bear only “ sour ” growth, such
as sedges and rushes, of little agricultural value; they usually
require reclamation processes before becoming adapted to ordi¬
nary crops. In old forests of northern climates a peaty and
more or less acid layer is sometimes formed on the surface,
above the black woods-earth, and retards somewhat the full
production of such land when taken into cultivation.2
Marshes and swamps, both fresh and salt, as above stated
usually show coffee-colored waters, which are also characteristic
of the streams that drain them, until by intermixture with
1 The antiseptic properties of sour humus are well exemplified in the perfect
state of preservation in which the remains of animals, wood implements, etc., are
found in bogs into which they have sunk in prehistoric times.
2 See Muller, Natiirliche If umusformen.
SOIL AND SUBSOIL.
123
waters containing lime salts, the ulmic substances are neutral¬
ized and precipitated. Such neutralization, preferably by
means of lime, is the first step towards the reclamation of lands
bearing “ sour ” vegetation. The acid reaction characterizing
the ulmic substances is also characteristic of many woodlands,
notably in the United States of the soils of the “ Long-leaf-
pine ” region of the Cotton States, both upland and lowland,
as well as of many deciduous forests in northern climates.
Hence liming, whether artificial or natural, effects a most not¬
able improvement, together with a marked change of vegeta¬
tion, in these lands.
It has been long known that after long-continued cultivation, soils
originally of neutral or slightly basic reaction become acid : and the
liming of such lands is an ancient practice in Europe. The matter,
however, received but scant attention until Wheeler and Hartwell, of
the Rhode Island Experiment Station, demonstrated the almost univer¬
sal acid condition of the older lands of that State, and the excellent
effects produced by neutralization with lime, or even with the alkali
carbonates.1 The current neutralization of the humus-acids is unques¬
tionably one of the cardinal advantages of calcareous lands ; for such as
contain only small amounts of lime carbonate will of course become acid
more quickly under cultivation.
Hnmin Substances. — In the presence of only a moderate
amount of moisture, therefore under the influence of a more or
less rapid circulation of air, and in the presence of earthy
carbonates (especially that of lime) to prevent the formation
of acids, or to neutralize them as formed, the normal process
of humification occurs; mainly under the influence of fungous
instead of bacterial growths. The various molds take a
prominent part in the conversion of the vegetable substance
into black, neutral, insoluble humus compounds. Such fungous
vegetation is always accompanied by the evolution of carbonic
gas, and the resulting fungous tissues are markedly richer in
nitrogen and carbon than the substance of the higher plants
from which they were derived (see chapt. 9). Com¬
parative analyses show that in the normal process of humifica¬
tion of vegetable substances, oxygen and hydrogen are elimi-
1 Reports of the Rhode Island Exp’t Station, 1895, an(I ff*
124
SOILS.
nated in the form of water and carbonic dioxid, while at the
same time there is an increase in the percentage of carbon, and
generally also of nitrogen; the latter more particularly in the
case of vegetable matter not very rich in that element. When
once humification is complete, oxidation, especially under arid
conditions, bears mainly upon the carbon and hydrogen, so
that the nitrogen content may rise to very high figures; while
another portion is ultimately wholly oxidized, with the forma¬
tion of nitrates, under the influence of the nitrifying bacteria,
this being the process chiefly efficient in the nutrition of vegeta¬
tion with nitrogen.
As a matter of course, the several organic compounds contained in.
plants may continue to exist in soils for some time, varying according
to conditions of temperature and moisture. Thus dextrin, glucose, and
even lecithin and nuclein have been reported to be found. The activity
of the numerous fungous and bacterial ferments under favoring condi¬
tions will, of course, limit the continued existence of such compounds
somewhat narrowly, so that they can hardly be considered as active soil
ingredients save in so far as they favor the development of the bacterial
flora.
Porosity of Humus. — One of the essential ' features of na¬
tural humus is its great porosity, whereby it not only becomes
highly absorbent of water and gases, but is also gradually oxi¬
dized, probably under the influence of bacteria. For this oxi¬
dation, as measured by the evolution of carbonic gas, pro¬
gresses most rapidly under the same conditions as to moisture,
temperature and access of air, that are known to be most favor¬
able to fungous and bacterial growth. Hence the formation of
carbonic dioxid in the soil is assumed to be the measure of the
intensity of such activity.
Physical and Chemical Nature of the Humus Substances. —
The humus substances are gelatinous when moist, but are
neither markedly adhesive or plastic. Like the other colloidal
substances of the soil, they serve to retain both gases and
vapors, including moisture, liquid water, and its dissolved
solids. In the natural, porous condition they are powerfully
absorbent of gases, including especially aqueous vapor. Dry
humus swells up visibly when wetted, the volume-weight in-
SOIL AND SUBSOIL.
125
creasing to the extent of two to eight times; so that humus
stands foremost in this respect among the soil constituents.
The density of natural humus is about 1.4, being the lightest
of the soil constituents. Hence soils rich in humus are “ light ”
not only in the farmer’s sense of being easily tilled when not
too wet, but also of light weight for equal volumes when com¬
pared with clayey and sandy soils. Some data bearing upon
these points are given in the table 1 below, for the substances
moderately and uniformly packed :
VOLUME-WEIGHTS OF
Humus.2 Clay. Quartz Sand.
.3349 1. 01 08 1.4485
When saturated with water, the same substances gave the
following figures :
Air-dry.
Saturated
with water.
Increase
°l
1 0
Humus 2 .
• -3565
1. 1024
209.2
Clay .
• 1-0395
1.6268
55-9
Quartz sand.
. 1.4508
1.8270
25-9
These data show strikingly the effects produced by the sev¬
eral physical soil constituents upon some of its physical prop¬
erties.
Chemical Nature. — While humus artificially produced by the
action of caustic alkalies upon sugar or cellulose is free from
nitrogen, all naturally occurring humus contains the latter.
It is not, however, present in the form of ammonia, as it cannot be
set free by treatment in the cold with lime or alkalies. When, how¬
ever, natural humus is boiled with these substances, ammonia is slowly
given off, but the process continues indefinitely and it seems to be im¬
possible to expel all the nitrogen in this manner. This behavior being
characteristic of amido-compounds, it is presumable, in view of the
slightly acid nature of the humus substances, that natural humus is
largely of an amidic constitution. Artificial humic acid, formed by the
1 Wollny, Zersetzung der Organischen Stoffe, pp. 242,243.
2 Peat pulverized and extracted with alcohol and ether to remove resinous sub¬
stances.
126
SOILS.
action of caustic alkalies upon sugar, gums or cellulose, combines with
ammonia as with other bases, and at first the ammonia can be readily
expelled from this as from other ammonia salts. But after the lapse of
some time it seems that the amidic condition is assumed, so that
caustic lye acts but very slowly and cannot expel the whole of the nitro¬
gen present. This is very important in connection with the practice
of fertilization, as any ammonia taken up by or generated in the soil is
thus in the course of time rendered comparatively inert, and unavailable
to vegetation until nitrified.
Progressive Changes. — The natural neutral humin and
ulmin, as found, e. g., in the lower portions of peat beds, are
in the course of time by oxidation converted into ulmic and
humic acids, capable of combining with bases ; by still farther
oxidation they form apocrenic and crenic acids, readily soluble
in water and in part forming soluble salts with lime, magnesia
and other bases. These acids act strongly upon the more
readily decomposable silicates of the soil, and in the course of
time may dissolve out, and aid in the removal by leaching, of
most of the plant-food ingredients as well as the ferric hydrate
of a soil. Thus red or rust-colored soils may be rendered al¬
most white by continued “ swamping ” with stagnant water,
and be greatly impoverished ; and it is doubtless largely through
this agency that the underclays of coal beds and the lower por¬
tions of peat beds, as well as peat and coal ashes, are almost
wholly destitute of mineral plant food.
The Phases of Humification. — The progressive changes in¬
volved in the process of humification of vegetable matter are
illustrated in the table below,1 together with the farther changes
by which such matter may ultimately be transformed into the
several varieties of coal, and finally into anthracite, which al¬
ready represents nearly pure carbon, but in nature has some¬
times been still farther transformed into graphite (black-lead)
and diamond.
1 Data recalculated, omitting ash.
SOIL AND SUBSOIL.
127
PROGRESS OF HUMIFICATION, AND FORMATION OF COAL.
(moisture and ash omitted from calculations.)
Cellu¬
lose.
Oak Wood.
Humin
and
Humic
Acid.
Peat. 1
Coals.
Fresh.
De¬
cayed.
Brown
Surface.
(Ulmin.)
Black.
Lignite
Brown
Coal.
(Bovey).
Scotch
Splint
Bitu¬
minous.
Penn’a
Anthra¬
cite.
40 in.
80 in.
Light
Brown.
Dark
Brown.
Carbon.. . .
44-44
50.60
S3-6o
56.20
49.4 to 59.7
57.80
62.00
64.10
69.50
84.20
94.80
Hydrogen.
6. 17
6.00
5.20
4-90
2-5“ 4-5
5-40
5.20
5.00
5-90
5.80
2.60
Oxygen . . .
49-38
35-8 “ 47-3
36.00
30.70
26.80
24.00
8.80
>
43-4°
41.20
38.90
V 2.60
Nitrogen. .
.3 “ 18.7
.80
3.10
4.10
.60
1.20
)
The steady increase of carbon and nitrogen, together with
a corresponding decrease of oxygen, are well illustrated in the
analyses, especially in the strictly comparable series of peat
samples from various depths. In this case there is also a steady
decrease of hydrogen, and an increase of ash from 2.72% in
the surface layer, to 9.16 at 80 inches depth. This increase is
due in the main, of course, to the progressive volatilization of
the organic matter in the forms of carbonic dioxid and marsh
gas (methan, CH4).
In considering this table it should not be forgotten that
while normal humus stands very close to peat, and the latter
when compressed in certain stages would be undistinguishable
from lignite or brown coal; yet both peat and lignite are
known to be formed under conditions permitting much less
access of air or oxygen than occurs in the formation of normal
black soil-humus. Hence even black peat cannot at once stand
in place of soil-humus when removed from its watery bed, but
requires considerable time and aeration (oxidation), and in
most cases neutralization with lime or marl, before it can serve
the purposes of humus in the soil.
Lignite and the progressively more carbonaceous coals are and have
been formed under the conjoined action of submergence and pressure,
sometimes also aided by heat ; and thus they cannot perform the func¬
tion of soil-humus, any more than the fire-clays or shales underlying
1 Detmer, Landw. Versuchst., Vol. 14, 1871.
128
SOILS.
them can resume their original soil-functions without prolonged weather¬
ing.
Amounts of Humus and Coal Formed from Vegetable Matter. — Only
very general and indefinite estimates can be given of the amount of
humus or coal formed from a given quantity of vegetable matter, since
these must vary according to the conditions under which the transforma¬
tion occurs. The greater or less access of air and of moisture, the
temperature and pressure under which the process occurs, will modify
very materially the quantitative as well as the qualitative result. In
the hot arid regions the fallen leaves may wholly disappear by oxida¬
tion on the surface of the ground, while under humid conditions they
are mostly incorporated with the surface soil. If we assume that in
the humification of plant debris (estimating their average nitrogen con-
Fig. 14. — Section of lignitized log showing contraction into solid lignite on drying.
tent at 1%), no nitrogen is lost, it would seem that in the humid
region one part of normal soil-humus might be formed from 5 to 6
parts of (dry) plant debris ; while in the extreme regime of the arid
regions, from 18 to 20 parts of the same would be required. But as
most probably some nitrogen also is lost in the process of humification,
a considerably larger proportion of original substance may be actually
required.
As to coal, it is usually assumed that it requires about 8 parts of
vegetable matter for one of bituminous coal. Much higher estimates
are made by some, and an observation made by the writer at the Port
Hudson bluff, Mississippi, in 1869, would seem to justify such estimates.
The above figure, from a sketch made at the time, shows the pro¬
portions to which a pine log about eight inches in diameter had shrunk
SOIL AND SUBSOIL.
129
in drying into a small sheet of lignitized wood ; the original trunk,
projecting from a bed of sand some forty feet below the surface, being
so porous and spongy that when wet it flattened somewhat by its own
weight ; it was connected with the little sheet of lignite by a spirally
twisted, tapering stipe.
Here evidently the proportion of lignite formed was a very minute
one, doubtless because of the long leaching to which the trunk had
been subjected. It thus seems impossible, as in the case of humus,
to assign any definite proportion as between woody matter and coal
formed from it.
Normal humification takes place only under the influence of
moderate temperature. When the temperature is too low, bac¬
terial and fungous growth are repressed or arrested ; when too
high, the fungous vegetation assumes a different phase, the
result of which is the almost total oxidation of the organic
matter, sometimes so accelerated as to initiate rapid com¬
bustion (“ fire-fanging ” of dung) ; leaving in any case but a
trifling organic residue of very high ash contents. 1
Eremacausis. — In the absence of a sufficient degree of mois¬
ture to co-operate with the other agencies of humification, the
final result in the soil is practically the same as in the “ fire-
fanging ” of dung. The organic matter is almost wholly de¬
stroyed by direct oxidation (eremacausis) with or without
the aid of minute organisms; leaving essentially only the ash
behind to be reincorporated with the soil. This is to a very
great extent the predominant process in the arid regions of the
Globe ; most of the soils formed in these climates being, there¬
fore, very poor in humus-substances, and deriving it almost
entirely from the decay of roots only.
The extent to which the humus of a soil may be derived from
the vegetable debris falling or growing upon the surface, varies
greatly with the climatic conditions as well with the nature of
the soil. In the forests of humid climates with loamy soils, not
only does the autumnal leaf-fall, as well as decaying twigs and
trunks, become obviously incorporated with the surface soil as
1 A striking illustration of this is afforded by Naegeli’s experiment of enclosing
several loaves of bread in a loosely closed tin-box. After eighteen months there
remained only seventeen per cent of air-dry mouldy matter, totally destitute of
starch.
9
*30
SOILS.
decay progresses on the lower surface, but active animal
agencies (see below) carry the organic remnants bodily down.
But where heavy clay soils prevail, these animal agencies are
much restricted by the compactness of the material ; only a
light surface-layer of mold would be formed, and the humus
of the lower soil layers must of necessity be derived from the
decay of the roots only. This origin is claimed by Kosticheff 1
for the high content of black humus in the tchernozem or
black earth of Russia. Following Hellriegel in determining
the weight of roots contained in successive equal layers of soil
from the surface downwards, Kosticheff gives for each six
inches the following data as found in the tchernozem, taking as
ioo the root-content of the surface layer:
Number.
Depth.
1
Roots.
1
Humus.
2
Roots.
2
Humus.
3
Roots.
3
Humus.
6 inches.
100
542
100.
8.11
100.
9.64
12 “
89.1
4-83
63-9
5-J9
80.3
7-77
18 “
66.9
3.62
48.3
3-92
70.0
6.71
24 “
47-3
2.56
35-o
2.84
58.4
5.61
30 “
47-3
2-59
26.0
2.1 1
38.2
3- 57
36 “
34-6
1.88
18.1
1.47
33-o
42 “
23-9
1.29
6-3
•51
16.2
1.56
48 “
14-4
.78
.70
54 “
6.7
•36
It will be seen that there is a very close correspondence of the humus
content with the root development in the several layers, and it seems
as if though but little of the humus could be derived from the surface
growth, which is that of the grasses of the steppe.
The climate of the black-earth country of Russia is, though not
properly arid, yet one of rather deficient and uncertain rainfall. But as a
consequence of extremely arid conditions, and in sandy lands, it may
even happen that the immediate surface soil contains less humus than
what, in the farmers’ habitual parlance, would be called the subsoil ;
because of the penetration of slow combustion for some distance into
the porous soils. It will then be lower down that, in the presence of a
favorable degree of moisture and lower temperature, the conditions of
normal humification are fulfilled.
1 Abstract in Ann. de la Science Agronomique, Tome 2, 1887.
SOIL AND SUBSOIL.
131
It is not always, then, that the commonly recognized distinc¬
tion between surface soil and subsoil based upon humus con¬
tent can be maintained. But the observation of everything
bearing upon this point is of the utmost importance in deter¬
mining both the agricultural value and the mode of treatment
of the land.
Losses of Humus from Cultivation and Fallowing. — The
fact that humus accumulates in woodlands and meadows,
where no cultivation is given, would naturally lead to the con¬
verse conclusion, viz., that cultivation causes loss of humus and
of its constituents. That this is actually the case is recognized
and widely acted upon in practice, and there is no question
that the general acceptance of stable manure as the most widely
useful fertilizer, despite its usually low content of plant-food
ingredients, is based upon the fact that it supplies vegetable
matter, in a condition highly favorable to its conversion into
humus. The most direct and cogent proof of the depletion of
the soil of both humus and nitrogen by continuous cultivation
of cereal grains has been given by Snyder,1 who determined
the loss both of humus and of nitrogen suffered by a Minnesota
soil during eight years’ continuous cultivation of wheat. The
total loss of nitrogen was 1700 pounds per acre, while only
350 pounds were utilized by the crop; about 1400 pounds being
dissipated as gas or leached out as nitrates. A conservative
estimate of the loss of humus suffered during the same period
was about a ton per acre annually, and this loss seriously de¬
creased not only the nitrogen-content, but rendered the soil
more compact and less retentive of moisture. But by rotation
of the wheat with clover in alternate years, very nearly an
equilibrium of both humus and nitrogen-content was obtained.
In addition, the amount of available mineral plant-food was de¬
creased by continuous grain culture. Ladd has made similar
observations in North Dakota, with similar results.
That excessive aeration results in serious losses of humus
as well as of nitrogen, is very obvious in the arid region, where
it is the habit to maintain on the surface of orchards and vine¬
yards during the dry, hot summers, a thick mulch of well-
tilled soil, thus preventing loss of water by evaporation. In
the course of years this surface soil becomes so badly depleted
1 Bull. No. 70 Minn. Exp’t Station, 1905.
132
SOILS.
of humus that good tilth becomes impossible, the soil becom¬
ing light-colored and compacted; while the loss of nitrogen is
indicated by the small size of the orchard fruits. Similar losses
are of course sustained in the practice of bare summer-fallow,
which at one time was almost universal in portions of the arid
region. The complete extirpation of weed growth thus
brought about, at first considered an unmixed benefit, has ulti¬
mately had to be made up for by the practice of green-manur¬
ing; since in the arid region the use of stable manure en¬
counters many difficulties.
Estimation of Humus in Soils. It has been usual to determine the
amount of humus in soils by means of (dry or wet) combustion, cal¬
culating the humus from the carbonic dioxid so formed, while measur¬
ing the nitrogen gas directly. But in this process the entire organic
matter of the soil, humified and unhumified, is indiscriminately in¬
cluded ; and it is wholly uncertain to what extent the latter will ulti¬
mately become humus, from the nitrification of which plants are pre¬
sumed to chiefly derive their nitrogen.1 In order to obtain definite
results, the actual, functional humus must be extracted from the soil
mass by some solvent which discriminates between the humified and
unhumified organic matter. This cannot be done by direct extraction
with caustic soda or potash, which inevitably dissolve unhumified mat¬
ters and tend to expel ammonia from the humus ; besides themselves
acting as humifiers (see this chapter, p. 125.)
Gr andean Method : Maii'ere Noire. — The only method now known
which accomplishes this separation, practically excluding the unhumi¬
fied while fully dissolving the humified matter — is that of Grandeau : the
extraction of the soil, first with dilute acid, in order to set the humic
substances free from their combinations with lime and magnesia ; and
their subsequent extraction with moderately dilute solutions of am¬
monia (or other alkali hydrates). Upon the evaporation of the am¬
monia-solution the humus is left behind in the form of a black lustrous
substance (“ matiere noire ” of Grandeau) much resembling the crust
of soot formed in flues from wood fires. As it contains a variable
amount of ash, it must be burnt and the ash subtracted from the first
weight.
1 The humus determinations thus made, which include nearly all those made by
German chemists, give the humus-content from 40 to 50° D too high. The French
determinations are mostly made by the method of Grandeau.
SOIL AND SUBSOIL.
133
Amounts of Humus in Soils. — While in peat, marsh and
muck lands the humus-content may rise above twenty per
cent, in ordinary cultivated lands it rarely exceeds about five
per cent, and very commonly falls below three per cent, even
in the humid regions. In properly arid soils we find a very
much lower average, rarely exceeding one per cent, and fre¬
quently falling to .30 and even less. This scarcity of humus
manifests itself plainly in the prevalently light gray tint of the
arid soils.
Meadows and woodlands generally show the highest humus-
content in their surface soils, gradually increasing while in that
condition ; while when taken into cultivation the humus-content
gradually decreases, owing to the free aeration and consequent
“ burning-out ” caused by tillage. Hence the humus must be
from time to time replaced by the use of stable manure, or
green-manure crops, to prevent injurious changes in the tilling
qualities of the land. Not only humus as such, but according
to Schloesing also the insoluble colloid humates, produce in
the soil a loosening effect or tilth (Germ. Bodengare), which
apparently cannot be brought about by any other substance.1
Humates and Ulmates. — That the insoluble humates of lime,
magnesia, iron, manganese and alumina are present in most
soils is conclusively shown by the composition of the solution
obtained by the extraction of soils with weak acid, as above
mentioned in connection with the quantitative determination
of humus according to Grandeau ; since these bases are almost
always extracted by the weak acid. When the brown solution
of alkali humate obtained in this process is carefully neutralized
with sulfuric or hydrochloric acid, or is mixed with solutions
of the above bases, flocculent, insoluble precipitates are formed,
while the solution is discolored. Similar precipitates may be
obtained with other metallic solutions, notably with that of
copper, which precipitates the humus-acids most completely.
Doubtless these compounds contribute greatly to the conserva¬
tion of the humus-content of soils, protecting it to a certain
extent from oxidation, and also preventing excessive acidity.
The brown tint of certain subsoils in the northern humid re-
1 The decrease of humus from wheat culture in the soils of Minnesota and North
Dakota has been studied by IT. Snyder and E. F. Ladd, respectively. In the
prairie lands of the latter State the total organic matter in the first six inches of
soil ranges fram 15 to as much as 26 °/0, and the humus alone from 4 to 7.8° ,0.
134
SOILS.
gions have been shown by Tollens and others to be due not to
ferric hydrate, as had been supposed, but to calcic, magnesic
and aluminic humates. None of the mineral bases or acids
present can be detected in the humic solution by the usual
reagents.
Mineral Ingredients in Humus. — That the mineral plant-
food ingredients present in the humus extracted by the Gran-
deau process, and which remain as ash when the matiere noire
is burned, are capable of nourishing plant growth, was directly
shown by Grandeau, Snyder and others. The former was in¬
clined to consider that those substances were mainly thus taken
up by plants, under natural conditions. This theory, however,
has not been sustained by subsequent investigations; the min¬
eral plant-food thus extracted is not a measure of the immediate
productiveness of the soils, as demonstrated by Snyder, and the
residual soils are not sterile. It is also still doubtful to what
extent the mineral bases and acids are naturally combined with
the humus-substances, it being contended by some that they are
brought into organic combination by the acid and ammonia
extraction. The investigations of Snyder and Ladd, above re¬
ferred to, prove however to some extent at least that the humus-
substances are naturally combined with them, and that prob¬
ably they are largely made available to plants through the
direct and indirect action of the humus compounds. This sub¬
ject is farther considered in chapter 19.
The nature and amounts of these mineral substances are
well exemplified in the subjoined full analysis by Snyder, of
the ash of the humus and humates extracted from a compound
sample of prairie soils of Minnesota, which had been thrown
down from the ammonia solution by simply neutralizing the
liquid : 1
ASH OF HUMUS FROM MINNESOTA PRAIRIE SOILS.
Insoluble matter2 .
Potash (KaO) .
Soda (NasO) .
Lime (CaO) .
Magnesia (MgO) . .
Peroxid of Iron (Fe203)
Alumina (ALO3) .
Phosphoric acid (P2OJ.
Sulfuric acid (S03)
Carbonic acid (CO2)
6i.97
7- 50
8- 13
0.09
0.36
3.12
3-48
12.37
.98
1.64
1 Precipitation with an excess of acid does not greatly change the results.
2 In California soils this is mostly silica soluble in carbonate of soda.
SOIL AND SUBSOIL.
135
The large amounts of the soluble alkalies potash and soda
thrown down with the humic matters are very striking, as is
the very large proportion of phosphoric acid. Lime and mag¬
nesia had, of course, been mainly eliminated by the prelimi¬
nary acid treatment.
Functions of the Unhumified Organic Matter. — The unhu¬
mified plant debris in the soil are not to be regarded as useless,
even aside from their potential conversion into active humus.
Not only do these remnants of vegetation lighten the soil,
rendering it more pervious to air and water, but in their pro¬
gressive decay they give off carbonic gas, which is active in
soil-decomposition ; and they serve as nourishment to the soil
bacteria upon which its thriftiness so greatly depends. See
below, chapter 9.
The Nitrogen-Content of Humus. — Since soil-humus' is
doubtless the chief depository of soil-nitrogen, and the main
source from which, through the process of nitrification, the
nitrogen-supply to plants is usually derived, its content of that
element is a matter of great interest. It has been customary
to estimate approximately the nitrogen-content of soils by the
proportion of humus-substance present ; and as the light tints
of the soils of the arid region indicate a small humus-content,
a scarcity of nitrogen seemed to be also indicated for these
lands. As this in a number of cases did not seem to accord
with actual experience, an investigation of the subject was
made at the California experiment station,1 with the results
shown in the subjoined table. In considering these results it
must be kept in mind that while arid conditions can rarely be
fulfilled in the humid region, humid conditions are quite fre¬
quently locally represented in the arid, in lowlands and on high
mountains; while moderately moist benchlands represent the
semi-arid regime.
1 Hilgard and Jaffa. On the Nitrogen-content of Soil-humus in the Humid and
Arid regions. Rep. Cal. Exp’t Station for 1892-4; Agric. Science, April, 1894;
Wollny’s Forsch. Geb. Agr. Phys., 1894.
SOILS.
136
HUMUS PERCENTAGE AND NITROGEN CONTENT IN SOILS OF THE ARID
AND HUMID REGIONS.
Station
Number
Soils arranged in order of nitrogen percentages in
humus.
Humus in
soil,
per cent.
Nitrogen
in Humus,
per cent.
Soils of the Arid Region (California).
2061
Dark clay loam, Arroyo Grande Valley, San Luis Obispo
County .
3.06
22.00
O
2291
Red soil, Orland, Glenn Co .
.71
21.10
1904
Sediment Soil, Porterville, Tulare Co . .
.90
I9.5O
1901
Sandy soil near Ceres, Stanislaus Co .
.64
l8.75
704
Sandy soil of plains, near Fresno, Fresno Co . . .
.60
18.66
6
Black adobe soil, Stockton, San Joaquin Co .
I.05
18.66
1679
Black adobe soil, Berkeley, Alameda Co.. . . . .
1.20
18.58
2324
Clay soil of desert, Imperial, San Diego Co .
.38
18.40
1167
Black clay loam soil, near Tulare, Tulare Co .
1.66
18.19
I536
Brown loam soil, Windsor Tract, Riverside, Riverside
County . . .
.20
18.OO
1126
Sandy loam soil, Paso Robles, San Luis Obispo Co. . . .
•55
17.27
2301
Red hill soil, Upper Lake, Lake Co .
.81
16.90
1607
Plateau soil of desert, Lancaster, Los Angeles Co .
•25
16.S0
”59
Sandy plains soil, Tulare, Tulare Co .
•37
l6.75
1900
Sandy soil, near Modesto, Stanislaus Co .
.84
16.65
m3
Clay loam soil (slate), Jackson, Amador Co .
•54
16. 60
1149
Adobe clay soil, near Paso Robles, San Luis Obispo
County .
•47
16.18
I53s
Mesa soil, Chino, San Bernardino Co .
•65
16.08
1147
Sandy loam soil, Paso Robles, San Luis Obispo Co. . . .
.66
16.06
2403
Valley Soil, Wheatland, Yuba Co .
1.50
16.00
1281
Red Mesa soil, Pomona, San Bernardino Co .
•58
i5-5°
1 1 17
Sandy granitic soil, near Jackson, Amador Co .
.80
i5-27
1406
Red loam soil, Arlington Heights, Riverside, Riverside
County .
•3°
15.00
1172
Red clay loam soil, east of Tulare, Tulare Co. .
•72
14-75
195S
Sandy Mesa soil, Nipomo, San Luis Obispo Co .
.85
M-45
1423
Chocolate-red soil, Carisa plain, San Luis Obispo
County . t . .
•39
M-36
1291
Sandy hill land, near Jackson, Amador Co .
.76
14-34
585
Wire-grass loam soil, Visalia, Tulare Co .
1. 00
14.10
863
Red ridge loam soil, Grass Valley, Nevada Co .
2.89
U-91
1907
Dark loam soil, near Chino, San Bernardino Co .
.92
13.26
IrI5
Sandy granitic soil, near Jackson, Amador Co .
•85
13.20
332
Plateau desert soil, Mojave, Los Angeles Co .
.28
12.50
2126
Gravelly soil, East Highlands, San Bernardino Co .
.62
n-75
1910
Ojai Valley soil, Nordhoff, Ventura Co .
1.64
1 1. 21
2187
Sandy loam soil, Soledad, Monterey Co .
•97
1 1. 10
1759
Sandy soil, Perris Valley, Riverside Co .
•53
1 1.04
774
Bench slope soil, Ontario, San Bernardino Co .
1 .20
i0-85
1984
Red soil, East Highlands “ “ “ .
•58
I0-5°
2325
Silt soil of desert, Imperial, San Diego Co . .
.65
10.70
1906
Light sandy soil, Pomona, San Bernardino Co .
•95
9.80
243°
Hillside adobe, Berkeley, Alameda Co . . .
1.85
8.70
Average of arid uplands .
•91
i5-23
c
d> -
U7Z
O C
*- c n
<u
u
£-5 8.
.670
.15O
.180
.120
.112
.196
.203
.070
.302
.036
.095
•137
.042
.062
.140
.090
.074
.105
,I06
.24O
.O9O
.123
•045
.100
.122
.036
.109
.146
402
.121
.112
•°35
.070
.183
.110
•059
.140
.060
.070
•°93
.160
•J35
SOIL AND SUBSOIL.
137
HUMUS PERCENTAGE AND NITROGEN CONTENT IN SOILS OF THE ARID
AND HUMID REGIONS.
Station
Number
Soils arranged in order of nitrogen percentages in
humus.
Humus in
soil,
per cent.
Nitrogen
in Humus,
per cent.
Nitrogen
in soil,
per cent .
586
Sub-irrigated Arid Soils (California).
Sandy plains soil, Tulare, Tulare Co .
1. 14
IO.79
.123
1466
Loam soiL, Miramonte, Kern Co .
.60
10.66
.064
1284
Moist land loam soil, Chino, San Bernardino Co .
I.99
10.20
.203
1 148
Swale soil, near Paso Robles, San Luis Obispo Co .
1. 16
965
.112
1714
Bench soil, Santa Clara River, Piru, Ventura Co .
.78
9-56
.074
77
Alluvial soil, Tulare Lake bed, Tulare Co .
•47
9-37
.045
1880
Creek bench soil, Niles, Alameda Co .
1. 19
8.90
.IO9
1903
Sediment soil, Porterville, Tulare Co . .
1. 12
8.50
.140
168
Alluvial soli, Santa Clara river, Santa Paula, Ventura Co
.84
7- 99
.067
1760
Green-sage land, Perris Valley, Riverside Co .
•91
7.70
.070
qo6
Alluvial soil, Colorado River, Yuma, San Diego Co....
•75
7-47
.050
1636
Red soil, Manton, Tehama Co .
2.00
6.86
•I37
1758
Alkali soil, Perris Valley, Riverside Co . .
.60
6.83
.071
1963
Sandy loam soil, Willows, Glenn Co .
•36
6.05
.022
2080
Sandy soil, Santa Maria Valley, Santa Barbara Co ....
1.64
5-36
.090
Average of sub-irrigated arid soils .
1.06
8.38
•°99
207
HUMID SOILS FROM ARID AND HUMID REGIONS
(California).
Eel River Alluvial soil, F^rndale, Humboldt Co .
1.25
6.96
.085
23T9
Alluvial soil, Hupa Valley, Humboldt Co .
7-83
6.70
•5T4
2I3
Marsh soil, Novato, Meadows, Marin Co .
1.54
6.36
.089
1704
Valiev soil, Hollister, San Benito Co .
.94
c.21
.049
2295
Tule soil, Upper Lake, Lake Co .
1.70
4.50
•0 77
1 10
Alluvial soil, Putah Creek, Dixon, Solano Co .
1.71
4-25
.072
37
Redwood Valley soil, Pescadero, San Mateo Co .
2.28
3-°7
.070
Average for California . . . . ....
2-45
5-29
•x35
26
OTHER STATES.
Bog soil, Michigan . .
233.02
6.08
22.0I2
Back-land clay loam, Houma, Louisiana .
5-°7
4.20
.218
Duff soil, Oregon .
13.84
3-49
•483
Sandy prairie soil, Harris Co., Texas .
2.13
3.66
.184
Average for other States .
7.01
378
•295
23
Red soil, Oahu Island, Hawaii (maximum) . . .
i-57
5-°7
.078
27
Guava soil, Hawaii Island (minimum) .
9-95
1.71
.170
Average of 5 soils, Oahu Island .
3- 01
6.07
•2 37
Average of 2 soils, Maui Island .
9.07
2.13
.286
Average of 4 soils, Hawaii Island .
6.17
2-54
.146
Average for Hawaiian Islands .
5.26
3-69
.169
Total for Humid soils, average .
OO
LO
4-23
.166
2 Introduced only for comparison of the nitrogen percentage in Ilumus and not
included in the average.
138
SOILS.
It thus appears that on the average the humus of the arid
soils contains about three and a half times as much nitrogen as
that of the humid ; that in the extreme cases, the difference goes
as high as over six to one (see Nos. 37 and 704) ; and that in
the latter cases, the nitrogen-percentage in the arid humus con¬
siderably exceeds that of the albuminoid group, the flesh-form¬
ing substances.
It thus becomes intelligible that in the arid region a humus-
percentage which under humid conditions would justly be con¬
sidered entirely inadequate for the success of normal crops, may
nevertheless suffice even for the more exacting ones. This is
more clearly seen on inspection of the figures in the third
column, which represent the product resulting from the multi¬
plication of the humus-percentage of the soil into the nitrogen-
percentage of its humus ; as appears in comparing the respective
averages, or Nos. 1167 and no and others. An additional
consideration is the probable greater ease with which the nitri¬
fying bacteria can act upon a material so rich in nitrogen.
We must not, then, be misled by the smallness of many
humus-percentages in the arid region, into an assumption of a
deficiency in the supply of soil-nitrogen.
Decrease of Nitroge?i- Conte?it in Humus with Depth . — Since the
oxidation of the carbon and hydrogen in the humus-substance, and the
consequent increase of its relative nitrogen-content, are manifestly de¬
pendent upon the presence of air and heat, it is reasonably to be
expected that the nitrogen- percentage of the humus should decrease
with the depth of the soil. That this is really the case is plainly shown
in the subjoined table, which gives the humus-percentages and the
nitrogen-content of the humus from the surface foot down to twelve feet,
in a soil on the bench of the Russian River, Cal., which is sub-irrigated,
and liable to more or less rainfall during the summer. It will be seen
that not only does the absolute humus-percentage decrease quite regularly
down to seven feet, at which point there evidently was at one time a
strong root development, causing a notable increase of the humus-con¬
tent; from which again there is a regular decrease down to the twelfth
foot. It will be noted that the nitrogen-percentage in the humus,
while not decreasing with the same regularity as the humus-content
itself, yet exhibits a general recession from 5.30 to 1.15 in the ninth
foot, to which direct oxidation doubtless never penetrates.
SOIL AND SUBSOIL.
139
HUMUS AND NITROGEN-CONTENT OF RUSSIAN RIVER SOIL.
Depth in feet.
Per cent Humus in
soil.
Per cent Nitrogen in
Humus.
Per cent Humus-
Nitrogen in soil.
1
1. 21
5-30
.064
2
1. 16
4*32
.054
3
1. 14
3-87
.044
4
1. 17
3-76
.044
5
•74
2.16
.016
6
.60
2.66
.016
7
•47
2.54
.012
8
.78
i-54
.012
9
•54
2.24
.012
10
•52
1. 15
.006
11
•53
I-5I
.008
12
• 44
1 .81
.008
Influence of the Original Materials on the composition of
Humus. — The great variability of the composition of humus
formed from different substances is well shown in the sub¬
joined table, representing the results of experiments made by
Snyder,1 who caused various substances to humify by mixing
the pulverized material intimately with a soil poor in humus,
and allowing the process to continue for a year. At the end
of that time the humus formed was extracted by the method
of Grandeau, outlined above, and analyzed, with the following
results.
Sugar.
Oat
Straw.
Green
Clover.
Wheat
Flour.
Saw¬
dust.
Meat
Scraps.
Cow
Manure. 3
Carbon .
57.84
54.30
54.22
51.02
49.28
48.77
4G93
Hydrogen .
3-°4
2.48
3-40
3*82
3-33
4.30
6.26
Nitrogen .
.08
2.50
8.24
5.02
0.32
10.96
6.16
Oxygen .
39-04
40.72
34.14
40.14
47.07
35-97
45.63
100.00
100.00
100.00
100.00
100.00
100.00
100.00
While it may be questioned whether the process of humifica¬
tion had in these materials really reached the point of sensible
completion in all cases (notably in those of sawdust and cow
1 Bull. No. 53, Minn. Exp’t Station, p. 12, Chem. of Soils and Fertilizers, p. 94.
2 The figures for cow manure are so far out of range with any others thus far
observed, that it seems reasonable to suppose that they are influenced by un¬
changed substances present in the excreta.
140
SOILS.
manure), the great variability of the products from different
materials is very striking. When the nitrogen-content is de¬
ducted the percentage composition of the products agrees
more nearly. Considering that the nitrogen is probably pres¬
ent in the amid form, it is natural that hydrogen should in a
measure vary with it, as in the case of the clover, flour and
meat humus. Nitrogen being the most variable ingredient of
humus, it seems probable that the variation of the proportion
of the humus-amids present is the most potent factor in the
variability of the composition of natural soil-humus.
Arranging these results in the order of their nitrogen-con¬
tent as in the table below, we see that the latter approximately
corresponds to the original protein-content of the humified sub¬
stances.
Humus from meat scraps . 10.96 °J0 Nitrogen.
u
((
green clover .
((
it
cow manure .
if
ii
wheat flour .
. 5-05
a
it
oat straw .
it
it
sawdust .
. 32
While the above data prove the correlation between the first
products of humification and the original substance, it must be
remembered that subsequently, under proper conditions, the
nitrogen-percentage in humus may, in the course of time, in¬
crease very greatly, even to a proportion considerably above
that contained in flesh itself. When we consider that ordina¬
rily, the latter, and the albuminoid substances generally, decom¬
pose in contact with air with an abundant evolution of ammonia
compounds, sometimes leaving only a little fat (adipocere)
behind, it is surprising that the decomposition within the soil
should have exactly the opposite result, viz., an accumulation
of the nitrogen. The causes of this marked difference are not
yet well understood, but it is probably due to the differences
in the kinds of bacteria that are active in the two cases.
Snyder has also shown that the richer the organic matter
humified is in nitrogen, the more energetically it acts in render¬
ing available the mineral matters of the soil for plant nutrition.
SOIL AND SUBSOIL.
141
Correspondingly, Ladd 1 has shown that with the increase of
humus in the soil, there is also a corresponding increase in the
amounts of mineral plant-food extracted from the soil by a
four per cent solution of ammonia, such as is employed in the
Grandeau method of humus-determination.
1 Bull., S. Dakota Station, Nos. 24-32, 35, 47.
CHAPTER IX.
SOIL AND SUBSOIL (Continued).
ORGANISMS INFLUENCING SOIL CONDITIONS; BACTERIA, ETC.
MICRO-ORGANISMS OF THE SOIL.
Intimately correlated with the humus-substances of the
soil, as well as with its temporary contents of the carbohydrates
(cellulose, gums and sugars) from which humus is formed,
is the multitudinous flora of micro-organisms always present
and exercising important functions in connection with the
growth of the higher plants. Extended researches by Adametz,
Schloesing and Miintz, Miquel, Koch, Fraenkel, Winograd¬
sky, Frank and many others, have thrown light upon the im¬
mense numbers and great variety of minute organisms, es¬
pecially of the bacterial group, present in soils, and upon their
distribution and activities in the same. It has been shown
that their numbers are greatest near (although usually not
at) the surface, decreasing rapidly downward and generally
disappearing wholly at depths between seven and eight feet;
the latter depth varying of course according to the nature
and porosity of the soil, and both depth and numbers being
greatest in summer.
Numbers of Bacteria in Soils. — Adametz found in one gram
of soil, 38,000 bacteria at the surface, 460,000 at ten inches
depth ; in a loam soil at the surface 500,000, at ten inches 464,-
000 in each gram of earth. Of mould and similar fungous
germs there were only 40 to 50 in the same, 6 species being
true molds, while four were ferments, including the yeasts of
wine and beer. Fraenkel found in virgin land from near Pots¬
dam, a sudden, marked decrease at depths of from three to
five feet; while in earth from inhabited places within the city of
Berlin, considerable numbers were still present at eight and
even ten feet, in some cases.
In the researches lately made by Hold at the bacteriological
142
SOIL AND SUBSOIL.
143
station at Liebefeld, near Bern, it was found that in cultivated
soils the number of bacteria greatly exceeds the figures given
by Fraenkel. He found a gram of moist soil to contain from
three to fifteen millions of bacteria. In the cultivated soil of
Liebefeld he found 5,750,000, in meadow land 9,400,000, in a
manure pile 44,500,000 per cubic centimeter. These figures
seem high for so small a quantity of material, but taking the
average size of a bacterium, a cubic centimeter might readily
contain six hundred millions. (Grandeau, Ann. Sci. Agrono-
mique, vol. 1, p. 461, 1905).
Mayo and Kinsley (Rep. Kansas Exp’t Station for 1902-3) have
made elaborate investigations of the numbers and kinds of bacteria
found in various soils in Kansas, in connection with different crops.
It is noteworthy that in most cases their figures exceed considerably
those given by European observers, as they often reach high into the
millions, in one case to over fifty millions, per cubic centimeter.1
Five fields with different soils were investigated ; the land being
described as follows : “ Field No. 1 is a black loam containing con¬
siderable humus ; field No. 2 is similar to field 1 but contains more
humus; field No. 3 is a thin soil with clay gumbo subsoil; fields Nos. 4
and 5 are black loams, but not as rich in humus as either No. 1 or
No. 2.”
The average bacterial contents of the several fields are given as
follows :
Field No. 1 . 33>93U747 Per cubic centimeter.
“ No. 2 . 53,596,060 “ “ “
“ No. 3 . 78,534 “ “
“ No. 4 . 8,643,006 “ “ “
“ No. 5 . 3,192,131 “ “ “
“The crop records of these fields for the past ten years indicate
that the crop yield has been (more or less ?) directly proportional to
the bacterial content of the soil of each field ; field 2 has produced the
largest yield, field 3 the least.”
Unfortunately no chemical analyses of any of these soils are com¬
municated ; but at the request of the writer samples of the soils of the
1 The mode of statement in the paper is not always quite clear as to the manner
in which the averages given were calculated. It must be remembered that these
; data refer to cubic centimeters of soil, or about twice the amount (i gram) used
by European observers.
144
SOILS.
first three fields were sent from the Kansas station for humus deter¬
minations (courteously made by Dr. H. C. Myers), which gave the
following results :
Field No. i . 2.19% of Humus.
“ No. 2 . 3-07% “ “
“ N0.3 . 1.85%“
While these humus-percentages are not directly proportional to the
bacterial content, a favoring effect of high humus-content is clearly
shown. The bacterial and the humus-content of these soils are sensibly,
even if not directly, correlated ; which might reasonably be expected,
since the organic matter and the humus are the bacterial food.
The investigation also showed wide differences in the bacterial con¬
tent of the same soil when different crops were growing on it. Thus in
samples taken on Aug. 15, there were found in the first twelve inches of
a black loam soil bearing timothy and clover, 1,380,000, in the same
with alfalfa and clover, 21,091,000, with maize from one to over two
millions. In soils from the western part of Kansas, the bacterial con¬
tent of the same crops was much less (as doubtless is the humus-con¬
tent), and it is noteworthy that the prairie buffalo grass shows through¬
out a relatively high bacterial content in the first foot of the soil, ranging
next to alfalfa. The root bacteria living on the legumes will naturally
increase the bacterial content of the soils on which they grow, more
than plants which, like maize, do not directly utilize bacterial action.
Multiplication of the Bacteria. — Marshall Ward and Duclaux have
made some special observations in regard to the rapidity with which
certain bacteria multiply. Duclaux summarizes the final conclusion
thus : taking as a basis the time of 35 minutes for the subdivision into
two, which has been frequently observed by Ward, there would be four
millions of bacteria produced in twelve hours. The first filaments had
plenty of room in a drop culture of one cubic millimeter ; but at the
end their total volume amounted to the tenth part of the total volume
of the drop. At the above rate, making 48 generations in 24 hours,
281,500 billions of organisms would be produced. (Grandeau, Ann.
Sci. Agron. Vol. 1, 1905, p. 456).
Aerobic and Anaerobic Bacteria. — As may readily be in¬
ferred, the cultural and other surface conditions exert a potent
influence both upon the kinds and abundance of the bacteria
and molds; since the life-functions of some are dependent upon
SOIL AND SUBSOIL,
145
the presence of free oxygen (“ aerobic ”), while others flour¬
ish best, or only, in the absence of air (“ anaerobic ”), or are
able to avail themselves of the presence of combined oxygen,
by reduction of oxids present. Their number is found, in
general, to be greatest in cultivated lands, and bacteria are
there by far predominant over the moulds. On the other hand,
the moulds gain precedence in woodlands and meadows, at least
so far as air can gain access; while in the deeper layers of the
same, as well as in peaty lands, bacterial life is always scanty.
This holds particularly in respect to the nitrifying organisms,
and others whose life-functions are dependent upon abundant
access of oxygen (aerobic).
Food Material Required. — All bacteria, like the fungi, are
dependent for their development upon the presence of adequate
amounts of some organic food-material, best apparently in
water-soluble form. In the soil it seems to be chiefly com¬
pounds of the carbohydrate group, especially various gums
derived from the decaying plant substance, or from stable ma¬
nure ; in artificial cultures, glucose is mostly found to be a
highly available food. When the decaying substance reaches
the state of humus, the latter seems to be available as food
only to comparatively few bacteria. The very abundant de¬
velopment of bacterial life seems to be among the most im¬
portant effects produced by stable manure upon the surface
soil, in establishing good tilth (“ Bodengare ” in German).
Functions of the Bacteria. — While there is still much uncer¬
tainty as to the exact functions performed by most of these
bacteria in respect to soil-formation and plant growth, there
are several kinds whose activity has been proved to be of the
utmost importance in one or both directions ; it having been
shown that when the soil is sterilized either by heat or anti¬
septic agents, certain essential processes are completely sup¬
pressed until the soil is re-infected and the conditions of bac¬
terial life restored.
Probably the chief in importance are those connected with
the processes of nitrification and denitrification , bearing as they
do upon the supply to plants of the most costly of the three
substances furnished by fertilizers. These organisms have
been first extensively studied by Winogradsky, while the con-
10
146
SOILS.
ditions of their activity have been largely developed by R.
Warington.
Nitrifying Bacteria. — The conversion of ammonia into ni-
trates is accomplished under
proper conditions by two or¬
ganisms, or groups of organ¬
isms; the first stage being the
formation of nitrites by the
round, often flagellate cells of
nitrosomonas (or nitrosoco-
cus). The second, the oxid¬
ation of the nitrites into ni¬
trates by very minute rod¬
shaped bacilli, named nitrobac¬
teria. The conditions under
which these bacteria can act
are quite definite in that, aside
from a supply of the nitrifiable
substance, a fairly high temperature (240 C. or 75 0 F.) and
a moderate degree of moisture, there must be a free access of
oxygen (air) ; and there must be present a base (or its car¬
bonate) with which the acids formed by oxidation can imme¬
diately unite. In an acid medium (“sour” soils) nitrifica¬
tion promptly ceases; as it also does whenever the amount of
base present has been fully neutralized. The bases most favor¬
able to nitrification are lime and magnesia in the form of car¬
bonates, an excess of which does no harm ; while in the case
of the carbonates of potash and soda, the amount must be
strictly limited.
Conditions of Activity.— Dumont and Crochetelle found that up to
.25 per cent, potassic carbonate acted favorably on the process; which
was, however, completely stopped by as much as .8 per ct. War¬
ington has shown that ammonic carbonate similarly prevents nitrifi¬
cation when exceeding about .37 per ct. Ammonia salts in general
appear to be antagonistic to the transformation of nitrites into nitrates.
Aside from the carbonates, some neutral salts favor nitrifi¬
cation very markedly ; while others tend to depress it.
Deherain found that .5 per cent of common salt suffices to pre-
Fig. 15. — Nitrosomonas. (Winogradsky).
Fig. 16. — Nitrobacterium (Winogradsky).
SOIL AND SUBSOIL.
147
vent nitrification altogether, while smaller amounts retard it
proportionally. According to Dumont and Crochetelle, potas¬
sium chlorid acts favorably up to .3 per cent, but at .8 per
cent, suppresses nitrification. Earthy and alkaline sulfates, on
the contrary, seem to act favorably throughout, at least up to
.5 per cent, this is especially true of gypsum, which, according
to Pichard, accelerates the process more than any other sub¬
stance known. Taking the effect of gypsum as the maximum,
be found that, other things being equal, the amounts of nitrates
formed were as shown in the table below, the effect of gypsum
being taken as 100 :
Gypsum . . . 100
Sodic Sulfate . 47.9
Potassic Sulfate . 35.8
Calcic Carbonate . 13.3
Magnesic Carbonate . 12.5
The above estimates are markedly confirmed by the observations of
the writer in the alkali soils of California. In these, nitrates exist most
abundantly when the salts contained in the soil are mainly sulfates ;
while wherever common salt or sodic carbonate are present in con¬
siderable amounts, the amounts of nitrate found are notably less. In
saline seashore lands nitrates are usually present in traces only. Wollny
has moreover shown that the nitrates themselves exert a repressive
influence on nitrification.
Effects of Aeration and Reduction. — While the fostering
effect of sulfates upon nitrification is very energetic in well
aerated soils, they become injurious whenever by a reductive
process in ill-drained lands, the sulfates are reduced to sulfids.
Under such conditions the process will in any case be much im¬
paired. On the other hand, the favoring effect of abundant
aeration was strikingly shown in the experiment made by
Deherain, in which a cubic meter of soil was left unmoved for
several months, while a similar mass was thoroughly agitated
once a week during the same time. The proportion of nitrates
formed in the latter case was as 70 to 1 formed in the quiescent
soil mass. It follows that the intensity of nitrification is essen¬
tially dependent upon the porosity of the soil; and that it is
thus greatly favored in the pervious soil-strata of the arid re-
148
SOILS.
gions. It also follows that thorough and frequent tillage and
fallowing greatly favor nitrification ; thus explaining one of
the beneficial results of these operations. At the same time,
it is true that we may thus in a short time seriously diminish
the reserve stock of nitrogen contained in the soil in the form
of humus-amids ; and since nitrates are exceedingly liable to be
lost from the soil in several ways, such excessive nitrification
is to be avoided.
Unhumified Organic Matter docs not Nitrify. — There can be
little doubt that the formation of ammonia from the amido-
compounds in humus is also the work of bacteria ; but this,
really the initial phase of the nitrogen-nutrition of plants, has
not yet been fully elucidated. That, however, it is essentially
only the ready-formed humus and not the unhumified debris
of the soil which participate in nitrification was shown by the
experiments of the writer, see chapter 19.
Denitrifying Bacteria. — Among the sources of loss of ni¬
trates in the soil is the action of denitrifying bacteria ; some of
which cause merely the reduction of nitrates to nitrites and
progressively to ammonia, while others cause gaseous nitrogen
to be given off from nitrites and nitrates, resulting in their
complete loss to the soil. While there are probably several
kinds of the latter class, the most rapidly effective is an organ¬
ism contained abundantly in fresh horse dung, and also on the
surface of old straw. This can readily be shown by subjecting
a very dilute solution (1-3 per cent.) of Chile saltpeter to the
action of fresh horse dung in a close flask, when nitrogen
and carbonic dioxid gases are evolved,
and in a few days the nitrate has totally
disappeared. In the course of time this
power of horse-manure disappears ; so that
“ rotted manure ” is practically free from
it and under proper conditions serves nitri¬
fication so effectively, that in the past it
has served extensively for the production
of saltpeter in the “ niter- plantations ” for
the industrial purposes; the material of which was loose
Pi %
w tf
ty**5*i,'A*
Fig. 17. — Bacillus denitri-
ficans 1. (Burri.)
SOIL AND SUBSOIL.
149
earth, marl and manure, kept moist and frequently forked
over for better aeration. Saltpeter is similarly produced in
stables, corroding the mortar of brick foundations. Neverthe¬
less, it is necessary to avoid the use, either together or at short
intervals apart, of Chile saltpeter and fresh manure ; the ma¬
nure if used first should be allowed to remain at least two
months in the soil before saltpeter is applied.
The reduction of nitrates to nitrites and ammonia is brought about
by quite a number of bacteria, mostly anaerobic, and such as consume
combined oxygen in their development. Thus the butyric ferment,
which in the absence of readily reducible compounds evolves free hy¬
drogen, will in presence of nitrates reduce the latter to nitrites, or form
ammonia by addition of hydrogen to nitrogen just set free by reduction.
Such reductive processes of course occur chiefly in soils rich in organic
matter, or ill-aerated. The ammonia so formed, while at first simply
combining with any humus acids present, may in the course of time be
itself reduced to the amidic condition, being thereby rendered relatively
inert, until again brought into action by ammonia-forming bacteria.
Ammonia-forming Bacteria. — A large number of different
bacteria appear to be concerned in the formation of ammonia
from compounds of the albuminoid group, (and probably from
humus). Among these is one of the most common in soils
(Bacillus mycoides, root bacillus), which while forming am¬
monia carbonate in solutions of albumen, is also capable of
reducing nitrates to nitrites and ammonia in presence of a
nutritive solution of sugar.
The “hay bacillus" (B. subtilis), so abundantly developed
in hay infusions, and one of the most abundant in cultivated
soils, has together with B. ellenbachensis, B. megatherium, B.
mycoides, and others, by some been credited with important
action in favoring vegetation ; so that a fairly pure culture of
B. ellenbachensis has been brought out commercially in Ger¬
many under the name of “ Alinit." Rigorous culture experi¬
ments made by Stutzer and others have, however, failed to
show any general benefit from the use of alinit in infecting
either land or seeds. But there is no doubt of the
Effects of Bacterial Life on Physical Soil Conditions. — It is
apparent that all conditions favoring the life of aerobic (air-
needing) bacteria tend also to produce the loose, porous state
SOILS,
150
(tilth) of the surface soil so conducive to the welfare of cul¬
ture plants, designated by German agriculturists as “ Boden-
gare.” Whether or not this con¬
dition is directly due to bacterial
processes, as is thought by Stut-
Fig. 18. — Bacillus subtilis. (Wollny, after
Brefeld.
Fig. 19. — Bacteria producing ammoniacal
fermentation : A , C. mycoides : B, B. stut-
zeri. (From Conn, Agr. Bacteriology.)
Fig. 20. — Bacillus magaterium. (From
Migula.)
zer (Landw. Presse, 1904, No.
1 1 ) it is assuredly a highly im¬
portant point to be gained, and
is essentially connected with the
presence of humus in adequate
amounts, which is also a favor¬
ing condition of abundant bac¬
terial life. It seems that the
preference given to the shallow
putting-in, or even surface appli¬
cation of stable manure, existing
in Europe, is largely based upon
the marked effect upon the loose¬
ness of the surface soil, generally
credited to the physical effect of
the manure substance itself, but
apparently largely due to the in¬
tensity of bacterial action thus
brought about.
Root-bacteria or rhizobia
of legumes. — Among the most
important bacteria, agricultur¬
ally, is that which enables plants
of the leguminous order — (peas,
beans, vetches, clovers, lupins,
etc.), — to obtain their supply of
nitrogen from the air independ¬
ently of those contained in the
soil. The source of nitrogen
to plants was long a disputed
question ; it was at first supposed
(by de Saussure) that it was ob¬
tained directly from the soil by
the absorption of humus; but this was disproved, and Liebig
then contended that it was derived directly from the atmos-
SOIL AND SUBSOIL,
151
phere through the ammonia in rain water. This was then
shown to be wholly inadequate ; and Boussingault proved con¬
clusively that plants do not take up nitrogen gas from the air.
This was subsequently denied by Ville; but investigation at
the Rothamstead agricultural station by Lawes and Gilbert
definitely confirmed Boussingault’s results. At the same time
they also proved very definitely that while grass and root crops
deplete the soil of nitrogen, clover and other leguminous crops
leave in the soil more nitrogen than was previously present,
even when the entire, itself highly nitrogenous, leguminous
crop is removed from the land. The improvement of lands
for wheat production by rotation with clover had long ago
become a practical maxim ; but the cause was not understood
until, in 1888, Hellriegel and Wilfarth announced that the
variously-shaped excrescences or tubercles which had long been
observed as frequently deforming the roots of legumes, are
caused by the attacks of bacilli capable of absorbing the free
nitrogen of the air and thus enabling the host-plant to acquire
its needed supply by absorbing the richly nitrogenous matter
thus accumulated in the excrescences. The minute rod-shaped
organism was named Bacillus radicicola by Beyerinck ; Rhizo-
bium leguminosanim, by A. Frank, who has published an ex¬
tensive treatise on the subject.1
Microscopic examination of the nodules shows their tissues
to contain partly motile, free
bacteria, partly others (bacte-
roids), which have assumed a
quiescent condition, and are
of much greater dimensions
than those of the motile form.
These relatively thick, and
sometimes forked, forms, dif¬
fering somewhat in each of
the group adaptations men¬
tioned below, constitute the
bulk of the cell-contents of the
nodules, and ultimately serve
for the nutrition of the host- from anodule of Square-pod pea, showing cells
plant with nitrogen. When filled with Rhizobia.2
1 Uber die Pilzsymbcose der Leguminosen, Berlin, 1890.
2 Original figure from drawing by O. Butler, Asst, in Agr. Dep’t Univ. of
California.
152
SOILS.
the growth of the excrescence is completed, the swollen, quies-
cent bacteroids gradually collapse and become depleted of
their nitrogenous substance; and finally the apparently empty
husk remains or drops off, carrying with it the minute cocci
which in the soil become active bacteria again. The nodules
are thus found mainly on the actively-growing roots, and at
the time when vegetation and assimilation are most active in
the plant. In autumn, or when the plants are in fruit, the roots
may be wholly destitute of nodules.
jf*. V
Fig. 25. — Square-pod pea. — Tetragonolobus purpureus. Fig. 26. — White Lupin. — Lupinus albus.
The adhesion of the nodules to the roots is mostly very
loose, and their falling-off when the seedlings are carelessly
transplanted, doubtless accounts for much of the difficulty
generally found in transplanting legumes when once es¬
tablished.
The figures annexed show the various forms assumed by the
nodules in different plants, and with them also the correspond¬
ing forms of the bacteroids of each. The latter, here shown
SOIL AND SUBSOII
153
Fig. 22. — Common Vetch.— Vicia sativa. Fig. 23. — Bur clover. — Medicago denticulata. Fig. 24.— Garden pea. — Pisum sativum.
154
SOILS.
magnified about 1000 times, are taken from the inaugural dis¬
sertation of D. Brock on this subject, published at Leipzig in
1891. It appears that the forms of the bacteroids are quite as
much varied as are those of the nodules they form.
Varieties of Forms. — While these bacilli seem to be normally
present in most soils, it seems to be necessary that they should
adapt themselves for this symbiosis 1 with each of several
groups of the legumes in order to exert their most beneficial
effects. In many soils there appears to exist a “ neutral form,
which requires about a season’s time or more to adapt itself
specially to the several leguminous groups so that a great ad¬
vantage is gained by infecting either the seeds or the soil with
the forms already adapted, when no similar plant has lately
occupied the same ground. Thus the bacillus of the clover
root is of little or no benefit to beans, peas or alfalfa, and the
root-bacilli of each of the latter are relatively ineffectual when
used to infect either of the other groups. The same is true of
the bacilli of lupins and of acacias, as applied to leguminous
plants of any other groups.2
Mode of Infection. — The infection is especially effectual
when applied to the seeds before sowing; and for that purpose
there may be used either the turbid water made by stirring up
in it some earth of a properly infected field, or else water
charged with a pure culture of the appropriate kind, commer¬
cially known under the name of nitragin, now manufactured
for the purpose. Or else, the field to be sown may be infected
by spreading on it broadcast, and promptly harrowing in, a
wagon-load of earth per acre from a properly infected field.
Such earth must not be allowed to dry, or to be long exposed
to light.
Specially effective (“virulent”) and hardy forms of such bacteria
have been produced under artificial culture by Dr. Geo. T. Moore of
the U. S. Department of Agriculture. These cultures can be sent by
mail on cotton imbued with them, for the infection of seeds.
1 “ Living together ” beneficially ; in contradistinction to parasitism, which is
injurious to the host plant.
2 It is asserted by some observers that the root bacilli producing differently-
shaped excrescences upon different legumes are distinct species ; but this view is
not sustained by the experiments of Nobbe and Hiltner, and seems intrinsically
improbable.
SOIL AND SUBSOIL.
155
It is very important that the bacillus should be present in
the earliest stages of the growth of the seedlings ; otherwise the
latter will undergo a longer or shorter period of starvation,
unless the soil contains, or is furnished with, a sufficiency of
available nitrogen to supply their immediate wants. When
such a supply is very abundant, the legume crop will sometimes
develop no nodules at all ; but the best crops appear to be the
result of a thorough infection, and abundant formation of the
excrescences.
Cultural Results. — The marked results obtained in certain
soils by inoculation with the legume-root bacillus are exempli¬
fied in the following table, showing results of experiments by
J. F. Duggar, at the Alabama Experiment station.1
TABLE SHOWING INCREASE OF PRODUCTION BY SOIL INOCULATION.
PER ACRE.
TOPS.
ROOTS.
NITROGEN.
lbs.
lbs.
lbs.
Value.
Hairy vetch, not inoculated .
194
387
7
$ 1.05
do. do. inoculated . .
3°45
M52
106
15.90
Crimson clover not inoculated .
106
266
4-3
•65
do. do. inoculated .
4840
1452
143-7
21.25
Such marked increases from soil inocculation cannot of
course be expected in cases where the soil has previously borne
leguminous crops of similar nature and therefore already con¬
tains the root bacteria. Hence Duggar found no increase of
production when inoculating for cowpea, land that had borne
that crop two years before and already contained the root bac¬
teria. In the arid region, where the almost universally calcare¬
ous soils usually bear a natural growth largely composed of
various leguminous plants, inoculation is likely to be less com¬
monly effective than in the humid region east of the Missis¬
sippi, where leguminous plants are much less generally present
in the native flora.
The distinctive agricultural function of supplying nitrogen
to the soils on which they grow, renders inexcusable the per¬
sistence of some writers and teachers in designating all forage
plants as “ grasses.” Whatever excuse there may have been
for this practice so long as the nitrogen-gathering function of
the legumes was unknown, disappears with this discovery, and
1 Bull. Ala. Exp’t Station, No. 96, 1898.
156
SOILS.
the misleading misnomer should be banished from agricultural
publications and lectures, at the very least.
Other Nitrogen- Absorbing Bacteria . — An increase in the
nitrogen-content of some soils, aside from the action of legu¬
minous root-bacteria, has long been observed. As already
stated, this increase was at first ascribed to certain green algse
often seen to develop on the soil surface; but it has now been
shown that the nitrogen-gathering function belongs to at
least two bacteria, one of which ( Clostridium pastorianum )
was discovered by Winogradski, the other ( Azotobacter
chroococcnm ) by Beyerinck, and has since been farther in¬
vestigated by Koch, Krober, Gerlach and Vogel, and last by
Lipman and Hugo Fischer. According to the latter it seems
likely that Azotobacter chroococcnm lives in symbiosis with
the green algae, all of which, like the Azotobacter itself, de¬
velop with special luxuriance on calcareous soils.
Lipman (Rep. Agr. Exp’t Station, New Jersey, 1903 and 1904)
describes as Azotobacter vinelandii a form somewhat different from the
A. chroococcus, the nitrogen-assimilating power of which he tested
quite elaborately. He exposed to air pure cultures of A. vinelandii in
nutritive solution containing the proper mineral ingredients, and glucose
20 grams per liter. 100 cub. centimeters of this solution was exposed
in flasks of respectively 250, 500 and 1000 cc. content, therefore having
greater surface in the larger flasks. After ten days, the amounts of
nitrogen fixed were found to be respectively 1.67, 3.19 and 7.90 milli¬
grams. When mannite solution was employed instead of glucose, a
similar fixation was observed ; and it was also shown that the presence
of combined nitrogen in the forms of nitrates or ammonium salts dis¬
couraged the fixation by the bacillus.
It was thus clearly proved that A. vinelandii at least does not need
symbiosis with algae to fix atmospheric nitrogen ; but experiments with
mixed cultures of the above bacillus and another (designated as No, 30
by Lipman) proved that when these two co-operate the absorption of
atmospheric nitrogen is nearly doubled. As it is probable that this is
the case also with other soil bacteria, the importance of this source of
nitrogen to plants is obvious ; provided of course that the proper nu¬
tritive ingredients are present in available form. Lipman shows that
among the organic nutrients, besides the sugars, glycerine and the salts
of propionic and lactic acids, and probably also others of the same
groups, can serve as nourishment to the nitrogen-fixing bacteria.
SOIL AND SUBSOIL.
157
DISTRIBUTION OF THE HUMUS WITHIN THE SURFACE SOIL.
The uniform distribution of the humus-contents of the sur¬
face soil, as shown in sections of the same, is by no means easily
accounted for. The roots from which its substance is so largely
derived are not so universally distributed as to account for
it ; but least of all can the rapid disappearance of the leaf-fail
and other vegetable offal from the surface be accounted for
without some outside agencies. Of these, the action of fun¬
gous vegetation, and of insects and earthworms, are doubtless
the chief ones.
Fungi. — When we examine a decaying root, we find radiat¬
ing from it a zone of deeper tint, as though from a colored
solution penetrating outward. But since under normal con¬
ditions humus is insoluble, this explanation cannot stand.
Microscopic examination, however, reveals that the outside
limit of this zone is also the limit to which the fungous fibrils
concerned in the process extend ; and as these fibrils are much
more finely distributed and much more numerous than the
roots of any plant, it is natural that the humus resulting from
their decomposition should be more evenly distributed than
the roots themselves.1
Such fungous growth is not, however, confined to dead and
decaying roots only. A large number of trees and shrubs,
among them pines and firs, beeches, aspen and many others,
also the heaths, and woody plants associated with them, appear
to depend largely for their healthy development, notably in
northern latitudes, upon the co-operation (“ symbiosis ”) of
fungous fibrils that “ infest ” their roots, enabling them to
assimilate, indirectly, the decaying organic (and inorganic)
matter which would otherwise be unavailable, and at the same
time converting that matter into their own substance. Fun¬
gous growths thus mediate both the decomposition and
rehabilitation of the vegetable debris.
The vegetative fibrils (mycelia) of several kinds of molds
are constantly present in the soil, and while consuming the
dead tissue of the higher plants, spread their own substance
throughout the soil mass. The same is true of the subter-
1Kosticheff, Formation and Properties of Humus; in abstract Jour. Chem. Soc*
*891, p. 61 1.
158
SOILS.
ranean or “ root ” mycelia of the larger fungi, toadstools,
mushrooms, which are commonly found about dead stumps
and other deposits of decaying vegetable and animal offal.
All these being dependent upon the presence of air for their
life functions, remain within such distance from the surface as
will afford adequate aeration ; the depth reached depending
upon the perviousness of the soil and subsoil. In the humid
region this will usually be within a foot of the surface, but in
the arid may reach to several feet. Ultimately these organ¬
isms contribute their substance to the store of humus in the
land.
On the surface of moist soils we frequently find a copious growth of
green fibrils, which may be either those of algae, such as Oscillaria, or
the early stages (prothallia) of moss vegetation. This vegetation has
been credited with absorption of nitrogen from the air, thus enriching
the soil ; but later researches have shown this effect to be due to
symbiotic bacteria (see above p. 156).
Animal Agencies. — Darwin first suggested that wherever the
common earthworm (Lumbricns) finds the conditions of ex¬
istence, it exerts a most important influence in the formation
of the humous surface-soil layer; and the limitation imposed
upon these conditions by the subsoil has doubtless a great deal
to do with the sharp demarcation we often find between it and
the surface soil. Briefly stated, the earthworm nourishes itself
bv swallowing, successively, portions of the surrounding earth,
digesting a part of its organic matter and then ejecting the un¬
digested earth in the form of “ casts,” such as may be seen by
thousands on the surface of the ground during or after a rain.
Darwin (The Formation of Vegetable Mold, 1881), has cal¬
culated from actual observation that in humid climates and in
a, ground fairlv stocked with these worms, the soil thus brought
up may amount to from one-tenth to two-tenths of an inch
annually over the entire surface; so that in half a century the
entire surface foot might have been thus worked over. Aside
from the mechanical effect thus achieved in loosening the soil,
and the access of air and water permitted by their burrows, the
chemical effects resulting from their digestive process, and the
final return of their own substance to the soil mass; also their
SOIL AND SUBSOIL.
159
habit of drawing after themselves into their burrows leafstalks,
blades of grass and other vegetable remains, renders their work
of no mean importance both from the physical and chemical
point of view. The uniformity, lack of structure and loose
texture of the surface soil, especially of forests, as compared
with subsoil layers of corresponding thickness, is doubtless
largely due to the earthworms’ work. It has frequently been
observed that when an unusual overflow has drowned out the
earthworm population of a considerable area, the surface soil
layer remains compacted, and vegetation languishes, until new
immigration has restocked the soil with them. Again, the
humus formed under their influence is always neutral, never
acid.
Wollny (Forsch, Agr., 1890, p.382), has shown by direct experimental
cultures in boxes, with and without earthworms, surprising differences
between the cultural results obtained, and this has been fully confirmed
by the subsequent researches of Djemil (Ber. Physiol. Lab. Vers.
Halle, 1898). In Wollny’s experiments, the ratio of higher production
in the presence of the worms, varied all the way from 2.6 per cent in
the case of oats, 93.9 in that of rye, 135.9 in that °f potatoes, 300 in
that of the field pea, and 140 in that of the vetch, to 733 per cent in
the case of rape. Wollny attributes these favorable effects in the main
to the increased looseness, and perviousness of the soil to air, and
diminished water-holding power. Djemil’s results all point in the same
direction ; and he shows, moreover, that the allegation that the roots
penetrate more deeply in the presence of the worms by following their
burrows, is unfounded, the descending roots often passing close to and
outside of these.
The work of earthworms is especially effective in loamy soils
and in the humid regions. In the arid region, and in sandy
soils generally, the life-conditions are unfavorable to the
worm, and the perviousness elsewhere brought about by its
labors already exists naturally in most cases. It is stated by
E. T. Seton (Century Mag. for June, 1904) that the earth¬
worm is practically non-existent in the arid region between the
Rocky Mountains and the immediate Pacific coast, from Mani¬
toba to Texas. In the Pacific coast region, however, they are
abundant, and do their work effectually.
i6o
SOILS.
Insects of various kinds are also instrumental in producing,
not only the uniform distribution of humus in the surface soil,
but also the looseness of texture which we see in forest soils
especially. Ants, wasps, many kinds of beetles, crickets, and
particularly the larvae of these, and of other burrowing crea¬
tures, often form considerable accumulations, due directly both
to their mechanical activity, and to their excrements.
The work of ants is in some regions on so large a scale as to
attract the attention of the most casual observer. Especially
is this the case in portions of the arid region, from Texas to
Montana, where at times large areas are so thickly studded with
hills from three to twelve feet in diameter, and one to two feet
high, that it is difficult to pass without being attacked by the
insects. The “ mounds ” studding a large portion of the
prairie country of Louisiana seem also to be due to the work
of ants, although not inhabited at present.
Larger burrowing animals also assist in the task of mixing
uniformly the surface soils, and aiding root-penetration, as well
as, in many cases, the conservation of moisture. Seton (loc.
cit.) even claims that the pocket gophers (Thomomys) in a
great degree replace the activity of the earthworms in the arid
region, where they, together with the voles (commonly known
there as field mice), exist in great numbers. Of course the
work of these animals, as well as that of the prairie dogs,
ground squirrels, badgers, etc., is incompatible with cultiva¬
tion. But the effects of their burrows on the native vegeta¬
tion, and the indications they give of the nature of the subsoil,
are eminently useful to the land-seeker.
Thus in the rolling sediment-lands of the Great Bend of the Columbia,
the observer is surprised to see the “ giant rye grass,” usually at home
in the moist lowlands, growing preferably on the crests of the ridges
bordering the horizon. Examination shows that this is due to the
burrowing of badgers, whereby the roots of the grass are enabled to
reach moisture at all times, even in that extremely arid region.
CHAPTER X.
SOIL AND SUBSOIL ( Continued )
THEIR RELATION'S TO VEGETATION.
Physical Effects of the Percolation of Surface Waters. —
The muddy water formed by the beating of rains on the soil
surface will, in penetrating the soil, carry with it the diffused
colloidal clay to a certain depth into the subsoil. We should
therefore expect that as a rule every subsoil will be more
clayey than its surface soil ; and this is found to be almost uni¬
versally the case in the humid region. Subsoils are therefore
almost always less percious and more retentive of moisture, as
well as of plant-food substances in solution, than their surface
soils, unless these are very rich in humus; and as the finest
particles are usually those richest in available plant-food, it
follows that subsoils will as a rule be found to contain larger
supplies of the latter than the surface soil. Common experi¬
ence as well as comparative analysis confirm both of these in¬
ferences so thoroughly, that it becomes unnecessary to adduce
examples in this place.
On the other hand, the reverse, upward movement of moist¬
ure caused by surface evaporation tends constantly to bring
any soluble salts contained in the soil mass nearer to the sur¬
face, thus increasing the stock of easily available plant-food in
the surface soil. In extreme cases, especially in the arid
region, this accumulation of salts may become excessive, and
seriously injurious to plant growth. (See “Alkali Soils,
chapters 21, 22.)
Chemical effects of Water-Percolation. — The accumulation
of plant-food in the subsoil is not, however, due only to the
mechanically-carried particles, hut also to the ingredients
carried in solution from the surface soil and redeposited in the
more retentive subsoils. Especially is this true of lime car¬
bonate, which is dissolved bv the carbonic acid formed chiefly
1 1 161
SOILS.
162
within the humic surface soil, and is often carried off in
amounts sufficient to obstruct drain tiles by its deposition in
contact with air (see chapt. 3). In the case of moderate rains,
however, it is carried no farther than the subsoil, and is there
redeposited, in consequence of the penetration of air, following
the water, and causing the carbonic gas to diffuse upward ;
thus leaving the lime carbonate behind. In the majority of
cases this results simply in a gradual enriching of the subsoil in
this substance; while the surface soil may become so depleted
as to require its artificial replacement by liming or marling.
The same general process occurs to a less extent, in the case of
magnesia.
Calcareous Subsoils — The fact that subsoils are more cal¬
careous than the corresponding surface soils is often of great
practical importance, in enabling the farmer to enrich his de¬
pleted surface soil in lime by subsoil plowing. The accumula¬
tion of lime carbonate in the subsoil also tends in a measure to
offset the extreme heaviness sometimes resulting from the ac¬
cumulation of clay.
Calcareous Subsoils and Hardpans. — When soils are very
rich in lime, and rains occur in limited showers rather than con¬
tinuously, the lime carbonate dissolved from the surface soil
may accumulate in the subsoil so as to either form calcareous
“ hardpan ” by the cementing of the subsoil mass; or it may
accumulate and partly crystallize around certain centers and
thus form white concretions, known to farmers as “ white
gravel." The latter is the form usually assumed in the re¬
gions of summer rains ; while in the arid regions the deficient
rainfall causes this substance to accumulate, and calcareous
hardpan to form, at definite depths depending upon the maxi¬
mum penetration of the annual rainfall ; sometimes in crystal¬
line masses of veritable limestone (“kankar” of India), or
sometimes merely as crystalline incrustations loosely cementing
the subsoil.
“Rawness” of Subsoils in Humid Climates. — From the
greater compactness of the subsoil which is almost universal in
the humid regions, the absence of humus and of the resulting
formation of carbonic and humic acids, it follows that its
minerals are less subject to the weathering process than are
SOIL AND SUBSOIL.
163
those of the surface soil. In the farmer’s parlance, the sub¬
soil is “ raw ” as compared with the surface soil; it is not so
suitable for plant-nutrition, and therefore must not be brought
to the surface to form the seed-bed, or be incorporated with
the surface soil to any considerable extent at any one time, if
crop-nutrition is to be normal. It is only in the course of time,
by exposure to atmospheric action as well as to that of the
humus, and of plant roots, that it becomes properly adapted to
perform the functions of the surface soil.
Soils and Subsoils in the Arid Region. — But however pro¬
nounced and important are these distinctions and differences in
the humid region, they are found to be profoundly modified in
the arid; where, as before stated, the formation of colloidal
clay is very much diminished, so that most soils formed under
arid conditions are of a sandy or pulverulent type. There is
then little or no clay to be washed down into the subsoil, hence
there is no compacting of the latter; the air consequently cir¬
culates freely down to the depth of many feet.
Thus one of the most important distinctions between soil
and subsoil is to a great extent practically non-existent in the
arid region, at least within the depths to which tillage can be
made to reach ; so that the limitations attached to subsoil-plow¬
ing in the countries of summer rains do not apply to the
characteristic soils of the arid regions.
Even the distinction in regard to humus is here largely ob¬
literated by the circumstance, already alluded to, that most of
that substance must, in the arid regions, be derived from the
decay of roots, which moreover reach to much greater depth in
these soils. Hence even in the uplands of the arid region it is
common to find no change of tint from the surface down to
three feet, and even more. This, like the free circulation of the
air in consequence of porosity, tends to render the distinction
of soil and subsoil practically useless; since it disposes of the
objection to “ subsoiling ” based upon the inert condition of the
subsoil, which in humid climates so effectually interferes with
the welfare of crops unless subsoiling is restricted to a fraction
of an inch at a time.
These fundamental differences in the soils of the two regions
are illustrated schematically in the subjoined diagram, which
shows on the left the contrast between clay or clay loam soils.
164
SOILS.
in which the depth of the surface soil-sample to be taken is
prescribed as nine inches by the rules of the Association of Am.
Official Chemists (in the writer’s experience it is more nearly
six inches as a rule). Alongside of the Eastern soil thus
characterized is placed a typical “ adobe ” soil from the grounds
of the California Experiment station, of which a sample show¬
ing uniform blackness to three feet depth was exhibited at the
World's Fair at Chicago in 1893. A t the right is a profile of
the noted hop soil on the bench lands of the Russian river. Cal.,
in which the humus-content was determined down to twelve
feet, the humus-percentage being .44% at that depth against
1.21% in the surface foot (see chapt. 8, p. 139). In this and
similar soils the roots of hops reach down to as much as
fourteen feet without much lateral expansion ; as shown in plate
No. 31 of this chapter. Similar conditions prevail in the sandy
uplands, as, e. g., in the wheat lands of Stanislaus county, Cal.,
mentioned above.
Taking the clay soils as a fair type for comparison, it would
seem that the farmer in the arid region owns from three to four
farms, one above another, as compared with the same acreage
in the Eastern states.
Subsoils and Deep-plowing in the Arid Region. — Up to the
present time this advantage is but little appreciated and acted
upon by the farmers of the arid region. They still instinctively
cling to the practice taught them by their fathers, and which is
still promulgated as the only correct practice, in most books on
agriculture. There are of course in the arid as well as in the
humid region, cases in which deep plowing is inadvisable ; viz,
that of marsh or swamp lands, as well as sometimes in very
sandy, porous soils, the cultural value of which often depends
essentially upon the presence of a somewhat consolidated, and
more retentive subsoil, which should not be broken up. But in
most soils not of extreme physical character, it is in the arid
region not only permissible, but eminently advisable to plow,
for preparation, as deeply as circumstances permit, in order to
facilitate the penetration of the roots beyond the reach of harm
from the summer’s drought; while for the same reason, subse¬
quent cultivation should be to a moderate depth only, for the
better conservation of moisture, and the formation of a pro¬
tective surface mulch (see chapter 13).
SOIL AND SUBSOIL.
TYPE OF EASTERN SOILS
Ft.
Upland.
r,- •iij77V7:7 ,Nvr» • t *1
• > ax :>Vv : v-A' , : .1 /</&.*> ♦ v\ • /*'’»’/»• n
:;*« vuv.-/>-.v . '-Vo; rr^./'O 7N 4
: v ' K • A- -. v:u*\ >1 7»vAvl«; V*. • £
5>
J2X-UY3-
3
4
>* -v^' y- * - t'v..'-* jCVu *<
;v«r -.'Ui:*' »<*«’! «?•£ ’ & *x O
■^V ■„ . i- — <8. y > f . ^ w v -*
«•- • - V>"r -V
5
•v >y ‘ l — »
t>'xiIL«s;Ar£-Cw”_
•' *■ ' V- **v
gpggt|
.ir
ka'U “C •'•'■ v IN ’.A- i-j
»Wv-. r 'J *- .. ~ ., x > i •*£ C’ • 1
a?8 a k Ilf E H r^Cu;< •’ ~
«£■ "* 5 vx % *. V- ftr^ (.s-,Jw
V^V 'C-v-?', T<4.
Ui-'m
r.:'- *8RI;v Ktx~*
.• — t * \ -
i >;
H
TYPES OF CALIFORNIA SOILS.
Up land clay-loam.
Bench land.
•-• ,VIJA I FOR M— •
*. v - ' « , - ~ A v— » / >*» \ - v‘'
MOIL MASS'
/ v > -v, /v
■ *«■. *« * «\ \ f . <r ”r «
Uh^-ViA>U^UU
h* ' o f A* -~ v— '
'i.v'-.’l\vA'3.
^/-U > Lfrll’ORM'-U-''
s *u v a ;♦ ;>*t;
i h*\ *U C. L<
ri'i \ • v * u ; / ,; s
y^r.K'.f v-v.r.* - /*- .
'-= -■ -^/*; ,'A i 'MV.-iyoi
-'ii v \ *-s »\ . Vv/S'f/rU
Fig. 27. — Soil Profiles illustrating differences in Soils of Humid and Arid Region.
SOILS.
1 66
It must not be forgotten that there are in the lowlands of
the arid region (river swamps or tides, seacoast marshes, etc.,)
soils in which surface soil and subsoil are differentiated as fully
as in the humid countries ; at least so long as they have not been
fully drained for a considerable length of time. In swamp
areas that have been elevated above the reach of overflow or
shallow bottom-water by geological agencies, even the heavy
swamp clays are fully aerated down to great depths, and roots
penetrate accordingly.
Examples of Plant-groivth on Arid Subsoils. — The fact that
in the arid region the surface-soil conditions reach to so much
greater depths than in the East and in Europe, is so important
for farming practice in that region that experimental evidence
of the same should not be withheld. Of such, some cases well
established as typical of California experience are therefore
cited.
It is well known that in the Sierra Nevada of California the placer
mines of the Foothills, worked in the early times, have long disappeared
from sight, having been quickly covered by a growth of the bull pine
(P. ponderosd). Much of this timber growth has for a number of
years past been of sufficient size to be used for timbering in mines, and
a second young forest is springing up on what was originally the red
earth of the placer mines, which appears to the eye as hopelessly
barren as the sands of the desert. In this same red sandy earth not
unfrequently cellars and house foundations are dug, and the material
removed, even to the depth of eight feet, is fearlessly put on the garden
and there serves as a new soil, on which vegetables and small fruits
grow, the first year, as well as ever. In preparing such land for irrigation
by leveling or terracing no heed is taken of the surface soil as against
the subsoil, even where the latter must be removed to the depth of
several feet, so long as a sufficient depth of soil material remains above
the bedrock.
The same is generally true of the benchlands ; the irrigator levels,
slopes or terraces his land for irrigation with no thought of discrimina¬
tion between soil and subsoil, and the cultural result as a rule justifies
his apparent carelessness. It is only where from special causes a con¬
solidated or hardpan subsoil is brought to the surface, that the land
when leveled shows “ spotted ” crops. Such is the case in some of the
“ hog-wallow ” areas of the San Joaquin valley of California, and in
SOIL AND SUBSOIL.
167
some cases where by long cultivation and plowing to the same depth, a
compact soil-layer or plowsole has been formed, and the land is then
leveled for the introduction of irrigation. In these cases a section of
the soil mass will usually show a marked difference in color and texture.
But, as a rule, in taking soil samples, no noticeable difference can be
perceived between the first and the second, and oftentimes as far down
as the third and fourth foot. The extraordinary root-penetration of
trees, shrubs and taprooted herbs, whose fibrous feeding-roots are found
deep in the subsoil and are sometimes wholly absent from the surface
soil, fully corroborate the conclusion reached by the eye. The roots
of grape vines have been found by the writer at the depth of twenty-
two feet below the surface, in a gravelly clay loam varying but little the
entire distance. In a similarly uniform and pervious material, the
loess of Nebraska, Aughey1 reports the roots of the native Shepherdia
to have been found at the depth of fifty feet.
Resistance to Drought. — These peculiarities of the soils of
the arid region explain without any resort to violent hypo¬
theses, the fact that many culture plants which in the regions of
summer rains are found to be dependent upon frequent and
abundant rainfall, will in California, and in the country west of
the Rocky Mountains generally, thrive and complete their
growth and fruiting during periods of four to six months of
practically absolute cessation of rainfall ; when east of the
Mississippi a similar cessation for as many zveeks will ruin
the crops, if not kill the plants. In continental Europe, in
1892, a six weeks’ drought caused almost all the fruit crops to
drop from the trees, and many trees failed to revive the next
season ; while at the very same time, the same deciduous fruits
gave a bountiful crop in California, during the prevalence of
the usual five or six months’ drought. This was without irri¬
gation, or any aid beyond careful and thorough surface til¬
lage following the cessation of rains in April or May, so as to
leave the soil to the depth of five or six inches in a condition
of looseness perfectly adapted to the prevention of evaporation
from the moist subsoil, and of the conduction of the excessive
heat of the summer sun. This surface mulch will contain
practically no feeding-roots, the paralysis or death of which
by heat and drought would influence sensibly the welfare of
the growing plant.
1 See Merrill, Rocks and Rockweathering.
SOILS.
1 68
Root-system in the Humid Region. — It is quite otherwise
where a dense subsoil not only obstructs mechanically the deep
penetration of any but the strongest roots, but at the same
time is itself too inert to provide sufficiently abundant nourish¬
ment apart from the surface soil, which is there the portion con¬
taining, alongside of humus, the bulk of the available plant-
food, and in which alone the processes of absorption and nu¬
trition find the proper conditions ; such as access of air and the
Fig. 28. — Root of an Eastern (Wisconsin) Fruit Tree. (Photograph by Prof F. H. King.)
ready and minute penetration of even the most delicate rootlets
and root-hairs. The largest and most active portion of the
root-system being thus accumulated in the surface soil, it fol¬
lows that unless the latter is constantly kept in a fair condition
of moistness, the plant must suffer material injury very quickly;
hence the often fatal effects of even a few weeks’ drought.
The same occurs in the arid region when often-repeated
shallow plowing has resulted in the formation of a “ plow-
sole ” which prevents the deep penetration of roots ; when a
SOIL AND SUBSOIL.
169
hot “ norther ” will often in a short time not only dry the
plowed soil, but will heat it to such extent as to actually bake
the roots it harbors. Under the same weather-conditions an
adjoining field, properly plowed, may almost wholly escape
injury.
Comparison of root development in ike arid and humid
regions. — Figures 28, 29 given here show the differences as
Fig. 29. — Prune Tree on Peach Root, at Niles, Cal.
actually seen in the case of fruit trees as grown in Wisconsin
and California, respectively, both in the absence of artificial
water-supply.
Adaptation of humid species to arid conditions. — Figures,
in No. 30, show the root systems respectively of the riverside
grape ( Vitis riparia ) as grown in the Mississippi Valley states,
and the natural development as found in the Rock grape of
170
SOILS.
Missouri and also in the wild grape vine of California. It will
be noted at once that the latter directs its cord-like roots almost
vertically from the first, until it reaches a depth varying from
12 to 1 8 inches, where it begins to branch more freely, but still
with a strong downward tendency in all. The roots of the
riverside grape, on the contrary, tend to spread almost hori¬
zontally, branching freely at the depth of a few inches and
B1PABIA Ololre dc Montp,
0 months old. '
St. Helena, Dec. 1809
Fig. 30. — Root Growth of Resistant Grape Vines.
manifestly deriving its supply both of plant-food and moisture
mainly from the surface soil. It is curious to observe the
behavior of this vine when cuttings are planted in California
vineyards as a resistant grafting-stock. Its first roots are
sent out horizontally, very much as is its habit in the East, so
long as the soil moisture is maintained near the surface. But
as the season advances, the more superficial rootlets are first
thrown out of action by the advancing dryness and heat of the
surface soil, and many finally die the first year.
SOIL AND SUBSOIL.
iyi
Not unfrequently the entire root system developed by the up¬
permost bud perishes; but usually its main roots soon begin to
recede from the threatening drought and heat of the surface,
curving, or branching downward in the direction of the moist¬
ure supply, and without detriment to their nutrition because of
the practical identity of the surface soil and subsoil. As the
portions of the roots near the surface thicken and mature,
their corky rind soon prevents their being injured by the arid
conditions to which they are subjected; while the root-ends,
finding congenial conditions of nutriment and aeration in the
moist depths, develop without difficulty as they would in their
humid home. Practically the same process of adaptation takes
place in every one of the trees, shrubs, or perennials belonging
to the humid climates, until their root system has assumed
nearly the habit of the corresponding native vegetation.
The photograph of the roots of a hop plant, grown on bench
lands of the Sacramento river, shows the roots extendi ng to 8
feet depth, but where broken off the main root is still nearly
two millimeters in thickness, proving that it penetrated at least
two feet beyond the depth shown in figure 31.
In the case of native annuals, either the duration of their
vegetation is extremely short, ending with or shortly after the
cessation of rains; or else their tap roots descend so low, and
the nutritive rootlets are developed at such depth, as to be be¬
yond reach of the summer’s heat and drought. For while it is
true that rootlets immersed in air-dry soil may absorb plant-
food, this absorption is very slow and can only be auxiliary to
the main root system which, instead of terminating in the sur¬
face soil as in the humid region, will be found to begin to
branch off at depths of 15 and 18 inches, and may then in sandy
lands descend to from 4 to 7 feet even in the case of annual
fibrous-rooted plants like wheat and barley.1 In the case of
maize the roots of a late-planted crop may sometimes be found
descending along the walls of the sun-cracks in heavy clay land
1 Shaler (Origin and Nature of Soils; I2th Rept. U. S. Geol. Survey, p. 311)
says ; “ Annual plants cannot in their brief period of growth push their roots more
than six to twelve inches below their root-crowns ” — a generalization measurably
true for the humid region only. According to F. J. Alway, the roots of cereals
penetrate to 5-7 feet in Saskatchewan, also.
1 72
SOILS
Fig. 31.— Hop Root from Sacramento Bench-land-
SOIL AND SUBSOIL.
173
poorly cultivated; and it frequently matures a crop without the
aid of a single shower after planting. See figures 33, 34.
The annexed plate (No. 32) shows the main roots of two
native perennial weeds of California, the goosefoot ( Cheno -
podium calif or nicum) and the figwort ( Scrophularia Cali¬
fornia) t common on the lower slopes of the coast ranges. The
soil was a heavy clay loam or “ black adobe " resulting from
the weathering of the clay shale bedrock, fragments of which
are so abundantly intermixed with the substrata that excava¬
tion of the roots became very difficult. Yet the main root of
the goosefoot went down below the depth of eleven feet.
The main root of the figwort, also, was followed below the
depth of ten feet without reaching the extreme end. This
proves clearly that the great penetration of the goosefoot wras
not, as might be supposed, due to its bulbous root. Yet such
thickening of the root just below the crown is a rather common
feature in arid-region plants, and can here be noted even in the
figwort, within whose botanical relationship bulbous roots are
almost unknown.
Any one accustomed to the cornfields of the Middle West,
where in the after-cultivation of maize it is necessary to re¬
strict very carefully the depth of tillage to avoid bringing up a
mat of white, fibrous roots, will be at once impressed with the
remarkable adaptability of maize to different climatic condi¬
tions, as exhibited in such cases and shown in figures 33, 34.
In southern California, in the deep mesa or bench soils, corn
stalks so tall that a man standing on horseback can barely reach
the tassel, and with two or three large ears, are quite com¬
monly grown under similar rainfall-conditions.
Importance of proper Substrata in the Arid Region. — The
paramount need of deep penetration of roots in the arid region
renders the substrata below the range of what is usually under¬
stood by subsoil in the humid climates, of exceptional import¬
ance. A good farmer anywhere will examine the subsoil to
the depth of two feet before investing in land ; but more than
this is necessary in the arid region, where the surface soil is
often almost thrown out of action during the greater part of
the growing season, while the needful moisture and nourish¬
ment must be wholly drawn from the subsoil and substrata;
i/4
SOILS
Extreme
limit
10 rt.6in,
Lx t rente
limit c
11 it.2in.=
i
vV
Fig. 32.— Deep-Rooting of Native California Goosefoot and Figwort.
SOIL AND SUBSOIL
1/5
Fig. 33.— Kentucky Maize, grown in region of Summer Rains. (Photography by A. M. Peter.)
SOILS
176
Fig. 34. — California Maize, Grown Without Rain or Irrigation.
SOIL AND SUBSOIL.
1 77
an examination of which should therefore precede every pur¬
chase of land, or planting of crops.
Such examinations are most quickly made by means of a probe con¬
sisting of a pointed, square steel rod five or six feet long, provided at
one end with a loop for the insertion of a cross -handle like that of a
carpenter’s auger. The handle being grasped with both hands, the
probe is forced into the soil with a slight reciprocating motion, by the
weight of the operator; who socn learns how to interpret the varying
kinds of resistance, and on withdrawing the probe carefully will generally
be able to determine if bottom water has been reached. Should this
easy method of examination not convey all the needful information, the
posthole auger may be resorted to ; and it is desirable that extra (three-
foot) rods or gaspipe joints be provided for the purpose of lengthening
the probe or auger, when necessary, to nine or twelve feet. It will
rarely be necessary to go to the trouble of digging a pit for such exam¬
inations ; but even this is to be recommended rather than “ buying a
cat in a bag ” in the guise of an unexplored subsoil.
Faulty Substrata. — A number of examples of “ faulty
lands," i. e., such as are underlaid by faulty substrata, are
given in the annexed diagram Fig. 35 ; the examples being
taken from California localities because of their having been
most thoroughly investigated. Similar cases, as well as others
not here illustrated, of course occur more or less all over the
world.
No. 1 shows a case which, though at first sight an aggravated
one of a rocky substratum, is in reality that of some of the best
fruit lands in the State. The limited surface-soil is very rich,
and is directly derived (as a “ sedentary " soil) from the
underlying bedrock slate. But this it will be noted stands on
edge , and the roots of trees and vines wedge their way along
the cleavage planes of the slate to considerable depth, deriving
from them both nourishment and moisture. Under similar
conditions the California laurel, usually found on the banks of
streams, grows on the summits of rocky ridges in the Coast
Ranges.
The case of No. 2 is quite otherwise. Here the shale lies
horizontally, and though much softer than the slate of the first
column, obstinately resists the penetration of roots ; so that the
land, though fairly provided with plant-food, is almost wholly
12
i ;8
SOILS
Z TO
C* >
TO
— J)
o
J £
Fig. 35.— Faulty Lands, California
SOIL AND SUBSOIL.
179
useless for cultivation. It is naturally covered with low,
stunted shrubs or chaparral ; only here and there, where a cleft
has been caused by earthquakes or subsidence, a large pine tree
indicates that nourishment and moisture exists within the
refractory clay stratum, and suggests blasting as a means of
rendering the land fit for trees at least.
No. 3 is a case similar to that of No. 2, only there is here a
dense unstratified mass of red clay, of good native fertility. It
is here that the expedient of blasting the tree holes with dy¬
namite was first successfully employed, in central California.
For lack of this, extensive tracts of similar land in southern
California, planted to orchards, have completely failed of useful
results after three years of culture.
No. 4 shows a typical case of calcareous hardpan obstruct¬
ing the penetration of roots, even though usually interrupted at
intervals, because of the formation occurring mostly in swales,
along which the sheets lie more or less continuously. Here
also, blasting will generally permit the successful growth of
trees and vines, whose roots frequently will, in time, wholly
disintegrate the hardpan and thus render the land fit for field
cultures. The depth at which such hardpan is formed usually
depends upon the depth to which the annual rainfall pene¬
trates. (See below, page 183).
Nos. 4, 5, and 6 all illustrate cases of intrinsically fertile,
very deep soils, shallowed by obstructions which in the case of
No. 4 are hardpan sheets, while in No. 5 the intervention of
bottom water limits root penetration, hence restricts the use of
the land to relatively shallow-rooted crops, and the use of only
a few feet of the profusely fertile soil. Such is the case where
bottom water has been allowed to rise too high, through the
use of leaky irrigation ditches.
No. 6 illustrates a case not uncommon in sedimentary lands,
where bottom water is quite within reach of most plants, but is
prevented from being utilized by the intervention of layers of
coarse sand or gravel, through which the water will not rise ;
and the roots, while they would be able to penetrate, are not
near enough to feel the presence of water underneath and there¬
fore spread on the surface of the gravel, suffering from drought
within easy reach of abundance of water. The “ going-
back ” of large portions of orange orchards in the San Ber-
l8o
SOILS
Fig. 36. — Almond Tree on Hardpan. Paso Robles Substation, Cal.
SOIL AND SUBSOIL.
I 8l
nardino Valley of California has been thus brought about; and
unfortunately this state of things is almost beyond the possi¬
bility of remedy.
Injury from Impervious Substrata. — The injurious effects of
a difficultly penetrable subsoil have already been discussed and
are selfevident. When the substratum is a dense clay, the rise
of moisture from below being very slow, it can easily happen
that the roots cannot penetrate deep enough in time for the
coming of the dry season, and that thus the crop will suffer.
The case will be still worse when hardpan cemented by lime
or silex limits root-penetration, as well as proper drainage.
In such cases the culture of field crops often becomes im¬
practicable, even with irrigation, as its frequent repetition, be¬
sides being costly, can rarely be commanded. In the case of
trees, the limitation of root-penetration results in the spreading-
out of the roots on the surface of the impenetrable layer ; as
shown in figure 36, which exhibits a root-development that
would be quite normal in the regions of summer rains, but is
wholly abnormal in the arid region, and results in the unpro¬
fitableness or death of the trees. It has often been attempted
in such cases to plant trees in large holes dug deep into the sub¬
soil and refilled with surface earth and manure. All such at¬
tempts result in failure, if only because the excavation in¬
evitably fills with water, which will soak away but very slowly
into the dense substrata, and will thus injure or drown out the
roots. Besides, the latter will remain bunched in the loose
earth, and will thus be unable to draw either moisture or
nourishment from the surrounding land. It is absolutely nec¬
essary to remedy this by loosening the substrata, if success is
to be attained.
Shattering of Dense Substrata by Dynamite. — The per¬
manent loosening of dense substrata is best accomplished by
moderate charges ( jA 1° Ya pounds) of “ No. 2 ” dynamite at a
sufficient depth (3 to 5 feet). The shattering effect of the ex¬
plosive will be sensible to the depth of eight feet or more, and
will fissure the clay or hardpan to a corresponding extent side-
wise. If properly proportioned the charge will hardly disturb
the surface; but if this be desired, from ij^to 2^2 pounds of
black powder placed above the dynamite will throw out suffi-
182
SOIL.
cient earth to plant the tree without farther digging. Where
labor is high-priced this proves the cheapest as well as the best
way to prepare such ground for tree planting ; and it has often
been found that in the course of time, the loosening begun by
the powder has extended through the mass of the land so as to
permit the roots to utilize it fully, and even to permit, in after
years, of the planting of field crops where formerly they would
not succeed.
Leachy Substrata. — While we may thus overcome the dis¬
advantages of a dense subsoil or hardpan, there is another diffi¬
culty not uncommonly met with in alluvial lands, which cannot
be so readily remedied. It is the occurrence, at from two to six
feet depth, of coarse sand or gravel, through which capillary
moisture will not ascend, but through which irrigation water
will waste rapidly, leaving the overlying soil dry. Then
unless very frequent irrigation can be given, the crop will
suffer from drought, unless indeed the gravel itself is filled
with bottom water upon which the root-ends can draw.
This case is a common one in the larger valleys of the arid
region, and in time of unusual drought the sloughs originally
existing, but since filled up, will be clearly outlined by the dying
crops, while outside of the old channels there may be no suffer¬
ing.
“ Going-back ” of Orchards. On such land as this, and on
such as has a shallow soil underlaid by an impervious subsoil,
trees will often grow finely for three to five years ; then sud¬
denly languish, or turn yellow and die, as the demand of their
larger growth exceeds what moisture or plant-food the shal¬
low soil and subsoil can supply. Enormous losses have arisen
from this cause in many portions of the arid region, but more
especially in California, owing to the implicit confidence re¬
posed even by old settlers, and still more by newcomers, in the
excellence of the lands, as illustrated by farms perhaps a short
distance away, but differently situated with respect to the
country drainage and the geological formations. All such
disappointments could have been avoided by an intelligent ob¬
servation of the substrata, either by probing or digging. Im¬
portant as is such preliminary examination in the region of
summer rains, it is a vitally needful precaution in the arid
SOIL AND SUBSOIL. 183
region, where the margin between adequate and inadequate
depth of soil and moisture-supply is much smaller.
When farmers note such distress in the orchard, the first idea usually
is that fertilization is needed. This in the almost universally very rich
lands of the arid region is rarely the case until after many years of
exhaustive cultivation, and is scarcely ever of more than passing benefit
in such cases. The first suggestion should always be an examination oj
the substrata , and especially of the deeper roots ; in the diseased ot
thirsty condition of which the cause of the “ die-back ” or yellowing
will commonly be found. Of course no amount of fertilization can
permanently remedy such a state of things, arising from impervious
substrata, coarse gravel, or shallow bottom water.
Hard pan. — By “ hardpan " is understood a dense and more
or less hardened layer in the subsoil, which obstructs the pene¬
tration of both roots and water, thus materially limiting the
range of the former both for plant-food and moisture, and
giving rise to the disadvantages following such limitation, as
described in the case of dense subsoils. The hardpans proper
differ from the latter, however, in being usually of limited
thickness only ; the direct consequence of their mode of forma¬
tion, which is not direct deposition by water or other agencies,
but the infiltration of cementing solutions into a pre-existing
material originally quite similar to that of the surface soil.
Such solutions usually come from above, more rarely from be¬
low, and are of very various composition. The solutions of
lime carbonate in carbonated water have already been referred
to in this connection; as has also the fact that corresponding
solutions of silica, associated more or less with other products
of rock decomposition (see chapters 2 and 4) are constantly
circulating in soils. The surface soil being the portion where
rock-weathering and other soil-forming processes are most
active, these solutions are chiefly formed there; and according
as their descent into the substrata is unchecked, or is liable to
be arrested at some particular level, whether by pre-existing
close-grained layers or by the cessation of rains, the subsequent
penetration of air, and evaporation of the water alone by shal¬
low-rooted plants, may cause the accumulation of the dissolved
matter at a certain level, year after year. Finally there is
184
SOIL.
formed a subsoil-mass more or less firmly cemented by the dis¬
solved matters, sometimes to the extent of stony hardness
(lime carbonate in the arid regions, kankar of India), more
usually soft enough to be penetrated by the pick or grubbing
hoe, and sometimes by the stronger roots of certain plants;
but resisting both the penetration and the assimilation of plant
food by the more delicate feeding roots.
Nature of the Cements. — The nature of the cements that
serve to consolidate the hardpan mass is substantially the same
as those already mentioned in the discussion of sandstones
(chapt. 4, p. 55) ; with the addition of those formed, usually
in connection with siliceous solutions, by the acids of the humus
group. The latter class of hardpans is especially conspicuous
in the case of swampy ground and damp forests, where “ moor-
bedpan ” and reddish “ ortstein ” (the latter particularly devel¬
oped in the forests of northern Europe, where it has been
studied in detail by Muller and Tuxen 1, are characteristic.
The latter gives for a characteristic sample of the reddish hard-
pan underlying a beech forest in Denmark a content of from
2.20 to 4.40% of ulmic compounds, and shows that the color
is due to these and not, as had been supposed, to ferric
oxid, which is present only in minute quantities.
Bog ore , Moorhedpan , Ortstein. — It is otherwise with moor-
bedpan, which often consists of a mass of bog iron ore per¬
meated or less with humous substances, which impart to it the
dark brown tint so often seen also in the “ black gravel ” spots
of badly-drained land. On the whole, however, ferric cements
are much less frequently found in hardpans than in sandstones
formed above ground.
Clay substance washed from the surface into the subsoil by
rains (chapter 10, p. 161) always helps materially to render
the hardpan impervious when afterwards cemented, a much
smaller proportion of the cementing material sufficing in that
case to form a solid layer. In such cases however the cement
is rarely of a calcareous nature, since lime prevents the diffu¬
sion and washing-down of the clay. It is mostly siliceous or
zeolitic; if the former, acid will have little or no effect upon
the solidity of the hardpan; while if zeolitic, acid will pretty
1 See Studien iiber die natiirlichen Humusformen,” by Dr. P. E. Muller.
SOIL AND SUBSOIL.
185
promptly disintegrate it. The presence of humus acids in the
cements, if not apparent to the eye, is readily demonstrated by
immersing the hardpan fragment in ammonia water or a weak
solution of caustic soda ; when if humus acids are the main
cementing substance the fragment will fall to crumbs, or be
softened to an extent corresponding to the amount of the
humus present. Calcareous hardpan is, of course, readily
recognized by its quick disintegration by dilute acid, with
evolution of carbonic gas.
In “alkali" soils containing sodic carbonate (“black
alkali ") there is commonly found at the depth of two or three
feet an exceedingly refractory hardpan resulting from the
accumulation of puddled clay (see above chapt. 4, p. 62) in
the subsoil, or sometimes even on the surface of depressed
spots. This hardpan, easily destroyed by the use of gypsum
and water, is described more in detail in chapter 22, on alkali
soils; it blues red litmus paper instantly.
The Causes of Hardpan. — The recognition of the cause of
hardpan is of considerable importance to the farmer, because
of the influence of the nature of the cement and the causes of
its formation upon the possibility and methods of its destruc¬
tion, for the improvement of the land.
It may be said in general that inasmuch as the cause of the
formation of hardpan is a stoppage of the water in its down¬
ward penetration, the re-establishment of that penetration will
tend to prevent additional induration ; moreover, experience
proves that whenever this is accomplished even locally, as
around a fruit tree in an orchard, the hardpan gradually
softens and disappears before the frequent changes in moisture-
conditions and the attack of roots. The use of dynamite for
this purpose in California has already been referred to; it seems
to be the only resort when the hardpan lies at a considerable
depth. When it is within reach of the plow, it may be
turned up on the surface by the aid of a subsoiler and will
then gradually disintegrate under the influence of air, rain and
sun. But when the hardpan is of the nature of moorbedpan,
containing much humic acid and perhaps underlaid by bog
iron ore, the use of lime on the land is indicated, and will in the
course of time destroy the hardpan layer. This is the more
desirable as in such cases the surface soil is usually completely
SOILS.
1 86
leached of its lime content, and is consequently extremely un¬
thrifty.
Woodlands of northern countries bearing beech and oak are
especially apt to be benefited by the action of lime on the
“ raw,” acid humous soil and underlying hardpan, which is
commonly underlaid by a leaden-blue sandy subsoil (“ Blei-
sand " of the Germans, “ Podzol " of the Russians) colored
brown by earth humates and mostly too moist in its natural
condition to permit of adequate aeration. These soils are
usually of but moderate fertility, and are best suited to forest
growth unless somewhat expensive methods of improvement
can be put into practice.
'* Plowsole." — An artificial hardpan is very commonly
formed under the practice of plowing to the same depth for
many consecutive years. The consolidated layer thus created
by the action of the plow (hence known as plowsole) acts
precisely like a natural hardpan, and is sometimes the cause of
the formation of a cemented subsoil crust simulating the nat¬
ural product. This is most apt to occur in clayey lands, and
greatly increases the difficulty of working them, while detract¬
ing materially from the higher productiveness commonly at¬
tributed to them as compared with sandy lands. Of course it
is perfectly easy to prevent this trouble by plowing to different
depths in consecutive years, and running a subsoil plow from
time to time. In this case, also, lime will generally be very
useful and be found to aid materially in the disintegration of
the “ plowsole.”
It is hardly necessary to insist farther upon the need of the
examination of land to be occupied, for the existence of hard-
pan or other faulty subsoil, which may totally defeat for the
time being the farmer's efforts, or make him lose his invest¬
ment in plantations after a few years. Probing by means of
the steel rod described above ( p. 177) or boring with a post-
hole auger; or finally, if necessary, digging a pit to the proper
depth (from four to six feet in the arid region), should
precede every purchase of new or unexplored agricultural
land.
Marly Substrata. — Among the causes of failure occasionally
found in the case of the “ going-back ” of orchards, is the
SOIL AND SUBSOIL.
187
occurrence of strongly calcareous or marly substrata, at depths
which in the humid region would not be reached by the roots,
but in the course of a few years are inevitably penetrated by the
roots of trees in the arid region. Then there appears a stunt¬
ing of the growth, and sometimes a yellowing of leaves, or
chlorosis, due to the influence of excessive calcareousness at the *
depth of four or five feet. For this of course there is no
remedy except the planting of crops which, like the mulberry,
Texas grapes, Chicasaw plum and others, are at home on such
lands ; which in the Eastern states are naturally occupied by
the crab apple, honey locust and wild plums.
CHAPTER XI.
THE WATER OF SOILS.
HYGROSCOPIC AND CAPILLARY MOISTURE.
When it is remembered that from 65 to over 90% of the
fresh substance of plants consists of water, the importance of an
adequate and regular supply of the same to growing plants is
readily understood. But it seems desirable, before discussing
the relations of water to the soil and to plant life, to consider
first the physical peculiarities which distinguish it from nearly
all other substances known. That it is colorless, tasteless, in¬
odorous, and also chemically neutral, alone constitutes a group
of properties scarcely found in any other fluid. But its special
adaptation to its functions in relation to vegetable and animal
life are much more fundamental, as is shown in the table of its
physical constants as compared with other well-known sub¬
stances, given below.
PHYSICAL FACTORS OF WATER COMPARED WITH OTHER SUBSTANCES (PER UNIT
WEIGHT).
Capillary ascent in glass tubes
of one mm. diameter.
Water . 14 mm.
Alcohol . 6 mm.
Olive oil . 1 mm.
Heat Relations.
Density.
Water at o° C. (freezing
pt.) . . 99988
Water at 40 (Maximum
density) . 1 .00000
Water at 150 C. (ordi¬
nary temperature) . . . .990
Ice at o° (freezing pt.). .92800
Specific Heats.
Water . 1.000
Ice . 502
Steam . 475
Clay, Glass... .1S0-.200
Charcoal . 241
Wood . 032
Gold, Lead . 032-.031
Zinc . 096
Steel . 1 19
Heat of fusion.
Water (Ice). . . 80 Cal.
Metals’. . 5-28 “
Salts, (inch sili¬
cates) . 40-63 “
Heat of Evaporation.
Water at 20° C .613 Cal.
“ “ioo°C.637 “
Alcohol . 209 “
Spirits of Tur¬
pentine . 67 “
Summarizing the meaning of the data given in the above
table with respect to organic life, we see, first, that water rises
higher both in the soil and in the tissues of the plant than any
188
THE WATER OF SOILS.
189
other liquid. Second, that as its density decreases in cooling
after a certain point is reached, it freezes at the surface instead
of at the bottom , as other liquids do; and as solid water (ice)
is lighter than fluid water, ice stays at the surface and is readily
melted when spring comes. Third, since its temperature
changes more slowly than that of any other liquid, it serves to
prevent injuriously rapid changes of temperature in plants and
animals as well as in soils. Its high “ heat of fusion ” also
serves to prevent quick freezing of plant and animal tissues, so
that the brief prevalence of a low temperature may be more
readily borne. Finally, the large amount of heat absorbed in
evaporation of water serves to keep both plants and animals
cool under excessive external temperatures which would other¬
wise quickly destroy life.
Capillarity or Surface Tension. — In this table it will be
noted, first, that water rises higher in fine (“capillary”) or
hair tubes than the other fluids mentioned, which fairly rep¬
resent all others. No other fluid approaches water in the
height to which it will rise 1 in either soils or plant tissues.
Were its capillary factor no higher than, e. g., that of oil or
alcohol, trees could not grow as tall as we find them, and the
water supply from the substrata, and all the movements of
water in the soil, and hence plant growth, would be similarly
retarded. It is easy to verify these differences by immersing
a cylinder of clay soil (or a cotton wick) in water on the
one hand, and in oil or alcohol on the other. Notwithstanding
the greater fluidity of alcohol as compared with water, the
latter will be found to fill the porous mass much more
quickly.
The smaller the diameter of the tube, the higher will the water rise
in it, and the greater will be the curvature of its upper surface, to which
the rise is sensibly proportional. But in the case of liquids which do
not “wet” the walls of the tube (as in that of mercury and glass), the
curve (meniscus) is convex, instead of concave, and the liquid is
depressed instead of rising.
It is in its relations to heat, however, that water is specially
distinguished from other substances; and these differences are
1 Excepting only the water-solutions of certain salts, among which common
salt, kainit and nitrate of soda are of agricultural interest. Common salt may in¬
crease the capillary rise to the extent of more than five percent.
SOILS.
190
most vital not only to living organisms, but to the entire econ¬
omy of Nature.
Density. — As regards the density or specific gravity of water
'(which is by common consent assumed as the unit of com¬
parison), it will be seen from the “ Density " table that whereas
all other bodies contract and become more dense as they grow
colder, water has its point of (fluid) “ maximum density ” at
40 C. (49°. 2 Fahr), and expands as it grows colder, until at
o° C. (320 Fahr.) it solidifies into ice. In so doing it de¬
parts still farther from the rule obtaining with all other bodies
(excepting certain mixtures, such as type metal) and again ex¬
pands so as to decrease the density from .99988 to .92800; thus
causing ice to float on water at the freezing point. Hence
water, unlike all other fluids, solidifies first on the surface; and
but for this, the thawing of the winter's ice, which would be
formed at the bottom of rivers and lakes, would be deferred
until late in summer. The expansion of water in freezing is
forcibly illustrated in the bursting of water pipes and pitchers
in winter; in the soil, the ice forming in the interstices serves
to loosen the compacted land and give it better tilth for the en¬
suing season.
Specific Heat. — Considering next, the column showing the
“ specific heat ” of water as compared with other substances, we
see that it exceeds all other known bodies in the amount of heat
required to change its temperature; hence again, its heat capa¬
city is taken as the unit to which all others are compared. The
figures given in the table show that even ice and steam require
for equal weights only about half as much heat (or burning of
fuel) to change their temperature ( e . g., 1 degree) as would
liquid water. But earthy matters, such as clay or soil and
glass, require only one-fifth as much heat for a similar change;
charcoal only about one-fourth as much. But vegetable mat¬
ter as represented by wood on the one hand, and gold and lead
on the other, require only about one-thirtieth as much heat as
an equal weight of water; zinc about one-tenth as much, steel
somewhat more.
It is thus plain that masses of water act powerfullv, more
than any other substance, as moderators of changes of temper¬
ature by their mere presence. The body of an animal or
plant is protected against violent changes by the presence of
THE WATER OF SOILS.
I9I
from 60% to 90% of liquid water, the temperature of which
can only be raised or lowered slowly ; and the presence of the
sea tempers the climates of coasts and islands as compared with
the heat or cold occurring in the interior of the continents.
Ice. — Again, it is shown in the table that the heat required
to melt ice is greater than in the case of any other substance,
especially the metals; which when once heated to the fusing
point, require only a very little more heat to become liquid.
The fusion of salts (including silicate rocks) requires more
heat than does that of the pure metals.
Vaporization. — In the amount of heat required for its vapor¬
ization water is also especially pre-eminent, and potent in its
influence upon organic life. The table shows that the evapor¬
ation of water requires six hundred heat units 1 as compared
with alcohol, requiring only two hundred; while spirits of
turpentine, the representative of a large proportion of vegetable
fluids, needs but sixty-seven.
The practical result is that evaporation of water from the
surface of animals and the leaves of plants, is exceedingl);
effective in preventing excessive rise of temperature, the heat
of the sun and air being spent in evaporating the perspiration
of animals and plants before an injurious rise of temperature,
such as would cause sunstroke in animals, and wilting or with¬
ering in plants, can occur. But since evaporation is most rapid
in dry air, it follows that the cooling effect will be the greater
in the arid regions than in the humid. In the latter, therefore,
sunstroke is much more frequent than in the fervid regions of
the arid west, even though the temperature in the latter may be
higher by twenty or twenty-five degrees Fahrenheit. White
men who would soon succumb if they attempted to work in the
sun in Mississippi or Louisiana when the thermometer stands
at 95 °F. will experience no inconvenience under the same con¬
ditions in the dry atmosphere of the Great Valley of California.
Solvent Pozver. — To the exceptional properties of water dis¬
cussed above, should be added another hardly less important
one, viz., that of being an almost universal solvent especially of
1 A heat unit, or “ calorie,” is the amount of heat required to raise the tempera¬
ture of a unit-weight (pound, kilogram, or gram) of water one thermometric degree.
According to the unit-weight and thermometric scale used, the figures will vary,
but in this text the basis is understood to be kilograms and the centigrade scale.
192
SOILS.
mineral matters, including even those which, like quartz, appear
to be most insoluble and refractory (see chapt. 3). The water
of the soil is thus enabled to convey to the roots of plants, in
solution, all kinds of plant food contained in the soil. It
should be noted that distilled (hence also rain-) water is a
more powerful solvent, e. g., of glass, than ordinary waters
containing mineral matter, and even free acids.
Practically, plants take up all their water supply from the soil
in the liquid form ; and hence the soil-conditions with respect to
this supply are of the most vital importance to plant growth.
The most abundant supply of mineral plant food may be wholly
useless, unless the physical conditions of adequate soil-mois¬
ture, access of air, and warmth, are fulfilled at the same time.
On the other hand, comparatively few plants are adapted to
healthy growth in soils saturated with water, or in water
itself; and but few among these are of special interest from
the agricultural standpoint.
Water-requirements of Growing Plants. — The amount of
water contained in any plant at one time, however large, is but
a small proportion of what is necessary to carry it through its
full development. When we measure the amount of water
actually evaporated through the plant in the course of its nor¬
mal growth, we find it to be several hundred times the quantity
of dry vegetable substance produced ; varying according to the
extent and structure of the leaf-surface, the number and size
of the breathing pores (stomata) of the leaves, and the
climatic conditions (including specially the duration of active
vegetation, and temperature during the same), from 225 to
as much as 912 times the weight of the mature, dry plant.
The following are extreme figures for water consumption of
different plants as reported by different observers, viz., Lawes
and Gilbert in England, Hellriegel in northern Germany,
Wollny in Southern Germany (Munich), and King in Wis¬
consin: Wheat, 225 to 359; barley, 262 to 774; oats, 402 to
665; red clover, 249 to 453; peas, 235 to 447; mustard and
rape, 845 to 912 respectively; the latter figure being the
maximum thus far reported. The highest figures given are
throughout very nearly those of Wollny, working in the very
rainy climate of Munich.
Evaporation from Plants in Different Climates. — It might
THE WATER OF SOILS.
193
be expected that in countries where the air is usually moist, the
evaporation will, other things being equal, be less than where it
is commonly far below the point of saturation. But the
“ guardian cells ” (stomata) of the leaf pores possess the power
of regulating, to a certain extent, the evaporation from the
leaf-surface in accordance with temporarily prevailing condi¬
tions, so as to allow free evaporation in moist air, but to pre¬
vent the wilting and drying-up of the leaf in hot and dry air,
save in extreme cases. Moreover, plants adapted to arid condi¬
tions are usually provided with additional safeguards in the
form of thick, non-conducting layers of surface cells, or long
channels connecting the interior tissue with the breathing-
pores on the surface. Often hairy, scaly or viscous coverings
serve the same end. On the other hand, when the air is very
moist, so as to check evaporation, water is sometimes found
secreted in minute droplets around the breathing-pores of the
leaves, since its ascent is a necessary condition of nutrition
and development.
Relation between Evaporation and Plant-growth. — There is
not in all cases any direct relation between the amount of evap¬
oration and plant growth ; but experience, as well as numerous
rigorous experiments have shown that under ordinary condi¬
tions of culture , and within limits varying for different soils
and crops, production is almost directly proportional to the
water supply during the period of active vegetation.
On the basis of Hellriegel’s results, showing that wheat uses
(in Germany) about 435 tons, or nearly four acre-inches of
water in the production of one ton of dry matter, and assuming
the ratio of grain to straw to be 1:1.5, King calculates the
following table of probable production under different moisture
conditions (Physics of Agriculture, page 140) :
YIELD PER ACRE.
Number of
Bushels.
Weight of Grain.
Tons.
Weight of Straw.
Tons.
Total Weight.
Tons.
Water used.
Acre-inches.
15
•45
•675
1.125
4.498
20
.60
.90
1.500
5-998
25
•75
1-125
1.875
7-497
3°
.90
1 -35°
2.250
8-997
35
1.05
1 • 57 5
2.625
10.495
40
1.20
1.800
3.000
1 2.000
194
SOILS.
S. Fortier has made several series of tests to determine the
actual yield of grain crops under field conditions when sup¬
plied with different amounts of water. Two of these were
made at the Montana experiment station in 1902 and 1903,
(see reports of these years), in large tanks placed in a field,
level with the ground. The results of the last year’s experi¬
ments are shown graphically in the figure below, from which
it will be seen that the
yield increased quite regu¬
larly with the amount of
water supplied, up to the
depth of 36 inches of
water.
It should be noted that
in this case (and as usual)
not only the quantity but
the quality of the grain
was greatly improved as
the water-supply in¬
creased, it becoming
larger and more uniform
in size.
Of similar experiments
made in the San Joaquin
Valley, California, in
1904, Fortier says:1
“ In e x p e r i m enting
with barley last winter
Fig. 37. — Experiments on Cereal production with . ' . . • r it
various amounts of water (Fortier, Report Mont. 1 ^ natural lailltall,
Expt. sta., 1903). which amounted to 4j4
inches during the period of growth, produced at the rate of
nine bushels per acre, while the application of sixteen inches
of water increased the yield to twenty-two bushels per acre.
In the same case; of wheat, the rainfall, alone, produced straw,
but no grain ; four inches of additional irrigation water pro¬
duced a yield at the rate of ten bushels, and sixteen inches of
water increased the yield to thirty-eight bushels per acre.”
--■Ill
Tank
NO I
Tonk
NO 2
Tank
No.4
Tan k
No 5
IP
in
Hi
■
Sil
Tank
NO. 6
HI
i§§§
in
IP
111
mb
■
iji
*
$
$
• ^
&
I
-u Q
/Pa/
/rn<jatton\
Grain
Straw I
fig. 1,
1 “ Water and Forest,” January, 1905. “ The Use of Water,” by S. Fortier.
THE WATER OF SOILS.
195
It is thus obvious that, other things being equal and with
conditions sufficiently favorable for the growth of crops, the
rule as formulated above is verified in practice.
Whitney (Bulletin 22, Bureau of Soils, U.S. Dept. Agr.), has carried
this rule so far as to claim that in all soils, the moisture supply is the
only important factor, and that so long as this is provided for, soil
fertility continues indefinitely without replacement of ingredients with¬
drawn. The latter conclusion is so thoroughly disproved by experience
as well as experiment that it hardly requires discussion here.
Whether plants, especially cultivated ones, are capable of
adapting themselves to arid conditions so as to be capable of
producing satisfactory crops with less water than is actually
consumed in the humid region, has not been directly deter¬
mined. Such is, however, the impression produced by farming
experience; and the fact that among the common weeds of arid
California are mustard and rape, cited by Wollny as requiring
over three times as much water as does maize for the pro¬
duction of one part of dry matter, lends color to the supposition
that in some manner these, and probably other plants, use more
water in humid than in dry climates (see this chapt. p. 212).
It is therefore impossible to assign a definite figure for the
amount of water required by vegetation at large; and even for
one and the same plant, only approximations conditioned upon
climatic factors can be given. We can in many cases, how¬
ever, assign for one plant, or for certain groups of plants, the
amounts of water producing the best results (“optimum”)
and the least amount (“ minimum ”) compatible with a paying
crop, that must be furnished during the growing season, to
produce certain results. For when instead of fruiting, it is
desired that the crop should produce the largest possible
amount of vegetable substance, as in the case of forage crops, a
larger amount of water will usually be serviceable.
Different conditions of Soil-Water. — Water may be con¬
tained in the soil in three different conditions, viz. :
1. From absorption of water vapor; Hygroscopic water.
2. Liquid water held suspended between the soil particles
so as to exert no hydrostatic pressure ; capillary water, or water
of imbibition.
1 See Wollny’s experiments, Forsch. Agr. Phys. Vol. 20, p. 58.
SOILS.
I96
3. Liquid water seeking its level ; bottom, ground or hydro¬
static water.
HYGROSCOPIC WATER.
Soils artificially dried so as to deprive them of all their mois¬
ture, when exposed to moist air absorb water vapor with great
energy at first ; both the rapidity of absorption and the amounts
absorbed, when full time is given, varying greatly with their
nature. Sandy soils, broadly speaking, absorb the smallest
amounts ; while clayey soils, and those containing much humus,
or finely divided ferric hydrate, take up the largest proportion.
The figure expressing the amount of aqueous vapor absorbed
at the standard temperature of 150 Cent., is called the coef¬
ficient of moisture absorption. For one and the same sub¬
stance, this coefficient rises as the grain becomes finer, the
surface being correspondingly increased (see chapt. 6).
The table below indicates the effect of the three substances
mentioned in increasing moisture absorption as compared with
a very sandy soil from the pine woods of Mississippi, and a
gray silt or “ dust ” soil from Washington, very fine-grained
but poor both in humus and ferric hydrate. (For details of
the physical composition of the Mississippi soils see table in
chapt. 6, p. 93). A highly ferruginous soil from Oahu shows
plainly the effect of that substance.
TABLE SHOWING INFLUENCE OF SILT, SAND, CLAY, FERRIC HYDRATE, AND
HUMUS ON MOISTURE ABSORPTION.
248
C/)
g s
2 A*
0
<13 J
e
CL x)
.2 c n
%
i*
Wash’n Dust
^ Soil. ^
Miss. White to
^ Pipe Clay. 'co
230
C/3
O .
0 ~
ES 0
£ £
yi
itrH
2
$
Miss. Ferrug- to
0 inous Clay Soil. "o\
Oahu. Ferrug-
'e&. • • ®
inous Laterite.
Miss. Marsh to
Muck. 0
2I5
-C3
(/)
u
d
W— <
^ *0
C/3
S
70
Ilygr. Moisture .
2.48
4.92
9.09
9-33
18.60
19.66
21.00
I S.40
Clay .
2.94
1 . 27
74.65
25.48
28.15
?
Tr.
Tr.
Ferric Hydrate .
1 .64
•CS
I2.IO
41 .00
Humus .
•55
•44
0.00
• So
little
3- jj
66.10
19.83
Finest Silts (01-.0250 mm.). . .
60. 10
45.04
23- r5
68.60
40.33
f ,r «
33-94
8.70
Sands, f. and c. (-0250-. 50 mm.)
31- 20
42.40
.20
4 7°
15. 6!
f 45- 00
70. 18
THE WATER OF SOILS.
I97
It will be noted that the greater fineness of grain in the
Washington dust soil induces a higher absorption of moisture
than occurs in the sandy soil from Mississippi, although th t
latter contains more clay. Comparison of the figure for the
Mississippi pipeclay and clay soil with the ferruginous soils,
from the same state and from Oahu, indicate plainly the in¬
fluence of the ferric hydrate in increasing absorption ; although
in the latter case the clay determination was not made, because
of the excess of ferric hydrate. The influence of humus is
plainly shown in the case of the marsh muck and soil, neither
of which contain any appreciable amount of either clay, or fer¬
ric hydrate in the finely diffused condition. The relatively
slight difference in the absorptions of muck and soil is due to
the only partial humification of the organic matter in the
former, while in the soil the humification is sensibly complete,
and the sand forming the body of the material serves to render
it more loose.
These data, referring to natural materials, while not as com¬
plete as could be desired, are sufficient to prove the facts, and
seem preferable to any artificially devised imitation of their
kind.
Influence of Temperature, and Degree of Air-Saturation. —
The amount of moisture absorbed varies materially both with
the temperature, and with the degree of saturation of the air
to which the soil is exposed. Schubler, Knop and other earlier
observers, operating with earth exposed to air only partly
saturated, and with soil layers of considerable thickness (in
watch glasses), found that the absorption decreased as the
temperature increased, according to a law formulated by Knop.
The writer found that under the conditions established in the
experiments of Knop and others, the air was not nearly satur¬
ated,1 so that these determinations are marred by ineliminable
1 It should be understood that it is by no means easy to insure full saturation
in any considerable volume of air.
It has generally been considered sufficient to cover with water the bottom of
the space in which absorption was to occur. The writer found that in order to
insure uniform results, it was necessary to cover the entire inner surface of the
vessel with wet blotting paper, and even then to exclude carefully all circulation
of air by padding the joints with such paper. When only the bottom of the box
was covered, samples placed at different levels above the water surface gave dis¬
cordant results. It was also observed that whenever the thickness of the soil
SOILS.
198
faults, the more as the soils used are only designated in general
terms, as “ garden soil,” “ loam,” “ peaty land,” etc., without
any definite indication of their actual physical or chemical con¬
stitution. The writer therefore undertook to correlate these
coefficients, determined with respect to completely saturated
air, with the physical composition of certain soils, as deter¬
mined by means of the methods heretofore described.
Some of the data so obtained are given in the table of physical soil
composition on page 93, chapt. 6. They have since been extensively
supplemented by additional determinations, but without materially
changing the coefficients approximately corresponding to the several
designations accepted in farm practice. Experiments conducted by
the writer have conclusively shown that Knop’s law of decrease oi
absorption with rise of temperature not only is not true for fully saturated
air, but must be reversed ; the fact being that the amount of water
absorbed by the soil increases in a fully saturated atmosphere (i.e., in
presence of excess of water) as the tempe?‘ature rises , at least between
15 and 35 degrees Cent. Thus, fine sandy soil which at 150 absorbed
2% of moisture, took up 4% at 34° ; while loam soil absorbing 7 % at
1 50, showed nearly 9% at 35 0 ; an increase of 2% in each case. But
in partially saturated air 3 it was found that, as stated by Knop, the
amounts absorbed steadily decrease, though not according to the law
announced by him. Taking as a unit the moisture absorbed at 150,
it was found that in air three-fourths saturated, f of the unit was taken
up by the soil ; at half saturation, nearly the proportional amount ; but
at one-fourth saturation the earths absorb materially more than a similar
proportion, being then capable of withdrawing moisture from greatly
layer exceeded about one millimeter, a long time was required for full saturation ;
during which inevitable changes of temperature would bring about a deposition of
dew on the soil, greatly exaggerating the absorptive coefficient.
In the chamber used at the California station for soil saturation, dimensions 12
X 18 X 19 inches high, the same soil was exposed on a shelf close to the sur¬
face of the water, another midway up, a third near the lower surface of the cover;
liquid water being in the bottom of the chamber, and the rest covered with wet
blotters. It was found that despite these precautions, the lowest soil layer
absorbed in the same time as much as ^°/Q more than the uppermost one.
2 The partial saturation to a definite extent was effected by means of solutions
of calcium chlorid of different degrees of concentration, according to the de¬
terminations of Wullner (Pogg. Ann.). These solutions were placed in a vride,
flat dish, over which a layer of soil 1 mm. in thickness was exposed, all being
covered with a bell glass lined inside with the same solution, so as to insure equal
saturation.
THE WATER OF SOILS.
199
undersaturated air. Since air thus undersaturated occurs not uncom¬
monly in the arid regions of the world, the fact that the soil cannot be
farther dried by such air of the same temperature, is of some practical
significance.
In view of the highly variable composition of soils and of
the doubtless varying hygroscopic properties of their several
physical constituents, it is not to be expected that any one nu¬
merical law will hold good exactly for all kinds of lands.
Mineral powders, colloidal clay, ferric hydrate, aluminic hy¬
drate, the zeolites, humus, and other hydrates known to occur,
doubtless each follow a different law in the absorption of mois¬
ture and gases; so as to modify the hygroscopic properties of
the soil in accordance with their relative predominance in each
case. (See table of absorption of gases, chapter 14).
Utility of Hygroscopic Moisture to Plant-growth. — The
early experimenters considered the hygroscopic moisture of
the soil to be of very great importance to the welfare of crops.
Within the last twenty-five years much doubt has been cast
upon this claim, even to the extent of stating that “ the
hygroscopic efficacy of soils must be definitely eliminated from
among the useful properties ” (Mayer’s Agriculturchemie, vol.
2, p. 1 3 1 ) . Yet Mayer himself concedes the cogency of the
experiments made by Sachs, which proved that dry soil im-
1 E. A. Mitscherlich (Bodenkunde fiir Land-und Forstwirthe, p. 156 et al.)
claims that all determinations of soil hygroscopicity thus far made are grossly
incorrect on account of the dew liable to be condensed on the soil layer from
fully saturated air, as the result of slight changes of temperature. He therefore
would have all such determination made either in an air-vacuum, or over a io°/0
solution of sulfuric acid.
Such dew-formation, however, cannot happen to any appreciable extent under
the conditions maintained in the writer’s work, viz, absorption within a thick-
walled (two-inch) wooden box of the dimensions given above, and sunk in the
ground in a cellar in which the temperature varies only a few tenths of a degree
during 24 hours. The soil layer of one millimeter thickness being put down in
the morning, the 7 hour absorption period falls at the time of slightly rising tem¬
perature, as an additional precaution against dew-deposition. Mitscherlich fails,
moreover, to show that this source of error produces any wide or serious dis¬
crepancies except under such long absorption periods as he finds it necessary to
use because of the great thickness of his soil layers. It is doubtful whether the
limits of errors in soil sampliug do not greatly exceed any of those involved in
the writer’s method, and whether such accuracy as is attempted by Mitscherlich is
of any practical significance.
200
SOILS.
mersed in a (probably not even fully) saturated atmosphere
is capable of supplying the requirements of normal vegetation ;
thus explaining the obvious beneficial effects on vegetation of
the summer fogs prevailing in portions of the arid region,
e. g., on the coasts of California and Chile.
Mayer’s experiments relied upon to prove the uselessness of hygro¬
scopic moisture to plant growth, were carried out in flower-pots, in
which it was plainly shown that the plants wilted before even the
visible liquid (capillary) moisture of the earth was entirely exhausted.
But this simply proves that under such artificial conditions, plants can¬
not withdraw moisture from the soil rapidly enough for their needs.
In nature , and notably in the arid regions, the chief supply of water is
received through the deep-going main roots, while the bulk of the
active feeding roots of the plant may be surrounded by almost air-dry
soil; under which conditions, as Henrici (Henneberg’s Journ., 1863, p.
280) has shown, slow growth and nutrition occurs even in such plants
as the raspberry, a native of humid climates. But in the arid region
this is the normal condition of the native vegetation through most of
the rainless summer. That a higher moisture-coefficient does not
necessarily imply that a larger amount of moisture can be withdrawn
from the soil by the plants, is undoubtedly true in some, but not in all
cases ; for in soils rich in humus, the moisture is more freely shared
with the roots than in non-humous, clay lands.
The higher moisture-absorption is however of the most un¬
questionable service in the case of the occurrence of the hot,
dry winds that so frequently threaten the entire crops of some
regions. In this case the soil containing the greater amount
of moisture requires a much longer time to be dried, and heated
up to the point of injury to the roots, than in the case of sandy
soils of low absorptive power, whose store is exhausted in a
few hours and then permits the surface to be heated up to the
scalding point, searing the stems and root crowns. That such
injury occurs much sooner in sandy lands than in well-culti¬
vated clay soils, is a matter of common note in the arid region.
Summary. — The significance of hygroscopic moisture in
connection with plant growth may then be thus summarized :
1. Soils of high hygroscopic power can withdraw from
moist air enough moisture to be of material help in sustaining
THE WATER OF SOILS.
201
the life of vegetation in rainless summers, or in time of
drought. It cannot, however, maintain normal growth, save
in the case of some desert plants.
2. High moisture-absorption prevents the rapid and undue
heating o£ the surface soil to the danger point, and thus often
saves crops that are lost in soils of low hygroscopic power.
Capillary Water.
The liquid water held in the pores of the soil, in the
form of surface films representing the curved surface seen
in capillary tubes, and therefore tending to cause the
water to move upwards, as well as in all other directions,
until uniformity of tension is established, is of vastly higher im¬
portance to plant growth than hygroscopic moisture. It not
only serves normally as the vehicle of all plant food absorbed
during the growth of the usual crops, but also, as a rule, to sus¬
tain the enormous evaporation by which the plant maintains
during the heat of the day, a temperature sufficiently low to
permit of the proper operation of the processes of assimilation
and building of cell tissue.
Comparatively few plants have roots adapted to healthy ac¬
tion while submerged in water, excluding them from free ac¬
cess of the oxygen of the air; and when such roots are formed
by plants not naturally growing in water or swampy ground,
they differ so far from earth roots in their structure that when
transferred to soil they usually die, normal earth-roots being
gradually formed instead. Conversely, there is for all land
plants a definite time-limit beyond which their roots cannot
live, or at least remain healthy, in submersion. Thus grain
fields will with difficulty recover from a week’s total submer¬
sion ; while young rice fields will resist considerably longer.
When in the resting (winter) condition vineyards will bear
submergence for thirty-five and even forty days, deciduous
orchards about three weeks; but when in the growing condi¬
tion, injury is suffered much more quickly.
It follows that whenever the soil-pores remain completely
filled with water for a length of time, there is danger to the
welfare of nearly all plants commonly cultivated in the tem¬
perate zones. It is therefore important to know how much
202
SOILS.
water will bring about this undesirable condition in the dif*
ferent kinds of soil.
To determine this point we may either employ the deter¬
mination of pore space by a comparison of the density of the
soil constituents (see chap. 7, p. 107) with the volume weight
of the soil ; or we may measure directly the amount of water
required to fill the pore-space. For the latter purpose it is
only necessary to measure the amount of water (conveniently
flowing from a graduated pipette) which, rising slowly from
below in a U-shaped tube so as to expel all the air before it,
is required to fill a definite weight or volume of the soil en¬
tirely full, so as to rise to its surface. We thus ascertain the
amount of empty space existing within the soil,1 which in the
absence of water will ordinarily be filled by air.
In most cultivated soils, as already stated, the air-space con¬
stitutes about 25% to 50% of their volume; and this space
when filled with water represents what is commonly termed
their maximum water capacity or saturation point. It is of in¬
terest to know this, because it has been ascertained from ex¬
perience that in order that plants may reach their best develop¬
ment, the capillary water present should not amount to more
than 60%, or less than 40% of its maximum water-holding
capacity; thus leaving about half the pore-space filled with air.
This optimum, however, varies somewhat for different plants,
some, like celery, being more tolerant of excess, and others
being more tolerant of a deficiency of moisture, as is the, e. g.,
egg-plant, originally a desert growth.
Capillary Ascent of Water in Soil Columns. — When a col¬
umn of dry soil (e. g., contained in a glass tube closed with
muslin at the lower end) is brought in contact with water, the
latter is soon seen to ascend in the soil, wetting it and thus
changing its color so as to permit of ready observation of its
progress. At first the rise is comparatively rapid, in some
cases as much as an inch in one minute; but it soon slows
down and after a time ranging from a few days to many
1 Simple as this operation appears to be, it is found to be by no means easy to
expel with certainty every small air bubble without resorting to means which
would destroy the natural condition of the soil ; such as boiling, or the use of the
air-pump. These determinations cannot therefore lay claim to gieat accuracy.
THE WATER OF SOILS.
203
months, reaches a maximum height beyond which the liquid
water will not rise. The ascent is most rapid, and stops
soonest, in coarse sandy soils ; it rises most slowly, but
in the end considerably higher, in heavy clay soils.
The most rapid continuous rise, and ultimately the highest,
occurs in salty soils containing but a small propor¬
tion of clay. The maximum height of capillary rise
thus far observed, viz. 10.17 feet, was noted in the case of
quartz tailings from a stamp mill, ranging from .005 mm. to
.016 mm. in diameter; but it took about 18 months’ time to
reach this maximum. The excessively fine texture of clay
opposes great frictional resistance to the movement of the
water, and the same is true of the finest silts, which, like clay,
remain almost indefinitely suspended in water. But it must be
remembered that while pure grains of silt will in wetting re¬
main unchanged in size, clay particles, and the clay incrusting
silt grains, will on wetting swell greatly, and thus fill up the
interstices, largely closing them up against the passage of
water.
These facts are exemplified and graphically illustrated below.
The soils selected for this illustration, from California lo¬
calities, are the following:
No. 233. Very sandy soil from near Morano, Stanislaus
County. Typical of the noted wheat-growing region of the
lower San Joaquin Valley, from northern Merced to Southern
San Joaquin Counties; bench or plains lands. First foot.
No. i/p 7. Sandy alluvial soil from near the confluence of
the Gila and Colorado rivers, near Yuma. Very deep, light
and easily cultivated. First foot, but almost identical to 15
feet.
No. 168. Silty alluvial soil from the old alluvium of the
Santa Clara River, near Santa Paula, Ventura County. Very
deep, very easily tilled; a typical alluvial loam of the arid
region.
No. 1697. Black adobe or clay soil, from the experiment
station grounds, Berkeley. A heavy clay soil, originally a
swamp deposit, becoming very tenacious when wet. An ex¬
cellent wheat soil.
The physical analyses of these soils are given below.
204
SOILS.
PHYSICAL ANALYSES OF TYPICAL SOILS.
Silt.
Sand,
Clay.
Fine,
<.25 to
.5 mm. h. v.
Coarse,
.5 to 2. mm.
h. V.
2.0 to
64 mm.
h. v.
No. 233. Morano sandy soil .
No. 1197. Gila bottom soil .
2.82
3.21
1 5.02
44.27
3-°3
5-53
15.24
25-35
349
15.42
25.84
1347
89.25
72.05
45.41
*3-37
No. 198. Ventura silty soil .
No. 1697. Berkeley adobe soil....
The most striking feature in this diagram is the very rapid 1
and high ascent in the combination of sediments represented
by the Gila bottom soil. It outstrips at once both the sandy
soil from Stanislaus, which contains a trifle less of clay, and
the silt soil from Ventura, from which at first sight it does not
seem to differ widely, but which contains considerably more
clay. It is doubtless the latter which so greatly retards the
motion of the water, as is still farther seen in the case of the
clay or adobe soil. It will be noted that on the second and
third days, the Gila soil had raised the water nearly twice as
high as the adobe, and that it took only 18 hours to raise it
nearly the same height as that attained by the Ventura silt in
so many days. But it ceased to rise after the 125th day,
while the Ventura soil, continuing for 195 days, finally rose
3 inches higher. The adobe also continued its rise, but did not
reach the same height as the Gila soil by nearly two inches.
There can be no doubt that the energetic and high rise of the
latter proves an important factor in the culture of these lands.
The coarse sandy soil reached its highest limit, 16^2 inches,
within six days, when the silty Gila soil stood at about double
that height.
Ascent of Water in uniform 2 Sediments. — Loughridge has
ascertained the rate of ascent of uniform sediments of differ¬
ent grain-diameters, with the results shown in the diagram
1 The ascent is of course most rapid, in the large tubes almost instantaneous,
when the capillary space is entirely clear ; but in the complex system of con¬
nected air spaces in soils, the curved paths and the friction obstruct the move¬
ment.
2 I. e., uniform between the narrow limits given.
THE WATER OF SOILS
205
Inches
60
LIMIT
,196 DAYS- -
186 DATS
«■
1
h
a
Sandy
Alluvial
Silt
Adobe
Soil
Soil
Soil
Soil
B janislaus Co.
Gila Hiver
Ventura
Uameda Co,
Fig. 38. — Columns showing heights to which water will rise by capillarity in soils of different
physical composition, and rates of ascent.
20 6
SOILS
«/)
u
ii
*-*
i>
a
ti
a
o
u,
1»
O
eft
-*-»
C
li
a
• *"4
1>
c/}
o
c/3
u
■*-*
£
i>
eft
• »4
b
a,
(G
CJ
o
ci
>-*
U«
THE WATER OF SOILS.
20;
subjoined, together with the maximum height reached by each.
The diagram is very eloquently illustrative of the great differ¬
ences in the capillary properties of granular sediments of the
various grades ; and it would seem that it ought to be possible
to deduce from it by a somewhat complex formula the rate
and height of ascent of water in any soil of known physical
composition. In nature, however, the presence of clay and
the greater or less degree of flocculation of mixed sediments
will always vitiate to a very great extent the results deducible
from such calculations ; hence the data conveyed by the observ¬
ations of Loughridge must be considered applicable only to
granular sediments free from clay and entirely deflocculated.
It is curious that in this case the “ clay ” showed a rise
markedly below that of the finest granular sediment, despite
the extreme fineness of its particles. This proves plainly that
the physical nature of colloid clay is unlike that of the granular
sediments ; as has been repeatedly mentioned above.
Maximum and Minimum of Water-holding Power. — It is
clear that at the base of the columns of soils just considered,
the maximum of water-absorption of which the soil is capable
will have been brought about ; while at the top of the same
column, the minimum of possible liquid absorption (continu¬
ous films of water) will exist. The same minimum moisture-
condition will be produced when a limited quantity of water is
placed with a large mass of soil ; the moisture will spread to
certain limits, until the surface films of water have all acquired
uniform tension ; and will then cease to extend, except by
evaporation and hygroscopic absorption.1 It is clear that the
same condition will be brought about in the course of time at
the top of a soil column in which water has percolated from
above ; and hence the minimum mentioned, aside from evapora¬
tion, represents approximately the usual condition of the soil
1 Ad. Mayer (Agriculturchemie 2, p. 141) designates this minimum content of
liquid water as the “ absolute ” water capacity of the same ; but it is not obvious
wherein this factor is better entitled to this name than would be the maximum
(see Wollny’s Forsch., 1892, p. 1 .) . M. Whitney (Rep. Proceedings Ass’n Agr. Coll.
& Exp’t St’ns, Nov. 1904) gives as a new observation the fact that in soils ap¬
proaching the drought condition water “ does not obey the ordinary physical laws
as we recognize them in capillarity.” This evidently refers simply to the well-
known phenomenon mentioned above.
208
SOILS.
near the surface within a variable time after a rain, or irriga¬
tion, when the descending water column has attained a length
corresponding to the height to which the water would have
risen from below in a tube arranged as shown on p. 205. It
is therefore a condition of very frequent occurrence in the arid
region.
Capillary Water held at Different Heights in a Soil Col¬
umn. — To determine the amounts of water held in the differ¬
ent portions in columns of soils in which water ascends by
capillary rise, the following plan was adopted by the writer in
collaboration with Loughridge (Rep. Calif. Sta. 1892-4, p.
99)-
Instead of glass tubes the soils to be tested were placed in
copper tubes one inch in diameter, divided into segments six
inches long, and flattened on one side. In the flattened side a
slot half an inch wide was left, and glass plates, held in posi¬
tion by rubber elastics, were cemented on the slotted side by
means of paraffin, to prevent a sifting-out of the soil. The
short sections can be connected at the ends like joints of stove¬
pipe, and the earths can be easily introduced in proper, even
condition. It was thus possible to gain access to any portion
of the column at any time, for the taking of samples.
WATER CONTENTS OF SOIL COLUMNS AT VARIOUS HEIGHTS ABOVE WATER LEVEL.
No.
233
1197
1679
Height above Water
Level.
Sandy Soil,
Morano.
Sandy Alluvium,
Gila.
Adobe, Berkeley.
47 inches
4-33
42 inches
10.26
36 inches
11.99
30 inches
15.26
24 inches
21.39
10.26 *
18 inches
27.63
29.48
12 inches
3-93
32.48
33-04
6 inches
14.15
35-°4
38-47
3 inches
38-49
1 inch
24-34
36.64
44.41
Since gravity limits the capillary ascent in a progressive ratio, as
shown in diagram 39, it is obvious that the true maximum saturation
1 This figure represents only a temporary condition; the full height of 46 inches
was not reached until the 195th day.
THE WATER OF SOILS.
209
can exist only in a very short (strictly speaking, an infinitesimally
short) vertical column. Ihe least practicable height for experimental
work being about 1 cm. (| in.), the writer has adopted for the purpose
of rapid determination of this factor, the use of a brass cylinder 1 cm.
high and of such width as to contain, for the sake of convenience, 25
or 50 cm. of soil. This cylinder has a finely perforated bottom, which
may be covered with filter paper; after being filled with soil which ha?
been struck level, and weighing, it is immersed to 1 mm. depth in dis¬
tilled water and allowed to rest for an hour ; then quickly dried outside
and beneath with filter paper, and again weighed. The amount of
water found by difference should for all practical purposes be referred
to the volume, not to the weight, of the soil, so as to eliminate the
error arising from the varying specific gravity of the latter.
In most cases the surface of the soil in the sieve cylinder remains
level after wetting ; but sometimes it swells so as to rise above its dry
level, even to the extent of nearly 30 °J0 (see chapter 7, p. 114).
This happens especially in strongly ferruginous soils. In the case of
“ black alkali ” soils, in wetting an enormous collapse sometimes takes
place (see chapter 22).
If it be desired to determine also the minimum liquid absorption
(see below), the surface of the wet soil is first covered with air-dry soil,
to absorb the surplus moisture, and finally with soil previously saturated
with hygroscopic moisture ; the added soil being each time thrown off
and finally the surface “ struck ” level with a tense silk thread before
weighing. Corrections must be applied for the usual increase in
weight, from the addition of soil, and for the hygroscopic moisture.
While the minimum of liquid absorption can thus be deter¬
mined quickly, without awaiting the capillary ascent of a water
column, and if sufficient time is given can also be determined
in higher columns, as proposed by Mayer (Wollny’s Forsch.
Vol. 3), the maximum cannot thus be determined without
gross inaccuracy. In determinations made by the writer it
was found that the figures for the minima of very different
soils (clayey and sandy) of the arid region, differ proportion¬
ally much less than do the respective maxima. In few of
these soils it was found to exceed about 10 per cent, and it
scarcely fell below 4 per cent even in very sandy soils. A
very deep, sandy soil, which had been irrigated in May, and
14
210
SOILS.
upon which no rain had since fallen, showed in July in the
second foot, upon which rested ten inches of fully air-dried soil
free from vegetation, a water-percentage of eight per cent.1
Capillary Action in Moist Soils. — In the preceding discus¬
sion the case of columns of air-dry soils, so common in the
arid regions, has been considered. It is obvious that a soil
column holding the minimum of capillary water may be of
any height; so that when, as happens in the open field, the
rain water soaks down beyond the range of capillary rise in a
given soil, the upper portions of the latter, above that range,
will remain at the minimum of moisture-content so long as it
is not depleted by evaporation. King has made extended
observations on soil columns ten feet high and moistened
throughout the mass. Capillary movement takes place in
moist soils much more rapidly than in dry ones, although
when sufficient time is given the final adjustment will of
course be the same. King’s experiments showed that evapor¬
ation at the surface of the tenfoot columns caused a sensible
depletion of the water content originally existing at the depth
of ten feet, in the course of 314 days. While so slow a
movement might not be of any benefit during the growth-
period of shallow-rooted annual crops, the fact shown is of
importance to permanent plantings, as of trees and vines.
Another and not so readily intelligible effect observed by
King is that when the surface-soil is wetted, moisture may be
withdrawn toward the surface from the lower layers. In one
experiment he found that when water was applied on the sur¬
face so as to add two pounds of water to each surface foot in
several soils, at the end of 26 hours there had been an increase
of three pounds in the same, and a loss of one and three quarter
pounds from the second and third feet. The cause of this
translocation is probably a “ distillation ” of the subsoil mois¬
ture toward the cooled soil ; the fact that it occurs is of prac¬
tical interest, since it seems to show that wetting the upper
1 Hall (The Soil, p. 66) gives for the minima in the case of soils examined by
him the following figures : coarse sandy soil, 22.2, light loam, 35.4, stiff clay, 45.6,
sandy peat, 52.8. These figures are very much higher than for apparently similar
materials used by the writer, and the differences exceed those between the
maxima given for the same. This discrepancy I am unable to account for.
THE WATER OF SOILS.
21 1
portion of the soil by cold rain or irrigation may tend to raise
additional supplies from below. At the change of seasons we
not uncommonly find, in digging tree holes or wells, a wet
streak at from 9 to 18 inches below the surface, caused evi¬
dently by the condensation of subsoil moisture, at the limit of
a cold zone resulting from the penetration of unseasonable tem¬
perature (“cold snap”) from above. Such movements of
soil-moisture by means of evaporation and recondensation
within the soil can of course take place even when the mini’
mum of liquid absorption has been reached and direct capil¬
lary movement has ceased. It is, as it were, dew within the
soil.
Proportion of Moisture Available to Growing Plants. — Not
all the capillary moisture contained in soils is available to
plants, as can readily be seen from the fact that many plants,
especially when growing in pots, begin to wilt while the soil
still appears visibly moist. The limit of wilting differs greatly
in different plants, and in the open ground it is difficult to as¬
certain that limit, because the deeper roots continue to supply
moisture from moister substrata. Hence potted plants wilt
while the soil appears much moister than when the same grow
in the field. King 1 has determined the amounts of moisture
down to 43 inches in a Wisconsin soil in which clover and corn
were at the wilting point, as in the following condensed table :
Clover.
Maize.
Fallow
ground.
First 12 inches, clay loam . . . .
8.44
7-03
17.01
Second 12 inches, reddish clay .
12.84
11.79
19.86
24 to 30 inches, sandy clay .
I3-52
10.84
18.56
40 to 43 inches, sand .
9 53
4.17
15-90
It is plainly shown here that the roots of clover and corn
were unable to utilize the higher moisture-content of the sub¬
soil-clay to the same extent as the smaller amounts present in
the surface foot, and in the sandy substrata. Evidently the
moisture in the clay soil was more tenaciously retained.
1 Physics of Agriculture, p. 135.
212
SOILS.
This is doubtless due, as King shows, to the equal thinness
of the moisture film remaining on the soil grains in either
case; the number of grains, and therefore the aggregate sur-
face holding these films, being much greater in the clay than in
sands ; hence the higher water content.
It is interesting to compare these figures given by King for
clover and maize at the wilting-point, and fallow ground adja¬
cent, with those given by Eckart (Rep. Expt. Sta. Haw. Sugar
Planters’ Ass’n., 1903) for those affording good growing
conditions for sugar cane on the (highly ferruginous) soils
of that station. The plots were irrigated at the rate of one,
two and three inches of water per week, allowance being
made for the rainfall. Two inches proved, on the whole, to
give the best average results for production. The moisture
determination of the soil under the two-inch regime gave an
average moisture content of 29.13% in the first foot of soil.
It is not stated what was the hygroscopic coefficient of that
soil, but it was probably very high; in the neighborhood of
21.5%, judging by the determinations made with six
Hawaiian soils at the California Station. This would indi¬
cate about 7.63% of free moisture as the optimum for sugar
cane.
Moisture-requirements of Crops in the Arid Region. —
Plants (particularly broad-leaved ones) which have made a
brash growth during a period of abundant moisture, will wilt
quickly when sunshine returns, and take some time to adapt
themselves to the drier conditions. On the other hand, plants
accustomed to dry air and scanty soil-moisture, will not wilt or
suffer under what would elsewhere be considered very rigorous
conditions. Loughridge 1 has made numerous determinations
of moisture in soils in which crops were beginning to suffer,
and others on similar soils that were growing normally, and
found that in general, not only were the differences in mois¬
ture content considerably less than in the case above quoted
from King’s observations, but that the amounts of free mois¬
ture required by various crops in the arid climate of Cali¬
fornia were surprisingly small.
The tables below show the results of observations made by
1 Rept. Cal. Expt. Sta. 1897-08, pp. 65-96.
THE WATER OF SOILS.
213
Loughridge during several drought years in California; so ar¬
ranged as to show the differences of moisture content for the
same crop in different soils. It will be observed that in all
cases where a crop growing on a clay soil could be compared
with the same on a lighter soil, the moisture required to keep
the crop in good condition was very much greater in the clay
than in the loam or sandy soils. In the case of apples, e. g.,
8.3% of water was abundant to keep the trees in excellent con¬
dition on a loam soil, while on a clay soil holding 12.3% the
condition was very poor. That this difference is due in the
main to the difference in the hygroscopic-moisture coefficient
of the respective soils, is plainly apparent in several cases. It
is therefore not the total moisture content, but the free mois¬
ture present in excess of what is held by hygroscopic absorp¬
tion, that determines the welfare of the plant.
By determining, first, the total moisture in the soils, as taken
in the field, then, after allowing them to become air-dry, deter¬
mining the maximum of hygroscopic moisture they would ab¬
sorb (see p. 198), Loughridge found by difference the amount
of free moisture, or liquid water which must be present in the
soil to prevent the crops from suffering. An exceptionally
good opportunity for these observations was offered by the
dry season of 1898, during which crops suffering and not
suffering, on identical lands, could easily be found. The de¬
terminations were always made for each foot of the upper
four feet of the land in the immediate neighborhood of the
trees or among the field crops. The first table exemplifies the
method of procedure; the second gives the summary of results
for the several crops and trees, as calculated from observations
made during the season.
214
SOILS.
TABLE SHOWING CONDITION OF CROPS ON VARIOUS SOILS UNDER
DIFFERENT MOISTURE-CONDITIONS.
Per cent Moisture in four feet.
Kind of Crop.
Wheat .
44
44
Maize .
44
Barley .
Sugar Beets. . . .
Vines .
44
Almonds .
44
Apples .
44
Apricots .
44
Figs .
44
Olives .
44
Peaches .
44
Prunes .
44
Citrus fruits... .
44 44
Kind of Soil.
Very sandy .
Sandy loam
Clay .
Clay adobe .
Sandy loam
Black adobe...
Black loam .
Loam .
Sandy loam
Loam . ...
Same field .
Loam .. .
Clay .
Loam .
Gravelly loam. .
Red loam .
Heavy loam ...
Red loam .
Sandy loam
Red loam .
44
Gray loam .
44
Sandy loam
Sandy soil .
Condition of
Crop.
Total.
Hygro¬
scopic.
Free.
Tons
per
acre.
Poor .
2.6
1.9
•7
56
Good .
12.8
5.6
7.2
576
Dead .
14.1
10.5
3-6
288
Very good .
12.9
8.8
4.1
328
Fair .
6.1
2-3
3-8
304
Wilting .
10.7
8.8
1.9
*52
Good .
12.4
5.6
6.8
544
Good .
8-5
5.0
3-5
280
Poor .
1.9
i-5
•4
32
Good .
8-5
6.6
i-9
178
Suffering .
7-9
6.9
1.0
80
Excellent .
8-3
5-5
2.8
224
Poor .
12.3
10.8
i-5
120
Excellent .
6-3
3-3
3.0
240
Poor .
6.9
5-o
i-9
152
Good .
5.2
3-8
1.4
112
Wilting .
8.6
8.6
0
0
Good .
5-2
3-8
1.4
1 12
Suffering .
1.9
1.9
0
0
Good .
8.2
5-°
3-2
256
Poor .
6.8
5-o
1.8
144
Excellent .
11. 2
9.0
2.2
176
Poor .
6.4
5-4
1.0
80
Good .
6-3
31
3-2
256
Leafless .
3-i
2.4
•7
56
TABLE SHOWING DROUGHT-ENDURANCE OF VARIOUS CROPS IN ARID
REGION.
Free water in four
feet of soil.
Per cent.
Tons
per acre.
0
to
1.0
80 |
1.0
to
1-5
120
1-5
to
2.
160
2
to
2.5
( 176
•J
\ 200
2-5
to
3
224
3
to
3-5
288
3
to
4
322
4
to
5
400
5
to
6
480
Crops that did well in lowest
amount of moisture men¬
tioned in first column.
Apricots, Olives, Grapes,
Peaches, Soy-bean.
Citrus, Figs.
Almonds, Plums, Saltbush.
Prunes.
Walnuts, Eucalyptus.
Apples.
Pears.
Hairy Vetch.
Wheat, Maize.
Sugar beets, Sorghum.
Crops that suffered in highest
amount of moisture men¬
tioned in first column.
Citrus, Pears, Plums, Acacia.
Almonds, Apples.
Barley.
Prunes.
Wheat.
Sugar beets.
CHAPTER XII.
THE WATER OF SOILS. — Continued.
SURFACE, HYDROSTATIC AND GROUND WATER ; PERCOLATION.
Since all the water of soils and plants is directly or indi¬
rectly derived from the rainfall (including therein snow and
hail), some general points regarding this factor require first
consideration. While it is not the object of this work to dis¬
cuss climatology in detail, yet the times of the year and the
manner in which precipitation comes, acts upon and is disposed
of in the soil under different climatic conditions, must of neces¬
sity form an essential part of its subject matter.
Amount of rainfall. — The rain falling in the course of a
year is usually stated in the form of “ inches ” (or centime¬
ters), implying the height of the water column that would be
shown at the end of the year had it all been allowed to accu¬
mulate; or, the sum of all the successive rains (including
snow) observed during the year. Since this amount ranges
all the way from nothing, or a mere fraction of an inch (as in
portions of the Andes, and of the great African and Asian
deserts) to as much as 600 inches or fifty feet (Cherapundji
in eastern India), the adaptation of agricultural practice to the
maintenance of the proper moisture-supply to crops is largely
a local question, oftentimes of not inconsiderable difficulty.
This is especially the case where torrential rains, yielding sev¬
eral inches of rain in a few hours, alternate with light, soaking
rainfall, as is very commonly the case in the interior of con¬
tinents, and more especially in the United States east of the
Rocky Mountains. Westward of the same the rainfall de¬
creases so rapidly that at or about the one-hundredth meridian
(the longitude of Bismark and Pierre, Dakota, and Dodge City,
Kansas) we already reach the annual average of 20 inches,
which is commonly assumed to be the limit below which crops
cannot safely be grown without irrigation. The “ cloud-
215
21 6
SOILS.
bursts ” occasionally occurring within these limits are usually
confined to mountainous regions, and the water they pour
down on the dry soil is rarely of any direct benefit to agricul¬
ture; hence they cannot be properly counted in the general
estimate of the effective rainfall. A region of high rainfall
(up to ioo inches and over), however, extends along the Pa¬
cific coast from northern California through western Oregon
and Washington across British Columbia to Alaska, to sea¬
ward of the Sierra Nevada, Cascade, and Alaskan coast ranges.
In the country east of the Mississippi river, the average an¬
nual rainfall ranges from 30 inches in the region of the Great
Lakes, and 45 to 50 inches on the north Atlantic coast, to 60
inches in Louisiana and up to eighty in southern Florida. The
average of the Mississippi Valley and Atlantic coast States is
usually stated at about 45 inches, which is distributed more or
less evenly throughout the year, excepting usually from six
to eight weeks of more scanty precipitation in the latter part
of August and in September — the “ Indian summer” season;
so that the winter is the season of greatest total rainfall.
Natural disposition of the Rain Water. — The rainfall is
naturally first disposed of in two ways, viz., a portion which
is absorbed by the soil, and another which is at once shed from
the surface and constitutes the “ surface runoff.” The portion
absorbed into the soil is subsequently disposed of either by
soakage downward into the subdrainage and through springs
and seepage1 into the streams and rivers; or by evaporation.
The latter again occurs in two different ways, viz., from the
soil-surface itself, or through the roots and leaves of plants.
The importance of each of these modes is sufficiently great to
entitle each to detailed consideration.
The Surface Runoff. — This portion of the disposal of rain
may range all the way from nothing to almost totality, accord¬
ing to the nature of the soil and the condition of its surface.2
1 The quiet seepage from the banks and beds of streams plays a much more im¬
portant part in the increase of volume of flow than is commonly supposed, because
unperceived save by measurement of the tributaries and comparison with the
main streams. This is especially true of the drainage in the arid region, where
the deep and pervious soils favor diffuse seepage as against definite spring flow.
2 Tourney (Yearbook U. S. Dep’t Agr. 1903) states that in the San Bernardino
mountains in southern California, the first rainfall (in December) was absorbed to
the extent of 95°/0 in forested areas, against only 60 °/0 in the non-forested ; but
THE WATER OF SOILS.
217
Sandy soils, especially when coarse, may absorb instantly even
a very heavy rainfall. Heavy clay soils when dry will at first
also absorb quickly quite a heavy precipitation ; but as the
beating of the raindrops compacts the surface, the absorption
quickly slows down, so that heavy downpours of brief dura¬
tion, while wetting thoroughly into a plastic mass the first two
or three inches of a clay soil, may leave all beneath dry, to be
very gradually moistened by the slow downward percolation
against the resistance of the air in the soil; while the greater
part of the later portion of the shower will drain off the surface
in muddy runlets. Certain soils classed as loams, having the
property of crusting readily by rain followed by sunshine (see
chapter 7, p. 1 1 1 ) , in heavy showers behave hardly better than
strong clay soils; shedding the water until the soaked crust
gives way, and is carried off in muddy streamlets. Then be¬
gins the cutting-away of the soil that, in portions of the Cotton
States, as well as north of the Ohio river, has been the cause
of extensive devastation of once fruitful culture lands, the site
of which is now marked by “ red washes ” and gullies but too
familiar to the eye in many regions, especially of the southern
United States.
Was king- aw ay and Gullying in the Cotton States. — Nowhere perhaps
have these effects been so severely felt as in portions of northwestern
and central Mississippi, and this case is so instructive as to deserve a
more detailed description. In the regions in question the soil stratum
consists of a yellow or brownish loam from three to seven feet in
original thickness, constituting a very desirable class of gently rolling
uplands, which at one time claimed to be the best cotton-growing
portion of the State. It was originally covered with an open forest of
oaks, with an abundant growth of grasses that afforded excellent pasture
to deer and cattle ; a natural park gay with flowers during most of the
season.
When these lands were taken into cultivation little or no attention
was paid to the direction of the furrows and rows of corn and cotton ;
that later, after the soil had been partially saturated, 6o°l0 only was absorbed in
the forested land, against 5°/0 in the non-forested. While it is generally admitted
that forests diminish the runoff, Rafter (Relation of Rainfall to Runoff, U. S.
Geol. Survey Paper, No. 80, p. 53) contends that in New York State the reverse is
true.
218
SOILS.
most commonly the plowing was done “ up-hill and down,” so that the
“ dead-furrow ” afforded a ready opportunity for the formation of washes
cutting into the subsoil, during the
torrential rains sometimes falling
during the summers. Even when
filled with soil by plowing, these
washes would frequently re-open
during rains, shedding the soil in a
muddy flood upon the lower lands.
The washing-away of the surface
soil, thus brought about, of course
diminished the production of the
higher lands, which were then com¬
monly “ turned out ” and left with¬
out cultivation or care of any kind.
The crusted surface shed the rain
water into the old furrows, and the
Fig. 40.— Erosion in Mississippi Table Lands, latter were quickly deepened and
causing destruction of agricultural value both of . . . . ... . . ,,
Uplands and Valleys. (McGee, 12th Ann. Rep.. Widened UltO gullies— “red Washes
u. s., 1890-91.) — whose presence rendered any
resumption of cultivation difficult. In the course of a few years the
soil-stratum of brown loam was penetrated into the loose or loosely
cemented sand which underlies it almost everywhere, and is very readily
Fig. 40a. — Erosion in Mississippi Table Lands, causing destruction of agricultural value both of
Uplands and Valleys. (McGee, 12th Ann. Rept. U. S. G. S., 1890-91.)
washed away. Soon the water, gaining yearly in volume, undercut the
loam stratum so as to cause it to “ cave ” into gullies in huge masses.
THE WATER OF SOILS.
219
which with the sand were carried into the valleys adjacent, filling the
beds of the streams so as to cause their flow to disappear under the
flood of sand. As the evil progressed, large areas of uplands were
denuded completely of their loam or culture stratum, leaving nothing
but bare, arid sand, wholly useless for cultivation; while the valleys were
little better, the native vegetation having been destroyed and only
hardy weeds finding nourishment on the sandy surface.
In this manner whole sections, and in some portions of the State
whole townships of the best class of uplands have been transformed
into sandy wastes, hardly reclaimable by any ordinary means, and
wholly changing the industrial conditions of entire counties ; whose
county seats even in some instances had to be changed, the old town
and site having, by the same destructive agencies, literally “ gone down
hill.” This destruction of lands was greatly aggravated by the civil
war, during which, and for some time after, large areas of lands once
under cultivation were left to the mercy of the elements.
Injury in the arid regions. — In the arid regions, where the
rainfall frequently comes in heavy downpours or “ cloud¬
bursts,” immense damage to pasture lands has been brought
about by overstocking, in Arizona and New Mexico; involving
the destruction of the natural cover of vegetation and the
loosening of the surface especially by sheeps after which a
heavy rainfall will carry off the surface soil, the muddy water
being gathered largely in the trails made by cattle going to
water. Thus gradually gullies are formed, which enlarging
more and more become ravines and cut up the pasture slopes
into “ bad lands,” useless equally for pasture and for agricul¬
ture.1 California, eastern Oregon and Washington, and Mon¬
tana, ofifer striking and lamentable examples of the same de¬
structive agencies.
Deforestation. — The deforestation of hill and mountain
lands has, the world over, led to similar results; causing not
only the destruction of pasture and agricultural lands, but also
the conversion of streams, flowing from springs and seepage
all the year, into periodic torrents, flooding the lowlands
during rains by the rapid running-ofif of the water from the
bare and hard-baked mountain slopes, and then running dry
1 Open Range and Irrigation Farming. R. H Forbes, in Forester, Nos. 7, 9,
1902.
220
SOILS.
within a short time, so as not even to afford drinking water to
pasturing cattle in summer. Thus for half a century the un¬
solved problem of the “ correction of the waters of the Jura
mountains” was before the Swiss and French governments;
and the great and costly public work involving re-forestation,
deflection of torrents and filling-in of deep ravines and gullies,
is not even yet nearly completed. In Spain, which in the time
of the Roman occupation was largely a forest country with
abundant rainfall, the same results are seen, notably in the
South, in the wide, and mostly dry, sandy beds of streams
once running deep and clear; and in the scarred hill-and moun¬
tain-sides, and scant vegetation of low shrubs (“chaparral”)
that replaces the once abundant tree growth, e. g., in Old and
New Castile. Unfortunately the lessons taught by the bitter
experience of the old world seem to require actual repetition
in the new, before means of prevention are even thought of.
Prevention of Injury to Cultivated Lands from excessive
Runoff. — The fundamental remedy for the injurious effects of
excessive runoff from the land surface is, of course, to facilitate
its absorption into the soil to the utmost extent possible, by
deep tillage; or in cases where this is undesirable (as when in
rainy climates excessive leaching of the land is feared), to so
direct and control the surface drainage that its flow shall no¬
where be so rapid as to carry with it any large amounts of
earth, or to wash out the furrows. To this end its fall must be
diminished by “ circling,” i. e., plowing nearly at right angles
to the slope instead of up-and-down, and on steep slopes especi¬
ally also by maintaining open furrows or ditches having a
gentle fall only, into which the water can shed and flow off
quietly in case the furrows, left in plowing, prove insufficient
to retain and shed gradually the water they cannot hold per¬
manently. The early adoption of this simple expedient would
have wholly prevented the enormous waste of fine agricultural
lands referred to above.
The underdraining of lands liable to washing is a costly but
highly effective means of preventing denudation; and the lay¬
ing of underdrains in gullies already formed, to prevent farther
deepening, is among the most obvious means of arresting
farther damage. The beneficial effects of underdrainage in
conserving moisture will be discussed farther on.
THE WATER OF SOILS.
221
ABSORPTION AND MOVEMENTS OF WATER IN SOILS.
The phenomena and laws of capillary ascent of water in
soils, as discussed in the preceding chapter, serve best to de¬
monstrate the general behavior of liquid water within differ¬
ent soils and their several grain-sizes ; because measurably in¬
dependent of the physical changes that almost unavoidably ac¬
company the percolation of water from above downward ;
whether such water comes in the form of rain, or irrigation,
or even when applied with the utmost precautions in the labor¬
atory. The “beating” of rains quickly compacts the surface
to a certain extent, varying with the nature of the soil, its con¬
dition of more or less perfect tilth, and the degree of violence
with which the rain strikes the surface. When the latter has
been compacted by a previous rain and then dried, “ baking ”
or incrusting the surface, the latter may almost wholly shed a
rain of brief duration, which, had the surface been loose, would
have been wholly absorbed, materially benefiting the crop.
Such surface-crusting is, therefore, injurious in preventing the
absorption of water from above; and in addition, it serves to
waste, by evaporation, the moisture contained in the under¬
lying soil and subsoil. For the crust being of a finer (single¬
grain) texture than the tilled portion beneath, it will forcibly
abstract from the latter, by absorption, its capillary moisture,
and evaporating it at the upper surface, continue to deplete the
land, to the great injury of crop growth, until destroyed by
cultivation.1
The flow of irrigation water produces the same compacting
effect, but to a less extent; the more as, unlike rain water, irri¬
gation water usually contains a certain amount of alkaline and
earth salts, which tend to prevent the diffusion of clay and of
fine sediments, and therefore the disintegration of the soil-floc-
cules into single grains. Nevertheless, it is in some soils as
necessary to cultivate after surface-irrigation as after rains,
in order to prevent great waste of moisture by evaporation.
Determination of rate of percolation . — When water is al-
1 This effect is well illustrated by the behavior of a dry brick laid upon a wet
sponge. It will quickly absorb all the liquid moisture contained in the latter,
while the sponge will be wholly unable to take any moisture from a fully-soaked
brick.
222
SOILS.
lowed to soak into an air-dry soil column without sensible shock
or motion, from a constant level, we obtain the nearest ap¬
proach to a definite determination of the relative permeability
of soils to water under the conditions usual in the arid region.
A number of determinations thus made is tabulated in the dia¬
gram given below, which embodies the observations made by
Mr. A. V. Stubenrauch 1 in connection with a more extended
investigation.
As these experiments were made with soils not in their field con¬
dition, but gently broken up with a rubber pestle, a standard of com¬
pactness was established by weighing the quantity which could con¬
veniently be settled into a tube space of ioo centimeters capacity by
tapping the sides and bottom of the tube, without touching the soil
itself. In this way the following standards were established : For the
University Adobe soil, 140 grams; for the Yuba loam soil, no grams;
for the Stanislaus sandy soil, 170 grams. Tubes 1^ inches wide were
used, and the soils were introduced in bulk, inside of a cylinder of stiff
paper upon which previously to rolling it up the soils had been thoroughly
mixed. After introducing the soil-filled paper roll it was gently with¬
drawn, leaving the soil column in the tube as uniform as before ; a con¬
dition almost impossible of fulfilment when the soil is introduced piece¬
meal. The tubes were, of course, left open at the lower end, using a
wire netting to keep the soil column in, so that the air could escape
freely before the descending water column.
The results thus obtained do not, of course, apply directly to the
same soils undisturbed in place in the field ; where, moreover, the air is
confined by the wetting of the surface and thus directly opposes pen¬
etration of the water. Still, they doubtless give a correct idea of their
relative permeability for water when in the tilled condition. The water
level was automatically maintained at the depth of half an inch above
the surface of the soil columns. Pore-spaces given are calculated from
volume-weight and specific gravity.
This diagram shows plainly that there is no direct relation
between the total pore-space in a soil and the facility of water-
penetration. The highest pore-space, in the fine-grained allu¬
vial loam, allows more rapid percolation than the heavy clay or
adobe soil, but is greatly exceeded by the coarser sandy soil.
In all it is very apparent that the downward movement slows
down as the water descends, doubtless because the great fric¬
tion in a longer column gradually diminishes the effect of hy-
1 Rep’t Calif. Exp’t Station for 1898 to 1901, p. 165.
Black Adobe,
42.83%
Pore space
THE WATER OF SOILS.
Loam,
57.36%
Porespace
223
Ins.
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FlG. 41. — Diagram showing differences in rates of percolation through different soils.
224
SOILS.
drostatic pressure. It may be presumed that at a certain dis¬
tance from the surface the downward movement becomes prac¬
tically uniform, and independent of the pressure from above.
Summary. — Two salient points are revealed by even a cur¬
sory inspection of the preceding diagram, viz. :
1. The downward percolation is most rapid in the same
soils in which the capillary ascent is quickest, that is, in the
coarse, sandy soil.
2. The rapidity of percolation decreases materially as the
wetted soil column increases in length.
The first point is readily foreseen and needs no comment. As re¬
gards the second, it results from the fact that as the wetted column
lengthens the frictional resistance increasingly counteracts the effects
of the hydrostatic pressure from above, until the water’s descent becomes
but little more rapid than would be its lateral diffusion, or its ascent at
the end of a similar column supplied by capillary rise from below. In
both cases the frictional resistance has so far counteracted the effect of
gravity that the capillary coefficients of the soil-material become the
controlling factors of the water movement.
Influence of Variety of Grain-sizes. — King (Physics of
Agriculture, pp. 159 ,160), compared the rapidity of the per¬
colation of water through definitely graded pure sands on the
one hand, and a sandy loam and a clay soil on the other. The
materials were arranged in 8-foot columns fully saturated with
water at the outset, and then allowed to drain freely. The
following abridged table shows the tenor of his results :
TABLE SHOWING RELATIVE RAPIDITY OF PERCOLATION IN PURE SANDS
AND SOILS, IN INCHES OF WATER DRAINED OFF.
Diameter of Uniform Sand
Grains.
First
30 minutes
Second
30 minutes.
Total
in one hour.
.475 mm.
10.25
4.68
M93
•155 “
5-67
4- 5 2
10.19
.083 “
1. 21
.85
2.06
First 21-
First 10
Second io
Total in
Soils.
23 hours.
days
days
about
tt
following.
following.
505 hours.
Sandy loam .
2.64
5-°7
.91
8.62
Clay loam .
1.96
2.1 1
•49
4.56
THE WATER OF SOILS.
22 5
This table is very instructive in showing- the great difference
in the rapidity of percolation in materials of uniform, even¬
sized grains, as compared with such as contain particles of
many different sizes, in which the interspaces of the larger ones
are filled more or less closely by the smaller sizes of particles
(see chapter 7, p. 109). While it is true that we have no defi¬
nite physical analysis of the soils here used, the differences are
so great as to be sufficiently striking. Compare the percolation
through the sand of .155 mm. uniform grain-size (a fine
sand), during the first half hour, with that through the sandy
loam during the first 21 hours. Twice as much water has
passed from the sand as from the soil in one forty-second part
of the time. Comparing similarly the finest sand, .083 mm. in
diameter, with the clay loam, we find the difference to be as
one to seventy-three. It is thus evident that but for the vari¬
ously assorted sizes of the soil-particles, water would not be
held long enough to supply plant growth.
Percolation in Natural Soils. — In artificial percolation ex¬
periments, as well as during a fall of rain, the gradual settling
of the fully wetted soil-column produces a compacting of that
portion of the mass, that increasingly impedes the downward
penetration. The effect of this under natural conditions is
readily seen in the fact that after the first, rapid absorption of
falling rain by the soil when in good tilth, there is a gradual
slackening of the process even when the rain is fine and slow,
causing a perceptible increase of the runoff until, should the
rain continue for some time, the absorption becomes so slow
as to cause all, or nearly all the water to drain off the surface.
The soil is then called “ saturated/’ having really arrived at
that point right at the surface, and to a depth varying accord¬
ing to the duration and amount of rain, and the natural per¬
viousness of the land.
When the rain ceases, the visible saturation of the surface
usually soon disappears in cultivated soils, and the zone of
saturation begins to descend. The progress of this descent
may be very strikingly observed in a series of holes (post-
holes) dug or bored across a ridge; as indicated in the sub¬
joined schematic diagram, in which the successive dotted lines
represent the levels of the descending “ bottom water ” at suc-
15
226
SOILS.
cessive intervals, as derived from the observation of the water
levels in the several holes.1
It will be seen that while at first the upper surface of the zone of
saturation coincides with the surface of the ground, in falling it
descends most rapidly on the highest ground, while at the lower levels
the holes may remain full or overflowing ; the drainage taking place
sideways as well as vertically. The curved surface connecting the levels
in the several holes gradually flattens, rapidly at first, then progressively
more slowly; the water disappearing entirely, first from the holes lying
highest, then successively from those at lower levels ; those located in
valleys or drainage channels remaining full until surface-water ceases to
run in such channels. But even after liquid water has ceased to be
visible in the holes, the descent of the water continues within that por¬
tion of the soil, tending (unless more rain should come before that time),
to establish the condition of equilibrium as existing in the soil columns
shown in the diagram on p. 205, chapt.i 1 ; such as results from the capil¬
lary ascent of water from below, but having above it a column of soil
of minimum water-content, of greater or less height according to the
length of time allowed for the water to descend. This is a very common
state of things during the long summer droughts in the arid region,
when neither rain nor irrigation has added to the water supply in the
soil for many months, and yet ordinary deciduous fruit trees mature
their normal crops. Frequently, however, before this state of equilibrium
is reached, evaporation from the surface so draws upon the water supply
within the first few feet, as to reduce the soil to undersaturation at the
lowest point of the descending column, so stopping farther descent and
soon reversing the direction of the movement. The latter is the usual
condition of scantily irrigated ground.
1 The exact record of these observations was unfortunately destroyed by fire
the soil was a heavy clay, and it took ten days before the water disappeared from
the lowest hole.
THE WATER OF SOILS.
227
Ground or Bottom Water, Water Table. — During and after
long-continued and abundant rains, the zone of supersatura¬
tion continues to descend until it finally reaches a more or less
permanent level, varying somewhat from season to season, but
on the whole usually definable for each region and locality;
being the depth to which wells must be sunk in order to secure
a fairly permanent water supply. This is called the water
table, ground water, bottom water, or “ first water.” 1 The
proportion of the rainfall that reaches the permanent water
level varies enormously, of course, in different soils and at
different times. With brief and moderate rains, in soils of
high water-holding power and slow percolation, it may never
reach the bottom-water level; this is very commonly the case
in the arid regions. Where, as in the humid regions, rains are
frequent or much prolonged, one half and even more may
finally reach the permanent level ; runoff and evaporation dis¬
posing of the balance.
Lysimeters. — For the determination of the amount of water percolat¬
ing to given depths, water-tight receptacles called lysimeters are usually
employed. The best way to establish such receptacles is to isolate a
unit-area (usually a square meter) by digging all around it to the depth
desired, then surrounding it with a metal sheet soldered tightly at the
cut edges, and finally driving in a sharp-edged, stiff metal sheet so as
to form the bottom when soldered to the upright walls ; leaving on one
side an outlet for the percolating water, which is then received into a
measuring receptacle somewhat like a rain gauge.
Hall (The Soil, p. 75) states that at Rothamstead, where an
average rainfall of 31.3 inches is distributed rather uniformly
through the season, and where the soil is a moderately clayey
loam, a little less than half percolates through 20 inches of
soil, and about 45% through 60 inches.
Surface of Ground Water; Variations. — The surface of the
1In contradistinction to other levels or “streams ” of water which may usually
be found lower down, separated from the first water by some impervious stratum
of clay, hardpan or rock, and very commonly under sufficient pressure to rise
somewhat higher than the point at which it was struck, owing to connection with
higher-lying sources of supply. When such pressure is sufficient to cause an
overflow at the surface of the ground, we have “ Artesian ” water as commonly
understood.
228
SOILS.
water table, however, is rarely level except in level and very
uniform ground, or after long periods of drought. The un¬
dulations of its surface conform, in general, to that of the
ground surface, but are less abrupt; so that the water lies
nearer to the surface in low than in high ground, as is indi¬
cated in the diagram above.
King 1 has shown, moreover, that the level of the ground
water shows sensible variations due to increased or diminished
barometric pressure, as well as to variations of temperature in
the soil, which cause the air in the pores to expand or contract
to a degree sufficient to bring about variations in the flow of
springs and underdrains to the extent of 8 and 15% respect¬
ively, in conformity with the daily changes of temperature
and pressure.
The Depth of the Ground Water most Favorable to Crops
cannot be stated in a general manner, as it depends materially
upon the nature of the crop, its root habit, and the nature of the
soil. As has already been said, the amount of soil-moisture
most favorable to plant growth is about half of the maximum it
can hold ; and this condition, as is shown in the table in chapter
11, p. 208, is reached about the middle of the maximum height
to which the water can rise by capillarity from the water level.
Below this point the access of air to the roots becomes too
limited, and in case of continuous rains the root-ends would
soon begin to suffer from want of aeration. On “ sub-irri¬
gated ” land, therefore, which is generally considered desirable,
crops must be carefully selected with respect to their root
habits. Thus while alfalfa needs considerable moisture to do
its best, its deep-rooting habit renders it undesirable when the
ground water is at less than five feet depth ; but red clover may
be grown even with the water level at three feet.
In clayey soils root-penetration is always less than in sandy
lands; and although in the former the capillary ascent of water
goes higher than in the latter, yet its movement in clays is so
much slower than in sandy materials that unless water is within
comparatively easy reach, the plants may suffer from drought.
Experience has long ago fixed the proper depth at which to
lay underdrains limiting the rise of bottom water, at from
three to four and a half or even five feet in clay soils; greater
1 Physics of Agriculture, p. 270.
THE WATER OF SOILS.
229
depths are only exceptionally used, partly because the laying
of drains then becomes too expensive.
A mass of four feet of clay-loam soil is commonly, then, con¬
sidered as sufficient to supply the needs of a crop ; it being
understood that in the humid region at least, such soils are
usually the richest in plant food, so that a deeper range of the
root system is not called for. It is quite otherwise in the sandy
soils of the same region, which being usually poor in plant
food, must afford a deeper penetration in order that an ade¬
quate amount of the same shall be within reach of the roots.
Sandy lands, then, should be deep in order to repay cultivation ;
and fortunately this is usually the case. But when this is
otherwise ; when for instance a sandy soil four feet in depth is
underlaid by impervious clay, underdrains may be quite as nec¬
essary as in the clay lands; since the depth of actually available
soil mass would otherwise be reduced to two or two and a half
feet only, by the water stagnating on the clay surface and rising
from 16 to 24 inches in the sand. Soils thus shallowed can
with difficulty be maintained in good productive condition even
by the most energetic fertilization.
Moisture supplied by tap roots. — In most cases, sandy lands
do not require underdraining; and in them, root-penetration
may reach to extraordinary depths in the case of certain plants,
especially when tap-rooted. Thus the roots of alfalfa (lucern)
are very commonly found to reach depths of twenty to twenty-
five feet, and even sixty feet has been credibly reported for the
same plant in the arid region. It is obvious that for such
plants, a high level of bottom water is wholly undesirable, since
they are enabled to obtain their moisture supply from great
depths, and can thus utilize for their nutrition much larger soil-
masses than can shallow-rooted plants.
Reserve of Capillary Water. — It must be remembered that it
is not only, nor usually, the bottom water that snpplies moisture
to plant growth ; for all soils of proper texture for cultivation
retain within them a certain amount of capillary moisture after
the ground water has reached its permanent level (see this
chap. p. 226), and when the tap or main roots are plentifully
supplied with water, the upper and chief feeding roots draw
but lightly upon the moisture within their immediate reach for
the purpose of leaf evaporation. This fact can be plainly ob-
230
SOILS.
served in the arid region, when on the advent of the summer
drought, young plantlets whose tap roots have reached a cer¬
tain depth continue to flourish and develop, while others prac¬
tically of the same age, but slightly behind, quickly succumb,
though the feeding roots of both may draw upon the same soil
layer. It is especially in sandy soils that moisture is naturally
thus conserved in the upper layers, because of the failure of the
water to rise by capillary ascent so as to evaporate from the
surface layer. It is often surprising to find a good amount of
moisture in the sandy soils of desert regions at the depth of
eight of eight or ten inches, when the surface is so hot as to
scorch the fingers ; and this moisture continues very uniformly
to great depths, probably to bottom water lying twenty or
more feet below the surface, which in such materials may
readily by reached by tap-rooted plants such as the “ sage¬
brush ” (Artemisia tridentata), the saltbushes (Atriplex) and
others.
Injurious Rise of Bottom Water resulting from Irrigation.
— In the deep, pervious sandy lands of the arid region, especi¬
ally where the rainfall is very low and can wet the soil annually
only to two or three feet depth, the substrata are sometimes
found to be barely moist to depths of thirty and forty feet,
and the short-lived spring vegetation carries off during its
growth all the moisture supplied by the winter rains. When
such lands are subjected to irrigation and the ditches carrying
the water are simply dug into the natural sandy land, the thirsty
soil absorbs the water greedily, so that even a considerable
volume of water makes but slow progress toward the farther
end of the canals. Gradually, as the rapidity of absorption
decreases, the diminution of flow becomes less sensible, but
still the loss thus experienced may be a very considerable per¬
centage of the whole supply. Thus in the Great Valley of
California, as well as in portions of Wyoming (Bull, 61, p.
32), the permanent loss from seepage is in the case of some
extensive irrigation systems estimated at fully 50 per cent.
When such lands have a considerable slope, the injury com¬
monly ends with the loss of the water, which in many cases is
again gathered and utilized at a lower level. But when the
lands have but a slight slope, the drainage may become so slow
as to permit of the gradual rise of the seepage water in the
THE WATER OF SOILS.
23I
substrata, until finally it may come to within a few feet of, or
actually to the surface.
Consequences of the Szvamping of Irrigated Lands. — The
injurious consequences of this swamping of the irrigated lands
may readily be imagined. The first effect is usually noted in
the sickening or dying-out of orchards and vineyards, conse¬
quent upon the submergence of the deeper roots, which in
such lands frequently reach to from fifteen to twenty feet be¬
low the surface. But even where pre-existing plantations are
not in question, the shallowing of the soil- and subsoil-strata
from which the plants may draw their nourishment, consti¬
tutes a most serious injury to the cultural value of the land.
It has become unsuited to deep-rooted crops; and where the
natural soil, alone, would have perpetuated fertility for many
years, fertilization becomes necessary within a short time.
The injury becomes doubly great when, as is frequently the
case, the rising bottom water brings up with it to the surface
soil the alkali salts which previously were distributed through¬
out many feet of substrata, frequently rendering profitable
cultivation impossible where formerly the most luxuriant crops
were grown.
Theoretically of course it is perfectly easy to avoid or rem¬
edy these troubles. It is only necessary to render the ditches
water-tight by puddling with clay, cement, or otherwise. But
the heavy cost of this improvement forms a serious obstacle
to its adoption by the ditch companies who are not themselves
owners of land. Thus, extensive areas of lands which when
first irrigated were among the most productive, have in the
course of eight or ten years become almost valueless to their
owners, to whom legislation thus far affords but distant prom¬
ise of relief ; although the case seems in equity to fall clearly
within the limits of the laws governing trespass.
Permanent Injury to Certain Lands. — In cases like those al¬
luded to the remedy usually available for higher ground-water
does not always afford relief, even when otherwise available.
Long-continued submergence produces in many soils effects
which cannot easily, if at all, be overcome by subsequent aera¬
tion. This is most emphatically true of soils containing a
large proportion of ferric hydrate in the finely divided form
in which it is usually present in “ red ” soils.
232
SOILS.
The first effect of the stagnation of water in such lands (as
already explained in a former chapter (3, p. 45) is to set up a
reductive (bacterial) fermentation of the organic matter of
the soil, transforming the ferric into ferrous hydrate, which
in the presence of the carbonic acid simultaneously formed, be¬
comes ferrous carbonate, readily soluble in carbonated water.
That this compound is poisonous to plant growth, has been
stated (chap. 3, p. 46). The carbonates of lime and magnesia
are simultaneously dissolved by the same, as is also calcic phos¬
phate, the usual form in which phosphoric acid is present in
the soil. Under the influence of partial aeration from the
surface, the ferrous carbonate is slowly re-transformed into
ferric hydrate, aggregated in the form of spots or concretions
of “bog ore” (see chapter 5, p. 66). In this process the
greater part of the phosphoric acid of the soil is also abstracted
from its general mass and concentrated in the bog ore (chap. 5,
p. 65), in which it is wholly unavailable to vegetation, and
cannot be made available while in the ground, by any known
process. The soil is therefore permanently impoverished in
phosphoric acid ; it is also deprived of its content of ferric hy¬
drate, and is transferred from the class of “ red ” to that of
“ white ” soils, well known everywhere to be unthrifty and to
require early fertilization. Not only is this true, because of
their almost invariable poverty in phosphoric acid, but also
usually in lime, which like the iron, if not leached out, is aggre¬
gated into concretions in the subsoil, leaving the surface soil
depleted of this important ingredient. The humus, also, is
either destroyed or at least “ soured ” at the same time.
Reduction of Sulfates. — Should such a soil contain any considerable
amount of sulfates, especially in the form of gypsum or calcic (or
magnesic) sulfate, the reductive process results in the formation of
iron pyrites (ferric sulfid, chap. 5, p. 75) ; while at the same time the
soil is often sufficiently impregnated with sulfuretted hydrogen as to
be readily perceived by the odor, or by the blackening of a silver coin.
This is very commonly the case in seacoast marshes, where a hole made
with a stick thrust into the mud will be found to give forth both car-
buretted and sulfuretted hydrogen, while a careful washing of the soil
will reveal the presence of minute crystals of iron pyrites. Hence the
need of prolonged aeration of marsh soils, effecting the peroxidation of
THE WATER OF SOILS.
233
the ferrous compounds, and the conversion of the pyrites first into
ferrous sulfate, and subsequently into innocuous, yellow, insoluble
ferric oxy-sulfate.
Ferruginous Lands. — The injurious effect of the swamping
of ferruginous lands has been especially conspicuous in some
of the irrigated rolling lands of the Sierra Foothills of Cali¬
fornia, where orchards planted in relatively low ground and
in full bearing have succumbed to the poisonous effects of the
ferrous carbonate formed in the subsoil, long before the water
had risen so high that, had the trees been grown afterwards,
they would have adapted their root system to the existing con¬
ditions and fared moderately well at least. Underdrainage of
the lower lands is, of course, the only possible remedy for this
state of things, although even then the root-penetration is much
more restricted, and therefore natural fertility of much
shorter duration, than would have been the case without the
rise of the irrigation water.
It is thus clear that in the practice of irrigation, the liability
of injury to the lower ground by “swamping’’ through the
rise of the ground water should always be kept in view ; that,
in fact, irrigation and provision for drainage should always go
hand in hand. The legal provisions facilitating the rights-of-
way for irrigation ditches should be made equally cogent with
respect to drainage.
CHAPTER XIII.
WATER OF SOILS ( Continued ).
THE REGULATION AND CONSERVATION OF SOIL MOISTURE.
In view of the commanding importance of an adequate
supply of water to vegetation, the possible and available means
of assuring such supply by utilizing to the best advantage both
rainfall and irrigation water, require the closest consideration.
Loosening of the Surface. — The first thing needful, of
course, is to allow the water free opportunity to soak into the
soil, so as to moisten the land as deeply as possible. That to
this end the surface should be kept loose and pervious by till¬
age, breaking up crusts that may have been formed by the beat¬
ing of rains, has already been discussed. In the case of heavy
clay soils, however, this alone is not always sufficient. The
most effectual way to loosen the land to greater depths than
can be reached by tillage, is by means of underdrains laid at
the greatest depth that is practically admissible.
Effects of Underdrains. — That drain tiles laid for the ex¬
press purpose of carrying off surplus water should help to con¬
serve soil moisture, seems at first sight to be a paradox. Yet
the explanation of the fact, which has been demonstrated by
long experience, is not difficult. The effect is most striking in
clay soils, for sandy soils are commonly naturally underdrained
already.
In discussing the changes of volume which soils undergo in
wetting and drying, the fundamental points in the premises
have already been mentioned (see chap. 7, p. 112). Clay soils
in drying shrink considerably, and re-expand on wetting, but
rather slowly ; moreover, some clays crumble when wetted
after drying, while others, very plastic when wet, crumble on
drying (see chap. 7, p. 116).
It follows that while a clay subsoil when kept permanently
wet, will form a uniform, pasty, difficultly penetrable mass :
234
THE WATER OF SOILS.
235
when subjected to frequent alternate wetting and drying, it
becomes fissured and crumbly, so as to resemble in its texture
a tilled soil. This frequent alternation of wetting and drying
is precisely what, in the course of time, is brought about by
underdrains; rendering clay subsoils pervious both to air and
water. The consequence is that even heavy rains can be fully
absorbed by the soil mass lying above the drains, the surplus
draining off readily in a short time. Roots therefore can not
only penetrate, but exercise their vegetative functions perfectly
at the full depth of the drains. They are still at liberty to pene¬
trate as much deeper as their demands for moisture may re¬
quire ; but the depth of four to four and a half feet is already
so much greater than in the humid region would usually be
reached by them in undrained clay soils, that commonly the
moisture successively retained within that mass is as much as is
required by them during the growing season. At the same
time, their feeding roots are so far below the surface, that
ordinary short droughts do not reach them at all ; while the
underdrains prevent any injurious stagnation of water around
them. It need hardly be added that the entire task of cultiva¬
tion is also greatly facilitated ; not only because drained soils
can be plowed within a few hours after the cessation of rains,
as against the same number of days that would have to elapse
in the undrained areas; but because tillage is easier, and less
draft is required, even when it is carried to a much greater
depth.
Underdrainage , then, must be counted as being among the
most effective means both of utilizing the rainfall so as to pre¬
vent loss from runoff and injury from washing, and of creat¬
ing a deep, loose, pervious soil mass, well adapted to root pene¬
tration as well as to the conservation of moisture; rendering
possible timely tillage and cultivation, and early development
of crops fully supplied with moisture and therefore secure
against loss from drought. The safety and improvement of
crops thus secured corresponds in the humid region to that
brought about by the command of irrigation water in the arid
countries. But it by no means follows that underdrainage can
therefore be dispensed with in the latter, or irrigation in the
former. Both have their proper place in both regions; but
from special causes underdrainage, as has already been stated,
SOILS.
236
should be widely used in irrigation countries to prevent the
injuries otherwise but too likely to arise from over-irrigation
(see chap. 12, p. 231 ).
Winter Irrigation. — In many regions where irrigation is
desirable but not absolutely necessary in ordinary seasons, or
where irrigation water is scarce in summer, much advantage
is gained by insuring thorough saturation of the land during
the latter part of winter, especially when spring or summer
crops are to be sown. The not inconsiderable time required
for water to reach its permanent level or the country drainage
in most soils, often insures the retention of a certain surplus
over what the soil can permanently hold, within the period
when it can be utilized by growing crops; whose roots more¬
over are more likely to penetrate deeply in land where there
is a steady increase of moisture as they descend, than when
the contrary condition is encountered. The use of winter
Hood-waters to saturate the land is therefore in many cases the
saving clause for a dry season.
METHODS OF IRRIGATION.1
The manner in which irrigation water is supplied to land
and especially to growing crops exerts such a potent influence
not only upon the welfare of the plants but also upon the condi¬
tion of the land, that a brief discussion of this topic seems
necessary.
The following methods are in use to a greater or less ex¬
tent :
1. Surface sprinkling.
2. Flooding.
A. By lateral overflow from furrows or ditches.
B. By the “ check ” system.
3. Furrow irrigation.
4. Lateral seepage from ditches.
5. Basin irrigation.
6. Irrigation from underground pipes.
1 Only a general outline of the principles of this subject is given in this volume;
special works must be consulted for working details. Among these the volume by
King on “ Irrigation and Drainage ” gives probably the most comprehensive
presentation of the subject for both humid and arid climates. Also bulletins of
the U. S. Dep’t of Agriculture.
THE WATER OF SOILS.
237
Surface Sprinkling. — This method seems to be the closest
imitation of the natural rainfall ; and yet it is in practice about
the most wasteful and least satisfactory of all. It is difficult of
application on any large scale, from obvious causes; on the
small scale, in gardens and on lawns, its disadvantages become
amply apparent. As usually practiced, from a rose spout or
spray nozzle, the water falls much more abundantly than in
the case of any desirable rain, within the short time allowed by
the patience of the operator. If continued for a sufficient
length of time to soak the soil to the desirable depth, it com¬
pacts the surface of the ground so as to render subsequent till¬
age indispensable. To avoid this, amateur gardeners usually
restrict the time of application, repeating the same at frequent
intervals, sometimes daily. The result is that the very slight
penetration of the water either fails to reach the absorbent
roots, so that it is of little use to them, and is evaporated
by the next day's sun or wind; or else it tends to draw the
roots close to the surface, where, unless the application of
water is actually made daily, they are sure to suffer from the
first intermission of the daily dose. In actual practice the
sprinkling method is therefore both inefficient and wasteful
of water, and exposes the plants to grave injury from any
cessation of the water supply.
Flooding presupposes land either level or only slightly slop¬
ing naturally, or rendered so artificially ; usually by means of
the plow and horse scraper.
Flooding by lateral overflow from large furrows, or ditches,
is very commonly practiced where the water supply is abundant
and large areas, such as alfalfa or grain fields, are to be irri¬
gated. The overflow is regulated by portable check-boards,
proceeding from the highest points to the lowest, and leaving
each temporary dike in place until the ground is adequately
soaked or the water reaches the next furrow below. In heavy
ground the operation may have to be repeated to insure proper
depth of percolation.
Check Hooding necessitates more careful leveling, and the
throwing up of small dikes, either temporary or permanent.
The costliness of the earth-work restricts the use of this
method materially, and the inconvenience caused in tillage by
238
SOILS.
the dikes is objectionable, especially in large-scale culture.
For the case of alfalfa fields, which remain permanently set
for a number of years, it is however the largely preferred
method. In the case of field cultures, the consolidation of the
surface that follows flooding on the heavier soils renders sub¬
sequent tillage necessary in all but very sandy soils; and hence
it should always precede broadcast sowing.
One disadvantage of the surface-flooding system is the slow
penetration of the water caused by the resistance of the air in
the soil to downward displacement ; its buoyancy acting di¬
rectly contrary to the percolation of the water. In close-
grained, heavy soils this objection is very serious, on account
of the loss of time involved when the irrigator’s time is limited.
On sandy lands the air bubbles up quite livelily at first, but this
soon ceases and the air is compelled to escape sideways as best
it can.
Furrow Irrigation. — By this method it is intended to soak
the land uniformly by allowing the water to flow through fur¬
rows drawn 3 to 8 feet apart, with a gentle slope from the
supply or head ditch ; the flow being continued until the water
has reached the far end of the furrows, or longer according to
the nature of the soil, especially if another ditch to receive the
surplus flow lies below. The furrows should subsequently be
closed by means of the plow or cultivator; but even if left
open they are much less a source of waste by evaporation than
would be a flooded surface. The water thus, in the main, soaks
downward and only reaches the surface by capillary rise, so
that the land between the furrows is not sensibly compacted
when the furrows have been made deep enough. Evidently
this is a much more rational procedure than surface flooding,
as it tends to leave most of the surface in loose tilth, while
penetrating to much greater advantage, because of the ready
escape of the air from the soil. It is the system naturally and
almost exclusively used in truck gardens and orchards, and
generally where crops are grown in drills or rows sufficiently
far apart to permit of cultivation.
The figure annexed 1 shows the manner in which water
sinks and spreads from furrows of various depths and widths,
1 Published by permission of the Department.
THE WATER OF SOILS.
239
Furrows 6 inches deep in Heavy Loam Soif
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Fig. 43. — Profiles of Water penetration in Furrow Irrigation.
240
SOILS.
as actually observed in the work of the Irrigation Division of
the U. S. Dep’t of Agriculture, under the direct supervision
of Prof. R. H. Loughridge of the California Station. The
mode of percolation is shown for two soils, a heavy loam and
a sandy one, both in the vicinity of Riverside, Cal.
The upper section shows the variation in penetration in one
and the same soil with the same kind of furrow, the broken
line indicating the cessation of the flow in the furrows; after
which there was a still farther penetration of the water to from
6 to 9 inches deeper.
The second section from above shows the percolation of the
water respectively in wide and narrow furrows of the same
depth. It is evident at a glance how much more effective is
the wide furrow in utilizing the limited time during which the
irrigator usually has the flow at his command.
The third section shows several practically important points
in favor of the wide and deep instead of narrow and shallow
furrow. It is seen that in doubling the width and depth, the
penetration has also nearly doubled. Moreover, it is seen that
in the deep furrow the water has not in the course of seven
hours reached the surface at all, being still six inches away; so
that in view of the diminishing ratio of capillary ascent, it
probably would not have reached the edge of the furrow, at
the surface, in less than thirty hours. Thus all surface evapo¬
ration, which oftentimes causes the loss of 50 % of the water
entering the shallow furrows, would be prevented ; and a dry
furrow-slice might be turned into the furrow immediately after
the cessation of the water-flow, effectually obviating the need
of subsequent tillage also. The cost of the latter, together
with the saving in water, and increased efficiency of the water
by deeper penetration, will much more than offset the addi¬
tional cost and trouble of plowing deeper furrows.
There is therefore every reason for doing away with the
wasteful, easy-going practice of irrigating in numerous shal¬
low furrows, by which the irrigator loses up to half of the
water paid for, by evaporation; is compelled to wait for the
soaked surface to dry before being able to turn back a furrow-
slice into the furrows to prevent the drying-out of their mois¬
ture; and by losing penetration of the water, is obliged to
THE WATER OF SOILS.
24I
irrigate again within a much shorter time than will be neces¬
sary if deep-furrow irrigation be used.
A similar experiment with deep and shallow furrows was
made at the Southern California station near Pomona in 1901,
as reported in Bulletin 138 of the California Station. The
results as far as they went were precisely similar, and upon
the basis of these the writer earnestly advocated deep-furrow
irrigation, and had the satisfaction of seeing it strongly
approved by orange-growers at Riverside and elsewhere, by
putting it into practice.
In addition to the saving and better utilization of the
water used, this mode of application has the advantage of
preventing the roots from coming too near the surface; it will
also largely eliminate “ irrigation hardpan ” or plowsole.
The results produced by long-continued shallow plowing and
irrigation in shallow furrows is well illustrated in the last of
the irrigation profiles, which shows the observations made on
the same land as the others, but where rational cultivation and
deep-furrow irrigation had not yet been introduced. It will
be seen that after applying, and of course paying for, the
water for three days, its average penetration was only about
eighteen inches ; so that the trees of the orchard received very
little benefit, and were supposed to be needing fertilization
when in fact they were simply suffering from lack of water
at the lower roots.
One somewhat unexpected point is shown by these dia¬
grams, viz., the slight sidewise penetration of the water; the
wetted areas having a nearly vertical lateral outline. This
means, of course, that unless the furrows run very near the
trees of an orchard, the soil immediately beneath the trees
will remain dry ; thus inducing the roots to spread sideways
and losing depth of penetration and soil. It will be noted
especially in the lower figure that here again the deep furrow
offers a material advantage over the shallow, the sidewise
spread being much more pronounced than in the shallow fur¬
row alongside.
Distance Between Furrozvs and Ditches. — The distance be¬
tween the furrows must, of course, be proportioned to the
readiness with which the water penetrates, being less as the
land is of closer texture. The distance between head ditches
1 6
242
SOILS.
must, on the contrary, vary in the opposite sense, since if these
are too far apart, the water near the head ditch will in sandy
lands be wasting into the subdrainage before the end of the
furrows is reached ; so that the distribution will be very un¬
even. The great differences observed between crops, and es¬
pecially trees, below and above the head ditches, are mainly due
to this unevenness in water distribution, caused by too great
distance between successive head ditches. Each farmer must
himself, however, determine by actual trial the proper dis¬
tances between ditches as well as furrows, for his particular
case; since everything depends upon the rapidity with which
water will penetrate the soil and subsoil. Actual tests to de¬
termine this point 1 should be the first step, before laying off
the system of ditches as well as furrows. It not uncom¬
monly happens that the failure to do this at first, compels a
subsequent total change of arrangements in this respect. (See
page 253 below).
Thus while in some very pervious land furrows may be six or even
eight feet apart, in other cases, in certain finely pulverulent or silty
soils such as the “ dust soils ” described in a former chapter ; (see chapter
6, p. 104), furrows drawn three feet apart may fail to allow the water to
penetrate so as to prevent grain on the middle foot from suffering from
drought after the water has run for twenty-four hours.
Irrigation by lateral Seepage. — Is in reality a mere modifi¬
cation of furrow irrigation, practiced in the case of lands very
readily permeable, and where water is abundant. The fields
are laid off in “ lands ” twelve to twenty-five feet wide, with
a deep furrow or narrow ditch between, from which water
percolates in a short time so as to overlap from the two sides.
In this case sometimes the water does not reach the surface
visibly at all; a very great advantage where alkali exists, as
surface evaporation, and the consequent accumulation of
alkali, is thus effectually prevented; while deep rooting is
favored to the utmost.
1 Such tests can be readily made by any one, by digging a pit to four or five feet
depth, and supplying water to a shallow basin dug into the surface 8 to 12 inches
distant from the vertical wall of the pit. The descent of the water is then readily
observed on the vertical side of the pit nearest to the water basin. Preliminary
tests with soil probe (see chap. 10, p. ) 1 77.
THE WATER OF SOILS.
243
Basin Irrigation. — In this method of irrigation, practiced
only in the case of trees and sometimes vines, and when water
is scarce, a wide circular furrow or basin is excavated around
each trunk and water is run either from one to the other, or
sideways from a furrow laid along the rows. The water
thus applied of course percolates immediately around the trunk
first, and in practice is found to follow also the large roots;
so that it goes precisely where it is most wanted, besides form¬
ing a vertical body of moist soil reaching to considerable depth,
where it is most desirable that the root system should follow.
By this deep penetration to natural moisture in the depths of
the soil, comparatively small quantities of water produce very
marked effects.
On the same principle, the grape vines which bear some of
the choicest raisins of Malaga on the arid coastward slopes,
are made to supply themselves with moisture, without irriga¬
tion, by opening around them large, funnel-shaped pits, which
remain open in winter so as to catch the rain, causing it to
penetrate downward along the tap-root of the vine, in clay
shale quite similar to that of the California Coast Ranges, and
like the latter almost vertically on edge. Yet on these same
slopes scarcely any natural vegetation now finds a foot-hold.
Similarly the “ ryats ” of parts of India water their crops
by applying to each plant immediately around the stem such
scanty measure of the precious fluid as they have taken from
wells, often of considerable depth, which form their only
source of water-supply. Perhaps in imitation of these, an in¬
dustrious farmer has practiced a similar system on the high
benches of Kern River, California, and has successfully grown
excellent fruit for years, on land that would originally grow
nothing but cactus. Sub-irrigation from pipes has been applied
in a similar manner.
A combination of the furrow- and basin-irrigation system is
sometimes practiced in southern California by drawing the
furrow so as to bring the tree within a square, one side of
which is left closed. The same result may be accomplished
by plowing cross furrows at right angles near the tree and
then placing checkboards so as to force the water along the
rows, zigzagging, on three sides.
The basin irrigation of orchards was originally largely
244
SOILS.
practiced in California, but has now been mostly abandoned
for furrow irrigation. The latter has been adopted partly
because it requires a great deal less hand-labor, partly under
the impression that the whole of the soil of the orchard is thus
most thoroughly utilized; partly also because of the injurious
effect upon trees produced at times by basin irrigation.
The explanation of such injurious effects is, essentially,
that cold irrigation water depresses too much the temperature
of the earth immediately around the roots, and thus hinders
active vegetation to an injurious extent, sometimes so as to
bring about the dropping of the fruit. This of course is a
very serious objection, to obviate which it might be necessary
to reservoir the water so as to allow it to warm before being
applied to the trees.1 In furrow-irrigation the amount of
soil soaked with the water is so great that the latter is soon
effectually warmed up, besides not coming in contact too in¬
timately with the main roots of the tree ; along which the water
soaks very readily when applied to the trunk, thus affecting
their temperature much more directly. It is for the farmer to
determine which consideration should prevail in a given case.
If the water-supply be scant and warm, the most effectual use
that can be made of it is to apply it immediately around the
tree, in a circular trench dug for the purpose. When on the
contrary, irrigation water is abundant and its temperature low,
it may be preferable to practice furrow irrigation, or possibly
even flooding.
As to the supposed more complete use of the soil under the
latter two methods, it must be remembered that while this is
the case in a horizontal direction, if irrigation is practiced too
copiously under the shallow-furrow system, it may easily hap¬
pen that the gain made horizontally is more than offset by a
corresponding loss in the vertical penetration of the root-
system. This is amply apparent in some of the irrigated
orange groves of southern California, where the fine roots of
the trees fill the surface soil as do the roots of maize in a
corn field of the Mississippi States ; so that the plow can hardly
be run without turning them up and under. In these same
orchards it will often be observed, in digging down, that at a
depth of a few feet the soil is too water-soaked to permit of
1 See below, chap. 17.
THE WATER OF SOILS.
245
the proper exercise of the root-functions, and that the roots
existing there are either inactive or diseased. That in such
cases frequent irrigation and abundant fertilization alone can
maintain an orchard in bearing condition, is a matter of
course; and there can be no question that a great deal of the
constant cry for the fertilization of orchards in the irrigated
sections is due quite as much to the shallowness of rooting
induced by over-irrigation, as to any really necessary exhaus¬
tion of the land. When the roots are induced to come to and
remain at the surface, within a surface layer of eighteen to
twenty inches, it naturally becomes necessary to feed these
roots abundantly, both with moisture and with plant-food.
This has, as naturally, led to an overestimate of the require¬
ments of the trees in both respects. Had deep rooting been
encouraged at first in the deep soils of the southern “ citrus
belt,” instead of over-stimulating the growth by surface fer¬
tilization and frequent irrigation, some delay in bearing would
have been compensated for by less of current outlay for fer¬
tilizers, and less liability to injury from frequently unavoid¬
able delay, or from inadequacy, of irrigation.
Irrigation b\ Underground Pipes. — Where economy in the
use of irrigation water is a pressing requirement, its distribu¬
tion through underground pipes affords the surest mode of
accomplishing that end, in connection with the application of
the water in accordance with the principles just discussed.
The enormous saving of water effected by its conveyance in
cement-lined ditches or concrete pipes, as compared with earth
ditches, if additionally combined with its application to in¬
dividual trees or vines, presents the maximum of economy
that can be effected. The actual use of this method is unfor¬
tunately limited in practice by the high first cost of piping;
but as its use renders unnecessary the digging of basins and
plowing of furrows and their subsequent closing-up, it is when
once established by far the cheapest system, both as to the use
of water and of labor.
\
The best results of this system are undoubtedly achieved by the
use of iron pipes for the distribution in field and orchard, whatever may
be the material used for the main conduits. The use of concrete and
tile in small sizes proves in the end very expensive, because of frequent
246
SOILS.
breakage, and leakage due to varying pressure in the supply pipes or
reservoirs ; as well as from even slight earthquake tremors, undermining
by water or by the burrowing of animals, and many other accidents
which do not affect an iron pipe system. The pipes must in any case,
of course, be laid deep enough to be out of reach of the deepest tillage ;
therefore not less than one foot, and preferably eighteen inches. A
proper construction of the outlets, permitting of exact regulation of the
flow and ready operation from above ground, as well as preventing
their being clogged by earth, rust, roots or burrowing animals, insects
etc., is of course of the greatest importance. A variety of devices for
this purpose is already on the market.
QUALITY OF THE IRRIGATION WATER.
Saline Waters. — Considering the large amount of water
annually used in irrigation, among the most needful precau¬
tions to be observed by the irrigator is in the testing of the
quality of his water-supply. First among the points to be
noted is the possible content of soluble “ alkali ” salts. While
in most cases what is called the “ rise of the alkali ” is due to
the salts already contained in the soil and subsoil, in but too
many the evil is either brought about, or greatly aggravated,
by the excessive saline contents of the water used in irrigation.
The effects of the use of saline irrigation water (containing
in this case about ioo grains per gallon, or 1700 parts per
million) are shown in the accompanying plate. The predom¬
inant ingredients of these alkali salts were common salt and
carbonate of soda. In the lands near Corona, Cal., where this
case was observed, the original alkali-content of the soil was
about 2500 pounds per acre in four feet depth, and had been
just quadrupled, with the results shown; viz., complete de¬
foliation of the orange trees, while on the same land, where
the trees had been irrigated with good artesian water, the
orchard was in fine condition.
Limits of Salinity. — It is not easy to assign a definite limit
of mineral content beyond which water should be considered
unfit for irrigation purposes ; partly because of the differences
in the kind of the mineral salts, partly because the nature of
,the soil and the amount of water at command, materially in-
.ffuence its availability.
Fig. 44. — Orange Trees Irrigated with Artesian Water. Fig. 45. — Lake Elsinore Water, Three Years.
THE WATER OF SOILS
247
248
SOILS.
Forty grains per gallon is usually assigned as the limit for
potable as well as irrigation waters. But if most or the whole
of such mineral contents should consist of the carbonates and
sulfates of lime and magnesia, the water while unsuitable for
domestic use may be perfectly available for irrigation, since
these salts are either beneficial or harmless in the amounts
likely to be introduced by the water. But if most or the whole
of such forty grains should consist of “ alkali salts ” proper,
viz., the sulfates, chlorids and carbonates of potash and soda,
or if they should contain even small amounts of the chlorid
and magnesium, they might render the water either wholly
unsuitable for irrigation, or if used it would be needful to
take the mineral content into consideration, by regulating its
application accordingly.
It has been found in California that practically the upper
limit of mineral content for irrigation water under the ordinary
practice lies below seventy grains per gallon in all cases; for
when this strength is reached, even though such water may
bathe the roots of almost any plant with impunity, yet acci¬
dental concentration by evaporation is so certain to happen,
that injury to crops is practically almost unavoidable.
In South Dakota and other parts of the American semi-arid region,
waters containing seventy grains and even more of alkali salts per
gallon are annually used during the short irrigation season. This can
be done harmlessly because the aggregate amount used is only small,
and the more abundant rainfall of that region annually washes the salts
out of the soil. But where almost the full amount of water required
by crops must be supplied by irrigation, the total amount of salts thus
introduced would speedily render the land uncultivable.
According to the observations of Means and other explo¬
rers 1 of the U. S. Dep’t of Agriculture, waters of much
higher mineral content are used for irrigation both in Egypt
and in the Saharan region, some going as high as 8000 parts
per million, or 214 grains per gallon. The cultivators are
said to be very skilful in the use of these waters, applying
them only to plants of known resistance, and in certain ways.
These ways include doubtless a good deal more time and pa-
1 Bull. No. 21, Bureau of Soils ; also circular No. 10, ibid.
THE WATER OF SOILS.
249
tience than American irrigators are ordinarily willing to be¬
stow upon their work. Much depends of course not only
upon the character of the salts in the water, but also upon the
long experience had in the old irrigation regions.
Mode of using Saline Irrigation Waters. — The fact that
abundant growths of native as well as cultivated plants may
sometimes be seen on the margins of “ alkali lakes ” where
water of over a hundred grains of mineral salts per gallon
continuously bathes the roots, while the same plants perish at
some distance from the water’s edge, points the way to the
utilization, in emergencies, of fairly strong saline waters; viz.,
by the prevention of their concentration to the point of injury
by evaporation. It is clear that when such waters are used
sparingly, so as to penetrate but a few feet underground,
whence the moisture re-ascends for evaporation at the surface,
a few repetitions of its use will accumulate so much alkali near
the surface as to bring about serious injury. If, on the other
hand, the water is used so abundantly that the roots may be
considered as being, like the marginal vegetation of alkali
lakes, bathed only by water of moderate strength, no such in¬
jury need occur; and what does accumulate in consequence of
the inevitable measure of evaporation occurring in the course
of a season, may be washed out of the land by copious winter
irrigation.
This, of course, presupposes that the land, as is mostly the
case in the arid region, is readily drained downwards when a
sufficiency of water is used. Alien this is not the case, e. a.,
in clay or adobe soils, or in those underlaid by hardpan, waters
which in sandy lands could have been used with impunity, may
become inapplicable to irrigation use.
Apparent Paradox. — The prescription to use saline waters
more abundantly than purer ones, in order to avoid injury
from alkali, though paradoxical at first sight, is therefore
plainly justified by common sense as well as by experience, in
pervious (sandy) soils; while in difficultly permeable ones,
their use may be either wholly impracticable, or subject to
very close limitation.
Sometimes the alternate use of pure and salt-charged water
serves to eke out a too scant supply of the former. But in
250
SOILS.
all such cases, close attention to the measure of water that will
wet the soil to a certain depth, and “ eternal vigilance ” with
respect to the accumulation of alkali near the surface, must be
the price of immunity from injury. In all cases the farmer
should know how much of alkali salts he introduces into his
land with the irrigation water, and watch that it does not ap¬
proach too closely, or exceed, the tolerance of his crops for
alkali salts, as given in chapter 26.
Use of Drainage Waters for Irrigation . — When lands
charged with alkali salts are being reclaimed by drainage, the
question sometimes arises whether the drainage-water may not
be used for irrigation, lower down. This of course depends
entirely upon the amount of alkali in the water, the nature of
the lands to be irrigated, and the manner of applying it. In
the Fresno drainage-district of California it has been shown
that some of the drainage-water contains not more than 25 to
30 grains per gallon of objectionable salts, and such waters
could of course be used on pervious lands with the precautions
above noted.
“ Black Alkali ” Waters. — As regards, however, waters con¬
taining any large proportion of carbonate of soda, it must be
remembered that even very dilute solutions of salsoda serve
to puddle the soil and thus render it difficultly tillable. When
such waters are used it is necessary to forestall injury either
by the use of gypsum in the reservoir or ditch, or by annually
using on the land a sufficient amount of gypsum to transform
the carbonate of soda into the relatively innocuous sulfate.
Variations in the Saline Contents of Irrigation Waters. — -
When irrigation waters are derived from deep wells, there is
little if any variation of their saline contents to be expected,
and a single analysis will serve permanently. But in the case
of relatively shallow wells, from which the water must be
raised by pumping, it not unfrequently happens that after a
series of seasons of short rainfall, saline waters are brought
up by the pump and may seriously injure crops and orchards.
Again, in the case of streams and rivers whose flow becomes
very small in summer, the saline content may increase to sev¬
eral times the amount carried at the time of high water.
Both kinds of cases occur in southern California, in Arizona,1
1 Bull. Ariz. Exp’t Sta. No. 44.
THE WATER OF SOILS.
251
New Mexico and other states of the arid region. The Gila,
Pecos and upper Rio Grande are cases in point, and to a cer¬
tain extent the Colorado of the West.
Muddy Waters. — In the latter as well as other streams of
Arizona, there is another point which sometimes creates diffi¬
culties to the irrigator, together with some current expense.
It is the amount of silt or mud carried by the water, which
while it is a benefit to the land over which it is spread, (“ warp¬
ing ") as in the classic case of the Nile, often clogs the irriga¬
tion ditches to such an extent as to cause considerable incon¬
venience and expense in cleaning them out. This is especially
the case in the streams draining pasture lands that have been
overstocked, and where the destruction of the natural herbage
allows the rain water to run off rapidly, at first forming run¬
lets and then gullies and ravines that originally were simply
cow-paths leading toward the watering places.1 The devasta¬
tion of lands thus caused in Arizona is almost as great as that
which has occurred in the Cotton states, as mentioned above
chap. 12, p. 217.
These variations in the character of the irrigation water
must of course be watched by the farmer who does not receive
directly from mountain streams, or from deep artesian wells
water known to have a constant content of saline matter.
The duty of irrigation water. — The amount of water
thought to be needed for the production of satisfactory crops
varies widely in different regions, ranging all the way from
about two feet to as much as eight annually, within the United
States; while in the sugar-cane fields of the Hawaiian Islands
as much as three inches per week, or over twelve acre-feet in
the course of the year, have been thought to be beneficial, if
not absolutely required for the best crop results.
As has been stated above (chap. 12, p. 215), the rainfall
limit below which irrigation becomes, if not absolutely essen¬
tial, at least a highly desirable condition for the safety of
crops, is usually assumed to lie at about 20 inches (500 mili-
meters). This general statement is, however, subject to ma¬
terial modification according to the manner in which the rain¬
fall is distributed. Thus in central Montana with 24 inches
of rainfall distributed throughout the year, irrigation is indis-
1 Bull. Arizona Exp’t Station Nos. 2, 38.
25 2
SOILS.
pensable; while in the Santa Clara valley of central California,
with an average rainfall of 15 inches falling through the
winter and spring, the growth of all ordinary field crops has
for fifty years not failed oftener than is commonly the case in
the humid region of the North Central states. This is be¬
cause in California the winter and spring are the growing sea¬
sons, while the rainless summers do not stand in the way,
for crops are already harvested ; and the deep rooting of trees
and vines provides these with the needful moisture from the
depths of the substrata (see chap, io, pp. 163 to 173).
It would thus seem that twenty inches of irrigation water
properly applied ought to be sufficient for all purposes, when
added to the natural rainfall, which is rarely entirely absent.
Yet in actual practice less than 24 acre-inches is rarely used,
and much more is the rule ; 72 to 96 ins. being sometimes used
in Arizona. Evidently enormous losses occur in practice, and
it is of the utmost importance to discover the causes of these.
Causes of Loss. — Since irrigation water is commonly mea¬
sured at the distributing weirs, loss from seepage and evapora¬
tion on the way to the fields is an obvious source of an over¬
estimate of the water actually supplied to the farmer. In
sandy districts the loss thus incurred is reliably estimated at
nearly 50% in many cases. The apparent duty of the water
is thus at once reduced to half its effect, and four instead of
two feet of water are supposed to have been used, and are
charged for.
Evaporation resulting from surface flooding or use in shal¬
low furrows may, again, cause the loss of from 30 to 50%
of the water that actually reaches the land ; so that in the lat¬
ter case, between seepage and evaporation the irrigator may
lose the effect of three-fourths of the water he pays for.
Loss by Percolation. — Finally, the water may be wasted on
the land itself in leachy soils by over-use, i. e., it may percolate
to a large extent beyond the reach of the roots when the flow
is continued too long; as will always be the case when the
head (supply) ditches are laid too far apart, so that the water
may be wasting into the country drainage just below the upper
ditch long before the water in the furrow reaches the lower
one; as illustrated in the upper one of the subjoined diagrams.
THE WATER OF SOILS.
253
That this will not happen when the head ditches are nearer
together, is shown in the lower diagram.
Figs 46, 47. — Diagram showing loss by percolation when head ditchers are too far apart.
The means of avoiding the mechanical losses have already
been discussed, and may be summarized thus : tightening of
leaky ditches; use of water in deep furrows; and ascertaining
the rapidity of percolation (see p. 242) so as to obtain a
proper gauge for the time during which water should run, and
for the distances at which head ditches or furrows should be
placed.
The importance of thus diminishing the losses of water is
obvious when it is considered that if the duty of water can be
reduced to twenty instead of forty or fifty acre-inches, twice
the area can be irrigated with the same amount of water, or
the cost of water correspondingly reduced. It should be noted
that when the land is leachy it may be pure waste to continue
the flow beyond a few hours ; but the irrigation must then be
more frequently repeated.
EVAPORATION.
Alongside of and supplementary to the best possible utiliza¬
tion of the rainfall and irrigation water, the prevention of un¬
necessary evaporation has to be considered. Evaporation
from the soil’s surface .implies not only unnecessary loss of
water that should have remained for the use of the crop, but
254
SOILS.
also the depression of temperature which, as a rule, is un¬
favorable to the best development of vegetation. It is only
in case of extreme stress from hot, drying wind that such
evaporation and the consequent depression of the temperature
of the surface soil can be of advantage to the farmer.
The amount of water evaporating either from a water-sur¬
face, or from a wet or moist soil, varies greatly according to
the climatic conditions, and the state of the weather; also ac¬
cording to the condition of the soil-surface. There are damp
climates, and days or periods when, the air being nearly sat¬
urated with moisture, evaporation even from a water-surface
will be almost insensible. On the other hand, with dry air
and a high temperature, enormous quantities of water may be
evaporated in the course of a day. The evaporation from
water-surfaces interests deeply those who supply, as well as
those who are supplied with, water from storage reservoirs;
evaporation from the soil-surface interests deeply all farmers,
and more especially irrigators whose water-supply is scanty,
or is paid for by them by measurement. Light rains, as well
as light surface irrigations, may at times evaporate almost
wholly without any effect save a lowering of the temperature
of the soil. In the case of snow, it is a well-known fact in
the northern arid regions that a light snowfall may in winter
evaporate entirely without imparting any liquid moisture to
the soil. A loss of 50% of the water actually brought upon
land by surface irrigation is of common occurrence in some
portions of the irrigated region.
The dependence of evaporation upon air-temperature under
conditions otherwise identical, is well illustrated by the ex¬
periments made in 1904 by S. Fortier 1 on the Experiment
Station grounds at Berkeley, California, at a time when un¬
der the influence of the sea breeze the average saturation of the
air might be assumed at about 70%. The tests were con¬
ducted in six tanks sunk into the ground so as to place the
water-surfaces on a level with it, and the water-temperatures
were maintained in four of the tanks by means of ice or heat¬
ing lamps. The results are shown in the following table :
1 Progress Report on Cooperative Irrigations in Calif.; Cir. No. 56, Office Exp’t
Stations.
THE WATER OF SOILS.
255
SUMMARY OF AVERAGE WEEKLY LOSSES BY EVAPORATION, WITH VARYING TEM-
PERATURES OF WATER, AT BERKELEY, CAL., IN JULY AND AUGUST, I904.
Temperature of water.
Weekly
evapora¬
tion.
Degrees Fahrenheit:
55-5 .
62.0 .
69.2 .
80.1 .
89.2 .
Inches.
0.42
0.77
i-54
3.08
3-92
A farther illustration is given in the subjoined table, show¬
ing maxima and mimima of monthly evaporation, as well the
totals of one (seasonal) year, in three California localities
where the air-saturation is considerably below that at Berkeley,
ranging in summer from 50% to 20% and even less (at
Calexico in the Colorado desert) :
SUMMARY OF EVAPORATION-LOSSES FROM WATER-SURFACES, AT POMONA, TULARE,
AND CALEXICO, CAL., FROM JULY I, I903, TO JULY 3 1, I904.
Pomona.
Tulare.
Calexico.
Month.
Inches.
Month.
Inches.
Month.
Inches.
Maximum .
Minimum .
Totals for year. . .
Aug. 1903
Feb. 1904
Q.07
2-57
66.92
July 1903
Jan. 1904
12.34
1.46
74.68
July 1903
Jan. 1904
14.48
4-39
108.23
Of these three stations, Pomona is located within reach of
the ocean winds, but distant 25 to 30 miles from the shore.
Tulare is situated in the upper San Joaquin valley, far in the
interior; Calexico is in the southern part of the Colorado
desert, with extremes of temperature ranging from 130 Fahr.
in winter to 1200 in summer.
Evaporation in Different Climates. — The following table
conveys some general data regarding average evaporation from
water-surfaces in different climates. Evaporation from the
soil-surface depends largely, of course, upon the mechanical
condition of the surface, the extent to which it is wetted, and
256
SOILS.
the rapidity with which moisture will be supplied from the
subsoil as the surface dries. A field plowed into rough fur¬
rows will evaporate more water than when harrowed, because
of the larger surface exposed ; and a harrowed field moderately
compacted by rolling will lose less water by evaporation than
when un-rolled, other things being equal. On the other hand,
a thoroughly compacted surface, even if suffering less loss at
first than a plowed or harrowed field, will continue to lose
moisture longer by withdrawing it from the substrata by its
superior capillary suction ; while a loose surface, once dried
out, will prevent farther loss from the subsoil very effectually,
as stated below.
TABLE SHOWING EVAPORATION, FROM WATER-SURFACE EXPOSED IN SHALLOW
TANKS, NEAR WATER OR GROUND SURFACE.
Years.
Inches.
Rothamsted, England . . .
9
17.S0 (16.6 to 1S.4)
London, “ . . .
14
20.66
Oxford, “ . .
5
3i-°4
Munich, Germany .
?
24.00
Emdrup, Denmark .
10
27.09
Cambridge, Massachusetts .
1
56.00
Syracuse, New York .
1
50.20
Logan, Utah . .
1
52-39
Tucson, Arizona .
1
75.80
Fort Collins, Colorado .
11
41.00
Fort Bliss, Texas. . . .
San Francisco, California . .
1
82.70
45 to 50
57-6
Sweetwater Reservoir, San Diego, California.
1
Peking, China .
?
38.80
Demerara, South America .
35-12
82.28
Bombay, Fast India . .
5
Petro- Alexandrowsk, West Turkestan .
?
96.40
Kimberley, South Africa .
?
98.80
Alice Springs, South Australia .
?
103.50
This table, the data for which are taken from various
sources, exhibits clearly the enormous variations in evapora¬
tion in different countries, and even in localities not very re¬
mote from each other. The low evaporation near London is
doubtless due to its foggy and hazy atmosphere, but it is not
clear why Rothamsted should show so low an evaporation
compared with Oxford. Tropical Demerara stands nearest to
Oxford in its evaporation; Bombay indicates its location on
THE WATER OF SOILS.
257
the hot and arid west coast of India, despite its nearness to
the sea. The inland localities in the desert regions of South
Africa, Australia and Western Turkestan, show how enormous
may be the losses from evaporation of irrigation water, unless
the latter is applied with special care for their prevention.
Thus, with the wasteful methods of irrigation prevailing in
portions of the American arid region, it is certain that in
many cases 50% and more of the water evaporates before it
reaches the crops.
Evaporation from Reservoirs and Ditches. — The evapora¬
tion from water-surfaces especially may, in many cases, ex¬
ceed the rainfall of the year, so as to materially diminish the
available water-supply in reservoirs. Thus the annual evap¬
oration from the reservoir-lakes forming part of the water-
supply of the city of San Francisco, ranges from 40 to 50
inches, while the rainfall averages less than 24 inches. Were
it not, then, for the prevention of evaporation hv a covering of
dry earth during summer, no moisture would remain in the
ground to sustain vegetation. In the cool coast climate of
Berkeley, Cal., directly opposite the Golden Gate and subject
to its summer fogs, evaporation from a water-surface main¬
taining, the average climatic temperature of 6o°, was found
to be inch during the month from the middle of July to the
middle of August, 1904. But at the high temperatures and
low degree of air-saturation prevailing in the great interior
valley, or in the Colorado desert, the evaporation from water-
surfaces is enormously increased, exceeding even the figure
given in the table for Bombay. Hence the great importance of
preventing all avoidable evaporation, particularly in the use of
irrigation water.
Prevention of Evaporation ; Protective Surface Layer. — The
loose tilth of the surface which is so conducive to the rapid
absorption of surface-water, is also, broadly speaking, the best
means of reducing evaporation to the lowest possible point.
For while it is true that the floccules of well-tilled soil permit
of the ready access of air, and therefore of evaporation, it is
also true that these relatively coarse compound particles are
incapable of withdrawing capillary moisture from the denser
soil or subsoil underneath; just as a dry sponge is incapable
17
258
SOILS.
of absorbing any moisture from a wet brick, while a dry
brick will readily withdraw nearly all the water contained in
the relatively large pores of the sponge (see chap. n). A
layer of loose, dry surface-soil is therefore an excellent pre¬
ventive of evaporation of the moisture from soils, and may
be regarded as the natural and most available means to be
used by the farmer, both for the prevention of evaporation
and to moderate the access of excessive heat and dryness to
the active roots.
As regards the desirable thickness of this protective layer
of tilled surface-soil, it should be kept in mind that in the
humid region, where rain can be expected at intervals of from
one to three weeks, the feeding roots may usually be found
within a few inches of the surface ; while in the arid region,
where irrigation is practiced at long intervals or sometimes
not at all, so that no water enters the soil oftener than from
two to six months, the roots necessarily vegetate at lower
depths, and hence the protective surface-layer can, and should
be, of greater thickness, to prevent the penetration of excessive
heat and dryness during the long interval.
The failure to appreciate this necessary difference often
leads to heavy losses on the part of newcomers to the arid
region, who in this as in other respects are apt to follow
blindly the precepts familiar to them in the East, until taught
better by sore experience. In the East and Middle West a
depth of three inches is considered the proper one for the pro¬
tective surface-layer; and in the case of maize even this is
considered excessive in many cases. In the arid region this
depth should be at least doubled where irrigation is not prac¬
ticed at least every four to six weeks ; and in some sandy soils
even seven and eight inches is not too much for effective
protection.
Illustrations of Effects of Surface Tillage. — The efficacy of
loose surface tilth in preventing evaporation, as compared
with mere superficial scratching or with the total omission of
cultivation, is well exemplified in a series of investigations
conducted on this subject during the extremely dry season of
1898, by the California Experiment Station; the seasonal rain¬
fall having during that year been on an average from one-
third to one-half only of the usual amount, so as to test to the
THE WATER OF SOILS.
259
utmost the endurance of all growing plants. Some of the
details of this investigation have been given above (p. 214) in
connection with the question of moisture requirements of
crops. Loughridge1 also investigated the moisture condi¬
tions in adjacent orchards differently treated in cultivation.
In one of these cases two orchards of apricots were separated
only by a lane, and the soil identical ; but one owner had omit¬
ted cultivation, while the other had cultivated to an extra depth
in view of the dry season apparently impending. The results
are best shown by the plates below, showing representative
trees and the annual growth made by each. The table an¬
nexed shows the differences in the moisture-content of the two
fields to the depth of six feet, in July :
MOISTURE IN CULTIVATED AND UNCULTIVATED LAND.
Depth in soil.
Cultivated.
U ncultivated.
Per cent.
Tons per
acre.
Per cent.
Tons per
acre.
First toot .
6.4
128
4-3
86
Second foot .
5-8
116
4-4
88
Third foot .
6.4
128
3-9
78
Fourth foot .
6-5
130
51
100
Fifth foot .
6.7
J34
3-4
68
Sixth foot .
6.0
120
4-5
90
Total for six foot .
6-3
756
4.2
512
The difference of 244 tons per acre of ground shown by the
analyses is quite sufficient to account for the observed differ¬
ence in the cultural result. The cause of this difference was
that in the uncultivated field there was a compacted surface-
layer of several inches in thickness, which forcibly abstracted
the moisture from the substrata and evaporated it from its
surface; while the loose surface soil on the cultivated ground
was unable to take any moisture from the denser subsoil.
The cultural results were that on the cultivated ground the
trees made about three feet of annual growth, and the fruit
1 Rep. Calif. Expt. Sta. for 1897-98, p. 65.
SOILS
26o
Cultivated. Figs. 48, 49. — Apricot Trees, Creek Bench Land, at Niles, Cal. Uncultivated.
THE WATER OF SOILS
261
Fig. 59. — New Growth and Fruit on Trees, Cultivated and Uncultivated. Creek Bench Land
at Niles, Cal.
262
SOILS.
was of good, normal size ; while the trees in the uncultivated
ground made barely three inches of growth, and the fruit was
stunted and wholly unsaleable. It may be added that when,
instructed by the season’s experience, the owner of the “ un¬
cultivated ” orchard cultivated deeply the following season,
his trees showed as good growth and fruit as his neighbor’s.
EVAPORATION THROUGH THE ROOTS AND LEAVES OF PLANT'S.
Undesirable as is the evaporation from the surface of the
soil, under all but exceptional conditions the evaporation from
the leaves of plants is one of the essential functions of veg¬
etable development. Not only because water serves as the
vehicle of the plant-food absorbed by the roots and to be or¬
ganized by and redistributed from the leaves, and the aeration
occurring in the latter must of necessity result in a certain
degree of evaporation; but largely because the conversion of
liquid water into vapor serves to prevent an injurious rise of
temperature in the leaves under the influence of hot sunshine
and dry air. It is undoubtedly for the latter purpose that
the greater part of the enormous amount of water required, as
above stated (chap. 11) for the production of one part of
dry substance, is actually used. When sufficient water to
supply the required evaporation through the leaves cannot be
brought up from the soil, the plant begins to wilt ; or in the
case of some plants with very thin and soft leaves the blade
normally begins to droop during the hottest hours of the day ;
thus escaping excessive exposure to the sun’s rays, and re¬
covering their turgor later in the afternoon.
The amount of water actually evaporated from orchard trees has un¬
fortunately not been directly determined, the investigations made in
this respect having borne mainly upon forest trees. The Austrian
Forest Experiment Station made a series of elaborate investigations on
this subject in 1878, and the following data (quoted from the Report
of the U. S. Dep’t of Agriculture for 1889) convey some idea of the
results.
It was found that the surface-areas of the leaves do not give reliable
results, but that these depend very largely upon the thickness (mass) of
the leaves. The dry weight of the latter was found, as in the case of
THE WATER OF SOILS.
263
field crops, to correspond most nearly so the observations made directly.
It was thus found that e. g. birch and linden transpired during their
annual period of vegetation from 600 to 700 pounds of water per pound
of dry leaves; oaks 200 to 300, while the figures for ash, beech and
maple were in between. On the other hand the conifers — spruce, fir
and pine — ranged, under the same conditions, from 30 to 70 pounds
of water only. In another year, these figures were increased for decid¬
uous trees to from 500 to 1000, the conifers, 75 to 200 pounds. This
great variability indifferent seasons, together with other elements of
uncertainty, render these figures only roughly approximate ; but it will
be noted that the figures for deciduous trees are in general of the same
order as those given above for field crops. Assuming the evaporation
for citrus trees to be approximately the same as for the European ever¬
green oak ( Q. cerris) viz. 500 pounds per pound of dry matter, and
taking the weighings made by Loughridge of the leaves of a 15 -year-
old orange tree at Riverside as a basis (40 pounds of dry leaves), the
water evaporated by each such tree would be about 20,000 pounds per
year, or about 1000 tons per acre of 100 trees. This is equivalent to
about 9 acre- inches of rainfall, out of the 35 inches commonly given.
Since different plants evaporate very different amounts of
water during a given time, according to their leaf-surface and
the number and size of their stomates, the maintenance of the
equilibrium between the soil-supply and the evaporation of
the leaf-surface requires correspondingly varying moisture-
conditions in the soil. Therefore desert plants, with their
elaborate structural provisions against leaf-evaporation, will
develop normally, and without wilting, under conditions which
in the case of most culture plants would result in severe in¬
jury or death. Since diminution of leaf-surface will in all
cases diminish evaporation, the heroic measure of cutting back
the twigs and branches of shrubs and trees in seasons of severe
drought is sometimes resorted to in order to save their life.
In Nature this diminution of leaf-surface may be observed in
many cases of desert plants, whose “ fugacious ” leaves are
developed during the rainy season, in winter and early spring;
dropping off so soon as the dry season begins, and leaving only
the green surface of twigs, stems or spines to perform the
functions of the leaves.
The shading of the ground by leafy vegetation will, of
.264
SOILS.
course, greatly diminish and sometimes suppress evaporation
from the soil-surface ; thus very nearly fulfilling the same con¬
ditions referred to above ( chap. 7, page 1 1 1 ) in discussing
the effect of natural vegetation in rendering tillage unneces¬
sary ; the beating of rains, and the formation of surface crusts,
being alike prevented. This fact is of essential importance in
contributing to the welfare of crops sown broadcast, where
subsequent cultivation is impracticable.
Weeds Waste Moisture. — The injurious effects of weedy
growth among culture plants are in most cases due quite as
much to the appropriation of moisture that should have gone
to the crop, as to the abstraction of plant-food, to which the
injury is generally attributed. This is much more obvious in
the arid region, where during the dry summers every pound of
moisture counts, than where summer rains obscure this in¬
fluence. It has led orchardists in California almost to an ex¬
cess of clean culture, resulting in the burning-out of the humus
from the bare surface-soil during the long, hot summers, and
an injurious compacting impossible to remedy by the most
careful tillage. It thus happens that greenmanuring, the
natural remedy for this evil, cannot safely be done there with
summer crops, but must be accomplished with winter crops,
such as can be turned under before the dry season begins. The
same objection holds against the growing of summer crops
between the orchard-rows.
DISTRIBUTION OF MOISTURE IN THE SOIL AS AFFECTED BY
VEGETATION.
The investigations of Wollny and others have long shown
quantitatively what common experience has taught the farmer,
viz., that a field in crops or grass is always drier within the soil-
mass penetrated by the roots than is a cultivated field bare of
crops, unless perhaps when heavily crusted on the surface. The
depletion of moisture caused by grass sward is the most easily
observed because of the shallowness of the root-system ; and
this is one cause at least why grass sward does not occur natur¬
ally in the arid region, and when planted cannot be maintained
without irrigation repeated at short intervals. Deeper-rooted
plants of course deplete the soil at different and varying levels;
THE WATER OF SOILS. 265
and where surface roots are few or absent it may readily hap¬
pen that the surface soil is moister than the subsoil.
This was very strikingly shown by the investigations of Ototzky in
the South- Russian steppes, in comparing both the moisture contents and
the depth of bottom water as between forest land and the open plains.
On the steppe near Chipoff, Government of Voronej, he found the
ground water at from 3 to 5 meters (10-16 feet) depth ; under the forest
in the same region and in identical underground formations, the water
level stood at 15 meters. In the Black Forest near Cherson, the water
is found at about 15 feet beneath the surface; under the steppe and in
cultivated ground it stood at 10 feet. At the same time the forest soil
was moister in the upper two feet than the soil of the steppe, where
surface evaporation (partly through shallow plant-roots, partly direct)
was greater than under the shadow of the forest ; under which, moreover,
there were few shallow rooted plants to draw upon the moisture of the
surface soil.
The great evaporation from forests is a matter demonstrated
by actual measurement; hence it is not surprising that certain
shallow-rooted trees should serve for the reclamation of wet
ground, as has been demonstrated on the large scale, e. g., in
the use of the eucalyptus in the Pontine Marshes of Italy, and
of the maritime pine in the Landes of western France. Thus
the sanitation of swampy districts through tree-planting has be¬
come one of the established measures in their settlement. But
this refers only to the evaporation from the trees themselves;
for in the shade of the forest, a free water-surface is found to
evaporate on the average only one-third as much as in open
ground. Of course there must be a correspondingly great
diffence in the amounts of evaporation from the soil-surfaces
in the respective areas.
The great draft made by the Eucalyptus globulus upon soil-
moisture has been also abundantly shown in California, where
on account of its rapid growth this tree has been largely used
for windbreaks. It was found that the trees deplete the
fields of moisture for from twenty to thirty feet on either side,
so as to materially reduce crops within that limit. For this
reason the pine and cypress has of late found greater accept¬
ance for this purpose.
266
SOILS.
Mulching. — Covering the soil with straw or similar loose
materials to prevent waste of moisture is a common garden
practice everywhere, although not usually applicable on the
large scale. It may readily however, be carried to excess, in
preventing not only evaporation but also the warming of the
soil which is so needful to the thrifty growth of plants. It
must not therefore be done too early in the season ; and after
cold rains it sometimes becomes necessary to remove the mulch
in order to allow the ground to become properly warmed.
Mulching in early spring is often used to retard blooming of
trees where spring frosts are feared.
In the arid region, sanding of the surface is sometimes re¬
sorted to for the prevention of the evaporation which brings
alkali salts to the surface. But the necessity of repeating this
dressing annually unless cultivation can be omitted, restricts
the use of this expedient to narrow limits.
The sanding of the surface of cranberry plantations in
swamps or bogs in the northern parts of the humid region
doubtless owes its efficacy largely, if not chiefly, to the re¬
tention of moisture, while at the same time it prevents the con¬
solidation of the surface, so as to render tillage unnecessary.
CHAPTER XIV.
ABSORPTION BY SOILS OF SOLIDS FROM SOLUTIONS.
ABSORPTION OF GASES. AIR OF THE SOILS.
ABSORPTION OF SOLIDS FROM THEIR SOLUTIONS.
Just as solids have the power of condensing gases upon
their surfaces, to an extent proportional to that surface, and
therefore to the state of fine division : so fine powders have the
power of withdrawing from solutions solids held in solution,
to an extent varying with the nature of the substance dissolved,
and the absorbing solid. The most commonly-known mani¬
festation of this principle is that sea-water filtering through
the sands of the shore, will at a certain distance become sensi¬
bly less brackish, and finally so nearly fresh as to be capable of
domestic use.1 The extent to which this occurs is in a measure
proportional to the fineness of the sand, and to the amount of
clay present in it. This is a clearly physical effect, independent
of any chemical action whatever; for it occurs equally with
quartz sand, charcoal, glass, limestone, or other rock powders
having no chemical effect upon the substance dissolved or
upon the liquid dissolving it. Very large amounts of water are
often required to remove all the soluble matter thus “ ad¬
sorbed.”
Decolorising Action. — One of the commonest applications
of this principle is the decolorization of colored solutions by
means of finely pulverized charcoal. This property of char¬
coal, as is well known, is extensively utilized in the arts, and
particularly in the refining of sugar; the charcoal used in this
case being preferably bone charcoal (“bone black”), which
on account of its state of extreme fineness, and separation by
the earthy particles with which it is associated, is more effective
than any other form. It is rendered still more effective, how-
1 In many cases this decrease of salinity is probably due to a slow influx of fresh
water from landward ; but very often it cannot be thus explained.
267
268
SOILS.
ever, by the extraction of these earthy particles (calcic carbom
ate and phosphate) by means of acid; for by removal of the
earthy particles, the surface of the charcoal is greatly increased,
and its decolorizing as well as its absorbing power increases
accordingly.
While in one and the same substance the decolorizing effect
is more or less directly proportional to the fineness of the parti¬
cles, corresponding to increased surface, it is nevertheless true
that in this case, as in that of the absorption of gases, there are
specific differences between different powders; so that for ex¬
ample no other substance can replace charcoal in the decoloriz¬
ing effect which it produces upon colored solutions. It must
not, however, be supposed that there is any special reason why
coloring matters, as such, should be taken up by preference.
Coloring matters are of all kinds of chemical composition, and
have in common only the fact that a relatively small amount
produces a very strong coloring effect ; hence their name, and
hence also the apparently extraordinarily strong effect pro¬
duced upon them by charcoal.
This effect is not, however, by any means greater than it is
in the case of many other compounds which are colorless.
Complex Action of Soils. — The powdery ingredients of
soils, of course, share this power with all other powders. In
the case of soils, however, the action is almost always much
more complex than in that of charcoal, because solutions that
are passed through the soil are apt to act chemically upon one
or the other of its ingredients, usually resulting in a partial
exchange of ingredients between the soil and the solution;
one or more of the constituents of the solution being retained
by the soil, while one or more of the (basic) soil constituents
pass into the solution, in combination with its acidic ingredi¬
ents.
Thus when a very dilute (1 or i<%) solution of potassic chlorid is
filtered through almost any soil, the first portions passing through will be
practically free from potash, but will contain the chlorids of calcium
and magnesium. But as more of the solution is passed through, potash
passes also ultimately without absorption. In addition to the zeolitic
and clay portions of the soil, the humus is very effective in absorbing
ABSORPTION BY SOILS. 269
mineral ingredients from solution, and retaining them in such manner
as to be readily available to plant growth. (See chap. 8, p. 1 24.)
In view of the almost invariable conjunction of physical and
chemical effects, it may be fairly said that no solution, at least
of mineral salts, can pass through the soil without being
changed in its concentration and chemical composition. It is
sometimes difficult to decide to which of the two classes of
effects the several changes may be due.
Purifying Action of Soils. — The disinfecting action of dry
soil, absorbing offensive gases from manure piles and from
earth closets, has already been alluded to. Similarly it is a
matter of common experience that the colored and otherwise
offensive drainage from manure piles, tanneries, dyeworks,
etc., is not only deodorized but also decolorized when passed
through a sufficiently thick layer of clay soil. The filtration
through fine sand by which the drinking waters of cities are so
commonly purified before delivery to the consumer are famil¬
iar examples of the same effects.
Equally familiar, however, is the fact that this power of
decolorization and retention of offensive compounds is limited ;
that after a while the filtering earth or sand becomes saturated,
and afterwards the water or drainage will pass through with¬
out any sensible purification.
It is therefore clear that this purifying effect of earth can¬
not be relied upon for the permanent protection of wells from
the surface-drainage from barnyard or house refuse. Even if
fissures or layers of sand or gravel should not intervene so as
to permit of the direct communication of surface-drainage with
wells, it is certain that in the course of a few years at most,
the intervening earth will become so far saturated with the
noxious ingredients that the latter will pass through unhin¬
dered, and may contaminate to a considerable extent the
domestic supply of drinking water.
Waste of Fertilizers. — The same, of course, holds true in
regard to manure-water, or soluble fertilizers of any kind used
on the soil of a field. The soil will retain them to a certain
extent ; but beyond that limit any surplus added will be quickly
washed through into the country drainage by the rains. More-
2yo
SOILS.
over, a soil once so saturated will yield to rain-water filtering
through it, notable amounts of all the ingredients absorbed in
it; and, at least so far as the physically condensed soluble in¬
gredients are concerned, long-continued leaching with pure
water will inevitably result in the withdrawal of additional
amounts of absorbed ingredients, apparently dividing them¬
selves up pro rata between the water and the soil.
It is obviously of the utmost importance to the farmer to
know to what extent the soil will retain manurial ingredients
against the influence of leaching rains; for unless this is
taken into consideration, it may readily happen that the fertil¬
izer supplied before a rainy season will be washed through be¬
yond the reach of plant-roots, and so practically become a dead
loss.
Absorptive Power Varies. — So far as the mere physical ab¬
sorption is concerned, it will readily be understood that a
coarse sandy soil exercises less retentive influence upon dis¬
solved substances than clay or humous soils. In the humid
region, where sand is substantially nothing but granular silica
(see above, chap. 6, page 86), the same may be measurably
true as regards the chemical absorption also. In the arid re¬
gion, on the contrary, a great many sandy or silt soils, very
poor in clay, exert fully as much chemical absorption as clay
soils, and are no more liable to the washing-out of soluble
fertilizers introduced than are the latter. For the chemical
absorption lies chiefly in the zeolitic portion of the soil (see
above chap. 3, p. 37, which in the humid region accumulates
in the clay, while in the arid it remains encrusting the sand and
silt grains.
Generalities regarding Chemical Absorption and Exchange.
— In regard to the leaching-out and absorption or retention of
substances important to agriculture, the following general
statement may be made :
The substances most likely to be leached out of soils are, of
bases: soda, magnesia and lime; of acidic constituents: chlor¬
ine, sulfuric acid and nitric acid. Lime sometimes passes
off with either of the above acidic ingredients, and also in the
form of carbonate.
Substances rather tenaciously retained in soils are : potash
ABSORPTION BY SOILS.
271
and ammonia among the bases, and phosphoric acid among the
acids.
Thus (as stated above) when a weak (one or two per cent)
solution of potassic chlorid or sulfate is poured upon a
column of good soil several inches thick, it will be found that
the first portions passing through are free from potash, but
contain the chlorids or sulfates of magnesium and calcium.
If potassic nitrate be used, lime and magnesia will pass off as
nitrates; while in the case of potassic phosphate, both ingredi¬
ents will be retained. A solution of gypsum (calcic sulfate)
will usually cause the passing-off of some of the magnesia, soda
and potash contained in the soil, in the form of sulfates; but
the amount of potash thus dissolved soon diminishes to a mere
trace. Solutions of potassic or ammonic phosphates will be
absorbed and retained by the soil to a very considerable extent,
before the soil becomes saturated.
While it is true that the degree to which the soil retains
the several ingredients may serve in a very general way to
indicate their richness or poverty in the same, the attempt to
make such experiments serve to determine the agricultural
needs of soils has met with but little practical acceptance.
Drain Waters. — The table on p. 22, chapter 2, illustrates
forcibly the working of the above principles, which are verified
by the composition of drain-waters. In all, the chief nutritive
ingredients of plants, except nitrogen, are present in traces
only; chlorids, nitrates and sulfates of sodium and mag¬
nesium form the bulk of the permanently soluble matter, with
usually a considerable proportion of calcic (and magnesic)
carbonate, depending upon the amount of the earth-carbonates
present in the soil, as well as upon that of oxidizable organic
matter from which carbonic acid can be formed. That calcic
carbonate filters readily through the soil has already been some¬
what elaborately discussed (see chap. 3, p. 41); one of the
results being that the surface soil is sometimes almost com¬
pletely depleted of this important substance, while it accumu¬
lates at a greater or less depth in the subsoil, or in under¬
drains, as the case may be.
Of the ingredients appearing in the above list, the one of
greatest agricultural importance is nitric acid, since chlorine
and sulfuric acid, as well as soda, are required only in very
2 72
SOILS.
small quantities by most culture plants; so that they rarely
need to be supplied in fertilizers. Nitric acid, however, is not
only one of the most important fertilizers, but also the most
expensive ; hence the passing-off of nitrates in drainage-water
is of such serious concern to the farmer, that the causes of its
occurrence, and the means of preventing such loss, should be
fully understood. This subject will, however, be more fully
considered farther on.
The above Distinctions not Absolute. — It should, however,
be also understood that while the above statements hold good in
a general way, yet the line drawn is by no means an absolute
one. For just as in the case of physical adsorption the long
passing-through of distilled water will gradually abstract the
substances condensed on the surface of the soil-grains, so an
overwhelming amount of a solution of any one kind will have
a tendency to substitute its own ingredients for those already
present in the soil, removing the latter to a greater or less
extent, even in the case of potash and phosphoric acid.
As an example in point, may be cited the case of the natural minerals
Analcite and Leucite, which Lemberg was able to reciprocally trans¬
form from their natural condition of soda- and potash-alumina silicates
merely by alternate treatment with solutions of potassium and sodium
chlorids respectively. (See chap. 3, p. 37). The same is true in the
case of the zeolitic matter of the soil. There is nevertheless a distinct
preference in the direction of the retention of potash as against soda ;
so that in the case of alkali soils, a large excess of potash is found to
be present in the zeolitic form, notwithstanding the presence of some¬
times very large amounts of the chlorid, sulfate and carbonate of soda.
This preferable retention of potash is, of course, of material advantage
in the case of the use of soluble potash-fertilizers, as well as in prevent¬
ing the waste of the potash of the soil itself.
ABSORPTION, OR CONDENSATION, OF GASES BY SOILS.
Like all bodies in a state of fine division, soils are capable of
absorbing a not inconsiderable amount of various gases. It
may be said that in general, other things being equal, the
amount thus condensed on the surface of the soil-grains is more
or less directly proportional to the facility with which the gas
ABSORPTION BY SOILS.
273
is condensed by either pressure or cooling. Hence the very
large amount of water-gas or vapor which may be absorbed by
soils, as shown in a preceding chapter. But excepting perhaps
the case of ammonia, moist soils are less absorbent of gases
than dry ones.
Oxygen and nitrogen, the main constituents of the atmos¬
phere, being difficultly condensable by either pressure or cold,
are absorbed by soils only to a relatively small, yet by no
means unimportant extent. The condensation of oxygen with¬
in the soil-mass is doubtless of considerable importance in the
processes of oxidation, as is shown by its partial replacement
by carbonic gas in the free air of the soil (see chap. 2, p. 17).
The intensifying of oxidizing action caused by surface conden¬
sation is well illustrated in the case of finely divided platinum,
in which hydrogen is brought to rapid combustion when mixed
with oxygen ; as well as by the effect of bedding tainted meat
in charcoal powder, when all odors of decay disappear, both
by absorption and oxidation, ammonia and carbonic gas alone
ultimately escaping through the powder.
Carbonic dioxid and ammonia gases , both normal consti¬
tuents of the atmosphere, and of high importance to plant nu¬
trition, are more readily condensable than either oxygen or
nitrogen, and consequently may be taken up by the soil in
larger relative proportions. Especially is this the case with
ammonia gas, which is not only readily condensed by pres¬
sure, but is also extremely soluble in water; so much so that
it rushes into a tube filled with this gas almost as quickly as
though it were a vacuum. Water will absorb at the ordinary
temperature, under normal pressure, about 700 times its vol¬
ume of ammonia gas ; but inasmuch as the proportion of the
latter in the atmosphere amounts to only a few millionths, the
actual amount taken up can only (as in the case of all gases)
be proportional to its proportion (or “ partial pressure ”) mul¬
tiplied into its coefficient of absorption. Consequently, water
exposed to the ordinary air can absorb at best only a small
fraction of a per cent of ammonia. Its presence in soils can
be readily demonstrated by passing through the warmed soil
a current of purified air, which is made to bubble through
Nessler’s reagent (potassio-mercuric iodid) solution.
18
SOILS.
2;4
Absorption of gases by dry soils. — Perfectly dry soils are
powerful absorbers of ammonia, and their absorption of this
gas, as well as of carbonic gas, can readily be shown by the
arrangement shown on the page opposite.
The two tubes shown to the left are filled with carbonic gas, those to
the right with ammonia gas. After being immersed in a mercurial
trough, there are introduced into each tube through the mercury small
cylinders (conveniently one cubic centimeter in volume) consisting re¬
spectively of a very sandy soil or loose hardpan, a gray plastic clay, a
gray clay soil or adobe, a very black “ adobe ” clay, and a highly ferru¬
ginous and humous soil (from Hawaii), which gives the highest absorp¬
tion of all ; next brown peat, and pine charcoal. The latter, and the
ferruginous soil, were also exposed for the absorption of carbonic gas.
All the absorbing cylinders are first heated for an hour to i io°C. (2i8°F)
for the purpose of expelling from them moisture, air, and other absorbed
gases. They are then quickly introduced into the tubes through the
mercury and allowed to absorb the gases enclosed until the mercury
columns cease to show any farther rise ; in which condition they are
shown in the figure.
It will be seen that this absorption is a different one, not
only for each of the different substances used, but is also
differently proportioned for the two gases. For it will be
noted that while the clay soil has absorbed a very much larger
amount of ammonia than the charcoal, and the sandy soil has
remained far behind both : yet the charcoal has absorbed a
considerably larger proportion of carbonic gas than either the
clay or the sandy soil, proving that charcoal has a strong
specific absorptive power for carbonic gas, independently of the
relative size of clay and charcoal particles respectively. The
sandy soil shows, by its low absorption even of ammonia gas,
the coarseness of its particles and the scarcity of clay in its
composition. The highest absorption of all is shown by the
ferruginous soil from Hawaii, containing nearly 40 % of
ferric oxid together with 3 1-3% of humus. The moisture-
absorption of this soil at the ordinary temperature is 19.7 per
cent. The difference in the absorbing power of the (non-
humous) gray clay and gray adobe soil indicates the strong in¬
fluence of humus upon the absorption ; which is still farther
emphasized by the difference between the gray and black adobe,
ABSORPTION BY SOILS. 275
the latter containing 1.2% of humus. As to the peat, since its
weight was only .5 grams against an average of 2 grams for
the soils employed, its absorptive power by weight doubtless
exceeds all other substances.
Fig. 51. — Absorption of Carbonic and Ammonia Gases by different Soils.
While the experiment shown in the figure serves as a con¬
venient and striking demonstration for lecture purposes, it is
of course not adapted to a direct comparison of the absorbing
powers of the several substances, because of different heights
of the mercurial columns counteracting the atmospheric pres¬
sure. For direct comparative measurement the tubes must be
sunk in mercury so as to equalize the levels inside and outside,
since the corrected volumes obtained by calculation would not
serve the purpose.
According to special measurements made under normal
atmospheric pressure, the writer found that a black clay soil
(“adobe”) absorbed (at 6o°F) over two hundred times its
bulk of ammonia gas, while under the pressure of one-fifth of
an atmosphere (as shown in the photograph) the absorption
was one hundred and twenty-three times its bulk. This ener¬
getic absorption of ammonia and related gases explains the
marked disinfecting effects which a covering of dry earth
exerts in the case of cemeteries, manure piles, and earth closets.
But the difference between the sandy soil and the clay soil in
276
SOILS.
the amount of absorption admonishes us that in all these cases,
to secure disinfection the earth to be used should contain as
much clay as possible, and should not be mere sand, as is
sometimes the case. It also shows that the addition of charcoal
to such materials does not increase their efficacy, as has been
supposed, but that an equal bulk of clay would be more effi¬
cient.
Of course, so soon as the absorbing cylinders used for this
experiment are exposed to the atmosphere, the principle above
stated in regard to “ partial pressure ” asserts itself. The ab¬
sorbed gases quickly begin to be given off, and in some hours
the equilibrium with the ordinary conditions of the atmos¬
phere is reestablished. That the strong absorptive power of
soils for ammonia is to some extent effective in maintaining
the supply of this substance by absorption from the atmos¬
phere, cannot be doubted.
Boussingault, and later Stenhouse, determined the absorp¬
tive power of wood charcoal for ammonia to be 90 and 98
volumes respectively.
THE COMPOSITION OF GASES ABSORBED FROM THE ATMOS¬
PHERE BY VARIOUS SOLIDS.
In 1864 and 1865 Reichardt and Blumtritt 1 investigated
elaborately the composition of gases driven off by heat from
various powders, including soils, exposed to the atmosphere.
All the substances examined were therefore “ air-dry,” there¬
fore to a certain extent moist ; and the presence of this aqueous
vapor of course modifies in a measure the results that would
have been obtained had the materials used been exposed to dry
air only. They found that, as had already been stated by
previous observers, the presence of capillary water diminishes
materially the absorption of gases, especially of those not as
easily absorbed by water as are carbonic gas and ammonia.
Contrary to what might have been expected from the more
ready condensation of oxygen by pressure or cold, in nearly all
cases nitrogen is absorbed to a greater extent than oxygen,
and sometimes exclusively so; so that in some cases the latter
was found to be present only in traces, as will be perceived
from the subjoined table:
1 Journal fur praktische Chemie, Vol. 98, p. 167.
ABSORPTION BY SOILS.
277
COMPOSITION OF GASES ABSORBED FROM THE ATMOSPHERE BY VARIOUS POWDERS
Substance.
Charcoal, coniferous, air dry .
“ moistened and air-dried .
Lombardy Poplar .
Peat .
Garden Earth, moist .
“ “ air-dried .
River Silt, air-dried. . .
“ “ slightly moistened .
“ “ air-dried .
Clay, long exposed .
“ slightly moistened .
Ferric Hydrate, commercial .
freshly precipitated, air-dried
Oxid, ignited .
Aluminic Hydrate, air-dried .
“ “ dried at ioo°C .
Prepared Chalk, 1864-65 .
“ “ 1865.... .
Calcic Carbonate, precipitated, 1864-65 .
“ “ “ 1865-66 .
Magnesic Carbonate .
Gypsum, finely powdered .
100 vol's gas contained
100
Grms
gave cc.
Gas.
100
Vol’s
gave
Vol’s.
Gas.
Nitogen.
Oxygen.
1
Carbonic
Dioxid.
Carbon
Monoxid.
16.21
100.00
0.0
0.0
0.0
140. 1 1
590
85.60
2.12
9.15
3 • 1 3
466.95
*95-4
83.60
0.0
16. 50
0.0
162.58
44-44
4.60
50.96
0.0
13-70
19.9
64-34
2.85
24.06
8.75
30.28
53-6
64.70
2.O4
33-26
0.0
40.53
48.07
67.69
0.0
18.61
*3 • 7°
24.12
29.2
67.34
0.0
30.56
2 . IO
26.52
30.05
67.40
9.09
16.07
7-44
2S-53
39-05
70.17
4-71
25.12
28.62
35.08
59-59
6-39
34.02
25'-59
275-o
33-26
i-43
65-3«
0.00
375-54
308.6
26-29
3-85
69. 86
0.00
39 4
52.4
82.87
*3 - 4 *
3-72
0.00
69.02
82 0
40.60
0-00
59.40
10.83
• 3.6
83.09
16.91
0.00
43-48
52.4
100-00
0.00
0.00
.
38-98
48.0
74-49
*5-49
10.02
65.09
80 • 81
19.19
0.00
51-53
52.0
77-37
15.09
7-54
729.21
124.9
63.92
6.72
29.36
17.26
80.95
19.05
0.00
Discussion of the Table. — It will be observed that in this table, the
largest amount of total gas given off by equal weights of any one sub¬
stance was in the case of carbonate of magnesia ; but it is quite probable
that in part, at least, this large amount of gas was due to the evolution
of carbonic gas from the easily decomposable carbonate ; the more as
the analysis of the gases shows over 29% of carbonic gas. But the
highest absorption by equal volumes of any substance is shown by the
ferric hydrate; next to this by the light poplar charcoal, and next by
the carbonate of magnesia. The high absorptive power here shown by
the ferric hydrate is of great interest in connection with the facts already
stated regarding the absorption of moisture and ammonia by ferruginous
soils (see page 274, this chapter) ; and the fact that the larger proportion
of the gas — as much as 70^ in one case — consisted of carbonic gas, is
particularly interesting in the same connection. Both in the amount of
gas contained, and in the proportion of carbonic gas therein, the ferric
hydrate exceeds even peat, the representative of humus in soils. It
will, however, be noted that in the garden soil, also, the proportion of
carbonic gas is very large, while that of oxygen is very low. It is curious
to note that in very few cases the proportion of oxygen to nitrogen is
the same as in the atmosphere ; in most cases the nitrogen predominates
considerably beyond its normal proportion, and in two cases, that of
2; 8
SOILS.
charcoal and of calcic carbonate (whiting), the gas was found to consist
of pure nitrogen.
We are forced to conclude that the substances here enumer¬
ated, as a rule, condense oxygen in smaller proportions than
they do nitrogen, or carbonic gas. As regards the carbon
monoxid mentioned in the table, it is doubtful that it was con¬
tained as such in the substance originally examined ; it may
readily have been formed under the influence of the heat re¬
quired in expelling the gases from the substances containing
organic matter. Among the important results shown in the
table, is the comparative determination of the gases in moist,
and in dry garden earth, showing that in the moist earth the
amount of gas absorbed ranged from less than one-half down
to almost one-fourth that absorbed by the dry. The import¬
ance of these differences in the case of the fallow can readily
be appreciated.
The changes in the absorptive power brought about by wetting and
drying, as shown in the above table, are very insignificant. In the case
of the charcoal, soil and silt the diminution may fairly be assumed to
be caused by the deposition of soluble salts on the surface, partly clog¬
ging the pores. In the case of the clay as well as in that of the river
silt, the inevitable content of organic matter in process of decompo¬
sition has doubtless influenced the result, as is suggested by the increase
of carbonic gas. That prepared chalk should in one case contain ex¬
clusively nitrogen gas, in the other case mixed gases, seems to indicate
a difference in the air to which it is exposed, or in the water employed
in its preparation ; the latter case agreeing substantially with the results
obtained from the precipitated carbonate. In both (as well as in the
carbonates of barium and strontium), the absorption of carbonic gas is
very small, or nil.
It thus appears that for the condensation of carbonic dioxid
gas, ferric and aluminic hydrates are prepotent among mineral
substances; while clays, river silts and soils may always be
expected to contain relatively large proportions of this gas in
absorption.
ABSORPTION BY SOILS.
279
THE AIR OF SOILS.
The Empty Space in Soils. — In dry soils the empty space,
usually amounting to from 35 to 50 per cent of its volume, is
filled with air; 1 in moist or wet soils the space unoccupied by
water is similarly filled. Hence when soils are in their best
condition for the support of vegetation (chap. 11, p. 202),
about one half of their interstices is filled with water, the other
half with air. Actual measurements of the amount of air
contained in well-cultivated garden soil have been shown by
Boussingault and Levy to range between 10,000 and 12,000
cubic feet per acre, substantially agreeing, therefore, with the
above statement. In uncultivated forest soil, on the contrary,
they found only from somewhat less than 4000 to 6000 cubic
feet of air per acre. Extended observations since carried out
by Wollny, Ebermayer, and others have in general confirmed
the earlier observations, while adding greatly to their signifi¬
cance in respect to their relations to plant growth, and to the
process of humification and soil-formation.
As a matter of course, when water evaporates from the soil
in drying, its place is taken by air so far as it is not filled by
capillary water drawn from below.
Functions of Air in Soils. — That roots require for the per¬
formance of their vegetative functions the presence of oxygen,
has already been discussed; but there can be no question that
the higher productiveness of well-cultivated soils is largely due
to the greater and readier access of air to the roots. Apart
from this direct function, however, the presence of oxygen in
the soil serves other important purposes, and among these
doubtless the most dominant is the promotion of the oxidation
of the organic matter of the soil through the agency of micro¬
organisms ; and more particularly that of nitrification, which
chiefly governs the supply of nitrogen to non-leguminous
plants. In the case of leguminous plants, the presence of air
as a furnisher of nitrogen as well as oxygen is absolutely
essential.
The injurious effects of insufficient aeration of the soil have
been repeatedly referred to already (pp. 45, 76). In water¬
logged soils reductive fermentations are soon set up, and the
1 The normal composition of atmospheric air is given on p. i6, chap. 2.
280
SOILS.
nitrates of the soils are reduced partly with the evolution of
nitrogen gas, partly to ammonia ; while their oxygen is con*
sumed to supply the demands of the roots. Ferric oxid is
reduced to ferrous carbonate, sulfates to sulfkts; thus de¬
ranging the whole process of plant-nutrition and absorption of
plant-food. If continued for any length of time these condi¬
tions end in the death of the plant. Too much importance can¬
not therefore be attached to the proper aeration of the soil and
subsoil.
Excessive Aeration; Compacting the Soil. — On the other
hand, excessive aeration of the soil may be injurious in caus¬
ing a serious waste of moisture; especially in arid climates,
where the hot, dry winds may readily destroy the germinating
power of the swollen seed when the seed-bed is too loose and
open, and later may injure or destroy the feeding roots. The
abundant growth of grain often seen in the tracks of a wagon
carrying the centrifugal sower, when the stand in the general
surface is very scanty, is usually due to the consolidation of the
seed-bed, and suggests at once the well-known efficacy of light
rolling to insure quicker germination and a better stand. Simi¬
larly, the rolling of grain fields in spring is often the saving
clause for a crop in dry years. But such needful consolidation
must not, of course, be carried to the extent of creating a sur¬
face crust which would subsequently serve to waste the subsoil
moisture. Hence, the soil-surface should be rather dry when
rolling is resorted to.
The pressing of the earth around transplanted plants, simi¬
larly, is a needful precaution, not only with respect to the dry¬
ing-out of the soil, but also to insure close contact between the
roots and the soil.
The Composition of the Free Air of the Soil usually differs
from the air above, in that besides being saturated with mois¬
ture, its nitrogen-content is slightly increased (by one-half to
over one per cent) ; the oxygen-content on the other hand, is
diminished, being in part (sometimes nearly to the extent of
one-half of its volume) replaced by carbonic gas, de¬
rived partly from its secretion by the roots, partly from the
oxidation of organic substances. It naturally follows that the
richer the soil in the latter, the more carbonic gas will be
formed under favoring conditions ; so that in freshly-manured
ABSORPTION BY SOILS.
28l
land the amount of oxygen transformed into carbonic gas will
be greatest, while in the surface-soil of ordinary fields, car¬
bonic gas rarely reaches to as much as one per cent. In all
cases, however, the content of carbonic gas in the air of the
soil is materially higher than that of the air above it, and thus
serves to intensify greatly the solvent and disintegrating effect
of the soil water upon the soil materials (see chap. 2, p. 17).
The soil-mass itself, however, retains carbonic dioxid with con¬
siderable tenacity, so that it is not possible to wash it out com¬
pletely by filtering water through it. When water containing
carbonic gas in solution is filtered through the soil, the gas is
sometimes completely absorbed, the water passing off free
from gas.
The presence of free carbonic gas in soils is readily demon¬
strated by passing through the warmed soil a current of air,
which is then made to bubble through lime water; a clouding
of the latter, and the ultimate formation of a precipitate of
calcic carbonate, proves the presence of the gas, and may also
serve to measure its amount.
From the fact that the free air in normal soils may contain
as much as one-fortieth of its bulk of carbonic gas, besides
what may be contained in the condensed form, we may con¬
clude that this gas is formed within them with considerable
rapidity; for otherwise, in view of the free communication and
diffusion with the outer air, such large amounts could not be
maintained in the surface-soil. Doubtless a considerable pro¬
portion of the carbonic gas normally contained in the atmos¬
phere is thus supplied from within the soil itself.
Relation of Carbonic Gas to Bacterial and Fungous Activity.
— It has been fully demonstrated by the researches of Koch,
Miquel, Adametz, Fuelles, Wollny and others, that the forma¬
tion of carbonic gas in the soil is not a purely chemical oxida¬
tion process, but is essentially dependent upon the presence and
life-activity of numerous kinds of organisms, bacterial as well
as fungous. The crucial proof of this fact is that the presence
of any antiseptic diminishes, and if exceeding certain propor¬
tions completely suppresses, the formation of carbonic gas;
while on the other hand all conditions known to be favorable
to the life of such organisms, viz., the proper conditions of tem¬
perature and moisture (varying with different kinds), increase
282
SOILS.
the formation of the gas. Such formation is of course, how¬
ever, conditioned upon the presence of oxygen. In the case of
most bacteria, there is a certain limit beyond which the pres¬
ence of their own product exerts an injurious or repressive
effect upon their activity; so that if the gas accumulates beyond
that limit, the rate of its formation decreases despite of other¬
wise favorable conditions.
It follows that the best life-conditions of these organisms
(even when anerobic) cannot be fulfilled below a certain
limited depth in the soil; and all observations show that their
number decreases very rapidly with increasing depth (see
chap. 9, p. 142), varying with the perviousness of the soil,
but rarely exceeding four or five feet in the humid regions;
though doubtless found at greater depths in the arid climates.
It is also obvious that the use of any antiseptic or poisonous
materials on the field or in the manure pile will tend to disturb
and restrain the useful activity of these organisms.
Putrefactive Processes. — Carbonic gas is formed also, but to
a much more limited extent, in putrefactive processes, occur¬
ring in the absence, or with only limited access, of air or
oxygen. These processes likewise are conditioned upon the
presence or activity of (largely anerobic) bacteria; but they
should not occur in normally constituted, and especially in tilled
soils, being as a rule inimical to the growth of cultivated
plants (see chap. 9, p. 145).
CHAPTER XV.
THE COLORS OF SOILS.
The natural coloration of soils forms a prominent part of
the characters upon which farmers are wont to base their judg¬
ment of land quality ; hence the origin and value of soil-colors
deserve consideration.
Black Soils. — From the oldest times down to the present a
“ rich, black soil ” has commanded attention and approval.
The black and brown-black colors being almost invariably due
to the presence of much humus (very rarely to an admixture
of carbon (graphite), of magnetic oxid of iron, or sesquioxid
of manganese), it is obvious that the farmers’ judgment coin¬
cides with a high estimate of the agricultural value of humus.
A discussion of this point will be found in another place; but
the popular judgment is based quite as much upon the experi¬
ence had in the advantages that usually accompany the pres¬
ence of humus. It largely characterizes low grounds, and
therefore alluvial lands, whose richness is due to far more gen¬
eral causes. But the shade of the blackness seen in the soil
deserves and usually receives close consideration. If tending
toward brown, acid humus or “ sour ” land is indicated; unless
indeed the surface soil should be bodily derived from decayed
wood, as in the primeval forests. Forest soils in general are
usually dark-tinted for some inches near the surface, owing
to the presence of leaf mold, and mostly have an acid reaction.
But the black tint is equally welcome to the land-seeker when
seen outside of alluvial and forest areas. Belts of “ black
lands” appear on hillsides and plateaus; and these lands,
though clearly not alluvial, are also found to be preeminently
productive ; witness the upland prairies of the western and
southern United States. These black soils are always charac¬
terized by the presence of a full supply of lime in the form of
carbonate, under the influence of which the most deeply black
humus is formed. In other words, the jet black tint is indica-
283
284
SOILS.
tive of calcareous lands ; and these, as will be more fully shown
below, are almost always highly productive.
From both points of view, then, the favorable judgment
passed upon black soils by practical men is justified.
But it is not necessarily true that soils showing no obvious
black tint are poor in humus; for in strongly ferruginous or
“ red ” soils its tint is frequently wholly obscured, though
when still visible it gives rise to the laudatory name of “ ma¬
hogany land,” which every farmer considers a prize.
Of course then it would be wholly incorrect to judge of the
agricultural value of land from its humus-content alone; for
its color may be entirely imperceptible and yet its amount and
nitrogen content be fully adequate to the requirements of
thrifty vegetation. Gray and even whitish soils very fre¬
quently fall within this category in the arid region.
The black tint is also favorable to the absorption of the
sun’s heat, and is therefore conducive to earlier maturity than
is to be looked for in light-tinted lands similarly located.
Wollny (Forsch. Agr. Phys. Vol. 12, 1889, p. 385), dis¬
cusses the influence of color on soils in relation to moisture and
content of carbonic acid. The results show in general simply
the effects due to increase of temperature when the soils are
either darker-colored throughout, or made so superficially.
" Red ” Soils. — Next to a black soil, a “ red ” one will usu¬
ally command the instinctive approval of farmers. The cause
of this preference is not as obvious as in the case of the black
tints; but the general consensus of opinion requires an ex¬
amination of its claims. It is of course easy enough to adduce
examples of very poor “ red ” soils, derived from ferruginous
sandstones that supply little else than quartz and ferric hy¬
drate; the Cotton States supply cogent examples in point, as
do also the lower Foothills of the Sierra Nevada of Cali¬
fornia. It is not, therefore, the iron rust or ferric hydrate that
renders the land productive ; but its presence is a sign of some
favorable conditions. First among these is, that ferric hydrate
cannot continue to exist in badly drained soils; a “ red ” soil
is therefore a well-drained one, and this is probably one of the
chief causes of the popular preference. The “ white land ”
sometimes seem in tracts otherwise colored with iron, is dis¬
tinctly inferior in production to the red lands; and examination
THE COLORS OF SOILS.
285
will generally show that from some cause, such white lands
have been subjected to the watery maceration which proves so
injurious (see chap. 3, p. 46, chap. 12, p. 231).
That finely-diffused ferric hydrate has a very high power of
absorbing moisture as well as other gases of the atmosphere,
has been shown in the preceding chapter; it stands in this re¬
spect next to humus itself, and hence highly ferruginous soils
need not contain as much humus as “ white ” soils from this
point of view. Like humus, also, it renders heavy clay soils
more easily tillable.
Origin of Red Tints. — Where crystalline rocks prevail, the
red tint usually indicates the derivation from the weathering of
hornblende; implying also, outside of the tropics, the presence
of sufficient lime in the land. Such lands are naturally pre¬
ferred to those of lighter tints derived from purely feldspathic
rocks (see chap. 3, p. 32), although they may be poorer in
potash than the latter.
But the red tint has also its intrinsic advantages in the more
ready absorption of the sun’s heat by the colored than by a
white surface. This is probably the chief cause of the higher
quality of wines grown on red hillsides in the middle and
northern vine districts of Europe, where everything that aids
earlier maturity is of the greatest importance. The function
of ferric oxid as a carrier of oxygen (chap. 4 p. 45) prob¬
ably also aids nitrification.
“ Yellow ” lands owe their tint, of course, to smaller
amounts of ferric hydrate, but share more or less in the ad¬
vantages of the “ red.”
White soils, or more properly those having very light gray
tints, are not usually looked upon with favor, especially in the
humid region. The causes of the unfavorable judgment cur¬
rent among farmers in respect to white soils has already been
partially explained in the discussion of the black and red tints.
The light color means the scarcity or absence of both humus
and ferric hydrate, and usually implies that the soil has been
subject to reductive maceration through the influence of stag¬
nant water; reducing the ferric hydrate to ferrous salts, oxidiz¬
ing away the humus, and accumulating in the form of inert
concretions most or all of the lime, iron and phosphoric acid of
the soil mass (see chap. 3, p. 46, chap. 10, p. 184). The
286
SOILS.
term “ crawfishy,” so commonly applied to white soils in the
eastern United States, expresses well the usual condition of
the white soils of that region ; which are very commonly in¬
habited by crayfish, whose holes reach water a few feet below
ground, and are surrounded on the outside by piles of white
subsoil mixed with “ black gravel ” or concretions of bog iron
ore. It is needless to say why such lands cannot command the
favorable consideration of the farmer; they cannot as a rule
be cultivated without previous drainage, and even after that
will usually prove unthrifty, “ raw,” and in immediate need of
fertilization by greenmanuring, and the use of phosphates.
In the arid region, lands of this character are of rare occur¬
rence, while (as has been explained above, chap. 8, p. 135),
the light gray or “ white ” tints are there a very common char¬
acteristic of even the very best soils. It is true that they are
poor in humus and in finely diffused ferric hydrate; but their
“ light ” texture renders the presence of humus for this pur¬
pose less needful, and as stated elsewhere (see chap. 8, p.
135), the high nitrogen-content of arid humus renders a
smaller supply adequate for vegetative purposes. As to iron,
its presence being more important as a sign of good drainage
and aeration than directly, its absence from soils of great
depth and loose texture is of no consequence ; especially when
the heat-absorption which it favors is not only not needed, but
is usually already in undesirable excess during the hot sum¬
mers.
White Alkali Spots. — In the valleys of the arid region, how¬
ever, very white spots commonly indicate the prevalence of
alkali salts, and to that extent are an unfavorable indication ;
especially when coupled with the occurrence of black rings or
spots, which indicate the presence of black alkali or carbonate
of soda (see chap. 22).
CHAPTER XVI.
CLIMATE.
Heat and Moisture are the main governing conditions of
plant growth. In a preceding chapter the relations of soils and
plant growth to water have been considered ; in the present one
the relations of both moisture and heat to soils and plants will
be discussed ; and to do this intelligibly to those not making
a specialty of such studies, it becomes necessary to introduce,
first, a summary consideration of the subject of climate.
Climatic conditions control, and to a great extent determine,
the industrial pursuits of every country ; all the more so as the
rapid communication and transportation by means of modern
appliances now brings every part of the globe in competition
with every other. The question is not now what it may be
intrinsically possible to do under certain climatic and geo¬
graphical conditions, but whether these things can be done with
a reasonable prospect of profit and commercial success, in
competition with other countries offering more or less of simi¬
lar possibilities. While it is true that the cost of labor fre¬
quently enters most heavily into such problems, yet favorable
or unfavorable climatic or soil-conditions may in many cases
turn the scale. Thus the high price of labor and fuel on the
Pacific coast of the United States would at first blush seem
to render competition with Europe and the East in the pro¬
duction of beet sugar commercially impossible; yet exception¬
ally favorable climatic and soil-conditions concur to turn the
scale in favor of California at least, so as to have placed that
state at the head of the sugar-producing states of the Union.
A general understanding of the climatic conditions which con¬
cern the United States more or less directly, is therefore need¬
ful to an appreciation of their agricultural possibilities.
Climatic Conditions. — The factors usually mentioned as
constituting climate are temperature, rainfall and winds.
Since the latter two factors, however, are themselves merely
287
288
SOILS.
the result of heat conditions, it is proper to discuss from the
outset the origin and mode of action of heat.
TEMPERATURE.
The temperature of stellar space outside of the atmosphere
is known to be very low. The increasing cold as we ascend to
greater heights, is a fact familiar to all. Langley has calcu¬
lated upon the basis of observations made at the summit and
foot of Mount Whitney in California, that the temperature of
space lies near 200° Cent. (360° F.) below the freezing point
of water; and this would be the temperature near the Earth’s
surface, were it not for the surrounding atmosphere. The lat¬
ter absorbs but a small amount of the sun’s direct heat rays
(which are of high intensity), as they penetrate it to the
Earth’s surface. But as the earth's surface is warmed, the
heat rays of lozv intensity which it emits cannot pass back
through the atmosphere to the sun or to outer space ; they are
“ trapped,” as it were, by the dense air resting near the earth’s
surface, which is then warmed partly by the radiation from,
partly by direct contact with, the soil. It is to the existence of
our atmosphere, then, that the possibility of our animal and
vegetable life in their present form is due; and a decrease of
the trapping effect on the sun’s heat rays makes itself quickly
felt when ascending, either in balloons or on high mountains.
Moreover, it is well known to mountain climbers that at great
elevations the sun’s heat is extremely intense at noon; even
though the temperature may fall to the freezing point at night,
owing to the failure of the thin air to prevent the radiation
back into space of the heat absorbed during the day. On the
high plateaus of the Andes and of Asia, therefore, very ex¬
treme climates prevail, on account of the great range of tem¬
perature between day and night.
Ascertainment and Presentation of Temperature-C onditions.
— The proper understanding of the temperature conditions of
any locality or region is by no means a simple matter. Shall
we study the daily, monthly, or annual changes of temperature,
or the means deduced from either or all of them, in order to
gain a clear insight into the climatic conditions that control
crop production and health conditions?
CLIMATE.
2f8g
The Annual Mean Temperature not a Good Criterion. —
Since one and the same figure may result equally from the
averaging of two widely divergent data, and from such as are
close together, it is clear that the mean annual temperature
cannot be a proper criterion of the agricultural adaptations of
a country. Thus an average temperature of 6o° F. might re¬
sult, equally, from the averaging of 65 and 55 degrees, or from
taking the mean of 15 and 105 degrees; yet the respective cul¬
tural adaptations would be widely different.
Extremes of Temperature are Most Important. — It is, on
the contrary, rather the extremes of temperature, more par¬
ticularly of cold, but frequently also of heat, together with the
total amount of heat available during the growing season,
that determines such adaptation so far as temperature is con¬
cerned; for no culture plant can be successfully grown where
the temperature during winter even occasionally falls for more
than a few hours below the point which it can resist; and for
each plant there is a certain aggregate requirement of heat to
carry it from germination to fruiting. Even different varie¬
ties of one and the same plant differ materially in the latter
respect, so that it is very important that in the selection of
varieties to be grown, this factor should be taken into con¬
sideration. It cannot be too strongly urged that the compari¬
son of annual means of temperature, so commonly made by
promoters of colonization schemes, must not be taken as a
guide either in the estimate of cultures in which the immi¬
grant may desire to engage, or by those in search of a climate
adapted to their health-conditions.
Seasonal and Monthly Means. — The statement of the mean
temperatures of the conventional four seasons — spring, sum¬
mer, autumn and winter — afford a much clearer conception of
climatic adaptations ; provided always that the extreme tem¬
peratures be considered at the same time. With the same un¬
derstanding, the monthly means are still more instructive; but
here again, it is most essential that the distribution and amount
of rainfall in each be regarded at the same time, since the most
desirable temperature is of no avail without the moisture re¬
quired for vegetation.
In some cases, e. g., that of California, it becomes neces¬
sary for practical purposes to regard the “ season, ” and not
19
290
SOILS.
the calendar year, as the unit or reference for crop production.
There the crops depend upon what rainfall may occur from
October to May, there being no summer rains of agricultural
significance, and outside of irrigated lands, almost all vegeta¬
tion save that of trees being in abeyance. In India, there are
two distinct growing seasons (“ kharif ” and “ rabi ”), corre¬
sponding to the two “ monsoon ” seasons; and no matter how
much rain may fall during one , almost total failure may occur
in other tropical and arid sections of that country.
The Daily Variations are of interest chiefly with respect to
health conditions, since most plants are more adaptable in this
respect than the average man.
RAINFALL.
Distribution Most Important. — The summary statements of
the annual rainfall are almost equally as deceptive as are those
of annual mean temperature, since quite as much depends on
the manner in which it is distributed through the year, as upon
its absolute amount; and also upon the manner of its fall.
Thus Central Montana has the same aggregate annual rainfall
as the country surrounding the Bay of San Francisco, viz.
about 24 inches; but while in the Franciscan climate this
amount of rain falls during one-half of the year, and that the
growing season, enabling crops to be grown without irrigation,
in Montana the rainfall is distributed over the entire season,
so that irrigation is absolutely essential for the successful pro¬
duction of crops. This so much the more as, while the winter
snowfall is very light, the rains of summer are largely torren¬
tial, running off the surface in muddy floods and giving little
time for absorption into the soil. Farther west, in Washing¬
ton, where grain crops are largely grown without irrigation,
the sowing of winter grain is impracticable because the dry
summer is immediately followed by the very light snowfall of
winter, which falls on dry ground. Fall-sown grain would
thus simply lie dormant in the ground through the winter,
with great liability to injury from stress of weather in early
spring, apart from the depredations of birds and rodents,
lienee grain is always sown there in spring only.
These examples may suffice to show that summary state-
CLIMATE.
2gt
ments of either temperature or rainfall by yearly means are
of little practical interest to the farmer. What he needs to
know is whether or not sufficient rains to mature a full crop
are likely to fall during the time that the growing temperature
prevails ; and what are the minima and maxima of temperature
— heat and cold — that his crops will be called upon to endure.
WINDS.
The third climatic factor mentioned, the winds, though
proverbial for their unreliability and inconstancy, are not only
very incisive in their action, but also to a considerable
extent of very definite local or regional occurrence and signifi¬
cance. Moreover, their occurrence, direction, temperature and
moisture-condition can, in regions whose climatology has been
reasonably well studied, be foretold with sufficient accuracy
to be of great use to the farmer.
Heat the Cause of Winds. — As already stated, the primary
cause of all winds is heat, substantially on the principle accord¬
ing to which draught is created in our domestic fires. The
hot air rising creates an indraught from all directions, especi¬
ally from that which it can most readily come; viz., from
the ocean,1 or from level lands, rather than across mountain
chains. Hence the sea-breeze in the after part of the day, when
the land has become heated; while the sea, requiring a much
larger amount of heat to change its temperature to a similar
extent, remains relatively cool. But at night the earth cools
more rapidly than the sea, by radiation ; hence toward evening
1 A striking case in point is the regular wind which in summer blows through
the “ Golden Gate,” a gap in the Coast Range connecting the Pacific Ocean
directly with the great interior valley of California, along the bays of San
Francisco, San Pablo, and Suisun. The great interior valley and adjacent moun¬
tain slopes becoming intensely heated during the rainless summer, the ascending
air is replaced by a steady indraught from the sea, which is bordered by a belt of
cold water causing fogs along the coast. The fogs are quickly dispelled on reach¬
ing the edge of the valley near the middle of its length ; whence steady breezes
blow northward and southward, up the valleys of the Sacramento and San
Joaquin respectively. These winds, popularly often, but erroneously, called trade-
winds, are really “ monsoons ” similar in their origin to those of India, which,
when coming from the sea cause rains, but when from the heated land itself are
hot and dry; as in the case of the sirocco of Italy and North Africa, the terral of
Spain and the northers of California.
292
SOILS.
the sea-breeze dies down, and toward and after sunset the
land-breeze takes its place.
The principle of this local change of winds, together with
the rotation of the earth, the absorption of moisture by air,
and the fact that the latter becomes cooler when it expands
on rising and warmer when it is compressed by descending,
serves to explain all the major phenomena usually observed
in connection with winds. The air of the equatorial belt,
heated throughout the year, necessarily rises and creates an
indraught from both north and south; but since the air thus
flowing in has a lower rotary velocity than the earth’s surface
at the Equator, it lags behind and so gives rise to northeast
and southeast winds, respectively, between the two tropics and
the equatorial belt. These regular winds, from the aid they
give to commerce in passing from continent to continent, are
known as the trade winds. On the other hand, the air that
has risen from the hot equatorial belt, cooling by expansion
as it rises and flowing northward and southward from the
Equator, on descending as it mainly does into the temperate
zones, has a higher rotary velocity than the land-surface and
so tends to give rise to southwest and northwest winds in the
northern and southern hemispheres respectively. At sea, on
coasts and in level inland regions to windward of mountain
chains, such winds are often quite regular during a portion of
the year.
Cyclones. — But local disturbances arising from heated land
areas or mountain slopes, as well as wide atmospheric changes
whose causes are not fully understood, give rise to waves of
alternating high and low barometric pressure, largely con¬
verting rectilinear or slightly curved wind-motion into whirls
or “ cyclones ” 1 ranging from a thousand to over two thou¬
sand miles in diameter. These in the case of low-pressure
waves or centers, toward which the air flows from the outside,
revolve in the direction contrary to the movement of the hands
1 This designation is popularly and incorrectly applied to the comparatively
limited, but very violent and destructive rotary storms or whirlwinds which
originate locally on the heated plains of the Middle West of the United States, and
are almost always accompanied by violent electric phenomena. These should
properly be called tornadoes. At sea such whirlwinds give rise to waterspouts, in
deserts to sand storms.
CLIMATE.
293
of a clock, and commonly produce rain in their east portion.
A high-pressure wave or center, from which the air naturally
flows toward the outside, will usually bring about an “ anti¬
cyclone ” area with fair, and in winter cold (“ blizzard ”)
weather, the direction of the whirl being, in this case, the re¬
verse, or in the same direction as the hands of a clock. Both
cyclones and anti-cyclones move in North America from west
to east, mostly entering from the Pacific Ocean off the north¬
west coast and traversing the continent with a slight south¬
east (or in the case of cold weather almost south) trend, with
a velocity of twenty to thirty miles an hour ; until upon reach¬
ing the region of the Great Lakes they generally turn north¬
eastward and pass into the Atlantic Ocean from the New Eng¬
land and Canada coasts. — It is upon these general facts,
roughly outlined here, that the weather forecasts are in the
main based ; taking into consideration, of course, the local or
regional conditions, topography, etc., which modify the appli¬
cation of the general rules.
In the southern hemisphere, the air-movements substantially
correspond to those observed in the northern, so far as not
modified by mountain chains ; as is especially the case in South
America.
INFLUENCE OF TOPOGRAPHY.
Rains to Windzvard of Mountain Chains. — The surface fea¬
tures or topography of the regions traversed by the air cur¬
rents or winds may materially modify both their direction and
their physical condition, especially as to moisture and temper¬
ature. Mountain chains may deflect them, or, causing the air
currents to rise on their slopes, and thus to cool by expansion,
the moisture these bring with them from the sea may be
partially, or sometimes almost wholly, deposited in the form of
rain or snow ; chiefly on the windward slopes. Then, continu¬
ing across the range, the air deprived of most of its moisture
cannot readily yield up more; hence the scarcity of rain —
“arid climate” — under the lee of mountain chains; as in the
Great Basin between the Sierra Nevada and Cascade ranges
on the one hand and the Rocky Mountains on the other, and
also on the Great Plains under the lee of the latter. The
294
SOILS.
abundant rainfall between the Mississippi river and the At¬
lantic coast is due to the moist winds coming from the warm
waters of the Gulf of Mexico and Caribbean sea, whose access
is not interfered with by any cross-ranges of mountains. But
the Great Plains lying between the Mississippi and the Rocky
Mountains are not within the sweep of the Gulf winds, whose
trend is SW to NE ; while they are equally out of reach of
moisture from the Pacific, all that having been successively de¬
posited on the intervening mountains; hence their deficient
rainfall.
Northward of the temperate zone the rainfall generally de¬
creases as we approach the arctic regions ; except where the in¬
fluence of warm ocean currents to windward creates com¬
paratively local exceptions, as in the case of Norway and
Alaska.
Fig. 52.— Composite Curve showing distribution of Rainfall in Europe, Africa and America pro¬
jected on 100 Meridian W. L.
The general Distribution of Rainfall on the globe is well
shown in the annexed diagram, which is copied by permission
of the author from his treatise on the “ Evolution of
Climates,” 1 and represents the mean deduced from data given
in the Atlas of Meteorology by J. G. Bartholomew. It is a
composite curve derived from the consolidation of four curves
showing the distribution of rainfall, viz, on the meridians of
1 “ The Evolution of Climates”; by Marsden Manson, July, 1903; also Amer
Geologist , Aug.-Oct. 1897.
CLIMATE.
295
20°E.L. ; the west coasts of Europe and Africa; the 30th
meridian W.L., in the Atlantic Ocean; and the west coasts of
North and South America, projected on the plane of the 100th
meridian W.L. The latter curve corresponds with remarkable
closeness to the mean curve here given. “ It is not intended
that these curves should include the rainfall upon meridians on
which the distribution in belts is interrupted by continental
influences, and by the irregular oblique belts of rain on the east
coasts. ” But it presents an admirable generalization upon
which, as a basis, the local disturbances may be studied.
It will be noted that the maximum of rainfall in the tropi¬
cal rain-belt lies several degrees to northward of the equator,
owing doubtless to the greater land area in the northern hemi¬
sphere. There is thus, on the whole, a narrower belt of de¬
ficient rainfall or aridity between the tropical and northern
temperate rain-belts, than in the southern hemisphere. The
southern temperate rain-belt touches only the extreme ends of
South America, Africa and New Zealand; elsewhere on the
ocean it has not been sufficiently observed as yet. The zones
of rainfall and aridity are, however, known to be subject to
seasonal oscillations of several degrees in latitude, owing to
the obliquity of the plane of the ecliptic, which shifts its posi¬
tion upon that of the equator.
Ocean Currents. — Since water as a fluid is subject to the
same circulatory motions which cause winds, it is to be ex¬
pected that ocean currents should exist corresponding to those
of the air, as characterized in general above. But as water
warms so much more slowly than air, its circulation would be
comparatively insensible were it not for the effects produced
by the air currents upon the surface of the sea, combined, as
in the case of the winds, with the effects of the rotation of the
earth. Without going into the details of the ocean currents in
the tropics, it may suffice to say that owing partly to the
moving and warming effects of winds, partly to the natural
circulatory motion of the water, two great warm currents flow
from the tropics northward, materially modifying what would
otherwise be the climates of the coasts they touch.
The Gulf Stream. — The current most generally known is
the Gulf Stream, flowing partly from the Gulf of Mexico and
the Caribbean Sea, partly from outside of the same along the
SOILS.
296
chain of the Lesser Antilles, along the southeast coast of the
United States (Florida, Georgia and South Carolina) ; but
owing to its greater rotational velocity it is soon, like the
winds of the same latitudes, deflected from a northward to a
NE. course, which carries it away from the American coast,
to impart some of its warmth, (probably mainly through the
winds that blow over it), to Great Britain and Ireland, Scandi¬
navia, and Western Europe generally; while the northern
American coast is left to be bathed by the icy polar current
flowing from the Arctic through Baffin’s Bay, which carries
icebergs far to the south in the way of the transatlantic traffic
between the Eastern States and Europe, and causes a differ¬
ence in climate that is well exemplified in the comparison of
the climate of New York with that of Naples, both lying in the
same latitude; and similarly of the bleak coast of Labrador
with that of Great Britain.
The Japan Stream. — On the eastern Asiatic Coast, a warm
current originating in the Sunda seas, flows off the coasts of
the Philippines and of China and bathes the Japanese islands;
hence it is known as the Japanese Current, or Kuro-siro. It is
partly this current which, failing to pass into the Arctic
through the shallow waters of Behring strait, renders the
coast climates of the northwest coast of America so much
milder and moister than is that in corresponding latitudes on
the east coasts of both continents. Alaska corresponds to Nor¬
way in its moist, foggy and relatively mild coast climate ; Brit¬
ish Columbia, Washington and Oregon participate in the bene¬
fits of the tempering influence of the return current of the
Kuro-siro. But as this return (“Alaska”) current passes
southward into the warmer seas off the California coast, its
influence is reversed ; it becomes a cold current in the warm
waters of the Pacific, and the warm, moist air of the ocean
being carried by the westerly winds across this cold stream
which flows along the shore of California, in summer dense
fogs are formed, which render navigation difficult and pro¬
duce a coast climate whose average summer and winter tem¬
peratures (e. g. at San Francisco) may differ by only a few
degrees, viz., 15.5 and 13. o° C. (60 and 56° F.); so that a
change of clothing from season to season is hardly called for.
The Alaska Current leaves the immediate coast of California
CLIMATE.
297
off Pt. Conception near Santa Barbara, gradually losing it¬
self southwestward, but still tempering the tropical heat in the
Hawaiian Islands. Hence the coast climate is much warmer
and less foggy in southern California; but throughout the
State in the interior valleys, screened from the coast winds by
the Coast ranges, the temperature in summer may rise several
degrees above ioo° F. for days together; although, owing to
the dryness of the air, the heat is not oppressive.
Contrasting Climates in N. W . America. — An even more
striking contrast, showing the effects of the warm ocean and
air currents, when intercepted by mountain chains, exists on
the Pacific coast farther northward, as already mentioned.
In Oregon and Washington first the low Coast ranges, and
then the higher Cascade mountains, obstruct the eastward
progress of the westerly ocean winds. The result is a very
heavy rainfall to coastward of and within the Coast ranges,
and an almost equally heavy precipitation on the western
slope of the Cascades. Standing on the crest of the latter in
summer, one may see to westward a rolling sea of clouds,
causing almost daily rains; while to eastward the eye ranges
over brown or whitish, dusty plains or rolling lands, almost
destitute of tree growth and quivering with heat, under a
deep blue sky untroubled by clouds for months.
A somewhat similar contrast is seen in the Hawaiian islands,
which are in the sweep of the subtropical northeast trade
winds, and on their windward (eastern) slopes have abundant
rains; while on the leeward slopes an almost arid climate pre¬
vails, calling for extended irrigation.
Continental, Coast and Insular Climates. — From what has
been said above, the striking differences of climate caused by
the position of any region with reference to the sea or other
large bodies of water on the one hand, and to mountain chains
on the other, can be readily understood; provided of course
that the direction of the winds and the trend of the mountain
chains be properly taken into consideration. Western coasts
in the temperate and subtropical regions will have a relatively
even, temperate and moist climate as compared with the in¬
terior of continents, from which the tempering influence of
the sea is cut off by mountain chains. Where no such chains
intervene the coast climate may extend far inland. The lat-
SOILS.
298
ter case is that of Europe, where the prevailing westerly winds,
warmed by the Gulf Stream, temper the climate as far east as
the borders of Russia, and northward to Norway; while to
southward the warm waters of the Mediterranean and Black
seas temper both heat and cold in Spain, southern France,
Italy and the Mediterranean border generally. But to east¬
ward, in Russia and Siberia, the climate becomes “ conti¬
nental ” to an extreme degree, with very cold winters and
very hot summers. The same is true of interior North Amer¬
ica, wherever the continental divide cuts off the tempering in¬
fluence of the westerly winds ; Montana, the Dakotas and the
Great Plains states generally being examples. The climate of
the Mississippi valley, as stated before, is tempered by the
winds blowing from the Gulf of Mexico, but with occasional
irruptions of the continental climate (sometimes reaching as
far east as the South Atlantic coast) in the forms of cold
“ blizzards/’ from which the coast climates of the Pacific and
of western Europe are practically free. The Atlantic coast
of North America (including the coast of the Gulf of Mexico),
moreover, not unfrequently suffers from the violent cyclonic
storms that originate in the Antilles and follow more or less
the direction of the Gulf Stream.
Islands, differing from continents mainly in their extent,
and having a relatively large proportion of coast, naturally
have climates controlled essentially by the surrounding ocean.
The insular or oceanic climates are therefore, as a rule, more
temperate and even than are those of the nearest mainland.
It is often said that the climate of western Europe is “ in¬
sular”; and owing to its position under the lee of the Gulf
Stream, this is eminently true of Great Britain.
Subtropic Arid Belts. — Where the surface features of the
land in relation to the ocean and prevailing winds do not in¬
terpose special obstacles, we find to poleward of both tropics
a climatic belt of greater or less width, in which the annual,
or at least the summer rainfall is too small to maintain annual
herbaceous vegetation throughout the season, even when the
temperature is favorable. These two “ arid ” belts are best
defined in Africa, where the northern one is represented by
the Sahara desert, lower Egypt and Arabia, while the south¬
ern one is exemplified in the Kalahari desert, to northward of
CLIMATE.
299
the Cape of Good Hope. The northern belt is continued into
Asia Minor, Palestine, Syria and Persia, and is again manifest
in northwestern India; but to eastward is stopped by the in¬
fluence of the great Himalaya range. The plateau countries
beyond, in Central Asia, are extremely arid, largely by
reason of their high elevation.
In Australia the southern arid belt is very strongly defined.
In North America, the arid belt is characteristically defined on
the Pacific Coast. It embraces all but the southernmost point
of the peninsula of Lower California, with about two-thirds
of the State of California; thence eastward across Sonora and
Arizona to New Mexico and western Texas. But here the
influence of the mountain ranges and high plateaus obscures
the subtropical belt as such, the arid climate continuing, east
of the great Pacific ranges, through Nevada, Utah, Wyoming,
Montana, Idaho, and eastern Oregon and Washington nearly
to the line of British Columbia on the north, and with gradu¬
ally decreasing aridity, into Colorado, Kansas, Nebraska, and
the Dakotas.
In South America the rainless seaward slopes of southern
Peru and northern Chile indicate the southern arid belt ; but
here, the great chain of the Andes intervening, the dry pampas
of Argentina, and the Gran Chaco of southwestern Brazil, like
the Nevada basin, though arid would naturally be referred to
the moisture-condensing influence of the Andes chain, under
the lee of which they lie. From this cause the region of de¬
ficient rainfall, which on the western coast ends to northward
of Santiago de Chile, is east of the Andes continued much
farther poleward, as in North America; reaching into Pata¬
gonia.
Utilization of the Arid Belts. — While, as already explained,
the distribution of the rainfall through the year is nearly as
important as its total amount, yet it is evident that even with
the minimum of twenty inches of total precipitation as the
measure for crop production, a very large proportion of the
land of the arid region cannot, even with the most elaborate
system of water conservation, be supplied with sufficient water
for ordinary crops, and must be otherwise utilized, mainly for
pasture purposes. This is rendered practicable to a much
greater extent than might be expected, because the rapid transi-
300
SOILS.
tion from the rainy to the permanent dry season cures the
standing herbage into hay, which affords good grazing during
the rainless season. Moreover, the use of drought-resistant,
browsing forage plants, both shrubs and trees, serves to sup¬
plement materially any deficiency in the supply of “ standing
hay,” especially in case the rains should toward the end be
unduly delayed. The same is true of the dried pods and
seeds of native herbage, which in some cases (bur clover,
lupins, etc.,) afford highly nutritious additions to the leafy
forage.1
1 See Rept. of the U. S. Commissioner of Agriculture for 1878, pp. 486-488 ;
Bull. Nos. 16 and 42, Wyoming Expt. Station ; Bull. No. 150 Calif. Expt. Station;
Bull. No. 51, Nevada Expt. Station ; South Dakota Station Bulletins Nos. 40, 69,
70,74; Kansas Expt. Station, Bulletin No. 102; New Mexico Expt. Station,
Bulletin No. 18; Montana Expt. Station, Bulletin No. 30; and others.
CHAPTER XVII.
RELATIONS OF SOILS AND PLANT GROWTH TO HEAT.
The Temperature of Soils. — The rapid germination of seeds,
as well as the development of plants to maturity, is essentially
dependent upon the maintenance of the appropriate tempera¬
ture. The temperature most favorable to germination or
growth, as well as the degree of tolerance of high and low
temperatures, varies greatly with different plants, governing
mainly what is known as their climatic adaptation. A knowl¬
edge of these points with reference to the several crops is
therefore of no mean importance to the farmer; for, to a cer¬
tain extent, he can control the temperature in the soil itself,
and he can mostly choose for sowing and planting, the time
when the soil shall have the proper temperature for rapid
germination or maturity. As a rule, it is not desirable to have
either seeds or seedling plants in the ground for any length
of time when the temperature is too low for active vegetation ;
for while they rest, other, lower organisms (fungi and bac¬
teria), adapted to low temperatures, may continue in full
activity at the expense of the vitality of the crop plant.
W ater exerts controlling Influence. — Since the capacity of
water for heat is approximately five times greater than that of
the average soil, equal weights being considered, it follows
that the temperature of soil-water must exert a controlling
influence over that of the soil. Taking the case of a cubic
foot of loamy soil, fully saturated with water, in which one-
third of the volume may be assumed to be water : the weight
of the dry soil being about eighty pounds per cubic foot, cal¬
culation shows that the amount of heat required to raise the
temperature of the water contained, one degree, will be fully
twice as great as for that required for the soil itself. It is
thus obvious that the control of soil-temperature is largely
dependent upon the control of the water-content of the same,
which has been discussed in a former chapter. Even in the
301
302
SOILS.
condition of moisture known to be most favorable to plants,
viz., one-half of the maximum water capacity, the influence of
the water-content upon the temperature will still he as great
as that of the entire soil mass. This consideration emphasizes
the importance of such control.
Cold and Warm Rams. — It is not surprising then that the
occurrence of cold or warm rains or the use of cold or warm
irrigation water at critical periods, may largely determine the
success or failure of the crop. It is well known that the oc¬
currence of a cold rain after vegetation has started actively in
early spring, may not only destroy the season’s fruit crop by
preventing the setting, or thereafter causing the dropping, of
the fruit, but may even, if the suppression of vegetative action
be continued for some length of time, result in serious injury
to, or death of trees. Widely extended disastrous experience
of the kind was had in California in February and March,
1887, resulting in the death of tens of thousands of fruit trees
and vines during that and the following season. It is obvious
that in such a case as this the rapid draining-off of the cold
water through underdrains would have materially mitigated,
if not wholly prevented, such injury.
Solar Radiation. — Aside, however, from such overwhelming
influences as the above, the soil temperatures are measurably
controlled by the extent to which they receive and absorb the
sun’s heat rays, whether directly or through the mediation of
the air. The direct effect of the sun’s rays upon the surface
is, upon the whole, the most generally potent, although warm
winds may occasionally exert a very strong influence. The
varying influence of the sun’s rays depends primarily upon
the change of seasons, which themselves result from the vary¬
ing angles at which the sun’s rays strike the surface; as well
as upon the duration of the day. The greater or less cloud¬
iness or fogginess of the sky, of course, exerts a decided effect
in this connection.
The Penetration of the Suns Heat into the Soil. — In the
temperate regions of the earth the daily variations of temper¬
ature cease to be felt at depths ranging from two to three feet,
according to the nature of the soil material and its more or less
compacted condition. The monthly variations, of course,
RELATIONS OF SOILS TO HEAT.
303
reach to greater depths ; while the annual variations do not
disappear in the temperate zone, e. g.f at Paris, Zurich and
Brussels, at a less depth than seventy-five feet. At these
depths of constant temperature we find approximately the
same temperature as that which we can deduce from the ther¬
mometric observations as the annual mean. From similar
causes the mean annual temperature of any place may be ap¬
proximately deduced from the observation of the water of
wells and springs derived from moderate depths. For below
the level of constant annual temperature the latter begins to
ascend steadily as we progress downward, owing to the in¬
terior heat of the earth.
Change of Temperature with Depth. — The following table
of observations made at Brussels illustrates the decrease of
annual range of temperature with depth :
At feet : Average temperature. Annual range.
3-25 . 7-2° C. 10.50 C.
15-6 . 13.5° C. 4-5° C.
30.8 . 16.4 C. 1. 30 C.
75-° . i7-o C. o.o° C.
It is interesting to compare with this record that of a well
sunk by Ermann at Yakutzk, Siberia, where the mean annual
temperature is — 9.7 C. (14.6 F. ). This temperature was
found a few feet below the surface. At 50 feet the tempera¬
ture was — 7.2 C. (190 F.) ; at 145 feet — 50 Cent. (230 F. ) at
350 feet — .9° C. (30.8° F.) showing that the ground was be¬
low the temperature of freezing water for some distance far¬
ther down ; so that the search for liquid water was abandoned.
We thus see that in the Arctic regions, owing to the pres¬
ence of water in the form of ice, the melting of which impedes
the access of solar heat, the level of no variation is found at
the distance of a few feet below the surface, despite the great
variations in temperature between the short but hot summer
and the extremely cold winter. In the tropics, also, the annual
temperature-variation disappears at a less depth than 2 feet,
in consequence of the very slight difference between the two
seasonal extremes of temperature.
Surface — Conditions that influence Soil-Temperature.
Among these color has already been mentioned, and to a cer-
304
SOILS.
tain extent discussed. While it is true that, broadly speaking,
dark-colored soils absorb more of the sun’s heat than light-
colored ones, other things being equal, it must still be under¬
stood, that the nature of the color-giving substance exerts a
very material influence upon the amount of heat absorbed.
Thus charcoal is among all known substances the one absorb¬
ing and radiating the sun’s heat rays most powerfully, and all
kinds alike; so much so, that its absorbent power is taken as
ioo. But other substances which to the eye appear equally
black, have by no means the same absorbing power. The heat
absorption by black humus is high, though not quite equal to
that of charcoal ; and many gray soils, though appearing to the
eye of rather light tint, really absorb more heat than others
which, to our perception, have the darker tint, but are colored
by other substances. Gardeners and especially vine growers in
the colder portions of Europe often take advantage of the
powerful absorbing power of carbon by spreading charcoal
or black slate powder over the surface of the soil where early
maturity is specially desired ; and slate powder is similarly
used by the peasants at Chamouni to hasten the melting of
the snow.
Heat of High and Lozv Intensity. — It must also be kept in
view that the surfaces, and especially the colors that favor ab¬
sorption of the intense rays of the sun, may comport them¬
selves quite differently toward heat rays of low intensity, such
as those thrown back from the soil at night when it cools.
Were this otherwise, a soil that absorbs much heat in the
daytime would lose it with corresponding rapidity at night.
But this is true only of charcoal ; in the case of most other
substances, there is a material difference in favor of the re¬
tention of the heat, of low intensity, by slower radiation into
a “heat-trapping” atmosphere.
Reflection vs. Dispersion of Heat. — Theoretically, a smooth
surface reflects more heat than a rough one, and warms much
more slowly by absorption ; as is strikingly shown by the use
of polished metal screens placed on walls to prevent their being
overheated by a flue near by. In the case of soils, also, the
condition of the surface affects materially the absorption of
heat, but not in accordance with the above rule so far as the
RELATIONS OF SOILS TO HEAT.
305
result is concerned. For it is found that, other things being
equal, a loose or cloddy surface disperses in many directions
the heat it receives, and does not permit it to penetrate by
conduction to so great extent as would a more compact soil,
whose smooth surface would waste less of the heat received
by radiation.
King has called special attention to the difference of temperature
existing between soils smoothed and compacted by a roller, and the
unrolled soil having a loose surface. He found that the former at a
depth of one and a half inches was as much as 5-5°C. (io°F.) warmer
than the loose soil, and that even at a depth of three inches a difference
as high as 3.5 °C. (6.5 °F.) existed between the two. He observed at
the same time that the temperature of the air over the unrolled ground
was considerably warmer than above the rolled, thus corroborating the
differences observed in the soil itself. But at night the heat is given
out more rapidly from the rolled than from the unrolled surface, the
latter acting as a non-conductor and keeping the soil warmer than that
of the more compact rolled land. King gives as the average difference
observed between rolled and unrolled land on eight Wisconsin farms,
i.6°C. (3°F.) in favor of the rolled land between 1 and 4 p.m.
It will thus be seen that the loose tilled layer, while im¬
peding the penetration of the sun's heat into the deeper por¬
tions of the soil during the day, on the other hand serves to
retain it at night better than a more compact soil. This ob¬
viously places it within the power of the farmer to exert con¬
siderable control over the soil-temperature at critical times;
restraining or favoring the access of the sun’s heat in accord¬
ance with the requirements of the climate or season, as the
case may be.
Influence of a Covering of Vegetation , and of Mulches . — A
cover of either living or dead vegetation depresses the tem¬
perature of the soil as compared with the bare land, as elabor¬
ately shown by Wollny and Ebermeyer. In the monthly aver¬
ages these differences rarely exceed .8° C. (1.5 degrees F.),
and are mostly below .50° C. (i° F.), but during different
parts of the day they may rise to 2.2 to 2.50 C. (4 to 4.50 F. ),
at 4 inches depth. In summer they are greater than at other
seasons. Of course the density of the vegetation or the thick¬
ness of the mulch influences them materially. Forests exert
20
3°6
SOILS.
the greatest cooling influence upon the soil, and next to these
the dense herbaceous crops, such as clover, and the legumes
generally.
Influence of the Nature of the Soil-Material. — Aside from
the surface condition, the nature of the material itself exerts a
certain influence, not only upon the rate of introduction of
heat, but also upon the amount taken up. Thus quartz sand
having the highest density (greatest weight per cubic foot)
and also the highest capacity for heat among the usual mineral
soil-ingredients, will, mass for mass, experience a smaller rise
of temperature than would clay or loam soil, of less density
or volume-weight, and also of lower heat-capacity. While
this holds good theoretically, differences corresponding to
this consideration rarely occur in nature, for the reason that
the much greater influence of the mechanical condition of the
soil mostly overbalances these effects. Thus Wollny has
shown that while quartz is a better heat-conductor than clay,
quartz cobbles or gravel will materially increase the tem¬
perature of the soil in which they are imbedded. Yet com¬
pact clay is a better conductor of heat than loose sand ; hence
the latter, when exposed to the intense heat of the summer
sun in the desert, becomes intensely hot on the surface, yet al¬
lows of the existence of abundant moisture at a depth of ten
or twelve inches; while clay in the same region, being usually
in a compacted condition, will show a lower surface-tempera¬
ture and will be warmer and drier at a depth at which sand
will still retain abundant moisture, and be comparatively cool
(See chap. 13, p. 257.) So much indeed depends upon the
state of mechanical division and flocculation in which the sev¬
eral soils may happen to be, that a hard-and-fast statement in
regard to their relations to heat cannot and should not be
given, as it would only lead to disappointments and practical
mistakes; the more as in all cases the moisture-condition ex¬
erts an influence predominating by far over that of the dry
material itself, and this moisture-condition is subject to rapid
changes, owing to intrinsic differences in the several classes
of soils. Wollny states as the result of his experiments, that
in summer sandy soils are warmest ; then humous, lime and
loam soils; while in winter humous soils are warmest, then
loams; and sand coldest.
RELATIONS OF SOILS TO HEAT.
307
Influence of Evaporation. — In treating of the Conserv¬
ation of Soil Moisture (chapter 13), the effects, conditions and
control of evaporation from the soil have already been dis¬
cussed from several points of view ; so that a summary review
of the subject must suffice in this place.
It has been stated above that in the case of an average loam
soil saturated with water, the heat required to raise the tem¬
perature of the water one degree would be about twice that
needed to so change the dry soil material itself. But if it is
required to evaporate the same amount of water from the soil,
nearly ten (9.667) times that amount of heat will be required;
or in the case assumed, twenty times as much as would suffice
to raise the temperature of the dry soil through an equal in¬
terval of temperature. While in a few cases the cooling of
the soil by evaporation is desirable, in the vast majority of
cases it is injurious to the progress of vegetation, and should
be restricted as much as possible by the means outlined in a
former chapter.
Formation of Dezv. — There is, however, another aspect of
evaporation from the soil which has been long misunder¬
stood, although the true state of the case was partially recog¬
nized long ago. Dew is in common parlance said to “ fall,”
it being supposed that, like rain, it is derived from the atmos¬
phere. While this is partially true, inasmuch as from very
moist, and notably from foggy air dew is frequently deposited
on grass and foliage generally, as well as on wood and other
strongly heat-radiating surfaces ; yet as a matter of fact, in
by far the majority of cases, as shown by H. E. Stockbridge 1
and confirmed by everyday observation, dew is formed from
the vapor rising from the warmer soil into a colder atmos¬
phere, and condensed on the most strongly heat-radiating sur¬
faces near the ground, such as grass, leaves both green and
dry, wood, and other objects first encountering the rising
vapor. In manifest proof of this it will be noted that very
heavy dews may be seen on the ground, when the roofs of
houses as well as the higher shrubs and trees remain perfectly
dry. In winter this may be most strikingly seen in the
deposition of hoar-frost in and immediately around the cracks
of plank sidewalks, whose surface remains dry.
1 “ Rocks and Soils,” pp. 175-189.
3°8
SOILS.
Dezv rarely adds Moisture. — Candid observations will con¬
vince any one, therefore, that in most cases the supposed addi¬
tion to the moisture of the soil from dews is an illusion.
Whatever dewdrops fall on the ground are in general simply
the return to the soil of a part of what came from it; while
the dew that evaporates from the bedewed leaves or other
objects represents simply a delayed outgo of moisture from
the soil, which for a time retards evaporation direct from the
soil, and thus effects a slight saving of moisture.
But while this is measurably true of inland and especially of continental
areas like the great plains of North and South America, it is also true
that in deep moist valleys, and on the rainy and foggy coast regions of
continents, dews are found to both fall and rise, not uncommonly to
such an extent as to be equivalent to a not inconsiderable aggregate
precipitation. Thus in the moist coast belt of Oregon and Washington
lying west of the Cascade range of mountains, the morning dews of
summer are frequently so copious that the water falls in showers from
the lower trees and shrubs, so as to necessitate the use of water-proof
clothing when traversing the woods in the morning, quite as much as
though rain was actually falling. In hilly and more especially in
mountainous regions the cold air descending from above and flowing
down in the ravines will often cause a heavy condensation of dew in
these, while the bordering ridges, which rise above the cold currents,
remain free from dew. These descending currents as a rule not only
bring no surplus moisture with them, but in their downward course
become warmer by contraction and therefore relatively drier. In these
cases also, therefore, the dew is purely moisture derived from the
ground, which in rising encounters the cold air and is thus condensed.
The fact that dew is most commonly derived from the soil
could have been foreseen from the other fact, long ascertained
and known, that during the night the soil is as a rule warmer
than the air above it; as has been shown by the earlier ob¬
servers, as well as more specifically by Stockbridge.
Dezv zvithin the Soil. — It is obvious that whenever dew is
formed above the surface of the soil, the air within the latter
must be at or near its point of saturation with vapor, as in
fact is usually the case a few inches below the surface. It
follows that when a depression of temperature occurs within
RELATIONS OF SOILS TO HEAT.
309
the soil, e. g., at night, dew must be deposited within tne soil
down to the depth to which the nightly variation reaches, in¬
creasing at that depth as the vapor from the warmer soil be¬
low rises, to be in its turn condensed. There is thus formed
at that level a zone of greater moisture, which may sometimes
be noted in digging pits, by a deeper tint, without any cor¬
responding variation in the nature of the soil. The daily re¬
petition of this process, at varying depths, and its greater or
less recurrence at or near the limit-levels of monthly and even
annual variations, must' exert a not inconsiderable influence
upon the vertical distribution of moisture in the soil ; which
instead of being usually found in horizontal bands or zones of
varying moisture-contents, is usually remarkably uniform for
considerable depths, despite the fitfully recurrent additions
from rains. It is at least probable that this process of dew-
formation within the soil materially assists capillarity in
effecting a measurably uniform vertical distribution of mois¬
ture. (See also page 207, chapter 11).
Plant-development under different Temperature — Condi¬
tions. — In the arctic regions the ground, frozen in winter to
unknown depths, may thaw to only three to five feet during
the summer, notwithstanding the great length and continuous
sunshine of the arctic day. The shallow-rooted arctic flora
develops very rapidly under the influence of the continuous
daylight and heat, in the course of from five to eight weeks.
The seeds of these plants must, of course, be capable of ger¬
minating at very low temperatures; and as a matter of fact,
we find that both in the arctic regions and in the higher mount¬
ains, certain plants are found growing and blooming on slopes
flecked with snow ; each plant surrounded by a small circle
of bare ground, where the snow has been melted under the
influence of the dark-tinted earth and leaves. It is clear that
here germination has occurred, the foliage has been formed,
and the roots have been exercising their vegetable functions,
in ground soaked with water practically ice-cold.
Germination of Seeds. — While wild plants of special adapta¬
tion may thrive in very low (or high) temperatures, it is also
true that few of our cultivated plants will germinate, and still
less grow thriftily, at such low temperatures. The limit be-
3io
SOILS.
low which most cultivated plants may be considered as remain¬
ing practically inactive lies between 4.4 and 7.20 C. (40 and
450 F.). Few tropical plants will germinate much below
23.8° (750 F.) and in some cases not below 350 Cent. (95 0
F.). Even maize and pumpkins, according to Haberlandt,
germinate most rapidly between 35 and 38.3° C. (95 and ioi°
F.), while for wheat, rye, oats and flax the best temperature
for germination lies between 21.1 to 26.1 (70 to 79°). Un¬
der the most favorable conditions of temperature and moisture,
some small seeds which readily absorb moisture will germinate
in from twenty-four to forty-eight hours, while at a lower
temperature they may require from three days to two weeks.
Thus Haberlandt found that while oats would germinate in
two days at a temperature of 17.2 to 17. 50 C. (63° to 63.5°),
it took a full week for germination when the temperature was
only 50 C. (41 0 F.). It is obvious that seeds remaining inert
in the soil for such lengths of time will be subject to a variety
of vicissitudes that may injure or destroy their vitality. There
are many bacteria and fungous parasites which at low tem¬
peratures are perfectly capable of attacking and destroying the
water-soaked seed. There is thus for each plant, from the
lowest to the highest, a certain temperature most favorable to
development; and both above and below this, the vegetative
activity is seriously interfered with or wholly checked. A
knowledge of these limits is manifestly of the utmost practical
importance.
The influence of too high a temperature in preventing the germina¬
tion of cinchona seed from India, was curiously exemplified when it
was subjected to a supposedly favorable steady temperature of 23.8°C.
(75°F.) under otherwise most favorable conditions. Not a single one
came up in the course of six weeks, and the box in which it had been
sown was put away outside of the hothouse as a failure. Within two
weeks a full stand of seedlings was obtained, at temperatures ranging
between 12.7 and i5.5°C. (550 and 6o°F.). The fact that the cinchona
is a tree of the lower slopes of the Andes (three to five thousand feet)
although at home strictly within the tropics, explains the apparent
anomaly.
PART THIRD.
CHEMISTRY OF SOILS,
CHAPTER XVIII.
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS IN RE
LATION TO CROP PRODUCTION.
The chemical constituents of soils have been incidentally
mentioned and discussed above, both in connection with the
processes of soil-formation, and with the minerals that mainly
participate therein. The manner of their occurrence and their
relations to plant life, so far as known, must now be consid¬
ered more in detail.
HISTORICAL REVIEW OF SOIL INVESTIGATION.
While the obvious importance of the physical soil-conditions
has long ago rendered them subjects of close study by Schiib-
ler 1 Boussingault and others, the chemistry of soils was very
generally neglected for a considerable period, after the hopes
at first entertained by Liebig that chemical analysis would
furnish a direct indication and measure of soil fertility, had
been sorely disappointed in respect to the only soils then in¬
vestigated, viz., the long-cultivated ones of Europe. The re¬
sults of chemical analysis sometimes agreed, but as often
pointedly disagreed, with cultural experiences; so that after
the middle of the nineteenth century, but few thought it worth
while to occupy their time in chemical soil analysis.
Popular Forecasts of Soil Values. — In newly-settled coun¬
tries, and still more in those yet to be settled, the questions of
the immediate productive capacity, and the future durability of
the virgin land are the burning ones, since they determine the
future of thousands for weal or woe. This need has long ago
led to approximate estimates made on the part of the settler,
1 The early work of Schiibler on soil physics, published at Leipzig in 1838
under the title of “ Grundsatze der Agrikulturchemie ” and now almost inaccessible
outside of old libraries, is remarkable as having anticipated very definitely much
that has since been brought forward and elaborated anew. He is really the fathet
of agricultural physics.
313
SOILS.
3H
by the observation of the native growth , especially the tree
growth; and where this consists of familiar species, normally
developed, such estimates on the part of experienced men,
based on previous cultural experience, are generally very ac¬
curate; so much so that in many of the newer states they have
been adopted in determining not only the market value, but
also the tax rate upon such lands, their productiveness, and
probable durability being a matter of common note.
Thus in the longdeaf pine uplands of the Cotton States, the scattered
settlements have fully demonstrated that after two or three years crop¬
ping with corn, ranging from as much as 25 bushels per acre the first
year to ten and less the third, fertilization is absolutely necessary to
farther paying cultivation. Should the short-leaved pine mingle with
the long-leaved, production may hold out for from five to seven years.
If oaks and hickory are superadd ed, as many as twelve years of good
production without fertilization may be looked for by the farmer ; and
should the long-leaved pine disappear altogether, the mingled growth
of oaks and short-leaved pine will encourage him to hope for from
twelve to fifteen years of fair production without fertilization.
Corresponding estimates based upon the tree growth and in
part also upon minor vegetation, are current in the richer lands
also. The “ black-oak and hickory uplands,” the “ post-oak
flats,” “ hickory bottoms,” “ gum bottoms,” “ hackberry ham¬
mocks,” “ post-oak prairie,” “ red-cedar prairie,” and scores
of other similar designations, possess a very definite meaning
in the minds of farmers and are constantly used as a trust¬
worthy basis for bargain and sale, and for crop estimates.
Moreover, experienced men will even after many years’ cul¬
tivation be able to distinguish these various kinds of lands
from one another.
Cogency of Conclusions based upon Native Grozvth. — Since
the native vegetation normally represents the results of
secular or even millennial adaptation of plants to climatic and
soil-conditions, this use of the native flora seems eminently
rational. Moreover, it is obvious that if we were able to in¬
terpret correctly the meaning of such vegetation with respect
not only to cultural conditions and crops, but also as regards
the exact physical and chemical nature of the soil, so as to
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 315
recognize the causes of the observed vegetative preferences*,
we should be enabled to project that recognition into those
cases where native vegetation is not present to serve as a
guide; and we might thus render the physical and chemical
examination of soils as useful practically, everywhere , as is,
locally, the observation of the native growths. To a certain
extent, such knowledge would be useful in determining the
salient characters of cultivated soils, also; and would be the
more useful and definite in its practical indications the more
nearly the cultural history of the land is known, and the less
the latter has been changed by fertilization. For, so soon as
the first flush of production has passed, the question of how
to fertilize most effectually and cheaply demands solution.
It was from this standpoint, suggested by his early experi¬
ence in the Middle West and subsequently most impressively
presented to him in the prosecution of the geological and agri¬
cultural survey of Mississippi, that the writer originally un¬
dertook, in 1857, the detailed study of the physical characters
and chemical composition of soils. It seemed to him incred¬
ible that the well-defined and practically so important distinc¬
tions based on natural vegetation, everywhere recognized and
continually acted upon by farmers and settlers, should not be
traceable to definite physical and chemical differences in the
respective lands, by competent, comprehensively-trained scien¬
tific observers, whose field of vision should be broad enough
to embrace concurrently the several points of view — geological,
physical, chemical and botanical — that must be conjointly con¬
sidered in forming one’s judgment of land. Such trained ob¬
servers should not merely do as well as the “ untutored
farmer,” but a great deal better.
“ Ecological ” studies. — Yet thus far we vainly seek in gen¬
eral agricultural literature for any systematic or consistent
studies of these relations. We do find “ ecological ” lists of
trees and other plants, or “ plant associations,” growing in cer¬
tain regions or land areas, described in some of the general
terms which may refer equally well to lands of profuse pro¬
ductiveness, or to such as will hardly pay for taxes when cul¬
tivated. Or when the productive value is mentioned, the
probable cause of such value is barely alluded to, even con-
jecturally, unless it be in describing the “ plant formations ”
3i6
SOILS.
as xerophytic, mesophytic or hydrophytic, upon the arbitrary
assumption that moisture is the only governing factor ; wholly
ignoring such vitally important factors as the physical texture
of the soil, its depth, the nature of the substrata, and the
(oftentimes abundantly obvious) predominant chemical nature
of the land. And on the other hand, we find even public sur¬
veys proceeding upon the basis of physical data alone, practic¬
ally ignoring the botanical and chemical point of view, and
inferentially denying, or at least ignoring, their relevancy to
the practical problems of the farm. 1
Early Soil Surveys of Kentucky, Arkansas and Mississippi.
— Among the few who during the middle of the past century
maintained their belief in the possibility of practically useful
results from direct soil investigation, were Drs. David Dale
Owen and Robert Peter, who prosecuted such work exten¬
sively in connection with the geological and agricultural sur¬
veys of Kentucky and Arkansas; and the writer, who carried
out similar work in the states of Mississippi and Louisiana,
with results in many respects so definite that he has ever since
regarded this as a most fruitful study, and has later continued
it in California and the Pacific Northwest. This was done in
the face of almost uniform discouragement from agricultural
chemists until within the last two decades; with occasional
severe criticisms of this work as a waste of labor and of public
funds.
Investigation of Cultivated Soils. — All this opposition was
largely due to the prejudices engendered by the futile attempts
to deduce practically useful results from the chemical analysis
of soils long cultivated, without first studying the less complex
phenomena of virgin soils; and these prejudices persisted
longest in the United States, even though in Europe the re¬
action against the hasty rejection of chemical soil work had
begun some time before ; as is evidenced by the methods em¬
ployed at the Rothamsted Experimental Farm in England, the
Agricultural College of France, the Russian agronomic sur¬
veys, and at several points in Germany. In none of these
cases, however, more than the purely chemical or physico¬
chemical standpoint was assumed ; although in Russia at least,
1 Bull. 22, Bureau of Soils, U. S. Dept, of Agriculture.
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 31 j
virgin soils were easily obtainable and their native growth
verifiable; and were actually in part made the subject of chemi¬
cal investigation.
In the course of their work, Owen and Peter always care¬
fully recorded the native vegetation of the soils collected; but
neither seems to have formulated definitely the idea that such
vegetation might be made the basis of direct correlation of
soil-composition with cultural experience. Owen repeatedly
expressed to the writer his conviction that such a correlation
could be definitely established by close study; but early death
prevented his personal elaboration of the results of his work.
Peter likewise stoutly maintained to the last his conviction that
soil analysis was the key to the forecasting of cultural possi¬
bilities; but not being a botanist he did not see his way to put
such forecasts into definite form.
Change of Views.
In the United States as well, the ancient prejudices have
now gradually given way before the urgent call for more de¬
finite information than could otherwise possibly be given to
farmers by the experiment stations, most of whose cultural
experiments, made without any definite knowledge of the na¬
ture of the soil under trial, were found to be of little value
outside of their own experimental fields. Even the multipli¬
cation of culture stations in several states, unaccompanied by
soil research, is found to be a delusive repetition of the same
inconclusive, random experimenting, since it takes into con¬
sideration only the climatic differences, but leaves out of con¬
sideration the potent factors of soil quality and soil variations.
At most these were usually mentioned by them in such inde¬
finite terms as “ a clay loam/’ “ a coarse sandy soil,” “ gray
sediment land,” and the like; frequently not even with a state¬
ment of the depth and character of the subsoil and substrata,
much less of their geological derivation or correlations. Thus
any one not happening to be personally acquainted with the
land in question would be wholly without definite data to cor- *
relate the results with his own case. It is quite obvious that
even if only to make possible the identification of new lands
with others that have already fallen under cultural experience,
3i8
SOILS.
and can therefore afford useful indications to the new settler,
a close physical and chemical characterization of lands should
be made the special object of study by the experiment stations
and public surveys, particularly in the newer states.
Advantages for Soil Study offered by Virgin Lands. —
Among the special advantages, then, offered by virgin soils for
the study of the correlations of soils and crops, the usual exist¬
ence of a native flora, representing the results of secular adapt¬
ation, is of fundamental importance. As it is at this time still
historically known of most lands west of the Alleghenies what
was their original timber growth, it is clear that their original
condition can still be ascertained by comparison with uncul¬
tivated lands of similar growth, usually not very far away;
and as their cultural history also is largely within the memory
of the living generation, the behavior of such lands under cul¬
tivation is known or verifiable. Foremost among the data
thus ascertainable is the duration of satisfactory crop produc¬
tion, and its average amount. To ascertain these surviving
data by inquiry among the farming population should be
among the foremost duties of those connected with soil sur¬
veys; and persons temperamentally unable to enlist the farm¬
er’s sympathy and interest in such inquiries must be consid¬
ered seriously handicapped, no matter what their scientific
qualifications may be. In no quest is it more literally true
that there is no one from whom the earnest inquirer may not
learn something worth knowing.
Practical Utility of Chemical S oil- Analysis ; Permanent
Value vs. Immediate Productiveness. — In many existing trea¬
tises so much emphasis is given to the alleged proofs of the in¬
utility of chemical soil examination in particular, that a special
controversion of these arguments seems necessary, in connec¬
tion with a detailed statement of what can, and in part has
been, done in that direction. Hence the often-repeated
allusion, in the sequel, to points bearing on this question.
Hence, also, the detailed discussion of many points which in
most agricultural publications are given only passing notice.
In all these discussions the difference between the ascertain¬
ment of the permanent-productive value of soils, as against
that of their immediate producing capacity, must be strictly
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 319
kept in view. The former interests vitally the permanent
settler or farmer; the latter concerns the immediate outlook
for crop production, the “ Dungerzustand ” of the Germans.
The methods for the ascertainment of these two factors are
wholly distinct, even though the results and their causes are
in most cases intimately correlated. The failure to observe
this distinction accounts for a great deal of the obloquy and
reproach that has in the past so often been heaped upon chem¬
ical soil-analysis and its advocates.
PHYSICAL AND CHEMICAL CONDITIONS OF PLANT GROWTH.
While it is true that plants cannot form their substance or
develop healthy growth in the absence or scarcity of the chem¬
ical ingredients mentioned on page xxxi of this volume, it is
also true that they cannot use these unless the physical condi¬
tions of normal vegetation are first fulfilled. Both sets of con¬
ditions are intrinsically equally important and exacting as to
their fulfilment; and the farmers’ task is to bring about this
concurrence to the utmost extent possible. The chemical in¬
gredients of plant-food can, however, be artificially supplied
in the form of fertilizers, should they be deficient in the soil ;
but as has been shown in the preceding pages, it is not always
possible to correct, within the limits of farm economy, phy¬
sical defects existing in the land. Hence, however important
is the natural richness of the soil in plant-food, the first care
should always he given to the ascertainment of the proper phy¬
sical conditions in the soil , subsoil and substrata. Without
these, oftentimes, no amount of cultivation, fertilization and
irrigation is effective in assuring profitable cultural results.
Condition of the Plant-food Ingredients in the Soil. — But
even the abundant presence of the plant-food ingredients, as
shown by analysis, will not avail, unless at least an adequate
portion of the same exists in a form or forms accessible to
plants. Of course this condition would seem to be best ful¬
filled by the ingredients in question being in the water-soluble
condition. But in the first place, plants are quite sensitive to
an over-supply of soluble mineral salts, as is evidenced by the
injurious effects produced by the latter in saline and alkali
lands. Furthermore, substances in that form would be very
320
SOILS.
liable to be washed or leached out of the soil by heavy rains
or irrigation, and would be lost in the country drainage. It
is therefore clearly desirable that only a relatively small pro¬
portion of the useful soil-ingredients should be in the water-
soluble or physically absorbed condition, but that a larger sup¬
ply should be present in forms not so easily soluble, yet ac¬
cessible to the solvent action which the acids of the soil and of
the roots of plants are capable of exercising. This virtually
available supply we may designate as the reserve food-store.
Finally, there is practically in all soils a certain proportion
of the soil-minerals in their original form, as they existed in
the rock-materials from which the soil was formed. These
minerals being usually in a more or less finely divided or pul¬
verulent condition, they are attacked much more rapidly by
the chemically-acting “ weathering ” agencies, viz., water,
oxygen, carbonic and humus acids, than when in solid masses ;
and thus, transformation of the inert rock-powder into the
other two classes of mineral soil-ingredients progresses in
naturally fertile soils with sufficient rapidity to produce, in a
single season, sensible and practically important results, known
as the effects of fallowing.
The Reserve. — The nature of these processes has been dis¬
cussed in chapters i to 4 ; and it will be remembered that two
of their most prominent results are the formation of clay, and
of zeolitic-compounds, the latter being, as heretofore stated
(pp. 36 ff) hydrous silicates of earths and alkalies, easily de¬
composable by acids, and also capable of exchanging part or
the whole of such basic ingredients with solutions of others
that may enter the soil. These zeolitic compounds therefore
fulfil two important functions in the premises, viz. : a ready
yielding-up of part of their ingredients to acid solvents, and
a tendency to fix, by exchange, a portion or the whole of the
soluble compounds that may be set free in, or brought upon
the land. The first-mentioned property is of direct avail in
that the soil-humus forms, and the roots of plants exude, acid
solvents on their surface, and can thus draw upon the reserve
store of food; the second tells in* the direction of preventing
the waste of water-soluble manurial ingredients supplied to,
or formed in the soil. (See above, chapter 3, page 38).
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 321
The reserve food-store may then be placed under the fol¬
lowing heads :
Hydrous or “ zeohtic ” silicates, from which dilute acids
can take up the bases potash, soda, lime and magnesia. These
silicates may be in either the gelatinous or powdery form ; in
the former case they may also occlude water-soluble sub¬
stances.
Carbonates of lime and magnesia, which are readily dis¬
solved by carbonated water as well as by the vegetable acids.
Phosphates of lime and magnesia, not very readily soluble
in carbonated water, but more readily attacked by the acids
of the soil and of plant roots; thus supplying phosphoric acid
to plants. The more finely divided they are the more readily
they are dissolved; some soils containing only crystalline
needles of apatite (see chap. 5, p. 63) only are nevertheless
poor in available phosphoric acid.
The natural phosphates of iron and alumina are practically
insoluble in all solvents at the disposal of vegetation and
though present in considerable amounts in some soils, (see
chapter 19, page 355), may be considered as being permanently
inert, and therefore not to be counted among the soil resources
for plant nutrition. As yet no artificial process by which
their phosphoric acid can be made available within the soil,
has been discovered.
Water-soluble Ingredients. — As regards these it has already
been explained that they are largely retained in the condition
of purely physical adsorption, as in the case of charcoal or
quartz sand, through which sea water filters and is thereby
partially deprived of its salts. But these can be gradually
withdrawn by washing with pure water alone, and still more
easily when stronger solvents are used. Since the soil-water
is always more or less charged with carbonic acid, and the
roots themselves secrete carbonic as well as stronger acids in
their absorption of mineral plant-food, there is no difficulty
about explaining the manner in which such physically con¬
densed ingredients are taken up.1
1 Whitney (Bull. 22, U. S. Bureau of Soils) claims on the basis of a large number
of (three-minute) extractions of soils made with distilled water, that these solutions
are essentially of the same composition in all soils ; that all soils contain enough
plant-food to produce crops indefinitely ; and that the differences in production
21
322
SOILS.
Recognition of the Prominent Chemical Character of Soils.
In a former chapter the soils formed from the several minerals
and rocks have been discussed in a general manner. We can
as a rule obtain some insight into the nature of any soil which
we can trace to its parent rock or rocks, if we are acquainted
with the composition of the latter.
Similarly, but in a much more direct manner, we can ob¬
tain a strong presumption as to the nature of any soil by de¬
termining the undecomposed minerals present in it. In all
ordinary cases the presumption must be that the decomposed
portion of the soil has been derived from the minerals still
found in it. Of course it may happen in the case of lands de¬
rived from widely distinct and distant regions that no such
characteristic minerals can be found; this is very commonly
true of the soils forming the deltas of large rivers, in which
sometimes the only remaining recognizable mineral is quartz
in its several forms, with occasional grains of such hardy
minerals as tourmaline, garnet, etc. Apart from such cases,
the hand lens or the microscope permits us to recognize in
most soils the minerals that have mainly contributed to their
formation, thus also gaining a clew to their prominent chem¬
ical nature.
Such recognition sometimes involves, of course, a somewhat
intimate knowledge of mineralogy; yet a little practice will
enable almost any one to identify the more important soil¬
forming minerals, under the lens or microscope, according to
the degree of abrasion or decomposition they may have un¬
dergone. The details of such researches lie outside of the
limits of this treatise, but some general directions on the sub¬
ject are given farther on.1
Acidity, Neutrality, Alkalinity. — A test never to be omitted
are due wholly to differences in the moisture supply, which he claims is, aside from
climate, the only governing factor in plant growth. The tables of analytical
results given in Bull. 22 fail to sustain the first contention ; the second is pointedly
contradicted both by practical experience, and by thousands of cumulative culture
experiments made by scientific observers ; the third fails with the second, except
of course in so far as an adequate supply of moisture is known to be an absolute
condition both of plant growth, and the utilization of plant-food. It is moreover
well known that it is not water alone, but water impregnated more or less with
humic and carbonic acids, that is the active solvent surrounding the plant root.
1 See Appendix B.
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 323
is that of the reaction of the soil on litmus or other test paper,
to ascertain its acid, neutral or alkaline reaction. Should the
latter occur quickly (by the prompt blueing of red litmus
paper), “ black alkali ” would be indicated; but a blueing after
20 to 30 minutes means merely that a sufficiency of lime car¬
bonate is present. An acid reaction (the reddening of blue
litmus paper) of course indicates a “ sour ” soil (see chap. 8,
page 122).
Chemical Analysis of Soils. — When the observations men¬
tioned above give no very decisive results or inferences as to
.the soil’s chemical character, the more elaborate processes of
qualitative and quantitative chemical analysis may be called in.
It would seem at first sight that these ought to yield very de¬
finite results to guide the cultivator; yet such is by no means
always the case. Both the previous history of the land, and
the method of anaylsis, influence materially the practical utility
of the results of chemical soil analysis.
The cause of this uncertainty becomes obvious when we
consider the three groups of ingredients outlined above, viz.,
the insoluble or unavailable, wholly undecomposed rock mine¬
rals; the “ reserve ,” consisting of compounds not soluble in
water but soluble in or decomposable by weak acids; and the
water-soluble portion, either actually dissolved in the water
held by the soil, or held by the soil itself in (physical) absorp¬
tion. While the latter portion is directly and immediately
available to plants, the amounts thus held are usually quite
small, and (outside of alkali lands) would rarely suffice for
the needs of a crop during a growing season.1 This demand
must be materially supplemented by what can be made avail¬
able from the soil minerals and the “ reserve ” by weathering,
conjoined with the direct action of the acids secreted from the
plant’s root-hairs upon the soil particles to which they are
attached. It is obvious that the greater or less abundance of
the plant-food in the soil-material upon which these processes
1 The investigations of King (On the Influence of Soil Management upon the
Water Soluble Salts in Soils and the Yield of Crops, Madison, 1903) show that from
some soils at least, a sufficiency of plant-food ingredients for a season’s crop may
be dissolved by distilled water alone, if the soil be repeatedly leached and dried
at 1 io°. Whether such a supply can be expected under field conditions, remains
to be tested.
324
SOILS.
may be brought to bear, must essentially influence the ade¬
quacy of the plant-food thus supplied. Moreover, the greater
or less extent to which these sources may have been drawn
upon previously in the course of cultivation, will similarly in¬
fluence that adequacy, on account of the diminution of the
readily available supply.
Water-soluble and Acid-soluble Portions most Important. —
It thus seems that while the undecomposed rock minerals are
indicative of the nature of the soil, but not directly concerned
in plant nutrition, the most direct interest attaches to the zvater-
soluble portion, and the acid-soluble reserve. Both of these
can, of course, be withdrawn from the soil by treatment with
acids of greater or less strength ; and it would seem that if
we knew just what is the kind and strength of the acid solvent
employed by each plant, we could so imitate their action as
to determine definitely whether or not the soil contains an
adequate or deficient supply of actually available food for the
coming crop.
We Cannot Imitate Plant-root Action. — In this, however,
we encounter serious difficulties. The acids secreted by the
plant roots are not the only solvents active in the dissolution of
plant-food ; as yet we know the nature of only a few ; and even
these, instead of acting for a long time (season) on a relatively
small number of soil particles touched by the root-hairs, can
in our laboratories only be allowed to act for a short time on
the entire soil-mass. Clearly, the results thus obtained can¬
not be a direct measure of the amount of plant-food which a
plant may take up in a given time; we can only gain com¬
parative figures. These, however, can be utilized by com¬
parison with actual cultural experience obtained in similar
cases.
Cultural experience must, of course, be the final test in all
these questions; and it is generally more fruitful to investi¬
gate the causes underlying such actual practical experience,
than to attempt to supply, artificially, the supposed conditions
of plant growth. The latter are so complex and so difficult
of control, that the results obtained by synthetic, small-scale
experiments are constantly liable to the suspicion that they
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS.
325
are partly or wholly due to other causes than those purposely
supplied by the experimenter.
Analysis of Cultivated Soils. — It is also clear that in view of the in¬
evitable complexity of the conditions governing vegetable growth, we
should whenever feasible proceed from the more simple to the more
complex. The failure to conform to this rule in soil investigation has
been the cause of an enormous waste of energy and work bestowed, at
the very outset, upon the most complex problem of all, viz., the investi¬
gation of soils long cultivated and manured ; lands which, having been
subject perhaps for centuries to a great and wholly indefinite variety of
crops and cultural practices, had thereby become so beset with artificial
conditions that without a previous knowledge of what constitutes the
normal regime in natural soils, the correlation of their chemical consti-
tion, as ascertainable by our present methods, with their production
under culture, became as complex a problem as that of motions of three
mutually gravitating points in space. Neither can be solved by the
ordinary processes of analysis, chemical or mathematical. Nevertheless,
though it was at one time contended that the minute proportion of
plant-food ingredients withdrawn from soils by cultivation could not be
detected by quantitative analysis, numerous examples have shown that
with our present more delicate methods this can in most cases be done,
though not always after a single year’s crop.
Methods of Soil Analysis. — The more or less incisive solvent agents
used in extracting a soil for analysis will of course produce results
widely at variance with each other. When fusion with carbonate of
soda, or treatment with fluohydric acid is resorted to, we obtain for
each soil-ingredient the sum of all the amounts contained in each of
the three categories — the unchanged minerals, the zeolitic “reserve,”
and the water-soluble portion. It was early recognized that the results
of such analyses bear no intelligible relation to the productive capacity
of soils ; for pulverized rocks of many kinds, or volcanic ashes freshly
ejected and notoriously incapable of supporting plant growth, might be
made to give exactly the same composition. The amounts of plant-
food ingredients thus shown might be several hundreds or thousands of
times greater than what one crop would take from the soil, and yet not
an ear of grain could be produced on the material. The only case in
which any useful information could be thus obtained would be that of
the absence, or great scarcity, of one or more of the plant-food in¬
gredients.
SOILS.
326
The next step was to use in soil analysis acids of such strength as to
dissolve all the zeolitic (and water-soluble) portion, leaving the un¬
weathered soil minerals behind ; it being assumed that the prolonged
action of the roots and soil-solvents would in the end act similarly to
the acids employed, such as chlorhydric or nitric acids.
But here also the results of analysis very commonly failed to cor¬
respond to cultural experience in the case of cultivated soils ; which
frequently failed utterly to produce satisfactory crops even when the
acid-analysis had shown an abundance of plant-food ingredients. Upon
this evidence, this method of soil investigation was also condemned as
being of little or no practical utility ; and this has ever since been a
widely prevalent view.
The preferable investigation of cultivated soils was due to
the fact that they are practically the only ones available in the
countries where the study of agricultural science was then
being prosecuted ; and the paucity of useful results there
achieved discouraged the undertaking of similar researches
where, as in the United States, the materials for the investiga¬
tion of the simpler cases — those of unchanged, natural or
virgin soils — were readily accessible. It was not apparent on
the surface that the indefinitely varied conditions introduced
by long culture would inevitably cause this lack of definite
correlation between the immediate productive capacity of a
soil and the composition of its acid-soluble portion, and that
yet the same might not be true of natural, uncultivated soils,
which have all been subjected, alike, only to the natural pro¬
cesses of weathering, and to the annual return of nearly the
whole of the ingredients withdrawn by plant growth.
Following the failure of the treatment with strong acids to
yield with cultivated soils results definitely correlated with
cultural experience, numerous attempts were made to gain
better indications by the employment of weaker acid solvents.
The pure arbitrariness of such diluted solvents was equaled
by the total indefiniteness and irrelevance of the results with
different soils. Only two rational alternatives seem to re¬
main, viz., either to push the extraction to the full extent be¬
yond which action becomes so slow as to clearly exclude any
farther effective action of plant acids ; or else to use the latter
themselves at such strengths as by actual experiment is found
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS.
32/
to exist in their root sap. The first alternative aims to ascer-
tain the permanent productive values of soils; the latter to test
their immediate productive capacity. Both alternatives are
purely empirical, and derive their only claim to practical value
from their accordance with practical experience (see chap¬
ter 19).
THE SOLVENT ACTION OF WATER UPON SOILS.
The almost universal solvent power of pure water has
already been alluded to in chapter 2 (see p. 18), and illustrated
by the analyses of drain and river waters. While these con¬
vey a general idea of the chief substances dissolved and car¬
ried off, the direct investigation of the solutions actually ob¬
tainable from the soil by longer treatment and with no more
water than is compatible with the welfare of ordinary crops,
necessarily gives somewhat different results. For when
drains flow during or after heavy rains the water has not time
to become saturated. The following data afford a clearer in¬
sight into the actual and possible solvent effects of water in
the soil, and its possible adequacy to plant nutrition unaided
by acid solvents.
Extraction of Soils with Pure Water. — Eichhorn and Wun-
der treated soils from Bonn, and from Chemnitz (Saxony) re¬
spectively for ten days and four weeks with about one-third of
their weight of water; the solutions thus obtained contain in
1,000,000 parts :
Bonn.
Chemnitz.
Silica .
48.0
1 1 5.4
II.O
128.0
384
Trace
?
31.0
100.2
58.6
25.7
7-5
304
83.6
374
11 7
?
Trace
• • • •
47.6
Potash (K20) .
Soda (NaaO) .
Lime (CaO) .
Magnesia (MgO) .
Peroxid of Iron (FeaOa) .
Alumina (AI2O3) .
Phosphoric acid (P2O5) . .
Sulfuric acid (SO3) .
Chlorid of Sodium (NaCl) .
328
SOILS.
These figures differ widely in most respects from those
given for drain and river waters. Potash especially is far more
abundantly present in the Bonn soil solution than in the drain
water, and so is phosphoric acid; while lime is not widely dif¬
ferent. Eichhorn therefore calculates that with a reasonably
adequate supply of water, these ingredients would fully suffice
for a full crop of wheat. The Chemnitz soil, on the other
hand, does not yield enough plant-food for more than a very
small crop upon the same assumptions.
Continuous Solubility of Soil-ingredients. — It seems to be
impossible to exhaust a soil’s solubility by repeated or con¬
tinuous leaching with water. This was demonstrated in 1863
and 1864 by Ulbricht 1 and by Schultze;2 their general con¬
clusions have quite lately been corroborated by King,3 as the
result of extended and very careful investigations.
Schultze experimented on a rich soil from Mecklenburg, by
continuous leaching with distilled water for six days, one liter
passing every twenty-four hours, with the following results.
RICH SOIL FROM MECKLENBURG (Schultze.)
1,000,000 PARTS OF EXTRACTS CONTAINED:
Total matter
dissolved.
Organic and
volatile.
Inorganic.
Phosphoric
acid.
First extract .
535-0
340.0
195
5.6
Second do .
120.0
57-o
63
8.2
Third do .
261.0
101.0
160
8.8
Fourth do .
203.0
83.0
120
7-5
Fifth do .
260.0
82.0
178
6.9
Sixth do .
200.0
77.0
123
44
Total .
L579-0
740.0
839-
41.4
It thus appears that while the first extraction removed the
main portion of the organic matter, the inorganic matters dis¬
solved were not greatly diminished in subsequent leachings;
and that phosphoric acid continued to come off to the last.
The rich soil used in this case gave results corresponding in
1 Vers. Stat. V. p. 207. 2 Ibid. VI. p. 41 1.
8 Proc. Ass’n Prom. Agr. Sci. 1904.
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 329
general to these from the Bonn soil, in the previous table.
From a poorer soil similarly treated by Ulbricht, described by
him as a ferruginous sand from Dahme, the leaching of which
was continued for thirty days in periods of three days each,
with a total of forty times its weight of water, the results
were as follows :
SOIL OF LOW PRODUCTION FROM DAHME (Ulbricht).
THE SEVERAL EXTRACTS CONTAINED IN 1,000,000 PARTS .*
First
Extract.
Second
Extract.
Third
Extract.
Fourth
Extract.
Fifth
Extract.
Sixth
Extract.
Potash .
7
6
7
7
Soda .
4i
1 1
26
17
• • • •
8
Lime .
96
70
55
48
62
• • • •
Magnesia .
14
10
9
7
8
• • • *
Phosphoric acid .
trace
2
trace
1
....
• • • •
Totals .
158
99
97
80
70
11
It will be seen that there is a considerable difference both in
the total amounts of matters dissolved and in the phosphoric
acid taken out by the water, as compared with the rich soil
treated by Schultze. The uniformity of the amounts of
potash removed at the successive leaehings is remarkable.
King's Results. — The same general features are again strik¬
ingly illustrated by King’s results, as given in the following
table. King’s first leaehings were always made by shaking up
the soil with ten times its dry weight of water for three
minutes, then after subsidence filtering the solutions through
a Chamberland (porcelain biscuit) filter, and then (without
evaporation) determining the ingredients dissolved, by very
delicate, mostly colorimetric methods. Subsequent leaehings
were made by packing the soil around the filters and washing
with five times the weight of water, taking about fifteen
minutes each time; but drying the soil at 120 degrees C.
between successive leaehings.
330
SOILS.
WATER EXTRACTION OF SOILS OF LOW AND HIGH PRODUCTION,
By F. H. KING.
PARTS PER MILLION.
SOILS OF LOW PRODUCTION.
Sassafras sandy j i extraction
soil. ( ii extractions
Norfolk, North j i extraction
Carolina sandy soil | 1 1 extractions
Average.
12.62
74-39
17.82
18.03
7-4i
53-84
13-94
I
218.25
135-35
147-45
21.76
64.16
203.96
221.33
2
21.17
58.30
22.91
30.64
10.15
42.82
20.42
1
166 08
162.98
125.00
27.II
80.34
172.42
148.52
2
192.60
149.20
136.23
24.44
72.25
126.13
184-93
2.-
5.60
170.20
8.24
122 20
146.20
SOILS OF HIGH PRODUCTION.
Janesville, Wis. ( 1 extraction
25-35
135-30
51.72
55-xo
16.96
125-43
29.31
2.67
40.28
Loam. } 1 1 extractions
3i3-7o
I 120.30
500.60
51.42
418.85
592.75
472.95
0.00
414.50
Hagerst'wn, Pa. ( 1 extraction
21-73
165.25
76.88
25-72
11. 51
187-59
97.09
1.67
21.17
Clay loam. ( 11 extractions
30X-55
967.80
463- 15
96.04
136.21
502.82
620.00
0.00
283.80
Average.
307.60
IO44.O5
487.88
73-73
277.03
547-79
546.48
0.00
349- 1 5
King’s observations show strikingly both the continuous
solubility of the soil, and the differences between the solutions
derived from soils of low and high productiveness; wholly
negativing the contention of Whitney that the solutions
from different soils are of practically the same composition.1
King also calls attention to the fact, shown in other experi¬
ments made in the extraction of soils without intermediate
dryings, that the amounts extracted were very much less in sub¬
sequent than in the first extraction ; doubtless because the evap¬
oration from the soil particles had carried a large proportion of
soluble matters to the surface, whence it was readily abstracted
by the first touch of the solvent water. At each drying not
only are the soluble matters again drawn to the surface, but
heating a soil even to ioo° renders additional amounts of soil
ingredients soluble both in water and in acids. It can scarcely
be doubted that the intense heating which desert soils undergo
during the warm season is similarly effective; and thus the
great productiveness of these soils under irrigation, and the
marvelously rapid development of the native vegetation when
1 Bulletin No. 22, Bureau of Soils, U. S. D. A.
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS.
331
rains moisten the parched soil, is in part at least accounted for
by this immediate availability of a large supply of plant-food.
Composition of Janesville loam. — In connection with the
above data given by King, it is interesting to note the compo¬
sition of the soil in the above table yielding the highest pro¬
portions of soluble matter, when analyzed according to the
method practiced by the writer (see chap. 19, p. 343). This
analysis was made under the supervision of Professor Jaffa
in the laboratory of the California Experiment Station by
Assistant Charles A. Triebel.
Loam Soil from Janesville , Wiseo?isi?i ; sample sent by Prof. F. H.
King, Madison, Wis.
This soil is a light friable loam, resembling the northern Loess in
color and texture ; it is highly productive. It is underlaid at 5 feet by
the drift gravel of that region, enclosing much calcareous material,
which evidently has had a large share in the formation of this soil, just
as is the case in southern Michigan.
The soil, when dried at no° C., consisted of
CHEMICAL ANALYSIS OF FINE EARTH.
Insoluble matter .
Soluble silica .
Potash (KO2) .
Soda (NaaO) .
Lime (CaO) .
Magnesia (MgO) . . .
Br. ox. of Manganese (Mn304) .
Peroxid of Iron (Fe203 .
Alumina (AI2O3) .
Phosphoric acid (P2O3) ... .
Sulfuric acid (SO3) .
Water and organic matter. .
69-35
10.89
•59
.04
.83
•5i
.08
3.60
5.26
.06
.10
8.72
Total . 100.03
It will be noted that in accordance with the interpretation of analyses
of soils as given in the next chapter, this is a high-class soil in every
respect, except that its content of phosphoric acid is only just above
the lower limit of sufficiency. But as is also shown below, in presence
of a large supply of lime even lower percentages of phosphoric acid are
adequate for long-continued production (see chap. 19, pp. 354, 365).
by rendering the substance more freely available ; and that this is true
in this case is shown by the result of King’s leachings, in which this
soil yields a maximum of 419 parts per million as against 80 and 64
parts in the poor soils, which at the same time yield only one fourth as
much of lime. Unfortunately we have no full analyses of these other
332
SOILS.
soils for comparison ; although they have served as a basis of comparison
lor years in the Washington Bureau of Soils.
Solubility of Soil Phosphates in Water. — The solubility of
the phosphate contents of soils has been elaborately investi¬
gated by Th. Schloesing fils.1 He found in the case of a num¬
ber of soils investigated by him that the amount of phosphoric
acid P2O5 in the soil-solution ranged from less than one mil¬
lionth (or one milligram per liter of water) in a poor soil, to
over three milligrams in a rich one. He also found that for
one and the same soil the amount so found was constant, if
about a week’s time were allowed for saturation. He calcu¬
lates that while in general the amount of phosphoric acid capa¬
ble of being supplied to the crop during a growing season of
twenty-eight to thirty weeks would suffice for but few crops,
the supply so afforded is in no case a negligible quantity, fre¬
quently amounting to more than half of the crop-requirements.
Experiments with various crops prove that these dilute solu¬
tions are utilized by all of them, sometimes to the extent of
completely consuming the content of the solution. The much
smaller content of phosphoric acid in drain waters is accounted
for by the lack of time for full saturation during the time that
the flow lasts. Whitney, (Bureau of Soils, Bulletin 22) has
extracted the soil-solution by means of the centrifuge from
several soils ; the contents of phosphoric acid thus found are in
general of the same order as those shown in the preceding table
by King, but much in excess of Schloesing’s figures ; notwith¬
standing the fact that Whitney’s soils had been in contact with
water for only twenty-four hours. The cause of this wide dis¬
crepancy is not clear.
Practical Conclusions from Water Extraction. — As regards
the practically useful conclusions to be drawn from the ex¬
traction of soils with pure water, the data given above, and
especially the results obtained by King, seem to prove that
there is a more or less definite correlation between the immedi¬
ate productiveness of soils and the amount and kinds of in¬
gredients dissolved ; especially in the case of phosphoric acid,
the adequacy of the supply of which for immediate production
1 Ann. de la Sci. Agron., 2de serie tome i, pp. 416-349; 1899.
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 333
is assumed to be thus demonstrable by many French chemists.
Moreover, a number of King’s results, tabulated in curves,
exhibit a remarkable general parallelism of the curves showing
totals of plant-food extracted by water, and actual crop pro¬
duction. This is the more remarkable since it is known to be,
not pure water, but such as is more or less impregnated with
carbonic acid at least, that is actually active in soil-solution
and plant-nutrition. The farther development of this method
may, it would seem, lead to definite conclusions at least in re¬
spect to the immediate productive capacity of cultivated, and
perhaps also of virgin soils. But it is not likely to give any
definite clew as to the durability of such lands.
ASCERTAINMENT OF THE IMMEDIATE PLANT-FOOD REQUIRE¬
MENTS OF CULTIVATED SOILS BY PHYSIOLOGICAL
TESTS. PHYSIOLOGICAL SOIL-ANALYSIS.
As has already been stated, the quantitative analysis of culti¬
vated soils by means of strong acids affords a presumptive in¬
sight into their immediate productiveness, and the kind of
fertilizer needed to improve it, only in case of the extreme
deficiency of one or several of the chiefly important plant-
foods. The limits of deficiency of these in virgin soils have
been discussed above; but since in cultivated soils amounts of
soluble plant-food so small as to be beyond the limits of ordi¬
nary analytical determinations, when distributed through an
acre-foot of soil may, when rightly applied, nevertheless pro¬
duce very decided effects, the indications thus obtainable are
not absolute. Thus a dressing of 150 lbs. of Chile saltpeter,
containing only about 24 lbs. of nitrogen, is capable of causing
the production of a full crop of wheat where otherwise, even
under favorable physical conditions, only a fraction of a crop
would have been harvested; provided, that all the other re¬
quisite ingredients were present to a sufficient extent and in
available form. Yet the amount of nitrogen thus added would
amount, in one acre-foot of soil to only .0008%, say eight ten-
thousandths of one percent; which, with the amounts of sub¬
stance usually employed in soil analysis, would be an unweigh-
able quantity, and might easily be overlooked.
Since the amounts of potash and phosphoric acid actually
334
SOILS.
taken out of the soil by one crop are in general of the same
order of magnitude as the above, what is taken out by one or
two crops will usually fall within the limits of analytical errors,
especially of those incurred in sampling the soil. Yet that the
changes caused by a number of successive crops can be proved,
even by the ordinary methods, has been abundantly verified.
For it seems that the losses of soil ingredients in cultivated
lands exceed considerably those calculated from the actual
drain represented by the crops.
Plot Tests. — There is, however, an obvious and apparently
simple method by which every farmer might make his own
fertilizer tests, on a small and inexpensive scale, the results of
which may afterwards be put in effect on his entire land. It
is to apply in proper proportions on plots (of say from one
twentieth to one fortieth of an acre), the several plant-food
ingredients usually supplied in fertilizers, singly as well as
conjointly with each other, leaving check unfertilized plots
around as well as among them. By comparison with these,
the cultural results should at once determine which of the
fertilizers can most advantageously be applied to the land.
Such tests when carried out with all the proper precautions
are often very decisive and practically successful. But they so
frequently suffer from seasonal influences (such as scanty or
excessive rainfall, cold or heat, etc.), inequality of soil condi¬
tions, failure to apply the fertilizers at the right time, or in the
right way, the depredations of insects and 'birds, and other
causes, that it generally takes several seasons’ trial to obtain
any definite results. On level lands of uniform nature and
depth, they are most likely to be successful ; while on undu¬
lating or hill lands it is not only very difficult to secure uni¬
formity of soil and subsoil on areas of sufficient size, but also
to prevent the washing of fertilized soil, or fertilizer in solu¬
tion, from one plot to the other by the influence of heavy rains
or irrigation ; thus wholly vitiating the experiments. In very
many cases, especially in the arid region, the results of such
trials have been practically nil, for the reason that physical de¬
fects of the soil, and not lack of plant-food, were the cause of
unsatisfactory production.
A full examination of physical conditions, as outlined in
previous chapters, should in all cases precede the application of
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS.
N
P
N
Chile Saltpeter.
Superphosphate.
Tankage.
P + N
Blank.
Superphosphate
and Chile
Saltpeter.
Blank.
P + K
P + N + K
Superphosphate
and sulfate of
Potash.
Blank.
Superphosphate
Chile Saltpeter and
Sulfate of Potash.
.
K + N
Blank.
Sulfate of Potash
and Nitrogen.
Blank.
P
K.
P
Bone meal.
Sulfate of
Potash.
Thomas Phosphate
Slag.
335
Scheme for Plot-tests of Fertilizers
336
SOILS.
fertilizers; such examination will at the same time serve to
determine the greater or less uniformity of soil-conditions,
which is of first importance to the cogency of fertilizer tests.
As a matter of fact, few farmers possess the necessary qualifi¬
cations to carry out such tests successfully, since their execu¬
tion requires a certain familiarity not only with the principles
and methods of experimentation, but also the faculty and
practice of close and reasoning observation; which, unfortu¬
nately, is not as yet a part of instruction in our schools. The
experience so often had in co-operative work between experi¬
ment stations and farmers is cogent on this point.
Those desiring to do such work, however, can make use of
something like the plan given above ; it being understood that
in the case of clay soils, the unplanted paths left between the
plots should be at least two feet in width ; in the case of sandy
soils the distance should be not less than three feet, and more
if the plots are located on a slope. The crop from each plot
should if possible be weighed as a whole; but if the plot be
large and the crop measurably uniform, an aliquot part, such
as one fourth, may be weighed instead. In regular experi¬
mentation the crops are weighed both in the green (freshly
cut) condition, and after drying. Since the dry matter is the
real basis of value in the case of most field crops, its weight
is the most important; as the water-content of green crops
may vary considerably. But in the case of vegetables as well
as fruit crops, not only must the weight of the fresh crop be
determined, but it should be sorted into the “ marketable ” and
“ unmarketable ” sizes and qualities. Failure to do this may
vitiate the entire experiment for practical purposes.
Pot Culture Tests. — The uncertainty attending plot culture
tests on account of the difficulty of controlling seasonal and
other external conditions, has resulted in the extended adoption
of indoor culture tests, usually conducted in zinc or “ gal¬
vanized ” cylinders of a size sufficient to contain from twelve
to twenty or more pounds of soil. These are kept in a green¬
house whose temperature and moisture-condition can be regu¬
lated at will, and where the soil-moisture is wholly under con¬
trol. For investigations of the effects of various kinds of plant-
food upon vegetable development, this method has served most
satisfactorily and effectually, and striking photographs of re-
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS.
337
suits thus obtained are seen on all hands : for which reason, to
save space, they have not been introduced into this volume. It
seems at first sight that the same method should serve admi¬
rably to determine the manure-requirements of soils under con¬
trolled conditions.
It must, however, be remembered that the field conditions as
regards subsoil, evaporation, ascent of moisture from below,
penetration and spread of roots, etc., in other words, all the
physical conditions so vitally concerned in crop production,
except the temperature and moisture-condition of the soil, are
wholly left out of consideration in this method. Hence the
application of the results so obtained to actual field conditions
can only be made with great caution, and are often widely dis¬
crepant with actual experience.
The method has of late been carried to an extreme by the U. S.
Bureau of Soils in the proposition to supplant the large soil-pots here¬
tofore used by small paraffined wire-cloth baskets, 3X3 inches in size,
in which the soil to be tested is sown with seeds which are allowed to
develop only for three to five weeks; it being claimed that the devel¬
opment occurring during that time is quite sufficient to indicate what
will be the ultimate outcome in crop production. But practical ex¬
perience has long ago demonstrated that these early stages of growth
cannot be relied upon to show the crop results to be expected. Yet
if this minute scale of pot-culture should, on further test, prove to give
truthful forecasts even in a mere majority of cases, the facility with
which it may be carried out will entitle it to favorable consideration.
A great deal more proof is needed on this point than the confident
claims of the Bureau indicate.
CHEMICAL TESTS OF IMMEDIATE PRODUCTIVENESS.
Testing chemical soil-character by crop analysis. — Another
method for the determination of immediate soil requirements
has been elaborated by E. Godlewski.1 The principle upon
which this method rests is that plants growing in a soil defi¬
cient in available plant-food of any one kind will in their ash
show a corresponding deficiency, or at least a minimum pro¬
portion of the same ; and that in many cases, the nature of the
1 Zeitschr. Landw. Vers. Oesterr., 1901.
22
338
SOILS.
\
deficiency manifests itself in the form or development of the
plant, so clearly as to render chemical analysis unnecessary
(see below, chapter 22).
To a certain extent the latter idea has been and is constantly
being utilized in practice. It is essentially involved in the
habit of judging of land by its natural vegetation; and by agri¬
cultural chemists and intelligent farmers, when they check ex¬
cessive growth of stems and leaf (indicating excess of nitro¬
gen) by the use of lime or phosphates; or prescribe the use of
nitrogenous manures when a superabundance of small, un¬
marketable fruit is produced. From the coincidence of such
indications with the results of the analyses of soils and ashes,
very definite and permanently valuable indications as to the
proper fertilization and other treatment of the land may be
deduced.
Godlewski insists strongly, and with a good deal of plausibility, upon
the importance of making such trials in the open field and not merely
in pots. While this is true, it is also true that such field experiments
suffer from the same liability to imperfection as the “ plot fertilizer-
test ” plan just described ; viz., that the season may exert a much more
powerful influence than the fertilization, and the tests may lead to
wholly erroneous conclusions unless the experiments are continued for
a number of years, and under skilled supervision. But when once the
normal ratio between the ash ingredients for a particular soil and
climatic region have been ascertained, the data will be of lasting benefit
to agriculture there, and perhaps, other things being equal, to the world
at large.
H. Vanderyst has discussed the entire subject of physio¬
logical soil analysis elaborately in the Revue Generale Agro-
nomique of Louvain, 1902-3 (Exp’t St. Record, April 1904,
Vol. 8, page 757) and shows in detail the conditions under
which it may be successful. Among these he reckons as full a
knowledge of the chemical characteristics of a soil as can be
obtained by chemical analysis.
Chemical Tests of Immediately Available Plant-food. — It is
scarcely doubtful that plants differ considerably in the energy
of their action upon the “ reserve ” soil ingredients; hence no
one solvent used by the analyst could represent correctly the
THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 339
action of plant-roots in general upon the soil, even if we could
give that action the same time (a growing season) and op¬
portunity afforded them in nature by the root-surface. We
are forced to proceed empirically; and among the numerous
solvents suggested for the purpose of soil extraction, that of
Dyer, already mentioned, viz., a one per cent solution of citric
acid, making allowance for such neutralization as may occur
in the soil, has seemed to the writer to give results most largely
in agreement with cultural experience. Walter Maxwell has
recommended aspartic acid in lieu of citric, as approaching
nearer to practical results, at least with sugar cane.
According to the investigations of Dyer, on Rothamstead
soils of known productiveness or manurial condition, it ap¬
pears that when the citric-acid extraction yields as much as
.005% of potash and .010% of phosphoric acid, the supply is
adequate for normal crop production, so that the use of the
above substances as fertilizers would be, if not ineffective, at
least not a profitable investment. These figures refer to the
ordinary field crops of England and to soils originally fertile
and well supplied with lime. It can readily be foreseen that
under other climatic and soil conditions, different figures may
have to be established. So far as the writer’s experience goes,
however, the above figures are very nearly valid for the arid
climates as well; only the figures obtained for arid soils are
usually far in excess of the above minimum postulates. Fig¬
ures for lime and nitrogen are given in chapters 8 and 19.
But the results obtained with the highly ferruginous soils of
Hawaii show that under such conditions, figures far exceeding
the minimum ones established by Dyer nevertheless coexist
with need of phosphate fertilization.
CHAPTER XIX.
THE ANALYSIS OF VIRGIN SOILS BY EXTRACTION WITH
STRONG ACIDS.
As stated already, the analysis of soils by extraction with
strong acids is intended to enlighten us, not in regard to their
immediate productiveness (the “ Dungerzustand ” of German
agricultural chemists), but as to their permanent value or pro¬
ductive capacity . As has been seen in the preceding chapter,
the efforts to unite investigators upon a generally applicable
and acceptable method for the testing of immediate produc¬
tiveness have not been very successful, and the number of
methods employed in different countries and by different
chemists within the same country are widely at variance, with
no immediate prospect of agreement. Moreover, in most
cases the effort is to combine both problems — temporary and
permanent productive capacity — in one method or operation;
which still farther confuses the issue.
Convinced that the only way to unification lies in the direc¬
tion of falling back upon a method that is based upon a natural
limitation about which there can be no difference of opinion,
the writer has, in following the lead of Owen and Robert
Peter, endeavored to settle definitely the natural limit of the
action of a suitable acid upon soils , and the time and strength
of acid producing the maximum effect.
Lough-ridge* s Investigation. — Systematic work on these
points was undertaken, at his suggestion, by Dr. R. H. Lough-
ridge in 1871 and 1872. The results of this work were pub¬
lished in the succeeding year in the Amer. Journal of Science,
and in the proceedings of the A. A. A. S. for 1873. They seem
to be of sufficient general interest to be reproduced here.
The soil selected for this purpose was a very generalized one,
representing large areas in the states of Kentucky, Tennessee,
Mississippi and Louisiana, bordering on the east the immediate
340
THE ANALYSIS OF VIRGIN SOILS.
341
valley of the Mississippi river, and known locally as the
“ Table lands; ” a noted cotton-producing upland region. The
brown or yellow, moderately clayey loam is of great uni¬
formity throughout its region of occurrence, and is evidently
derived from such widely-spread sources that it represents no
special rock or complex of rocks. Its natural growth is a mix¬
ture of oaks and hickories, strong and well-developed trees,
such as any land-seeker would at once approve for settlement.
Its cotton product when fresh was a 400-pound bale of cotton
lint per acre. It may therefore well be considered a typical
generalized soil of the humid upland of the Mississippi valley.
Its physical analysis is given in chapter 6, it being No. 219
of the table on p. 98.
Strength of Acid used. — Three different strengths of acid
were simultaneously employed, viz., chlorhydric of 1.10,
1. 1 15 and 1. 160 density. With these the soil was digested at
steam heat in porcelain beakers covered with watch glasses for
five days each, then evaporated and analyzed as usual. The
results were as follows :
ANALYSIS WITH ACID OF DIFFERENT STRENGTHS.
Ingredients.
Sp. G. of Acid.
1. 10
1-115
1. 160
Insoluble residue .
71.88
70.53
74-15
Soluble silica .
11.38
12.30
9.42
Potash .
.60
•63
.48
Soda . .
•!3
.09
•35
Lime .
.27
.27
•23
Magnesia ....... .
•45
•45
•45
Br. ox. Manganese .
.06
.06
.06
Ferric Oxid .
5-*5
5-ii
5.04
Alumina .
6.S4
8.09
6.22
Sulfuric acid .
.02
.02
.02
Volatile matter .
3-14
3-14
100.02
100.69
99.29
Amount of soluble matter .
24.00
27.02
22.27
Amount of soluble bases .
i3-5o
14.70
12.83
It will be noted that the strongest acid produced the smallest
amount of decomposition of the soil silicates, e. g. the silica
soluble in carbonate of soda solution being 3% less than in the
case of the acid of medium strength; a result possibly due to
342
SOILS.
some difficultly-soluble compound formed on the surface of
the soil grains. The weakest acid had a stronger solvent
power; but the maximum effect was produced by the acid of
i . 1 1 5 density. This being also the most readily obtainable, by
simple steam distillation of acid of any other strength, the
writer adopted it as best suited to the purposes of soil analysis.
To ascertain the time required for the desired action, viz.,
the solution of the plant-food ingredients to the extent likely to
be of any avail to growing plants, digestions of the same soil
were made in the same manner for periods of i, 3, 4, 5 and 10
days, with the acid of 1.115 density. The results were as fol¬
lows :
ANALYSIS AFTER DIFFERENT TIMES OF DIGESTION.
No. of Days’ Digestion.
Ingredients.
1
3
4
5
10
Insoluble Residue .
76.97
72.66
71.86
7o-53
71.79
Soluble Silica .
8.60
11. 18
1 1.64
12.30
10.96
Potash . .
•35
•44
•57
•63
.62
Soda . .
.06
.06
•03
.09
.28
Lime .
.26
.29
.28
.27
.27
Magnesia .
.42
•44
•47
•45
•44
Br. Ox. Manganese .
.04
.06
.06
.06
.06
Ferric Oxid. . .
4-77
5.01
5-43
5- 11
4.85
Alumina .
5-i5
7-38
7.07
7.88
7.16
Phosphoric acid .
.21
.21
.21
.21
.21
Sulfuric acid .
.02
.02
.02
.02
.02
Votatile matter .
3-14
3- '4
3-M
3-!4
3-T4
Total .
Amount of soluble matter..
Amount of soluble bases.. .
99 63
19.67
11.05
100.68
24.88
13.68
100.55
25-57
i3-9i
100.69
27.02
14.49
99.80
24.87
13.68
While these results pointed clearly to the five-day period as
being sufficiently effective so far as the plant-food ingredients
are concerned, it was not easy to understand why a ten-day
digestion should be less incisive than a five-day one. Instead
of repeating the ten-day experiment, it was thought preferable
to re-treat the residue from the five-day digestion for five days
more. The result was that only more silica and alumina went
into solution — in other words, additional clay was alone being
decomposed. This being of no interest in the matter of plant
nutrition, the five-day period was definitely adopted by the
THE ANALYSIS OF VIRGIN SOILS.
343
writer for his work; and it, together with the acid of 1.115
density, is the basis of all the results given in this volume, ex¬
cept where otherwise stated. There appeared to him to be
no good reason for the acceptance of the arbitrary method of
soil-extraction suggested by Kedzie and since adopted by the
Association of Official Agricultural Chemists; the more as to
do so would throw out of comparison all the previous work
done by Owen, Peter, and himself and his pupils, which had
already been definitely correlated with the natural conditions
and with cultural experience.1
Virgin Soils with High Plant-food Percentages are Always
Productive. — In strong contrast to the contradictory evidence
deduced from the analysis, by any method, of cultivated soils
when compared with cultural experience, it seems to be gener¬
ally true that virgin soils showing high percentages of plant-
food as ascertained by extraction with strong acids (such as
hydrochloric, nitric, etc.), invariably prove highly productive :
provided only that extreme physical characters do not interfere
with normal plant growth, as is sometimes the case with heavy
clays, or very coarse sandy lands. — To this rule no exception
has thus far been found. The composition of some represen¬
tative soils falling within this category is given in the annexed
table, which at the same time conveys some idea of the propor¬
tion of acid-soluble ingredients usually found in the best class
of natural soils.
Discussion of Table. — It will be noted in this table that while
the total of the matters soluble in acids (inclusive of silica)
ranges from a little below 50 to over 77 per cent, the total of
directly important mineral plant-food ingredients (potash,
lime, magnesia and phosphoric acid), constitute in moderately
calcareous soils only from about 2.5 to somewhat over four
per cent of the whole. Yet if all these were in available form,
the supply would be abundant for many hundreds and even
1 While regretting to thus “ secede ” from the fellowship of his colleagues, the
writer cannot but regret equally their voluntary decision to do over again, or
lightly reject, all that had been done before in correlating soil-composition and
plant-growth. He still thinks that it is idle to expect any unification, national or
international, of methods of soil analysis based upon purely arbitrary prescriptions,
unless previously shown to be definitely correlated with natural and cultural con«
ditions ; as is measurably the case with Dyer’s method.
TABLE EXEMPLIFYING HIGH PLANT-FOOD PERCENTAGE IN SOILS.
344
SOILS.
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THE ANALYSIS OF VIRGIN SOILS.
345
thousands of crop years. For, one-tenth of one per cent in
the case of the clayey soils of the preceding table would amount
to about 3500 pounds per acre-foot, and to 4000 in the case of
the sandy ones. Hence the amount of phosphoric acid in e. g. ,
the Mississippi delta soil from Houma would suffice for the
production of about 440 crops of wheat grain (at 20 bushels
per acre) if only one foot depth were drawn upon; but as the
roots of grain easily penetrate to twice and half and three
times that depth even in the humid region, the number might
be tripled. As a matter of fact, however, that soil has pro¬
duced full crops for from forty to fifty years only; yet this is
considered an exceptionally long duration of profitable pro¬
duction without fertilization.
The first and last soils in the above list represent probably the highest
types of productiveness known. The Yazoo bottom soil has produced
up to one thousand pounds of cotton lint per acre when fresh, and is
still producing from four to five hundred pounds after thirty years’
culture. The Arroyo Grande soil of California with its extraordinary
percentages of phosphoric acid and nitrogen, as well as exceptionally
high proportion of available phosphoric acid and potash, has made such
a record of productiveness, and high quality of the seeds produced,
that it has for a number of years been excluded from competition for
prizes offered by seed-producers elsewhere, in order to give other sections
a chance. Both these soils are rather heavy clays, but readily tillable
in consequence of their abundant lime-content. The remarkably high
content of acid-soluble silica, indicating the presence of much easily
available zeolitic matter, is doubtless connected with the exceptional
productiveness.
Experience, then, proves that lands showing such high
plant-food percentages will yield profitable harvests for a long
time without fertilization, or with only such partial returns
as are afforded by the offal of crops. Also that when fertiliza¬
tion comes to be required, instead of supplying all the ingre¬
dients usually constituting fertilizers, only one or two of these
will as a rule be actually needed, and even these in smaller
JThe Rio Grande and Colorado bottom soils contain amounts of lime carbonate
largely in excess of reqnirements, 2 to 3° 0 of that compound being all that is
needed to insure all the advantageous effects of lime in any soil (see this chapter,
page 367).
346
SOILS.
amounts than in “poor” lands; thus materially reducing the
expense of fertilization. The high production and durability
of such lands therefore amply justify their higher pecuniary
valuation ; for which there would be no rational permanent
ground if they required fertilization to the same extent as
poor lands. In other words, if the entire amount of soil-in¬
gredients removed by crops had had to be currently replaced
equally in all cases (as is implied in the hypothesis, advanced
by some, that the chemical composition of soils is of no prac¬
tical consequence), the high prices which from time imme¬
morial have been paid for black prairie and rich alluvial lands
as against meagre uplands and barrens, would have been so
much money wasted.
The explanation of these advantages evidently lies largely
in the larger amounts of soil ingredients annually rendered
available in rich soils by the fallowing effect of the atmospheric
agencies, because of the generous totals present. The actual
amounts of soil ingredients thus rendered accessible to plants,
other things being equal, are evidently more or less directly
proportional to the totals of acid-soluble plant-food ingredients
present. And if this is true in cultivated lands, the inevitable
conclusion is that the same must be true of virgin lands; whose
productive capacity and duration can therefore be forecast by
such analyses. It will be observed that the above data, which
could be indefinitely increased by corroborative analyses, seem
to establish the fact that about one per cent of acid-soluble
potash, one of lime, the same, or less, of magnesia, and .15%
of phosphoric acid, are thus shown to be “ high ” percentages
of these ingredients in virgin soils.
It is not easy to see how the above conclusions can be suc¬
cessfully controverted ; they are, moreover, thoroughly in ac¬
cordance with cultural experience. Difficulties of interpreta¬
tion arise mainly in the case of medium soils, which show
neither very high nor very low percentages of plant-food ; and
which raise the question of what amount or percentage con¬
stitutes “ adequacy ” of each of the several substances.
Low Percentages. — On the other hand, whenever in virgin
soils acid-analysis shows the presence of but a very small pro¬
portion of one or several of the essential ingredients, we have
THE ANALYSIS OF VIRGIN SOILS.
347
a valuable indication as to the one of these that will first be
required to be added when production slackens.
What are “ Adequate ” Percentages of Potash, Lime, Phos¬
phoric Acid and Nitrogen ? — It is evident that a very critical
discussion of cultural experience can alone answer this ques¬
tion ; and at first sight such experience often appears very con¬
tradictory when compared with the results of analysis.
One of the chief causes of such apparent discrepancies is readily in¬
telligible when we consider the differences in root-development of the
same plant in different soils. In “light ” or sandy lands the roots may
penetrate to several times the depth attained by them in heavy clay
soils. Having thus within their reach a soil-mass several times larger,
and aerated to a much greater depth, it is but reasonable to expect that
in deep, sandy lands plants would do equally well with correspondingly
smaller percentages of plant-food than would suffice in clay soils, in
which the root-range is very much more restricted. The well-known
fact that the production of heavy clay lands may be increased by their
intermixture with mere sand, adding nothing to their store of plant-
food, emphasizes this expectation and elevates it into a maxim. On
this ground alone, therefore, it is evident that the mere consideration
of plant-food percentages found, can be a true measure of productive¬
ness only in the case of virgin soils with high percentages.
Soil Dilution Experiments. — The extent to which dilution
with mere “ lightening ” materials can be carried without im¬
pairing production, can of course be determined for concrete
cases only; but the following experiment made at the Cali¬
fornia Station is a case in point :
One kilogram of the heavy but highly productive black clay
soil of the experimental grounds of the University of Cali¬
fornia was used in each of five experimental cultures, each
made in duplicate, in cylindrical vessels of zinc-covered (“ gal¬
vanized ”) sheet iron, all proportioned alike in height and
diameter, but containing respectively one, two, four, five and
six volumes of total soil. In the smallest was placed one kilo¬
gram of the undiluted, original soil, in the others successively
the same amount of the soil thoroughly mixed with one. three,
four, and five volumes of a dune sand fully extracted with
chlorhydric acid, and washed with distilled water. The water-
348
SOILS.
capacity of each of the mixtures was determined and the earth
in the pots kept at the point of half-saturation generally ad¬
mitted to be the optimum (best condition) for plant growth.
Each pot was sown with ten seeds of white mustard, subse¬
quently reduced to five plants selected for their vigor.
The (“galvanized”) vegetation pots were made as nearly
as possible of similar proportions in depth and width for each
dilution, so as to give opportunity for the proportional develop¬
ment of the root systems. The photographs show the latter
as nearly as practicable in their natural form, restored after
washing off the adherent soil. It was of course extremely dif-
Fig. 55. — Same, diluted 1 to 3.
DEVELOPMENT OF ROOTS OF WHITE MUSTARD IN CLAY SOIL, DILUTED WITH
VARIOUS PROPORTIONS OF PURE SAND.
Fig. 54. — Adobe Soil diluted with Sand, 1 to 1.
THE ANALYSIS OF VIRGIN SOILS.
349
ficult to preserve intact the extreme circumferential rootlets
and hairs; yet the general development is correctly shown.
Fig. 56.— Adobe Soil diluted 1 to 4. Fig. 57.— Adobe Soil diluted 1 to 5.
35°
SOILS.
Fig. 58. — Soil-dilution Experiment: Photograph showing Mature Plants.
The following table shows the percentage composition of
the original as well as the diluted soils, while the photographs
show the development of the plants in their successive stages,
COMPOSITION OF BLACK ADOBE AND SAND DILUTIONS.
Chemical analysis of fine earth.
Original
soil.
I : 0
1 : I
Dilutions.
1:3 1:4
1 : 5
Insoluble matter .
51. 50
77.23
88 6 2
90 00
02 A'*
Soluble silica .
10.00
9.50
4-75
'3.80
y 4^
3-17
Potash (K20) .
•73
.36
.18
.15
.12
Soda (Na20) .
.20
.10
•05
.04
•03
Lime (CaO) .
1. 15
•57
.29
.25
.19
Magnesia MgO) .
1.08
•54
.27
.22
.18
Br. ox. of Manganese (Mn304) .
.04
.02
.01
0.1
.01
Peroxid of Iron (Fe2(J3) .
8.43
4.22
2. 1 1
1.68
1.40
Alumina (A1203) .
7.92
3-96
1.98
1.58
1.32
Phosphoric acid (P205) .
.19
.10
•°5
.04
.03
Sulfuric acid (SO-J .
.04
.02
.01
.01
.01
Carbonic acid (C02) .
Water and organic matter .
6-34
3-27
1.64
1.31
1. a)
Loss in analysis .
1.18
.09
.04
.03
.03
Total .
100.00
100.00
100.00
100.00
100.00
Humus .
1. 21
.60
O 1
“ Ash .
•94
•47
•23
— y
.19
.16
Nitrogen, p. cent, in Humus.
18.58
18.58
18.50
18.58
18.58
“ p. cent, in soil .
.203
.10
•05
.64
.034
THE ANALYSIS OF VIRGIN SOILS.
351
so far as these could be observed; the continued attacks of
mildew and plant lice preventing full maturity being attained.
The restricted volume of soil occupied by the roots in the undiluted
adobe soil, together with the very abundant development of root-hairs,
is very striking. A marked change in these respects is manifest in the
first dilution, and increasingly so as dilution increases ; the paucity of
root-hairs is very marked in the last (greatest) dilution, in which, as
the photograph of the plants shows, the development was decidedly
behind that in the pot containing dilution 1:4. The latter in fact
showed the best development not only in this case, but in two other
series of tests conducted at the same and subsequent times ; and strangely
enough, also in the pulverulent, “ sandy loam ” soil of the southern
California substation tract. In the latter series, which for lack of space
cannot be figured here, the main difference was that in the undiluted
soil the roots filled the entire soil mass, instead of remaining near the
surface, as in the pure adobe. It is possible that the latter was too wet
when given the full half of its water-capacity, although, as the figures
show, the water was slowly introduced from below by means of glass
tubes, ending within a shield to prevent puddling.
Limitation of Root Action. — These results, representing five
soils of different percentage-composition and physical char¬
acter, but identical chemical composition and ratios between
the several ingredients, and similarly acted upon by the atmos¬
pheric agencies in the past, illustrate strikingly the impossi¬
bility of judging correctly of a soil's productiveness from per¬
centages of chemical ingredients alone. It is clear that the
physical characters of the land as well as its depth, must be
essentially taken into account. But there is obviously a cer¬
tain limit beyond which greater perviousness and root-penetra¬
tion cannot make up for deficiency in the absolute amounts of
plant-food within possible reach of the plant ; for in the case of
excessive dilution these are rendered partially inaccessible
within the time-limits of a season’s growth.
It is hardly necessary to say that these experiments require
repetition with the aid of the experience acquired in these first
trials, not only in the laboratory but also in the field. It will
be especially interesting to compare with the results obtained
in these strongly calcareous soils, the effects of dilution in such
352
SOILS.
soils as those of Florida, mentioned below; the probability be¬
ing that where lime is naturally deficient, the effects of dilu¬
tion will be much more pronounced in diminishing production,
because of the absence of the previous favorable action of lime
upon the availability of the soil-ingredients.
Lozuest Limit of Plant-food Percentages and Productive¬
ness found in Virgin Soils. — The subjoined table shows some
of the very low plant-food percentages found in natural soils,
all being of a sandy character :
Mississippi Soils.
Florida Soils.
Homo-
chitto
Bottom.
Shell
Ham¬
mock.
Pine
Woods.
Pine
Flats.
Pine Lands.
First
Class.
Second
Class.
Number of Sample.
68
83
206
214
6
7
CHEMICAL ANALYSIS OF FINE
EARTH,
Insoluble matter .
t ,
94.46
ck.6i ) ,
Soluble silica .
< 92.ID
96.08
93-23
95-59
1.67
.88) 96-S«
Potash ( K20) .
•i5
.05
.26
.06
.19
.12
.Soda (Na20) .
.04
.06
.07
•05
.04
.06
Lime (CaO) .
.12
.IO
.12
.02
.07
.06
Magnesia ( MgO) .
.21
.12
.18
.07
.04
.04
Br. ox. of Manganese ( Mn304) .
.28
•05
•!5
•05
.06
•05
Peroxid ot Iron ( Fe2C)3) .
I.l8
•S2
1.25
.46
• 32
.22
Alumina (A1203) .
3.22
.46
2.36
.85
.92
•47
Phosphoric acid (P305) .
.08
.IO
•03
.02
. I I
• oq
Sulfuric acid (S03) .
.05
Trace
.02
Trace
.09
.06
Carbonic acid ( C( )2'> .
Water and organic matter .
2.7O
3.02
2-33
2.28
1.88
I. 8l
Total .
IOO. 19
100.56
100.00
99-45
99.85
99.49
The average of plant-food percentages in all these soils is
quite low, and at first sight there seems to be little choice be¬
tween them. Yet two of them — Nos. 68 and 88, from Missis¬
sippi — are not only quite productive at the outset, but also
fairly durable. This becomes measurably intelligible when it
is known that both are of great depth, and so well drained that
roots can descend for many feet ; while the composition of the
soil-material is almost identical for three or four feet. On the
other hand, both Nos. 206 and 214 are quite shallow, being un¬
derlaid by sand almost devoid of plant-food at about two feet.
In addition, both have extremely low percentages of phos¬
phoric acid; while the rest show near .10% of that ingredient,
an amount which, as will be seen hereafter, is considerably
THE ANALYSIS OF VIRGIN SOILS.
353
above the recognized limit of deficiency. The two Florida
soils however bear only pine; they are underlaid by almost
clean sand at two or three feet, and are therefore quickly ex¬
hausted. It will also be noted that their lime-percentage is
only about half of that of the two first-named Mississippi
soils, both of which bear a strong growth of deciduous timber
trees, grape vines, and other vegetation indicating the presence
of lime carbonate.
It is noteworthy, also, that the popular classification of the
two Florida soils corresponds exactly with the differences in
the percentages of plant-food; those in the “ second-class ” soil
being uniformly lower than those in the one designated as first-
class. This indicates, again, that as between soils of similar
character and origin, the production and durability arc sensibly
proportional to the plant-food percentages when the latter fall
below a certain limit ; a point more fully illustrated farther on.
In the light of the above experiment and tables, it becomes
pertinent to consider what arc the lowest percentage limits of
each of the more important plant-food ingredients compatible
with profitable production.
LIMITS OF ADEQUACY OF THE SEVERAL PLANT-FOODS IN VIRGIN
SOILS.
It is obvious that the lower limits of adequacy of the critical
plant-food ingredients are best ascertained in the case of virgin
soils containing very small amounts of some one ingredient,
while fairly or fully supplied with the rest. In such cases,
which are not at all infrequent, the use of the deficient ingre¬
dient as a fertilizer should produce a very marked effect so
soon as the first flush of production (always noted in fresh
soil) is over. This first productiveness may, even in poor
lands, range from one to three years, when there is a sudden
decline.
Lime a Dominant Factor. — When we investigate the cases of
such lands, it soon becomes apparent that besides the low per¬
centage of any one ingredient, the proportions of others pres¬
ent require consideration. Among these, lime in the form of
carbonate stands foremost. Its presence exerts a dominant
and beneficial influence in many respects, as is readily apparent
23
354
SOILS.
from the prompt change in vegetation whenever it is intro¬
duced into soils deficient in it. In discussing the results of
soil analysis, its consideration is of first importance in fore¬
casting correctly the adequacy or inadequacy of other soil in¬
gredients (see chapter 20, page 379). For in general, we find
that lower percentages of potash, phosphoric acid and nitrogen
are adequate , when a large proportion of lime carbonate is
present. — This has already been referred to in connection with
the table of soils of low percentages, given above. In the in¬
terpretation of results obtained by analysis this point must al¬
ways be kept in view ; and in the numerical statements made
below, it must be understood that they refer to virgin soils
sufficiently supplied with lime to assure a constant excess of
lime carbonate, maintaining the conditions of nitrification and
insuring the absence of acidity. (See chapter 9, page 146).
Potash. — In respect to potash, the writer was led by his
early investigations in the State of Mississippi to conclude that
less than one-fourth of one per cent (.25) of potash consti¬
tuted a deficiency likely to call for early fertilization with
potash salts; while as much as .45% of the same seemed to
cause the land to respond but feebly to such fertilization. He
has not found it necessary to revise materially that early con¬
clusion, whether from his own work or from that of others.
Within the last decade. Prof. Liebscher of Gottingen 1 has ar¬
rived at this identical figure from analyses made of soils upon
which he had conducted a seven-year series of fertilizer tests;
he having found that potash fertilization produced no sensible,
or at least no paying results on land giving that figure,
and otherwise well provided with plant-food. The different
(lower) figures given by Schloesing, Risler and other French
chemists in discussing the soils of France are doubtless due to
the weak acid and short period of digestion employed in the
analysis; an unfortunate discrepancy of methods which pre¬
cludes any direct comparison of results.
These figures apply both to the arid and the humid regions in the
temperate zones. In the tropics we find very much lower percentages
quoted as adequate ; thus in the laterite soils of India and Samoa,
1 Untersuchungen uber die Bestimmung des Dimgerbediirfnisses der Ackerboden
und Kulturpflanzen, von G. Liebscher; Journal fur Landwirtschaft 43 (1895),
Nos. 1 & 2, pp. 48-216.
THE ANALYSIS OF VIRGIN SOILS.
355
according to Wohltmann, in the soils of Jamaica according to Fawcett
and in those of Madagascar according to Muntz and Rousseaux.1
There, potash-percentages . over .10% seem to be high, and in Mada¬
gascar some lands in fair production range as low as .01 °jc. The soil-
extractions have however in these cases been made with a weaker acid
than above specified, so that some increase of the figures (perhaps 33
to 50 °f0) will have to be allowed for. But even then there can be no
question that a far less amount of potash, as determined by acid-ex¬
traction, is found sufficient for crop production in the tropics ; doubtless
because of the very intense decomposing ( “ fallowing” ) effect of the
continuous heat and moisture, tending also to a rapid decomposition
of organic matter and a proportionally rapid formation of carbonic and
nitric acids. Such soils are of course constantly kept in a leached con¬
dition, as a result of the heavy and continuous rainfall.
Phosphoric Acid. — As regards the lower limit of adequacy
of phosphoric acid, there is a remarkable agreement in the in¬
vestigations made everywhere. It was placed at .05% by the
writer as long ago as i860, as the result of investigations made
in the State of Mississippi ; and the same figure has since been
arrived at independently by agricultural chemists in France,
Russia, Germany and England. The cause of this remarkable
agreement is undoubtedly the readiness with which the phos¬
phates that come under consideration at all for the nutrition
of plants, are dissolved by almost any acid treatment likely
to be used in soil analysis. Almost the same agreement exists
in regard to the “adequacy” of .1% of P205; while all soils
showing percentages between .1 and .05% are considered weak
on this side, and liable to need phosphate fertilization soon.
One-fourth of one per cent is an unusually high percentage
in most countries; .30% and over is exceptional in non-fer-
ruginous soils. But as stated on a previous page, a high per¬
centage of lime carbonate may offset a smaller percentage of
phosphoric acid, apparently by bringing about greater avail¬
ability; and a similar effect seems to result from the presence
of a large supply of humus.
On the other hand, very large percentages of finely divided
ferric hydrate may, especially in the absence of lime carbonate,
1 La Valeur Agricole des Terre s de Madagascar. Ann. de la Science Agrono
■Clique, 2’me serie, tome 1, 1901.
356
SOILS.
render even large supplies of phosphoric acid inert and use*
less, by the formation of the totally insoluble ferric phosphate.
Aluminic hydrate probably acts in a similar manner. The
following table gives examples in point, as regards ferric
hydrate.
HAWAIIAN SOILS SHOWING HIGH CONTENTS OF FERRIC OXID.
(Rept. Cal. Exp. Sta. 1894-5, page 27.)
Oahu.
Hawaii.
Number of Sample.
No. 21.
No. 22.
No. 24.
No. 26.
No. 27.
Coarse Materials> 0.55“™ .
2.00
2.50
4.00
3.00
5.00
Fine Earth .
98.00
97-5°
96.00
97.00
95.00
CHEMICAL ANALYSIS OF FINE
EARTH.
Insoluble matter .
15.84
14.49
26.99
28.66
21.07
Soluble Silica .
14.07
3°-37
10.26
7-35
2.68
Potash (KoO) .
•45
.26
.40
.61
•44
Soda (Na0Oj .
.14
.08
.26
•17
•25
Lime (CaO) .
.26
1.04
•52
.68
.28
Magnesia (MgO) .
.65
.80
.96
1.04
.60
Br. ox. of Manganese (M1I3O4)..
•°5
•°3
.21
.20
.07
Peroxid of Iron (FesCL,).. .., _
39-°5
19.68
19.10
18.23
3°. no
Alumina (AI2O3) .
14.61
18.29
21.41
20.18
14.38
Phosphoric acid ( P2(J5) .
.19
•32
.64
.70
•97
Sulfuric acid (SO3) .
•03
.09
•32
.21
.29
Carbonic acid (C(_)2) . .
Water and organic matter .
14.18
J459
18.60
21.65
28.60
Total .
99- 5 2
100.04
99.67
99.61
99-73
Humus . .
3-35
3-24
4.84
5-43
9-95
“ Ash .
3. 12
2 22
2.76
3-56
6.70
** Nitrogen, p. c. in Humus..
3-3°
9.800
2.800
3.100
1.71
“ “ , p. c. in soil .
.1 12
•3M
•i34
.168
• 17
Phosph. acid in humus ash .
.1 10
.166
.580
•5°°
Soluble in 2 °/Q Citric acid. . . .
.004
.020
•°35
•°37
.025
in Nitric acid, 1.20 sp. g. . . .
.190
•32°
.640
.700
•97°
in Chlorhydric acid i.H5sp. g
•43°
•35°
1.600
1.280
Hygroscopic moisture I5°C .
18.50
21.25
23.07
23-14
23.81
Unavailability of Ferric Phosphate. — It will be noted that in the soils
from Oahu with an overwhelming amount of ferric oxid (mostly in the
form of hydrate or rust) the citric acid has taken up only an insigni¬
ficant amount of phosphoric acid; nitric acid took up 40 to 50 times as
much, and chlorhydric doubled even this. In the much less ferruginous
Hawaiian soils, though containing more alumina, the citric acid ex¬
tracted nearly ten times as much ; proving that it is chiefly ferric oxid,
and not the alumina as has been supposed, that causes the insolubility
THE ANALYSIS OF VIRGIN SOILS.
357
of phosphoric acid in soils and doubtless also in fertilizers. The very
unusually high content of phosphoric acid in the Hawaiian soils, ex¬
ceeding all others on record, so far as known to the writer, emphasize
the effects of ferric hydrate upon soluble phosphates ; while the fact
that these very soils are greatly benefited by the use of phosphate fer¬
tilizers, proves that the Dyer (citric acid) method for the determination
of available phosphoric acid which in soils Nos. 21 to 26 yielded results
largely in excess of the established limit in European soils, cannot be
successfully applied to these highly ferruginous soils. It should also be
noted that the amounts of phosphoric acid found in the humus extracted
by the Grandeau method is in the first two Hawaiian soils over ten
times the amount extracted by citric acid, but that while they rise and
fall together, no definite quantitative ratio exists between the two.
It is obvious that in such soils, fertilization with water-solu¬
ble phosphates would be likely to result in the quick partial
withdrawal of the same from useful action, and that any ex¬
cess not promptly taken up by the crop, is likely to become
inert and useless. It will evidently be desirable to use the
phosphates in the form of bone-meal or basic slag (Thomas
Phosphate), which because of their difficult solubility will be
acted upon but very slowly, if at all, by the ferric and aluminic
hydrates.
Nitrogen. — In determining the nitrogen-content of the soil,
a great variety of methods has been followed. Some include
all that can be obtained by the combustion of the organic mat¬
ters of soil and from the nitrates present in the same; while
others, the writer among the number, believe that the mainly
important source of nitrogen to the plant being the nitrifica¬
tion of the humus-nitrogen, the determination of the humus
by the method of Grandeau, and of the nitrogen contained in
it, should be the standard; the unhumified vegetable matter
being of no definitely ascertainable value, and the nitrates
varying from day to day and being liable to be lost by leach¬
ing at any time ; therefore forming no permanent feature of the
soil. Considering the variety of methods, the unanimity with
which about one-tenth of one per cent (.10) has been assumed
as the ordinarily adequate percentage is remarkable. In view
of the extremely variable amount of nitrogen in the humus
(ranging from 1.7 to nearly 22%), the amount of the latter
353
SOILS.
cannot, of course, afford even an approximation to the nitro
gen-content ; except that as in the humid region, the nitrogen-
percentage is not known to exceed about 5 or 5.5%, an ap¬
proximate estimate can be made on that basis. In the arid
region, according to location, the nitrogen-percentage may be
from three to six times greater for a similar amount of humus.
(See chap. 8, p. 135). In the writer’s experience, a nitro¬
gen-percentage of.i% in the arid region is a very satisfactory
figure, indicating that the need of nitrogen-fertilization is not
likely to arise for a number of years.
Nitrification of the Organic Matter of the Soil. — In order to test the
question whether or not the nitrogen of the unhumified debris existing
in surface soils is directly nitrifiable, the writer selected a soil which in
its natural condition sustains intense nitrification, so that at some points
it contains as much as 1200 pounds of sodic nitrate per acre. The
composition of this soil, representing the land of the “ ten-acre tract ”
of the southern California sub-station, is as follows :
SOIL FROM “ TEN-ACRE TRACT,” SOUTHERN CALIFORNIA SUB-STATION, NO. 1284.
Coarse Materials > o.55mm . . 1.00
Fine Earth . 99.00
CHEMICAL ANALYSIS OF FINE EARTH.
Insoluble matter .
Soluble silica .
Potash (K2O) .
Soda (Na20) .
Lime (CaO) .
Magnesia (MgO) ... .
Br. ox. of Manganese (MmCL) .
Peroxid of Iron (FeaCE) .
Alumina (A12C>3) . .
Phosphoric acid (P2O5) .
Sulfuric acid (S03) .
Carbonic acid (CO2) .
Water and organic matter .
Total .
Water-soluble matter, per cent .
Sodic nitrate, per cent .
Humus .
“ Ash . . ; .
“ Nitrogen, per cent, in Humus .
“ “ , per cent, in soil .
Total Nitrogen in soil .
“ “ in unhumified matter .
Available Potash ......... j citric )
Available Phosphoric acid j method )
Hygroscopic Moisture . . . . .
absorbed at . . . x 50 C.
100.00
62.62
8.30
•95
.50
5.07
.84
.06
6-43
3.88
.21
.06
3.66
6.02
70.92
99.70
•T37
1.99
XI3
10.30
. 20T.
•330
.127
•03
5.81
THE ANALYSIS OF VIRGIN SOILS.
359
It will be noticed that this is a rather strongly calcareous soil, (nearly
9% of calcic carbonate), slightly impregnated with alkali, of which aboul
one-ninth is saltpeter. One portion of this soil was thoroughly leached
with distilled water until not a trace of nitrates could be detected in the
leachings. Another portion was treated for the removal of humus
according to the Grandeau method (see chapter 8, page 132); the ex¬
tracted soil showed under the microscope an abundance of vegetable
debris, some slightly browned as from incipient humification.
The calcic and magnesic carbonates withdrawn in the humus-extrac¬
tion were then restored to the soil in the form of finely divided pre¬
cipitates and thoroughly mixed in, first in the dry and then in the wet
condition ; the extracted soil being repeatedly wetted with turbid water
from the leached soil, in order to replace and reinfect it with the nitri¬
fying bacteria. Both soils were then spread out in flat glass dishes and
placed in a wooden box containing also a similar flat dish with distilled
water, upon which played the draught from the inlet pipe opening into
the outer air, with outlet-holes in the cover at the opposite end ; thus
keeping the air within fairly moist. In addition, the soils themselves
were moistened with distilled water every three days and restored to a
loose condition by stirring. The whole was placed so as to maintain,
during the greater part of the 24 hours, a temperature of from 30 to
35 degrees C. At intervals the samples of both soils were leached and
color-titrated for their nitrate content by the picric-acid test. The
results, calculated as sodic nitrate, during two years were as follows :
Nitrate formed during: .
Four months.
Twelve months.
Two years.
. . * * *
Leached natural soil .
.012
None.
.0420
.0030
.061
.0042
Extracted soil .
It will be noted that in the course of four months, nitrification had
not sensibly set in in the extracted soil ; while in the leached natural
soil the nitrate-content had reached to three-fifths the amount originally
present, and in the course of a year the nitrate-content of the latter
was more than double that of the original (unleached) soil ; while that
in the extracted soil had only reached one-seventh of the same. At
the end of two years we find a still farther increase of nitric nitrogen in
both, the ratio between the two remaining about the same (1 : 14).
At the same time the ratio of increase attained at first had materially
diminished in the water-leached soil, probably on account of the accumu¬
lation of the niter itself.
360
SOILS.
It thus appears that although the nitrogen of the unhumified
organic matter constituted about 40% of the total in the origi¬
nal soil, it would during the entire year have contributed only
to an insignificant extent to the available nitrate-supply; while
the fully humified “ matiere noire ” contributed fourteen times
as much. During the ordinary growing-season of four or five
months the unhumified organic matter would have yielded
practically nothing to the crop.
Functions of the unhumified Vegetable Matter. — The chief
utility of the unhumified matter in the soil consists of course
in its gradual conversion into true humus, in the course of
which it evolves carbonic gas to act on the soil minerals ; while
at the same time it helps to render the soil more porous and
thus facilitates the action of the aerobic bacteria, for which it
serves as food. Hence the addition of vegetable matter to soils
not already too “ light ” is always advantageous, so long as
it does not introduce injurious, non-humifiable ingredients,
like turpentine in the sawdust of resinous pines. But it is al¬
ways advisable to first use such matter as litter for stock, in
order to better prepare it for the processes of humification,
under the influence of ammonical fermentation, such as occurs
in the decay of green plants or animal matter. A portion of
the ash ingredients also is quickly utilized by solution in the
soil-water.
Matiere Noire the Only Guide. — According to these results
it is clear that in order to gain any tangible indications with re¬
spect to crop-bearing, it is the nitrogen in the humus proper,
the matiere noire only, that should serve as the basis; and that
as a current source of nitrogen to the plant, the unhumified
matter is hardly entitled to more consideration than the “ in¬
soluble silicates/’ For, the favorable conditions for nitrifica¬
tion under which the above experiment was conducted, will
very rarely be even approached under field conditions.
What are the Adequate Nitrogen Percentages in the Humus f
The nitrification of the matiere noire being, apparently, the
main source of plant-nutrition with that element under ordin¬
ary conditions, the question naturally arises as to what may be
considered an adequate nitrogen-content of that substance, so
as to permit a full supply of nitrates to the crop.
THE ANALYSIS OF VIRGIN SOILS.
361
The data extant on this subject are rather scanty, and thus
far have all been obtained at the California Experiment Sta¬
tion.* 1 2 But they seem to be very cogent in proving that the
growth of crops removed from the soil causes a rapid deple¬
tion of the nitrogen in the humus-substance, and that so soon
as the nitrogen-percentage in the same falls below a certain
point, the soil becomes “ nitrogen-hungry ; ” so that the applica¬
tion of nitrogenous fertilizers is needed and is very effective.
The data in the table below, as well as the figure of a culture
experiment (No. 52 below), illustrate this point.
ADEQUACY AND INADEQUACY OF NITROGEN CONTENTS OF HUMUS.
Collec¬
tion
Num¬
ber.
Kind of
Soil.
Locality.
Per cent.
Humus in
Soil.
Per cent.
Nitrogen
in Humus-
Per cent.
Nitrogen
in Soil .l
6
Black Adobe.
Near Stockton, San loaquin
Co., Cal .
1.05
18.66
.196
1679
do
Virgin Soil, University
Grounds, Berkeley, .
1.20
18.58
.203
1842
do
Ramie plot, Univ. Grounds,
10 years cultivated .
1.80
4.17
•075
1841
do
Grass plot, Univ. Grounds,
10 years cultivated .
1.65
3-4 0
.056
29
Dark loam.
Sugar-cane land, Maui, H.
T .
10.90
3-15
•347
27
Dark loam.
Guava-land hills, near Hilo,
Hawaii Isl’d .
9-95
1.71
.170
Nos. 6 and 1679 show the usual humus- and nitrogen-percentages in
the “ black adobe” or ‘‘prairie” soils of California. Nos. 1842 and
1841 represent the same soil as 1679, upon which, however, ramie and
ray grass had respectively been growing, without fertilization, for about
ten years ; showing that while the humus-content of the soil has increased,
the nitrogen-content of the humus has decreased in the case of ramie by
72.78%, in that of the grass by 76.78% ; reducing the land to figures
commonly found in the humid region. In the case of the ramie, the
partial return through the leaves has resulted in a higher humus-content,
1 The Supply of Soil Nitrogen , Rep. Cal. Expt. Station, 1892-93, page 68 ; ibid.,
1894-95, page 28 ; The Recognition of Nitrogen Hungriness in Soils , in Bull. 47, Div.
of Chemistry, U. S. Department of Agriculture, 1895 > Landw. Presse, No. 53, July
1885. See also for detailed data chapter 8, page 135.
2 Calculated upon the true humus substance (matiere noire), not by determining
total (inch unhumified) nitrogen in the soil.
362
SOILS.
together with higher nitrogen-percentage, than in the case of the grass,
which in the several cuttings annually made, caused a greater depletion
in nitrogen and a smaller accession of humus. The grass was very
weak in its growth and partially dying out.
No. 29, the sugar-cane land from Maui, was still in fair production,
but beginning to weaken as against its first production. No. 27,
the guava land from Hawaii, originally bore a luxuriant cover of
wild guava, but after bearing one fair crop of seed-cane and one of
ratoons, the cane planted on it “ spindled up ” and died so soon as the
seed-cane planted was exhausted. Both the island soils, originally
derived from the weathering of the black basaltic lavas of the region,
were well supplied with mineral plant-food (see above, page 356), and
the humus-content in both was exceptionally high ; and neither was in
an acid condition. The difference in their nitrogen-content, both in
the totals and in the humus itself, suggested that notwithstanding the
relatively high total of nitrogen in No. 27, it might be nitrogen-hungry,
in view of the low percentage of the nitrogen in the humus.
Confirmatory Experiment. — A pot-culture with wheat, the
results of which are shown in the figure below, fully confirm
Fig. 59. — Growth of Wheat on Guava Soil from Hawaii Island.
this suspicion. One kilogram of soil was used in each of two
pots, one being fertilized with half a gram of Chile saltpeter.
THE ANALYSIS OF VIRGIN SOILS.
3<53
The experiment could not be carried to full completion on ac¬
count of the overwhelming invasion of mildew ; but the figures
speak for themselves. Moreover, a field trial made on the
island with saltpeter, in pursuance of the writer’s recommen¬
dation, resulted in a luxuriant growth of the cane.
Data for Nitrogen-adequacy. — It appears from the facts
shown above, that for the growth of grasses a nitrogen-per¬
centage in the humus of 1.7 is wholly inadequate, no matter
how much humus may be present. A percentage of 3.15 in
the Maui soil, No. 29, containing nearly 1 1 % of humus, gave
only a fair crop of sugar-cane ; on the Berkeley grass plot, with
3.40% and only 1.65 of total humus, the ray grass was barely
maintaining life. The ramie, with 4.17% of nitrogen in the
soil-humus, was still doing fairly well.
It is doubtless impossible to give one and the same absolute
figure for nitrogen-deficiency for all plants and soils. Where
the conditions of nitrification are favorable, as in the presence
of much of the earth carbonates, a smaller percentage may
suffice for the same plants that elsewhere suffer ; and it is highly
probable that different minima will be found for plants of dif¬
ferent relationship and root-habits. But there is every reason
to believe that in the nitrogen-percentage of soil-humus , con¬
sidered in connection zvith other chemical and physical condi¬
tions and soil derivations , we have a means of ascertaining the
needs of plants with respect to nitrogen-fertilization, if proper
study be given to the subject. Broadly speaking, it appears to
be necessary to keep the nitrogen-percentage of soil-humus near
4 % to insure satisfactory production.
It having been suggested that the frequent and disastrous
crop failures on the noted tchernozem or black-earth soils
of Russia might be due in part at least to nitrogen-depletion
of the humus, the writer obtained through the courtesy of
Prof. P. Kossovitch of St. Petersburg soil samples from the
center of the Black-earth region, both cultivated and unculti¬
vated. These samples are in appearance exactly like some of
the dark alluvial soils of Louisiana and California, and ap¬
proach them very nearly in the essentials of composition, as
will be seen from the table below :
364
SOILS.
ANALYSES OF BLACK SOILS,
Tchernozem
(Russia.)
Alluvial
Black clay lands.
Virgin.
Culti¬
vated.
Louisiana.
No. 240.
California.
No. 1 167.
Back -land
Houma.
Black-land
Tulare.
CHEMICAL ANALYSIS OF FINE EARTH.
(No coarse material in soils.)
Insoluble matter .
48.38
55-°9
35-48
62.43
Soluble silica .
13.21
12.28
20.76
16.99
Potash ( K20) . .
.72
•52
1.03
1.09
Soda (NasO .
.20
.13
.13
•77
Lime (Cab) .
J-51
I-3I
•72
1.46
Magnesia (MgO) .
•73
•75
.88
1.44
Br. ox. of Manganese (Mn304) .
•°5
•03
.01
.06
Peroxid of Iron (Fe3Q3). .
7.12
4.80
7.10
4.98
Alumina ( A1,03) .
5.22
4-73
1 5-45
6.87
Phosphoric acid (P206) .
.14
.13
•J5
.12
Sulfuric acid (Sb,) .
.07
.08
•25
.02
Carbonic acid (Cb2) .
• • • •
» • • •
Water and organic matter .
00 ^
19.94
CO
....
Total .
100.13
99-79
100.48
100.59
Humus .
5- 11
5-54
5-°7
i-33
“ Ash .
1.80
1.40
•9i
•36
“ Nitrogen, per cent, in Humus..
463
4.22
• • • •
“ “ per cent, in soil. . ..
.27
.24
• • • •
....
Available Potash . ( citric acid )
.014
.010
• • • •
Available Phosph. acid ( method )
.01 1
.008
.08
.01
Hygroscopic Moisture .
12.07
18.82
5-38
absorbed at .
• • • •
i7°C
i3°C
i5°C
It will be seen that the Russian soil is of high fertility ac¬
cording to the standards given above, and that the nitrogen-
content of the abundant humus is amply within the limits of
adequacy suggested by the experience in California and Ha¬
waii. The humus-content of the arid California soils is char¬
acteristically low as compared with the Russian tchernozem
as well as with the Houma back-land of humid Louisiana;
but its nitrogen-content is doubtless at least three times that of
the latter, as is that of the humus of similar lands in which
it has been determined.
THE ANALYSIS OF VIRGIN SOILS.
3<5$
INFLUENCE OF LIME UPON SOIL FERTILITY.
Assuming as substantially correct the numerical data given
above in respect to the three leading ingredients of plant-food
— phosphoric acid, potash and nitrogen, — the dominant role
of lime in soil fertility, already mentioned, requires some
farther illustration and discussion.
“ A Lime Country is a Rich Country — The instant change
of vegetation when we pass from a non-calcareous region to
one having calcareous soils, has already been alluded to. (See
this chapter, p. 354). But it is not necessary to be a botanist
to see the change in the prosperity of the farming population
as one enters a lime district. The single log-cabin with, prob¬
ably, a wooden barrel terminating the mud-plastered chimney,
is replaced, first by double log-houses, then by frame, and far¬
ther on by brick buildings, with the other unmistakable evi¬
dences of prosperity. Thus this is seen in passing from the
mountain region of Kentucky into the “ bluegrass ” country,
which is throughout underlaid by calcareous formations; and
thus, likewise, in crossing the strike of the formations of Ala¬
bama, Mississippi and Louisiana, or any other region where un¬
derlying calcareous formations have contributed to the for¬
mation of the soils, as compared with some adjacent district
where this is not the case. The calcareous loess areas border¬
ing on the Mississippi river and some of its chief tributaries,
are conspicuous cases in point, as are also the prairies of Illi¬
nois and Indiana.
Effects of High Lime-content in Soils. — The table below il¬
lustrates the fact that in the presence of high lime-percentages,
relatively low percentages of phosphoric acid and potash may
nevertheless prove adequate; while the same, or even higher
amounts, in the absence of satisfactory lime-percentages prove
insufficient for good production.1
1 This statement appears contradictory of the observations of Schloesing fils
upon the solubility of phosphoric acid in presence of lime carbonate (Am. Sci.
Agron., tome i, 1899), but the natural conditions seem to justify fully the above
conclusion.
SOILS SHOWING LOW PHOSPHORIC ACID PERCENTAGE
3 66
SOILS
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THE ANALYSIS OF VIRGIN SOILS.
367
Nos. 139 and 1 7 1 are heavy black prairie soils of high productive capa¬
city, whose production had, at the time of sampling, lasted almost un¬
diminished for over twenty years. Nearly the same is true of the two
California soils, Nos. 499 and 1113; which, however, are ferruginous
loams of only moderate clay-content. In all, the percentage of phos¬
phoric acid shown by the analysis is at or below the recognized limit
of deficiency, while the lime-content of all is as high as is required for
the welfare of any soil, however constituted. The potash-percentage
also is low in all except the “red foothill soil,” No. 1113.
Passing to the soils of low lime-content, we find the two Mississippi
soils, poor in both potash, lime and phosphoric acid, so low in produc¬
tion as to be wholly unprofitable in cultivation without previous ferti¬
lization; No. 559, from California, produced two fair crops of barley
and then no more. No. 207, is the soil of Eel river bottom, California ;
profusely productive at first, by virtue of its high content of both potash
and phosphoric acid; but “giving out” under a few years’ culture of
clover or alfalfa (which draw heavily upon lime), and quickly restored
to productiveness under the influence of dressings of quicklime. In
this case the soil had become acid, a condition which always militates
against the success of culture plants, and more especially against those
of the leguminous relationship.
What are Adequate Lime Percentages f — We have in the
presence or absence of the natural vegetation peculiar to cal¬
careous soils (“ calciphile ”) an excellent index of the pres¬
ence or absence of such amounts of lime carbonate as fulfil the
conditions of its beneficial effects. Lists of such plants for the
United States are given farther on ; they agree almost through¬
out with such plants as are everywhere recognized by Ameri¬
can farmers as indicating productive soils.
All soils bearing such vegetation show with red litmus paper,
when wetted, a neutral reaction at first, which after the lapse of
twenty or thirty minutes turns to a blue alkaline one ; such as
is given under the same conditions by the carbonates of lime
and magnesia.
But the reverse is not necessarily true ; for we occasionally
find soils containing considerable amounts of lime carbonate
that yet fail to bear lime vegetation. This is the case of ex¬
tremely heavy clay soils, as exemplified in the table below
in the case of the last three soils; while the first, No. 220, ex-
368
SOILS.
emplifies a case where although potash is exceptionally high,
only scrubby oak growth is produced in presence of an amount
of lime that in sandy lands would show profuse lime growth.
TABLE ILLUSTRATING THE NEED OF HIGH LIME-PERCENTAGES IN HEAVY
CLAY SOILS.
*
Mississippi.
California.
Flatwoods,
Pontotoc
Co.
Hog-wal-
low, Jasper
Co.
Ridge
Prairie,
Smith Co.
Yellow
ridge, Ala¬
meda Co.
No. Sample... . .
230
242
203
4
CHEMICAL ANALYSIS OF FINE
EARTH.
Insoluble matter . I
Soluble silica . f
77-S 5
76.76
5I*75
86.00
Potash (K2O) .
.7 5
• 'll
• SI
.19
Soda (Na^O) . . .
.1 1
.19
2 2
•15
Lime (CaO) .
.18
.42
.48
.48
Magnesia MgO .
•83
.67
1. 01
•45
Pr. ox. of Manganese (Mn304). ..
•17
•56
.10
.04
Peroxid of Iron (FeaOs) .
5.90
4.12
2379
4.01
Alumina (AI2O3) . . .
10.30
10.06
10.85
5-53
Phosphoric acid (P2O5) .
.05
.06
•*5
.06
Sulfuric acid (SO3) .
.03
.06
.02
.02
Carbonic arid tCOA .
Water and organic matter .
3-69
5-73
n-39
4.05
Total .
99.86
99.17
100,29
100.99
LTvprosronir Moisture .
9-3
6.8
19.7
absorbed at . 0 C
22.0
air-dry
17.0
All of the soils in this table are heavy clays, very difficult to
till; in all, the lime-percentage falls below .5%; and none
bear any lime vegetation, the Mississippi soils having a stunted
growth of black jack and post oaks, such as is universally
known to indicate soils too poor for profitable cultivation. The
California soil bears stunted live oak ( Q . agrifolia ) ; but not
being as heavy as its brethren from Mississippi, though un¬
thrifty, is more readily improved.
Comparison with the two first sandy soils in the table on p. 352 shows,
that with plant-food percentages equal to, or even much below those
here shown, not only was vigorous lime growth present, but crop-pro-
duction was good and even high.
THE ANALYSIS OF VIRGIN SOILS.
369
We are thus led to the conclusion that the greater the clay
percentage in a soil, the more lime carbonate it must contain
in order to possess the advantages of a calcareous soil ; and
that while in sandy lands lime growth may follow the presence
of only .10% of lime, in heavy clay soils not less than about
.6% should be present to bring about the same result. This
is apparent to the eye in that the dark-tinted humus characteris¬
tic of truly calcareous lands, does not appear in clay soils until
the lime-percentages rise to nearly 1 % ; while in sandy lands a
much smaller amount (say .2%) will produce this effect.
European Standards . — It is of interest to consider, in connection
with preceding discussions, the estimates given by Maercker of Halle,
of the practical value of soils corresponding to chemical composition
as ascertained by analysis with strong acids, substantially in accordance
with the methods adopted by the writer.
PRACTICAL RATING OF SOILS BY PLANT-FOOD PERCENTAGES ACCORDING TO
PROF. MAERCKER, HALLE STATION, GERMANY.
Grade of Soil.
Potash.
Phosphoric
Acid.
Lime.
Total
Nitrogen.
Humus
Nitrogen.
Clay Soil.
Sandy Soil.
Poor .
Below 0.05
Below 0.05
Below .10
Below .05
Below .05
Medium .
0.05 — 0.15
.05 — .10
.10— .25
.10 — .15
.05 — .10
Normal .
0.15 — 0 25
.10— .15
.25 — .50
.15 — .20
.10 — .15
Good... .
0.25 — 0.40
•IS— -25
.50 - I. OO
.20 — .30
.15 — .25
Rich .
Above 0.40
Above .25
Above 1. 00
Above .30
Above .25
Av’age for California. . .
O.7O
0.08
1.08
.102
“ “ Arid Reg. . .
•73
.12
I.
36
• II
(?)
“ “ Humid Reg.
.22
.11
•
II
.12
.166
It will be observed that according to Maercker’s valuation, the aver¬
age California soil is “ rich ” in potash and lime, but only “ medium ”
as regards its contents of phosphoric acid and nitrogen. Jn this respect,
and almost throughout, Maercker’s ratings are in remarkable agreement
with those made by the writer as far back as 1860.* It also appears
that Maercker’s figures for “ normal ” soils correspond to those of the
American humid regions ; the “ arid ” figures for potash and lime being
“ abnormally ” high.
1 See discussions of analyses of Mississippi soils in the Report on the Agriculture
and Geology of Mississippi, i860; same in Rep. On Cotton Production, Tenth
Census, 1880, Vol. 5; also Appendix to the Report on the Experiment Stations of
the University of California, 1890, p. 163.
24
370
SOILS.
Unfortunately neither Maercker’s method of preparing the
soil extract, nor his ratings as given in the table, are accepted
by all soil chemists even in Germany. As will be seen by
reference to Wohltmann’s work on the soils of Samoa and
Kamerun (chap. 21, p. 404), his methods and numerical esti¬
mates differ widely from those given by Maercker, and also
from those adopted by the Prussian soil surveys. Reference to
the analyses of the soils of Madagascar by Miintz and Rous-
seaux, given in the same chapter, page 406, shows still another
different method, although as it happens their numerical esti¬
mates do not differ very widely from those of Wohltmann. In
both cases, a special, more incisive extraction is made for the
determination of potash. Why the same more energetic action
is not used for the other ingredients also, is not stated, and is
obscure. Fortunately, in all cases the action is at least suffi¬
ciently strong to secure the dissolution of all the lime existing
in the form of carbonate, and of all, or nearly all, the phos¬
phoric acid not securely locked up as ferric phosphate; the
latter being inert, is of no special interest (see Analyses of
Hawaiian Soils, this chapter, page 256).
CHAPTER XX.
SOILS OF THE ARID AND HUMID1 REGIONS.
Composition of Good Medium Soils. — In the preceding
tables examples have been given of rather extreme types of
soils, both rich and poor throughout, and also of such as are
deficient in one or several of the important ingredients. In the
table below are given the analyses of some of the good aver¬
age farming lands; uplands of several states, both of the humid
and arid regions. In the former, the representative timber
trees of such lands are the black, red, white and (less charac¬
teristically) the post, black-jack, Spanish, overcup and locally
some other oaks ; grading higher in proportion to the presence
of more or less hickory, and lower as the latter is replaced by
pine. In the states south of Ohio, the “ oak and hickory up¬
lands ” are what the farmer usually looks for, outside of the
valleys or bottoms.
Criteria of Lands of the Tzvo Regions. — In the country west
of the Rocky Mountains, the timber, while locally very char¬
acteristic, cannot be as broadly used as a criterion, partly on
account of its scarcity, partly because the dominant factor in
the growth of trees is moisture , which is measurably independ¬
ent of chemical soil-composition. The latter, moreover, on ac¬
count of climatic conditions, already alluded to (chapter 1 6 ) ,
does not vary as materially in the arid as the humid region, on
account of the almost universal presence of larger proportions
of lime carbonate ; the variations of which in the humid region
govern largely the vegetative changes. For we there find the
timber grozvth of the lozvlands ascending into the uplands so
1 In the discussion in this chapter the “ humid region ” referred to is always that
of the temperate zones, unless expressly otherwise stated. The most humid region
of all — the tropics — is treated under a special head.
371
UPLAND SOILS OF HUMID REGION,
372
SOILS.
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SOILS OF THE ARID AND HUMID REGIONS.
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374
SOILS.
soon as the latter becomes decidedly calcareous ; as is abun¬
dantly exemplified in the loess or “ bluff ” formations border¬
ing the Mississippi, Ohio, and Missouri rivers, where the black
walnut, tulip tree, ash, honey-locust, together with the lowland
oaks, hickories and cane usually characterizing the stream
bottoms, grow abundantly and with luxuriant development on
the adjoining steep hill country as well (see below, chapters
24, 25).
Soils of the Humid Region. — Taking a view, first, of the
table showing the soils of the humid region, it appears that
the change of vegetation from walnut and hickory to the short¬
leaved pine bears no visible relation to the increase or decrease
of potash or phosphoric acid, but is plainly governed mainly by
the amount of lime present. Where the short-leaved pine pre¬
vails the soil is almost always either neutral or shows the
alkaline reaction in the course of half an hour; but where the
long-leaved pine predominates the soil has almost always an
acid reaction. The latter is also usually found in bottoms in
which the loblolly pine ( P . taeda) prevails, and where, al¬
though the soil may show a fair proportion of lime in the
analysis, it does not exist in the form of carbonate.
The examples here given are from lands not derived from ,
or underlaid by, limestone formations. Where the latter exist
the percentage of lime is usually materially increased ; as it is
also in the lowlands or bottoms when compared with adjacent
uplands (see above, chapter 10, p. 162; chapter 18, p. 331);
as well as in the delta lands of rivers.
Soils of the Arid Region. — Even a cursory comparison of the
soils of the arid regions of the Pacific slope with those of the
humid, as given in the above tables, shows some striking points
of difference. The most obvious is the uniformly high per¬
centage of lime, and usually also of magnesia, in the arid soils,
and that quite independently of underlying formations, calcare¬
ous or otherwise. This occurs despite the fact that while lime¬
stone formations are very prevalent east of the Rocky Moun¬
tains, they are quite scarce west of the same. The red (Lar¬
amie) sandstones of Wyoming, the slates of the foothills of
the Sierra Nevada, the clay shales, granites and eruptives of
the Coast Ranges of California, Oregon and Washington,
SOILS OF THE ARID AND HUMID REGIONS.
375
and the varied black rocks of the great lava sheet of the Pacific
Northwest, all alike produce soils of high liwie content as com¬
pared with Eastern soils not derived from calcareous forma¬
tions. This fact has already been referred to, but is more
fully illustrated in the table below.
Aside from the lime-content, however, it will be noted in the
preceding table that the potash-content of the arid soils is on
the average considerably higher than in those of the humid
region. In fact it is hard to find west of the Rocky Mountains
(except where high elevation causes a humid climate) any
soils as poor in potash as are many of the commonly cultivated
lands of the Eastern United States.
Other ingredients do not show such marked differences from
the purely chemical standpoint: yet, as will be shown below,
the forms in which silica and alumina occur are also not incon¬
siderably modified.
General Comparison of Soils from the Arid and
Humid Regions of the United States.1 — In order to
verify the conclusions just mentioned upon the broadest basis
possible, the following table has been compiled from all avail¬
able sources; partly published, partly in manuscript only, hav¬
ing remained in the writer's hands since the cessation of the
Northern Transcontinental Survey, prosecuted from 1880 to
1883, under the auspices of the Northern Pacific Railroad, in
Washington and Montana. The published data are derived
partly from the records of State surveys, partly from the soil
work connected with the Tenth Census; partly also from those
of Experiment Stations. In most cases it has of course been
necessary to restrict the comparison to such analyses as have
been made by substantially identical methods, for reasons al¬
ready given ; but in the cases of some states from which numer¬
ous analyses made by the Kedzie method, adopted by the As¬
sociation of Official Chemists, were available, the average has
been given but the name of the state starred, to indicate that
the percentages, excepting phosphoric acid, are lower than they
would be if made by the method adopted by the writer, par¬
ticularly as regards potash. The adoption of the one-milli¬
meter mesh for the fine-earth sieve instead of the half-milli-
1 Abstracted and revised from Bulletin No. 3, U. S. Weather Bureau, 1893.
SOILS,
meter size also creates an unfortunate and ineliminable dis¬
crepancy.
In order to exhibit clearly the influence of climate as distinct
from other local conditions, it was also necessary to eliminate,
in both the arid and humid regions, the soils directly derived
from, or connected with calcareous formations; such as the
prairies of the Southwestern States, the Bluegrass region of
Kentucky, etc. This rule having been applied impartially to
the soils of both climatic regions, it can hardly be questioned
that the conclusions flowing from a discussion of the results of
the comparison are entitled to as much weight as are those of
any comparison based on large numbers of observations made,
not with reference to the special point under consideration, but
with a practical object of which the governing conditions were
more or less uncertain, and required to be ascertained by a pro¬
cess of elimination.
The table gives, first, the averages for each ingredient for each of the
states represented, the number of analyses from which the averages are
derived being given in each case. 1 hese averages are given separately
for the states of the humid and the arid regions respectively ; and at
the base of each group the grand average is shown in two forms. The
first gives the figures as derived from the aggregate number of soil
analyses in each great group, being 696 for the humid, 178 for the
transition region and 573 for the arid, divided into the totals resulting
from the summation of each ingredient for the whole 696, 178 and 573,
respectively.
The second form is that in which the soils of each state are considered
as representative of the general character of such state, as the result of
intentional selection ; such as actually occurred in the cases of those
included in the census work of 1880. The figures given here are
therefore the result of a summation of the state averages as such, and
of their division by the number of states represented.
It will be noted that while these two modes of presentation do change
the figures a little, yet in either form the same general result is out¬
lined with striking accuracy. It is also notable that notwithstanding
the less complete extraction of soil-ingredients in the starred states,
the general ratios between arid and humid soils remain substantially
the same. For Western Oregon, local calcareous formations compel
omission of three lime figures from the averages.
AVERAGE COMPARISON OF SOILS IN THE HUMID AND ARID REGIONS OF THE UNITED STATES.
SOILS OF THE ARID AND HUMID REGIONS.
377
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SOILS.
378
New Mexico. — Few analyses of New Mexico soils have been
made, but the average results of six partial determinations
made by Goss, and one full analysis made by Hare according
to the method of the writer, and given below, show substantial
accord with the averages of the above table. The averages of
Goss’ determinations are: Potash .780, Phosphoric acid
.221, Nitrogen .108 per cent.
CHEMICAL ANALYSIS OF RIO GRANDE SILT (by Prof. R. F. Hare.)
Deposited on on land by irrigation.
Insoluble matter . 63.70
Potash (KaO) . 1.06
Soda NaaO) . .22
Lime (CaO) . 4-97
Magnesia (MgO) . 2.43
Br. ox. of Manganese (Mn304) . .14
Peroxid of Iron (Fe303) . 5-^°
Alumina (AlaOs) . 6.86
Phosphoric acid (P3O5) . * . .16
Sulfuric acid (SOa) • . *13
Carbonic acid (COa) . 7-45
Water and organic matter . 9.98
Humus . 1.17
“ Nitrogen . 11.11
“ “ per cent, in soil . .13
Hygroscopic Moisture
absorbed at .
°C
2.63
DISCUSSION OF THE TABLE.
Lime. — Considering in this table, first, lime, a glance at the
columns for the two regions shows a surprising and evidently
intrinsic and material difference, approximating in the average
by totals to the proportion of 1 to 1 1 ; in the average by states,
1 to 14 This difference is so great that no accidental errors
in the selection or analysis of the soils can to any material de¬
gree weaken the overwhelming proof of the correctness of the
inference drawn upon theoretical grounds, viz., that the soils of
the arid regions must be richer in lime than those of the humid
countries. For the differences in derivation would, in view of
the wide prevalence of limestone formations in the humid
regions concerned, produce exactly the reverse condition of
things from that which is actually found to exist; and if fur¬
ther proof were needed it can readily be found in the detailed
discussion of the analyses of the soils of the arid areas forming
SOILS OF THE ARID AND HUMID REGIONS.
379
the contrast. This shows that for instance, in Washington
highly calcareous soils are directly derived from the black
basaltic rocks ; while similarly, calcareous lands are found in
California to be the outcome of the decomposition of granites,
diorites, lavas, clay-shales and sandstones.
It is not easy to overrate the importance of this feature of
the soils of the arid region, as it is intimately connected with
other theoretically and practically important facts, in part al¬
ready mentioned.
Summary of Effects of Lime Carbonate in Soils. — It is best
to summarize, briefly, at this point, the advantages (and possi¬
ble disadvantages), resulting from the presence of a proper
amount of lime carbonate in soils, so far as these are at present
understood.
Physically , even a small amount of lime carbonate, by its
solubility in the carbonated soil-water, will act most beneficially
in causing the flocculation of clay and in the subsequent con¬
servation of the flocculent or tilth condition, by acting as a
light cement holding the soil-crumbs together when the capil¬
lary water has evaporated; thus favoring the penetration of
both water and air, and of the roots themselves. It should be
added that according to the experience of the writer, amounts
of lime carbonate in excess of 2% do not add to the favorable
effects, except as would so much sand.
As to chemical effects, among the most important are : —
1. The maintenance of the neutrality of the soil, by the
neutralization of acids formed by the decay of organic matter,
or otherwise.
2. The maintenance, in connection with the proper degrees
of moisture and warmth, of the conditions of abundant bac¬
terial life (see above, chapter 9, p. 146) ; more especially those
of nitrification, thus supplying the readily assimilable form of
nitrogen. Also in favoring the development and activity of
the root bacteria of legumes, and of the other nitrogen-gather¬
ing bacteria, such as Azotobacter (ibid. p. 156).
3. The rendering available, directly or indirectly, of re¬
latively small percentages of plant-food, notably phosphoric
acid and potash ; as shown in the preceding pages.
4. The prompt conversion of vegetable matter into black,
SOILS.
380
neutral humus, and (as shown in the case of the soils of the
arid region) the concentration of the nitrogen in the same;
while accelerating the oxidation of the carbon and hydrogen,
as shown by S. W. Johnson and others.
6. It counteracts the deleterious influence of an excess of
magnesia in the soil, as first shown by Loew,1 and verified by
his pupils in Japan.
7. In alkali soils, according to Cameron and May, it coun¬
teracts the injurious action of the soluble salts upon the
growth of plants, not only in the form of carbonate, but also in
those of sulfate and chlorid.2
8. As a matter of experience, both in the case of grapes and
orchard as well as wild fruits, an adequate but not excessive
supply of lime in the soil will produce sweeter fruit than when
lime is in small supply.
9. An excess of carbonate of lime in soils (from eight to
twenty per cent and more), constituting “ marliness,” tends to
seriously disturb the nutrition and general functions of many
plants (calcifuge), and to produce a suppression or diminution
of the formation of chlorophyll and starch ; as in the case of
grape vines, citrus fruits and others, which nevertheless flour¬
ish best in lands moderately calcareous.
Among the points thus enumerated the third and fourth re¬
quire some comment. Without pretending to define exactly
how lime acts in rendering other ingredients more available to
plant assimilation, attention may be called to the fact that lime
carbonate may be considered as acting similarly to, albeit more
mildly than, caustic lime, in the displacement of other bases
from their compounds. It doubtless acts thus in liberating
potash from its zeolitic compounds. As to phosphoric acid,
the connection of the effect of lime carbonate with the remark¬
able availability of that substance when present in the form of
tetra-basic salt, in the case of phosphate slag, is at least possible.
As to the action of lime carbonate in forming humus,3 no one who
has observed the characteristic dark black tint of our calcareous
1 Bull. No. 1, Div. Veget. Physiol, and Plant Pathol. U. S. Dept. Agr. ; et al.
2 Loeb (Publications of the Spreckel’s Physiological Laboratory of the Univer¬
sity of California, has shown a similar protective influence of the lime salts in
sea-water, against the other salts, in the case of the lower marine organisms.
3 “ Black Soils ; ” Agric. Science, January, 1892.
SOILS OF THE ARID AND HUMID REGIONS. 381
“ prairie soils” can question the fact; which moreover is perfectly ex¬
plicable upon the analogy already alluded to, with caustic lime, which,
together with caustic alkalies (potash and soda), is known to act power¬
fully in the conversion of vegetable matter into humus. That instead
of liberating the nitrogen in the form of ammonia, as do the caustic
hydrates, the milder carbonate should only cause the formation of humic
amides, is quite intelligible. That such is really the case, has been
conclusively proved by the investigations of the writer made conjointly
with M. E. Jaffa (Rep. Sta. Cal. Agr. Expt. 1892-4) ; the general result
being that while in the humid region the average nitrogen-content of
soil- humus is less than 5 %, in the upland soils of the arid region
(where all soils are calcareous) that percentage rises as high as 22.0 °f0y
with a general average of between 15 and 1 6°f0. That such highly
nitrogenous material can be more readily attacked by the nitrifying
bacteria than when a large excess of other oxidable matter is present,
is at least a legitimate presumption, especially in view of the very active
nitrification known to take place in the arid regions everywhere. So
long as a large excess of carbohydrates is present, the oxidation of these
will naturally take precedence over that of the relatively inert nitrogen.
The accumulation of the latter in the humus-substance of the arid
region, where oxidation of the organic matter of the soil is very active,
points strongly to this view of the case.
Magnesia. — While the differences in respect to the propor¬
tions of lime are the most prominent and decided, yet the re¬
lated substance, magnesia, shows also a very marked and con¬
stant difference as between the soils of the humid and arid
regions. It will be observed that the general average for mag¬
nesia in the soils of the Atlantic Slope is about double that of
lime; Florida and Rhode Island being the only states in which
the average is lower for magnesia than for lime. In the
arid region, on the contrary, magnesia on the general average
is nearly the same as lime; in the average by states, some¬
what less ; thus bringing the ratio for the two regions for mag¬
nesia up to one to six or seven. This also is so decisive a
showing that no accident could bring it about. We must con¬
clude that climatic influences have dealt with magnesia simi¬
larly as with lime; which from the standpoint of the chemist is
just what might be expected, since magnesia carbonate behaves
very much like that of lime toward carbonated waters.
382
SOILS.
That magnesia is a very important plant-food ingredient is
apparent from its invariable and rather abundant presence in
the seeds of plants, where it takes precedence of lime. Its func¬
tions in plant nutrition have been specially investigated by O.
Loew,1 particularly with respect to its relations to lime. As
already stated in connection with the soil-forming properties
of magnesian minerals (see chapter 2), soils containing large
proportions of magnesia generally are found to be unthrifty,
the lands so constituted being frequently designated as “ bar¬
rens/’ Loew finds that certain proportions of lime to magnesia
must be preserved if production is to be satisfactory, the pro¬
portion varying with different plants, some of which (e. g.
oats) will do well when the proportion of lime to magnesia is
as 1 :i, while others require, that that ratio should be as 2 or 3
is to 1, to secure the best results. In general it is best that
lime should exceed magnesia in amount.
Loew explains the injurious action of magnesium salts thus : The
calcium nucleo-proteids of the organic structures are transformed in
presence of soluble salts of magnesium into magnesium compounds,
while the calcium of the former enters into combination with the acid
of the magnesium salt. By this transformation the capacity for im¬
bibition will change, which must result in a fatal disturbance of functions.
The presence of soluble lime-salts will prevent that interchange. Thus
certain algae perished in a solution containing 1 per 1000 of magnesium
nitrate, but remained alive when .3 per 1000 of calcium nitrate was
added.
Magnesia seems to be specially concerned in the transfer of
phosphoric acid through the plant tissues, in the form of
dimagnesic-hydric phosphate, which is rather soluble in the
acid juices of plants. It is probable that, apart from the re¬
lations just referred to, such excess of lime as is known to pro¬
duce chlorosis in plants interferes with the transfer of the mag-
nesic phosphate. Some plants, as already stated, dispose of an
excess of lime by depositing it in the form of oxalate, while
others (such as the stone crops) excrete it on the surface of
1 Bull. No. 18, Div. Vegetable Physiology and Plant Pathology; Bull. No. I
Bureau of Plant Industry, U. S. Dept, of Agr. ; Bull. College of Agriculture, Tokyo
Vol. 4, No. 5.
SOILS OF THE ARID AND HUMID REGIONS.
383
leaves and stems in the form of carbonate. But others seem
to possess this power to a limited extent only.
In the case of soils containing much magnesia the proper *
proportion between it and lime may easily be disturbed by the
greater ease with which lime carbonate is carried away by car¬
bonated water into the subsoil, thus leaving the magnesia in
undesirable excess in the surface soil. Hence the great ad¬
vantage of having in a soil, from the outset, an ample propor¬
tion of lime. From this point of view alone, then, the analyti¬
cal determination of lime and magnesia in soils is of high
practical value.
Aso, Furuta and Katayama (Bull. Coll. Agr. Tokyo, Vol. 4 No. 5 ;
Ibid. Vol. 6), have by direct experiment determined the most advan¬
tageous ratio of lime to magnesia in several crop plants. They find
for rice and oats 1:1, for cabbage 2:1, for buckwheat 3:1; there being
apparently a connection between the extent of leaf-surface and lime
requirement, since leaves contain predominantly lime, while in the fruit,
magnesia predominates.
Manganese . — A decided difference in the manganese content
of the arid as against the humid soils appears in the table, the
ratio being about 11 : 13 in favor of the humid soils. Man¬
ganese has not been regarded as being of special importance to
plant growth in general, although, as already stated, some
plants contain a relatively large proportion of manganese in
their ashes ; thus, e. g., the leaves of the long-leaved pine of the
cotton states.1 But no definite data showing the importance of
this element to crops were available until Loew and his co¬
workers at Tokyo2 established its stimulating action in a num¬
ber of cases, in which crop production was materially increased
by the use of protoxid salts of manganese. Aso 3 applied man¬
ganous chlorid to an experimental plot of thirty square meters,
at the rate of twenty-five kilos of Mn304 per acre, and thus
obtained a yield of rice one-third greater than on the control
plot, at a cost of about $2.00, while the value of the increase
of the product was nearly $68.00. More experimental evi¬
dence on this subject is required to establish the general value
1 Rep. Agr. and Geology of Mississippi, 1S60, p. 360.
2 Bull. Agr. Coll. Tokyo, Vol. V., Nos. 2 and 4. a Ibid. Vol. 6.
384
SOILS.
of the large-scale use of the salts of manganese; which are
obtained in large quantities as a comparatively valueless by¬
product of the bleaching industries.
The “ Insoluble Residue
Remembering, in discussing the facts shown by the table,
that the fundamental difference between the regime of the
humid and arid regions is the presence in the latter of an al¬
most continuous leaching process, in which the carbonated
water of the soil is the solvent ; remembering, also, that the
least soluble portion of rocks and soils is quartz or silica ( sand,
as usually understood), it would be predicable that this ingredi¬
ent should in the humid region be found to be more abundant
in soils than in the arid. This portion is represented by the
“ insoluble residue ” of the table.
Inspection shows that both in the averages of the single
states, and in both of the general averages, this difference be¬
tween the soils of the humid and the arid regions of the United
States is strongly pronounced ; the ratio being substantially as
69% in the arid region to 84% in the humid.
We must then conclude that the leaching process must have
influenced materially other soil ingredients than lime, which
have remained behind in such amounts as to depress the per¬
centage of insoluble residue in the soils. It remains to be
shown what are the substances so retained.
Insoluble and Soluble Silica and Alumina.
The ingredient most nearly correlated with the insoluble
residue is the free silica which remains behind with it when the
acid with which the soil has been treated is evaporated to dry¬
ness. The silica is separated from the practically insoluble,
undecomposed minerals by boiling with a strong solution of
sodic carbonate. The amount of this “ soluble silica ” is obvi¬
ously the measure of the extent to which the soil-silicates have
been decomposed in the treatment with acid.
The most prominent of these is usually supposed to be clay —
the hydrous silicate of alumina that in its purest condition
forms kaolinite or porcelain earth. Any alumina found in the
SOILS OF THE ARID AND HUMID REGIONS. 385
usual course of soil analysis is generally referred to this min¬
eral, which contains silica and alumina nearly in the proportion
of 46% to 40%.
In very many cases, however, the reference of these two in¬
gredients to clay is manifestly unjustified. This is clearly so
when (as not unfrequently happens) the amount of alumina
found exceeds that which would form clay with the ascertained
percentage of soluble silica ; it is almost as certainly so when,
in addition to the alumina, other bases (notably potash, lime
and magnesia), are found in proportions which preclude their
being in combination with any other acidic compounds pres¬
ent. The only possible inference in such cases is that these
bases, together with at least a portion of the alumina, are pres¬
ent in the form of hydrated, and therefore easily decomposable
silicates or zeolites.
The subjoined analysis by R. H. Loughridge, of a clay obtained in
the usual process of mechanical soil analysis (by precipitating with com¬
mon salt the turbid water remaining after 24 hours subsidence in a
column of 200 millimeters) from a very generalized soil of northern
Mississippi, shows one of the many cases in which the numerical ratios
of the several ingredients are incompatible with the assumption that
silica and alumina are present in combination as clay (kaolinite) only :
ANALYSIS OF COLLOIDAL CLAY.
Insoluble matter . 15.96
Soluble silica . 33.10
Potash KaO) ... . 1.47
Soda (NaaO) . 1.70
Lime (CaO) . .09
Magnesia (MgO) . 1.33
Br. ox. of Manganese (MmCb) . .30
Peroxid of iron (FeaC>3 . 18.76
Alumina (AlaOa'* . 18.19
Phosphoric acid (P2O5) . .18
Sulfuric acid (SO3) . -o6
Carbonic acid (COa) . .00
Water and organic matter . 9.00
Total . 100.14
If in this case we assign all alumina to silica, as required for the
composition of kaolinite or pure clay, there yet remains a trifle over
twelve (12.17) per cent of silica to be allotted to the other bases present.
Deducting from this the ascertained amount of silica soluble in sodic
carbonate, pre-existing in the raw material (.38 per cent), we come to
11.79 Per cent, as the amount of silica which must have been in com-
25
SOILS.
386
binations other than kaolinite, viz., hydrous silicates, or soil zeolites,
formed either with the bases other than alumina shown in the analysis
or, more probably, containing some of the alumina itself in essential
combination.
We are thus enabled to obtain from the determination of the soluble
silica an estimate of the extent to which these soil zeolites, that form
so important a portion of the soil in being the repositories of the reserve
of more or less available mineral plant-food, are present in the soils of
the several regions. A glance at the table shows that the general
average of soluble silica is very much greater in the soils of the arid
regions than in those of the humid, approximating one to two in favor
of the arid division.'
Differences in the Sands of the Arid and Humid Regions. —
In chapter 5 mention has been made of the fact that while
in the humid regions, “ sand as a rule means quartz grains,
mostly with a clean surface and very frequently rounded and
polished, in the arid regions even the coarse sand grains consist
of, or are covered with, a great variety of minerals in a parti¬
ally decomposed condition. This is owing to the absence of
the abundant rainfall which in humid climates continually
washes down the finely divided, half-decomposed mineral mat¬
ter into the subsoil ; while in arid climates the light rains can¬
not produce any such washing effect and hence the sand grains
remain inerusted with the products of either their own decom¬
position, or of that of neighboring particles ; it being therefore
not concentrated in the finer portion only, viz., the clay and
finest silts. This fundamental difference, which is illustrated
in the analytical table below, at once explains why in the arid
regions generally, sandy soils are found so highly productive
that, owing to their easy cultivation they are preferred to the
clayey lands, in which tillage and irrigation are more difficult.
1 Looking at the details of the several states, we find that on the arid side
Washington has a relatively low figure for soluble silica, which in the average, how
ever, is overborne by the high figures for California and Montana. The explana¬
tion of this fact probably lies in the derivation of the majority of the Washington
soils examined, from lake deposits brought down gradually from the humid region
at the heads of the Columbia drainage, where sandy beds are very prevalent,
while the country rock — the basaltic eruptives — are very basic, and moreover slow
to disintegrate. In California and Montana the rocks are infinitely varied, and the
general outcome of their weathering is plainly a predominance of complex hydrous
silicates in the soils, as compared with humid regions.
SOILS OF THE ARID AND HUMID REGIONS.
387
It is a well-known fact that on the “ sands of the desert ” when
either irrigated, or wetted by rain, vegetation at once springs
up with remarkable luxuriance, even on sand drifts; and this
productiveness appears to be quite as lasting as that of
“ strong ” clay soils of the humid regions.
This difference is curiously illustrated on the southern edge of the
“ black adobe ” or prairie soil area which surrounds Stockton, Cal.
Here we find on the opposite sides of a small stream (French Camp
slough) the two extremes, of heavy clay and the sandy soils which for
many years made Stanislaus county the “ banner ” county for wheat.
The grain product of both banks ranked alike in quantity and quality
in average years; but in extreme seasons sometimes one, sometimes the
other failed, according to the weather conditions which favored one or
the other soil. No one would think of sowing wheat on so sandy a
soil in the humid States.
TABLE ILLUSTRATING DIFFERENCE IN SANDS OF THE HUMID AND ARID REGIONS.
Clay.
Per cent in
Soil.
Potash.
Lime.
Magnesia .
Phosphoric
Acid.
Soluble
Silica.
Alumina.
Summation.
Mississippi1 .
21.64
•32
•03
.29
.04
7->7
3-97
11.82
California 1281 Chino2 .
7.60
.l6
.14
• 17
.04
1.70
*•35
2 . 56
do. Jackson3 .
16.43
•13
.12
,08
.05
2-83
213
Silt .06 — .oi5mm. diam .
D J T
Mississippi .
35-10
.41
•is
•36
.07
2.87
1.36
5.22
California (Chino) .
i8-53
.24
•53
.29
.06
4.96
1.76
7.84
Jackson .
34-90
.IO
.04
.08
.02
2.50
2.44
5.l8
Silt .016 — .025 mm. diam .
Mississippi .
13.67
.12
.09
.IO
.02
•32
•17
.82
California, Chino .
5-49
•05
. 1 1
.02
.OI
.80
•5*
I. CO
“ Jackson .
9.96
.08
.04
. IO
.007
1.01
I.OI
2.25
Silt .025 — .036 mm. diam .
Mississippi .
•36
California, Chino .
3-92
lost
“ Jackson .
7.68
.06
.02
•05
.006
0.82
•74
1 .70
Silt .036 — .047 mm. diam .
Mississippi . .
•55
trace
California, Chino .
6.40
.05
.18
.07
.OI
.80
.64
1.66
“ Jackson .
8.2 1
.04
.OI
.003
OOI
•43
1. 12
Coarse Silt 047 — .072 mm. diam .
California, Chino .
7.92
.06
23
•03
.02
.89
•59
1.79
“ Jackson .
5.91
.OI
.OI
.013
.003
.42
•30
•77
Fine sand .072— .12 mm. diam .
California, Chino .
11.S7
.06
.26
.IO
•03
.98
1.43
Jackson .
j.03
.OI
.OI
.005
.003
.28
.09
.40
Sand .12 — .50mm diam .
California, Chino .
.1 I
.69
.12
.04
J 2.43
i-59
4.98
Jackson .
IO. IO
Not detd
It thus appears that while in the Mississippi soil, solubility of
plant-food practically ceased at grain-diameter of .036 mm, in
1 Analyses by R. H. Loughridge. 2 Analyses by L. M. Tolman. 8 Analyses by
E. H. Lea.
388
SOILS.
the arid California soils, as large an amount was found in
the sand-grain sizes between .12 and .50 millimeters as in the
fine silt .016 to .025 mm. in Mississippi.
Hydrous Silicates are More Abundant in Arid than Humid
Soils. — This predominance of hydrous silicates in the soils of
the arid regions should not be a matter of surprise when we
consider the agencies which are brought to bear upon these soils
with so much greater intensity than can be the case where the
solutions resulting from the weathering process are continu¬
ally removed as fast as formed, by the continuous leaching
effect of atmospheric waters. In the soils of regions where
summer rains are insignificant or wanting, these solutions not
only remain, but are concentrated by evaporation to a point
that, in the nature of the case, can never be reached in humid
climates. Prominent among these soluble ingredients are the
silicates and carbonates of the two alkalies, potash and soda.
The former, when filtered through a soil containing the carbon¬
ates of lime and magnesia, will soon be transformed into com¬
plex silicates, in which potash takes precedence of soda, and
which, existing in a very finely divided (at the outset in a
gelatinous) condition, serve as an ever-ready reservoir to
catch and store the lingering alkalies as they are set free from
the rocks, whether in the form of soluble silicates or carbonates.
The latter have another important effect : in the concentrated
form at least, they, themselves, are effective in decomposing
silicate minerals refractory to milder agencies, such as calcic
carbonate solution; and thus the more decomposed state in
which we find the soil minerals of the arid regions is intelligi¬
ble on that ground alone.
It must not be forgotten that lime carbonate, though less effective
than the corresponding alkali solutions, nevertheless is also known to
produce, by long-continued action, chemical effects similar to those
that are more quickly and energetically brought about by the action of
caustic lime. In fact, the agricultural effects of “liming” are only in
degree different from those produced by marling with finely pulverized
carbonate ; and in nature the same relation is strikingly exemplified in
the peculiarly black humus that is characteristic of calcareous lands,
but which can be much more quickly formed under the influence of
caustic lime on peaty soils.
SOILS OF THE ARID AND HUMID REGIONS, 389
In the analysis of silicates we employ caustic lime for the setting-
free of the alkalies and the formation of easily decomposable silicates,
by igniting the mixture ; but the carbonate will slowly produce a similar
change, both in the laboratory and in the soils in which it is constantly
present. This is strikingly seen when we contrast the analyses of
calcareous clay soils of the humid region with the corresponding non-
calcareous ones of the same. In the former the proportions of dis¬
solved silica and alumina are almost invariably much greater than in the
latter, so far as such comparisons are practicable without assured absolute
identity of materials. That is, calcareous clays or clay soils are so sure
to yield to the analyst large precipitates of alumina, that experience
teaches him to employ smaller amounts for analysis than he would of
non-calcareous materials, in order to avoid unmanageably large bulks of
aluminic hydrate. It is but rarely that even the heaviest non-calcareous
soils yield to the acid usually used in soil analysis more than 10 per
cent, of alumina; while heavy calcareous clay (prairie) soils commonly
yield between 13 and 20 per cent.1 It would be interesting to verify
this relation by artificial digestions of one and the same clays with
calcic carbonate at high temperatures, as it must always be extremely
difficult to insure absolute identity of all other conditions in natural
materials.
In most of these cases, what is true of alumina is also true of the
soluble silica. But since the latter is constantly liable to be dissolved
out by solutions of carbonated alkalies, it is not surprising that this
relation is not always shown.
Aluminic Hydrate. — In numerous cases, the amount of
alumina dissolved in analysis is greatly in excess of the soluble
silica, so as to force the conclusion that a portion of the latter
must be present in a different form from that of clay (kaoli-
nite) ; the only choice being between that of complex hydrous
silicates ( none of which, however, could contain as large a per¬
centage of alumina as clay itself) and aluminic hydrate. The
latter is alone capable of explaining the presence of more
alumina than silica in easily soluble form ; 2 and the visible
occurrence of “ gibbsite ” and “ bauxite ” in modern forma-
1 Report of the Tenth Census, Vols. 5 & 6 ; see especially the analyses of soils
from Mississippi and Alabama. Also the Reports of the California Experiment
Station.
‘2 Excepting the relatively rare minerals of the Allophane, Kollyrite, and
Miloshite group.
390
SOILS.
tions renders this a perfectly simple and acceptable explanation.
Since these minerals are known to be incapable of crystalli¬
zation, we are moreover led to the presumption that it will as a
rule be found in the finest portions of the soil, viz., in the
“ clay ” of mechanical analysis.
Some illustrations of these conditions are given below, for soils from
Mississippi and California. The soluble silica being all assigned to
kaolinite, the rest of the alumina must be assumed to be present as
hydrate, since no other compound could fulfil the stoichiometrical re¬
quirements.1 The table therefore shows the differences between the
amounts of alumina found by analysis, and those assignable to kaolinite,
calculated to the mineral bauxite — the most abundant, as well as the
one containing the medium proportion of water, among the three
naturally occurring aluminic hydrates.
TABLE SHOWING EXCESS OF ALUMINA OVER SILICA IN SOILS ; CALCULATED AS
BAUXITE.
Num¬
ber.
Name of Soil.
County.
State.
Total solu¬
ble in HC1.
Si0.2
Al2Os.
Correspond¬
ing to
Bauxite.
Other
Solu.
Matters.
*95
Prairie .
Alcorn. . .
Mississippi.
28.57
3-6
14. 4
14.12
2.92
346
Dark Loam .
Chicasaw
U
10.32
6.6
I I .2
6.91
.86
28S
Flatwoods Clay .
Pontotoc.
it
26.94
5.0
-3
8-75
3.48
676
Red Volcanic .
Lake ....
California.
41.00
5-9
22.6
21.90
2.00
332
Mojave Desert .
Kern . . .
t «
24.82
5.0
9 2
6. 10
5.13
191
Red Foothill .
Merced.. .
44
23-32
4-5
8.8
6.20
3.05
705
Red Chaparral .
Shasta....
it
28.75
5-5
14.4
12.10
1. 12
706
“ “ Subsoil..
i i
l*
28.40
4-7
17-4
16.70
I.32
573
Tulare Plains .
Tulare....
29.27
3-4
8.7
7.20
n.(6
701
D ry Bog .
U
•4
27.29
4-3
12.4
IO.9O
5 04
1004
“ Slickens ” Sed .
Butte....
41
30.80
8.0
14.2
9.20
j.95
656
(( t(
Y uba ....
it
22.23
3°
IO.4
9.80
2. IQ
5 1 7
Brownish Loam .
Butte . . ..
it
29.80
4.8
12.0
9.80
4.42
561
Black Loam .
it
H
3o.2t
3-2
13.0
12 80
4.67
563
Sacramento Alluvium.
it
23.46
2.7
IO.4
IO.9O
4.58
863
Red Foothill .
Nevada ..
it
56.80
II.O
36.4
33.60
1.22
861
41
45.46
11 -5
22.0
I4.IO
3-97
It is apparent from this table that if, as is probable, the aluminic
hydrate accumulates in the “ clay ” of the analysis, it will in some cases
form a very considerable percentage of the same, and detract to that
extent from its plastic, adhesive and other properties. But it must be
remembered that the assumption upon which this table is calculated,
leaves out of consideration the zeolitic portion, which as the 6th column
shows, is frequently quite large as measured by the bases found, to
1 Since any complex zeolite would contain less alumina than kaolinite, this
assumption more than covers the possible zeolitic alumina.
SOILS OF THE ARID AND HUMID REGIONS.
391
which no other form of combination can be assigned. Since some of
the alumina undoubtedly takes part in the formation of such zeolites,
the silica must to that extent be withdrawn from the estimate made for
kaolinite. While it is impossible to make any definite numerical al¬
lowance for this fact, it clearly will tend in many cases to increase
materially the amount of alumina that must be assigned to the hydrate
condition. It will be noted that in most cases given, the alumina per
cent is rather large.
The relatively large number of such cases shown in the table
for California soils is not a matter of accident ; for even a cur¬
sory glance at the columns of analyses of California (and
Washington and Montana) soils, shows that the cases in
which the alumina exceeds the silica in amount are rather pre¬
dominant, while the reverse is the case in the humid region.1
But it must not be inferred that the reverse relation is not also
frequently observed even in the arid region ; it occurs in fact
in close proximity to the localities where some of the most
striking instances of excess of alumina over soluble silica have
been found.
Thus Nos. 86 1 and 863 from the neighborhood of Grass Valley,
which show this excess most strikingly, occur within 15 miles of local¬
ities which show almost the reversal of the numbers given for the two
former, and at a level of about a thousand feet lower. It would seem,
on the w'hole, that the excess of alumina occurs most frequently in con¬
nection with soils formed from eruptive rocks ; in the case referred to,
from volcanic ash. It will require more detailed study to detect the
causes of these marked differences.
Retention of Soluble Silica i?i Alkali Soils. — It is somewhat surprising
that, contrary to the expectation one would naturally entertain, the
alkali lands, so frequently rich in the carbonates of the alkalies that
would dissolve free silica, on the contrary, show most frequently an
excess of soluble silica over alumina. This is probably to be explained
from the very liberal opportunities afforded in the alkali soils for the
formation of complex zeolitic masses by the retention in soil of the
soluble alkali salts, and the abundance of lime always present in them.
As already stated, we usually find in alkali soils a very large proportion
1 See for comparison the data given in vols. 5 and 6 of the report of the Tenth
Census of the United States.
392
SOILS.
of both alkaline and earthy bases in acid-soluble silicate combinations.
But much farther research is needed to explain fully the marked dis¬
crepancies observed in this respect between soils not only occurring in
closely contiguous localities, but also showing marked similarities in
their general composition.
Ferric Hydrate. — There is no obvious reason, from the
chemical standpoint, why iron, that is, ferric hydrate or iron
rust, should be more abundant in the soils of the arid regions,
as the averages given in the table suggest ; moreover, the fact
does not impress itself upon the eye, since the orange or reddish
tints are by far more common in the humid than in the arid
regions of the United States at least. The California average
is considerably influenced by the very highly ferruginous soils
from the foothills of the Sierra Nevada, and by the black
(magnetite) sand so commonly present; that of Oregon by the
black, highly ferruginous country rock (basalts), from which
they are partly derived. The average for Montana is not
higher than that of three states of the humid region, and less
than that of Kentucky. We might imagine a cause for deple¬
tion of iron in the soils of the humid areas in the frequency
with which humid moisture and high temperature will during
the summers concur toward the bringing about of a reducing
process in the soil, which by getting the iron into proto-car¬
bonate solution would make it liable to be leached into the sub¬
soil, as is frequently the case; yet the resulting “ black gravel ”
or bog ore, in its various forms, is of not infrequent occurrence
in the arid regions also. A constant quantitative difference due
to climatic conditions does not appear to be shown by the data
thus far at command, but the finer distribution of the ferric
hydrate in the humid temperate as well tropical regions is
obvious to the observer, from the frequent redness of humid
and tropical soils.
Manganese. — An unexpected and apparently well-defined
contrary relation appears to be shown as regards the related
metal manganese ; the average percentage of which is in all
cases less in the arid than in the humid region. The cause of
this relation is altogether obscure; it is too frequent to be ac¬
cidental.
Phosphoric Acid. — As regards that highly important soil
SOILS OF THE ARID AND HUMID REGIONS.
393
ingredient, phosphoric acid , the indication in the table that
there is no characteristic difference in the average contents in
soils of the arid and humid regions, respectively, is doubtless
correct. This substance is so tenaciously retained by all soils
that there is no obvious reason why there should be any ma¬
terial influence exerted upon its quantity by leaching, or by
any of the differences in the process of weathering that are
known to exist between the two climatic regions. Moreover,
it is apparent that the average for the arid region is made up
out of very widely divergent figures; that of California excep¬
tionally low (lower than any of those for the states of the
humid regions), while those for Washington and Montana are
exceptionally high. The latter is due to country rocks
(“basalts”) showing abundance of microscopic crystals of
apatite, which in some cases raise the contents of the soils in
phosphoric acid to nearly twice the average given for the
states.
The forecast that for most California soils, fertilization with
phosphates is of exceptional importance, has already been
abundantly confirmed by cultural experience. Few definite
data are as yet available from other arid states, where fertil¬
ization is thus far sporadic and unsystematic. But it is pre¬
dicable that in view of the presence of an excess of lime carbon¬
ate in the arid soils, and the unfavorable effect of this com¬
pound on the rapid solubility of tricalcic phosphate demon¬
strated by Schloesing, Jr.,1 by Bottcher and Kellner 2 and
Nagaoka,3 fertilization with readily available phosphate fertil¬
izers will be found necessary among the first, all over the arid
region, especially in view of the scarcity of humus in arid soils.
A curious instance of the effects of continued warm maceration in
rock decomposition is afforded by the highly ferruginous soils derived
from the black basaltic lavas of the Hawaii Islands. These lavas, like
the basalt sheet of the Pacific Northwest, contain a large amount of
crystallized phosphate minerals, notably apatite and vivianite. A cor¬
respondingly large proportion of phosphoric acid is found in the soils
1 Ann. Sci. Agronomique, tome I, 1899.
2 Landw. Presse, 1900, No. 52; ibid. 1901, Nos. 23 and 24.
3 Bull. Univ. Tokyo, Vol. 6, No. 3. Production was diminished to less than one
half when lime was used with bone meal, and actual assimulation of phosphoric
acid to one fifth.
394
SOILS.
derived from these rocks, up to nearly two per cent.1 But almost tht
entirety if this substance is present in the form of an insoluble, basic
iron compound, difficultly soluble even in acids, and rendering it wholly
unavailable to vegetation. So that actually the most pressing need of
most of these soils is phosphate fertilization. The same is probably
true of some of the highly ferruginous soils of California and of the
Cotton States.
Sulfuric Acid. — From the absence of the leaching process
in the soils of the arid region, we should expect that sulfates
would be more abundant in them than in the soils of the humid.
This is certainly true in the case of the alkali soils, which are
characteristic of the regions of deficient rainfall. See below,
chapter 22.
Hence the showing made in the general table, indicating that sulfates
are equally abundant in the soils of the humid than in those of the arid
regions, is surprising in view of the efflorescences of alkali sulfates so
frequently observed in the latter. This is obviously due to the fact
that the majority of such alkali soils has, on account of their local nature
and usually heavy lime content, been excluded from the comparison ;
which otherwise would have made a very different showing.
Potash and Soda. — The compounds of the alkali metals
potassium and sodium, being on the whole much more soluble
in water, even without the concurrence of carbonic acid, than
those of calcium and magnesium, the leaching process that
creates such pronounced differences in the case of the two
earths must affect the alkali compounds very materially.
Comparison of the soils of the two regions in this respect
shows, indeed, very great differences in the average contents
of potash and soda. For potash the ratio is .216 to .670 per
cent, on the general average, and .187 to .670 per cent., in the
average by states; for soda, .140 per cent, to .350 per cent,
on the general average, and .110 per cent, to .420 per cent, in
the average by states. For both, therefore, the general aver¬
age ratio is as one to between three and four for the humid as
against the arid region.
It is curious that an approximation to the ratio of one to
1 See table, chapter 19, p. 256.
SOILS OF THE ARID AND HUMID REGIONS.
395
two, or somewhat less, is maintained in the average propor¬
tion of soda to potash in both regions ; but this does not by any
means hold good in detail, very high potash-percentages being
often accompanied by figures for soda very much below the
above ratio. This is the result of an important difference in
the chemical behavior of the two alkalies, which has already
been alluded to in connection with the discussion of the zeo¬
lites. (See chapter 3, p. 38).
The process of “ kaolinization” being that by which clays
are formed out of feldspathic minerals and rocks such as
granite, syenite, trachyte, etc., results in the simultaneous form¬
ation of solutions of carbonates and silicates of potash and
soda. These coming in contact with the corresponding com¬
pounds of lime and magnesia, also common products of rock
decomposition, are partly taken up by the latter, forming
complex, insoluble, hydrous silicates (zeolites). In these,
however, potash whenever present takes precedence of soda ;
so that when a solution of a potash compound is brought in
contact with a zeolite containing much soda, the latter is par¬
tially or wholly displaced and, being soluble, tends to be washed
away by the rainfall into the country drainage. Hence potash,
fortunately for agriculture, is tenaciously held by soils, while
soda accumulates only where the rainfall or drainage is in¬
sufficient to effect proper leaching, and in that case manifests
itself in the formation of what is popularly known as “ alkali
soils ; ” namely those in which a notable amount of soluble
salts exists, and is kept in circulation by the alternation of rain¬
fall and evaporation, the latter causing the salts to accumulate
at the surface and to manifest themselves in the form of saline
crusts or efflorescenses. Alkali lands are a characteristic
feature of all regions of scanty rainfall, and are found more or
less on all the continents. The substances composing the alkali
salts are retained not only in their soluble form, but by their
continued presence influence profoundly, in several ways, the
processes of soil formation. A more detailed discussion of
this important subject is given in chapters 22 and 23.
Arid Soils are Rich in Potash. — One of the most important
practical conclusions flowing from the comparison of the pot¬
ash contents of the humid and arid soils respectively is that
while in the former, potash is usually among the first sub-
SOILS.
396
stances to be supplied by fertilization when production lan¬
guishes, in the arid regions it will as rule come last in order
among the three ingredients commonly so furnished. Aside
from the water-soluble potash salts always forming part of
the salts of the alkali lands proper, which in many cases will
alone hold out for many years under the demands of cultiva¬
tion,1 they rarely contain much less than one per cent, of acid-
soluble potash; occasionally rising as high as 1.8 per cent.
That in such lands potash-fertilization is uncalled-for and in¬
effective, hardly requires discussion ; while on the other hand,
phosphates are commonly required for full production after
ten or fifteen years of cultivation without returns. Nitrogen
usually comes next in order, but sometimes is the first need.
The constant indiscriminate purchase and use of all three ingredients,
so urgently recommended by fertilizer manufacturers because of their
success in the humid Eastern States, is therefore very poor economy for
the farmers of the arid region. Excepting cases of very intense culture,
e.g. of vegetables or berries, the use of potash salts is but rarely remuner¬
ative, and therefore uncalled-for, in arid soils for a number of years.
Humus. — The figures shown in the table for the average
humus-percentages in the soils of the two regions do not ade¬
quately represent the very important differences actually ex¬
isting; partly because of the inadequate number of determina¬
tions made by the same method (Grandeau’s), partly because
of the differences in the composition, and especially in the
nitrogen-content of this substance, which render direct com¬
parison delusive. A detailed discussion of the marked differ¬
ences existing between the humus of arid and humid soils in
this respect has already been given (chapter 8, p. 135); show¬
ing that the high nitrogen-percentage in the arid humus prob¬
ably compensates largely the lower humus-percentage, while
rendering nitrification more rapid, because the oxygen is not
consumed by overwhelming amounts of carbon and hydrogen ;
which, as is already known, take precedence of nitrogen in the
oxidation of humus substances. Nitrates are almost always
1 In the light alkali lands of the southern California Experiment Substation at
Chino, the average content of water-soluble potash in ten acres amounts to the
equivalent of 1,200 pounds of potash sulphate per acre. Outside of this the acid-
soluble potash of the soil is .95° 0., equal to 38,000 pounds per acre-foot.
SOILS OF THE ARID AND HUMID REGIONS.
397
more abundant in the soils of the arid region than in those of
the humid, sometimes to the extent of influencing injuriously
the quality of certain crops, such as tobacco and sugar beets.
Nevertheless, nitrogen is ordinarily, in the arid region, the sub¬
stance requiring replacement next to phosphoric acid. And
when considered in connection with the small humus-content,
so liable to burning-out, this places green-manuring with le¬
guminous plants among the first and most vital improvements
to be employed there.
The Transition ( semi-humid or semi-arid ) Region. — The
sloping plains country lying between the Rocky Mountains
and the Mississippi, quite arid at the foot of the mountains,
but with rainfall increasing more or less regularly to eastward,
form a transition-belt between the arid and humid region of
which but a small portion has been systematically studied in
respect to its soil formations. The analyses made of soils of
the two adjacent states of Minnesota and North Dakota, have
been placed in the general table (p. 377) to show how far in
their general relations their soils correspond to the generaliza¬
tions deduced from the comparison of the decidedly arid and
humid soil areas chiefly represented in the table. Although it
has not been possible, for lack of detailed data, to eliminate
the soils originating from calcareous formations, it will be
seen that those of semi-arid Dakota differ from those of more
humid Minnesota, almost throughout, as would be anticipated
from the studies of the extremes, given in this chapter.
CHAPTER XXL
SOILS OF ARID AND HUMID REGIONS ( Continued ).
SOILS OF THE TROPICS.
Within the ordinary limits of atmospheric temperatures,
and in the presence of adequate moisture, chemical processes
active in soil-formation are intensified by high and retarded by
low temperatures, all other conditions being equal. We can
usually artificially imitate, and produce in a short time by the
application of relatively high temperatures, most of the chemi¬
cal changes that naturally occur in soil-formation. While it is
true that the changes of temperature are nearly as great in the
tropical as in the temperate climates, these changes all occur
at a higher level and within the limits favoring bacterial and
fungous action.
This being true we should expect that the soils of tropical
regions should, broadly speaking, be more highly decomposed
than those of the temperate and frigid zones, and that the
intensified processes continue currently. This fact has not
been as fully verified as might be desirable, by the direct
comparative chemical examination of corresponding soils from
the several regions, owing to the want of uniformity in
methods and the fewness of such investigations in tropical
countries. Yet the incomparable luxuriance of the natural as
well as artificial vegetation in the tropics, and the long duration
of productiveness that favors so greatly the proverbial easy¬
going ways and slothfulness of the population of tropical
countries, offers at least presumptive evidence of the practical
correctness of this induction.
In other words, the fallowing action, which in temperate
regions takes place with comparative slowness, necessitating
the early use of fertilizers on an extensive scale, is much more
rapid and effective in the hot climates of the equatorial rainy
belt; thus rendering currently available so large a proportion
398
SOILS OF THE ARID AND HUMID REGIONS.
399
of the soil’s intrinsic stores of plant-food, that the need of
artificial fertilization is there largely restricted to those soils
of which the parent rocks were exceptionally deficient in the
mineral ingredients of special importance to plants, that or¬
dinarily form the essential material of fertilizers. Quartzose,
magnesian, and other soils resulting from the decomposition
of “ simple ” rocks will, of necessity, be poor in plant-food
everywhere.
Humus in Tropical soils. — Another inference from the cli¬
matic conditions of the tropics is that the properly tropical
soils are likely to be rich in humus, as a result of the luxuriant
vegetation which in the decay of its remnants must leave abun¬
dant humic residues. This seems to be generally verified
wherever the interval between rainy seasons is not too long;
for otherwise, under the great and constant heat of the tropics
a rapid burning-out of the humus, such as is known to occur
in the arid regions, must also take place. A good example
illustrating the intertropical regime as regards humus is given
in the table in chapt. 8, p. 137, showing the humus-content of
some Hawaiian soils. Both are of the same order as in the
soils of the temperate humid region, though the nitrogen-con¬
tent evidently can, consistently with productiveness, range
lower than has thus far been observed in temperate climates.
This again forms a striking contrast with the soils of the arid
regions.
It is greatly to be regretted that not even approximate de¬
terminations of the organic matter, much less of the humus-
substance proper, have been made by any of those who have
analyzed tropical soils ; excepting those made of Hawaiian
soils at the California Experiment Station.
The “ loss by ignition ” is of course always very largely
water, mostly referrible to ferric hydrate and clay substance,
the latter presumably essentially in the form of kaolinite.
When, therefore, ferric oxid and alumina have been deter¬
mined, we may approximate to the amount of total organic
matter by making allowance for ferric hydrate at the rate of
about 14% of the ferric oxid, for kaolinite at that of 34.92%
of the alumina found. Deducting these amounts of water
from the total “ loss by ignition,” we may obtain at least an
approximate idea of the organic matter, and the probable
400
SOILS.
availability of the nitrogen determined by the analysis. See
chapter 19, p. 357.
While the continuous heat and moisture of the tropics concur
toward rapid rock-decomposition, it must be remembered that
the copious rainfall is equally conducive to an intense leaching
effect. Striking examples of this action occur in the Hawaiian
Islands, in the highly ferruginous soils resulting from the
decomposition of the black (pyroxenic and hornblendic) lavas
that are so characteristic of the volcanic effusions of that
region. The soils formed from these rocks are sometimes so
rich in ferric hydrate (iron rust) that they might well serve
as iron ores elsewhere. But these soils are very unretentive,
and though very productive at first they are soon exhausted,
the abundant rains having sometimes deprived them of almost
every vestige of lime, and of most of the potash contained in
the original rock. At the same time the abundant phosphoric
acid of the original rock has been reduced to almost total
unavailability by combination with ferric oxid, just as in the
case of the bog ore of the temperate climates ; so that phosphate
fertilization is urgently needed in these lands, though showing
high percentage of phosphoric acid. (Chapt. 19, p. 356.)
Soils highly colored by ferric hydrate occur rather fre¬
quently in the tropics, and have received the general name of
“ laterite ” soils. Curiously enough, the intense reddish tint
mostly shown in these soils, and which is emphasized in the
“ terra roxa ” of the Brazilians, and the general “ red ” aspect
of Madagascar, and of the Malabar and Bengal coasts, is by
no means always accompanied by markedly high percentages
of iron oxid ; but the latter is very finely diffused, so as to be
very effective in coloration. The plant-food percentages of
tropical soils are generally quite low, so that in the temperate
humid regions such lands would be adjudged to be rather poor.
Yet they mostly prove quite productive and lasting, even with¬
out fertilization.
This is doubtless to be explained by the continuous and rapid rock
and soil-decomposition which goes on under tropical climatic conditions,
already alluded to ; so as to supply enough available plant-food for the
demands of each season’s vegetation, analogously to the proverbial
“ nimble penny.” This is supplemented also by the rapid decay and
eaching-out of the ash ingredients of the rapidly decaying and dying
SOILS OF THE ARID AND HUMID REGIONS.
401
vegetation. Nitrification must likewise, of course, be very active under
the continual heat and moisture, and the humus formed under these
circumstances is likely to be quite poor in nitrogen. On this latter
point, however, definite data are almost wholly wanting.
Investigations of Tropical Soils. — The most extended chemi¬
cal investigations of properly tropical soils have been made by
Wohltmann in his investigations of the soils of India, German
Southwest and Southeast Africa, and Samoa ; 1 and by
Muntz and Rousseaux of soils collected under Government
auspices in Madagascar. Leather, Bamber and Mann have also
analyzed a large number of soils of India. But we find in
many of these cases a failure to specify distinctly the local
climatic conditions, and even the depth to which the samples
have been taken ; so that the investigator is obliged to examine
laboriously the local climates, and especially the amount and
distribution of rainfall, before being enabled to discuss intelli¬
gently the data given. Even Wohltmann, in his discussion of
- North African and Saharan soils, classes these distinctly arid
types among the tropical ones.
Again, the dry seasons intervening between the tropical
rains, varying in length and from locality to locality, obscure
somewhat the relations of the soils to the climatic conditions.
Under the lee of mountains, even of slight altitude, we find
xerophytic (arid-land) vegetation, as has been noted by many
observers in Brazil, even near the Amazon ; in Hawaii, in
Jamaica, and in Madagascar. Unless, therefore, a close dis¬
crimination is exercised by field observers, many contradictory
results will appear in analyses of soils of inter-tropical coun¬
tries. This is naturally the case in India, where the topo¬
graphic surface conformation and seasonal climatic conditions
are so complicated and contrasted. On the whole, the results
obtained in Samoa, Kamerun and Madagascar seem, of those
available, to be the most characteristic of true tropical condi¬
tions. In comparing these with the soils of low plant-food
percentages in the temperate humid region (see chapter 19,
p. 352), it must be remembered that those mentioned as being
productive are so by virtue of great depth and relatively high
1 1 Samoa Erkundung, by F. Wohltmann, Kolonial-Wirthsch, Komitee, Berlin,
1904.
26
402
SOILS.
proportions of lime; while in the tropics, the intense leaching
process prevents lime from reaching any high absolute or
relative percentages, save where limestone formations prevail.
Moreover, the mode of preparation of the soil extracts for
analysis by Wohltmann, and by Muntz and Rousseaux, differ
so widely from that forming the basis of discussion of soil-com¬
position in this volume, that it becomes necessary to make
separate allowances in each case ; since some of the ingredients,
phosphoric acid, lime and magnesia, are fully dissolved by
the weaker treatments, while others, — e. g., potash — are not,
and are therefore not directly comparable with the data ob¬
tained in the writer’s work. The analyses made in India by
Leather and others have apparently been made substantially
in accordance with the author’s methods and may be considered
directly comparable.
SOILS OF SAMOA AND KAMERUN.
Wohltmann has investigated the soils of Samoa, notably
those of the main island of Upolu, under the auspices of the
German “ Kolonial-Wirthschaftliche Komitee ” in 1903, and
gives the results of his observations and analyses in a report
published at Berlin in 1904. The analyses are quite numerous,
but unfortunately are made by a special method which renders
them only partly comparable with those of any other analyst.
Wohltmann’s method is this : “ 450 grams of fine earth (below 2
millimeters diameter) is treated for 48 hours with iL liters of cold
chlorhydric acid of 1.15 density. Another portion, designed for a fuller
determination of potash, is treated for one hour with the same acid,
boiling hot. Potash was determined in both soil extracts ; the hot
extract gave from one-third to twice the amount obtained in the cold
extraction.” 1
Wohltmann justifies this method by the statement that it has yielded
him results more nearly in accord with experience than any other tried,
both with tropical and European soils.
Under these conditions only a few of the determinations in Wohlt¬
mann’s analyses are directly comparable with those upon which the discus-
1 Wohltmann states that the hot extraction sometimes yielded as much as five
times more than the cold ; but no such case appears in his reports on Samoa and
Kamerun.
SOILS OF THE ARID AND HUMID REGIONS.
403
sions in this volume have been based. The figures for nitrogen and
phosphoric acid may be assumed to be fully comparable ; that of lime will
in general represent fully only that which is present in the forms of
carbonate, sulfate and humate, and a part of that existing in zeolitic or
hydrous silicate form. Of the two potash determinations only the one
made in hot extraction will be even remotely comparable, being pro¬
bably at least 30% lower than would have been obtained by the writer’s
method.
Even thus, however, Wohltmann’s results are highly in¬
structive. He gives the following summary of his mode of
interpreting such analyses :
Very rich.
Good.
Inadequate.
Potash .
.2
.1
•°5
Lime and Magnesia .
1.0
•4
.07
Phosphoric acid .
.2
.1
.06
Nitrogen . . .
.2
.1
.05
It will be observed that the figures of this table differ ma¬
terially only in the matter of potash from those given in chap¬
ter 19, p. 354; for the latter substance they would have to be
multiplied by from 2 to 4, according to the lime-content and
other conditions.
With this understanding a number of Wohltmann’s analyses
of soils from Samoa and Kamerun are given below, the pot¬
ash determinations made with hot acid being placed in par¬
entheses after the other.
Soils of Samoan Islands. — A discussion of these analyses shows, from
the writer’s point of view, a very low content of potash and lime, with
the peculiarity that both are somewhat higher at the depth of a meter
than in the surface ten-inches. This is probably to be accounted for
from the very high content of organic matter (humus), which is apparent
from the high “ loss by ignition,” a very large proportion of which must
be credited to the burning of the organic matter. That this humus
reaches to the lowest depths examined, is clear from the nitrogen-con¬
tent given for these samples. Wohltmann, whose estimate of these
soils agrees in most respects with the writer’s, attributed to them a very
satisfactory nitrogen-content. This would be true of the total ; but as
404
SOILS.
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SOILS OF THE ARID AND HUMID REGIONS.
405
he has not determined either the true humus or its nitrogen-content, it
remains uncertain whether or not a sufficiency is in an available form,
and whether their case may not be like that of the Hawaiian soil men¬
tioned above (chapter 19, p. 362), in which despite 10% of humus and
.17% of nitrogen, the land was found to be nitrogen-hungry. Again,
as regards the phosphoric acid, which Wohltmann considers satisfactory
to high, it is questionable to what extent it is rendered unavailable by
the very high content of ferric hydrate. We are thus left in some un¬
certainty as to the real manurial requirements of the Samoan soils,
which doubtless represent very closely also those of Tutuila, the chief
American island of the group.
It is probable that for crops requiring so much potash as do the
banana and cacao trees, potash is the first need when they cease to
produce well on these soils.
Soils of Kamerun. — In the soils of Kamerun, also analyzed by
Wohltmann, and of which two are placed alongside of those of Samoa,
it is at once seen that the materials from which they have been formed
are richer in both potash and lime than the parent rocks of the Samoan,
and not quite so rich in iron. They are also very rich in organic
matter, evidently down to the depth of a meter, as are those of Samoa.
It is probably due to the high humus-content that these soils, washed
as they have been by the second-highest rainfall in the world (about 35
feet annually) have not been as thoroughly leached as have been those
of the Brahmaputra valley. The annual rainfall of Samoa is only from
nine to eleven feet on the lower levels, but ranges as high as 18 feet at
higher elevations.
It is noticeable that in most of these true tropical soils the
content of magnesia is considerably above that of lime; a fact
readily intelligible from the more ready solubility of lime in
carbonated water. It is hardly doubtful that this dispropor¬
tion will in many cases explain a lack of thriftiness, which
could be effectually remedied by a simple application of lime
or marl, without resorting to the more costly fertilizers.
THE SOILS OF MADAGASCAR.
The soils of the island of Madagascar have been analyzed to
the number of about 500 by Muntz and Rousseaux, under the
auspices of the French government.1 So large a number of
1 Annales de la Science Agronomique, tome ier, 1901, fasicules 1, 2, 3.
406
SOILS.
analyses should give a very full understanding of the agricul¬
tural capacity and adaptation of so comparatively limited an
area; unfortunately, we are here again confronted by more or
less imperfect data accompanying the samples collected by
government agents, and by the use of an analytical method
different from those of all other nations, and hence incom¬
mensurable except, as in the case of Wohltmann’s method, in
regard to certain ingredients.
The French chemists use nitric instead of chlorhydric acid;
cold for phosphoric acid and lime, boiling-hot for five hours
for potash ; considering the remainder as of no practical import¬
ance. Since nitric acid is in general much less incisive than
chlorhydric in its solvent power, comparison with the analyses
made by other nations becomes difficult. As in the case of
Wohltmann, magnesia, lime, and phosphoric acid may be con¬
sidered to be quite thoroughly extracted by the treatment;
while extraction of possibly available potash is doubtless very
incomplete. On the whole, however, the estimates of soil-
fertility based on percentages is very nearly the same as those
assigned by Wohltmann in the table given above. Like
Wohltmann, they emphasize the axiom that the same percent-
age-gauge of fertility cannot be applied in the tropics as in the
temperate zones.
General Character of the Island. — The island of Madagascar,
lying between the nth and 25th degrees of south latitude, is
quite mountainous in its central and eastern portion, where
the coast falls off pretty steeply into the sea, leaving only
a narrow coast belt of properly agricultural land in the
lower valleys and at the mouth of the torrential streams.
The mountains rise at one point to the height of nearly 10,000
feet. The western portion of the Island is much less broken,
has much plateau land with low intersecting ranges and
streams of moderate fall, with considerable alluvial lands near
the coast. The rocks are almost throughout gneisses and
mica-schists, which, as heretofore stated (chapter 4, p. 51),
form mostly poor soils. There are a few areas of eruptive
rocks and tertiary calcareous deposits, and on these the lands
are much more thrifty. The rocks and red soils of the central
mass, however, extend seaward almost everywhere.
The rainfall is high on the east side, where the moisture of
SOILS OF THE ARID AND HUMID REGIONS.
407
the southeast trade winds is first condensed, the precipitation
reaching ten to twelve feet (120 to 144 inches) annually.
The western portion is relatively dry, but rains fall more or less
throughout the year ; while in the eastern and central moun¬
tainous part there is a distinct subdivision into a wet and a dry
season. Here, while the rivers are largely torrential, many
large fertile valleys have been created by the heavy denudation
of the mountain slopes. This is especially the case in the
Imerina province (in which the capital, Tananarivo, is sit¬
uated), and here the valley soils are deep, and rich in humus.
The western portion is but thinly forested. The soils of most
of the island are “ red ” with ferric hydrate, resembling the
laterite soils elsewhere; yet the iron percentages are not usually
very heavy, ranging mostly from 4 to 6, more rarely to 10%
and more, of ferric oxid. Most of the red soils are clayey,
crack open in summer and become very hard in drying.
Of the 476 soils analyzed by Miintz and Rousseaux, 156 are
from the province of Imerina, 56 from the adjacent province
of Betsileo, therefore 212 from the central, mountainous part
of the island. The remainder are scattered around the coasts ;
the most productive being apparently those of the northern
end, Diego Suarez, which is mostly underlaid by the eruptive
rocks forming the mountain mass of Mount Amber, from
which numerous fertile valleys radiate. The valleys of the
west coast also, in the provinces of Bara, Tulear and Betsiriry,
have some very productive soils.
The subjoined table, giving fourteen analyses selected as rep¬
resentative from the mass of material presented by Miintz and
Rousseaux, gives a fair general idea of the character of the
soils of the great island. It is at once apparent that lime and
potash are extremely deficient in the soils of the mountain
slopes of central and southern Madagascar, these substances
having, as elsewhere in the humid region, been leached down
into the valleys; and the materials being mostly quite clayey,
these valley soils have not, as in the case of the sandy alluvium
of the Brahmaputra, themselves been again leached of their
mineral ingredients. Practically these valleys seem to form
the only profitably cultivable area of the central portion; while
along the larger river courses, such as the Mangoky, Ikopa,
Mahajamba and others, good alluvial “ bottoms ” and deltas
ANALYSES OF MADAGASCAR SOILS BY MUNTZ AND ROUSSEAUX,
408
SOILS.
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SOILS OF THE ARID AND HUMID REGIONS.
40$
form available lands. It seems to the writer that, in view of
their own expressed opinion that tropical soils are not to be
gauged on the same percentage-basis of soil-ingredients as
those of temperate regions, Muntz and Rousseaux rather un¬
derestimate the productive value of many of these lands; re¬
garding which the field notes report good production, ar.d
the crops of which are certainly not the first that they have
borne in the course of Malagassy history. It is as though their
anxiety to forestall overestimates of agricultural prospects by
intending settlers, had led them to somewhat overshoot the
mark.
Be that as it may, the influence of the tropical climate and
rainfall upon the composition of these soils is certainly very
marked. While gneiss is not credited with producing first-
class soils, its usual content of orthoclase feldspar should at
least insure a respectable average content of potash; but this,
it will be seen, is mostly not the case; and that of lime seems
even worse, aside from the case where, as in some regions near
the coast (especially in the west and south), calcareous forma¬
tions, probably of tertiary age, have contributed to soil-for¬
mation. At some points there seem to exist phosphate deposits,
well known elsewhere to occur in such rocks, which impart to
the soils exceptionally high percentages of phosphoric acid,
even exceeding one per cent. The phosphates of course remain
practically untouched by the leaching processes, and appear to
be somewhat widely diffused; so that the soils of Madagascar
may be said to be, on the whole, well supplied with this import¬
ant plant-food.
In the central province of Imerina the valleys and lower
slopes show a fair content of both lime and potash ; but in the
province of Betsileo, adjoining it on the south, nearly every
one of the soils analyzed is reported as containing only
“ traces ” of lime, together with very small amounts of potash
in most cases. The ultimate analyses of ignited red earths,
of which an average is here given, are of interest in this con¬
nection.
ULTIMATE ANALYSIS OF IMERINA RED SOILS, IGNITED ; AVERAGE OF THREE.
Silica . 55-2
Potash . .3
Lime . trace
Magnesia . 1.1
Ferric oxid . 10.6
4io
SOILS.
It is quite obvious that only leaching-down and concentration
of the feeble resources of such material in the valleys can pro¬
duce soils worthy of permanent cultivation.
One point, however, is strikingly illustrated in several of
the analyses given in the subjoined table. We find in the
original quite a number of cases in which the field notes report
considerable fertility, while the chemists’ judgment is very
unfavorable. Thus we find recorded for the soil No. 267,
taken near the village of Anjozorabe, in the Maintirano region,
“ luxuriant vegetation and remarkable crops,” with such mi¬
nute proportions of potash, lime and phosphoric acid that the
authors are compelled to say that the land offers “ no cultural
resources.” The same occurs in the cases of soils Nos. 370,
261, and several others having either “ good crops ” or “ abun¬
dant natural vegetation.” Unless we assume that in these
cases the samples were not properly taken, we are obliged to
conclude that under the local climatic conditions, such minute
amounts of plant-food are developed with sufficient rapidity to
supply good growth. This would be quite parallel to the case
of the tea soils of Assam, whose production lasted 30 years
before showing exhaustion, on plant-food percentages only
slightly greater than those here noted, and determined by a
much more incisive method.
It is thus quite obvious that a different standard of inter¬
pretation must be applied to tropical soils as compared with
either the temperate humid, or the arid regions ; and that uni¬
form methods of analysis are needed to evolve a definite rule
from the present uncertainties.
THE SOILS OF INDIA.
The soils of India have been investigated to some extent by
the geological survey of India; by Voelcker, who went there
on a special mission to investigate agricultural conditions ;
and since, more especially by Leather, Bamber and Mann ; and
by Moreland. Leather’s account is the most complete on the
general subject and can best serve as the basis for a review of
the entire peninsula.1
According to Dr. Leather, “ the four main types of soils to
1 On the Composition of Indian Soils. Agr. Ledger, 1898, No. 2.
SOILS OF THE ARID AND HUMID REGIONS.
411
be dealt with, and which certainly occupy by far the larger of
the Indian cultivated area,” are : The I ndo -Gauge tic alluvium ,
covering the chief cultivable areas of the Indo-Gangetic plain ;
the black cotton soils or regur, occupying the main body of the
plateau of the Central provinces (the Deccan) from the
Vindhya range south ; the red soils lying on the metamorphic
rocks of Madras ; and the ff laterite ” soils which are met with
in many parts of India. To these should be added the alluvial
soils of the Brahmaputra valley, in Assam. It is hardly to
be expected that so large an area as that of India, with its
diversified topography, and a climate ranging from about four
inches of rainfall in the northern Pandjab to the world's
maximum in Assam, and southward to typical tropical condi¬
tions, could be even thus briefly characterized. The observers
have rarely given for the several soils analyzed, special local
and climatic data, which cannot always be obtained from the
official publications ; so that it is not easy to discuss them from
the points of view of aridity and humidity.
The Indo-Gangctic Plain. — The general rain-map of India
shows the Pandjab and Rajputana to be arid throughout;
thence eastward the rainfall increases to 25 and 30 inches on
the Ganges; notwithstanding which, alkali (reh) is abundant
about Aligarh, Meerut and Agra. Thence toward Calcutta
there is a steady increase of rainfall until, at the head of the
Bay of Bengal, 70 inches is reached.
If under these conditions the Indo-Gangetic plain admits of
any generalizations as regards soil composition, it must be at¬
tributed in the main to its predominantly alluvial character.
It should therefore be relatively rich in lime, magnesia and
potash. So far as the first is concerned, Leather remarks that
the only rocky particles larger than sand to be found in all
this large belt of land is the nodular limestone called kankar,
formed by the deposition of calcium carbonate within the soil,
at the depth of a few feet. It occurs very generally in India,
and as stated above (chapters 9 and 19), this occurrence of
calcareous hardpan, of varying hardness, is almost universal in
the arid regions. The analysis given in the table, selected
as representative from those given by Leather, show that
the general forecast is realized in them, as soils of an arid
region.
ANALYSES OF SOILS OF INDIA.
412
SOILS
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SOILS OF THE ARID AND HUMID REGIONS.
413
The Brahmaputra Alluvium in Assam. — Aside from the
immediate alluvium of the Indus, of which no definite data are
available, the Indo-Gangetic plain represents the drainage of
the southern slope of the Himalaya chain. That of most of
the northern slope is represented by the Brahmaputra, which
not only orginates in a region of heavy precipitation — Thibet —
but continues in the same throughout its course, and rounding
the easternmost spur of the Himalaya range enters, in southern
Assam, upon the region of the maximum rainfall known. Its
alluvial deposits should therefore show the reverse character¬
istics of those of the Ganges; they should, as thoroughly
leached soils, be poor in lime, magnesia and potash. We have
fortunately on this subject the excellent work done by Mr.
H. H. Mann for the Indian Tea Association, the report of
which was published in 1901, and contains, besides a large
number of analyses, good descriptions of the general soil and
cultural conditions of the Assam tea districts, with suggestions
for their improvement.
The tea plantations of Assam are located almost wholly on
the new and old alluvium of the Brahmaputra river, bordered
on the north by the eastern spur of the Himalayas, on the
south by the low ranges of the Khasia hills. The soil is mostly
quite sandy, the late alluvium gray in color, the older reddish
and more loamy. Of the four analyses given in the»table and
fairly representing the average character of these soils, the two
first are from the north side, the latter two from the south side
of the river.
It will be noted that the prominent feature of all these soils
is an extremely low percentage of lime, the general average
being about .08% as against nearly 1.0% in the average
Indo-Gangetic soils. In the latter, potash ranges between .65
and .70% ; in the Assam soils between .25 and .35. Magnesia
averages nearly 1.3 in the Indo-Gangetic, against about .50 in
the Assam tea soils. It is thus apparent that the same general
facts as regards the leaching-out of soil ingredients already
shown for eastern and western North America are strikingly
verified in northern India ; but reversed as regards the points
of the compass. The preferential leaching-out of lime as com¬
pared with magnesia and potash, is here again well exemplified.
It would be interesting to have an analysis of the Brahma-
4H
SOILS.
putra water to compare with that of the Ganges. That tea
should flourish for twenty to thirty years in such soils, is a
good indication of one cause at least of the total failure of tea
culture in California, where tea plants are difficult to maintain
alive, and after 25 years form rounded, scrubby bushes not
over four feet high. Similar failures of tea on calcareous soils
are on record from India. The low lime-content of the Assam
soils, then, does not necessarily imply that these soils should
be limed to maintain tea production. According to Mann,
the main deficiency is in nitrogen, as the figures imply ; but
whether his recommendation of green-manuring with legu¬
minous crops to increase the nitrogen-supply is practicable
without first supplying more lime to the Assam soils, is ques¬
tionable. Since phosphoric acid is also low, his recommenda¬
tion to use freely the basic or Thomas slag is doubtless a good
one, since lime would thus also be moderately increased.
Bamber gives a number of analyses of tea soils from low
ground in Assam, which are very rich in vegetable matter and
quite acid. Like those reported by Leather, these “ bhil ” soils
are very poor in lime and nitrogen, but fairly supplied with
potash and phosphoric acid.
The Regur or Black Cotton Soils of Southern India . — The
second-greatest reasonably uniform soil-area of India is that
covered by the regur, or black cotton soils, in south central
India, notably the Deccan, where these soils are said to have
been cultivated without fertilization for 2000 years and are still
fairly productive.1 Both in their physical character, chemical
composition, and cultural characteristics, these regur soils
are very similar to the “ prairie soils ” of the Cotton states
and especially to the “ black adobe ” of California. Like the
latter they are of unusual depth without change of tint; they
crack wide open during the dry season on account of their high
clay content ; and the soil is thus partly inverted by the surface
soil falling into the cracks. To the latter fact Leather as-
1 That is to say, they now produce about 600 pounds, or 10 bushels of wheat
per acre, as do the Rothamstead soils after fifty years’ exhaustive cultivation.
Probably both have come down to the permanent level of production correspond^
ing to the amount of plant-food made currently available each year by the fallow¬
ing process in originally very rich soils. The present product of cotton on the
regur lands does not seem to be on record; judging by the wheat product it
should not be over one hundred pounds of lint per acre.
SOILS OF THE ARID AND HUMID REGIONS.
415
cribes, in part, the long duration of fertility in the regur lands.
The regur also contains fragments of calcareous hardpan (here
called guvarayi), just as in the Great Valley of California.
The eighteen analyses of regur given by Leather agree so
nearly in their essential points that it is admissible to average
them ; two other examples are however also given in the table.
It will be noted that while the contents of lime, magnesia and
alumina are uniformly high, the content of potash has a wide
range; it rises very high (1.14%) in the maximum, while the
average is fair.
One conspicuous defect of these soils is their extremely low
content of nitrogen, in view of which their lasting productive¬
ness is difficult to understand ; unless it be that, as in California,
their high lime-content causes a copious crop of leguminous
weeds, constantly replacing the nitrogen supply.1 Unfor¬
tunately we have no determinations of humus or of its nitrogen-
content. Leather attributes the black color of the regur to>
some mineral substance rather than to humus ; hut his argu¬
ments are not quite convincing, so long as the Grandeau test
has not been made. In view of the low rainfall and the close¬
ness of the texture of regur, it is probable that little if any
nitrates are currently washed out of the black cotton lands.
The regur soil-sheet seems to be underlaid over the greater
part of its area by a basaltic eruptive sheet (not by meta-
morphic rocks, as stated by Leather), and it is not easy to con¬
ceive how such a soil stratum can have been formed from such
rocks as a sedentary formation. Elsewhere such soils are
usually rather light and porous, as is the case in the Hawaiian
and Samoan islands ; and very high in iron-content. The
regur has the character of an alluvial backwater or lake de¬
posit; but how such a formation can have occurred on the
Deccan plateau, is a question not easily answered.
Red Soils of the Madras Region. — Interspersed with and to
seaward of the regur lands there are in the Madras presidency
considerable bodies of “ red ” lands, which appear to be
sedentary soils formed from underlying dark-colored, mostly
eruptive rocks. Some of these are very rich in lime and pot¬
ash, others very poor, and it seems impossible to classify them
1 See Voelcker, Report on the Improvement of Indian Agriculture, 1892, p. 4^
par. 60.
SOILS.
416
under any definite category either from the chemical or physical
point of view, except as to their red tint. Even this tint, how¬
ever, is not always found associated with exceptionally high
contents of iron oxid, but due rather to its fine diffusion in the
soil mass. As compared with the regur, with which the
“ red ” areas are interspersed, these soils contain, on the aver¬
age, less lime, potash and ferric oxid ; and phosphoric acid is
uniformly low. The alluvial (brown and black) soils from
the same region, exemplified in the table, are doubtless derived
partly from the regur, and their color and composition varies
accordingly.
“ Laterite Soils:" — These are defined by Wohltmann ( Trop-
ische Agricultur, 1892) as being “ the characteristic sedentary
soils ( Verwitterungsboden) of the tropics, formed under the
influence of heavy precipitation, high temperatures and
drought.” This definition does not indicate their derivation
from any particular rock, such as laterite is supposed to be ; but
its definition puzzles even geologists, and so, as Leather ob¬
serves, the definition of laterite soils will naturally puzzle
agricultural chemists. Accordingly it is difficult to deduce
from the analyses given any definite common characters.
Leather describes those analyzed by him as red or reddish,
sandy and gravelly, the gravel or cobbles often incrusted with
a dark-smooth crust of limonite, which to the uninitiated looks
as though the rock itself had been fused and vitrified. The
samples from Lohardaga and Singhbhum show the effects of
these limonite crusts upon the composition of the soils, which
resembles that of the Hawaiian soils mentioned above ; but in
the latter the iron oxid is wholly pulverulent. But it is prob¬
able that, as in the case of the latter, the high content of
phosphoric acid shown in the statement (.64 for the Lohardaga
soil) is tightly locked up in the insoluble form of ferric phos¬
phate. Wohltmann’s definition of laterite soils seems best rep¬
resented by the “ terra roxa ” of Brazil, which as he states has
.02 to .08% of potash, .02 to .10% of lime, and .045 to
.10% of phosphoric acid. Humus and nitrogen are very de¬
ficient in all these soils.
While most prominent in the coast region of Bengal, they
also occur not only near Madras (Saidapet) but also in the
SOILS OF THE ARID AND HUMID REGIONS.
417
belt of high rainfall on the Malabar (western) coast of the
Indian peninsula.
The productiveness of the laterite soils seems throughout to
be only moderate, yet much higher than would be expected of
soils of similar composition in the temperate zones, where the
rate of soil-formation is so much slower than in the tropics.
From the analyses of “ coffee soils ” from Yarcand in the
Sheveroy hills, north of Madras, we learn that coffee does well
with a fairly liberal supply of lime (.30 to .44%) and phos¬
phoric acid, but is satisfied with a much smaller amount of
potash than is found in the tea soils of Assam.
A farther systematic investigation of the soils of India, with
simultaneous accurate observations on their depth, subsoil,
geological derivation, topographical location and relations to
rainfall, could not fail to yield very important practical results.
The examination of samples collected and sent in by persons
unfamiliar with the proper mode of taking soil specimens, and
the information which should accompany them, always in¬
volves a great deal of uncertainty and waste of labor, and in¬
definiteness of results.
INFLUENCE OF ARIDITY UPON CIVILIZATION.
In connection with the facts given and discussed above, as
to the relative productive capacity of lands of the humid and
arid regions, it becomes of interest to consider what influence,
if any, these differences may have had in determining the
choice of the majority of the ancient civilizations in favor of
countries where nature imposes upon the husbandman, who
supplies the prime necessaries of life, the onerous condition of
artificial irrigation.1
Preference of Ancient Civilizations for Arid Countries. — A
brief review suffices to establish the fact of such choice. Aside
from Egypt, the permanent fertility of which is ascribed to the
inundations of the Nile, we find to westward the oases of the
Libyan and Sahara deserts, the high fertility of which has
become proverbial and has caused them to be cultivated from
ancient times to the present. Similarly, 011 both sides of the
1 Verhandlungen der Deutschen Physiologischen Gesellschaft in Berlin, Decem.
ber, 1892; North American Review, September, 1902.
27
418
SOILS.
Mediterranean Sea, we find that, instead of the humid forest
country, it was in the arid but irrigable coast countries, such as
the vegas of Valencia, Alicante, Granada, Malaga, and the
even more arid domain of which Carthage was the metropolis;
and farther east, in the Graeco-Syrian archipelago and the ad¬
jacent coasts, that noted centers of civilization were developed
and maintained. Thence the arid belt requiring irrigation
extends from Egypt and Arabia to Palestine, Syria, Assyria,
Mesopotamia and Persia, and across the Indus through the
anciently recognized regions of Indian civilization — Sindh,
the Panjab, Rajputana and the Northwestern provinces — to
the Ganges, embracing such well-known centers as Lahore,
Delhi, Meerut, Agra, etc., inhabited by much more hardy and
progressive races than the humid and highly productive tropical
portions of the Indian peninsula. Throughout the extensive
and important portion of northern India, irrigation is neces¬
sary to maintain regular production ; and in default of it,
periodic famines ravage the country. Thousands of years ago,
millions upon millions of treasure were expended there upon
irrigation works, as has again been done in modern times ; yet
in the rainy, forested districts we still find large areas prac¬
tically tenanted by wild beasts. In Asia Minor, as well as in
Central Asia, the remains of ancient cities once surrounded by
richly productive irrigated fields, are found where at present
only the herds of nomads pasture. The Khanates of southern
Turkestan with their historic cities, illustrate the same obsti¬
nate bias in favor of arid climates. Similarly, in the New
World, it was not in the moist and exuberantly fertile forest
lands of the Orinoco and Amazon, but on the arid western
slopes of the Andes, that the civilization of the Incas was de¬
veloped. In Mexico, also, it was the high central, arid plateau,
not the bountifully productive ticrra caliente, over which the
Aztecs chose to establish the main centers of their empire.
Even to northward, the inhabitants of the high, dry plains of
Arizona and New Mexico were, as their descendants of the
Pueblos are to-day, superior in social development to their
forest-dwelling neighbors of the Algonquin race. From time
immemorial they have practiced irrigation in connection with
cultivation, maintaining a comparatively dense population on
very limited areas.
SOILS OF THE ARID AND HUMID REGIONS.
419
It might be thought that the desire to avoid the labor of
clearing the forest ground was the motive which guided the
choice of the ancient nations toward the cheerless-looking, tree¬
less regions.
But if we consider the cost and labor of establishing and
maintaining irrigation ditches, it certainly seems that a
stronger motive, based on the intrinsic nature of the case, must
have influenced their selection. Neither can we with anv
degree of plausibility ascribe the preference for the arid open
country to the fear of enemies lurking in the forest, since war
was in early times practically the normal condition of man¬
kind, and was waged with little hesitation wherever booty was
in sight. It has also been asked how the ancients could have
known of the high productive capacity of arid lands ; but no
one who has ever seen the springing-up of luxuriant vegeta¬
tion after the periodic overflows of the arid-region streams, or
the same surrounding the springs in the deserts, would ask that
question.
Irrigation necessitates Co-operation. — Irrigation enterprises
can be accomplished in a very limited degree only by individ¬
uals or even families. Its permanently successful execution re¬
quires the co-operation of at least several social groups, ulti¬
mately of communities and states, if it is not to give rise to
acrimonious contentions or actual warfare ; witness the “ shot¬
gun policy ” resorted to in the arid West in times not very
remote. Irrigation, in other words, compels co-operative social
organization quite different from and far in advance of that neces¬
sary in humid countries. And such organization is mani¬
festly conducive to the preservation and development of the
arts of peace, which means civilization. The most ancient
systematic code of laws known to 11s is that of Hammurabi, the
king of arid Assyria.
The high and permanent productiveness of arid soils induces
permanence of civil organization. — In humid countries, as is
well known, cultivation can only in exceptional cases be con¬
tinued profitably for many years without fertilization. But
fertilization requires a somewhat protracted development of
agriculture to be rationally and successfully applied in the
humid regions, and the Germanic tribes, like the North-Ameri-
can Indians, seem to have shifted their culture grounds fre-
420
SOILS.
quently in their migrations. No such need was felt by the
inhabitants of the arid regions for centuries, for the native
fertility of their soils, coupled with the fertilizing effects of
irrigation water bringing plant-food from afar, relieved them
of the need of continuous fertilization ; while in the humid
regions, the fertility of the land is currently carried into the sea
by the drainage waters, through the streams and rivers, causing
a chronic depletion which has to be made up for by artificial
and costly means. What with the greater intrinsic fertility
and the great depth of soil available for plant growth, much
smaller units of land will suffice for the maintenance of a
family in arid countries; a fact which is even now being il¬
lustrated in the irrigated region of the United States, where
ten acres of irrigated land instead of 40 or 160, as in the East,
form the unit.
The arid regions were, therefore, specially conducive to
the establishment of the highly complex polities and high
culture, of which the vestiges are now being unearthed in what
we are in the habit of calling “ deserts;” the very sands of
which usually need only the lifegiving effects of water to
transform them into fruitful fields and gardens. It is also
quite natural that the wealthy and prosperous communities
so formed should in the course of time have excited the
cupidity of the “ barbarous ” forest-inhabiting races, and as
history records, have been over and again overwhelmed by
them — a similar fate often afterwards overtaking the con¬
querors in their turn, after the Capuan ease of their existence
had weakened their warlike prowess. At the present time,
the arid regions of the old world are still largely suffering from
having been overrun by the nomadic Turanians, whose
original habitat — Mongolia and Turkestan — while also arid,
does not permit of the ready realization of the advantages
above outlined, on account of the rigorous climate brought
about by altitude. Mahometanism first expelled, and has
since repelled, occidental civilization from the arid regions of
the Old World, remaining to-day as an obstacle to its prog¬
ress. The peaceful aggression of railroads and telegraphs
now seems likely to gradually overcome this repulsion; and
when Constantinople and Bagdad shall be linked together by
the steel bands, the desert will lose its terrors, and Mesopotamia
SOILS OF THE ARID AND HUMID REGIONS.
421
and Babylonia will again become garden lands, as of old,
under the abundant waters of the Euphrates and Tigris.
Until the water-supplies of the arid countries shall have been
more definitely gauged, it is impossible to foretell to what ex¬
tent food-production may be increased by their cultivation
under irrigation, after the relief from political misrule shall
have rendered such undertakings safe. But it can even now be
foreseen that with improved modern methods of cultivation,
the productive area of the world can be vastly increased by the
utilization of the countries where, as the Turcomans say, “ the
salt is the life of the land.”
CHAPTER XXII.
ALKALI SOILS.
Alkali Lands and Sea-shore Lands. — Alkali lands proper, as
already stated, are wholly distinct in their nature and origin
from the salty lands of sea-coast marshes, past or present.
The latter derive their salts from sea-water that occasionally
overflows them, or from that which has evaporated in segre¬
gated basins or estuaries ; and the salts impregnating them are
essentially “ sea salts,” that is, common salt, together with
bittern (magnesium chlorid), Epsom salt (magnesium sulfate)
gypsum, etc. (see chapter 2, p. 26). Very little of what would
be useful to vegetation or desirable as a fertilizer is contained
in the salts impregnating such soils ; and they are by no means
always intrinsically rich in plant-food, but vary greatly in this
respect.
While sea-shore lands are by no means always of high fer¬
tility even when freed from their salts, especially when very
sandy, it is otherwise when they occur near the mouths of
streams or rivers, whose finest sediments they then receive.
From such lands are formed the profusely productive Polders
of Holland and northern Germany, and the equally noted
“ colmates ” of France and Italy. These, so soon as freed
from salt, may be considered as possessing the same advantages
as “delta " alluvial lands, and from the same causes; notably
the accumulation of the finest sediments derived from the
rivers' drainage basins.
Origin. — Alkali lands proper bear no definite relation to the
present sea ; they are mostly remote from it or from any other
sea bed, so that they have sometimes been designated as
“ terrestrial salt lands." Their existence is in the majority of
cases definitely traceable to climatic conditions alone. They
are the natural result of a light rainfall, insufficient to leach
out of the land the salts that always form in it by progressive
weathering of the rock powder of which all soils largely con-
422
ALKALI SOILS.
423
sist. Where the rainfall is abundant, that portion of the salts
corresponding to “ sea salts ” is leached out into the bottom
water, and with this passes through springs and rivulets into
the country drainage, to be finally carried to the ocean.1 An¬
other portion of the salts formed by weathering, however, is
partially or wholly retained by the soil ; it is that portion chiefly
useful as plant food.
It follows that when, in consequence of insufficient rainfall,
all or most of the salts are retained in the soil, they will contain
not only the ingredients of sea-water, but also those useful to
plants. In rainy climates a large portion even of the latter
is leached out and carried away. In extremely arid climates,
on the contrary, the entire mass of the salts remains in the
soils ; and, being largely soluble in water, evaporation during
the dry season brings them to the surface, where they may
accumulate to such an extent as to render ordinary useful
vegetation impossible; as is seen in “alkali spots,” and some¬
times in extensive tracts of ‘ alkali desert.” Three compounds,
viz. the sulfate, chlorid and carbonate of sodium, usually form
the main mass of these saline efflorescences. Magnesium sul¬
fate (Epsom salt) is in many cases a very abundant ingredient;
some calcium sulfate is nearly always present, and calcium
chlorid is not infrequently found.
In some cases the above salts are in part at least derived from the
leaching of adjacent or subjacent geological deposits impregnated with
them at the time of their formation. Such is the case in portions of
Wyoming, Colorado and New Mexico, in the Colorado river delta, and
in the Hungarian Plain ; and it is in these cases especially that the
chlorids of calcium and magnesium also form part of the saline mixture.
Geographical Distribution of Alkali Lands. — In looking over
a rainfall map of the globe 2 we see that a very considerable
portion of the earth’s surface, forming two belts to poleward
of the two tropics, has deficient rainfall; the latter term being
commonly meant to imply any annual average less than 20
inches (500 millimeters). The arid region thus defined in¬
cludes, in North America, most of the country lying west of
the one hundredth meridian up to the Cascade Mountains, and
1 See Chapter 2, p. 26.
2 See above, chapter 16, p. 294.
424
SOILS.
northward beyond the line of the United States ; southward, it
reaches far into Mexico, including especially the Mexican
plateau. In South America it includes most of the Pacific
Slope (Peru and Chile) south to Araucania; and eastward of
the Andes, the greater portion of the plains of western Brazil
and Argentina. In Europe only a small portion of the
Mediterranean border is included ; but the entire African coast-
belt opposite, with the Saharan and Libyan deserts, Egypt and
Arabia, are included therein, as well as, south of the Equator, a
considerable portion of South Africa (Kalahari desert). In
Asia, Asia Minor, Syria (with Palestine), Mesopotamia,
Persia, and northwestern India up to the Ganges, and north¬
ward, the great plains or steppes of central Asia eastward to
Mongolia and western China, fall into the same category; as
does also a large portion of the Australian continent.
Utilization of World-wide Importance. — Over these vast
areas alkali lands occur to a greater or less extent, the excep¬
tions being the mountain regions and adjacent lands on the side
exposed to the prevailing winds. It will therefore be seen
that the problem of the utilization of alkali lands for agricul¬
ture is not of local interest only, but is of world-wide import¬
ance. It will also be noted that many of the countries referred
to are those in which the most ancient civilizations have ex¬
isted in the past, but which at present, with few exceptions, are
occupied by semicivilized people only. It is doubtless from
this cause that the nature of alkali lands has until lately been
so little understood, that even their essential distinctness from
the sea-border lands has been but recently recognized in full.
Moreover, the great intrinsic fertility of these lands when
freed from the noxious salts, has been very little appreciated;
their repellent aspect causing them to be generally considered
as permanently waste lands.
Repellent aspect. — This aspect is essentially due to their natural
vegetation being in most cases confined to plants useless to man, com¬
monly designated as “ saline vegetation,” 1 of which but little is usually
relished by cattle. Notable exceptions to this rule occur in North and
South America, Australia, and Africa, where the “saltbushes” of the
former and the “ karroo ” vegetation of the latter form valuable pasture
1 See Chapter 23.
ALKALI SOILS
425
Fig. 60. — Alkali Lands in San Joaquin Valley, California.
420
SOILS.
and browsing grounds. Apart from these, however, all efforts to find
culture plants for these lands generally acceptable, or at least profitable,
in their natural condition, have not been very successful.
Figure 60 illustrates the usual aspect of alkali lands in the San
Joaquin valley of California. It will be noted that the alkali-covered
surface is only in spots, with clumps of vegetation between, so that
cattle can find both pasture and browsing on a portion of such lands,
even though the plants so growing are not usually of the most desirable
kind. We find in all arid regions, however, considerable areas either
wholly destitute of vegetation, or bearing only such saline growth as is
rejected by all kinds of domestic animals.
Effects of Alkali upon culture plants. — In land very strongly
impregnated with alkali salts, most culture plants, if their seed
germinates at all, will show a sickly growth for a short time,
“ spindle up ” and then die without fruiting. In soils less
heavily charged the plants may simply become dwarfed, and
fruit scantily. The effect on grown trees around which alkali
has come up, is first, scanty leafage and short growth of shoots,
themselves but sparsely clothed with leaves. This state of
things is well shown in figures 61 and 62, which represent
apricot trees growing but a short distance apart, but one com¬
ing within range of an expanding alkali spot. The characteris¬
tic sparseness of the foliage of the “ alkalied ” tree as compared
with the adjacent one is well shown.
Nature of the injury to plants from Alkali. — When we
examine plants that have been injured by alkali, we will mostly
find that the visible damage has been done near the base of the
trunk, or root crown; rarely at any considerable depth in the
soil itself. In the case of green herbaceous stems, the bark is
found to have been turned to a brownish tin^e for half an inch
or more, so as to be soft and easily peeled off. In the case of
trees, the rough bark is found to be of a dark, almost black,
tint, and the green layer underneath has, as in the case of
herbaceous stems, been turned brown to a greater or less extent.
In either case the plant has been practically “ girdled,” the
effect being aggravated by the diseased sap poisoning more or
less the whole stem and roots. The plant may not die, but it
will be quite certain to become unprofitable to the grower.
It is mainly in the case of land very heavily charged with
ALKALI SOILS.
42/
Fig. 61.— Unaffected. APRICOT TREES ON ALKALI GROUND. Fig. 62 —Yielding to Alkali.
428
SOILS.
common salt, as in the marshes bordering the sea, or salt lakes,
that injury arises from the direct effects of the salty soil-water
upon the feeding roots themselves. In a few cases the grad¬
ual rise of salt water from below in consequence of defective
drainage, has seriously injured, and even destroyed, old orange
orchards. The natural occupancy of the ground by certain
native plants may be held to indicate that the soil is too
heavily charged with saline ingredients to permit healthy root
growth or nutrition until the excess of salts is removed. (See
below, chapters 23 and 26).
The fact that in cultivated land the injury is usually found
to occur near the surface of the soil, concurrently with the
well-known fact that the maximum accumulation of salts at
the surface is always found near the end of the dry season,
indicates clearly that this accumulation is due to evaporation
at the surface. The latter is often found covered with a
crust consisting of earth cemented by the crystallized salts,
and later in the season with a layer of whitish dust resulting
from the drying-out of the crust first formed. It is this dust
which becomes so annoying to the inhabitants and travelers in
alkali regions, when high winds prevail, irritating the eyes and
nostrils and parching the lips.
Effects of Irrigation. — One of the most annoying and dis¬
couraging features of the cultivation of lands in alkali regions
is that, although in their natural condition they may show
but little alkali on their surface, and that mostly in limited
spots, these spots are found to enlarge rapidly as irrigation is
practiced. Yet since alkali salts are the symptoms and result
of insufficient rainfall, irrigation is a necessary condition of
agriculture wherever they prevail. Under irrigation, neigh¬
boring spots will oftentimes merge together into one large one,
and at times the entire area, once highly productive and perhaps
covered with valuable plantations of trees or vines, will become
incapable of supporting useful growth. This annoying
phenomenon is popularly known as “ the rise of the alkali ” in
the western United States, but is equally well known in India
and other irrigation regions.
The soil being impregnated with a solution of the alkali
salts, and acting like a wick, the salts naturally remain behind
on the surface as the water evaporates, the process only stop-
ALKALI SOILS.
429
ping when the moisture in the soil is exhausted. We thus not
infrequently find that after an unusually heavy rainfall there
follows a heavier accumulation of alkali salts at the surface,
while a light shower produces no perceptible permanent effect.
We are thus taught that, within certain limits, the more water
evaporates during the season the heavier will be the rise of the
alkali ; provided that the water is not so abundant as to leach
the salts through the soil and subsoil into the subdrainage.
Leaky Irrigation ditches. — Worst of all, however, is the
effect of irrigation ditches laid in sandy lands (such as are
naturally predominant in arid regions), without proper pro¬
vision against seepage. The ditch water then gradually fills
up the entire substrata so far as they are permeable, and the
water-table rises from below until it reaches nearly to the ditch
level; shallowing the subsoil, drowning out the deep roots of
all vegetation, and bringing close to the surface the entire mass
of alkali salts previously diffused through many feet of sub¬
strata.
Surface and Substrata of Alkali Lands. — Aside from the
desert proper, in the greater portion of the alkali country
“ alkali spots,” i. e. ground covered with saline efflorescences
and showing little or no vegetation, are interspersed with larger
areas apparently free from salts and covered with the ordinary
vegetation of the region. A view of such country is given in
a plate on a previous page. The alkali spots are usually some¬
what depressed below the surrounding lands, and after rains
remain covered with water for some time ; the water frequently
assuming a brown or blackish tint after standing.
When a pointed steel probe is pushed down within such an
alkali spot, it will usually be found that, although the soil may
appear quite sandy, it is penetrated with some difficulty ; while
outside of the spots, the probe does not encounter serious re¬
sistance until it reaches the depth of two or three feet, when it
frequently becomes impossible to penetrate farther without
the aid of a hammer. On the margin of the spots, the transi¬
tion from utter barrenness to a luxuriant vegetation of native
weeds is mostly quite sudden ; as is shown in the figure, p. 425.
Vertical Distribution of the Salts in Alkali Land. — The re¬
sults of a comparative examination of such land before and
430
SOILS.
after irrigation,1 are shown in the annexed diagrams; in which
the kind and amount of salts is shown for every three inches of
vertical depth, down to four feet, by curves whose extension
from left to right indicate the several percentages, while the
outer curved line gives the total of salts for each of the several
depths.
Fig. 63 represents the condition of the salts in an “ alkali spot” as
found at the end of the dry season at the Tulare substation, California.
The soil was sampled to the depth of two feet at intervals of three
inches each. It is easy to see that at this time the bulk of the salts
was accumulated within the first six inches from the surface, while
lower down the soil contained so little that few culture plants would be
hurt by them.
How Native Plants Live. — Fig. 64 represents similarly the state cf
things in a natural soil alongside of the alkali spot, but in which the
native vegetation of brilliant flowers develops annually without any
■hindrance from alkali. Samples were taken from this spot in March,
near the end of the wet, and in September, near the end of the dry
season, and each series fully analyzed. There was scarcely a noticeable
difference in the results obtained. It is seen in the figure that down to
the depth of 15 inches there was practically no alkali found (0.035%),
and it was within these 15 inches of soil that the native plants mostly
had their roots and developed their annual growth. But from that
level downward the alkali rapidly increased, and reached a maximum
(0.529%), at about 33 inches; decreasing rapidly thence until, at the
end of the fourth foot in depth, there was not more alkali than within
the first foot from the surface. In other words, the bulk of the salts
had accumulated at the greatest depth to which the annual rainfall
(7 inches) ever reaches, forming there a sheet of tough, intractable clay-
hardpan. The shallow- rooted native plants germinated their seeds freely
on the alkali-free surface ; their roots kept above the strongly-charged
subsoil, and through them and the stems and foliage all the soil mois¬
ture was evaporated by the time the plants died. Thus no alkali was
brought up from below by evaporation. The seeds shed would remain
uninjured, and would again germinate the coming season.
1 Hilgard and Loughridge, Bulletin No. 128, California Experiment Station; Re*
port California Experiment Station, 1894-95, p. 37 ; Bulletin No. 30, Office o t
Experiment Stations; Wollny’s Forsch. Geb. Agr. Phys., 1896. ,
Amounts of Ihgreoichts w 100 of Soil.
.24 .28 32 .36 40 .44 .48 S2 ,S6 .60 .64 .68
ALKALI SOILS
431
432
SOILS
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Tulare Experiment Sub-Station, California.
ALKALI SOILS.
433
It is thus that the luxuriant vegetation of the San Joaquin
plains, dotted with occasional alkali spots, is maintained ; the
spots themselves being almost always depressions in which
the rain water mav gather, and where, in consequence of the in¬
creased evaporation, the noxious salts have risen to the surface
and render impossible all but the most resistant saline growth ;
particularly when, in consequence of maceration and fermenta¬
tion in the soil, the formation of carbonate of soda has caused
the surface to sink and become almost water-tight.
Upward Translocation from Irrigation. — Fig. 65 shows the
corresponding profile of the same soil after several years’ irri¬
gation. The upward movement of the salts is clearly seen by
comparison with the previous figure; and the surface soil has
become so charged with salts that the seeds of culture plants
refuse to germinate.
Ten feet from this bare alkali ground, on which barley had
refused to grow, a crop of barley four feet high was harvested
the same year, without irrigation. Investigation proved that
here the condition of the soil was intermediate between the two
preceding diagrams. The irrigation water had dissolved the
alkali of the subsoil, and the more abundant evaporation had
brought it nearer the surface ; but the shading by the barley
crop and the evaporation of the moisture through its roots
and leaves had prevented the salts from reaching the surface
in such amounts as to injure the crop, although the tendency to
rise was clearly shown. By the use of gypsum, moreover, the
injuriousness of the alkali had been somewhat diminished.
The same season, grain crops were almost a failure on alkali-
free land in the same region ; and in connection with this result
it should be noted as a general fact that alkali lands always re¬
tain a certain amount of moisture perceptible to the hand dur¬
ing the dry season, and that this moisture can be utilized by
crops; so that at times when crops fail on non-alkaline land,
good ones are obtained where a slight taint of alkali exists in
the soil. Actual determinations showed that while a sample of
alkali soil containing .54% of salts absorbed 12.3% of moisture
from moist air, the same soil when leached absorbed only 2.5%
— a figure corresponding to that of sandy upland loams.
Alkali in Sandy Lands. — In very sandy lands, and particu¬
larly when the alkali is “ white ” only, the tendency to accumu-
28
434
SOILS
Tulare Experiment Substation, California.
ALKALI SOILS.
435
lation near the surface is much less, even under irrigation. In
the natural condition the salts are in such cases often found
quite evenly distributed through soil columns of four feet, and
even more. This is an additional cause of the lesser injurious-
0 .02 .04 06 .08 .10 12 .14- .16 .18 .20 .22
ness of “ white alkali.” An illustration of the distribution of
the salts in very sandy lands, from the Tulare substation, is
given in Fig. 66. Here we see that the maximum is not at,
but some distance below the surface, the entire saline mass is
43^
SOILS.
lower down than in the more clayey loam of the same locality,
and is more widely distributed in depth.
Distribution of Alkali Salts in Heavy Lands. — The mode of
distribution of alkali salts in the heavier, close-grained soil of
the Chino experimental tract in southern California, is illus¬
trated in Fig. 67. This land is permanently moist, from a
water-table ranging from five to seven feet below the surface
in ordinary years. There is therefore no opportunity for the
formation of “ alkali hardpan " as in the case of the Tulare
soil ; the salts always remain rather near the surface, viz. with¬
in twelve to fifteen inches. But being in much smaller average
amounts than at Tulare (an average of about 5300 lbs. per
acre), quite a copious natural vegetation of grasses, sunflowers,
and “ yerba mansa ” covered the whole surface, save in a few
low spots.
A similar mode of distribution of the salts is found in the
still more clayey “ black adobe ” lands of the Great Valley of
California. The scanty rains cannot penetrate these soils to
any great depth, so that evaporation will soon bring the salts
carried by them back to within a short distance of the surface.
Their accumulation there is frequently indicated by the entire
absence of any but the most resistant alkali weeds, even though
the total of salts in the land may not be very great.
Salton Basin. — A peculiar state of things is illustrated in the
Salton Basin, which represents what was at one time the head
of the Gulf of California, and at the lowest point of which,
268 feet below sea level, there now lies a large deposit of rock
salt. It has been cut off from the present Gulf by the delta
deposits of the Colorado river, which now, however, overflows
into the Basin at times of extreme high water. Although
appearing level to the eye, the general slope of the country is to
the lowest point of the former sea-bottom.
The region, now in progress of settlement by means of irrigation
water brought from the river near Yuma, was investigated with respect
to its alkali conditions in 1900 (Bulletin No. 140, Calif. Agric. Expt.
Sta). The annexed diagram 68 shows the distribution of the salts to a
depth of 21 feet. It will be noted that here also the alkali content
becomes insignificant at 4 feet depth, but increases again to a second
maximum at about 1 5 feet, below which there is a second decrease ;
Amounts of Ingredients in 100 of Soil
ALKALI SOILS,
437
o
Fig. 67. Amounts and composition of alkali salts at various depths and points in the ten-acre tract at the southern California Experiment Station ;
taken last week in April, 1895.
iM
438
SOILS
Fig. 68.— Graphic illustration of distribution of salts in Salton River section, Californin.
ALKALI SOILS.
439
below this, at 20 feet, there is a final very heavy increase, not only of
the total salts but especially of common salt, which evidently represents
the drainage toward the salt deposit. Above this level there is a very
remarkable predominance of Glauber’s salt (sodium sulfate), also observ¬
able elsewhere, e . g. near White Plains, New, whose name is derived
from the copious surface accumulation of the sulfate. It seems a-
though this must have been formed in some way from the common
salt.
Horizontal Distribution of Alkali Salts in Arid Lands. — The
constant occurrence of “ alkali spots " in arid lands shows at
once the great inequality of horizontal distribution of alkali
impregnation. This is as prominent in level lands as on slopes,
and in extremely arid regions it is mostly not possible to recog¬
nize even verv considerable differences without close examina-
J
tion. Thus in lands appearing exactly alike on the surface,
on the edge of the Salton basin in California, on the same forty
acre 1.4% (56,000 pounds per acre) was found in the surface
four feet at one point, and a hundred yards away, 12.5%
(500,000 pounds). The mapping of alkali lands is therefore
somewhat precarious unless carried into great detail. More¬
over, it has been found that the location of the salts changes
from year to year, especially in irrigated land, as might be ex¬
pected. Those cultivating alkali lands have therefore to exer¬
cise constant watchfulness, unless the salts have been defi¬
nitively eliminated by underclrainage over a considerable area ;
as merely local operations may be rendered ineffectual by the
migration of the salts from neighboring tracts not reclaimed.
Alkali in Hill Lands. — As a rule, hill lands themselves are
remarkably free from alkali, even in the arid regions ; except
when water is gathered in depressions, where strongly saline
waters may be found in Washington, Montana and elsewhere.
But on level plateau lands, where drainage is slow or imperfect,
alkali appears as freely as it does in the same regions in the
stream bottoms. In the latter the leachings and seepage of the
uplands naturally causes a concentration of the salts, and thus
we find alkali salts incrusting the surface in the valleys of the
streams, as c. g., that of the Yellowstone, Musselshell, Judith,
Yakima and others in the north, and of Green river, Platte,
Pecos, and Rio Grande farther south ; as well as in numerous
valleys of central and southern California.
440
SOILS.
Usar Lands of India. — These lands have been investigated
first by the “ Reh Commission " appointed to investigate the
causes of the deterioration of lands in the Aligarh district
(south of Delhi, between the Ganges and Jumna rivers), in
1876. The occasion of this appointment was the appearance
of “ reh ” (alkali salts) in a region which had previously been
free from them.1 Subsequently, a more elaborate investigation
of the subject was made by Dr. J. W. Leather, Agricultural
Chemist to the Government of India.2 From these documents
it appears that “ usar lands ” exist largely not only in the
Northwestern Provinces and Oudh, but also in the Panjab,
especially on the lands bordering the Chenab river ; likewise to
a slight extent in the Bombay presidency. Leather's investi¬
gation shows that not all the lands designated by the natives as
usar contain soluble salts in injurious amounts, some being
simply lands having very hard, clayey soils difficult to till with
the imperfect methods employed. Yet the general phenomena
of the true “ reh " lands are practically identical with those of
the American alkali lands, including also the calcareous hard-
pan, there called kankar. Owing probably to the long culti¬
vation of the Indian lands (mostly under irrigation), the salts
are there at their maximum in the first foot, decreasing as
depth increases. It is noteworthy also that in the majority of
cases the predominant salt is carbonate of soda or black alkali,
which there as in California renders the lands impervious to
water until treated with gypsum. This fact accounts for the
popular use of the same name for non-saline impervious clay
soils, and the alkali or reh lands proper.
We have an entirely analogous case in the “ Szek ” lands of
the Hungarian plain, some of which are simply poor refractory
soils containing a trace of soluble salts ; while lower down in
the valley of the Theiss we find genuine alkali lands, both
black and white, which have long furnished carbonate of soda
for local use and commerce. In this case, however, the alkali
salts seen to come largely, in some cases wholly, from under¬
lying saline clays whose salts in coming to the surface suffer
1 An abstract of the report of this commission is given in the Report of the
California Experiment Station for 1890.
2 See Agricultural Ledger, 1897, No. 13; ibid. 1901, No. 13.
ALKALI SOILS.
44I
precisely the same transformations experienced in California
and India, in presence of calcic carbonate (see below, p.
450 ff).
The accounts given by v. Middendorff of the nature and oc¬
currence of alkali lands in Turkestan (Ferghana) agree en¬
tirely with those given above for California and India; as do
also tbe investigations made by other Russian observers on the
saline lands of the steppes of European Russia.
COMPOSITION AND QUANTITY OF ALKALI SALTS.
Black and White Alkali. — Broadly speaking, the world over
alkali salts consist mainly of three chief ingredients, already
mentioned, namely, common salt, Glauber’s salt (sulfate of
soda), and salsoda or carbonate1 of soda. The latter causes
what is popularly known as “ black alkali,” from the black
spots of puddles seen on the surface of lands tainted with it,
owing to the dissolution of the soil humus;2 while the other
salts, often together with Epsom salt and bittern (Magnesium
chlorid), constitute “ white alkali,” which is known to be very
much milder in its effect on plants than the black. In most
cases all three are present, and all may be considered as prac¬
tically valueless, or noxious, to plant growth.
Nutritive Salts in Alkali. — With them, however, there are
almost always associated, in varying amounts, sulfate of pot-
1 In this designation are included, in this volume, both the normal (mono-) car¬
bonate and the two other compounds, the bi- or hydrocarbonate and the inter¬
mediate (so-called sesqui-) compound or trona; all of which are commonly present
simultaneously, but in utterly indefinite relative proportions, varying from day
to day and from inch to inch of depth, inasmuch as their continued existence
depends upon the greater or less formation of carbonic acid in the soil, and the
access of air. Hence their separate quantitative determination at any one time is
of little practical interest. All naturally occurring carbonate of soda contains, and
sometimes consists of, these “super-carbonates,” according to the greater or less
exposure to air and solar heat. They are much milder in their action on plants
than the mono-carbonate, which unfortunately, in the nature of the case, always
predominates near the surface, and thus injures the root-crown.
2 A wholly different kind of “ black alkali ” exists in some regions, especially in
the delta lands of the Colorado of the West and in the Pecos and Rio Grande
country in New Mexico. In these cases the dark tint is due, not to a humic
solution, but simply to moisture, which is tenaciously retained by the chlorids of
calcium and magnesium impregnating the land, thus contrasting strongly with the
gray tint of the general dry soil.
442
SOILS.
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ALKALI SOILS.
443
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444
SOILS.
ash, phosphate of soda, and nitrate of soda, representing the
three elements — potassium, phosphorus, and nitrogen — upon
the presence of which in the soil in available form, the welfare
of our crops so essentially depends, and which we aim to supply
in fertilizers. The potash salt is usually present to the extent
of from 5 to 20 per cent of the total salts ; phosphate, from a
fraction of one to as much as 4 percent; the nitrate from a
fraction of one to as much as 20 percent. In black alkali the
nitrate is usually low, the phosphate high ; in the white, the re¬
verse is true. Both relations are readily intelligible from a
chemical and bacteriological point of view.
Estimation of Total Alkali in Land. — The investigations
detailed above having shown that in California at least, out¬
side of the axes of valleys no practically important amount of
alkali salts is usually found at a depth exceeding four feet, it
became possible to determine approximately the amounts of
salts that would have to be dealt with when irrigation and
evaporation should bring the entire amount to or near the sur¬
face; a necessary prerequisite to the determination of possible
cultures. While, as already shown, the salts occur lower down
in very sandy lands, yet the diagram on p. 435 shows that even
then, an estimate on this basis would not be very wide of the
truth. It is at least probable that the same is measurably true
of level alkali lands elsewhere, when not underlaid by geologi¬
cal deposits impregnated with salts.
The total amount of these salts ordinarily found in alkali
lands (i. e. in such as in the dry season show saline efflores¬
cences on the surface) is from about one tenth of one per cent
to as much as three per cent of the weight of the soil, taken to
the depth of four feet. The percentage of salts having been
determined in samples representing a tract, it becomes easy to
calculate, approximately, the total amounts of each salt present
per acre, on the basis of the weight of the soil per acre foot.
For the soils of the arid region, such weight will usually range
from three million five hundred thousand to four million
pounds per acre-foot; the latter being the most usual figure, of
which it may be conveniently remembered, that forty thousand
pounds represent 1 per cent. We are thus enabled to esti¬
mate e. g. the amount of gypsum required to neutralize the
carbonate of soda in the salts, or the amounts of valuable nutri-
ALKALI SOILS.
445
tive ingredients — potash, phosphoric acid and nitrates — present
in the land in the water-soluble form.
As has been shown in the preceding discussion, the analysis
at the surface foot alone, which has frequently been alone
made, gives no definite clew whatever to the total amounts of
salts to be controlled. A full estimate is of special importance
in enabling us to forecast what culture plants are likely to suc¬
ceed on a given tract, by reference to the table of “ tolerances ”
given below (chapter 23, page 467).
Composition of Alkali Soils as a Whole. — As may be im¬
agined, the presence of the alkali salts finds expression in the
analytical statement of their composition, although not to the
extent usually anticipated from their superficial aspect. The
table annexed gives the composition of fourteen alkali soils,
taken to the depth of one foot, at times when there was no visi¬
ble accumulation of salts on the surface. The averages of the
several ingredients determined are given in the fifteenth col¬
umn, and a comparison of its figures with those of the
general table on page 377 of chapter 20 will show some
marked characteristics. We find the average potash-content
to be but little less than twice as great as in the general average
for the state of California ; in the case of lime the ratio is nearly
as one to three, in the case of magnesia nearly one to two; in
that of phosphoric acid, one to two and a half, of which in the
presence of carbonate of soda an unusually large proportion is
in a readily soluble, often in the water-soluble, condition (see
preceding table).
The usual proportion of soda, of one-fourth to one-half of
the amount of potash, is changed to one-half or three-fourths;
in the case of the strongest alkali lands soda may equal or even
exceed the potash content. As the latter, however, is in¬
variably high to very high, it does not happen as frequently as
might be supposed that the soda content exceeds that of potash
as shown by the usual method of soil-extraction with water.
That the potash percentage should always be high in alkali lands, is
hardly surprising when it is considered that the continued presence of
the salts resulting from rock decomposition affords opportunity for the
full exercise of the preference with which potash is known to be retained
COMPOSITION OF ALKALI SOILS AS A WHOLE.
446
SOILS.
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ALKALI SOILS
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443
SOILS.
in soils by the formation of complex zeolitic silicates. In most cases
the potash-percentage exceeds .75%, and rises as high as 2.0% ; as is
shown in the table.
This table exhibits also another standing characteristic of
alkali soils, which is to be anticipated from the conditions of
their formation ; viz, high lime-content, which sometimes rises
to the extent of marliness.
In phosphates, also, alkali soils are almost always high; and
an unusually large proportion is found to be readily soluble.
In presence of much carbonate of soda, nitrates are usually
scarce or altogether absent ; while owing to the action of the
alkaline solution upon the humus, ammonia salts, or even free
(or carbonated and therefore readily dissociated and assimi¬
lated) ammonia may be present, so as to be perceptible to the
senses by its odor in hot sunshine. But in the case of “ white
alkali, ” more especially of the sulphate in moderate amounts,
nitrification is exceedingly active and nitrates may sometimes
rise to as much as 20% of the soluble salts. As alkali spots are
usually low in the central portion and therefore more moist
than around the edges, we sometimes find ammonia salts in the
middle of a spot, while nitrates are abundant along the mar¬
gin of the same. These differences, first demonstrated by an
investigation made by Colmore,1 illustrate some of the reac¬
tions that are essentially concerned in the agricultural avail¬
ability of alkali lands. A summary of Colmore’ s results is
given in the table below.
Cross Section of an Alkali Spot. — The spot examined lies
outside of Tulare, California, substation; it being late in the
season, when the bulk of the salts is found near the surface,
the samples were taken to the depth of one foot only, at points
four feet apart, from the center out.
1 Report of the California Exp’t St’n for 1892-94, p. 141.
ALKALI SOILS.
449
AMOUNT AND COMPOSITION OF SALTS IN ALKALI SPOT FROM CENTER TO
CIRCUMFERENCE, 4 FEET APART, I FT. DEPTH.
Mineral Salts.
1
Center
of spot.
2
Four
feet.
3
Eight
feet.
4
Twelve
feet.
5
Outer
margin
Potassium sulfate .
Sodium sulfate .
6.70
19.84
9-55
12.85
11.92
23.72
19.26
23-97
13-95
16.96
Magnesium sulfate .
3-°7
.07
•95
2.05
8.29
Sodium chlorid .
13.80
23-73
24.12
24.23
29.60
Sodium carbonate .
5072
50.96
37-55
35-49
29.94
Sodium phosphate .
5-57
2.88
•87
?
1.04
Sodium nitrate .
•30
?
.87
p
.13
Totals .
100.00
100.00
1 00.00
100.00
100.00
Organic matter .
30.00
24.80
19.48
23.36
20.31
Total soluble in soil .
.78
•54
.70
•37
•34
Mineral salts. .
.38
.40
•54
•25
•23
While the table shows an obvious irregularity in some of the data at
the eight-foot point, arising doubtless from an irregularity of surface or
of texture overlooked in taking the samples, we find a very remarkable
regularity of progression in the cases of potassium sulfate, sodium
chlorid, sodium carbonate and sodium phosphate in the other four
samples. The maxima of the “ black alkali ” and the soluble organic
matter (humus) coincide, as does that of the phosphate ; the total
mineral salts at the outer margin are only a little over half of what is
found at the center. This is natural, as owing to the deflocculating
effect of the black alkali, the center is nearly a foot lower than the
margin. The lowering of the nitrate-content at the outer margin is
obviously due to the luxuriant vegetation growing adjacent.
Reactions between the Carbonates , Chlorids and Sulfates of Alkalies
and Earths. That a soluble earth-salt, such as the sulfate or chlorid of
calcium, will react upon an alkaline carbonate solution so as to form an
alkali sulfate, and e.g. lime carbonate, is well known ; the neutralization
of the sodic carbonate in the soil by means of gypsum, above referred
to, is based upon this reaction. It is not so well known that the latter
may be reversed, partly or wholly, by the presence of carbonic acid in
the solution of the soil. Although observed as early as 1824 by Brandes,
and again in 1859 by A. Muller, this reaction is not mentioned in text¬
books and attracted no attention as a source of naturally occurring
alkali carbonates which in the past have formed the basis of extensive
commerce from the Orient, until in 1888, the writer together with Weber
29
450
SOILS.
and later with Jaffa, investigated it quantitatively.1 It was found that
up to .75 grms. per liter, the entire amount of sodic sulfate present in
solution is transformed into carbonate in presence of calcic carbonate,
by a current of carbonic dioxid ; but the amount so transformed does
not continue to increase beyond about 4 grams per liter. A correspond¬
ing amount of calcic sulfate is formed. In the case of potassic
sulfate, the transformation also occurs, proportionally to the molecular
weight. This relation is shown in the subjoined diagram, which also
shows in the curves on the left, the residual alkalinity left after evapora¬
tion and drying the residue at ioo° C.
Grams per Liter KHCO#
Fig. 69. — Progressive Transformation of Alkali Sulfates into Carbonates. (The figures along
upper line represent tenths of one per cent.)
The corresponding reaction occurs also, of course, between
sodium chlorid and calcium carbonate, but not to the same
extent, because unlike the difficultly soluble gypsum, the reac¬
tion product is the very soluble calcium chlorid, the presence of
which in the solution limits the reaction much sooner than
when most of the decomposition product is thrown down in
1 Proc. Am. Soc. Agr. Sci., 1888 ; ibid., 1890; Rep. Cal. Expt. Sta., 1890, p. 100;
Ber. Berlin, Chem. Ges., 1893 » Am. Jour. Sci., August 1896.
ALKALI SOILS,
451
the solid state. The calcium chlorid not uncommonly found in
some alkali regions is undoubtedly the product of the above re¬
action.
As the saline solutions in the soil are mostly quite dilute, and
calcic carbonate is always present, it follows that whenever
under the influences which favor the oxidation of organic mat¬
ter in the soil, and the activity of the plant roots, carbonic gas
is formed somewhat copiously, alkali sulfates and chlorids
present may be partially or wholly transformed into carbonates
within the soil. As a matter of fact, it is found that this trans¬
formation occurs most readily in the moister portions of the
soil and subsoil, and invariably so zvhen an alkali soil is
“ swamped ” by excessive irrigation or rise of bottom water;
while the reaction is again reversed whenever free access of air
reduces the carbonic dioxid below a certain point. It thus be¬
comes intelligible why in the diagrams showing the distribu¬
tion of the salts (this chapter pp. 431 and 432), we always
find the sodic carbonate relatively decreasing as the surface
is approached.
Thus, also, is explained the fact that sodium carbonate is
formed more abundantly toward the center of the root system
of alkali plants, such as the greasewood, beneath which the soil
is always more abundantly charged with “ black alkali ” than
is the surrounding earth.
Good aeration of the soil mass, then, is essential in main¬
taining the neutralization of the “ black alkali ” soils brought
about by the use of gypsum (land plaster).
Inverse Ratios of Alkali Carbonates and Sulfates. — Ac¬
cording to the above considerations, it is not surprising that
we should often find an apparent inverse ratio between the
alkali sulfates and carbonates in soils so closely adjacent that
their salts must be presumed to be similar in composition. A
striking example is shown in fig. 70, in which this inverse ratio
becomes apparent four times in succession in one and the same
soil profile. While this inference is plain on the face of the
diagram, it is not quite easy to explain in detail how this alter¬
nation came about from the condition observed two months
previously. Most probably it was caused by corresponding
alternations of weather, in which short, warm spring showers
alternated with similarly brief periods of drying north winds ;
Amounts of Ingredients In 100 of Soil
452
SOILS
Fig. 70. — Amounts and Composition of Alkali Salts at various depths in partly reclaimed Alkali Land. Tulare Experiment Substation, California.
ALKALI SOILS.
453
the latter causing a reversal of the formation of sodic carbonate
that had been induced by the former.
Exceptional Conditions. — While the phenomena of alkali
lands as outlined above probably represent the vastly predomi¬
nant conditions on level lands, yet there are exceptions due to
surface conformation, and the local existence of sources of
alkali salts outside of the soil itself. Such is the case where
salts ooze out of strata cropping out on hillsides, as at some
points in the San Joaquin Valley in California, and in parts of
New Mexico, Colorado and Wyoming; also where, as in the
Hungarian plain, saline clays underlie within reach of surface
evaporation.
Again, it not infrequently happens that in sloping valleys or
basins, where the central (lowest) portion receives the salts
leached out of the soils of the adjacent slopes, we find belts of
greater or less width in which the alkali impregnation may
reach to the depth of ten or twelve feet, usually within more or
less definite layers of calcareous hardpan, likewise the outcome
of the leaching of the valley slopes. Such areas, however, are
usually quite limited, and are at present scarcely reclaimable
without excessive expenditure ; the more as they are often un¬
derlaid by saline bottom water. In these cases the predominant
saline ingredient is usually common salt, as might be expected
and as is exemplified in the Great Salt Lake of Utah, in the
Antelope and Perris Valleys, and in Salton basin in California;
in the Yellowstone valley near Billings, Mont.1 in the Aralo-
Caspian desert, and at many other points.
Conclusions. — Summing up the conclusions from the fore¬
going facts and considerations, we find that —
( 1 ) The amount of soluble salts in alkali lands is usually
limited ; they are not ordinarily supplied in indefinite quantities
from the bottom-water below. These salts have mostly been
formed by weathering in the soil-layer itself.
(2) The salts move up and down within the upper four or
five feet of the soil and subsoil, following the movement of the
moisture; descending in the rainy season to the limit of the
annual moistening as a maximum, and then reascending or not,
according as surface evaporation may demand. At the end of
1 Farmer’s Bull. No. 88, U. S. Dept. Agr., 1899.
454
SOILS.
the dry season, in untilled irrigated land, practically the entire
mass of salts may be within six or eight inches of the surface.
(3) The direct injury to vegetation1 is caused largely
within a few inches of the surface, by the corrosion of the bark,
usually near the root crown. This corrosion is strongest when
carbonate of soda (salsoda) forms a large proportion of the
salts; the soda then also dissolves the vegetable mold and
causes blackish spots in the soil, popularly known as black
alkali.
(4) The injury caused by carbonate of soda is aggravated
by its action in puddling the soil so as to cause it to lose its
crumbly or flaky condition, rendering it almost or quite un-
tillable and impervious. It also tends to form in the depths of
the soil-layer a tough, impervious hardpan, which yields neither
to plow, pick, nor crowbar. Its presence is easily ascertained
by means of a pointed steel sounding-rod.
(5) While alkali lands share with other soils of the arid
region the advantage of unusually high percentages of plant-
food in the insoluble form, they also contain, alongside of the
noxious salts, considerable amounts of water-soluble plant-
food. When, therefore, the action of the noxious salts is done
away with, they should be profusely and lastingly productive ;
particularly as they are always naturally somewhat moist in
consequence of the attraction of moisture by the salts, and are
therefore less liable to injury from drought than the same soils
when free from alkali.
1 For a general statement and discussion of the physiological effects of saline
solutions on plants, see chapter 26.
CHAPTER XXIII.
UTILIZATION AND RECLAMATION OF ALKALI LANDS.
Alkali-Resistant Crops. — The most obvious mode of utiliz¬
ing alkali lands is to occupy them with crops not affected by the
noxious salts. Unfortunately but few such crops of general
utility have as yet been found for the stronger class of alkali
lands. The question is always one of degree, which frequently
cannot be decided without an actual determination of the
amount and kind of salts to be dealt with, to which the crops
can then be adapted in accordance with the greater or less sensi¬
tiveness of the several plants, as indicated in the table of toler¬
ances given farther on. But aside from this, there are certain
general measures and precautions which in any case will serve
to mitigate the effect of the alkali salts. Foremost among
these, and applicable everywhere, is the prevention of evapora¬
tion to the utmost extent possible.
Counteracting Evaporation. — Since evaporation of the soil-
moisture at the surface is what brings the alkali to the level
where the main injury to plants occurs, it is obvious that evapo¬
ration should be prevented as much as possible. This is the
more important, as the saving of soil-moisture, and therefore
of irrigation water, is attainable by the same means.
Three methods for this purpose are usually practiced, viz.,
shading, mulching, and the maintenance of loose tilth in the
surface soil to such depth as may be required by the climatic
conditions.
As to mulching, it is already well recognized in the alkali
regions of California as an effective remedy in light cases.
Fruit trees are frequently thus protected, particularly while
young, after which their shade alone may (as in the case of
low-trained orange trees) suffice to prevent injury. The same
often happens in the case of low-trained vines, small-fruit, and
vegetables. Sanding of the surface to the depth of several
inches was among the first attempts in this direction; but the
455
456
SOILS.
necessity of cultivation, involving the renewal of the sarid each
season, renders this a costly method. Straw, leaves, and ma¬
nure have been more successfully used ; but even these, unless
employed for the purpose of fertilization, involve more ex¬
pense and trouble than the simple maintenance of very loose
tilth of the surface soil throughout the dry . season; a remedy
which, of course, is equally applicable to hoed field crops, and
is in the ease of some of these — e. g., cotton — a necessary con¬
dition of cultural success everywhere. The wide prevalence
of “ light ” soils in the arid regions, from causes inherent in
the climate itself, renders this condition relatively easy of ful¬
filment.
Turning-under of Surface Alkali. — Aside, however, from
the mere prevention of surface evaporation, another favorable
condition is realized by this procedure, namely the comming¬
ling of the heavily salt-charged surface-layers with the rela¬
tively non-alkaline subsoil. Since in the arid regions the roots
of all plants retire farther from the surface because of the
deadly drought and heat of summer, it is usually possible to
cultivate deeper than could safely be done with growing crops
in humid climates. Yet even there, the maxim of “ deep prep¬
aration and shallow cultivation ” is put .into practice with ad¬
vantage, only changing the measurements of depth to corre¬
spond with the altered climatic conditions. Thus while in the
humid States, three to four inches is the accepted standard of
depth for summer cultivation to preserve moisture without
injury to the roots, that depth must in the arid region fre¬
quently be doubled in order to be effective ; and will even then
scarcely touch a living root in orchards and vineyards, particu¬
larly in unmanured and unirrigated land.
A glance at fig. 63, chapt. 22, p. 431), will show the great
advantage of extra-deep preparation in commingling the alkali
salts accumulated near the surface with the lower soil-layers,
diffusing the salts, say through twelve instead of six inches of
soil mass. This will in very many cases suffice to render the
growth of ordinary crops possible if, by subsequent frequent
and thorough cultivation, surface evaporation, and with it the
re-ascent of the salts to the surface, is prevented.
A striking example of the efficiency of this mode of proced¬
ure was observed at the Tulare substation, California, where a
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 45;
portion of a very bad alkali spot was trenched to the depth of
two feet, throwing the surface soil to the bottom. The spot
thus treated produced excellent wheat crops for two years — the
time it took the alkali salts to reascend to the surface.
It should therefore be kept in mind that whatever else is
done toward reclamation, deep preparation and thorough culti¬
vation must be regarded as prime factors for the maintenance
of production on alkali lands.
The Efficacy of Shading, already referred to, is strikingly
illustrated in the case of some field crops which, when once
established, will thrive on fairly strong alkali soil, provided
that a good thick “ stand ” has once been obtained. This is
notably true of the great forage crop of the arid region, alfalfa
or lucern. Its seed is extremely sensitive to “ black ” alkali,
and will decay in the ground unless protected against it by the
use of gypsum in sowing. But when once a full stand has been
obtained, the field may endure for many years without a sign
of injury. Here two effects combine, viz., the shading, and the
evaporation through the deep roots and abundant foliage,
which alone prevents, in a large measure, the ascent of the
moisture and salts to the surface. The case is then precisely
parallel to that of the natural soil (see p. 432, chapter 22), ex¬
cept that, as irrigation is practiced in order to stimulate produc¬
tion, the sheet of alkali hardpan will be dissolved and its salts
spread through the soil more evenly. The result is that so soon
as the alfalfa is taken off the ground and the cultivation of
other crops is attempted, an altogether unexpectedly large
amount of alkali comes to the surface and greatly impedes, if
it does not altogether prevent, the immediate planting of other
crops. Shallow-rooted annual crops that give but little shade,
like the cereals, while measurably impeding the rise of the
salts during their growth (see fig. 70, page 452) frequently
allow of enough rise after harvest to prevent reseeding the
following season.
“ TV eutraliffng ” Black Alkali. — Since so little carbonate of
soda as one-tenth of one per cent, may suffice to render some
soils uncultivable, it frequently happens that its mere trans¬
formation into the sulfate is sufficient to remove all stress from
alkali. Gypsum (land plaster) is the cheap and effective agent
to bring about this transformation, provided water be also
453
SOILS.
present. The amount required per acre will, of course, vary
with the amount of salts in the soil, all the way from a few
hundred pounds to several tons in the case of strong alkali
spots; but it is not usually necessary to add the entire quantity
at once, provided that sufficient be used to neutralize the sodic
carbonate near the surface, and enough time be allowed for the
action to take place. In very wet soil, and when much gypsum
is used, this may occur within a few days; in merely damp soils
in the course of months; but usually the effect increases for
years, as the salts rise from below.
The effect of gypsum on black-alkali land is often very strik¬
ing, even to the eye. The blackish puddles and spots disappear,
because the gypsum renders the dissolved humus insoluble and
thus restores it to the soil. The latter soon loses its hard,
puddled condition and crumbles and bulges into a loose mass,
into which water now soaks freely, bringing up the previously
depressed spots to the general level of the land. On the sur¬
face thus changed, seeds now germinate and grow without hin¬
drance; and as the injury from alkali occurs at or near the sur¬
face, it is usually best to simply harrow in the plaster, leaving
the water to carry it down in solution. Soluble phosphates
present are decomposed so as to retain finely divided, but less
soluble earth phosphates in the soil.
It must not be forgotten that this beneficial change may go
backward if the land thus treated is permitted to be swamped
by irrigation water or otherwise. Under the same conditions
naturally white alkali may turn black (see above, chapter 22,
p. 451). Of course, gypsum is of no benefit whatever on soils
containing no “ black ” alkali, but only (“ white ”) Glauber’s
and common salt.
Removing the Salts from the Soil. — In case the amount of
salts in the soil should be so great that even the change worked
by gypsum is insufficient to render it available for useful crops,
the only remedy left is to remove the salts, partially or wholly,
at least from the surface of the land. Three chief methods are
available for this purpose. One is to remove the salts, with
more or less earth, from the surface at the end of the dry
season, either by sweeping or by means of a horse scraper set
so as to carry off a certain depth of soil. Thus sometimes in a
single season one-third or one-half of the total salts may be got
UTILIZATION AND RECLAMATION OF ALKALI LANDS.
459
rid of, the loss of a few inches of surface soil being of little
moment in the deep soils of the arid region. Another method
affording partial relief is to flood the land for a sufficient
length of time to carry the alkali three or more feet below the
surface, then carefully preventing its reascent by suppressing
evaporation (see this chapter, p. 455) as much as possible.
The best of all, the final and universally efficient remedy, is to
leach the alkali salt out of the soil into the country drainage ;
supplementing by irrigation water what is left undone by the
deficient rainfall.
It is not practicable, as many suppose, to wash the salts off
the surface by a rush of water, as they instantly soak into the
ground at the first touch. Nor is there any certain relief from
allowing the water to stand on the land and then drawing it off ;
in this case also the salts soak down ahead of the water, and
the water standing on the surface remains almost unchanged.
In very pervious soils and in the case of white alkali, the
washing-out can often be accomplished without special provis¬
ion for underdrainage, by leaving the water on the land suffi¬
ciently long. But the laying of regular underdrains greatly
accelerates the work, and renders success certain.
Leaching-Down. — In advance of underdrainage, it is quite
generally feasible, where the land has been leveled and diked
for irrigation by surface flooding, to leach the salts out of the
first three or four feet by continued flooding, thus taking them
out of reach of the crop roots, or at all events giving the seed
an opportunity to escape injury from alkali. This plan is es¬
pecially effective in the case of alfalfa, the young seedlings of
which are very sensitive, while the grown plant is rather re¬
sistant. In order to obtain this relief so as to know what is
being accomplished, the farmer should ascertain beforehand
how fast water will soak down in his ground j1 for in heavy clay
soils, and especially in those containing black alkali, the soak-
age is sometimes so slow that the upward diffusion of the salts
keeps pace with the downward soakage ; in which case nothing
is accomplished by flooding, and underdrainage is the only
remedy. But in most soils of the arid region flooding from
three days to a week will remove the alkali beyond reach of
the roots of ordinary crops. If subsequently irrigation is done
1 See p. 242, Chap. 13.
460
SOILS.
by means of deep furrows, the alkali salts may be either kept
at a low level continuously, or if the land be at all pervious, the
alkali may ultimately be permanently leached out into the sub¬
drainage by farther hooding. When the alkali has not accumu¬
lated near the surface to any great extent, irrigation by deep
furrows may, alone, afford all the relief needed.
In the case illustrated by figures 71 and 72, irrigation by
shallow furrows with water too strongly charged with salts
had so far added to the natural alkali-content of the land that
Fig. 71. — Lemon Orchard Affected by Alkali; Before Deep Irrigation.
the lemon trees were being defoliated. Upon the advice of the
California Station the deep-furrow system was adopted, and
within two years the results were as shown in figure 72,
the salts having been carried down and diluted so as to be¬
come harmless.
Underdrainage the Final and Universal Remedy for Alkali.
— When we underdrain an alkali soil, we adopt the very means
by which the existence of alkali lands in the humid regions is
wholly prevented ; the leaching-out of the soluble salts formed
in soil-weathering as fast as they are formed. The long and
abundant experience had with underdrainage in reclaiming
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 46i
saline sea-coast lands, applies directly and cogently to alkali
lands. It is the universal remedy for all the evils of alkali,
and its only drawback is the first expense, and the necessity for
obtaining an outlet for the drain waters, which cannot always
be bad on the owner's land. Hence it requires co-operation or
legislation to render the great improvement of underdrainage
feasible. Such legislation is well established in the old world,
and has been enacted in several states even of the humid
region. Where irrigation is practiced as a matter of necessity,
Fig. 72. — The Above Orchard after Alkali was Driven Down by Deep Irrigation, followed by
Cultivation.
underdrainage is a correlative necessity, both to avoid the evils
of over-irrigation and to relieve the land of noxious alkali
salts.
The drainage law now existing in California does not go
farther than to authorize the formation of drainage districts,
within which the necessary taxes may be levied ; and there is
some difficulty in securing popular action. But bitter experi¬
ence will doubtless in time compel unanimity, such as now ex¬
ists, e. g ., in Illinois, where drainage is not nearly so urgently
needed as it is in the irrigation States.
462
SOILS.
Possible Injury to Land by Excessive Leaching. — It should
not be forgotten, however, that excessive leaching of under¬
drained land by flooding is liable to injure the soil in two
ways: first, by the removal of valuable soluble plant- food; and
further, by rendering the land less retentive of moisture, such
retention being favored by the presence of small amounts of
alkali salts, not sufficient to injure crops. After the salts have
been carried down to a sufficient depth to prevent injury to
annual crops, and with proper subsequent attention to the pre¬
vention of surface evaporation, the flooding will not need to
be repeated for several years. Thus in many soils excellent
crops may be grown even in strong alkali land, pending the
establishment of permanent drainage systems.
The importance of thoroughly washing the alkali deeply into the
soil before the seed is planted, and keeping it there by proper means
until the foliage of the plant shades the soil sufficiently to prevent the
rise of moisture and alkali, is well illustrated in fields in the region of
Bakersfield, Cal., where alfalfa is now growing in soils once heavily
charged with alkali. From one of these fields samples of soil were
taken where the alkali was supposed to be strongest beneath the alfalfa,
and also from an adjoining untreated alkali spot, which was said to
represent conditions before alfalfa was planted. The results are given
in pounds per acre in four feet depth.
Sulfate.
Car-
Common
Total
bonate.
Salt.
Alkali.
Alkali spot before alfalfa was planted.
60,120
720
175,840
236,680
Alfalfa field ; alkali washed down . . . .
14,400
. . .
1,040
18,640
Here the surface foot of the natural soil contained nearly 140,000
pounds of common salt, a prohibitory amount. Similar experience has
been had near Yuma, Arizona.
Difficulty in Draining “ Black ” Alkali Lands. — An import¬
ant exception to the efficacy of draining, however, occurs in
the case of black alkali in most lands. In this case either the
impervious hardpan or (in the case of actual alkali spots) the
1 Bull. 133, Cal. Expt. Sta., by R. H. Loughridge.
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 463
impenetrability of the surface soil itself will render even under¬
drains ineffective unless the salsoda and its effects on the soil
are first destroyed by the use of gypsum, as above detailed.
This is not only necessary in order to render drainage and
leaching possible, but is also advisable in order to prevent the
leaching-out of the valuable humus and soluble phosphates,
which are rendered insoluble (but not unavailable to plants)
by the action of the gypsum. Wherever black alkali is found
in lands not very sandy, the application of gypsum should
precede any other efforts toward reclamation. Trees and
vines already planted may be temporarily protected from the
worst effects of the black alkali by surrounding the trunks with
gypsum or with earth abundantly mixed with it. Seeds may be
similarly protected in sowing, and young plants in planting.
Swamping of Alkali Lands. — It should, however, be remem¬
bered that the swamping of alkali lands, whether of the white
or black kind, is fatal not only to their present productiveness,
but also, on account of the strong chemical action thus induced,
greatly jeopardizes their future usefulness. Many costly in¬
vestments in orchards and vineyards have thus been rendered
unproductive, or have even become a total loss.
Reduction of Alkali by Cropping. — Another method for
diminishing the amount of alkali in the soil is the cropping
with plants that take up considerable amounts of salts. In
taking them into cultivation, it is advisable to remove en¬
tirely from the land the salt growth that may naturally cover
it, notably the greasewoods ( Sarcobatus , Allenrolfea) , with
their heavy percentage of alkaline ash (12 to 20 per cent).
Crop plants adapted to the same object are mentioned farther
on. Such crops should also, of course, be wholly removed
from the land.
Total Amounts of Salts Compatible with Ordinary Crops ;
Tolerance of Culture Plants. — Since the amount of alkali that
reaches the surface layer is largely dependent upon the varying
conditions of rainfall or irrigation, and surface evaporation, it
is difficult to foresee to what extent that accumulation may go,
unless we know the total amount of salts present that may be
called into action. This, as already explained, can ordinarily
be ascertained by the examination of one sample representing
464
SOILS.
the average of a soil column of four feet. By calculating the
figures so obtained to an acre of ground, we can at least ap¬
proximate the limits within or beyond which crops will suc¬
ceed or perish. Applying this procedure to the cases repre¬
sented in the diagrams (pp. 434, 452, chapter 22) and estimat¬
ing the weight of the soil per acre-foot at 4,000.000 pounds, we
find in the land on which barley refused to grow the figures
32,470 and 43,660 pounds of total salts per acre, respectively
corresponding to 0.203 per cent, for the first figure (the second,
representing' only the two surface feet, is not strictly compar¬
able). For the land on which barley gave a full crop, we find
for the Mav sample 25,550 pounds, equivalent to 0.159 per cent,
for the whole soil column of four feet. It thus appears that for
barley the limits of tolerance lie between the above twTo figures.
It should be noted that in this case a full crop of barley was
grown even when the' alkali consisted of fully one-half of the
noxious carbonate of soda ; proving that it is not necessary in
every case to neutralize the entire amount of that salt by means
of gypsum, which in the present case would have required
about gl/2 tons of gypsum per acre — a prohibitory expenditure.
Relative Injuriousness of the Several Salts. — Of the three
sodium salts that usually constitute the bulk of “ alkali,” only
the carbonate of soda is susceptible of being materially changed
by any agent that can practically be applied to land. So far as
we know, the salt of sodium least injurious to ordinary vege¬
tation is the sulfate, commonly called Glauber’s salt, which
ordinarily forms the chief ingredient of “ white ” alkali.
Thus barley is capable of resisting about five times more of the
sulfate than of the carbonate, and quite twice as much as of
common salt. Since the maximum percentage that can be re¬
sisted by plants varies materially with the kind of soil, it is
difficult to give exact figures save with respect to particular
cases. For the sandy loam of the Tulare substation, Cali¬
fornia, for instance, the maximum for cereals may be approxi¬
mately stated to be one-tenth of 1 per cent, for salsoda; a
fourth of 1 per cent, for common salt; and from forty-five to
fifty one-hundredths of one per cent of Glauber’s salt. For clay
soils the tolerance is in general markedly less, especially as re¬
gards the salsoda; since in their case the injurious effect on the
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 465
tilling qualities of the soil, already referred to, is superadded
to the corrosive action of that salt upon the plant.
Effect of Differences in Composition of Alkali Salts on Beets. — The
marked differences which may occur as the result of even slight variations
in the proportions of the several salts is well illustrated in the subjoined
diagram of observations made by Dr. G. W. Shaw, of the Cal. Expt.
station, upon beet fields in the neighborhood of Oxnard, Cal. The
Fig. 73. — Alkali curve showing percentage of Alkali Salts in field of Sugar Beets, Oxnard, Calif.
Fig. 74. — Beets from corresponding positions in the above field.
lands lie not far from the sea-shore, and saline water underruns them
for considerable distance inland. The soil and subsoil are quite sandy,
so that it takes irrigation water only about seven hours to penetrate
30
466
SOILS.
from the surface to bottom water at seven feet depth. The land 00
which these observations were made are apparently level to the eye,
though probably the alkali belts on which the sugar beets were “ poor ”
are slightly depressed swales.
It will be noted that here the beets were “ good ” where the
sulfate (Glauber’s salt) ranged up to .8%, with .10 to .20 of
common salt ; but that so soon as the latter rose above .20, the
beets were poor despite the low percentage of Glauber’s salt;
then became “ good ” again so soon as the common salt fell
below .20%, although the Glauber’s salt increased.
TOLERANCE OF VARIOUS CROP PLANTS.
The following table, compiled by Dr. R. H. Loughridge
mainly from his own observations,1 gives the details of the
tolerance for various culture plants as ascertained at the several
experiment substations in California, as well as at other points
in that State and in Arizona where critical cases could be
found. It is thought preferable to investigate analytically such
cases in the field, rather than to attempt to obtain results from
small-scale experiments artificially arranged, in which sources
of error arising from evaporation and other causes are most
difficult to avoid.
The table is so arranged as to show the maximum tolerance thus far
observed for each of the three single ingredients, as well as the maximum
of total salts found compatible with good growth. In view of the ex¬
tremely variable proportions between the three chief ingredients found
in nature, this seems to be the only manner in which the observations
made can be intelligibly presented, until perhaps a great number of such
data shall enable us to evolve mathematical formulae expressing the
tolerance for the possible mixtures for each plant, Fc/r it is certain
that the tolerance-figures will be quite different in presence of other
salts, from those that would be obtained for each salt separately ; or for
the calculated mean of such separate determinations, proportionally
pro-rated. It must also be remembered that in all alkali soils, lime
carbonate is abundantly present, as is, nearly always, a greater or less
amount of the sulfate (gypsum). As already stated, according to the in¬
vestigations of Cameron not only these compounds, but also calcium
chlorid, exert a protective influence against the injury to plant growth
from compounds of sodium and potassium. The figures here given can
1 Bulletins Nos. 128, 133 and 140, Calif. Expt. Station.
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 467
therefore be regarded only as approximations, subject to correction by
farther observation. They are arranged from the highest tolerances
downward, for each of the three ingredients, as well as for the totals.
The latter are not, of course, the sums of the figures given in the pre¬
ceding columns, but independent data.
HIGHEST AMOUNT OF ALKALI IN WHICH FRUIT TREES WERE FOUND
UNAFFECTED.1
Arranged from highest to lowest. Pounds per acre in four feet depth.
Sulfates
(Glauber’s Salt).
Carbonate
(Salsoda).
Chlorid
(Common Salt).
Total Alkali.
Grapes .
40,800
Grapes .
7.550
Grapes .
9,640
Grapes .
45,70°
Olives .
30,640
Oranges .
3.84°
Olives .
6,640
Olives .
40,160
Figs .
24,480
Olives .
2,880
Oranges .
3,360
Almonds .
25,560
Almonds .
22,720
Pears .
1,760
Almonds .
2,400
Figs .
26,400
Oranges .
18,600
Almonds .
1,440
Mulberry .
2,240
Oranges . . .
2 1 ,840
Pears .
17,800
Prunes .
1,360
Pears .
1,360
Pears .
20,920
Apples .
14,240
Figs .
1,120
Apples .
1,240
Apples .
16,120
Peaches .
9,600
Peaches .
680
Prunes .
1,200
Prunes .
1 1 ,800
Prunes .
9,240
Apples .
640
Peaches .
1,000
Peaches .
1 1,280
Apricots .
8,640
Apricots .
4X0
Apricots .
960
Apricots .
10.080
Lemons .
4,480
Lemons .
480
Lemons .
800
Lemons..' .
5,760
Mulberry .
3.360
Mulberry.. . .
Piers .
Mulberry .
5,76o
OTHER TREES.
Kolreuteria . . . .
5 1 ,040
Kolreuteria .
• 9,920
Or. Sycamore. .
. 20,320
Kolreuteria. . . .
Eucal. am .
34,72°
Or. Sycamore...
• 3,200
Kolreuteria ....
Or. Sycamore . .
• 42,760
Or. Sycamore.. .
19,240
Date Palm.. . . . .
2,800
Eucal. am .
2,960
Eucal. am .
Wash. Palm.. . .
I3>°4°
Encal. am .
Camph. Tree.. .
Wash. Palm....
. . 15,200
Date Palm .
Camph. Tree. . .
5,5°°
5,280
Wash. Palm .
Camph. Tree. . . .
. 1,200
320
Wash Palm _
Date Palm .
Camph. Tree. . .
. . 8,32s
. . 7,020
SMALL CULTURES.
Saltbush .
. 125,640
Saltbush .
Modiola .
Saltbush .
Alfalfa, old . . .
102,480! Barley .
.. 12,170
Saltbush .
.. 12,520
Alfalfa, old .
.110,320
Alfalfa, young.
. 11,120
Bur Clover .
.. 11,300
Sorghum .
Alfalfa, young. .
• 13,120
Hairy Vetch.. .
• 63,720
Sorghum .
Celery .
Sorghum .
Sorghum .
. 61,840
Radish .
( )nions .
.. 5,810
Hairy V etch . . .
Sugar Beet.. . .
52.640
Modiola .
Potatoes .
... 5,810
Radish .
Sunflower .
52,640
Sugar Beet .
Sunflower .
. . 5,440
Sunflower... .
• 59,840
Radish .
. 51,880
Gluten Wheat. .
. . 3,000
Sugar Beet2. . . .
Sugar Beet .
. . 59,840
Artichoke .
. 38,720
Artichoke .
Barley .
Modiola .
• 52,420
Carrot .
Lupin .
Hairy Vetch. . .
Artichoke .
Gluten Wheat.
20,960
Hairy Vetch... .
. 2,480
Lupin .
Carrot .
Wheat .
• i5,I2°
Alfalfa .
Carrot .
Barley .
Barley .
12,020
Grasses .
. . 2,300
Radish .
Gluten Wheat..
• 24,320
Goat s Rue . . .
10,880
Kaffir Corn. . . .
Rye .
Wheat .
. 17,280
Rye .
9,800
Sweet Corn....
Artichoke .
Bur Clover. . . .
Canaigre .
. 9,160
Sunflower .
Gluten Wheat..
. . 1,480
Celery .
13,680
Ray Grass .
6,920
Wheat .
Wheat .
Rye .
Modiola .
. 6,800
Carrot .
Grasses .
Goat’s Rue ....
Bur Clover . . .
• 5>7°°
Rye .
White Melilot..
440
Lupin .
Lupin .
• 5,44°
Goat's Rue ...
Goat's Rue .
Canaigre .
White Melilot.
Celery .
• 4,920
. 4,080
White Melilot..
Canaigre .
. . 480
Canaigre .
80
Onions .
Potatoes .
• 38,48°
Saltgrass .
44,000
Saltgrass .
Saltgrass .
Saltgrass .
1 The several columns of figures are independent of each other; the “total”
alkali is not the summation for the three salts in the same line.
2 Figures taken from Bulletin 169, Calif. Expt. Station, June, 1905.
468
SOILS.
Comments on the Above Table. — Considering- in this table,
first, the plants suitable for the stronger class of alkali lands,
it may be said generally that the search for widely acceptable
kinds has not been very successful. It is true that cattle will
nibble green salt grass ( Distichlis spicata) , but will soon
leave it for any dry feed that may be within reach. The enor¬
mous amount of salts which it will tolerate in the soil on
which it grows, and the doubtless correspondingly large
amount of those salts which it will absorb, judging from its
taste, sufficiently explain the reluctance of cattle to feed on it
to any considerable extent.
The same is true of all the fleshy plants that grow on the
stronger alkali lands, and are known under the general desig¬
nation of “ alkali weeds.” When stock unaccustomed to it
are forced by hunger to feed on such vegetation to any con¬
siderable extent, disordered digestion is apt to result ; which
in such ranges, however, is often counteracted by feeding on
aromatic or astringent antidotes, such as the gray sagebrush
and the more or less resinous herbage of plants of the sun¬
flower family.
In the Great Basin region, lying between the Sierra Nevada
and the front range of the Rocky Mountains, there are, aside
from the grasses, numerous herbaceous and shrubby plants
that afford valuable pasturage for stock,1 2 and some of these
grow on moderately strong alkali land ; the same is true in
California. It is quite possible that some of these will be found
to lend themselves to ready propagation for culture purposes
as well as they do for restocking the ranges. But thus far
none have found wider acceptance, probably because their stiff
branches and upright habit render them inconvenient to handle.
It will require more extended experience and experiment be¬
fore any of these will be definitely adopted for propagation by
farmers and stockmen.
1 See Bulletin No. i6of the Wyoming Experiment Station; also Bulletin Nos,
2 and 12 of the Division of Agrostology, and Farmers’ Bulletin No. 108, U. S.
Department of Agriculture.
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 469
Saltbushes , arid Herbaceous Crops.
Australian Saltbushes. — Experience in California indicates
that in the more southerly portion of the arid region, un¬
palatable native plants may be largely replaced, even on the
ranges, by one or more species of the Australian saltbushes
( Atriplex spp .), long ago recommended by Baron von Mueller
of Melbourne; of which one (A. sernibaccata) has proved emi¬
nently adapted to the climate and soil of California and is
readily eaten by all kinds of stock. The facility with which it
is propagated, its quick development, the large amount of feed
yielded on a given area, even on the strongest alkali land ordi¬
narily found, and its thin, flexible stems, permitting it to be
handled very much like alfalfa, seem to commend it especially
to the farmers’ consideration wherever better forage plants can¬
not be grown and the climate will permit of its use. It does
not, however, resist the severe cold of the interior plateau
country, and is wholly out of place in the Pacific Coast region
where summer fogs prevail. Most of the other Australian
species have an upright, shrubby habit, which adapts them bet¬
ter to browsing than to pasture proper. The same is true of
the Argentine species (A. Cachiyuyum) , which in its native
pampas is highly esteemed for that purpose, and succeeds well
in California. Of other Australian saltbushes, A. halimoides ,
vesicaria and leptocarpa are the most promising; the latter is
somewhat similar in habit to the sernibaccata, but is not as
vigorous a grower. Since some of the saltbushes take up
nearly one fifth of their dry weight of ash ingredients,1 largely
common salt, the complete removal from the land of a five-ton
crop of saltbush hay will take away nearly a ton of the alkali
salts per acre. This will in the course of some years be quite
sufficient to reduce materially the saline contents of the land,
and will frequently render possible the culture of ordinary
crops.
Modiola. — Alongside of the saltbushes, the Chilean plant
1 Analyses made at the California station show 19.37 percent of ash in the air-
dry matter of Australian saltbush. (See California Station Bulletin No. 105;
E. S. R., vol. 6, p. 718). Analyses of Russian thistle have been reported showing
over 20 per cent of ash in dry matter. (See Minnesota Sta. Bulletin No. 34; Iowa
Sta. Bull. No. 26; E. S. R., vol. 6, pp. 552-553).
470
SOJLS.
Modiola procumbens, now generally known as modiola simply,
deserves attention, as it makes acceptable pasture where alfalfa
fails to make a stand on account of alkali. It is a trailing plant
with medium-sized, roundish foliage, and roots freely at the
joints where they touch the ground. Unlike the saltbushes it
is therefore a formidable weed where it is not wanted; but as
according to California experience it resists as much as 52,000
pounds of salts per acre, even when 41,000 of these is common
salt, it is likely to be useful in many cases, particularly as an
admixture to a saltbush diet for stock, as it does not absorb
as much salt as the latter. It seems best adapted to pasturage.
As the table shows that, once grown to the age of a few
years, alfalfa will resist a percentage of alkali next to the salt¬
bush, it will generally be worth while, in lands otherwise
adapted to alfalfa, to prepare the land by leaching-down (see
above) so as to secure a stand of the more valuable crop.
Native Grasses.1 — Of all known plants that stock will eat
somewhat freely, the tussock grass ( Sporobolus airoides, of
which a figure is given farther on), a native of the southern
arid region, endures the largest amounts of alkali ; having been
found growing well on land containing the enormous amount
of nearly half a million pounds of salts per acre, although it
will thrive with only 49,000 pounds in the soil. What it will
do under cultivation has never been fairly tested ; but its bare
tussocks, killed by the excessive browsing of stock, testify to
its acceptableness as forage. It does not seem to absorb ex¬
cessive amounts of salts.
Aside from the alkali grass proper (DisticJilis) , mentioned
above, the so-called rye grass of the Northwest ( Elymus con-
densatus) is probably, next to the tussock grass, the most re¬
sistant species among the wild grasses. Its southern form,
with several others not positively identified, occupies largely
the milder alkali lands of southern California. This grass,
though rather coarse, is regularly cut for hay in the low
grounds of Oregon and Washington.
1 It should be understood that the plants so referred to are exclusively the true
grasses, reeognized as such by every child, and not forage plants generally; which
are sometimes so designated ; not only by farmers, but by some authors who fail
to appreciate the practical importance of the distinction, which makes it necessary
that farmers should be taught to understand it.
UTILIZATION AND RECLAMATION OF ALKALI LANDS.
471
Doubtless some of the indigenous grasses of the interior
plateau region and of the great plains east of the Rocky Moun¬
tains, such as the buffalo and grama grasses, as well as several
of the wheat grasses ( Agropyron ) and bunch grasses ( Fes -
tuca, Poa, Stipa, etc.) will prove resistant to larger propor¬
tions of alkali than the meadow and pasture grasses of the
regions of summer rains.
Cultivated Grasses. — The superficial rooting and fine
fibrous roots of the true annual grasses render them, as a
whole, rather sensitive to alkali ; yet the cereals — barley, wheat,
rye and oats — resist, as the table shows, the average alkali
salts to the extent of from 17,000 total salts, with not exceed¬
ing 1500 pounds of carbonate, in the case of the more delicate
varieties of wheat, to over 25,000 pounds per acre in the case
of barley, which with the gluten wheats and rye seems to have
the highest tolerance-figure. The special adaptation of gluten
wheats to arid conditions is thus emphasized. The roots of
these cereals are comparatively stout, with thick epidermis.
Among the cultivated forage grasses proper, the Australian
variety of the English ray (generally miscalled rye) grass
seems most resistant. The eastern fescues, Kentucky blue
grass, and others at home in the humid region are easily in¬
jured, as those who try to maintain lawns on alkali-tainted
lands, or by irrigation with alkali waters, know to their sorrow.
To these grasses common salt and bittern (magnesium chlorid)
seem to be particularly injurious, and they tolerate but little
“ black alkali.”
On the rather close-textured soil at Chino, California, the
loliums, including the darnel (‘‘California cheat”), and the
Australian and Italian ray (“ rye") grasses, succeed fairly on
land containing as much as 6,000 pounds of (white) salts.
Most other cultivated grasses failed conspicuously alongside
of these. It must be remembered that in more loose-textured,
sandy lands than those in which these tests were made, the
above figures for tolerance would probably be increased by 30
percent or more.
Maize is rather sensitive to alkali, and suffers even on
slightly alkaline land, owing doubtless to the large develop¬
ment of fine white rootlets near the surface, so familiar to
corn-growers. The Sorghums , and especially Egyptian corn
472
SOILS.
(durra) are much less sensitive, as the table shows, and are
among the first crops to be tried on alkali lands. The related
millets share this resistance more or less, and we often see on
cultivated lands in the alkali region fine stands of barnyard
grass ( Panicum crusgalli) of which the variety (?) P. muti-
cum is said by observers of the U. S. Dept, of Agriculture to
be specially resistant, and acceptable to stock. One of the most
successful grasses on the light alkali lands near Chino, where
most of the commonly cultivated grasses fail, was a near
relative of the barnyard grass, the Eleusine coracana, which
produces heavy crops of a millet-like grain much relished by
poultry, and also by stock. This grass, largely grown in
Egypt, has succeeded well all over the ground whose alkali
content ranges up to 12,000 pounds per acre, but failed where
the salts reached 38,840 pounds in the surface foot. Next to
this, in point of success, were the pearl millet ( Pennisetum
typhoideum) and teosinte, Hungarian brome grass, and Japan¬
ese millet, on land containing about 9,000 pounds of (chiefly
“ white ") salts per acre.
Other Herbaceous Crops. Legumes. — Both the natural
growth of alkali lands and experimental tests seem to show
that this entire family (peas, beans, clovers, etc.) are among
the more sensitive and least available wherever black alkali
exists; while fairly tolerant of the white (neutral) salts. Ap¬
parently a very little salsoda suffices to destroy the tubercle¬
forming organisms that are so important a medium of nitro¬
gen-nutrition in these plants. Excepting the melilots, alfalfa
with its hard, stout and long taproot, seems to resist best of all
these plants.
As a general thing, taprooted plants, when once established, resist
best, for the obvious reason that the main mass of their feeding roots
reaches below the danger level. Another favoring condition, already
alluded to, is heavy foliage and consequent shading of the ground ;
alfalfa happens to combine both of these advantages. There has been
some difficulty in obtaining a full stand of alfalfa in the portion of the
Chino substation tract containing from 4000 to 6000 pounds of (largely
black) alkali salts per acre ; but once obtained, it has done very well.
The only other plant of this family that succeeds well on
this land, and even (at Tulare) on soil considerably stronger
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 473
(probably between 20,000 and 30,000 pounds) are the two
melilots, M. indica, and alba ; the latter (the Bokhara clover)
is a forage plant of no mean value in moist climates, but some¬
what restricted in its use in the arid region because of the
very high aroma it develops, especially in alkali lands ; so that
stock will eat only limited amounts, best when intermixed
with other forage, such as the saltbushes. The yellow melilot
is highly recommended by the Arizona Experiment Station as
a green-manure plant for winter growth ; but farther north it
is a summer-growing plant only, and is refused by stock. As
already stated, very few plants belonging to this family are
naturally found on alkali lands, and attempts to grow them,
even where only Glauber’s salt is present, have been but very
moderately successful.
For most of the legumes the limit of full success seems to
lie between 3000 and 4000 pounds to the acre. A marked ex¬
ception, however, occurs in the case of the hairy vetch, as
shown in the table, where it is credited, on the basis of re¬
peated experiments, with a tolerance of nearly 70,000 pounds.
This amount was attained, however, in rather sandy soils.
Probably some of the Algerian vetches will likewise prove
more resistant than those which are natives of humid climates.
Mustard Family. — As in the case of the legumes, wild plants
of the mustard family are rare on alkali lands; and correspond¬
ingly, the cultivated mustard, kale, rape, etc., fail even on land
quite weak in alkali. Their limit of tolerance seems to lie near
4,000 to 5,000 pounds per acre even of white salts. Hence
turnips and radishes do not flourish on alkali lands.
Sunflower Family. — Several of the hardiest of the native
'4t alkali weeds " belong to the sunflower family, and the com¬
mon wild sunflowers ( H elianthus calif ornicus and H. annuus)
are common on lands pretty strongly alkaline. The cultivated
Russian sunflower, as the table shows, resists the effects of
nearly 60,000 pounds of total alkali, of which 52,640 pounds
was sulfate (Glauber's salt), and 5440 common salt. This, it
will be seen, is a very high tolerance, so that this sunflower,
yielding such excellent poultry feed, is very widely available
Correspondingly, the “ Jerusalem artichoke,” itself a sun¬
flower, is among the available crops on moderately strong
alkali soils ; and so, doubtless, are other members of the same
474
SOILS.
relationship not yet tested, such as the true artichoke, salsify,
etc. Chicory, belonging to the same family, yielded roots at
the rate of twelve tons per acre, on land of the Chino tract
containing about 8.000 pounds of salts per acre.
Root Crops. — It seems to be generally true that root crops
suffer in quality, however satisfactory may be the quantity,
harvested on lands rich in salts, and especially in chlorids
(common salt). It was noted at the Tulare substation (Cali¬
fornia) that the tubers of the artichoke were inclined to be
“ squashy ” in the stronger alkali land, and failed to keep well;
the same was true of potatoes, which were very watery ; and
also of turnips and carrots. It is a fact well known in Europe,
that potatoes manured with kainit (chlorids of potassium and
sodium) are unfit for the manufacture of starch, and are gen¬
erally of inferior quality. But this is found not to be the case
when, instead of the chlorids, the sulfate is used; hence the ad¬
vice, often repeated by the California station, that farmers de¬
siring to use potash fertilizers should call for the “ high-grade
sulfate ” instead of the cheaper kainit, which adds to the in¬
jurious salts already so commonly present in lowland soils of
the arid region. Such root crops are, however, available for
stock feed.
The common beet (including the mangel-wurzel) is known
to succeed well on saline seashore lands, and it maintains its
reputation on alkali lands also. Being especially tolerant of
common salt, it may be grown where other crops fail on this
account ; but the roots so grown are strongly charged with
common salt, and have, as is well known, been used for the
purpose of removing excess of the same from seacoast-marsh
lands. Such roots are wholly unfit for sugar-making.
It is quite otherwise with Glauber's salt (sodium sulfate) ;
and as this is very commonly predominant in alkali lands,
either before or after the gypsum treatment, this fact is of
great importance, for it frequently permits of the successful
growing of the sugar beet ; as has been abundantly proved at
the Chino ranch, where land containing as much as 60,000
pounds of salts, mostly this compound, has yielded roots of
very high grade, both as to sugar percentage and purity. But
the analyses of the Oxnard soil show that more than 10,000
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 475
pounds of common salt will be required to render sugar beets
unsatisfactory for sugar-making.
Passing to stem crops, we find that asparagus, originally
itself a denizen of the sea-board, resists considerable amounts
(not yet exactly determined) of common salt as well as of
Glauber’s salt. It is even claimed that when grown with a
dressing of common salt the asparagus is more tender and
savory. But it is quite sensitive to “ black alkali,” which must
be neutralized with gypsum to render it harmless.
Celery did well with 13,640 pounds, of which nearly 10,000
was common salt. But with 30,000 pounds the plants were
killed.
Rhubarb was a conspicuous failure, even in the weak and
mostly “ white ” alkali lands of the Chino station tract.
Textile Plants. — Japanese hemp , while voung, seemed to
have a hard struggle with the alkali, but at the end of the sea¬
son stood eight feet high. The ramie plant, also, will bear
moderately strong alkali, apparently somewhat over 12,000
pounds per acre. Flax has not been tested in cultivation ; but
the wide distribution of wild flax all over the arid portions of
the States of Oregon and Washington, would seem to indicate
that it is not very sensitive. Another textile plant, the Indian
mallow ( Abut it on anicennae) , was found to fail on the Chino
alkali soil. But its close relative, cotton, does not seem to be
specially sensitive, according to the experience had with it in
the Merced river bottom in California; and its culture is exten¬
sive in Egypt, where no particular care seems to be exercised in
selecting the land for the crop. It is just possible that the
saline content of the soil has in California, as well as in the
Atlantic sea-islands, contributed to the superior length of the
fiber shown in the measurements made during the Census work
of 1880.1
Tolerance of Shrubs and Trees.
Grapevines. — The European grape, Vitis vinifera, is quite
tolerant of white or neutral alkali salts, and will resist even a
moderate amount of the black so long as no hardpan is allowed
to form. At the Tulare substation it was found that grape-
1 Report on Cotton Culture; 10th Census of the United States, vol. 5, pp. 23
to 34.
SOILS.
476
vines did well in sandy land containing 35,230 pounds of alkali
salts, of which one half was Glauber's salt, 9,640 pounds cor-
bonate of soda, 7,550 pounds of common salt, and 750 pounds
nitrate of soda. They were badly distressed where, of a total
of 37,020 pounds of alkali salts, 25,620 pounds was carbonate
of soda ; while where the vines had died out, there was found a
total of 73,930 pounds, with 37,280 pounds of carbonate. The
European vine, then, is considerably more resistant of alkali
even in its worst (black) form, than barley and rye, at least
on sandy land; and it seems likely that the native grapevines of
the Pacific coast, calif ornica, and arizonica, would resist even
better ; a point still under experiment.
Experience, however, has shown that vines rapidly succumb
when by excessive irrigation the bottom water is allowed to
rise, increasing the amount of alkali salts near the surface, and
shallowing the soil at their disposal. Such over-irrigation has
been a fruitful cause of injury to vineyards in the Fresno re¬
gion, and would doubtless if practiced kill most of the vines at
the Tulare substation, which are now flourishing. In such
cases, sometimes the formation of hardpan is followed by that
of a concentrated alkaline solution above it, strong enough to
corrode the roots themselves, and not only killing the vines,
but rendering the land unfit for any agricultural use whatso¬
ever. The swamping of alkali lands, whether of the white or
black kind, is not only fatal to their present productiveness,
but, on account of the strong chemical action thus induced,
greatly jeopardizes their future usefulness. Many costly in¬
vestments in orchards and vineyards have thus been rendered
unproductive, or have even become a total loss.
It should be remembered in this connection that as the roots
of vines will, when unobstructed, go to depths of fifteen and
even twenty feet, a subsequent rise of the bottom water from
leaky irrigation ditches will drown out the ends of the deep
roots and thus cause the whole root system to become diseased,
inevitably resulting in unproductiveness, if not death, of the
vine.
, Citrus Trees. — Although the high figure of nearly 27,000
pounds for the tolerance of citrus trees, as given in the table,
seems to place them rather high on the list, such high tolerance
actually occurs only in very sandy soils, and when common
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 477
salt is in small proportion. Generally speaking, the citrus
tribe are rather sensitive to alkali salts, and more especially to
common salt. In fact, as to the high tolerance-figure given in
the table, observed in sandy land, the alkali there contained
only a trace of common salt. Young seedling trees are par¬
ticularly sensitive; so that it is often difficult to obtain a stand
even when, later on, the feeding roots descend beyond the
reach of injury. In the close-textured lands of Chino, young
trees hardly maintained life with more than 5,000 pounds of
total salts. Near Riverside, full-grown trees perished under
the influence of bottom water containing 0.25%, or 146 grains
of salt per gallon, which impregnated the ground ; correspond¬
ing to about 9,000 pounds per acre in four feet.
In the sandy loam lands near Corona, trees eight years old
suffered severely when by irrigation with alkali-water the
alkali-content of the land reached 11,000 pounds per acre; as
illustrated in Figs. Nos. 44, and 45. At another point in
the same region, two representative trees were selected for
comparison, five rows apart on land absolutely identical; one
of these retained its leaves, though suffering, the other was
completely leafless. The leaching of the alkali to the depth of
four feet gave the following results, calculated to pounds per
acre :
Sulfates. Carbonates. Chlorids. Total.
Poor tree . 4,720 1680 2>52o 8,920
Better tree. . . 4,120 2,360 720 7,200
Ftere it is apparently the excess of common salt to which the
difference is due, and this despite the higher content of carbon¬
ate of soda in the soil bearing the better tree.
On the other hand, at the Tulare substation orange trees
(sour stock) maintain vigorous growth and good bearing in a
very sandy tract which to the depth of seven feet showed an
aggregate content of 26,840 pounds of salts (or 22,780 to
four feet depth) ; but which is never irrigated. (See diagram
No. 66). The salts in this case consists wholly of sulfate and
carbonate of soda in the ratio of fifty-four to forty-two, im¬
plying the presence of nearly 12,000 pounds of salsoda within
reach of the tree roots ; yet in the absence of common salt, no
perceptible injury or even stress upon the trees has been noted.
According to observations made in San Diego county, Calif.,
478
SOILS.
lemon trees are even more sensitive to common salt than
oranges, since a total content of 8,000 pounds per acre, about
one-third of which was common salt, seemed to render the
trees wholly unprofitable.
In view of these facts, showing that common salt is the por¬
tion of alkali by far most injurious to citrus trees, great care
should be taken in the use of irrigation waters to exclude those
charged with that compound ; and also to avoid locating citrus
orchards on land already impregnated with common salt.
The olive tree, as the table shows, is among the most re¬
sistant to alkali salts, approaching the grape in this respect.
This might have been anticipated from its extended culture in
the arid regions of the old world, including Palestine and
northern Africa, where alkali lands abound. It is probable
that the figure given in the table does not yet show the extreme
limit of its endurance.
California experience with the date palm , as the table shows,
credits it with an endurance not exceeding 8320 pounds of
total salts. This is doubtless an underestimate, for in the
Sahara desert and Egypt it is credited with being the culture
which will succeed in stronger alkali than any other cultural
plant ; and, according to Mr. Means of the United States De¬
partment of Agriculture, it is sometimes irrigated with water
containing as much as 200 grains of salts per gallon. It should
be remembered, however, that these trees always grow in very
sandy lands ; and in the desert regions it is often grown below
the surface of the ground, so as to render it wholly independ¬
ent of the alkali accumulations on the surface. The extreme
limit of its endurance must therefore remain in doubt until
more extended experiments have made more definite data
available.
Deciduous Orchard Trees.
Among deciduous orchard trees, strangely enough, the
almond stands alongside of the fig in alkali-resistance, as indi¬
cated in the table. The peach seems to be much more sensitive,
ranking near the apricot and prune, whose tolerance is less
than half as high. That the pear and apple, generally counted
among the more northern fruits in the humid region, should
excel these stone fruits in endurance of alkali, is rather unex-
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 479
pected ; and the figures concerning the whole group of these
rosaceous fruits admonish us that it is unsafe to predict, with¬
out trial, what may be the outcome of culture tests. Thus
plum trees, apparently in good condition, sometimes suddenly
begin to fail when starting to bear ; the fruit appears normal
on the outside for a time, but the pit fails to form, being at
times flattened out like a piece of pasteboard ; and the fruit
does not mature. Yet there is no observable injury to the base
of the trunk, or to the roots. On the other hand, pears do well
even when the outside bark around the root-crown is black¬
ened by the action of the alkali salts. But 38,000 pounds, even
of sulfate, proves too much for the pear.
The quince appears to be materially more resistant than the
apple or pear. It probably ranges alongside of the fig, the soil-
adaptations of which it shares in other respects also.
The English walnut resents even a slight taint of black
alkali; but is fairly tolerant of “white" salts, as is shown in
the peculiarly suitable light loam soils on the lower Santa Clara
river, in Ventura county, as well as in Orange county, Cali¬
fornia.
Close figures for the limits of alkali tolerance in the case of
deciduous orchard trees cannot easily be given or determined,
owing to the difficulties inherent in the differences of root pene¬
tration in the several soils and localities; as well as the fact
already alluded to, that in close-textured soils the tolerance is
in general decidedly less than in sandy lands. Hence the
figures in the table must be taken as more nearly represent¬
ing relative tolerances, rather than absolute data to be ap¬
plied in every case. As regards the stone fruits, it should
be remembered that the Myrobalan root, being at home in
Asia Minor, where alkali abounds, should when practicable be
used wherever alkali conditions exist, in preference to all but
the almond, which seems to resist well, even on its own root,
but has not as wide a range of adaptations as a grafting stock
as the myrobalan. While most of the other stone fruits at the
Tulare substation were on myrabalan roots, the stock of those
in outside orchards was mostly in doubt. It is also to be kept
in mind that different varieties of the same fruit — e. g., pears
and apples — show a not inconsiderable variation in their resist¬
ance.
480
SOILS,
Timber and Shade Trees.
Of trees, forest and shade, suitable for alkali lands, some
native ones call for mention. One is the California white or
valley oak ( Quercus lobata), which forms a dense forest of
large trees on the (almost throughout somewhat alkaline)
delta lands of the Kaweah River in California, and is found
scatteringly all over the San Joaquin Valley. Unfortunately
this tree does not supply timber valuable for aught but fire¬
wood or fence posts, being quite brittle.
The native cottonwoods, while somewhat retarded and
dwarfed in their growth in strong alkali, are quite tolerant of
the white salts, especially of Glauber’s salt. As they usually
grow near to the water, their tolerance for alkali salts is diffi¬
cult to ascertain.
Of other trees, the oriental plane, or sycamore, and the black
locust have proved the most resistant in the alkali lands of the
San Joaquin Valley; and the former being a very desirable
shade tree, it should be widely used throughout the regions
where alkali prevails more or less. The ailantns is about
equally resistant, and but for the evil odor of its flowers, de¬
serves strong commendation.
Of the enealypts, the narrow-leaved Eucalyptus amygdalina
(one of the “red gums”) and the closely related viminalis,
seem to be least sensitive, and in some cases have grown in
alkali lands as rapidly as anywhere. The rostrata , as well as
the pink flowered variety of sideroxylon, are now doing about
as well as the amygdalina at Tulare, where at first they seemed
to suffer. The common blue gum, globidus, is much more
sensitive.
Of the Acacias, the tall-growing A. melanoxylon (“black
acacia ”) resists pretty strong alkali, even on stiff soil; as can
be seen at Tulare and Bakersfield, California, where there are
trees nearly two feet in diameter. The beautiful A. lophantha
(Albizzia) has in plantings made along the San Joaquin Valley
railroad shown considerable resistance, likewise; but it is quite
sensitive to frost.
Of other Australian trees, one of the Australian “ pines, ”
( Casuarina equisetifolia) , is doing well on fairly strong alkali
land in the San Joaquin Valley.
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 481
A remarkably alkali-resistant shrub or small tree is the
pretty Kcelreuteria paniculata from China, which at Tulare is
growing in some of the strongest alkali soil of the tract. Un¬
fortunately it is available mainly for ornamental purposes; its
wood, while small, is very hard and makes excellent fuel.
Of trees indigenous to the Atlantic and East Central United
States, the Tulip tree, the Linden, and most other trees of the
humid region, including the English oak ( Quercus pedun-
culata) become stunted in alkali soils. The honey locust, being
particularly adapted to calcareous lands, does moderately well
on alkali lands, but its thorns and imperfect shade render it
not very desirable. The black locust and the elms have on the
whole done best. The eastern maples are not successful ; but
the California maple (Acer macro phyllum) and the box elder
( Ncgundo calif ornica) have done fairly well in the lighter
alkali lands of the San Joaquin Valley.
The Conifers — Pines, firs, cedars, cypress, etc., are very
sensitive to black alkali and will not endure much even of the
“ white ” salts. Even the native juniper of the mesas carefully
adheres to the portions — breaks and upper slopes, hilltops, etc.
— which are more or less leached by the scanty rains of these
regions.
INDUCEMENTS TOWARD THE RECLAMATION OF ALKALI LANDS.
The expense involved in the reclamation of strong alkali
lands naturally gives rise to the question whether adequate
advantages are likely to be derived from such expenditure;
specially when the last resort — underdraining and leaching — -
has to be adopted.
Those familiar with the alkali regions are aware how often
the occurrence of alkali spots interrupts the continuity of fields
and orchards, of which they form only a small part, but enough
to mar their aspect and cultivation. Their increase and ex¬
pansion under irrigation frequently renders their reclamation
the only alternative of absolute abandonment of the invest¬
ments and improvements made, and from that point of view
alone it is of no slight practical importance. Moreover, the
occurrence of vast continuous stretches of alkali lands within
the otherwise most eligibly situated valley lands of the irriga¬
tion region forms a strong incentive towards their utilization.
3i
482 SOILS.
There is, however, a strong intrinsic reason pointing in the
same direction, namely, the almost invariably high and lasting
productiveness of these lands when once rendered available to
agriculture. This is foreshadowed by the usually heavy and
luxuriant growth of native plants around the margins and be¬
tween alkali spots (see fig. 60) ; i. e., wherever the amount
1st year, 2d year, 3d year, Fourth year — 42 bushels.
Fig. 75. — Wheat grown on black alkali land at Tulare Substation, California, showing improve
ment in successive years of reclamation treatment.
of injurious salts present is so small as not to interfere with
the utilization of the abundant store of plant-food which, under
the peculiar conditions of soil-formation in arid climates, re¬
mains in the land instead of being washed into the ocean.
Extended comparative investigations of soil composition, as
well as the experience of thousands of years in the oldest
settled countries of the world, demonstrate this fact and show
UTILIZATION AND RECLAMATION OF ALKALI LANDS. 483
that so far from being in need of fertilization, alkali lands usu¬
ally possess extraordinary productive capacity whenever freed
from the injurious influence of the excess of useless salts left
" “ : y~ “ ' “ v'CT/'
in the soil in consequence of deficient rainfall. (See analyses,
chapter 22, pp. 436, 437).
Among many striking examples of the results of such re¬
clamation, is that represented in the annexed figure (75), of
Fig. 76. — Grains grown on alkali land at Tulare Station, California.
484
SOILS.
grain grown on strong alkali land, before and after reclama¬
tion treatment. On the original land even “ alkali weeds ”
would hardly grow ; while afterward a wheat crop represent¬
ing forty-two bushels per acre was grown. Additional illus¬
trations are shown in the second figure (76), showing crops of
wheat and barley as grown on partly reclaimed land at the
Tulare substation.
While it is certainly true that when rightly treated, alkali
lands can be rendered profusely and lastingly productive, yet
close attention and constant vigilance are needed so long as the
salts remain in the soil; and no one not determined to give
such land such full attention, should undertake to cultivate it.
PART FOURTH.
SOILS AND NATIVE VEGETATION.
CHAPTER XXIV.1
THE RECOGNmON OF CHARACTER OF SOILS FROM THEIR
NATIVE VEGETATION ; MISSISSIPPI.
Climatic and Soil-Conditions. — Next to climatic conditions,
chief among which are temperature and moisture, the physical
and chemical nature of the soil and subsoil is the most potent
factor in determining the natural vegetation of any region.
The limitations we observe in the adaptation of cultivated lands
to certain crops, even with artificial help, must be much more
strongly pronounced when no such aid is given, and the strug¬
gle for the survival of the fittest is continued, subject only to
seasonal variations, for thousands of years. It is obvious that
within the limits of the regional flora, the natural vegetation of
any tract represents the best adaptation of plants to soils , in
the results of long periods of the struggle for existence be¬
tween competing species; the survivors being those best
adapted to the entire environment.
In countries uninhabited by man the chief conditions outside
of the direct influence of climate and soil that may materially
affect the results of the competition are connected with the
animal creation ; and within the latter, insects are probably the
most influential, beneficially in the part they play in the fertil¬
ization of flowers, injuriously in their role as parasites. Since
in the absence of man, the effects of fire would ordinarily be
conditioned upon the occurrence of thunderstorms, its effects
would then properly come under the head of climatic influences.
But while these and some other disturbing factors must not
be forgotten in considering the relations of soils to the
natural vegetation borne by them, the common consensus of
mankind has long recognized the intimate connection existing
between the two, and has everywhere made it the basis of at
least a general estimate of the agricultural value of the land
concerned.
1 The special object of this chapter as a whole has seemed to the writer to re¬
quire a repetition of much that is already said in the preceding chapters.
48 7
488
SOILS.
NATURAL VEGETATION THE BASIS OF AGRICULTURAL LAND
VALUES IN THE UNITED STATES.1
In countries long settled, as in Europe, where the nature of
the original forest is unknown or a matter of tradition only,
the adaptations of the several kinds of land to culture plants
and forest trees has been gradually ascertained by cultural ex¬
perience, and their designations, values and uses determined
accordingly. In the United States, the character of the origi¬
nal forest growth is mostly in evidence, or is definitely known
by tradition, even in the older states. West of the Alleghenies,
there is as yet little difficulty in this regard, partly because
even where the original forest growth has disappeared its
character remains on record, the assessed land values being
very commonly based upon the tree growth of the wild land.
In the Southern States especially, the classification of uplands
into “ pine lands " and “ oak lands ” is universal, and is associ¬
ated with certain limits of valuation, both by assessors and
purchasers. Within each of these two classes, however, there
are well-defined gradations of cultural value according to the
kind (species) e. g., of pine or oak that occupies the ground,
either alone, or in intermixture with other trees whose pres¬
ence or absence is considered significant. In the case of
“ bottoms ” or alluvial lands, corresponding distinctions and
classifications obtain ; we hear of hickory, beech, gum, and
cherry bottoms, hackberry hammocks, etc. each name being
associated with certain cultural values or peculiarities of soil,
well understood by the farming population.
INVESTIGATION OF CAUSES GOVERNING THE DISTRIBUTION OF
NATIVE VEGETATION.
It seems singular that such well and widely understood
designations and important distinctions should not long ago
have been made the subject of careful investigation and pre¬
cise definition by agricultural investigators. For apart from
their practical importance as guides to the purchaser of land,
or settler, this correlation of land-values and natural vegetation
is of the utmost interest in offering an opportunity for re¬
searches on the factors which determine the choice of these
several trees and the corresponding shrubby and herbaceous
1 See above, pp. 313 to 315, chapter 18.
RECOGNITION OF CHARACTER OF SOILS.
48a
growths. Moreover, the cultural results and adaptations
corresponding to certain natural growths being known from
experience, a thorough knowledge of the soils so characterized
should enable us to project into new lands, where experience
is lacking, the benefits of experience already had ; even in cases
where, from some cause, the natural vegetation is different, or
absent. Only very fragmentary and casual observations in
this line are on record thus far, almost the only generally
recognized chemical characterization of plant habit being that
of calciphile (lime-loving), and calcifuge (lime-repelled) ones,
but with few attempts at more than local application. Yet,
to ascertain by the physical and chemical examination of soils
what are determining factors of certain natural vegetative
preferences, which are invariably followed by certain agricul¬
tural results, should not be an unsolvable problem, and its
practical importance should justify its most active investiga¬
tion.
Investigations in Mississippi. — In his explorations connected
with the Geological and Agricultural Survey of the State of
Mississippi, as well as, later on, in similar researches carried
on in other states, the writer was forcibly struck with the
close correspondence of the limits of geological formations
with those of vegetative zones ; so much so that he was led tcr^
rely very largely on the latter as indicative of the probable
occurrence of outcrops that otherwise, in a level country, would
have passed unperceived.
These observations upon the correlations between virgin
soils and their native vegetation having originally been made
by the writer, in great detail, in the state of Mississippi, from
1855 to 1872, and that state being from natural causes a pecul¬
iarly cogent illustration of such correlation : it seems advisable
to describe first, somewhat in detail, the facts observed there,
and subsequently to compare them with what has been observed
elsewhere bv him or others.
No claim is made to an even approximately exhaustive pres¬
entation of the whole subject, even within the United States;
nor is it intended to give complete lists of vegetation.1 The
1 Such lists, so far as the State of Mississippi is concerned, may be found in the
writer’s Report on the Agriculture and Geology of Mississippi, i860. See also
Plant Life of Alabama, by Charles Mohr.
49°
SOILS.
object is to give such facts as have been fairly well established
by observation, hoping that more thorough investigations in
the same line will thereby be stimulated.
VEGETATIVE BELTS IN NORTHERN MISSISSIPPI.
The diagram below is a sketch-map of the most northern
part of Mississippi, showing the narrow parallel belts of suc¬
cessive geological formations or terranes running north and
south, which bear the varying zones of vegetation character¬
istic of each one, as indicated in the legend beneath.
SOIL REGIONS OF NORTHERN MISSISSIPPI, SHOWING CHANGES FROM EAST TO
WEST, AND LIME PERCENTAGES IN SOILS.
Lime, p.c.
Soil Character.
Vegetation.
I.
s
1
0
Clay loams, clay.
Oaks, sweet gum, tulip tree, walnut, red cedar,
ash, hickories.
2.
.05— .14
Sandy loams, sands.
Short-leaf pine, post, scarlet and black-jack oaks,
black gum, chestnut.
3*
1 . 00 — 1 . 40
“ White lime ” prairie ; clays Red cedar, crab apple, Chickasaw plum, sturdy
and clay loams. post and black-jack oaks, honey locust.
4-
0
I
0
rO
Mellow red loams of “ Pon¬
totoc ridge. ”
Oaks, hickories, walnut, tulip tree, ash, cherry,
umbrella tree.
5-
.08 — .18
Heavy gray clay soils, some
gray sands. “ Flatwoods.”
Scrubby post and black-jack oak, short-leaf pine.
6.
•15— -25
Sandy ridges and uplands,
broken.
Post, black-jack, scarlet and upland willow oaks,
small; some chestnut.
7-
•25— -35
Mellow clay loams of “Table Fine black, red, post, Spanish and black-jack oaks,
lands.” I hickories, sweet gum.
8.
2 . 00 — 5 . 00
Calcareous sandy silt, “Bluff
loess” “Cane Hills.”
Oaks as above, tulip tree, ash, honey locust, lin¬
den, sassafras, umbrella tree, cane.
9-
.40— I . IO
Mississippi Bottom.
Basket, white and black oaks, ash, tulip tree,
honey locust, pecan, shellbark hickory, walnut,
hackberry, cane.
ga.
1 . 12 —
Yazoo backland buckshot
clay.
96.
.40
Sandy alluvium, “ Frontland.
Sweet gum, maple, willow oak, elm, hackberry.
10.
.26 — .40
Light sandy loam of “ Dog¬
wood ridge.”
Dogwood, sweet gum, holly, ash, sassafras, prickly
pear.
Limestone Belt. — Beginning on the east we have, first, a narrow belt
of limestones of the carboniferous formation, on which there is a fine
RECOGNITION OF CHARACTER OF SOILS.
49I
growth of various oaks, with walnut, hickory, sweet gum, tulip tree and
red cedar, and a very productive soil.
“ Pine Hills." — Next adjoining on the west comes a belt of sandy,
non-calcareous beds of the lower Cretaceous formation, about 18 miles
wide. It has a hilly surface, and outside of the narrow valleys, the
prevalent timber is short-leaved pine and scrubby black-jack oak, with
some post oak and small black gum, and a few large chestnut trees.
“ Prairie ” Belt. — Westward of this belt we descend into a level
“prairie” region, six to twelve miles wide; the “white lime country,"
having heavy black clay soils, underlaid by the cretaceous “ rotten lime¬
stones which are profusely productive. The sparse tree growth con¬
sists of stout, vigorous and dense-topped post and black-jack oaks, with
clumps of crab apple, Chickasaw plum thickets, and an occasional red
cedar.
Pontotoc Ridge. — West of the prairie belt we ascend into a ridgy hill
country, twelve to fourteen miles wide ; the “ Pontotoc ridge,” formed
of the soft limestones and marls of the upper cretaceous formation, and
covered with a deep red soil, which bears a rich growth of oaks, with
hickory interspersed, and black walnut, umbrella and tulip tree even on
the ridges. This. is one of the finest agricultural regions of the State.
Flatwoods. — From the Pontotoc ridge and its fine lands and timber
we descend to westward into the “ Flatwoods ” belt, three to eight
miles wide ; a level country underlaid by heavy gray non-calcareous
clays of the tertiary formation, from which most of its soil is directly
formed. It bears a pretty dense growth of the same species of oaks
that characterize the prairies farther east, but the form, habit and size
of the trees is so different that many of the inhabitants believe them to
be different species. The black-jack oak looks like small, dense-topped
apple trees ; the post oak, on the contrary, has an open top of the form
of a short-handled, spreading broom. The soil is poor and unthrifty,
as are the few disappointed settlers, who bought the land on the strength
of its oak-tree growth. (See page 500).
Brown Loam Region. Table Lands. — Adjoining the Flatwoods on the
west is a broad upland region, with a brownish-yellow soil and subsoil,
extending nearly to the edge of the Mississippi bottom. In its eastern
portion it is rather broken and hilly, with sandy ridge soils, a mixed
growth of oaks and short-leaved pine, and occasional chestnuts ; a fair
farming country only. To westward the ridges become lower and
broader, assuming a plateau character. The pine disappears, and black,
Spanish, red and white oak, with much hickory, largely replaces the
black jack and post oak; thus characterizing the fertile brown-loam
49 2
SOILS.
u table-lands ” that extend through western Tennessee and Mississippi
into Louisiana, and have long been noted for their high production of
fine upland cotton.
Cano Hills. — On the western border of the table-land region, and
here forming a strip only a few miles wide along the edge of the Mis¬
sissippi bottom, but from 70 to 450 feet above it, lies the remnant of
what farther south constitutes a wide and important agricultural belt ;
the Bluff or Loess formation, locally known as “ the Cane Hills.” The
soil is largely composed of grains of sand and silt cemented by lime
carbonate ; it is therefore calcareous, and as on the Pontotoc ridge,
described above, we find here the black walnut, the tulip tree, ash and
others, elsewhere restricted to the alluvial “ bottoms,” on the ridges
themselves, from sixty to a hundred feet above the stream beds.
Mississippi Bottom. — At the western foot of this bluff there lies the
great Mississippi Bottom, with its rich soils and varied forest growth.
This also, however, subdivides into at least three distinct soil and vege¬
tative zones, viz., the sandy “ Frontlands,” which lie on the immediate
banks of the great river and its main branches, and the heavy clayey
“ Back-land ” areas, whose soils are partly the product of modern
swamp deposits from backwaters, partly result from the disintegration
of strongly calcareous clays constituting the lower part of the Bluff or
Loess formation. A third natural subdivision is the “ Dogwood ridge,”
a narrow belt of slightly elevated land, mostly above ordinary overflows,
which extends diagonally from the Mississippi river to the Yazoo bottom,
and seems to be the continuation of “ Crowleys ridge” in Arkansas.
Each of these soil belts has its own characteristic forest growth, as in-
-N^icated in the table below the map.
We have here along an east-and-west line of about 200
miles, eleven markedly distinct zones of vegetation, readily
recognized as such by every farmer, and each underlaid by a
distinct geological terrane. It does seem as though a close
study of these and of the soils overlying them should lead to
some definite results showing the physico-chemical causes of
these differences.
Lime apparently a governing Factor. — The connection of
some of these changes in vegetation with the calcareous nature
of the corresponding formation has already been referred to.
As regards four of the eleven divisions, this is obvious even to
the casual observer, and is well known to the population, who
1
RECOGNITION OF CHARACTER OF SOILS.
493
speak of the “ lime country ” or belts being, as a matter of
common knowledge, the best land ; in full accord with what, in
Kentucky and elsewhere, has passed into a popular maxim.1
Taking as a guide the trees and plants which characterize
the obviously calcareous lands, our next step should be to
verify, if possible, the fact that wherever these occur naturally,
lime is abundant in the soil in comparison with those lands in
which such vegetation does not occur naturally, or perhaps
even fails to flourish when planted without special fertilization.
This the writer has sought to do, first in connection with the
survey work of the state of Mississippi, and subsequently in
the wider field that has since come under his observation.
SOIL BELTS IN SOUTHERN MISSISSIPPI.
In Mississippi, the general conclusions derived from the ob¬
servations made on the northern cross section, are corroborated
many times over in other portions of the state. Aside from the
cretaceous prairie region, there runs across the middle of the
state a belt of varying width, of calcareous tertiary beds, which
also give rise to more or less extensive tracts of “ black
prairie ” lands, interspersed with non-calcareous, mostly sandy
ridges, the lower slopes of which, influenced by the calcareous
beds, bear an oak and hickory growth, while the higher por¬
tions have only pine, and usually remain uncultivated. South¬
ward of this “ central prairie ” belt lies the long-leaf-pine
forest area of the state, underlaid throughout by sandy, non-
calcareous formations, with poor sandy soils, save here and
there in patches, which can be at once recognized by the re¬
placement of the long-leaved pine by a vigorous oak growth ;
as is also the case where the pine area abuts against the calcare¬
ous “ Cane Hills ” on the west. The bottom soils of this
region are largely “ sour,” and bear the gallberry ( Prinos
glaber), bay galls {Per sea Carolina), ti-ti (Clift onia mono-
phylla), candleberry ( Myrica cerifera), various whortle¬
berries, the pitcher plants (Sarracenia) , yellow star grass
( Aletris ), sundews, Xyris, Eriocaulon, and other plants of
similar habits.
1 ** A lime country is a rich country.”
494
SOILS.
Vegetative and Soil Features of the Mississippi Coast Belt.
— South of the long-leaf pine area lie the coast flats, with soup
sandy soils underlaid by stiff clays. On these “ pine mead¬
ows ” of the Mississippi coast occur some of the most striking
cases of modifications of vegetation due to physical and chem¬
ical causes.
As is well known, the long-leaved pine habitually belongs to
the dry sandy uplands of the Gulf States; the deciduous cy¬
press, on the other hand, is most characteristic of the swamps,
where its roots are permanently submerged in water. But on
the pine meadows of the Mississippi coast we see these two
incongruous trees growing side by side, though sadly worsted
by their mutual concessions ; their heights usually ranging from
12 to 15, rarely as much as 18 feet.1 Yet both preserve their
characteristic forms, the cypress being an exact miniature re¬
production of the usual level-topped swamp form, except as to
the “ knee ” feature; while the pine differs only in stature from
its giant brethren of the pine hills, from which it can be traced
down through all grades of transition. The soil on which this
growth occurs is a sour, sandy one, one and a half to three feet
in depth, underlaid by a solid, impervious gray clay, above
which is usually found several inches of coffee-colored bottom
water, which drains slowly into the sluggish water-courses,
themselves carrying brownish, sour, but very clear waters.
Analysis shows the soil to be sour and extremely poor, especi¬
ally in its lime and phosphates (see chapter 19, p. 352) ; its
1 R. M. Harper, who has graphically described the vegetative features of the
coastal plain of Georgia (Contr. from the Dep. of Bot. Colum. Univ. Nos. 192,
215, 216, 1902-05; also Bull. Torr. Bot. Club 29-32), claims the deciduous cypress
of the wet pine-barrens and ponds therein, the vegetation of which greatly re¬
sembles that of the pine meadows of the Mississippi seacoast, to be a distinct
species, Taxodium imbricarium , the leaves of which are imbricated, instead of
two-ranked and with spreading leaflets. He supports this distinction mainly by
the differences in habit from the Louisiana swamp cypress, and the fact that the
imbricated form occurs wholly on non-calcareous land, while the other is at home
in the calcareous alluvial areas. The imbricated form has been observed and
commented on before, as a mere ecological variation, and in the writer’s opinion
this is all that can be claimed, in view of the much greater differences in the form
of other trees, notably oaks, illustrated below, caused also by lime. There would.
h fortiori , be reason for claiming at least three different species of post oak and
black-jack (and two of willow oak), which differ not only in tree form but also in
the form and number of leaf lobes, and yet can be traced into one another by
innumerable transition forms. If new species are to be established on such grounds,
it is hard to see where the variations manifestly due to environment are to come ia
RECOGNITION OF CHARACTER OF SOILS.
495
herbaceous vegetation consists exclusively of very small-seeded,
“ calcifuge ” plants (sedges, orchids, Juncus, Hsemodoraceae,
Xyris, Polygala, etc.). This land is wholly unproductive and
affords but indifferent pasturage, except the first season after
burning-over; probably because of the effect of the minute
amount of ashes so added. As the coast is approached, the
clay subsoil has an increasing depth of sandy soil-mass above
it, and on these “ sand hammocks ” the long-leaved pine grad¬
ually assumes more and more of its usual stature; the cypress
disappears, and the Cuban pine (here called pitch pine) grad¬
ually comes in ; while the sedgy vegetation diminishes and
finally disappears. On this land crops may be grown as in the
long-leaf-pine uplands.
But on the immediate coast, evidently under the influence of
the aboriginal “ shell mounds,” the yellow sandy soil becomes
blackish from the (humus-forming) effect of the lime thus
supplied; and concurrently the coast liveoak (Q. virens ), grape
vines, the Hercules club ( Aralici spinosa), “ l’herbe a trois
quarts” ( V erbesina sp. ), and numerous leguminous plants
(which are wholly absent from the pine meadow- s) take pos¬
session of the land, which is very productive and has been
specially utilized in the growing of Sea Island cotton. Here
the clay stratum is 15 to 20 feet below the surface, and roots
penetrate to great depths in the pervious soil, whose great
thickness makes up for its low percentage of plant-food (see
table below). This land is distinctly limited by the extent of
the shell heaps, past or present, and shows a respectable per¬
centage of lime.
PINE MEADOWS
Sane hammocks'
SFA75LAN0
COTTON SOIL
— — — ~~ B/ocA- Cloy- with- OyJlers-and-Cypress^Stu r ^
Fig. 78. — Schematic profile of the Mississippi Coast Belt, through Jackson County.
The annexed schematic profile (fig. 78) illustrates these
changes of soil and vegetation, which furnish a striking ex-
SOILS.
496
ample of the effective modification of vegetative features by
physical and chemical soil-conditions.
It would be difficult to find a more striking exemplification
of the effect of lime carbonate, not only upon the vegetation
but also upon the physical and chemical characters of the hope¬
lessly unproductive soil of the sand hammocks and pine mead¬
ows; no longer brown and sour, but jet black and neutral,
modifying favorably every physical quality. Humus likewise
nowhere shows its benefits more strikingly.
Table of Lime-Percentages. — The table below shows the
average lime percentages observed in most of the several vege¬
tative areas mentioned above. To meet the objection some¬
times made that the vegetative changes noted may be due to
the larger amounts of phosphoric acid and potash frequently
found in calcareous lands, the percentages of the latter are also
given. Considering the origin of limestones, such a connec¬
tion is not unexpected, but it is far from constant. On the
contrary, the frequent co-occurrence of much lime and high
production with small percentages of phosphoric acid and
potash leads to the conclusion, already discussed (see chapter
19, p. 365), that in presence of abundance of calcic carbonate,
smaller percentages of phosphoric acid may be considered ade¬
quate than when lime is deficient, on account of greater avail¬
ability. Almost the same may be said of potash ; and it is
quite possible that the presence of large amounts of lime tends
to prevent the leaching-out of this base, in consequence of
greater facility for the formation of zeolites. Illustrations of
this kind have already been given (chapters 3, 22).
Definition of “ Calcareous Soils." — It will be noted that the
very obvious and important changes of vegetation are brought
about by comparatively slight differences in lime-content. In
fact, only two of the soils enumerated above would, according
to the estimates usually given in books on soil composition, be
considered as properly calcareous. But the decisive feature
in this matter must evidently be the native vegetation , which
expresses the nature of the land much more clearly and author¬
itatively than any arbitrary definition or nomenclature can
possibly claim to do. A soil must be considered as being cal¬
careous whenever it naturally supports the vegetation char¬
acteristic of calcareous soils.
TABLE SHOWING NATIVE FOREST GROWTH, POPULAR ESTIMATE OF DURABILITY AND INITIAL PRODUCTION, AND PERCENTAGES OF LIME,
PHOSPHORIC ACID AND POTASH, IN MISSISSIPPI LANDS.
RECOGNITION OF CHARACTER OF SOILS.
497
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498 SOILS.
DIFFERENCES IN THE FORM AND DEVELOPMENT OF TREES.1
It will be noted that in the above table, as well as in the dis¬
cussion preceding it, identical species of trees are ascribed to
vegetative areas of widely different productive capacity. Per¬
haps the most striking example is that the cretaceous prairies
and the adjoining flatwoods belt, standing respectively highest
and lowest in the scale of productiveness, are yet bearing
specifically identical tree-growth, to-wit, the post oak ( Quercus
minor) and the black-jack oak (Q. marylandica) . While to
the field botanist 2 there can be no question as to the absolute
specific identity of the two trees as growing on the respective
areas, yet the mode of development of both is so different in
the two cases, that, as before remarked they are popularly sup¬
posed to be different “ kinds.”
Forms of the Post Oak. — The post oak of the prairie lands is
a tree 50 to 70 feet high, with a stout, excurrent, rather conical
trunk, often somewhat curved to one side above, and densely
clothed from within 12 or 15 feet of the ground with com¬
paratively short, sturdy branches set squarely to the trunk,
much crooked (geniculate), often reflexed downward; alto¬
gether forming a dense head, beneath whose thick foliage, a
bird or squirrel is quite secure from the hunter’s aim. — In the
flatwoods, on the contrary, the post oak has a thin, rather short
trunk, divided up at 15 or 20 feet height into long, rod-like
branches, spreading broom-fashion, and scantily clothed with
1 It is a matter of regret to the writer that owing to the long distance intervening
and the difficulty of securing competent and sympathetic observers for such work,
it has not been possible for him to secure photographs of the tree-forms here dis¬
cussed. At the time his own observations were made, photography w’as prac¬
tically unavailable as yet, and the figures given are therefore based upon sketches
made at the time, and partly upon recollection. They represent types rather than
definite individuals, which were however described when fresh in mind, in the
Report on the Agriculture and Geology of Mississippi, i860, pages 254 et seq.
2 It has been already, and doubtless will be again and increasingly, attempted to
make distinct “ species ” of these widely different forms of trees. But this is
simply begging the question. Mere external diagnostic marks will not avail here ;
it would have to be shown that the seed of these different forms do not produce
the other forms under changed conditions. Until this has been done, the number¬
less transition forms which he that runs may observe in the field, throw upon the
species-makers the onus of proof of differences of specific value — if it be possible
to define such value.
RECOGNITION OF CHARACTER OF SOILS
499
short twigs bearing tufts of leaves ; thus forming an open head,
in which no creature can hide effectually. On the brown-loam
table-lands, again, the post oak has a straight, rather slender,
excurrent trunk with long and more or less crooked limbs pro¬
jecting at a large angle, sometimes even drooping, and freely
divided up into lateral, leafy branches ; the trees attain from
40 to 55 feet in height. Again, on the high sandy ridges
which are interspersed in the eastern portion of the brown loam
area, we find, generally associated with a similarly depauper¬
ated form of the black-jack oak, and with the Upland Wil¬
low oak (Q. cincrca) , a form of the post oak intermediate be¬
tween that of the Flatwoods and the Table lands; twelve to
fifteen feet high, with thin trunk, “ sprangling ” long, crooked
branches, clothed with sparse tufts of leaves. These four
strikingly distinct types are shown schematically, in their ex¬
treme development, in the subjoined figures.
It is hardly necessary to say that between these extreme
forms there are many degrees of transition, corresponding to
the transitions between the several soil-classes respectively rep¬
resented by them ; or they may be developed into depauperated
types. Thus, for example, the forms of the post and black-jack
oak found on the sandy ridges of the yellow loam region,
hardly need experience in the observer to interpret them as
characterizing a wretchedly poor soil.
Forms of the Black-jack Oak. — Not less striking are the
characteristics of the forms of the black-jack oak as developed
upon these several kinds of land. The black-jack of the prai¬
ries is a low tree with a dense rounded head, often somewhat
flattened above, and a low, thick-set trunk divided up into
square-set branches, so densely clad with foliage that no light
penetrates into the interior, and birds can safely hide and nest
within it. The height rarely exceeds 35 feet, the head being
20 to 30 feet across.
The Flatwoods form, on the contrary, rarely exceeds 15
feet in height, with a very rough bark and a small, rather
dense, rounded top, giving the whole the appearance of a small
apple tree. Practically the same form is seen on poor, clay
ridges of “ hogwallow ” land.
On the brown-loam lands the black-jack, like the post oak,
has a rather slender, often somewhat crooked, hut excurrent
500
SOILS
Loam Upland. Sandy Ridges. Flatwoods. Black Prairie
Fig. 79. — Extreme Forms of Post Oak ( Quercus minor Marsh.., obtusiloba Mich).
RECOGNITION OF CHARACTER OF SOILS
501
trunk 35 to 50 feet high, with more or less crooked limbs of
moderate length, well provided with leafy branches, but form¬
ing altogether a rather open crown. A depauperated form of
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this type occurs on the sandy ridges of the yellow-loam region
and is 12 to 15 feet high, with slender, crooked branches,
clothed with scanty foliage ; as shown in Figure No. 80, along¬
side of the other typical forms.
502
SOILS.
In all these variations of the tree forms, there is also a con¬
comitant variation in the forms and other characters of the
leaves. Thus in the compact forms of the black-jack oak, the
trilobate leaf is almost completely obliterated, the leaf being
simply rounded-cuneate, somewhat auriculate at base. In the
sparse-branched upland forms the leaves are deeply three-
lobed, and the ferruginous tomentum of the lower surface is
much less pronounced. The lobation of the post oak also
varies considerably both in the numbers of lobes and in their
obtuseness. Similar differences prevail in the case of the
black and Spanish oaks ; thus in the latter, the long terminal,
falcate lobe is always most pronounced on “ rich ” soils, while
on poor ones the trilobate leaf predominates.
Of course all these forms may be found bearing acorns, so
that they undoubtedly represent adult trees.
Characteristic Forms of other Oaks. — Similar general fea¬
tures are repeated in the case of the other species of oaks, and
also more or less in other kinds of trees ; though mostly less
pronouncedly than with the two species above described.
Among the more striking are the two forms of the willow oak
(Q. phcllos ), which on low, undrained ground assumes the
low, rounded, “ apple-tree " form, while on well-drained up¬
lands of good fertility it is a beautiful, slender tree producing
almost the effect of the acacia type; it is then a sign of first-
class land. The scarlet oak rather reverses these types ; on
good, “ brown-loam ” upland it is of rounded form, not very
tall, with sturdy, rough-barked trunk ; while on poor hillside
lands its tall, smooth, white trunk stands out as a conspicuous
admonition to the landseeker to beware of a poor purchase.
The black and Spanish oaks also indicate, by tall thin trunks,
a deterioration of the land as compared with the lower and
more sturdy growth on areas relatively richer in lime.
Sturdy Growth on Calcareous Lands. — One feature invari¬
ably repeated, not only in Mississippi but throughout the
United States, is that in many strongly calcareous soils the
growth of all trees , as well as of shrubs and of many herbace¬
ous plants, is of a more sturdy and thick-sct habit than that
of the same species grown on thin, sandy, or generally on non-
calcareous land. This effect is quite as apparent in the arid
RECOGNITION OF CHARACTER OF SOILS.
503
region of the Pacific Coast as in the Atlantic States, on the
prairies of the Middle West, and of the Gulf Coast. The ex¬
perienced fanner recognizes this habit of the tree-growth as a
sign of good land, and the reverse, viz., trees of lank, tall and
thin growth, as evidence to the contrary, from the Atlantic to
the Pacific.
Cotton Plant. — The cotton plant affords very striking evi¬
dences of this influence of lime. On the bottom lands of a
creek in Rankin county, Mississippi, the writer found a
“ patch ” of cotton with luxuriant stalks reaching above the
head of a man on horseback, but almost devoid of “ squares ”
or blooms. The soil was very dark and rich-looking, but was
derived from a non-calcareous tertiary terrane surrounding the
heads of the stream. A few rods below, the latter crosses the
line of a calcareous terrane, from which copious marly debris
have been washed down on the bottom soil. Here the cotton
was just half as high as above, and thickly covered with
squares, blooms, and bolls.
Another similar example was noted on the Chickasawhay
river, in Wayne county, Miss. Where that stream flows
through the non-calcareous, lignitiferous area of the tertiary
formation, its bottom lands bear cotton crops of medium pro¬
ductiveness only, the stalks being of the usual height of about
three feet, and only fairly boiled. But a short distance below
the point where the soft marls of the marine tertiary are cut
into by the stream, the cotton plants on the bottom lands are
from 18 to 20 inches high only, closely branched, and literally
thronged with cotton bolls, so that the fields appear a solid
mass of white. The only objection urged against this land is
that to pick such cotton “ breaks the backs " of the pickers.
The tree growth of the bottom, of course shows a correspond¬
ing change.
Lime Favors Fruiting. — In connection with the obvious
changes of form and stature caused by the presence of an
abundant supply of lime carbonate in soils, there is another
that has been long noted in cultivation, but is no less striking
in the native vegetation. The abundant fruiting of oaks on
such lands as compared with the same species on non-cal¬
careous soils is a matter of common note in the Mississippi
504
SOILS.
Valley states; and the same is true of other trees, and of her¬
baceous plants as well. The fruit on the lime soils is often
smaller, unless much humus is present ; but the statement made
in Europe that cultivated fruits, and especially grapes, are
sweeter on calcareous lands, is abundantly verified in the native
fruits of the Mississippi Valley states as well ; where the various
wild berries, haws, plums, etc., are well known to the younger
part of the population to be much sweeter and higher-flavored
in certain (calcareous) localities than in others, besides being
usually more abundant.
This is entirely in accord with the well-known fact that the
application of lime checks the excessive wood and leaf growth
resulting from excess of nitrogen as well as moisture ; while on
the other hand, the injurious effects of overdressing with lime
or marl are known to be repressed by the use of stable manure,
or by green-manuring. The repression of excessive wood
growth by lime would seem to offer a simple explanation of the
compact habit of growth on calcareous lands ; and the extraor¬
dinary sweetness of fruits grown in the arid region as com¬
pared with the same in the humid, is fully in accord with the
high lime-content of the arid lands.
Stunted Growth. — In practice it will be found in most cases
that a stunted native growth is due not so much to lack of
plant-food in the soil, as to unfavorable physical conditions.
Among these, shallowness, and extreme heaviness of the soil
are the most common causes. The “ scab lands,” underlaid by
impervious rock at a depth too slight for culture plants, as in
many plateaus of the Pacific Northwest, and in rocky or mount¬
ainous regions generally, are cases in point. Strata of imper¬
vious clay often produce the same result ; but in this case,
should such clay be intrinsically capable of supporting plant
growth, the land can often be made available for orchard pur¬
poses by blasting with dynamite (see chapter io, p. 181).
The post oak (and black-jack) flats of the Mississippi Valley
states are familiar examples of land whose dwarfed tree growth
causes it to be avoided by settlers; similarly, a dwarfed growth
of red elm ( Ulmus rubra), hackberry and ash indicates in the
flood plain of the Red river of Louisiana a heavy “ waxy ” red
clay, or “ gumbo ” land, scarcely available for agricultural pur-
RECOGNITION OF CHARACTER OF SOILS.
505
poses.1 The gray or white “ crayfishy ” bottom and bench
lands of the Southwestern States, so poor in lime, phosphates
and humus as to be worthless under existing conditions, are
characterized by an easily recognized scrubby growth of Water
and Willow Oaks (Q. nigra , or aquatica, and phellos), with
low, rounded tops ; while the same trees, when well developed,
indicate highly productive lands.
Physical vs. Chemical Causes of Vegetative Features. — The
extent to which the modifications of form alluded to above are
referable to chemical and physical causes respectively, can be
approached by the discussion of the presence or absence of cer¬
tain trees from soils of extreme physical character, but other¬
wise normally constituted. As has been shown above, the
black-jack and post oaks belong, as species, equally to the
heaviest and lightest soils within the state of Mississippi ; to
the black and yellow “ prairie ” soils, as well as to the sandy
ridges of the vellow-loam region ; showing for these two species
as such, an independence of physical conditions and an ex¬
traordinary adaptability, found in few other trees. They are
frequently found either alone or associated with only a few
other species of local adaptation, such as, in the prairie lands,
the crab-apple, wild plum, and the juniper or red cedar. On
the soils of intermediate or loam character, on the contrary,
they are always associated with other oaks as well as with
hickory, and in that association attain what may be considered
their normal type or form.
.From the fact that the dense, rounded top is formed by the
black-jack oak both on the rich prairie lands and on the poor
soils of the Flatwoods, it would seem that that form is the out¬
come of a physical cause, viz, the extreme “ heavy-clay " char¬
acter of both kinds of land ; and we may note that exactly the
the reverse effect is observed in the form growing on the poor
sandy ridges, as shown in fig’s 79 and 80. Yet it will also be
noted that in the case of the post oak, the poor, heavy-clay
soil of the Flatwoods produces an open, broom-shaped top,
while the form assumed on the sandy ridges is substantially the
same for both species. Care must therefore be exercised in
drawing general conclusions as to the effects produced by
either physical or chemical causes, alone, upon tree forms.
1 Rep. of Geological Reconnoissance of Louisiana; New Orleans, 1873, P- 27-
506
SOILS.
Lowland Tree Growth. — The variations occurring in the val¬
leys or alluvial bottoms are less obvious to superficial observa¬
tion, yet equally important and cogent to the close observer.
In the properly alluvial lands, one dominant condition, that of
adequate moisture supply, is almost always fulfilled, irrespec¬
tive of soil quality. In addition to this, as stated in chapter
2 (see page 24), practically all the alluvial lands of the
humid region may be considered as being of a more or less cal¬
careous character, as compared with the adjacent uplands.
These two important conditions dominate in a great measure
the minor ones of variation in soil-texture. Yet where, as
is largely the case in the southern part of the State of Missis¬
sippi, the amount of calcic carbonate is insufficient to overcome
the sourness of the soil, the vegetative contrasts become ex¬
tremely striking and characteristic, as explained above.
Contrast Between " First " and “ Second " Bottoms. — A
very striking phase of transition between the alluvial bottoms
and the uplands proper in the Cotton States are the second bot¬
toms or hammocks of the streams, whose soil and tree-growth
in most cases differ markedly from those of the first bottom;
and these being usually closely adjacent, often afford a very
striking contrast to the latter. From some antecedent geologi¬
cal cause not fully understood, these hammocks, usually ele¬
vated from 4 to 10 feet above the present flood plain, have
almost throughout soils of a fine sandy, pulverulent or silty
nature, frequently in strong contrast to heavy clay soils in the
first bottom.
They seem, moreover, to have been at some time subject to
prolonged maceration under water, resulting in the reduction
of the ferric oxid, and its accumulation in the lower portion
of the deposit in the form of bog-ore spots or “ black gravel.”
Since such a process always results in the abstraction of phos¬
phoric acid from the general mass of the soil, to be accumulated
in the bog ore in an inert condition,1 these hammock soils,
usually whitish or gray in color, are almost throughout poor
in phosphates as well as in lime ; the latter having been defini¬
tively leached out. The resulting vegetation, as may be
imagined, is widely different from that of the bottom proper,
1 See Chapter 2, p. 24.
RECOGNITION OF CHARACTER OF SOILS.
507
as well as, frequently, from that of the adjacent uplands; and
though level and fair to see, these hammocks are usually un¬
thrifty and last but a short time under exhaustive cultivation.
Accordingly, their forest growth is prevalently that of the
poorer class of uplands, viz., small-sized post and black-jack
oaks, and in the low ground depauperated water oak, or less
commonly willow oak, of the low, stunted type indicative of a
a soil of inferior productiveness. The luxuriant growth of the
present alluvial bottom is often seen within a few feet of the
unthrifty vegetation of these hammocks. It is usually only in
the limestone regions, and in the lower course of the larger
streams, that the hammocks or second bottoms are found to be
of good fertility.
The Tree Growth of the First Bottoms. The Cypress. —
Among the trees occupying the low ground of the first bottom
in the southern Mississippi states, the deciduous cypress ( Tax-
odium distichum ) deserves special mention as an example of
extreme variation in form. In sloughs and swampy tracts, as
is well known, the cypress grows with roots submerged
throughout the season, excepting only the excrescences known
as “ knees,” which project above the water, probably perform¬
ing some function in connection with the aeration of the root,
which is essential to the root functions in all plants. The
trunk rising from the water is supported by numerous pro¬
jecting buttresses for from 8 to 15 feet above the water; higher
up it becomes cylindrical for a height of from 40 to 70 feet,
then divides up into a few widely spreading, thick, almost
conical branches, whose twigs and foliage form an almost level
surface to the head. This level-topped forest growth char¬
acterizes at once the submerged areas of the river and coast
swamps.
But the cypress is by no means confined to the swamps and
sloughs; it is also found occupying the better class of hammock
lands, 1 2 or 15 feet above water level. In this case, however,
the tree assumes a shape and growth so wholly different from
that described above as to lead to a popular assertion of a dif¬
ference of species. As a matter of fact, however, the cones of
these upland cypresses, when dropping into the water be¬
low them, reproduce exactly the common swamp form. The
extraordinary difference in the aspect of the tree under these
5o8
SOILS.
different conditions is best seen in the subjoined diagram,
showing the upland cypress to assume the form of the tall
willow oak, with which it is sometimes locally associated.
The trees from which the annexed sketch is taken grew
within thirty feet of each other, on Yellow creek, a small
tributary of the Tennessee river, in Tishomingo county, Miss.
The soil stratum is underlaid by a shaly limestone, and bears
lime vegetation.
Swamp. Upland.
Fig. 8i. — Forms of Deciduous Cypress on overflowed and on bench-land.
The fact that the deciduous cypress grows without difficulty
on the moister class of lowlands in California, 12 or 15 feet
above bottom water, is of interest in this connection. It then
assumes the upland form shown in the figure above, although
not growing quite as tall. The calcareous nature of these soils
is probably an important factor in this apparently incongruous
adaptation of a subtropical swamp tree to arid conditions. In
its swamp form the cypress usually grows in rather shallow,
heavy clay soil, into the dense subsoil of which the roots pene¬
trate but little.
RECOGNITION OF CHARACTER OF SOILS.
509
Other Lowland Trees. — The lowland hickories, like their
brethren on the highlands, seem on the whole to prefer the
lighter or loamy bottom soils to those of a heavier character.
This is especially true of the Pecan. The latter, as well as the
shell-bark hickory, is especially indicative of the highest class
of bottom soils. The black walnut, while apparently also best
suited in loamy soils, is also more or less found on heavy bot¬
tom lands, provided they are sufficiently calcareous ; and the
same is measurably true of the tulip or white-wood tree. The
most frequent occupants of heavy bottom lands, however, are
the black gum and sweet gum, so that “ gum swamps ” are
usually found to be of that character.1 But in the prairie
region, where the bottom soils are very calcareous and heavy,
as well as in corresponding soils of the “buck-shot ” lands of
the great Mississippi Bottom, the chestnut-white (cow- or
basket- ) oak sometimes occupies such ground almost exclu¬
sively. Among the accompanying trees are especially the
honey locust, the crab-apple, mulberry and sweet gum, as well
as ash.
General Forecasts of Soil Quality in Forest Lands. — While
the oaks and pines mentioned as forming the bulk of the timber
constitute in the cotton states the prima facie evidence, as it
were, of the general character of the land, there are numerous
other trees and plants which serve the discriminating land-
seeker as a guide for the quality of the soils in different locali¬
ties. While everywhere, well-developed black, red, Spanish
and white oaks are considered as signs of a high quality of
land, the tall, thin scarlet, the upland willow, and the bar¬
rens scrub oak are considered as indications detracting mate¬
rially from the producing value wherever they prevail. The
various hickories are throughout considered as indicating good
land when mixed with the oaks, or by themselves ; while the
presence of walnut, linden and tulip tree will usually raise the
estimate of uplands to the highest class. On the other hand,
the occurrence of small black-gum trees and short-leaved pine,
with low huckleberry, among the oaks of whatever kind, ac-
1 Hence perhaps the vernacular name “gumbo ” for heavy, adhesive clay soils
in the north central states ; which may also, however, be derived from a compari¬
son with the “ gummy ” pods of the cultivated okra or gumbo plant.
5io
SOILS.
companied as they usually are by the disappearance of the
black, white and Spanish oaks, will materially depress the land-
values.
The appearance of well-formed oaks, as well as of hickory,
is therefore at once welcomed as an evidence of soil improve¬
ment, while that of low huckleberry bushes and small black
gums indicates the reverse. An increase in the thickness and
retentiveness of the soil stratum is also usually indicated by
the occurrence of short-leaved pine in the long-leaf-pine areas.
The black, red, white, and Spanish oaks belong altogether
to soils of medium physical constitution, only their size upon
such lands depending upon the relative richness in plant-food;
but without such changes producing any notable variation in
their form. Clearly then, these species are intolerant of ex¬
treme physical conditions, and are practically restricted to soils
of “ loamy ” character and easy cultivation.
CHAPTER XXV.
RECOGNITION OF THE CHARACTER OF SOILS FROM THEIR
NATIVE VEGETATION. UNITED STATES AT LARGE.
EUROPE.
The application of the above data outside of Mississippi can
mostly be verified only in a fragmentary way from such data
as are casually given in the reports of State Surveys, as well
as from such observations as the writer has been able to make
personally elsewhere. In the latter category the most copious
refer to the states of Alabama, Louisiana and Illinois.
Alabama. — The observations of Prof. Eugene A. Smith,
and those of Dr. Chas. Mohr, are especially valuable and cogent
as to the close correspondence of the soil and vegetative phe¬
nomena with those observed in Mississippi,1 They are faith¬
fully reproduced on the corresponding geological areas, includ¬
ing also the Flatwoods. Northwest of Mobile, on the Missis¬
sippi line, the long-leaf-pine forest is interspersed with more
or less continuous areas bearing a fine oak growth, with hick¬
ories and other trees indicating a calcareous soil. This fea¬
ture is most extensively developed in Alabama in what is
known as the “ lime-sink region,” on the borders of which the
vegetative transition in passing from the non-calcareous sandy
pine land, can be observed in the most striking manner and
with frequent alternations. Northward of the long-leaf-pine
belt, the tertiary and cretaceous areas show in Alabama the
same features as in Mississippi, viz., black calcareous prairies
alternating with ridge lands, among which in the cretaceous
area the Pontotoc ridge is represented by a series of isolated
knobs, popularly known as Chunnenugga ridge, closely re¬
sembling the former in its soils and vegetative character.
In northern Alabama, according to Dr. Smith, on the vari¬
ous stages of the Carboniferous formation, ranging from a
1 See Plant Life of Alabama, by Charles Mohr, Vol. VI. Contr. U. S. Nat
Herb., U. S. Dep’t Agr.; Alabama Ed. of Same, Ala. Geol. Survey, 1901.
5H
512
SOILS.
sandy or conglomerate character to that of limestones of vari¬
ous degrees of purity, soils contrast strikingly with each other,
agreeing closely with those seen in the neighboring part of
Mississippi. Here, moreover, the contrast between the natural
vegetative character as well as cultural value of the lands de-
rived from the magnesian limestones (the “ barrens " ) con¬
trasts strikingly with those originating in the purer limestones,
on which the blue grass is at home.
Louisiana. — As to Louisiana, whose geological formations
correspond closely to those of Mississippi, it may be said in
general that the vegetative phenomena coincide completely with
those observed in Mississippi. The “ white-lime country ” of
northeastern Mississippi is represented in Louisiana only by
patches occurring here and there on a line laid from Lake
Bistineau to the coast at Petite Anse Island. But the chief
characteristics of the calcareous area, among them especially
that of the occurrence of red cedar and clumps of crab-apple,
persistently reappear. The “ Central Prairie Region ” of
Louisiana is quite narrow, but on it there reappear precisely
the same characteristics described in connection with that area
in Mississippi. In the long-leaf-pine region of Louisiana there
occur, as in Mississippi, some isolated patches of a calcareous
character, the largest of which is on the Bayou Anacoco in Ver¬
non Parish, near the western border of the State. As we
emerge from the sandy lands of the long-leaf pine area to that
underlaid by the calcareous formation, we find, first, a change
to oak and short-leaved pine, then the oak forest alone ; finally,
on a level black prairie of considerable extent, the post and
black-jack oak in their thick-set form, clumps of crab-apple, red
haw and honev locust, here and there a red cedar; exactly as
has already been described in connection with the prairie lands
of Mississippi. To southward of the long-leaf-pine area lies a
broad belt of level, generally treeless, sandy prairie, in part
dotted with groves of timber, but otherwise with nearly the
same peculiar, small-seeded herbaceous vegetation observed in
the corresponding portion of Mississippi. But in Louisiana
there intervenes between these gray sour lands and the shell
hammocks of the immediate seacoast with their groves of live
oak, a belt of black calcareous prairie, increasing in width and
clayeyness towards the West, and acquiring considerable exten-
RECOGNITION OF THE CHARACTER OF SOILS.
513
sion in the corresponding portion of Texas. On these prairies
we again find the calciphile vegetation, including the honey
locust, clumps of crab apple and red haw, etc., but not usually
any oak growth, except (near the seacoast) the live oak. In
the hilly country of northern Louisiana there is reproduced
substantially the vegetative character of the “ short-leaf pine
and oak ” uplands of Mississippi (see map on p. 490, chapter
2 4), save in that, owing to the occasional outcropping of the
calcareous materials of the Tertiary, small prairies with black
soil are spotted about here and there. Bordering the Missis¬
sippi Bottom there are a series of oak-upland ridges with a
brown loam soil corresponding to the fertile area in north¬
western Mississippi, with small patches of the “ Cane hills ”
loess soils, bearing a corresponding tree growth.1
In Western Tennessee the vegetative zones so distinctly
shown in the adjacent portion of Mississippi are not so strik¬
ingly outlined, but so far as they do exist, the phenomena ob¬
served accord exactly with those heretofore described. The
same holds true of Western Kentucky, as is well set forth and
graphically described in the reports of the geological surveys
of that state by Dr. David Dale Owen, and later by Dr. R. H.
Loughridge.
North Central States. — North of the Ohio River the mater¬
ials of the geological formations are not nearly as much varied
as they are south of the same ; consequently the vegetative
features are also much more uniform. It must be remembered
that from the Alleghenies nearly to the Mississippi, the states
of Ohio, Southern Michigan, Indiana and Illinois are largely
covered by drift deposits overlying the older formations, except
that along the Ohio and Mississippi rivers lies the calcareous
loam of the Loess or Bluff formation.
Within the states mentioned, however, not only are the older
underlying formations very generally calcareous, but calcar¬
eous sand and gravel form a large proportion of the drift de¬
posits, which in most cases overlie the rocks. Hence we find
from the Alleghenies to the Mississippi a predominance of the
oak forests which characterizes calcareous soils, as in the bet¬
ter class of uplands in Mississippi and Tennessee; interrupted
1 See “ Final Report of a Geological Reconnoisssance of Louisiana,” published
by the New Orleans Academy of Science in 1871.
33
5i4
SOILS.
only here and there by sandy belts or ridges bearing inferior
growth, among which, again, the black-jack and post oaks,
with short-leaved pine, are conspicuous. But in a large portion
of Illinois, as well as in Western Indiana, the oak forest is in¬
terrupted by more or less continuous belts, and sometimes by a
wide expanse, of black prairie, generally treeless or bearing
only clumps of crab-apple and haw, and underlaid more or less
directly by the carboniferous limestones, whose disintegration
has materially contributed to the black prairie soils ; which are
noted for their high and long-continued productiveness. The
lower ground is characterized, besides clumps of crab-apple
and red haw, by the frequent occurrence of the honey locust,
the lead plant ( Amorpha frnticosa) , the button-bush ( Cephal -
anthus Occident alls') , and among herbs by the polar plant
( Silpliiwn laciniatum) , the prairie burdock (S. tcrcbinthin-
accum) , the swamp rose-mallow (Hibiscus moscheutos) , the
sneezewort ( Helenium autumnale) , the wild indigo ( Baptisia
tinctoria and leucophcca) .
The black-jack and post oak are not nearly as frequently
found on the prairies of Illinois as on those of Mississippi and
Alabama ; but where they occur they assume a similar habit, in¬
cluding the occurrence of the dwarfed, apple-tree-shaped form
on the low ridges with heavy yellow clay soil, that sometimes
intersect the prairies. The post oak, moreover, in a form quite
similar to that described as occurring on the Flatwoods of
Mississippi, forms the timber of the “ post oak flats ” occasion¬
ally found between the low ridges bordering the streams, or
along the edges of the prairies. The herbaceous vegetation of
these post oak flats distinctly characterizes them as being poor
in lime. In the loamy uplands, where the calcareous ingre¬
dient is more abundant, the open-headed form of the black¬
jack and post oak are also found, interspersed with a luxu¬
riant growth of black, red and white oak, with more or less of
hickory, which here assume a magnificent development, much
superior to that seen south of the Ohio. These yellow-loam
uplands correspond very closely in their soil-composition and
agricultural character to the brown-loam area of Mississippi
and Tennessee, which lies inland from the Loess belt. Where
these uplands approach the prairie or the outcrops of a lime¬
stone formation, there is usually added to the oak growth the
RECOGNITION OF THE CHARACTER OF oJ
'17
linden, the wild cherry and the ash; the latter two also usually
appear in the bottoms of the streams and on the slopes ad¬
jacent, together with the walnut and butternut, and in the
lowest ground the sycamore.
The tree growth of the Loess belt bordering the Ohio and
Mississippi, so far as climatic differences permit, agrees almost
precisely with that described in the corresponding portions of
Mississippi and Tennessee. The change from the oak and
hickory growth covering the yellow-loam uplands toward the
more calcareous area is evidenced by the appearance of large
sturdy trees of sassafras, together with the linden and sugar
maple. Descending from the “ bluff ” toward the rich bottom-
prairie with its black, heavy soil, we at once encounter the
familiar indices of the more highly calcareous land, viz., the
honey locust, clumps of crab apple and red haw, with hack-
berry, Kentucky coffee tree and mulberry on the lower ground ;
In late summer and during autumn, a tall growth of the iron
weed ( V ernonia ), several Eupatoriums ( E . perfoliatum and
purpureum, the white and the purple boneset) and of the blue-
spiked Verbena are very characteristic, as are also several spe¬
cies of Cassia (Carolina coffee, etc.,) and the swamp rose-mal¬
low.
Upland and Lowland Vegetation in the Arid and Humid
Regions . — In the humid countries there is commonly a marked
difference between the vegetation of the uplands and lowlands,
arising not merely from the difference in the moisture supply,
but evidently of a specific nature. When we discuss the char¬
acteristic plants in detail, it becomes obvious that it is lime
vegetation that, in most cases, forms the characteristic dif¬
ferences between upland and lowland forest growth ; a nat¬
ural consequence of the leaching-down of the lime from the
higher land to the lower levels. By way of counter-proof we
find that when the uplands themselves are of a calcareous
nature, a part at least of the lowland flora ascends into
them. As prominent examples may be mentioned the Tulip
tree (Liriodendron) , black walnut, ash, Kentucky coffee tree,
Hercules’ club, etc., which are lowland trees over the greater
part of their area of occurrence; but in the loess or Cane hills
bordering the Mississippi and its larger tributaries, as well as
in the limestone regions of the southwestern and western states,
5i4
SOILS.
are conspicuous in the uplands as well. The tall southern cane
( Arundinaria macrosperma) , usually considered a plant of the
low river bottoms, originally covered the loess or “ Cane hills ”
of the lower Mississippi, with their highly calcareous soils.
The same is true of many other trees and shrubs characterizing
limy lands. Of course there are some whose habitat is depend¬
ent upon the concurrent presence of both lime and moisture,
such as the sycamore, cottonwood, hackberry, pawpaw, etc.,
which are naturally found only in stream bottoms or on low
hammocks.
In the arid region, on the contrary, the main difference in
upland and lowland vegetation is (outside of mountain in¬
fluences) entirely referable to moisture-conditions; the proof
being that so soon as the uplands are irrigated the lowland
flora takes possession. Both uplands and lowlands being
abundantly calcareous, there then is no cause for any material
differences. This substantial uniformity of upland and low¬
land plant growth is particularly striking in the comparatively
restricted floras of Eastern Oregon and Washington, and in
Montana, where the more luxuriant growth of the valleys is al¬
most the only contrast seen when their vegetation is compared
with that of the uplands adjacent.
Forms of Deciduous Trees in the Arid Regions. — Since, as
shown above, the soils of the arid regions are almost through¬
out calcareous, we should expect that the forms of the native
trees would in general conform to the rule given above. As
regards the deciduous trees this is very generally true : We
rarely see on the Pacific slope, south of Oregon, anything to
compare with the tall oaks of the Atlantic forests. The native
oaks are as a rule of low, spreading growth, with stout, short
trunks ; and as they rarely form dense forests, the timbered
areas have an orchard-like appearance, characteristic of the
landscapes of the arid region, from the Mezquit Plains of
Texas to Eastern Oregon and Washington. Only where a
very abundant supply of moisture prevails do we find occa¬
sional exceptions. The trees of the humid region when trans¬
planted to California have a perverse tendency to branch low,
so that only the most persistent trimming-up will induce them
to form trunks at all like those found in their native climes. In
RECOGNITION OF THE CHARACTER OF SOILS.
517
some cases no amount of trimming will result in the formation
of anything more than bushes.
It may be objected that the arid climate as such, and not the
calcareous nature of the soil, is the cause of this tendency. It
is unquestionable that this low-branching habit is a distinct
advantage to the plants, whose trunks would otherwise be fre¬
quently scorched by the hot summer sun ; as happens when
Eastern settlers try to grow “ standard ” fruit trees, with the
result that a “ sore/' or sunburnt streak is formed on the south¬
west side of the exposed trunk. All orchard trees should
therefore be pruned “ vase-shape ” in arid climates, partly for
this, partly for other reasons. But this cannot explain the
fact that seedlings from eastern acorns act precisely as do accli¬
mated trees ; so that it is not a case of the survival of the
fittest to endure arid conditions.
Tall Growths of Conifers. Moreover, while the rule holds
good with almost all deciduous trees, it is not applicable to the
Conifers; which in the case of the Sequoias (redwoods and
“big-trees”), sugar pine and others, exemplify some of the
tallest growths known in the world. The Eastern Cedar or
Juniper grows tall only on sufficiently calcareous soils, and in
the Mississippi Valley states at least, wherever it occurs is an
unfailing indication of calcareous lands. The extended oc¬
currence of the spruce on the Allegheny Ranges, where lime¬
stone formations prevail so largely, seems to indicate a similar
preference for calcareous lands. And this is certainly true of
the black locust, which reaches its extreme southern range in
the cretaceous hills of Northeastern Mississippi, showing the
stout, stocky form it also assumes when planted in the calcare¬
ous black-prairie lands of Illinois.
Herbaceous Plants as Soil Indicators. While herbaceous
plants are not as generally considered by land-seekers in judg¬
ing of soil fertility and character, it goes without saying that
very many are quite as characteristic as the tree vegetation,
especially when deep-rooting, so as not to indicate merely the
character of a few inches of surface soil.
In the Middle West of the United States especially, a large
number of the Composite serve as marks of high productive
capacity. This is particularly true of the larger species of
the sunflower tribe, among which Helianthus grosse-scrratus
SOILS.
518
and doronicoides are perhaps the most generally notable ; while
farther west, beginning with Kansas, the “ Sunflower State,”
and its northern neighbor, H. annuus, whether native or intro¬
duced, becomes conspicuous also. The Silphiums (compass
sunflowers) have nearly the same significance, S', laciniatum
and perfoliatum being prominent on the prairies of Illinois and
Indiana ; but in land under cultivation they are mostly re¬
placed by a luxuriant growth of the Ragweed, Ambrosia tri-
fida. Various species of Bidens (beggar ticks), notably the
B. aristata and cernua, accompany the true sunflowers in the
lower grounds of these regions, as do also Heliopsis laezns ,
Coreopsis triperis and Rudbeckia ( Obeliscaria ) pinnata.
Rudbeckia hirta and purpurea , though also occurring on rich
soils, are not characteristic of them. The larger species of
golden rods (Solidago) , notably S. canadensis, rigida and
speciosa (not ordinarily distinguished by farmers) share
substantially the distribution of the large sunflowers men¬
tioned above. Of the Asters, only A. novcc-anglice serves aj»
a reliable guide to high-class lands in the Middle West,1 but
a very copious growth of asters and solidago of various species
is always a welcome indication of land quality, and indicates
soils of good lime content, if not absolutely calcareous.
Leguminous Plants. — It is generally understood that most
leguminous plants, and among them especially the clovers, in¬
dicate rich, or rather, calcareous lands. The very large pro¬
portion of lime contained in the ash of legumes at once creates
this presumption, which is fully confirmed by experience so far
as our ordinary culture plants of that relationship are con¬
cerned. The favoring effect of lime on the development of
bacteria, so essential to the full development of cultivated
legumes, has already been referred to. The favoring effect of
gypsum sown even in small amounts with clover and other
legumes, may probably be referable to the known action of that
salt in promoting nitrification, which in the first stages of
leguminous growth is so highly favorable to a vigorous and
early start of the crop, and to a more copious production of the
nitrogen-assimilating nodules. The quick change noted in
meadows and pastures of languishing production so soon as
moderately limed, by the appearance of clover among the herb-
1 In view of its specific designation and the reputed poverty of New England
soils, this is rather unexpected.
RECOGNITION OF THE CHARACTER OF SOILS.
519
age, at once reminds us that the Rhizobia do not flourish in
acid lands. The great prevalence of leguminous plants of all
kinds in the arid region — clovers (not fewer than twenty-three
species in California alone), Lupins, Astragalus and related
genera, at once remind us of the universal prevalence of
calcareous soils in these regions, as shown above. Mntatis
mutandis , we find precisely the same general facts in the arid
regions of the other continents.
Nevertheless, it must be kept in mind that not all plants of
the leguminous order are positively “ calciphile.” Within the
United States, it is especially the genera Dcsrnodium ( Mei -
bomia) and Lespedeza, which are very numerously represented
in the long-leaf pine region of Mississippi, where the soils are
so poor in lime. Whether under these conditions these plants
develop the rhizobian nodules, has not, so far as the writer
is aware, been definitely observed. Certain it is that quite
a number of these plants occur on both calcareous and non-
calcareous soils, and on the latter assume a much more vigor¬
ous development than in the pine woods. But it is evident that
they, with a few others (e. g. Galactia mollis, Cassia chamce-
crista and nic titans) are more or less indifferent to the lime-
content of soils, and cannot therefore be relied upon in judg¬
ing the quality of lands. In Mississippi and northern Ala¬
bama, the Tephrosia virginica (“ devil’s shoestring”), associ¬
ated with chestnut and short-leaved pine, is characteristic of
the poorest non-calcareous lands, and bears seeds but very
scantily. It disappears so soon as calcareous lands are ap¬
proached, together with the chestnut tree.
EUROPEAN OBSERVATIONS AND VIEWS ON PLANT DISTRIBUTION
AND ITS CONTROLLING CAUSES.
The writer has thus far presented and discussed mainly his
own observations made in the United States, without refer¬
ence to the previous and contemporaneous work on the same
subject in Europe. There arose certain discrepancies which
could not well be explained without a previous full consider¬
ation of American conditions.
As is well known, for nearly twenty years the accepted
theory in Europe was that of Thurman,1 which attributes the
1 Essai de Phytostatique appliquee a la chaine du Jura et auxcontrees voisinesi
2 vols. 8vo. Berne, 1849.
520
SOILS.
distribution of the native floras entirely to physical conditions ;
thus anticipating by more than half a century the correspond¬
ing hypothesis lately brought forward by the U. S. Bureau of
Soils. Thurmann classes plants simply as hydrophile and
xerophile, thus differing from most of our modern ecologists
merely in omitting the transition phase of “ mesophytes,”
which now serves as a convenient pigeon-hole for an indefinite
variety of plants.
While gradually many were led by their observations to
doubt the correctness of Thurmann’s exclusive physical theory,
Fliche and Grandeau 1 were apparently the first to impair by
their investigations the confidence in the accepted view. They
investigated exhaustively the conditions under which the mari¬
time pine and the chestnut tree, both antagonistic to lime,
would flourish, and proved that the presence of any consider¬
able amount of lime in the land would cause them to languish
or die, although the physical conditions so far as ascertainable
were exactly alike. It is interesting to note what were the
lime-percentages which caused these differences; viz, for
the “ noncalcareous ” soil and subsoil, respectively, .35 and
.20%; for the calcareous land, 3.25 and 24.04%, the latter
evidently being decidedly “ marly.” The composition of the
ash of these trees is very instructive, and is therefore given in
full. Alongside of the ash of the maritime pine on the two
soils is given that of the Corsican pine, a lime-loving tree.
COMPOSITION OF PINE ASHES ON CALCAREOUS AND NON-CALCAREOUS LANDS.
Maritime Pine,
Pinus Pinaster.
Corsican Pine,
Pinus Laricio.
Potash . .
Soda .
Lime . .
Magnesia .
Ferric Oxid .
Silica .
Phosphoric acid .
On non-calcareous soil.
16.04
1.91
40.20
20.09
383
9. 18
9.00
On calcareous soil.
4-95
2.52
56.15
18.80
2.07
6.42
9.14
On calcareous soil.
1356
2.24
49-13
13-49
329
7- 14
11 33
Total .
100.25
IOO.O4
100. 18
Ash per cent . .
1.32
i-54
2-45
1 Annales de Chimie et de Physique, 4me serie, tome 29 ; ibid. 5me serie,
Tome 2. Also, ibid, tome 18, 1879.
RECOGNITION OF THE CHARACTER OF SOILS.
521
It is very interesting to note in these analyses the inverse ratio in the
absorption of potash and lime by the maritime pine, which seems to be
unable to defend itself against excessive absorption of lime and thus
experiences a dearth of potash which naturally interferes with the for¬
mation of starch and chlorophyl ; hence probably induces the chlorosis
so well known to occur on excessively calcareous soils. The lime-loving
Corsican pine takes up a larger total amount of ash and more phos¬
phoric acid, and nearly three times as much potash, but considerably
less lime than did the maritime pine on the same calcareous soil.
The corresponding analyses made by Fliche and Grandeau, of the
leaves and wood of chestnut grown on the same two kinds of soils, gave
in general the same results ; and they add that the smaller content of
iron absorbed by the calcifuge trees when grown on calcareous soil point
also to a deleterious influence upon the normal formation of chlorophyl.
Following Fliche and Grandeau, Bonnier 1 made corro¬
borative tests by sowing seeds of the same plants, both cal-
ciphile and calcifuge, upon the two kinds of soils, and noting
the differences in their mode of growth and internal structure.
Calciphile, Calcifuge and Silicophile plants.
The subject has been somewhat exhaustively discussed by
Contejean2 who enumerates and has classified under the three
general heads of calciphile, calcifuge and indifferent, over
1700 species of European plants. Unfortunately he had but
few soil analyses at his disposal, and was inclined to consider
as non-calcareous, most soils that gave no effervescence with
acids. But notwithstanding this disadvantage so far as his
contention of the efficacy of chemical soil-composition, and
especially of lime is concerned, he disproves very effectually
the physical theory of Thurmann, by numerous examples from
France and elsewhere in Europe ; and also disposes very defi¬
nitely of the claim that there is a special class of “ silicophile ”
plants. He concludes that silica (and sand) is merely a neu¬
tral and inert medium which offers refuge to the plants “ ex¬
pelled ” by lime; and that clay similarly exerts no chemical but
1Bull. de la Societe Botanique de France, tome 26, 1879.
2 Geographic botanique. Iufluence du terrain sur la vegetation. Baillere et
et Fils, Paris, 1881, 143 pp.
522
SOILS.
only a purely physical action. That potash, phosphoric acid
and nitrogen, while most essential as plant-foods, exert other¬
wise little if any effect on general plant-distribution. He al¬
ludes similarly to magnesia ; and his final conclusion is that
“ chemical are in general more potent than physical influences/’
and that the most widely active influences are carbonate of
lime and chlorid of sodium. He does not, of course, deny the
potent influence of moisture upon plant distribution.
Since these publications were made, many observers have
investigated the subject, and the broad distinction between
lime-loving or calciphile and lime-repelled or calcifuge plants
has been very generally recognized and discussed : but the
cause of this discrimination by plants is still more or less the
subject of controversy. Some still claim that the calcifuge
plants (such as the chestnut, the huckleberries and whortle¬
berries, the heather and many other Ericaceae, most sedges,
etc.) are repelled by calcareous lands because they need a large
supply of silica, which they suppose cannot well be assimilated
in presence of much lime; hence they also designate the calci¬
fuge plants as “ silicophile ” ; while others attribute the prefer¬
ence of calciphile plants to the physical effects produced upon
the soil by lime, as outlined above (chapter 20, page 379).
The contention that the presence of much lime in soils ren¬
ders silica insoluble and hence unassimilable by plants, is at
once negatived by the fact that waters exceptionally rich in
silica, partly simply dissolved by carbonic acid, partly in the
form of water-soluble alkali-silicates, are very abundantly
found in the arid region. This is especially the case in Cali¬
fornia, where moreover a number of species of very rough¬
surfaced horsetail rushes and grasses prove the ready absorp¬
tion of silica when wanted, even in strongly calcareous soils.
But the question is whether the supposed class of silicophile
plants is a reality or merely a theoretical fiction, based upon
the habit of speaking of “ siliceous ” soils as a class apart from
other and especially heavier or clay soils. As a matter of fact,
the siliceous soils usually so called are simply those poor in clay
and lime — in other words, “ light ” lands, the outcome of the
weathering of quartzose rocks into sandy soils, which in the
humid region are always poor in lime because thoroughly
leached. In the arid region, on the contrary, sandy lands are
RECOGNITION OF THE CHARACTER OF SOILS.
523
quite commonly just as calcareous as the heavier soils, and
show no “ silicophile ” flora.
According to the writer’s observations and views, it being
obvious that some plants are practically indifferent to the pres¬
ence or absence of lime in the soil except in so far as it influ¬
ences favorably the physical conditions, moisture must always
stand first as the condition of maximum crop production, and
as a conditio sine qua non of the best development of plants on
all kinds of soils; its best measure being a matter of special
adaptation to each species. But this being understood, he
agrees with Contejean as to the commanding influence of lime
in determining the adaptation of soils to plants, both cultivated
and wild. At the same time, it is obvious that the absence of
the opportunity to observe really native vegetation, adapted to
the soils through ages, has created for European observers
difficulties which are readily solved where original native
floras are available.
Schimper 1 says pointedly that observations prove that the
differences between the location of plants on calcareous and
siliceous soils are not constant, but vary from province to
province; that e. g., the list of indifferent (bodensteter) plants
for the Alps do not hold good in the Dauphine, still less be¬
tween the Carpathians and Skandinavia. According to
Wahlenberg the following species are calciphile in the Carpath¬
ians, and according to Christ indifferent in Switzerland :
Dryas octopctala , Saxifraga oppositifolia, most of the legumin¬
ous species, Gentiana nivalis, G. tenella, G. verna, Erica carnea,
Chamceorchis alpina, Carex capillaris. Geum reptans is re¬
ported by Bonnier to be exclusively calciphile on Mont Blanc,
exclusively silicophile in the Dauphine; indifferent in Switzer¬
land. A great number of similar contradictions are reported
by others as well, and the entire subject thus becomes rather
vague; so that Schimper and others suggest that climatic con¬
ditions may in part be responsible for these discrepancies.
In all, or nearly all these cases, it is tacitly assumed that the
underlying geological formation has essentially been the source
of the soil, and that its character is determined accordingly.
But this assumption is wholly arbitrary unless confirmed
by actual direct examination. A soil-formation overlying
1 Pflanzengeographie, p. 1 1 1 & ff.
524
SOILS.
limestone on the slopes of a range may be wholly derived from
non-calcareous formations lying at a higher elevation, or may
have been leached of its original lime-content by abundant
rains. The feldspars constituting rocks designated as granite,
may or may not be partially or wholly of the soda-lime in¬
stead of the potash series ; the mica may or may not be partially
replaced by hornblende, in which cases the soil would be cal¬
careous to the extent of determining the character of the flora
as calcifuge or calciphile, without its being at all evident in the
physical character of the soil, which would still be “ granitic ”
or “ siliceous." Such observations in order to be critically
decisive, clearly require that the observer should be, not merely
a systematic botanist, nor a mere geologist or chemist, but all
these combined. There is good reason to believe that most or
all of these supposed contradictions would disappear before a
critical physical and chemical examination of both the soils and
the rocks from which they are supposed to have been derived.
Contejean himself, in placing so many of his long catalogue of
plants into the doubtful groups, suggests many cases in which
the above considerations may explain the apparent dis¬
crepancies.
What is a calcareous soil f The definition adopted for this
volume has been given in a previous chapter (chapter 19, page
367) ; viz, that a soil must he considered calcareous so soon as
it naturally supports a calciphile flora — the “ lime vegetation ”
so often referred to above and named in detail. Upon this
basis it has been seen that some (sandy) soils containing only
a little over one-tenth of one per cent, of lime show all the
characters and advantages of calcareous soils ; while in the case
of heavy clay soils, as has been shown, the lime-percentage
must rise to over one-half per cent, to produce native lime
growth. While in the United States observations of the con¬
trasts between calciphile and calcifuge floras are easily made
in the field, and the facts must attract the attention of any
f aii ly qualified observer, in Europe they would have to be made
the subject of special cultural investigation based upon soil
analysis ; a procedure not yet fully accredited abroad, any more
than in the United States. In a general way it has however
been recognized by Maercker, as shown at the end of the pre¬
ceding chapter. How far this estimate was based upon Ameri-
RECOGNITION OF THE CHARACTER OF SOILS.
525
can precedents, can now be only conjectured. Certain it is
that the European definition of calcareous soils remains to the
present day a wholly different one from that stated above;
and from this have arisen the greater part of the doubts and
differences of opinions among European botanists as to the
classification of plants in relation to calcareous soils. Two
per cent, of lime (equivalent to nearly double the amount of
carbonate) is the prevailing European postulate for a cal¬
careous soil. Some go so far as to postulate effervescence
with acids, requiring about 5% of the carbonate.
Predominance of Calcareous Formations in Europe. — It
is not generally recognized even among geologists how
abnormally predominant are limestone formations in Europe.
In all works on European agriculture we find the “ lime
sand ” mentioned as a normal ingredient of soils, specially
provided for (or against) in the operations of soil exami¬
nation. Its presence is the rule, its absence the exception.
Soils as poor in lime as are those of the long-leaf and short-
leaf pine regions of the United States, are there very excep¬
tional and (like the “ Haideboden ” of northern Germany)
have long remained almost uncultivated. Calcareous soils
being the rule in the regions of intense culture, the ideas
of both agriculturists and agricultural chemists have in
Europe, in the main, been based upon them as normal soils;
so that instead of comparing calcareous, and non-calcareous
soils properly speaking — i. e., such as would not bear native
lime-vegetation — the majority of comparisons has actually
been made between soils which, in the American sense, were
all or chiefly within the calcareous class. It is characteristic
of this state of things that the injuriousness of an excess of
lime is among the foremost themes of European (especially
French and English) agricultural writers, as against the bene¬
ficent effects prominently assigned to lime in America. No
such popular saying as that “ a lime country is a rich coun¬
try ” exists in Europe ; on the contrary, we constantly hear,
and see in books, the mention of “ poor chalk lands,” and in
France especially the deleterious effects of excess of lime upon
crops is the theme of remark. Excess of lime in their marly
lands has been the despair of French vintners, and Viala was
specially sent to America to find some vine to serve as a
526
SOILS.
grafting stock which would resist the tendency to chlorosis
which renders many of the American phylloxera-resistant
vines useless to the viticulturists of France. Viala did not
find such grape-vines until he reached the cretaceous (chalk)
area of Texas, where the native vines had long ago adapted
themselves to marly soils; and these vines have solved the
problem for French viticulture.
And England, France, Belgium and most of western
Europe are rich countries, largely owing to their abundant
limestone formations ; and it may be questioned whether, had
this been otherwise, Europe would so long have remained the
center of civilization ; for starving populations are not a good
substratum for high mental culture and progress. It may
equally be asked whether the invariably calcareous character
of arid soils, as heretofore shown,, has not, together with
their general high quality, been largely a determining factor
in the location and persistence of so many ancient civilizations
in arid lands; as outlined in chapter 21, page 417. In this con¬
nection, the proper distinction between calcareous and non-
calcareous soils passes from the domain of natural science to
that of the history of human civilization.
CHAPTER XXVI.
THE VEGETATION OF SALINE AND ALKALI LANDS.
Marine Saline Lands . — While the saline alluvial lands of
the sea-coast differ both in their mode of origin and in their
nature from the alkali soils or “ terrestrial saline lands,” as
they have been called in Europe, their vegetation has in many
respects a common character. Not only is there much simi¬
larity, sometimes even identity, in the kinds of plants inhab¬
iting these lands, but their saline ingredients induce certain
changes of form and structure in plants not properly “ saline ”
but more or less tolerant of soluble salts, by which the saline
or alkali character of the lands may be recognized.
Just as in the case of lime we must distinguish between the
plants definitely repelled by a large amount of this substance
in the soil (calcifuge), while others prefer the soils in which
lime is abundant (calciphile) , and still others appear to be in¬
different to its presence and are governed in their habitat
by the physical conditions presented : so in the case of saline
lands the salts may attract or repel certain plants. The lat¬
ter class is much the largest ; while there is also a number of
plants which are more or less indifferent to the presence of
salts, provided these be not in very great excess. Such plants
constitute the next-largest class; while those attracted by salts,
and whose welfare is conditioned upon their presence, are
comparatively few in number, and still fewer among them are
of economic importance. Hence the soluble salts have largely
a negative importance for agriculture ; the question usually
being how to utilize the land until the undesirable surplus of
salts can be got rid of, partially or wholly, as the case may be ;
the former usually in sea-shore lands, the latter in the alkali
lands proper; in which a small remnant, not sufficient to injure
crop plants, is usually desirable (see chapt. 23, p. 462).
General Character of Saline Vegetation. — Those familiar
with seashore marshes cannot fail to note the fleshiness and
527
528
SOILS.
succulence of the characteristic plants. This “ incrassation ”
belongs not only to the saline flora proper, but is acquired to a
greater or less degree when plants not ordinarily at home on
saline ground are transferred to it artificially, or by saline
overflows; while at the same time the leaves usually become
smaller, and the growth more compact. Correspondingly,
when saline plants are transferred to non-saline ground, the
leaves generally become thinner and larger, and the growth
more slender. The well-known “ Russian thistle ” is a case
in point, as is also its close relative, the soda saltwort (Sal-
sola soda) ; although the latter does not often venture as far
from the saline lands as does the former ( Salsola kali tragus),
which now seems to have become a world-wide weed, with
only a shade of preference for alkali lands.
Structural and Functional Differences Caused by Saline
Solutions. — It has been definitely shown by the investigations
of Schimper, Brick, Hoffmann, Lesage, Rosenberg and
others, that the peculiarities or changes of structure brought
about by saline solutions are essentially those pertaining to
xerophile (drought-enduring) vegetation; which in general
tend to the diminution of evaporation from the plant surfaces.
It may be said, roughly speaking, that the absorption of water
by the roots begins to diminish so soon as the concentration
of the saline solution approaches or exceeds one-half of one
per cent ; while when it rises as high as three per cent., water-
absorption by the roots ceases even in the wettest soils, and the
plant suffers from drought quite as much as from any di¬
rectly injurious effects of the salts. Different plants of
course differ in the measure of concentration which brings
about these phenomena, which vary also with the character of
the soluble salts. It is stated that injurious or useless salts
like common salt act at lower concentrations than e. g., salt¬
peter, which is useful. The difference in external structure
are : diminution of the size of leaves, assumption of cylindrical
or spinous forms, sinking-in of the breathing pores below the
outer surface, dense hairy covering, resinous exudations, etc.
Internally we find that xerophile plants have developed on
their upper or outer leaf-surfaces instead of one, several lay¬
ers of “palisade” (long and erect, closely-packed) cells,
through which transpiration is extremely slow, as is also the
SALINE AND ALKALI LANDS.
529
transmission of heat. When salt-tolerant plants are grown on
saline soils, their palisade cells are relatively lengthened.
Coincident with these external means for the retardation
of evaporation, the leaves of xerophiles are frequently sup¬
plied with special water-storage cells, which supply moisture
for the physiological processes when the root supply falls
short. The cactus tribe and similar-looking plants are ex¬
amples of the latter provision, which causes even animals
suffering from thirst to resort to them, although they eschew
the saline vegetation.
Absorption of the Salts. — The true halophytes or exclusive
salt plants, which refuse to grow on lands not containing a
large proportions of salt, often absorb so much salt that on
drying it blooms out on their surface ; they usually have, even
when green, a distinctly salty taste, and their ash is rich in
chlorids, specially of sodium. Such is the case of the
samphire, common in saline marshes everywhere. The total
ash is usually very high, often varying with the salinity of
the water or soil in which they have grown. Thus the salt-
content of the ash of samphire may vary by several per cent.
In other cases, as in that of one of the Australian saltbushes
investigated at the California station, neither the ash content
nor the composition of the ash varies materially whether the
plant be grown on strong alkali land, or on uplands whose
total saline content does not exceed (in four feet depth)
.015% or 2500 pounds per acre.
The following table gives the composition of the ash of
this saltbush alongside of that of two other prominent alkali-
plants of the same relationship, occurring, one in the San
Joaquin valley of California, in strongly saline lands, the
other in the Great Basin region of the interior, on lands
strongly impregnated with carbonate of soda. All these, it
will be seen, take up very large amounts of sodium salts,
notably the chlorid ; the Australian plant most so, the “ grease-
wood ” of the Great Basin least so ; a large proportion of the
alkali salts being evidently, in the latter case, contained in the
form of organic salts, which in the ash become carbonates.
It will be noted that the saltbush hay contains nearly one-
fifth of its (airdry) weight of ash, of which nearly 40% is
common salt. It therefore has a distinctly salty taste, and is
34
530
SOILS.
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SALINE AND ALKALI LANDS.
531
always moist to the touch, containing ordinarily over 15%
of moisture. It is therefore much liked by stock when fed
intermixed with other hay, and thus supplies all the salt
needed by cattle. The greasewood is much less liked by stock,
and bushy samphire is wholly rejected by them. Comparing
with these fleshy plants the ash of the two grasses, the first a
world-wide “ salt grass/’ the other a common grass of the
American arid region, we note that not only do they contain
much less soluble ash than the saltbushes, but especially much
smaller amounts of sodium salts; proving that even when
growing in company with the saltbushes on strongly impreg¬
nated land, they can repel from absorption these to them use¬
less or injurious salts. But in the case of the “ shad scale,”
also a “ saltbush ” of the Great Basin, the ash-content is
remarkably low — only about one-fifth of that of its Australian
relative — and it differs widely from the latter in having but
a very low proportion of soda, and a very high one of lime
and potash, approaching in these respects to our usual forage
crops ; and being also fairly rich in nitrogen, it forms accept¬
able browsing when other pasture plants are scarce. It there¬
fore does not exert the laxative action produced by the exclu¬
sive feeding on the more saline herbages.
The exceptionally high ash-content of the cactus or prickly
pear, also given in the table, arises, it will be noted, not from
the soluble salts but from the absorption of extraordinarily
high proportions of lime and magnesia. Owing probably to
the latter substance, and also the oxalate form in which lime
is usually found in the cactus tribe, this plant when used as
forage is also somewhat laxative.
Altogether, this table offers remarkable examples of wide
differences in the kind and amount of ash ingredients ab¬
sorbed by plants growing upon similar soils and under identi¬
cal climatic conditions ; indicating a selective power which no
merely physical theory of soil-action in plant growth can ex¬
plain.
Injury to Plants from the Various Salts. — The early ob¬
servers, especially Contejean, were predisposed from their
observations of lime on vegetation to ascribe the action of salt
upon marine vegetation to the sodium component. But the
wide differences in the effects of different sodium compounds,
532
SOILS.
notably of common salt and Glaubers salt, led some to the con¬
clusion that the acidic ingredients are the chief determin¬
ing factors. Moreover, it was soon found that a single salt
is more injurious than a mixture of several, such as sea
water. This also led to the inference that the varying degree
of dissociation of these salts essentially influences the effects.
Kearney and Cameron have investigated these relations,1 and hav<
by artificial cultures in solutions of varying concentration and com.
position studied the behavior of plant roots and the limits of theii
endurance. They found for the several salts occurring in alkali soils,
taken separately, the following figures, in 100,000 parts of water:
Magnesium sulfate . 7
“ chlorid . . 12
Sodium carbonate . 26
“ sulfate . ... ..... 53
“ chlorid . 116
“ bicarbonate . 167
Calcium chlorid . 1,377
It will be noted that in many respects the results given in this table
stand in marked contrast to the facts observed in alkali lands every¬
where ; and therefore while interesting physiologically, are not directly
applicable to practice. Magnesium sulfate, which according to this
table is the most injurious of all, is a common ingredient of alkali lands
from Wyoming to New Mexico, as also is sodium sulfate ; yet there,
as well as in the Musselshell valley in Montana, and at many other
points, it shows no specially deleterious action either upon native or
cultivated plants, and in Europe as well as in New England the mineral
kieserite is freely used as a fertilizer at many points. That sodium
sulfate should be twice as harmful as sodium chlorid or common salt,
and half as harmful as the carbonate or black alkali, is again wholly
contrary to actual experience, which as shown elsewhere in this chapter,
indicates that the majority of plants will tolerate between three and
four times as much of sodium sulfate as of common salt; while the ratio
of tolerance as against the carbonate seems sometimes to rise as high
as ten to one.
It is clearly evident, however, that it is the metallic or basic ingre¬
dient that in the main determines the toxicity of these salts. The
universal presence of lime in some form in all alkali lands doubtless
1 Report No. 71, U. S. Den’t of Agriculture, 1902.
SALINE AND ALKALI LANDS.
533
explains the discrepancies mentioned, since lime is especially potent in
counteracting the injurious effects ; thus throwing additional light upon
the importance of the lime-content of alkali soils proper, and also upon
the causes of the narrow limitations of the littoral (marine saline) flora;
inasmuch as, unlike alkali soils, marine alluvial lands are by no means
always calcareous. Cameron goes so far as to attribute the favorable
effects of gypsum upon black alkali not so much to the conversion of
the latter into neutral sulfate, as to the effect of gypsum solution in
counteracting the saline effects. This interpretation, however, seems
rather far-fetched, since there can be no question about the double
decomposition of gypsum with carbonate of soda ; or the intense injur¬
iousness of carbonate of soda in the actual corrosion of vegetable
tissues. The corresponding protective influence of various salts, more
especially of those of lime, against the injurious effects of pure common
salt on marine animals, has already been mentioned (chapter 20, page
380), and later investigations by Osterhout on marine algae, show the
same relation to hold true for them also.
Reclamation of Marine Saline Lands for Culture. — The
reclamation of sea-coast lands and marshes for agricultural
use is based in general upon the same methods as those al¬
ready outlined for alkali lands in chapter 20; except that in
this case no chemical neutralization is possible, since common
salt cannot be changed by any practically feasible means. It
must be removed by leaching, and this, in the humid countries
in which such reclamations have chiefly been made, is usually
done by the agency of rains, aided by ditching. The
“ polder lands thus reclaimed along the shores of the North
Sea, from Belgium to Prussia, are especially esteemed for
their productiveness, doubtless owing to the alluvium of the
numerous rivers tributary to that sea, which is distributed
along its shores and in the numerous inlets and bays. The
tides are of course excluded by dikes provided with gates
opening outward, so as to permit of the outflow of rain-
or irrigation-water used for leaching purposes.
Out of reach of stream alluvium no exceptional fertility is
to be expected of sea-shore lands, which then commonly assume
the form of sand dunes or bars, incapable of nourishing any
cultural vegetation. Of the latter, the groups listed below as
tolerant of alkali salts, may also be considered with reference
534
SOILS.
to reclaimed sea-shore lands ; the first cereal to succeed being
usually barley, the first root crop, beets. Asparagus is also
available while salt is being leached out.
THE VEGETATION OF ALKALI LANDS.
The general character of alkali-land vegetation is not unlike
that of saline sea-shore lands ; some species of plants are com¬
mon to both, but the alkali lands harbor a much greater variety
of plants, owing to the differences in climates and soils as
well as to the nature of the impregnating salts. Moreover,
owing to the very causes which underlie the presence of these
salts, viz, aridity, the xerophile or dry-land character of the
alkali-land flora is much more pronounced than that of the
saline sea-shore vegetation. In view of the very complex
conditions, the discussion of the alkali-flora is of necessity
much more complex than that of the marine group; and the
data for its full elucidation with respect to the nature of the
soils and salts are as yet very incomplete.
RECLAIM ABLE AND IRRECLAIMABLE ALKALI LANDS AS DIS¬
TINGUISHED BY THEIR NATURAL VEGETATION.
While, as shown above (chapter 20), the adaptation or
non-adaptation of particular alkali lands to certain cultures
may be determined by sampling the soil and subjecting the
leachings to chemical analysis, it is obviously desirable that
some other means, if possible available to the farmer himself,
should be found to determine the reclaimability and adapta¬
tion of such lands for general or special cultures.
In alkali lands, as in others, the natural plant-growth affords
such means, both as regards the quality and quantity of the
saline ingredients. The most superficial observation shows
that certain plants indicate extremely strong alkali lands
where they occupy the ground alone ; others indicate pre¬
eminently the presence of common salt ; the presence or ab¬
sence of still others form definite or probable indications of
reclaimability or non-reclaimability. Many such characteris¬
tic plants are well known to and readily recognized by the
farmers of the alkali districts. “ Alkali weeds ” are com-
SALINE AND ALKALI LANDS.
535
monly spoken of almost everywhere ; but the meaning of this
term — i. c., the kind of plant designated thereby — varies ma¬
terially from place to place, according to climate as well as the
quality of the soil. It is obvious that if these characteristic
plants were definitely observed, described and named, while
also ascertaining the amount and kind of alkali they indicate
as existing in the land, lists could he formed for the several
regions, which would indicate, in a manner intelligible to the
farmer himself, the kind and degree of impregnation with
which he would have to deal in the reclamation work ; thus
enabling him to go to work on the basis of his own judgment,
without previous chemical examination.
A study of the lands of California having this purpose in
view, was undertaken in the years 1898 and 1899 by the Cali¬
fornia Station ; but lack of funds prevented its prosecution
beyond the ascertainment of those plants the abundant oc¬
currence of which prove the land to be irreclaimable without
the use of the universal remedy, viz, underdrainage, which on
the large scale is usually beyond the means of the land-seeker.
The botanical field work and collection of soil samples was
carried out by Mr. Jos. Burtt Davy; the chemical work, as
heretofore, being done by Dr. R. H. Loughridge. The re¬
sults here reported are therefore essentially their joint work.
It is hoped that in the future, a more comprehensive study and
close comparison of the native vegetation with the chemical
determination of the quality and kind of alkali corresponding
to certain plants, or groups of plants, naturally occurring on
the land, may enable us to come to a sufficiently close estimate
of the nature and capabilities of the latter from the native
vegetation alone, or with the aid of test plants purposely
grown, for the farmers' purposes.
Plants Indicating Irreclaimable Lands. — The plants herein¬
after mentioned and figured are, then, to be understood as
indicating, whenever they occupy the ground as an abundant
and luxuriant growth, that such land is irreclaimable for ordi¬
nary crops, unless underdrained for the purpose of washing
out surplus salts. The occurrence merely of scattered, more or
less stunted individuals of these plants, while a sure indi¬
cation of the presence of alkali salts, does not necessarily show
that the land is irreclaimable.
SOILS.
53*5
The plants which may best serve as such indicators in
California are the following :
Tussock-grass ( Sporobolus airoidcs Torr.), Fig. 82.
Bushy Samphire ( Allenrolfea occidentals (Wats.) Ktze.),
Fig- 83.
Dwarf Samphire (Salic ornia subterminalis Parish, and
other species), Fig. 84.
Saltwort (Snaeda torreyana Wats., and S', suffrutescens ,
Wats.), Fig. 85.
Greasewood (Sarcobatus vermiculatus (Hook.) Torr.),
Fig. 86.
Alkali-heath ( Frankenia grandifolia campestris Gray),
Fig- 87.
Cressa ( Cressa truxillensis Choisy), Fig. 88, perhaps
identical with C. crctica auct.
Salt-grass (Distichlis spicata) , Fig. 89.
Tussock grass ( Sporobolus airoidcs, Torr.) ; Fig. 82.
(“ Buneh grass ” of New Mexico).
The three sets of Tussock-grass soil which have been
analyzed show that the total amount of all salts present is
in no case less than 49,000 pounds per acre, to a depth of
four feet ; and that it sometimes reaches the extraordinarily
high figure of 499,000 pounds. Of these amounts the neutral
salts (Glauber’s salt and common salt) are usually in the
heaviest proportion (Glauber’s salt, 19,600 to 323,000 pounds
per acre; common salt, 3,500 to 172,800) ; the corrosive sal-
soda varying from 3,000 to 44,000 pounds. — Tussock-grass
apparently cannot persist in ground which is periodically
flooded. It is of special importance because it is an acceptable
forage for stock.
Tussock-grass is a prevalent alkali-indicator in the hot,
arid portions of the interior, from the upper San Joaquin
Valley, the Mojave desert, and southward; also through
southern Nevada and Utah as far east as Kansas and Ne¬
braska. In the San Joaquin Valley it has not been found far¬
ther north than the Tulare plains, although east of Reno it
occurs near Reno. Coville observes that in the Death Valley
region “ it is confined principally to altitudes below 1,000
meters” (3,280 feet). Hillman, however, reports it from
SALINE AND ALKALI LANDS
5 37
Fig. 82 — Tussock Grass — Sporobolus airoides Torr.
533
SOILS.
near Reno, Nevada, at an altitude which cannot he much less
than 4,500 feet.
The tussocks formed by this grass, which are unfortunately
not shown in the figure, sometimes appear as veritable little
grass trees, and when denuded by the browsing of cattle seem
like trunks 18 and 20 inches high. It is therefore very easily
recognized ; but it should be noted that in view of the extra¬
ordinary range of its tolerance, shown above, its scattered
occurrence does not necesarily indicate irreclaimable land.
Bushy samphire. ( Allenrolfea occidcntalis (Wats.)
Ktze.) Fig. 83.
This plant is locally called greasewood, but as this name is
much more commonly used for Sarcobcitus vermiculatus, it
seems best to call Allenrolfea “ bushy samphire," as it closely
resembles the true samphire (Salicornia) .
Bushy Samphire usually grows in low sinks, in clay soil
which in winter is excessively wet, and in summer becomes a
“ dry bog." Wherever the plant grows luxuriantly the salt
content is invariably high, the total salts varying from 3 27,-
000 pounds per acre, to a depth of three feet, to 494,520
pounds in four feet. The salts consist mainly of Glauber’s and
common salts (a maximum of about 275,000 pounds each) ;
salsoda varies from 2,360 to 4,800 pounds per acre. The
percentage of common salt and total salts is higher than for
any other plant investigated, and the content of Glauber’s salt
is also excessive. The areas over which this plant grows
must therefore be considered among the most hopeless of
alkali lands, for although its salts are “ white,’’ submergence
during winter precludes the growth of Australian saltbushes.
Full underdrainage alone could reclaim the soil-areas it occu¬
pies. Bushy Samphire is common on low-lying alkali lands
in the upper San Joaquin Valley, California, and extends
northward along the eastern slopes of the Coast Range to
Suisun Bay. It is also abundant in the Death Valley region,
apparently overlapping the southward range of the Sarco-
batus, the greasewood properly so-called.
Dwarf samphire ( Salicornia subterminalis, Parish, and
other species of the interior) ; Fig. 84.
The three or four species of Dwarf Samphire which grow
SALINE AND ALKALI LANDS
539
Fxg. 83. — Bushy Samphire — Allenrolfea occidentalis (S. Wats.) G. Ktze
540
SOILS.
in the interior valleys of the State are not usually very abund¬
ant, save locally. Wherever the species do occur, however,
they may be considered as indicating excessively saline soils.
Fig. 84. — Salicornia subterminalis. Alkali samphire.
A. Much-branched form.
B. Slender form.
C. Flower with the perianth removed showing the simple pistil and the two stamens.
D. Portion of flowering spike, showing two joints. The flowers are impressed in the joints in
opposite clusters of three. In each cluster the middle flower stands slightly above the two laterals
as shown in the lower joint.
Dwarf Samphire soil has shown a total salt content of 441,-
880 pounds per acre in a depth of four feet. The neutral
Glauber’s salt amounts to 314,000 pounds, almost as much as
in Tussock-grass soil; common salt up to 125,640 pounds
SALINE AND ALKALI LANDS.
541
while the salsoda varies from 2,200 to 12,000. We may con¬
sider the plant as indicative of almost the highest percentage of
common salt, Glauber’s salt and total salts. Like the preceding
species it indicates land strongly charged with salts, more
especially common salt, and susceptible to cultivation only
after reclamation by under-drainage.
Salicornia subterminalis, S. herbacea (L.), .S', mucronata,
and another species, all occurring inland, differ materially in
habit and botanical characters from the one so conspicuous in
submerged salt marshes along the seashore ; but all alike indi¬
cate strongly saline soils, reclaimable only by thorough drain¬
age.
Saltwort ( Suaeda torreyana, Wats., S', suffrutescens,
Wats., and perhaps one other species) ; Fig. 85.
Samples of saltwort soil from Bakersfield and Byron
Springs, California, taken to a depth of one foot and three
feet respectively, show that this plant grows luxuriantly in a
soil containing 130,000 pounds of total salts per acre in the
first foot, and with 10,480 pounds of the noxious salsoda, and
39,760 pounds of common salt in three feet; while only a
sparse growth is found on soils containing only 3,700 pounds
of salts in three feet. It thus appears to indicate a lower
percentage of salsoda than does Greasewood, but a higher
percentage than Bushy Samphire. Further investigation is
necessary to determine the exact relation of the different salts
to the growth of the plant, and as to whether carbonates occur
in large quantity ; but enough data have been gathered to show
that a luxuriant growth of Suaeda torreyana indicates a soil
reclaimable only by thorough-drainage.
Suaeda torreyana occurs on low alkali lands throughout
the State of California, from San Bernardino to Honey Lake,
in the desert sinks, and in the Great Valley, in appropriate
locations. Sometimes it is replaced by S', suffrutescens and
perhaps other species, but all the saltworts appear to grow in
similar habitats, and it is probable that the soil-conditions are
practically the same for all these species. They indicate land
too heavily impregnated for the growth of ordinary crops,
but which will perhaps allow the Australian saltbush to suc¬
ceed.
542
SOILS.
Fig. 85. — Saltwort — Suaeda Torreyana, Wats.
Greasewood ( Sarcobatus vermiculatus (Hook. Torr.) ;
Fig. 86.
This, the true Grcasczvood of the desert region east of the
Sierra Nevada, and not either of the plants known under that
name in the San Joaquin Valley and in Southern California,
invariably indicates a heavy impregnation of the land with
black alkali or carbonate of soda. Since, as before stated,
black alkali is most likely to occur in low ground, we fre¬
quently find the true greasewood forming bright green
patches in the swales, and on the benches of periodic streams,
as well as on the borders of alkali ponds or lakes. Stock un¬
accustomed to it will frequently go to these patches on a run,
SALINE AND ALKALI LANDS. 543
only to turn away badly disappointed after taking a few bites/
the plant being both bitter and salty.
Fig. 86. — Greasewood (proper) — Sarcobatus vermiculatus (Hook) Torn
A. Appearance of a branch when not in blossom.
B. Spiny-branchlet from the same.
C. Branchlet bearing cones of male flowers.
D. Cone of male flowers, enlarged.
E. Branch bearing fruits.
F. Cluster of fruits, enlarged.
G. Vertical section through a fruit, showing the seed with its curved embryo, (enlarged).
Where a luxuriant growth of this plant is found, the soil
may contain from 38,000 to 117,000 pounds of total salts per
acre, of which sometimes nearly half is carbonate of soda;
the content of common salt is usually low, and Glauber’s salt
544
SOILS.
or sulfate of soda, sometimes with considerable proportion of
epsom salt, forms a variable proportion of the total.
Greasewood is distinctly a plant of the Great Basin, only
reaching California in the adjacent counties of Lassen, Alpine,
Mono, and northern Inyo. It is very abundant on the lower
levels of Honey Lake valley, Cal.
The Sarcobatus is chiefly found on silty or sandy soils of
good native fertility (see page 445, chapter 22), so that when
its excess of salsoda is neutralized by means of gypsum, the
land becomes very productive. Unfortunately the cost of the
amount of gypsum required to render such soils adapted to the
tolerance of most culture plants is often prohibitive; but
where the correction of only small spots is called for, the
“ white alkali ” resulting from the gypsum treatment would
be tolerated by many culture plants.
Alkali-heath ( Frankenia grandifolia campestris Gray) ;
Fig. 87.
Fig. 87. — Alkali-Heath — Frankenia grandifolia campestris A Gray.
Alkali-heath is perhaps the most widely distributed of any
of the California alkali plants. Its perennial, deep-rooting
SALINE AND ALKALI LANDS.
545
habit of growth, and flexible, somewhat wiry rootstock,
which enables it to persist even in cultivated ground, render it
a valuable plant as an alkali indicator. The salt-content
where Alkali-heath grows luxuriantly is invariably high,
ranging from 64,000 to 282,000 pounds per acre; salsoda
varies from 680 to 19,590 pounds; common salt ranges from
5,000 to 10,000 pounds. Such soils would not be benefited by
the application of gypsum, as the salts are already largely in
the neutral state. Of useful plants only Saltbushes and Tus¬
sock-grass are likely to flourish in such lands, when not too
wet.
While Alkali-heath is thus one of the most alkali-tolerant
plants, it is at the same time capable of growth with a mini¬
mum of salts (total salts 3,700 pounds, salsoda 680 pounds).
Where only a sparse growth of this plant occurs, therefore, the
land should not be condemned until a chemical examination
of the soil has been made.
Alkali-heath is found on soils of very varying physical tex¬
ture and degrees of moisture; while on soils of uniform
texture and moisture-conditions, but differing in chemical
composition, it varies with the varying salt-content.
It has been found that Australian saltbush (A triplex semi-
baccata) can be successfully grown on the “ goose-lands,” of
the Sacramento Valley, on soil producing a medium crop of
Alkali-heath ; it remains to be shown whether it will do
equally well on soils producing a dense and luxuriant growth
of the same.
Alkali-heath is widely distributed throughout the interior
valleys of California ; a closely related form grows in the salt-
marshes of the sea-coast.
Cressa ( Cressa cretica truxillensis Choisy) ; Fig. 88.
Cressa soils show a low percentage of the noxious salsoda,
but comparatively heavy total salts (161,000 to 282,000
pounds per acre.) Common salt varies from 5,760 to 20,840
pounds per acre in four feet. The maximum is lower than in
the case of Alkali-heath, but Cressa seems to be much more
closely restricted to strong alkali than does the former species.
Cressa appears to be as widely distributed through the in¬
terior valleys of California as Alkali-heath. The Cressa is a
35
546
SOILS.
cosmopolitan plant, occurring, as its name indicates, on the
Ionian Islands, as well as in North Africa, Syria, and other
arid countries of the world.
Salt-grass, Distichlis spicata. — This grass is of world¬
wide distribution, and always indicates a sensible content of
soluble salts, without apparently any special preference for
either of the three most commonly occurring ones. Its maxi¬
mum tolerance, as will be seen by the preceding table, is very
high, yet at the same time it will grow luxuriantly on lands
containing so little that other saline plants like the samphires,
saltwort or greasewood will refuse to grow. On the shores of
Fig. 88, — Cressa — Cressa cretica truxillensis, Choisy.
Honey Lake, California, it may often be seen incrusted with
the salts of the water concentrated by a long season of
drought, yet maintaining life, though somewhat stunted. On
lands lightly impregnated, stock will often eat it quite freely,
so that it has been mistaken for Bermuda grass, to which its
habit and foliage bears some resemblance. But Bermuda
grass, while not as sensitive to alkali as most forage grasses,
will probably not bear much over 12,000 pounds per acre.
The mere presence of the salt grass cannot therefore be
taken as a definite indication of anything more than that there
is an unusual amount of salts in the soil ; whether or not there
SALINE AND ALKALI LANDS
547
Fig. 8g. — Salt-Grass — Distichlis spicata. (L.) Greede.
548
SOILS.
is more than will be tolerated by the ordinary culture-plants,
must be judged either from the accompanying plants, or by
experiment or analysis.
Relative Tolerance of the Different Species. — The follow¬
ing table shows in systematic order the tolerance of the several
plants discussed above, for the different salts, so far as the
data available permit. The column marked optimum shows
under what proportions of salts the plants grew in about equal
luxuriance, therefore under, apparently, the most favorable
conditions. Both above and below the proportions mentioned
in that column, the luxuriance (size) and (usually) the
abundance of the plants was less; showing that while excess¬
ive amounts of salts depressed their welfare, yet they also
suffered when the proportions dropped below a certain point.
Whether this was partly or wholly the result of competition
with other plants, is an unsettled question.
SALINE AND ALKALI LANDS
549
TABLE SHOWING MAXIMUM, OPTIMUM, AND MINIMUM OF SALTS TOLERATED BY EACH
OF THE SEVERAL ALKALI PLANTS.
Total Salts.
Bushy Samphire . .
Dwarf Samphires .
Alkali-heath .
Cressa .
Saltworts . .
Greasewood .
Tussock-grass .
Carbonate (Salsoda).
Tussock-grass .
Alkali-heath .
Greasewood . . .
Dwarf Samphires .
Saltworts .
Cressa .
Bushy Samphire .
Chloride (Common Salt).
Bushy Samphire .
Dwarf Samphires .
Saltworts .
Cressa .
Alkali-heath .
Tussock -grass .
Greasewood .
Sulphates (Glauber’s salt).
Dwarf Samphires .
Bushy Samphire .
Cressa .
Alkali-heath .
Saltworts .
Greasewood .
Tussock Grass .
Pounds Per Acre in feet.
Optimum.
494»32o
441,880
j 281,960 |
i 64,300 I
281,960
130,000
58,560
49,000
23,000
*19,590 \
680 )
18,720
12,120
10,480
5.440
4,800
212,080
125,640
39,760
20,840
10, 180 )
5.76° f
6,200
3,680
314,040
277,640
275,520
I 275,520)
I 34.530 f
44. 160
36.160
19,640
Maximum.
494,520
441,880
499,040
281,960
1 53,020
58,560
499,040
44,460
19,590
18,720
12,120
12, 120
5,440
4,800
275,160
125,640
52,900
20,840
212,080
172,800
3,680
314,040
277,640
275,520
323,200
104,040
36,160
323,200
Minimum.
135,060
441,880
3,720
161,160
3,720
2,400
49,000
3,040
680
1,280
2,200
1,120
680
1,500
56,800
125,640
1,040
5,76o
1,040
3,530
160
314,040
50,080
134,880
1,560
1,560
960
19,640
* This plant grows with equal luxuriance in soils containing only 6S0 pounds of carbonates.
APPENDICES.
APPENDIX A.
DIRECTIONS FOR TAKING SOIL SAMPLES. ISSUED BY THE
CALIFORNIA EXPERIMENT STATION.
In taking soil specimens for examination by the Agricultural Ex¬
periment Station, the following directions should be carefully observed;
always bearing in mind that the examination, and especially the
analysis, of a soil is a long and tedious operation, which cannot be
indefinitely repeated.
First. — Do not take samples at random from any points on the land,
but consider what are the two or three chief varieties of soil which,
with their intermixtures , make up the cultivable area, and carefully
sample these, each separately ; then, if necessary, sample your particular
soil, noting its relation to these typical ones.
Second. — As a rule, and whenever possible, take specimens from
spots that have not been cultivated, nor are otherwise likely to have
been changed from their original condition of “ virgin soils” — e.g., not
from ground frequently trodden over, such as roadsides, cattle-paths, or
small pastures, squirrel holes, stumps, or even the foot of trees, or spots
that have been washed by rains or streams, so as to have experienced a
notable change, and not be a fair representative of their kind.
Third. — Observe and record carefully the normal vegetation, trees,
herbs, grass, etc., of the average virgin land ; avoid spots showing
unusual growth, whether in kind or in quality, as such are likely to
have received some animal manure, or other outside addition.
Fourth. — Always take specimens from more than one spot judged to
be a fair representative of the soil intended to be examined, as an
additional guarantee of a fair average, and mix thoroughly the earth
taken from the same depths.
Fifth. — After selecting a proper spot, pull up the plants growing on
it, and sweep off the surface with a broom or brush to remove half-
decayed vegetable matter not forming part of the soil as yet. Dig or
bore a vertical hole, like a posthole, and note at what depth a change
of tint occurs. In the humid region, or in humid lowlands of the arid,
553
554
APPENDIX A.
this will usually happen at from six to nine inches from the surface,
and a sample taken to that depth will constitute the “soil.”
In California and the arid region generally, very commonly no change
of tint occurs within the first foot, sometimes not for several feet ;
hence, especially in sandy lands, the “ soil ” sample will usually be taken
to that depth, so as to represent the average of the first foot from the
surface down.
Samples taken merely from the surface , or from the bottom of a hole ,
have no definite meanings a?id will not be examined or reported upon.
Place the “ soil ” sample upon a cloth (jute bagging should not be
used for the purpose, as its fibres, dust, etc., become intermixed with
the soil) or paper, break it up, mix thoroughly, and put at least a quart
of it in a sack or package properly labeled, for examination.
This specimen will, ordinarily, constitute the “ soil.” Should the
change of color occur at a less depth than six inches, the fact should be
noted, but the specimen taken to that depth nevertheless, since it is
the least to which rational culture can be supposed to reach.
In the same way take a sample of each foot separately to a depth
of at least three feet ; preferably four or five, especially in the case of
alkali soils, or suspected hardpan.
Sixth . — Whatever lies beneath the line of change, or below the min¬
imum depth of six inches, will constitute the “ subsoil.” But should
the change of color occur at a greater depth than twelve inches, the
“ soil ” specimen should nevertheless be taken to the depth of twelve
inches only, which is the limit of ordinary tillage ; then another speci¬
men from that depth down to the line of change, and then the “ sub¬
soil ” specimens beneath that line.
The depth down to which the last should be taken will depend on
circumstances. It is always necessary to know what constitutes the
foundation of a soil, down to the depth of three feet at least , since the
question of drainage, resistance to drought, root-penetration, etc., will
depend essentially upon the nature of the substratum. In the arid
region, where roots frequently penetrate to depths of ten or twelve feet
or even more, it is frequently necessary to at least probe the land to
that depth or deeper. The specimens should be taken in other respects
precisely like that of the surface soil, each to represent the average oj
not more than twelve inches Those of the materials lying below the
third foot from the surface may sometimes be taken at some ditch or
other easily accessible point, and if possible should not be broken up
like the other specimens.
APPENDIX A.
555
If there is hardpan or heavy clay present, an unbroken lump of it
should be sent, for much depends on its character.
Seventh. — When in the case of cultivated lands, it is desired to
ascertain the cause of differences in the behavior or success of a crop
on different portions of the same field or soil area, do not send only
the soil which bears unsatisfactory growth, but also the one bearing
normal, good growth, for comparison. In all such cases, try to ascertain
by your own observations whether or not the fault is simply in the sub¬
soil or substrata ; in which case a sample of surface soil sent for exam¬
ination would be of little use. In such examinations the soil probe will
be of great service, and save much digging or boring.
Eighth. — Specimens of alkali or salty soils should preferably be taken
towards the end of the dry season, when the surface layers will contain
the largest amount of salts. A special sample of the first six inches
should in that case be taken separately by means of a post-hole auger,
and then, in a different spot close by, a hole four feet deep should be
bored, and the earth from the entire four-foot column intimately mixed
before the usual quart sample is taken. Samples of the plants growing
on the land should in all cases be included in the package, as they in¬
dicate very closely the agricultural character of the land.
All samples taken while the land is wet should be air-dried before
sending; in the case of alkali soils this is absolutely essential.
Ninth. — All peculiarities of the soil and subsoil, their behavior under
tillage and cultivation in various crops, in wet and dry seasons, their
location, position, “ lay,” every circumstance, in fact, that can throw
any light on their agricultural qualities or peculiarities, should be care¬
fully noted, and the notes sent by mail. Without such notes , specimens
cannot ordinarily be considered as justifying the amount of labor involved
in their examination. Any fault found with the behavior of the land
in cultivation or crop-bearing should be specially mentioned and de¬
scribed. The conditions governing crop-production are so complex
that even with the fullest information and the most careful work, cases
are found in which as yet the best experts will be at fault.
APPENDIX B.
SUMMARY DIRECTIONS FOR SOIL— EXAMINATION IN THE
FIELD OR ON THE FARM.
While the general principles upon which the cultural value and adap¬
tations of lands should be judged, have been given in the text of this
volume, it seems advisable to summarize their practical application to
land examination here, for convenient reference.
The directions given in Appendix I for the sampling of soils having
been carried out, the samples so taken may be subjected to farther
examination by any intelligent farmer to good purpose, and often with
great saving of time and expense.
Spread the samples from the several depths in regular order upon a
table or bench, and note the differences in color and texture apparent to
the eye or touch, and whether they will or will not crush readily between
the fingers, wet and dry. Whatever the fingers can do, can similarly be
done by the harrow, cultivator, clod crusher or roller.
The tilling qualities of the surface soil and immediate subsoil are the
first and most important matter to be ascertained ; including especially
their behavior to water. Place some airdried lumps in a shallow dish
with a little water ; observe whether they take up the water quickly or
slowly, and whether in so doing the lumps fall to pieces or retain their
form. Slow penetration, and maintenance of form, will at once indicate
a soil somewhat refractory and difficult to till ; while if the water is taken
up easily and the lump falls to pieces, the land is easily cultivated and
will absorb the rainfall and irrigation water readily. The darkening of
the tint on wetting will also give an approximate idea of its humus-
content.
Then take a wetted lump and work it between the fingers and on
the palm of the hand, until its “ stickiness ” or adhesiveness ceases to
increase. This “ hand test ” is of first importance and in skilful hands
will largely supersede the need of elaborate mechanical analysis. It
will at once enable the operator to classify the soil as a light or heavy
loam, clay loam or clay soil ; it will show directly what will be the result
of plowing the land when wet, the liability to the formation of a plow-
556
APPENDIX B.
557
sole, and whether a single or a double team will generally be needed to
cultivate it properly. Also whether stock can be allowed to pasture the
land soon after rain. Comparison with the known land of neighbors
will also thus become easy, and in a measure the crops best adapted to
the physical qualities of the soil, subsoil and substrata, taking into
account their respective depths, will at once be at least approximately
determined. The presence of coarse and fine sand in greater or less
amounts will also be thus readily ascertained, allowing estimates of the
percolative properties ; the latter can, of course, be more practically
tested in the field, in the manner described in chapter 13, page 242.
A more definite estimate of the amount and kind of sand present in
the soil materials can be obtained by washing the kneaded sample into
a tumbler, and allowing a thin stream of water to flow into it from a
faucet while gently stirring the turbid water. The clay, together with
the finest silts, will thus be carried off over the rim of the glass, and
sand of any desired degree of fineness, according to the strength of the
stream of water used, will be left behind. The kind and amount of
these sandy materials can then be estimated, or definitely ascertained
by weighing or measuring.
This will, generally speaking, be as far as the uninstructed farmer can
readily go ; but these simple operations will give him an insight into the
nature of his soil and subsoil that will enable him to avoid a great many
costly mistakes.
RECOGNITION AND MEANING OF THE SEVERAL SOIL MINERALS.1
Those somewhat familiar with scientific methods and operations, and
supplied with pocket lens or microscope, can profitably go much farther
towards the definite ascertainment of the permanent cultural value of
the land, by the study of the minerals of which the sand is composed,
and which as a rule represent those from which the entire soil has been
formed ; therefore indicate in a general manner its chemical compo¬
sition. Such examinations are specially feasible and important when
soils are not far removed from their parent rocks, as in most of the
arid region, and in the states north of the Ohio. In the Southwestern
states, in the coastal plain of the Gulf of Mexico, the original soil
minerals have usually been too far decomposed to admit of definite
identification. Sand is there as a rule made up of quartz grains of
many varieties, with only an occasional tourmaline and pyroxene.
Among the prominent soil minerals, quartz is almost always recogniz-
1 For more details see chapters 3 and 4.
558
APPENDIX B.
able by its glassy luster and the irregular fracture — absence of definite
planes or facets of cleavage, causing the grains to be abraded or rounded
nearly alike in all directions. The feldspars , on the contrary, always show
a tendency to cleave into fragments having definite, obviously oblique
angles, which are perceptible even when the grains are somewhat worn ;
because of the difference in the ease with which wear takes place in the
several directions. Potash feldspar , moreover, which is the most im¬
portant to be recognized because it indicates a relatively large supply
of potash in the natural soil, is but rarely glassy in luster, but mostly
dull white, or reddish-white. — The lime and lime-soda feldspars rarely
show as definite forms, because of their tendency to form complex
crystalline aggregates (twins) : and their definite recognition requires
somewhat complex (polarizing) appliances in connection with the mi¬
croscope. In such cases, however, the accompanying minerals (horn¬
blende, pyroxene, mica and others) often afford valuable indications,
because of their known association with soda-lime feldspars in certain
rocks.
An abundant occurrence of hornblende fragments, characterized by
their flat, tabular form, and bottle-green or black tint, indicate, almost
always a fairly good supply of lime in the soil, but leaves the potash-
supply in doubt. Pyroxene (distinguished by its smooth, polished sur¬
face from the angularly-weathering, usually rusty hornblende fragments)
rarely occurs with potash feldspar ; and soils strongly charged with it
are mostly poor in potash.
Mica occurs in so many rocks and is of so little consequence as a
soil--ingredient from the chemical point of view, because of its difficult
decomposition, that its presence can mostly only serve to corroborate
or contradict conclusions as to the derivation of a soil from some par¬
ticular rock or region. But mica serves a good purpose in improving
the tilling qualities of soils. Its thin scales must not be mistaken for
the tabular fragments of hornblende.
Calcite in its several forms is mostly easily recognized both by its
form under the microscope, and by the effervescence its granules show
when touched with an acid. This effervescence can generally be ob¬
served on touching the wetted soil with chlorhydric acid, so soon as the
content exceeds two per cent ; but something depends upon the size of
the grains, as when these are very small, the giving-off of gas is less readily
noted. To facilitate it, the wetted soil may be warmed before touch¬
ing it with the acid. The recognition of the presence of lime carbon¬
ate in soils is so important as to justify considerable trouble in render¬
ing it definite. When the aid of a chemist cannot be commanded,
APPENDIX B.
559
fairly definite conclusions may be drawn frcm the character of the
native vegetation ; regarding which, detailed information may be found in
Parts III and IV of this volume. But where, as in the arid region, this
criterion is not available, since the controlling factor there is the mois¬
ture supply, a presumption may be gained by the application of a slip
of moistened red litmus paper to the wetted soil. Should the red
paper be turned blue within one or two minutes it would indicate the
presence of carbonate of soda (“ black alkali ”) as well as of lime car¬
bonates : but if blued only after twenty minutes or more, it would indicate
the presence of the carbonates of lime and magnesia. If not changed
at all, the conclusion would be that either lime carbonate is in very
small supply, or that the soil is in an acid condition. (See chapter 8,
p. 122).
Saline and Alkali Soils. — The presence of an unusual or injurious
amount of soluble salts , as in the case of seacoast and alkali soils, is
commonly easily ascertained in the field ; where, if the surface soil is
at all seriously contaminated with soluble salts of any kind, these may
be seen on the surface during a dry season, forming a whitish efflores¬
cence, which in most cases is definitely crystalline. In doubtful cases
a tablespoonful of the surface soil may be leached with water, and the
first ten or fifteen drops caught in a clean, bright silver spoon and
evaporated. Or the soil may be stirred up with about twice its bulk of
water and the mixture be allowed to clear by settling, then evaporating.
A slight whitish film will almost always remain in the spoon ; but if the
amount be somewhat considerable, the presence of soluble salts is very
readily recognized by pouring a few drops of clear water on one side of
the spot, and then allowing it to flow gently over the spot to another
place, where it is again slowly evaporated. Any considerable amount of
salts present will be shown both in the diminution of the original spot,
and in the soluble residue accumulated where the water was last
evaporated. Should common salt be present to any considerable extent,
the residue in the silver spoon will, if the last drops be allowed to
evaporate slowly, show square or cubical crystals to the naked eye, and
certainly to a common pocket lens. The residue may also be tested
with red litmus paper for carbonate of soda, which would quickly turn
it blue.
More detailed examination requires chemical reagents and experience,
but the above tests should be sufficient to prevent the mistaking of
mere white spots, whose humus has been destroyed by fermentation
caused by bad drainage, with true alkali caused by excess of soluble
salts ; a mistake not uncommon in both the arid and humid regions.
APPENDIX C.
SHORT APPROXIMATE METHODS OF SOIL EXAMINATION
USED AT THE CALIFORNIA EXPERIMENT STATION.
BY R. H. LOUGHRIDGE.
The California Experiment Station has for many years given the
farmers of the State the privilege of having their soils examined to as¬
certain any physical defects, deficiency in plant-food, or the presence
of alkali salts. They have quite generally taken advantage of this, and
the number of samples of soil sent in each year has been very large.
A complete analysis of a soil-sample requires fully 15 days; hence
the necessity of adopting some quick methods for the determination of
the main elements of fertility, viz., humus, lime, potash, and phosphoric
acid, that would at the same time give results sufficiently accurate
for practical purposes. Similarly for alkali salts in the soil ; the leach-
ing-out and analysis of which often occupies more than a week.
The following methods have been adopted, which shorten the time
of examination for the plant-food of a soil to about one hour, except
for potash, which requires a much longer time. For alkali salts the
time is reduced to two days, and less if a pressure filter be used.
Humus. — The Grandeau method of ammonia extraction requires the
removal of the lime and magnesia with weak hydrochloric acid, wash¬
ing out of the acid and then digestion with weak ammonia ; all of which,
with a soil rich in humus, may require many days, though a number of
samples may be put through at the same time.
The method adopted to determine adequacy or inadequacy of the
humus (for this is all that is intended in this examination) is completed
in less than half an hour. It is based on the color of the humus-extract
and avoids the necessity of removal of the lime from the soil.
The soil is pulverized in a mortar with a rubber pestle, and passed
through a half-millimeter sieve. Seven grams of the fine earth is placed
in a test tube with 15 or 20 cc. of a ten percent solution of caustic
potash and boiled for ten or fifteen seconds, then allowed to settle.
The humus is dissolved and the density of the color of the solution is
an indication of adequacy or inadequacy. A dense black, non-trans-
560
APPENDIX C.
561
lucent solution shows the presence of at least one per cent of humus
in the soil ; a deep brown translucent color indicates about one-half of
one percent ; while a light brown color clearly shows a deficiency in the
soil, and a need of a good green-manure crop.
Lime. — Two grams of fine earth is treated with a little hydrochloric
acid, boiled for a few seconds, and ammonia is added to precipitate
the iron and alumina ; the whole, with the soil-residue, is quickly thrown
on a filter to separate the mass from the lime solution, and washed.
After adding ammonium chlorid the lime is precipitated with oxalate
of ammonia, and its adequacy for soil-fertility judged of by the turbid¬
ity of the solution, or the bulk of the precipitate. Or the latter may
be filtered off, dried and weighed. We thus obtain a measure of the
carbonate and humate of lime present, by comparing it with the pre¬
cipitate obtained from a soil whose percentage of lime has been cor¬
rectly ascertained.
Potash. — The determination of potash in the soils requires more time
than either of the other ingredients, and is more rarely made by us.
Our knowledge of the soils of the State of California obtained through
mvny analyses, gives us a clue to those localities where potash would
probably be deficient, as well as to those whose soils are generally ex¬
tremely rich in potash ; the percentages reaching usually from .5 to as
much as 1.5 per cent and more.
For the determination, two grams of the fine earth is digested in
hydrochloric acid over a steam bath for two days, the insoluble residue
filtered off, the filtrate evaporated to dryness to render the silica in¬
soluble, again filtered and the iron, alumina and lime removed by pre¬
cipitation with ammonia and oxalate of ammonia and filtration. The
filtrate is then evaporated to dryness, the ammonia salts destroyed with
apua regia or driven off by heat, and the alkalies changed to chlorids.
Any residue is then filtered off and platin-chlorid added to precipitate
the potash, which is separated and determined in the usual way, either
by reduction of the platinum by ignition, or by measurement in a
Plattner’s potash tube.
Phosphoric Acid. — The determination of phosphoric acid is based on
the volume of the phospho-molybdate precipitate in a tube made like
a Plattner’s potash tube, but having a wider interior diameter for the
smaller portion (not greater than 3 millimeters), and a length of 50
mm. With this diameter, one mm. in height of the precipitate obtained
by our short method indicates one one-hundredth of one per cent of
phosphoric acid in the soil. The unit of measure must be obtained for
36
APPENDIX C.
562
each tube, unless of uniform diameter, and is ascertained by taking a
soil whose phosphoric-acid percentage has been determined gravimet-
rically and giving it the following quick treatment; which must, of
course, be closely followed in each soil to be examined :
Two grams of the fine earth is ignited in a platinum dish to destroy
the organic matter, transferred to a test-tube containing 5 cc. of nitric
acid and made to boil for only a couple of seconds, thus preventing the
solution of silicates to any material extent. It is not allowed to stand,
but a little water is immediately added and it is quickly thrown on a
small filter and washed with a little water. The phosphoric acid is then
precipitated with molybdic acid at the proper temperature ; allowing it
to settle, the liquid is drawn off and the precipitate transferred to the
measuring- tube. It settles into the small part in a short time if the
latter is not too narrow, and is then measured with a millimeter scale.
This represents the percentage as found in the soil by the gravimetric
method, and serves as a guide for other examinations, whose agreement
with gravimetric determinations is generally quite close, and quite suf¬
ficient for practical purposes. The rapidity with which the solution is
made and separated from the soil is a matter of special importance for
comparative results, or determination of percentages ; for if the acid
solution be allowed to stand for some time before filtration from the
soil, silica passes into solution also, and the volume of the molybdate
precipitate is increased by it ; thus vitiating the results and adding to
the time required for the method. By this short method the practically
important phosphoric acid in the soil may be approximately deter¬
mined within half an hour.
SHORT METHOD FOR ALKALI SALTS.
The old method of obtaining solutions of the salts by leaching the
soil on a filter until all of the alkali had been washed out has been
replaced by the following short one. 50 or 100 grams of the well-
mixed soil is placed in a bottle containing 200 cc. of water, shaken up
occasionally during 12 hours and allowed to settle. The solution may
then be passed through a common filter (or preferably a pressure filter)
and an aliquot part (usually 50 cc.) of the filtrate evaporated to dry¬
ness in a platinum basin and ignited at a temperature just below redness
to destroy any organic matter that may be present. The basin and
contents are weighed and the soluble salts are dissolved in a very little
water and separated by filtration through a small filter into a 50 cc.
cylinder and the alkali carbonates and chlorids determined by titration,
being calculated as sodium compounds.
APPENDIX C.
563
The material remaining on the filter and in the basin, consisting of
insoluble earth, carbonates and calcium sulfate, is gently ignited in the
basin and weighed ; the difference between this and the first weight
gives approximately the total soluble salts, which should substantially
correspond to the titrations made.
The sulfates are determined by differences between these and the
total alkalies. The solution may contain some sulfate of magnesia, or
calcium and magnesium chlorids, and these are determined gravime-
trically.
Nitrates, which may have been destroyed in the first ignition, are
determined in the original solution by the picric method. Any mag¬
nesia rendered insoluble by the ignition may usually be accounted for
as chlorid, unless much nitrate is present which is rarely the case in
carbonated alkali. If much nitric acid was found, it should be first
assigned to magnesia.
'
iMtej 1 c i.: fa pilSHtil » -v'l
.
■
INDEX.
A.
PACK
Absorption and movements of water in soils . 221
of solids from solutions . 267
of gases by soils . 272, 275
Acacias, tolerance of alkali . . 480
Accessory minerals . 50
Acid, strength used in soil analysis . 341
Acidic and basic eruptive and metamorphic rocks . 49
Acidity, neutrality, alkalinity of soils . 322
Acids of different strengths, analysis with ; table . 326, 341
Action of plants in soil formation, mechanical and chemical . 19
Aeration and reduction as influencing nitrification . 147
effects of insufficient, in soils . 280
excessive, injury in arid regions . 280
Aerobic and anerobic bacteria . 144
Air, functions in soils . 279
“ of soils, composition of . 280
Air-space in soils ; figure . 108
Alabama, vegetation and soil-characters . 51 1
Alaska current, effects on California climate . . 296
Alinit . 149
Alkali carbonates and sulfates, inverse ratio . 451, 452
carbonates, effects on clay . 62
effects on culture plants ; figure . 426, 427
Alkali-heath, range, tolerance of alkali, figure . 544, 545
Alkali lands, crops for strong . 468
effects of irrigation on . 428
efficacy of shading . 457
exceptionally productive when reclaimed . 483
fertilization not needed in . 483
formation from leachings of slopes . . 453
geographical distribution of . 423
high and lasting production when reclaimed . 482
inducements toward reclamation of . 481
in the San Joaquin valley, Cal., figure . . 425
possible injury to, from excessive leaching . 462
565
566
INDEX.
PAGE
Alkali lands, summary of conclusions . 453
surface and substrata of . 429
utilization and reclamation of . 455
of world-wide importance. . 424
vegetation of . 534
Alkali-resistant crops . 455
Alkali salts, black and white . 441
composition of . 439
composition of ; general table . 442, 443
distribution in heavy lands . . . 436, 437
effects on beet crop . 465
horizontal distribution of . 439
in hill lands . 439
in sandy lands . 433, 435
in Salton Basin, distribution of . 436, 438
leaching-down of . 459
nature of . 423
plant food in . 441, 444
reactions between . 449, 450
reduction by cropping . 463
relative injuriousness of . 464
removal from the soil . 458
removal by deep-furrow irrigation ; figure . 460, 461
tolerance of various crop plants ; table . 466, 467
total in lands ; estimation of . 444
underdrainage the universal remedy for . 460
upward translocation from irrigation . 433
vertical distribution in soils . -429, 431, 432, 434
Alkali soils and seashore lands . 422
calcareous character of . 28
composition of, as a whole . 445, 446, 447
how native plants live in . 430
origin of . 422
repellent aspect, cause of . 424
retention of silica in . 392
Alkali spots, white . 286
Alkali, rise of . 428
turning under of surface . 456
weeds as cattle food . . . 468
study of, by Loughridge and Davy . 535
Aluminic hydrate, in soils of California and Mississippi ; table . 101, 390
Alluvial soils . 12
Ammonia-forming bacteria . 149
Ammonia gas, absorption of, by soils ; figure . 274, 275
Amnionic carbonate, effects on glass . 18
Ancient civilizations, preference for arid countries . 417
rare in humid countries . 418
Apatite . 63
INDEX.
567
J>AGK
Arid and humid climates, rock-weathering in . 47
Arid and humid regions, criteria of soils of . 371
contrast between soils of . 28
soils of . hi, 371
Arid and humid soils, general comparison ; table . 375, 377
Arid belts, subtropic . 298, 299
utilization of . 299
Arid conditions, local, in tropical countries. . . . 401
Aridity, influence upon civilization . 417
Arid region, bunch grasses on soils of . 111
standing hay in . 300
upland soils of ; table . 373, 374
Arid soils, productiveness induces permanent civil organization . 412
Arroyo Grande and Yazoo buckshot soils . 345
Asparagus, resistant to salts . 475
Atmosphere, composition of ; table . 16
Azotobacter . 156
Lipman on . 156
B.
Bacteria, active in soil-formation . 20
aerobic and anaerobic . 144-
denitrifying . 148
food and functions of . 145
in soils, numbers of . — . 142
micro-organisms of soils . 142
multiplication of . 144
nitrifying . 146
Bacterial life, effect on soil, condition . 149
relation of carbonic dioxid to . 281
Bacteroids .. . I5I
Mork figures . I52» J53
Basaltic rocks . 49
Basalts, red soils from . 52
Basic slag . 64
Basin irrigation, advantages of . 243
Bauxite in soils . . . . 101 » 39°
Beet, sugar, effects of salts on . 474
tolerant of common salt . 474
Bhil soils . .
Bicarbonate of soda . 7^
Black-alkali lands, difficulty in draining . 462
neutralizing of . 457
waters, use of . 25°
why so called . 7^
Black earth of Russia, humus in ; table. . 130
Black sand . 45
568
INDEX.
PACK
Black prairie soils . 53
Black soils and lands . 283
Blizzards in continental America . 298
Blown-out lands . 9
Blue tint in clays and subsoils . 45
Bodengare . . . I49> I5°» 281
Bog ore, formation of, in subsoils . 46, 66
Bones, composition of . 64
Bone meal, efficacy of . 65
Borax, borate of soda . . 79
Bottom water . .... 227
rise of, from irrigation . 227, 230
Bottoms, first and second, contrast between . 506, 507, 509
Bottoms, first, tree growth of . 507, 509
Brahmaputra alluvium, Assam . 413
Brown iron ore . 44
“ Buckshot ” soils of Yazoo bottom . . . 116
“ Bunch grasses ” as alkali-resistants . 471
Burning-out of humus, effects of . 118
Burrowing animals, work in soil-formation . 160
C.
Calcareous clay, crumbling on drying . 116
formations, predominance in Europe . 525
soils, definition of . . . .367, 496, 524
solubility of alumina and silica in . 389
subsoils, and hardpans . 162
Calciphile, calcifuge and silicophile plants . 521
Cal cite, calcareous spar . 39
recognition of . 39
Caliche, in Chile, Nevada, and California . 66, 67
Capillarity . . . 189
Capillary water, reserve of . 229
rise of . 202 to 207
Carbonated water, action on feldspar . 32
action on silicates . 18
universal solvent . 17
Carbonate of soda . 77
injury to soils and plants . 78
Carbonates, chlorids and sulfates of earths and alkalies, reactions
between . 449, 450
Carbonic acid . 17
secreted by roots . 20
Carbonic dioxid, absorption of, by soils . 274
heavily absorbed by ferric and aluminic hydrates. . . . 278
occurrence, formation . 17
relation to fungous activity . 281
INDEX.
569
PAGE
Cascade range, climatic divide in N. W. America . 297
Caves in limestone regions . 41
Celery, moderate tolerance of alkali . 475
Centrifugal elutriator, Yoder’s . 92
Cereals, alkali-resistance, barley, gluten wheats . 471
Channels, cutting-out by gravel . 6
Charcoal, absorption of gases by . . 276, 277
Chemical absorption by soils . 270
action of roots . 20
analysis of soils (in general) . 323
character of soil, recognition of . 322
decomposition, causes intensifying . 21
processes of soil formation . 16
Chile saltpeter . 66
Chernozem . 130
analyses of, table . 364
Chestnut, American, a calcifuge tree . 491, 519
Chlorin, largest ingredient of sea water . 27
Chlorite . 36
Chlorosis of vines in marly lands . 526
Churn elutriator, Hilgard’s ; figure . 91
Circling of hill lands . 220
Citrus fruits, injury to, from alkali . 478
lemons most sensitive . 478
sensitiveness to common salt . 477
Classification of rocks . 47
of soils . 10
Clay as a soil ingredient . 83
colloidal . 59
functions of, in soils . 59
maintains crumb structure . no
Clays, claystones, clay shales . 48
colors of . 58
formation, flocculation and deposition of . 33
maturing of . 60
plasticity and adhesiveness, influence of fine powders on . 85
influence of ferric hydrate on . 85
Clay-sandstones, soils from . 57
Clays, separation of, by subsidence, by centrifuge . 89
varieties, enumeration of, and characters . 57* 5^
fusibility of . 5&
Claystones, soils from . 59
Cleavage of rocks . 3
Cleopatra’s needle . 2
Climate . 2^7
Climatic and seasonal conditions . 21
Climates, continental, coast and insular . 29 7
Coffee soils, calcareous . 4r7
5/o
INDEX.
Colloidal clay, amount in soils. Table .
analysis of, by Doughridge .
effects of alkali carbonates upon .
investigation by Sclilcesing .
properties of .
separation of, by boiling and kneading .
Colloid humates .
Colluvial soils . .
Colors of soils, advantages of .
Common salt, injuriousness in soils .
recognition of .
removal from soils. . .
Conglomerates .
Conifers, tall growth of, in arid regions .
Contraction of soils in wetting and drying .
Co-operation, favored by need of irrigation .
Corsican and maritime pine, asli analyses .
Cotton, compact growth and heavy boiling on calcareous soils .
Cracking of clay soils in drying .
Cressa ; range, tolerance of alkali, figure . . . 545,
Creep .
Crops, alkali-resistant . . .
Crumbling of calcareous clays on drying .
Crumb-structure of soils ; figure .
Crusting of soils, effects of. . 111, 117,
Cultivated soils, analysis of .
investigation of .
Cultural experience the final test .
Cutting-out of channels by water-borne gravel .
Cypress, different forms of ; figures . 507,
D.
Date palm, resistance to alkali .
Decomposition, chemical, of rocks .
Decolorizing action, of soils, charcoal .
Deep-rooting of native plants in arid region .
Deforestation, effects of .
Deltas, formation of .
Denitrifying bacteria .
Deserts, effects of winds in .
Desert sands, only lack water to become productive
Dew, formation of .
rarely adds moisture to soils .
within the soil .
Differentiation of soil and sub-soil, causes of .
Distance between furrows and ditches .
Dolomite .
PAGE
84
385
62
59
61
61
133
12
283
76
76
76
48
517
1 14
419
520
503
1 13
546
12
455
116
no
221
325
316
324
6
508
478
16
219
7
148
8
420
307
308
308
121
241
42
INDEX.
571
PAGE
Drainage, rights-of-way for . . 461
Drainage waters, use for irrigation . 250
Drain waters, analyses of, table . . 22
leaching effects of . . 271
Drouth, resistance to, in arid soils . 167
Dust soils, nature of . . 104
slow penetration of water in . 105
Dust storms . 9
Dynamite, used for shattering dense substrata . . 181
Earth’s crust, known thickness . xxix
Earthworms, action of in soil-formation . 158
Ecological studies . 314
Egypt, obelisks of . 2
Elements constituting earth’s crust, table of . . . . xxix
important to agriculture, list of . . xxxi
Elutriator, Hilgard’s, figure . 91
Epsomite, epsom salt, in soil . 78
Eremacausis . 129
Erosion in arid regions . 219
in Mississippi table lands ; figures . 218
lowering of land by . 15
of rocks by sand ; figure . 10
Eruptive rocks, basic and acidic . 49
rocks, soils from . 52
Eucalyptus, tolerance of alkali . 480
European observations on plant distribution . 519
standards of plant-food adequacy — Maercker’s table . 369
Europe, predominance of calcareous formations in . 525
Evaporation and crop yields, calculated . 193
and crop yields, observed (Fortier) . 194
and plant growth . 193
counteracting, in alkali lands . 455
dependence on air temperature ; Fortier’s experiments,
table . . 255
from reservoirs and ditches . 257
from water surfaces . 254
wet and moist soils . 254
in different climates . 192, 256
in different localities, California . 255
restrained by loose surface layer . 255
through roots and leaves, amount of . 262, 263
Expansion by oxidation . 18
F.
Farmyard or stable manure . 72
Feldspars, weathering of . 31
products of . 32
572
INDEX.
PAGE
Ferghana, alkali lands in . . 441
Ferric hydrate, effects of . 100
functions of, in soils . 285
high absorptive power of . 277
in Hawaiian soils ; table . - . 356
more diffused in humid than in arid soils. . . 392
Ferric phosphate, unavailability of . 356
Ferroso-ferric hydrate and oxid . 18, 45
Ferrous oxid . 18
Ferruginous lands, injury from swamping of . 233
Fertilizers, mineral . 63
waste of, by leaching . 269
Flocculation and floccules . 91
Flocculated structure ; cements maintaining . no, in
Flood-plains of rivers . 14, 15
Fool’s gold . 75
Force exerted by roots . 19
Forecasts, general, of soil quality in forest lands . 507
of soil values, popular . 313
Forest trees, forms of . . . 499 to 502
of Atlantic states on alkali lands . 481
Form and development of trees, differences in . 498
Forms of leaves, variation in . . . 502
black-jack oak . 499, 501
post oak . 499, 500
trees, deciduous, in arid region . 516
willow, scarlet, black and Spanish oaks . 502
Freezing water, effects of . 3
Frost, effect of soils . 118
Fruiting, favored by lime in soils . 503
Fungi and molds, action of . 123
functions in humus-formation . 157
G.
Gases, absorption of, by soils . 272, 275
partial pressure of . 276
Germination of seeds . 309
Glacier flour, fineness and fertility of . 5
physical analysis of . 5
Glaciers, grinding and abrasion by ; figure . 3
Glauber’s salt . 77
Glauconite, in calcareous sandstones . 56
Gneiss soils . 51
Gobi desert, migration of lakes . 9
Going-back of orchards . . . 182
Grain-sizes, effect on percolation ; table . 224
influence on soil texture . 100
INDEX.
573
PAGB
Grandeau method of humus estimation . 132
Granite soils, potash and phosphoric acid in . 50
Granitic rocks, weathering of . . . 47
sand, formation in arid climates . 2
Grano-diorite soils, of Sierra Nevada . 51
Granular sediments, influence upon tilling qualities . 102
Grape-vine, alkali, tolerance of . 475
Grasses, cultivated, sensitive to alkali . 471
Greasewood, range, tolerance of alkali ; figure . 542, 543
Greenstones, soils from . 51
Ground water, depth most favorable to crops . 228
variation of surface of . 228
Gulf-stream. ... . 295
Gypsum or selenite, formation from sea-water evaporation . 42
how recognized . 42
H.
Halite . 76
Hardpans, causes, formation and cements of . 185
Hardpan, physical, analysis of . 103
plowsole . . . . 241
Hawaiian Islands, humid and arid sides of . 297
soils, analyses of . 356
Hay bacillus ; figure . 149, 150
Heat and cold, effects on rocks . 1
of high and low intensity . 304
reflection and dispersion from soil surface . 304
relations to soils and plant growth . 301
trapping of suns . 288
Heaviest clay soils, physical analysis of . 115
Heaving-out of grain . 119
Hematite . 44
Herbaceous plants as soil indicators . 517
Hog-wallows . 1 14
Hornblende and pyroxene . 33
weathering of . 33
Horsetail rushes, secretion of silica by . 31
Humates and ulmates . 133
cementing effects of . 111
Humid and arid climates, rock-weathering in . 47
Humid region, upland soils of ; table . 372> 374
Humification in soils . 20
normal conditions of . 129
tests ; Snyder, tables . 14°
Humin substances, formation of . 123
Humus, amidic constitution of . 125
and coal, amountsof,from vegetable substance . 128
574
INDEX.
PAGI
Humus, amount in soils . . . 133
ash of, from Minnesota soils, analysis . . . 134
decrease of nitrogen-content with depth . . 135
determination in soils . - . 132
distribution in the surface soil. . . . . 157
functions in soils., . 21
in arid and humid regions . 138
in black ea|tli of Russia . 130
in Minnesota soils . 131
in North Dakota soils . 133
in the surface soil . 120
losse& from cultivation and fallow . 131
nitrogen of . 124, 135
percentage in soils, and nitrogen-content of, tables. ..135, 136, 137
porosity of . 124
progressive changes in soils . 126
relation to bacterial content . 144
scanty in arid soils, but rich in nitrogen . . . 397
substances, physical and chemical nature of . 124
variation of, with original materials . 139
volume weight of, table . 125
versus adipocere . 140
Hydraulic elutriation . 90
Hydro-mica . 35
Hydrous silicates in soils of arid region . 388
Ice-flowers on soils . 119
Immediate plant-food requirements, ascertainment of . 333
productiveness, chemical tests of . 337
productiveness vs. permanent value of soils . . . .318, 327
India, climatic contrasts . 401
Indian soils, table of analyses . 410, 412
types of soils . 411
Indo-Gangetic plain ; calcareous hardpan, kankar . 41 1
Injury from excessive runoff, prevention of . 220
to plants from the various salts . 531
to soils and plants from carbonate of soda . 78
Insects, work in soil-formation . 160
Insoluble residue of soils ; less in arid than humid . 384
Insufficient rainfall, leaves sea salts in soils . . . . 28
Insular climate, of Britain, western Europe . 298
Introduction . xxix
Injury from swamping, permanent . 232
Iron carbonate solution, how formed . 44
coloring clays . 58
minerals . 44
pyrites, how recognized. . . . . 75
INDEX.
575
PAGH
Irrigation, basin, advantages and disadvantages . 244
by check 'flooding . 237
flooding . 237
furrows . 238
lateral seepage . 242, 241
shallow, deep and wide furrows ; diagram . 239
surface sprinkling. . . . . . 237
underground pipes . 245
ditches, leaky, effects on alkali lands . ’ . 429
excessive surface rooting caused by . 245
methods of . 236
necessitates co-operation . 1 . . . 419
Irrigation water, abundant use of saline . 249
duty of . 251
economy in use of . 243
effects of saline, figures . 247
heavy losses in using . 252
limits of salinity . 246, 248
loss by evaporation . 252
loss by percolation ; diagram . 253
quality of . 246
saline, how to use . 249
testing penetration of . 242
temperature of . 244
Irrigation, winter, advantages of . 236
Isinglass . 43
*
J-
Janesville loam, chemical analysis of . . . . 331
Japan current . 296
Jasper and hornstone pebbles, weathering of . 30
K.
Kainit, composition of . 71
Kaolinite and clay ; kaolin . 32
assumes plasticity on trituration with water.* . 60
crystalline form of . 22, 59
lacks plasticity. . 60
Kaolinization, results in zeolite-formation . 395
slow in arid regions . 87, 386
L.
Landholding, units of, smaller in arid than in humid region. . 420
Landlocked lakes, water of . 27
Land plaster as a fertilizer ; effects on soils . 43
5/6
INDEX.
PAG*
Landslides . 12
Laterite soils, Wohltmann’s definition . 416
Terra roxa of Brazil . 416
Leaching of the land . 22
Legumes, bacteria of . 150
mostly sensitive to alkali . 472
Leguminous plants, mostly calciphile ; exceptions . 518
Leucite, potash content. . 32
Lichens, action on rock-surfaces . 19, 20
Lignites and coal, how formed . 127
Lime a dominant factor in productiveness . 353
Lime carbonate in sea water . . 26, 27
removed from earth’s surface . 41
summary of effects in soils . 379
Lime-content, effects of high, in soils . 365
effects on availability of phosophates, table . 366
“ Lime-country is a rich country ” . . . 365
Lime, excess of, in arid soils . 378
Lime feldspars, leave lime carbonate in soils . 32
in alkali lands protects plants from salts . 532
lands, failure of tea on . 414
Lime-loving trees . 490 to 429, 497
Lime, most abundantly leached out . 24
percentages, what are adequate . 367
in coast-belt soils . 496, 497
in heavy clay soils ; table . 368
Lime renders lower amounts of plant-food adequate . 354
Limestone countries . 53
, Rotten . 54
soils, excluded from comparison of arid and humid soils. . . . 376
residual . 53
Limestones, impure, as soil-formers . 40, 53
residual soils of, how formed . . . 40
soft, or marls. . . . 4o
slow disintegration of pure . 63
Limit of acid action on soils, investigation of, by Lougliridge . 340
Limonite . 44
Loamy and sandy soils, show little shrinkage . 117
Loose surface layer, illustration of effect, figure . 258, 260
prevention of evaporation by . 257
Loss of humus in summer mulch . 132
Louisiana, vegetation and soil-characters . 512
Lowland tree-growth . 506
Lysimeter . 227
M.
Madagascar, character and soils of . . . . . 405, 406
climate and rocks of . 406
INDEX.
577
PAGE
Madagascar, methods used by Muntz and Rousseaux . 406
potash and lime leached into valleys . 407
red soils . 407, 409
table of soil analyses . 408
Madras, red soils of . 415
Magnesia, effects of excess over lime . 382
exceeds lime in tropical soils . 405
high in arid soils . . 381
leached out next to lime . 24
proper proportions to lime . 383
Magnesian limestones as soil- formers . . . 42
Magnesian soils largely poor . . 36
Magnetite . 45
Maize and sorghums, alkali-resistance . 471
Maize roots in humid and arid region . 175, 176
Manganese, more in humid than arid soils . 383
stimulant effects on crops . 383
Marble and limestones, formation of . 39
Marls, gypseous and calcareous . 43
Marly substrata . 186
Marine saline lands . 527
first crops for . 533
reclamation for culture . 534
Matiere noire ; active nitrification of . 132, 360
Mechanical analysis of soils . 88
Melilots, white and yellow, alkali resistance . 473
Mesas of arid region . 14
Mesopotamia, rehabilitation of . , . 421
Metamorphic rocks . 46
Methods of irrigation . 236
soil analysis . 325
Mica as a soil ingredient . 35
weathers slowly . . 35
mistaken for gold and silver . 35
Mica-schist soils . 51
Micro-organisms of soils . 142
Mineral fertilizers . 63
ingredients of soils, minor . ... 63
Minerals injurious to agriculture . 73
major soil-forming, and rock-forming, list of. . 29
tints of . 18
unessential or injurious to soils . 75
Mirabilite . 77
Mississippi, changes in vegetation from east to west in northern . 490
investigations in, by writer . 489
northern, vegetative belts in ; map . 490
vegetative belts, descriptions of . 490, 491, 492
Mississippi river, sediment carried by . 7
578
INDEX.
PAGS
Mississippi, southern, central prairie, long-leaf-pine belts . 493
coast-belt; pine meadows; profile . 495
live-oak or shell hammocks . 495
Mississippi valley, climate of . . 298
Mississippi water, annual variations in . 25
generalized composition of . 25
Modiola, of Chile . 469
Moisture hygroscopic, table . 196
influence of temperature and air-saturation . 197
method of determining . 197, 198
Mitscherlich’s objections . 199
utility to plant growth . 199
available to growing plants . 21 1
distribution in soil, as affected by vegetation . 264
evaporated from forests . 265
Eucalyptus . . 265
in Russian forests and steppes . 265
requirements of crops in the arid region . 212
Roughridge’s tables of same . 214
supplied by tap roots . 229
useful to crops retained by alkali lands . . 433
wasted by weeds . 264
Moraines, in North Central states . . 5
Mosses, follow lichens in rock decomposition . 20
Moulds and fungi, action of . . 123
Mountain chains, arid climate under lee of . . 294
effects of, on rainfall . 293
Muddy waters . 251
Muir glacier, analysis of mud . 5
Mulches, loss of humus . 132
Mulching with straw, sand . 266
Mustard family, sensitive to alkali . 473
Myrobalan root, use for grafting in alkali lands . 479
N.
Native vegetation, basis of land values for farmers . 488
causes governing its distribution not an unsolvable
problem . 489
result of struggle for existence . 487
Native grasses for alkali lands . 470
Native growth, cogency of conclusions based on . 314
New Mexico, soils from ; analysis . . . . 378
Nile water, Letheby’s analyses of . 25
Nitrate deposits, origin of . 67
of soda . 66
Nitrates, waste of, by leaching . .24, 68
Nitrification, active in matiere noire . 360
INDEX.
579
PAGE
Nitrification and denitrification .
in alkali lands . .
in soil of “ ten-acre tract.” .
intensity in arid climates .
list of substances favoring .
of organic matter in soils, experiments .
not active in unhumified matter . . 359,
Nitrifying Bacteria .
Nitrobacterium ; conditions of activity . . .
Nitrogen-absorbing bacteria .
Nitrogen, absorbed more abundantly than oxygen .
accumulation of, in humus .
adequacy in humus, lowest limit of .
in soils .
availability of, in soils ; ascertainable .
content of humus .
deficiency, pot test, figure .
determination of, in soils .
hungry soils ; table ... .
percentages in humus, what are adequate . ...
supply of plants, views on .
Nitrosomonas, figure . .
Nodules of legumes . .
North Central States, herbaceous vegetation on calcareous soils ... .514,
lowland growth in uplands, when . . .
vegetation and soil-character .
Nutritive salts in alkali .
145
68
359
68
147
358
360
146
146
156
278
124
363
357
363
135
362
357
361
360
150
246
151
5i5
5i5
513
441
O.
Ocean currents, Gulf-stream and Japan-stream . 295 296
Olive, resistance to alkali . 478
Organic and organized constituents of soils . 120
Organisms influencing soil-conditions . 142
Oxalic acid, secretion by lichens . . . . . . 19
Oxidation, expansion by . 18
Oxids constituting earth’s crust ; table . 31
Oxygen, action in weathering rocks . 18
proportion of, in earth’s crust . . . 30
P.
Pamperos . 9
Peat bogs . 122
Peaty soil, shrinkage . iJ7
Percolation in natural soils : diagram . 223, 225, 226
rate of, as influenced by grain-sizes . 224
Permanent value of land vs. Immediate productiveness . 34°
580
INDEX.
PAGB
Physical and chemical causes of vegetative features . 505
conditions of plant growth . 319
Physical analyses, correlation with popular names . 96
results of . 94
table. Mississippi and California soils . 98
analysis of soils . 88
constituents of soils . 10
Physico-chemical investigation of soils . 313
Physiological soil analysis . 333
Phosphate fertilizers, importance of . 65
Phosphate fertilization, in arid region . 393
in California . 393
Phosphoric acid, limits of adequacy in soils . 355
minute amounts leached from soils . 24
no constant difference between arid and humid soils. . 393
rendered inert by ferric hydrate . . . 355
Phosphorites, low-grade, of Nevada, Russia . 63, 64
Plane tree, oriental, resistant to alkali . . 480
Plant-adaptation “ varying from province to province ” . 523
Plant associations, plant formations . 315
Plant distribution, Thurman’s physical theory of . 519
Plant-development under different temperatures . 309
Plant-food, accumulation in finest parts of soils . 87
high percentages mean high land value . 346
ingredients, condition of, in soils . 319
in virgin soils, lowest limit of, table . 352
limits of adequacy . 353
minute amounts may produce large crops . 410
percentages, what are high . 346
percentages, low . 346
water-soluble, reserve, unavailable . 320
Plant-growth on arid subsoils . 166
Plants, deep-rooting in arid region . 174
indicating irreclaimable alkali lands . 535, 536
Plant root action, cannot be imitated in laboratory . 324
Plasticity, absence of, in fine powders . 60
of clay, causes of . 60
lost by burning . 60
Plot tests, difficulties and uncertainties of . 334
plan of, figure . 335
Plowsole, how formed, by shallow irrigation . 186, 241
Poor chalk lands. ... . 525
Pore-space . 108
Porosity of humus . 124
Port Hudson bluff, lignite in, figure . 128
recession of . 116
Potash, abundant in arid soils . . . . . . 395
and soda in arid and humid region . 394
INDEX.
58l
PAGE
Potashes, production of detrimental to agriculture . 69
Potash feldspar, supplies potash to soils . . . 32
fertilization first in humid, last in arid region . 396
from sea water . 69
limits of adequacy in soils . 354
minerals, orthoclase feldspar . 68
preferential retention of, in soils . 272
Salts, Stassfurt . 69
slightly leached out . 24
sulfate, high-grade . 71
Pot-culture tests . 336
Powders, absorption of various gases by, table . 277
Prairie soils, black . 53
Preparation of soils for physical analysis . 89
Productive capacity and duration, forecast of . 346
Progress of humification and formation of coal, table . 126, 127
Pulverulent soils of arid regions . 87
Purifying action of soils . 269
Putrefactive processes, relation to carbonic gas and anaerobic bacteria. . 282
Putty soils . 103
Pyroxene, augite . . . . 33, 34
Q.
Qualifications required for soil study . 524
Quality of irrigation water . 246
Quince, resistance to alkali. ... . 479
Quartz and allied rocks . 29
sand most prominent ingredient of soils . 30
veins, formation of . 31
R.
Rain belts, temperate and tropical . 295
Rainfall, amount of . 215
distribution in California and Montana . 290
in the United States . 215
most important . 290
on the globe, figure . 294
influence on soil formation . 22
insufficient, forms alkali soils. . . 28
leaves lime behind. . . . 28
natural disposition of . 216
Rains, beating . 221
cold and warm . 3°2
Reclaimable and irreclaimable alkali lands . 534
Red foothill soils of California . 34
Red or rust-colored soils . 34
advantages of . 284
582
INDEX.
PAGE
Regur soils, Deccan, India . 414
formation of . 415
“ guvarayi ” hardpan . 415
present production . 414
Reh of India . . 440
Reserve plant-food in soils . 320
of zeolites, carbonates, phosphates . 321
Residual soils . . 11, 13, 22
Rhizobia, adaptation to symbiosis . 154
inoculation of soils with . 154
increase of crops by inoculation with . 155
of legumes . 150
mode of infection . 154
varieties of forms . 154
Rhubarb, sensitive to alkali . 475
Rhyolites, soils from . 53
River bars, formation of . 7
Rivers, amount of dissolved matters carried by . 24
flood-plains of . 13, 14
sediment carried by . 24
waters, analyses of, table, discussion . 23, 24
white and green . 4
Rock crystal . . 29
Rocks as soil-formers . 47
chemical decomposition of . 16
cleavage of . 3
definition of . xxix
disintegration of, under extremes of temperature . 2
effects of heat and cold on . . 1
erosion of by sand . 10
forming minerals . 29
fragments, rounding of, by flowing water . 6
Rock powder . 85
Rock-weatliering in arid and humid climates . 47
Rohhumus . 122
Rolling of soils, of influence of, on heat . . . 305
Root action, limitation of . 351
Root bacillus, figure . 149, 150
Root crops, effects of alkali upon . 474
Root development in the arid and humid regions . 169 to 176
Rooting, deep, from proper irrigation . 243, 245
Roots, chemical action of . . . . 21
force exerted by . 19
secrete carbonic acid . 20
Root system in the humid region ; figure . 168
Rotten Limestone, soils from, analyses . 54
Runoff of rain water . ... 216
INDEX.
533
PAGE
Russia, black earth of ; roots and humus in . 130, 363
Rye grass, giant, of Northwest ; uses . . 470
S.
Saline and alkali lands, vegetation of . . . 527
plants, analyses of ashes of . 530
selective power of . 53 t
Saline and xerophile vegetation, similarity of . 528
Saline contents of waters, variations of . 250
solutions, structural and functional differences caused by . 528
vegetation, general character of . . . 527
Saltbushes, Australian, growth and use in California . 469
of Great Basin, probable usefulness . 468
Salt-grass; range, tolerance of alkali, figure . . 546, 547
Sal to 11 Basin, profile of salts in . . . 438
Salts, absorption of, by saline plants . . . 529
Saltwort : range, tolerance of alkali, figure . . . . 540, 542
Samoa and Kamerun soils, analyses by Wohltmann ; method . 402
table of . 404
Samphire, Bushy and Dwarf ; range, alkali-tolerance, figure _ 538, 539, 540
Sand blasts, effects on cobbles . 10
coarse, effect of, on clays . 105
erosion of rocks by ; figure . 10
hammocks, of Gulf coast . 56
Sands of arid and humid regions, differences in . 86, 386
table of analyses . 387
Sand, silt and dust . 85
Sandstones . , . . . , . ... 48
argillaceous . 57
calcareous, formation of . 56
rich soils from . 56
dolomitic, often form poor soils . 56
ferruginous, poor soils from . 56
siliceous, poor soils from . 55
varieties of . 55
zeolitic, soils from . 57
Sandstone soils, lightness of . 55
soils, poor, of humid region . 55
Sand storms . 9
Sandy lands, of arid regions, highly productive . 386
Sandy soils . 30
Scheme's elutriator, figure . 90
Shrinkage, extent of, in drying soils ; figure . 113, 114
Schiibler on calcareous soils . 115
Sea water, average composition of, table . 26
chief ingredients useless to plants . 28
minor constituents of . 27
sources of salts in . 26
584
INDEX.
PAGB
Sedentary soils . 11,13, 40
Sedimentary rocks . 47, 48
Sediment deposited by Mississippi in Gulf . 7
Sediments, exhibition of, from physical analysis . 95, 96
number of, in physical analysis . 93
table of diameters and hydraulic values . 94
Seeds, germination of . 309
Semi-humid and semi-arid region . 377, 397
Serpentine . 36
Sieves, use in physical analysis of soils . 88
Silica, absorption and secretion by plants . 31
and alumina, soluble ; quantitative relations . 385
solubility in water . 31
soluble, retained in alkali soils . 391
Silicate minerals . 31
Silicates of soda and potash, soluble . . . 31
Silicon, abundance of, in rocks . xxxi
Silicophile plants, a fiction . 522
Sinkholes . 43
Soapstone . 36
Soda in arid and humid regions . 394
Soda, nitrate of . 66
Sodium salts, leached out by drains and rivers . 24
Soil analysis, change of views regarding . 317
discrepant methods used in . 402
practical utility of . 318
Soil and subsoil, causes and processes of differentiation . 120
ill-defined . 120
Soil bacteria, numbers of . 141
Soil character, recognition from native vegetation . 487, 51 1
Soil-dilution experiments . 347
figures . 348, 349, 350
table of . 350
Soil-examination, short approximate methods for, used at California
station . 560
summary directions for, in field or farm . 556
Soil-formation influenced by rainfall . 22
physical processes of . 1
Soil-forming processes accelerated by high temperatures . 398
Soil-grains, number of . 99
surface of . 99
determination by air-flow . 99
by “ Benetzungswarme ” . 99
investigation, historical review of . 313
moisture, regulation and conservation of . 234
phosphates, solubility in water ; Schloesing fils . 332
probe, mode of using . 177
profiles in arid and humid region . 165
INDEX.
585
PACK
Soil, samples, directions for taking, by Calif. Station . 553
sedentary or residual . 11, 13, 40
study, qualifications needed for . 524
surveys, early, of Kentucky, Arkansas and Mississippi . 316
temperature, annual range near surface in arctic and tropical regions 303
change with depth ; table . 303
influence of evaporation on . 307
influence of soil material . 306
influence of surface conditions, . 303
influence of vegetation and mulch . 305
tests by crop analysis, Godlewski, Vanderyst . 337, 338
by extraction with organic acids ; Dyer, Maxwell . 339
water, different conditions of . 195
Soils, acid-soluble and water-soluble portions most important . 324
alluvial . 12, 13
ancient, in geological formations . xxix
calcareous, definition of . . . 367, 496, 524
classification of, figure . 11
colluvial . 12, 24
definition of . xxix
derived from various rocks . 49
effects of crusting on . 221
indefinite action of dilute acids on . 326
interpretation of analyses ; Wohltmann . 403
physico-chemical investigation of . 313
(see Table of Contents)
Solar radiation, influence of . 302
Solubility, continuous, of soils in water . . . 328
King’s table, rich and poor soils . 330
Schultze’s table, rich soil . 328
Ulbricht’s table, poor soil . 329
Solvent action of water upon soils . 327
power of water . J7
Solubility, increased with nitrogen-content . 14 1
Sour grasses . 1 23
humus, antiseptic properties of . 122
soils . 122
Souring of soils, by cultivation . 123
Stable or farmyard manure . 7 2
composition of, table . 73
green-manuring only substitute . 74
method of using, in humid region. . . 74
physical effects of . 73
use of, in the arid region . . 74
Stalactites and stalagmites . 41
Stassfurt Salts, discovery of . 69
importance to agriculture . 7°
origin of . 7°
586
INDEX.
PAGB
Stassfurt Salts, nature of . 71
Stonecrops, succeed mosses . . 20
Stone fruits, resistance to alkali . 478
Stratified rocks, derived from crystalline . 29
Stunted growth, caused by shallow or very heavy soils . 504
Sturdy growth on calcareous lands . 502, 503
Subsidence method . 89
Subsoils, arid region . 163
and deep plowing . 164
calcareous . 162
rawness of, in humid climates . 163
Substrata in arid region, importance of . 173
faulty, with figures . . . 177 to 180
impervious, injury from ; figure . 181
leachy . 182
marly . 186
Subterranean rivers . 41
Sulfate of potash, high-grade . 71
of soda, dust from . 77
injuriousness to plants . 77
occurrence in arid regions . 77
Sulfates, reduction of . 232
Sulfuric acid in arid and humid regions . 394
Summer mulch, loss of humus in . 132
Sunflower family, resistance to alkali . 473
Sun’s heat, penetration into the soil . 302
Surface crusts, formation of . hi, 117
physical analyses of . 118
Surface, hydrostatic and ground waters . 215
Surface waters, chemical effects of percolation . 161
physical effects of percolation . 161
Swamping of alkali lands, consequences of . 45 1, 463
irrigated lands, results of . 231
Symbiosis, adaptation to, of Rhizobia . * . 154
Szek of Hungarian plain . 440
T.
Tabashir . 31
Talc and serpentine . 36
Tap-roots, moisture supplied by . 229
Tea, failure on calcareous lands . 414
Temperature, annual mean of . 289
conditions, ascertainment and presentation of . 288
extremes, on high mountains and plateaus . 288
of stellar space . 288
seasonal, monthly and daily means . 289, 291
Temporary vs. permanent productive capacity of soils . 340
INDEX.
587
PAGE
Tennessee and Kentucky, vegetation and soil-character . 513
Terraces, river and lake . . 14
Testing penetration of irrigation water . . . 242
Textile plants, tolerance of alkali. . 475
Thomas or basic slag . 64
Thurman’s physical theory of plant distribution . 519
Tillage ; effects of ; figure . 109, no
how maintained in nature . in
Titanium in soils . xxxi
Time of acid-digestion, different ; table . 342
Tolerance of alkali by culture plants . 463
alkali plants ; table . 548, 549
Topography, influence of, on climate . 293
Trachytes . 53
Trona, Urao . \ . 77
Tropical soils . 398
are highly leached . 400
often highly colored with iron . 400
do not need early fertilization . . 399
humus in ; abundant, but low in nitrogen . 399
few determinations made . 399
possible calculation of . 399
investigations of . 401
laterites, not always rich in iron . 400
mostly have low plant-food percentages . 400
resemble the “ nimble penny.” . 400
Tubercles of legumes, figures . 151, 154
Tufa, calcareous . 41
Tussock grass, food value of . 470
range, alkali-tolerance, figure . ..... .536, 537
U.
Ulmin substances . 122
Underdrainage, advantages of . 235
Underdrains, effects of . 234
Unhumified organic matter does not nitrify . 148
Unhumified vegetable matter, utility of . 135, 360
United States, good field for comparative soil study . 524
Upland and lowland growth in arid and humid regions . 515
Usar lands of India, character of . 440
not all alkali lands . 440
V.
Vegetative belts, lime a governing factor of . 492
Virgin lands, advantages of soil study in . 318
Virgin soils, analysis by extraction with strong acids . 340
Vivianite . .... 65
588
INDEX.
PAGE
Volatile part of plants . xxxii
Volcanic ash, form soils rapidly ; soils from . 20, 52
Volcanic glass . 53
Volume of soils, changes on wetting and drying . 122
Volume-weight of soils . 107
W.
Walnut, black, a lime-loving tree . 490 to 497
tolerant of white alkali . 479
Washing-away and gullying of land . 217
Water, capillary . 201
ascent in soil columns, figure . 202, 205
uniform sediments, figure . 204, 207
held at different heights in soil column, table . 208
expansion and contraction in absorbing . 208, 209
maximum and minimum of waterholding power, ter¬
mination of ; figure . . 202, 207
movements in moist soils . 210
carbonated, solvent power . 17
carrying power . 14
controlling factor of soil temperature . 301
density of . 190
effects of flowing . 5
Water-extraction of soils, practical conclusions from . 332
Water, hard . 41
hygroscopic . 196
of land-locked lakes . 27
loss of, by irrigation in shallow furrows . 240
physical factors of . 188
regulation of temperature by . 191
relations to heat . 189
requirements of growing plants . 192
plants in arid regions . 195
sidewise penetration of, in soils . 241
of soils (chapters on) . ..188, 215, 234
solvent action upon soils . 327
solvent power . 17, 191
Water-soluble plant-food . 321
specific heat of . 190, 191
table . 227
vaporization of . 191
Watery soil extracts, from European soils ; tables . 327, 329
American soils, King . 329, 330
Wave action on shores, figure . 7
Weathering, by oxygen, carbonic acid, water . 16, 17
“ in humid and arid regions . 2, 86
Weight of soils, per acre-foot . 107
INDEX.
589
PAGE
White soils, nature of, in humid regions . 285
in arid regions . 286
Wind deposits . 105
Winds, action of, in forming soils . 8
cyclones, and anticyclones . 293
effects of, in deserts . 8
heat the cause of . 291
land and sea breeze . 291
trade, and monsoons . 291, 292
Winter irrigation . 236
Wire-basket tests, of Bureau of Soils . 337
X.
Xerophile vegetation, similarity to saline . 529
Y.
Yazoo bottom, soils of . . . 116
Yazoo buckshot M and Arroyo Grande soils . 345
Z.
Zeolites, decomposition by acids . 36, 38, 39
exchange of bases in analcite and leucite . 37
formation of . 37
importance in soils . 38
rocks cemented by . 38
Zeolitic sandstones . 57
AUTHORS REFERRED TO
[Note. — In cases where no special credit is given in this volume for investigations made or data
given from the Southwestern States and the Pacific Coast, these should be understood as work done,
mostly under the writers direction, or by himself and assistants, in connections with the geological
surveys of Mississippi and Louisiana, as well as the Tenth Census of the United States, by Drs.
Eugene A. Smith and R. H. Loughridge; the chemical work for the Pacific Northwest, under the
auspices of the Northern Transcontinental Survey, by M. E. Jaffa and Geo. E. Colby ; that in Cal¬
ifornia, at the Experiment Station, by the latter two, Dr. R. H. Loughridge, and temporary assistants.
It would be impossible to segregate, without excessive prolixity, the credit to be assigned to each
of these participants.]
A.
Adametz, L., 142, 281.
Agassiz, L., 4.
Aso, K., 383.
B.
Bamber, — , 401, 410, 414.
Batholomew, J. G. 294.
Bejerinck, M. W., 1 51, 156.
Blumtritt, E., 276.
Bonnier, G., 521.
Bottcher, O., 393.
Boussingault, J. B., 151, 276, 313.
Brick, — , 528.
Brock, see Morck, D.
Burri, R., 148.
Butler, O., 151.
C.
Cameron, F. K., 380, 466, 532, 533.
Clarke, F. W., XXX, XXXI, 23.
Colby, G. E., note above.
Colmore, C. A., 448.
Contejean, Ch., 521, 523, 531.
Coville, F. V., 536.
Crochetelle, J., 146, 147.
Djemil, — , 159.
Duclaux, P. E., 144.
Duggar, J. F., 155.
Dumont, J., 146, 147.
Dyer, B., 339, 357.
E.
Ebermayer, E., 279, 305.
Eckart, C. F., 212.
Eichorn, — , 327.
Ermann, G. A., 303.
F.
Fawcett, W., 355.
Fischer, Hugo, 156.
Fliche, P., 520, 521.
Forbes, R. H., 219.
Fortier, S., 194, 254.
Fraenkel, L., 142.
Frank, A., 151.
Fuelles, P., 281.
Furry, F. E., 73.
Furuta, T., 383.
G.
Darton, N. H., 10.
Darwin, Ch., 158.
Davy, J. B., 535.
Deherain, P. P., 146, 147.
Detmer, W., 127.
Geikie, J., 14.
Gerlach, — , 156.
Gilbert, G. K., 2.
Gilbert, J. H., 151, 19J.
Godlewski, E., 337, 393
Goss, A., 376, 530.
591
592
AUTHORS REFERRED TO.
Grandeau. L., 132, 133, 139, 357, 520,
521.
H.
Haberlandt, F., 310.
Hall, A. D., 210, 227.
Hare, R. F., 378.
Harper, R. M., 494.
Hartwell, B. L., 123.
Headden, H. P., 18.
Hedin, Sven, 9.
Hellriegel, F., 130, 151, 192.
Henrici, 200.
Hillman, F. H., 536.
Hiltner, L., 154.
Hoffmann, R., 528.
Hohl, J., 143.
Hunt, T. S., 23.
J.
Jaffa, M. E., 135, 381, 450, 530.
Johnson, S. W., XXV, 60, 380.
K.
Katayama, T., 383.
Kearney, T. H., 532.
Kedzie, R. C., 343, 375.
Kellner, O., 393.
King, F. H., 99, 108, 109, 168, 192, 193,
210, 2ir, 212, 224, 228, 236,305, 325,
328* 332-
Kinsley, J. S., 143.
Knop, W., 197.
Koch, R., 156, 281.
Kossovitch, P., 363.
Kosticheff, P., 130, 157.
Krober, , 156.
Krocker, F., 22.
Kuntze, O., 67, 68.
L.
Ladd, E. F., 131, 133, 134, 141.
Langley, S. P., 288.
Lawes, J., 151, 192.
Lea, E. C., 387.
Leather, J. W., 401, 410. 41 1, 412, 414 to
417, 440.
Lemberg, J., 272
Lesage, M., 528.
Letheby, H., 23.
Liebig, J. von, 150, 313.
Liebscher, G., 354.
Lipman, J. G., 156.
Loeb, J., 380.
Loew, O., 23, 42, 38?, 383.
Loughridge, R. H., 87, 207, 213, 214,
240, 259, 340 to 342, 385, 430, 462, 466,
5X3> 535* 56°-
M.
Maercker, M., 65, 369.
Mann, H. H., 401, 410, 413.
Manson, M., 294.
Maxwell, W., 339.
May, D. W., 42, 380.
Mayer, A., 199, 207, 209.
Mayo, N. S., 143.
Mazurenko, D. P., 87.
Means, T. H., 248, 478.
Merrill, G. P., 2, 13, 167.
Middendorff, V., 441.
Mitscherlich, E. A., 99, 199.
Miquel, P., 142, 281, 359.
Mohr, Chas., 489, 51 1.
Moore, G. T., 154.
Morck, D., 154.
Muller, A., 449.
Muller, P. E., 122, 184.
Muntz, A., 142, 355, 370, 401, 402, 406 to
410.
Murray, John, 23, 24.
Myers, H. C., 6, 144.
N.
Naegeli, C. v., 129.
Nagaoka, M., 65, 393.
Nobbe, F., 154.
O.
Osterhout, W. J. V., 533.
Ototzky, L., 265.
Owen, D. D., 316, 317, 343, 513.
P.
Peter, A. M., 175.
Peter, R., 316,317, 343.
Pichard, P., 147.
Porter, J. L., 23, 24.
Pumpelly, R,, no.
AUTHORS REFERRED TO.
593
R.
Rafter, G. W., 217.
* Ramann, E
Reade, T. M., 41.
Regnault, V., 26.
Reichert, E., 276.
Richthofen, F. von, no.
Risler, E., 354.
Rosenberg, S., 528.
Rousseaux, E., 355, 370, 401, 402, 406 to
410.
Rudzinski, D., 87.
Russell, I. C., 24.
S.
Saussure, H. E. de, 150.
Schimper, A. F. W., 523, 528.
Schloesing, Th., 59, in, 354.
Schloesing, Th., fils, 332, 393.
Schmidt, C., 23.
Schone, H. E., 90.
Schiibler, J. J., 116, 197, 313.
Schultze, H., 328, 329.
Seton, E. T., 159, 160.
Shaler, N. S., 12.
Shaw, G. W., 465.
Smith, E. A., 511.
Snyder, H., 131, 133, 134, 139.
Stenhouse, — , 276.
Stockbridge, H. E., 307, 308.
Stone, C. H. H., 25.
Stubenrauch, A. V., 222.
Stutzer, A., 149.
T.
Thurmann, J., 519, 520.
Tolman, L. M., 387.
Tourney, J. W., 216.
Traphagen, F. W., 23.
Tuxen, C. F. A., 184.
U.
Udden, J. A., 106.
Ulbricht, R., 328.
V.
Vanderyst, H., 338.
Ville, G., 1 51.
Voelcker, J. A., 22, 410.
Vogel, J. H., 156.
W.
Wagner, P., 65.
Ward, M., 144.
Warington, R., 108, 146.
Washington, H. S., XXX.
Way, J. T., 22, 73.
Weber, A. H., 450.
Wheeler, H. J., 123.
Whitney, M., 94, 195, 207, 316, 321, 330,
332, 337-
Wilfarth, H., 151.
Williams, W. E., 60, 100.
Winogradsky, S., 146, 156.
Wohltmann, F., 355, 370, 401, 402 to
405, 406, 416.
Wolff, E., 22, 73.
Wollny, E., no, 113, 125, 147, 159, 195,
264, 279, 281, 284, 305, 306.
Wiillner, — , 198.
Wunder, G., 327.
Y.
Yoder, P. A., 92.
Z.
Zoller, P. H., 22.
* This writer’s valuable “ Boden Runde ” (1905) uufortunately came to hand too late to be con¬
sidered in this volume.
Printed in the United States of America.
S Hilgard, E.W.
591 Soils
H6
cop. 3
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