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Rep)ac<?VM<? >it -for 

Copyright, 1906, 

Set up and electrotyped. Published July, 1906. Reprinted 
August, 1907. 

Cop. I 

Berwick & Smith Ca. Norwood, Mau., U.S^ 


X. Oeigik and Formation of Son^. 

Chapter I. Physical Processes of Soil Ponnation. 

" II. Chemical Processes of Soil Ponnation. 

'* III. Chief Soil-forming Minerals. 

" rv. The Various Rocks as Soil-Pormers. 

" V. Minor Mineral Ingredients of Soils. Mineral Fertilizers. 

Minerals Injurious to Agriculture. 

2. Physics of Soils. 

Chapter VI. Physical Composition of Soils. 

*' VII. Density, Pore Space, and Volume-Weight of Soils. 

" VIIL Soil and Subsoil ; Causes and Processes of Differen- 

tiation ; Humus. 
** IX. Soil and Subsoil ; Organisms Influencing Soil-Con- 

^ ditions. Bacteria. 

** X. Soil and Subsoil in their Relations to Vegetation. 

*' XI. Water of Soils ; Hyg^roscopic and Capillary Moisture. 

" XII. Water of Soils ; Surface, Hydrostatic, and Ground- 

water ; Percolation. 
** Xm. Water of Soils ; Conservation and Regulation of Soil 

Moisture. Irrigation. 
** XrV. Absorption by Soils of Solids from Solutions. Absorp- 

tion of Gases. The Air of Soils. 
XV. Colors of Soils. 
XVI. Climate. 
XVII. Relations of Soils and Plant-Growth to Heat 

3. Chemistry op Soils. 

Chapter XVIII. Physico-Chemical Investigation of Soils in Relation 

to Crop Production. 
" XIX. Analysis of Virgin Soils by Extraction with Strong 

Acids, and its Interpretation. 
*• XX. Soils of Arid and Humid Regions. 

*• XXI. Soils of Arid and Humid Regions continued. 

•• XXII. Alkali Soils, their Nature and Composition. 
'* XXin. Utilization and Reclamation of Alkali Lands. 

It summary OF CHAPTERS. 

4. S0113 AND Native Vsgbtation. 

Chapter XXIV. Recognition of the Character of Soils from their 
Native Vegetation. Mississippi. 
" XXV. Recognition of the Character of Soils from their 
Native Vegetation. United States at large, Europe. 
«« XXVL Vegetation of Saline and Alkali I^ands. 


PRjtPACB zziii 

IivTRODUcnoN, zxix. — Definition of Soils, zxix. — Elements Constituting the 
Baitb*s Crust, xziz. — Average Quantitative Composition of the Earth's 
Crust, zxix. — Clarke's Table, xxx. — Oxids Constitute Earth's Crust, xxx. 
—Elements Important to Agriculture ; Table, xxxL— The Volatile Part 
of Plants, TTxii. 


AOKifCXBS OF Soil, Formation, x.— i. Physical Agencies, x.— 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 Flour and Mud, 4.—** Green" and "White" Rivers, 4.— 
Moraines, 5. — Action of Flowing Water, 5. — Enormous Result of Cor- 
rasion and Denudation, &— 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. 


Cbxmicai, Procbssbs of Son, Forbcation, 16. — 2. Chemical Disintegra- 
HonsorDecom^sition^ 16. — Ingredients of the Atmosphere, 16. — Effects 
of Water ; of Carbonic Acid, 17. — Carbonated water a universal solvent, 
17. — Ammonic carbonate, effect on silicates, 18. — Action of oxygen ; on 
ferrous compounds, 18. — Action 0/ Plants and their Remnants ^ 19. — A, 
Mechanical ; Force of Root Penetration, 19. — B, Chemical ; Action of 
Root Secretions, 19. — Bacterial Action, 20.— Humification, oo.— 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.— ^ea Water, Composition of ; Waters of 
Land-locked Lakes, 25. — Results of Insufficient Rainfall ; Alkali 
Lands, 28. 



Rock- AND Soti^-FOrming Minsrai^, 29.-Hi2ttartz, quartzite, jasper, horn- 
stone, flint, 29.— Solubility of silica in water ; absorption by plants, 30. 
— Silicate Minerals, 31. — Feldspars, their 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. 


Thb Various Rocks as Soii^Formbrs, 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, ^T,—NaturcU 
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, 6o.~Separation of 
Colloidal Clay, its Properties, 61. — Effects of Alkali Carbonates on 
Clay, 62. 


Thb Minor Minbrax, Ingrbdibnts op S0113 ; Minbrai, Fbrtxi^izhrs, 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 


of these Deposits, To.^Natnre of the Salts, 71.— Kainit, yi.—Potash 
Salts in Alkali Soils, 72.— Fannyard or Stable Manure ; Chemical 
Composition, Table, 72.~Bfficacy 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 Lands ; not very Injurious, 77 — Trona or Urao ; Car- 
bonate of Soda, "Black Alkali," 77. Injury Caused in Soils, 78.— 
Bpsomite or Epsom Salt, 78. — Borax, 79. — Soluble Salts in Irrigation 
Waters, 79. 


Physicai. Composition op Soii«s, 83.— Clay as a Soil Ingredient, 83.— 
Amounts of Colloidal Clay in Soils, 84. — Influence of Pine Powders on 
Plasticity, 85.— Rock Powder ; Sand, Silt and Dust, S6,^WeaiAerin^ 
in Humid and Arid Regions, 86. — Sands of the Humid Regions, 86. — 
Sands of Arid Regions not Sterile, S6.— Physical Analysis 0/ 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. — Schone'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, loi. — Aluminic Hydrate, loi .—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. 


DBicstTY, PoRS-SPACB AND VOI.UMB-WKIGHT OP 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, iii. — 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, Ph3rsical Analyses, 117. — Effects of Frost on the Soil ; 
Heaving ; Ice-flowers, 118. 



SoUr AND SnB9oii«; Causbs and Procsssss op Dippsrsntatiation 
Humus, 120.— Soil and Subsoil ill-defined, i2o,-~The Organic and Or- 
ganized Constituents 0/ 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. — Losses of Humus from Cultivation 
and Fallowing, 131. — Estimation of Humus in Soils; Unreliability of 
Combustion Methods, 132. — Grandeau Method, ** Mati^re 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. 


Sou^andSubsoii* (continued) , 142. — Organisms Inpluencing Sou^-Condi- 
TiONS. Bactsria, 142. — Micro-organisms 0/ the Soit, 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. Figiu-es, 146.— Conditions of their Activity. Table, 146. 
— Effects of Aeration and Reduction, 147. — Unhumified Organic Matter 
does not Nitrify, 148— Unhumified Vegetable Matter, Functions in Soils, 
148. — Denitrif3ring 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 Humus in the 
Surface Soil, 157. — Fungi, Moulds and Algae, 157. — Animal Agencies— 
Earthworms, Insects, Burrowing Quadrupeds, 158. 


Son, AND SuBSOU, in Thsir Rbi^tions to V«G«Tation, 161.— Physical 
Effects of the Percolation of Surface Waters, 161. — Chemical Effects ; 
Calcareous Subsoils and Hardpans, i6i. — "Rawness'* of Subsoils in 


Hnmid Climates, 163. — 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 Sjrstem of an Eastern (Wis- 
consin) Fruit Tree, 168. — Comparison of Root Development in the 
Arid and Humid 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, I'j^^^Importance oj 
jyvper Substrata in the Arid Region, 175. — Injury from Impervious 
Substrata. Figure, 177. — Faulty Lands of California. Figure, 178. — 
Shattering of Dense Substrata by Djrnamite, 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. 


Tbm Watkr of S0113. Hygroscopic and Capuxary Moisturb, 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 Plantain 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, 211.— Moisture Require- 
ments of Crops in the Arid Region, 211. — Tables of Observations in 
California, 214. 


SuRFACB, Hydrostatic and Ground Water. Percoi^tion, 215.— 
Amount of Rainfall, 215. — Natural Disposition of Rain Water, 216.— 
The Surface Runoff, 216.— Washing-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 


Ground Water most Favorable to Crops, 228.^Moi8tare 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. 


Water op Soii^s ; Thb Rsguz^tion and Conservation op Soii, Moist- 
ure ; Irrigation, 234.— Loosening of the Surface, 234.~Effects of 
Underdrains ; Rain on Clay Soils, 235. — Winter Irrigation, 236. — 
Methods 0/ Irrigation, 2^6,~-^vaisLZt 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. — Eucal3rptus for Drying 
Wet Lands, 265.— Mulching; Effects on Temperature and Moisture, 266. 


Absorption by Soils op Souds prom Soi«utions. Absorption op Gases, 
AiropSoii«s, 26t.— 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 Condensation of Gases 
by the Soil, 272. — Proof of Presence of Carbonic and Ammonia Gases in 
Soils, 273.— Absorption of Gases by Dry Soils. Figure, 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 Fimgous 
Activity, 281. — Putrefactive Processes, 282. 



Colors of Soils, 285.— 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. 


CUMATS, 287.~Heat and Moisture Control Climates, 287.— Climatic Con- 
ditions, il^T.-^ Ascertainment and Presentation of Temperature Condi- 
turns^ 288.— Annual Mean not a Good Criterion, 289.— Extremes of 
Temperature are most Important, 289.— Seasonal and Monthly Means, 
289.— Daily Variations, 290.— 7)4^ Rainfall, 290.— Annual Rainfall not 
a Good Criterion, 290. Distribution most Important, TOfi,— 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. 


RSLATiONS OP Soils and Plant Growth to Hbat, 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. 


Physico-chbmical Invbstigation 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, 3i6u — 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, 


322. — Chemical Anal3rsis, 323. — Water-Soluble and Acid-Soluble Por- 
tions most Important, 324. — We cannot Imitate Plant-root Action, 324 
Cultural Experience the Pinal Test, 324.— Analysis of Cultivated Soils, 
325. — Methods of Analysis, 325.-7%^ Solvent Action 0/ 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 Loam, 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 Pood ; 
Dyer's Method, 338. 


Anai^ysis of Virgin Soils by Extraction with Strong Acids and its 
Intbrprbtation, 340. — Loughridge's Investigation on Strength of Acid 
and Time of Digestion, y^o.— 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; Mati^re Noire the Only Guide, 
360.— What are Adequate Nitrogen Percentages in the Humus ? 360.— 
Table of Humus and Nitrogen-Content of Califomian and Hawaiian 
Soils, 361.— Confirmatory Experiment. Figure, 362.— Data for Nitrogen- 
Adequacy. Table, jfi^^,-— 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. 


S0113 OF THB Arid and Humid Rbgions, 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 


by Motstnre, 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, t;^^^.— Magnesia : Its r61e in Plant Nutrition, 
Tfii,— Manganese : Its Stimulant Action, 383. — The ''Insoluble Res- 
idue *' or Silicates, 384.— %SI(7/m^^ Silica and Alumina, 384. — Anal3rsis 
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, ^8S,—Aluminic Hydrate. Table, 389.— Retention 
of Soluble Silica in Alkali Soils, y^i.— Ferric Hydrate, y)2,'-Phosphoric 
Acid, 392.— Sulfuric Acid, 394.— /b/ojA 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. 


Soiu OP Arid and Humid Rbgions Continued, y^,— Soils of the Tropics, 
398. — Humus in Tropical Soils, 399. — Investigations of Tropical Soils, 
^i.—Soils of Samoa and Kamerun, 402.— Soils of the Samoan Islands, 
4P3. — Soils of Kamerun, 404.— 5i?i75 of Madagascar, ^o^.—Soils of 
India, 410. — The Indo-Gangetic Plain, 411. — The Brahmaputra Al- 
luvium in Assam, 413. — Black Soils of Deccan, 414. — Red Soils of the 
Madras Region, 4i5.--Laterite Soils, ^id,-^ 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. 


Ajlkau Soils, 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.—** Szck " 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, ^^.--Composition of 


Alkali Soils as a whole. Tables, 445. — Presence of much Carbonate of 
Soda, 448.—- Cross Section of an Alkali Spot. Table, ^^.— 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, 


Utn^iZATiON AND Rbci^maTion OF Ai^KAU I^AND, 455.— Alkali-resistant 
Crops, 455. — Counteracting Evaporation, 455.— Tuming-under of Sur- 
face Alkali, 456. — Shading, 457.— Neutralizing Black Alkali, 457.— 
Removing the Salts from the Soils, 458.— Scraping off, 458.— I^aching- 
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. Effect? 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. 


Thb Recognition of Soil C haracter 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, ^^.—Differences 
in the Form and Development of Trees^ 498. — Forms of the Post Oak. 
Figures, 498. — Forms of the Black Jack Oak. Figures, 500. — Charac- 
teristic Forms of other Oaks, 502.— Sturdy Growth on Calcareous Lands, 
502.— Growth of Cotton, 503.— Lime Favors Fruiting, and compact 
Growth, 504.— Physical vs. Chemical Causes of Vegetative Features, 
505.— Lowland Tree Growth, 5o6.~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, 



TATION. United States at Large, Europe, 511.— 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 
Non-calcareous Lands. Table, 520.— Calciphile, Calcifuge, and Indifferent 
Plants, 521. — Silicophile vs, Calciphile Flora, 523. — What is a Calcareous 
Soil ? 524. — Predominance of Calcareous Formations in Europe, 525. 


Tbs Vegetation op Saune and Axkali Lands, s2T,^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. — Redaimable 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. 


A.— Directions for taking Soil Samples, issued by the California Experiment 

SUtion, 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, 56a 
General Index, 565. 
Index of Anthors referred to, 591. 


This volume was originally designed to serve as a tcxt- 
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 
r^ons, 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- 

xviii PREFACE. 

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 d 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- 

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 



process of adaptation of plants to climates and soils, by nat- 
ural selection and the survival of the Attest. The natural 
floras and sylvas are thus the expression of secular, or rather, 
millennial experience, which if rightly inteqireted 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 univer^l practice of 
settlers in new regions, of selecting lands in accordance with 
the character of the forest growth thereon; it is even legally 
recognised 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 tlieir 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/' * J 

It is certainly true that mere physico-chemical analyses, nth 
assisted by other data, will frequently lead to a wholly errone- 
ous estimate of a soirs 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, 
wc 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 

^ "The Soil An^jwm dL the Geologia^ Sur*«yi ol Kentucky »i4 ArTrimiai ^ 
%. W* J^luuoii in AM. /OUR. SCL, Sept, i$6i. 



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 


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 
fanner, e. g.y 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 accoimt of limited 

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- 

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. 


fisRKXLSY, California, 
Acvembir 15, 1905. 


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 cat^ory 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 aj^roximate 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- 



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 op the elements to a depth op ten kilometera 

Solid Crust Ocean Mkan, 

(93 Per Cent). (7 Per Cent). Including Air. 

O^gen 4729 85.79 49-98 

Silicon 27.21 • 25.30 

Aluminum 7.81 7.26 

Iron.... 5.46 5.08 

Calcium 3.77 0.05 3.51 

Magnesium 2.68 0.14 2.50 

Sodium 2.36 1. 14 2.28 

Potassium 2.40 004 2.23 

Hydrogen 0.21 10.67 o-94 

Titanium 0.33 0.30 

Carbon 022 0.002 0.21 

Chlorin o.oi 2.07 0.15 

Phosphorus ... 0.09 

Manganese 0.08 0.07 

Sulphur 0.03 0.09 0.04 

Banum 0.03 0.03 

Nitrogen 0.02 

Fluorin 0.02 0.02 

Chromium.... o.oi o.oi 

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, 1. e., as 
" oxids." H. S. Washington ^ 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 

^ U. S. Geol. Survey, Professional Paper No. 14, p. 108. 


Washington. Clarke. 

Silica SiO. 57.78 59.89 

Alumina A1,0, 15.67 15.45 

Peroxid of Iron... .••... Fc^Oi 3.'^! 2.64 

Protozid of Iron FeO 3.84 3.53 

Magnesia MgO 3.81 4.37 

Lime CaO 5.18 4.91 

Soda NatOi 3.88 3.56 

Potash KtO 3.13 lit 

Water, basic HtO+ 142 1.52 

Water, acid HjO— .36 .40 

Ferric Sulphid. FeSt 1.03 .60 

Phosphoric add PtOs .37 .22 

Manganese Protoxid 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.^ 

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: 


Potassium Carbon 

Sodium Hydrogen 

Calcium Oxygen 

Magnesium Nitrogen 

Iron Phosphorus 

Manganese Sulphur 

Aluminum Chlorin 

Utanlum Fluorin 


Of this list, titanitmi, though a very constant ingredient of 

' A trifling amount of chlorin is found oxidized in the form of sodium perchlor* 
at«, in the nitre deposits of Chile. 


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). 

lodin 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 arc 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- 


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. 





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. 



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 fock 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 ^ 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 

' 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. 


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 ivater, — The irresistible force exerted 
by the expansion of water in freezing, amounting to about 9 
percent 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 i), 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 


and shoved by it, exert upnrjn the rocky channel 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 

I-i». i.-l': 

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 nrud from the foot of Muir glacier,^ 
Alaska, at its sea front, made by Professor Lough ridge» shows 
the prevalent fineness of the materials brought down by the 
glacier waters. 

i Collected by Dn W. E. RUrer of the UitivcrsUy of Cdifornifti 





Per Cent. 


J0O22 — .016 mm, 
.016 to .02 J mm. 
x>2^ to .036 mm. 
.036 to .047 mm. 
.047 to .072 mm.; 
.072 to .12 mm.' 
.12 to .16 mm. 

1. 14 


Fme silt 

Fine silt 

Medium silt 

Coarse silt 

Coarse silt 

Fine sand 

Medium sand ..... ........ r ... . 


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 quality 
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 Hozcin^ icatcr. — The action of flowing water is 
doubtless at this time the most potent mechanical agency of 
sr)il formation. From the sculpturing <yi the original simple 
forms in which geological agencies left the earth's surface 


into the complex ones of modern mount ain 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. gr^^^I ^tid 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 

¥i<M* 3.— Ertuiaii oi Hawaiuui HiDj* near llopuluU. { Phot, by H. C Myer&J 

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 frooi the terniinal ice cave at the lower end of the 
glacier, to the rounded sliingle foimd a few miles below. 
On slopes where w^ater flows only during rain or the melting 
of snow% the same erosive effects may he 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 powder of water 
erosion convincingly shown. Tn the United States the stu- 
pendous gorges of the Columbia and Colorado rivers, the 


former cut to a depth of over 2000 feet into hard basalt rock. 
the latier to over 5,000 fcet» partly into softer materials, partly 

ftnto granite, are perhaps the most striking examples of this 

f power; the manifestations of whicli can, however, be as con- 
vincingly seen in thousands of minor rivers and streams. 
All the niateriats so carried off from the higher slopes are 
illy deposited on a lower level ; whether only a short distance 
iway on a lower slope (colluvial soils), or farther away in the 

lfl*xid plain of streams, rivers, or lakes (alluvial soils). Other 

rthings 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, 
forniing river bars, flood plains, and deltas. The fineness of 
the material of delta soils, like that of those made from glacier 

r flour, insures them the same advantage, viz. great fertility and 

' durability. 

It is calculated that the Mississippi River carries into the 
If of Mexico annually some 7469 miUions 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 
miies to the depth of one foot. 

IVatr- Action, — The powerful effects of the beating of waves 
abrupt shores of seas or lakes are in evidence all over 
^the world, and these eff^ects are so characteristic that they can Ije 
rccrjgnized even where no sea or lake exists at present. Gravel 
and sand are carried in the surf and serve as grinding ma- 
terials, w^caring even the hardest rocks into grooves, rills, chan- 

'' '^'^^ ' 


nels and caves, defining sharply the varying degrees of hard- 
ness or tough resistance in different parts of rocky cliflfs; 
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 Winds. — 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 
sanify desert, to leeward of the stony area, where the winds are less 
violent and regular, and where, therefore, the sand has been dropped 


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 

In the cultivated portions of the Mojave and Colorado 
deserts in California, plowing of the land during a dry time is 
not uncommonly followed by a bodily removal of the loosened 
s^)il 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, Vol. 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, ha? 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 Xorth .\merica, the pampas of South 
America, the plateaus of Mongolia and es|)ecially 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 
**pamper(<s '' at times compel them to proceed with the same 
precautions as in a fog; and the same is true of the northeast 
winds blowing off the Sahara desert on the west coast of 

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 
Xorth America, where the geological composition of the " bad 
lands " is frequently impressed u|)on the rock surfaces very 
prominently. The strikingly grotesque forms are frerjuently 



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 shuws 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 chffs 
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 may be noted in the cob- 

Fio. 4.—" Aiu»br(>oni rqcki,^' produced bf Wlad istloni Wyomlug. (DanoA.) 

ble-deserts, where we frequently find the cobbles worn away 
on the windward side in a %Try characteristic manner; the lee 
side remaining rounded and smooth, while the structure of the 
rock is strongly outlined on tlie windward side. 


The physical Constituents of soils are thus» in the most gen- 
eral terms, first, rock pomdcr ( " sand '*) more or less changed 


by weathering; second, clay, as one of the chief results of the 
weathering process of silicate minerals; and thirdly, humus, the 
darK-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. 


Fig. ^— Diagnun iUuttrating the genetic relation of difFereat 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 l)ears some 
of the distinctive characters of the parent rock, and its composi- 
tion and adaptations may, in a measure. l>e 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 ^ 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. Alluz'ial Soils. — When soils are the result of deposition 
by streams, the material having been gathered along the course 

* 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 Kep. U. S. Cleol. 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. 


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 stilt 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 

According to the calculation of Merrill (Rocks, Rock-weathering, and 
Soils, p. 188) granite when transformed into soil without /oss would 
increase in weight by ^^ ^c \ 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 dep<:)siting 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 cultiv^^tion impracti- 
cable, or at least unprofitable. As the slope and velocity de- 

14 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,^ 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 "), 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 

^ Geikie, " Text-book of Geology, 3d ed. 


washed away to be redeposited as alluvium at a greater or less 

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 
^-day-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. 

Lmccring 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. 



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 : 



Carbonic dioxid 


Water vapor... 

Volume Per Cent. Weight Per Cent. 

I to 4 millionths 
Variable ; 48 to 83 grams per 
cubic meter, when satu- 
rated between 0« and 



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,^ 
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 (lUO) in air as well as in soils, it is 
usual and convenient to speak of carbonic dioxid {CO3) gas when so occurring as 
carbonic acid (HaCOs), of which it produces the effects (CO,-fH,0=HjCO,). 






applied to rocks; while the corresponding but more complex 
ictjon within the soil itself is usually temied fallowing. 

Effects of tVater. — Since but few substances, particularly 
among those forming rocks, are totally insoluble even in pure 
watcr,^ and some (such as gypsum) niay 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 e\Tn 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 cfficacVi is 

Corhonic diaxid, in contact with water forming carbonic 
atid, 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 x>f vegetable and animal substances, such as wood, 
charcoal and all other fuels; by the respiration of animals; 
in 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 genera] atmosphere^ but locally in considerably 
higher proportions because of proximity to sources of forma- 
tion, and of its greater density as compared with air f i J4 as 
against i ). 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 water a universal solvent. — While limestones 
are the rocks most obviously acted npon 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 
qttartzite may be considered as sensibly proof against it. 

J Scse Chapter 18. 

1 8 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 ^ 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, like 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 disolved .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 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 wedgfing, 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. 

(&) 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 derivwl 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 

HumiHcation, — While the mechanical action of the roots and 
the chemical effect of the acids of their root secretions are very 


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 

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 vegetaWe 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- 





In the general consideration of the soil-forming processes, 
it has been stated that soils formed by the disintegration of 
rocks " in place," i. ^., 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 im.portant 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 ccnnpari- 
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 

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- 






Roth AH' 



(0. WoLFr.) 







L^K meter 


Polish, K,0.... ,...*. 
Sodi, ka^O.., 

S t 
5 7 



4 4 





6. ft 

»5 3 



8. a 


Trace . 




10. J 






Llniv> CaO ► 

Kla^eiia, M[^, • ^ - , ^ . 

IroB Qxid^ ^'*|Cit* 

Atiimina, AliUj , 

Silicii SiO, , ,, ., 



II. r 
■ >l 









C*rbonic Add, COj... 

Phot* Acid, P|0**--- 
Sttlf uric Acid* SO,.... 
Cttlortn^ D 

aj 5 






tr-5 , 

57' 5 

»7 t 





Kltt%i»ti», NyOi 

NUf«]^tn»t, Nn, 

Tal%i llfneril Matter.. 


CflFrttted Tota]......» 

Ori^itLC Matter.. + **... 






3 ' 








J J. 7 

*54 9 






ii5 J 




111. a 



J 39- a 

35 16 




■ ? 




3 : :g 3 

S : 8 S^ 

* » - ■ 
: $ ^ : : 

8 r ir: 

1 ^ t : 





i 5 .? 

1 ? ^ L?f h 

f: ^ is : 


lie z 
f 1 r it 

it ^ i »t y ; i 



: : t 

i S 8 : 


: 1 ; 'c ' 


« » i i » ■ « : : 

r si: s is 3 t r i : 





1 r 


rf \ 


: £: : 




mi 5 

I ft : 

W 1* 





tin ' 

: g 8 i : 


: 5 y : 



^s i - " i 1 

t = r i 
srj? : : 

i 5 t i 
: 2 C : 



: 3 ^ : 




I ti i\ ^. m^ % s.<^»^ r £ ^. 

r * - ' 

35 N 

I ^ 

fi rs 

8 t 


^! ^ ? S 




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 ^^ 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,* 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 

' Rivers of North America, p. 80. 



ftikon and Dwina show wider differences than any two other 
raters in the list, iniless it he the St. Lawrence, another 
^Tiorthcm stream. The Missouri and Rio Grande show by 
their hig!i content of soda, chlorin and sulfuric acid their 
origin in arid climates, where alkali lands prevaih The water 
of (he Nile is here represented by two analyses/ one showing 
the season when the water is '* red '' and of high fertili;;ing 
quality because of the sediment it brings down from the 
mountains of Abyssinia ; the other the *' green '* and relatively 
dear water which comes from the great lakes and through the 
" sudd " or grassy swamp region near the junction of the 
Gaielle river with the Nile, Of the analyses given of the 
'llissis^ippi 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. 
jeol, Surrey, the direct determination of potash and soda 
eing in this case included* As will be seen, and might be ex- 
ted, the average of the Mississippi water corresponds quite 
irly to that of nineteen of the world" s great rivers as given 
Murray, The very great variation in the content of sul- 
fates is evidently due to the occasional heavy influx of the 
^'pseous waters of the Washita and Red rivers when in flood; 
rhilc the minimum content (in January) agrees almost pre- 
cisely with the general average, Murray's table would hardly 
l>c 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 IVaicr. — The nature of the substances permanently 

1 TTic coirectness of Litheb^V aAaly»es has been disputed^ partly because of their 
^^kgreemertt wiih forns^r anilys^ in the very high amount of lime, partly because 
ot tile high pota»h<ontenc in the Low-Nile water. The }ime content ls» however* 
eoti ^tm^ by the pajtia] analyses made by Maihey in 1887* which gives aji average 
of 44.1 lor the y^r, while the older analyses, made in Europe, of iramsf^Ud water 
£«ive Qsily half as much. Letheby working on the 9 pot wa^ doubtlesis more iiearly 
fight in iJib respect. IfU figure for potash in the " Low* Nile " water agrees with 
former deCerminatioas, but that in the ** High* Nile " is approached only by that in 
th« Dwina water. 1 1 may be suspected that the sodi is too low and potaih too 
h^h in thta a&aljBii. 

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. 


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 


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 



of shellfish, corals, etc. I^east 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 teachings 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 teachings 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 directiy 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- 
<tisputably derived from the sea-water, and contains, among other sub- 
stances not directiy 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 
graduaUy 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 fiuorin 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- 
nxmly 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." ^ 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. 

^ 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. 



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 rodcs, 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- 

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 




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 

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 


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 homstone 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. 


Silica occurs in nature combined with the oxids of most 
metals, forming silicates ; but most abundantly with the earths 
(lime, magfnesia, 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 kao/in, which is essentially a mixture of kaolinite with fine silex 
and more or less of undecomposed feldspar, and is of a chalky texture. 



FomtaHon of Clays. — When instead of remaining in place, 
this kaolin is washed away and triturated tn the transportation 
by water, it is partially changed from its orig-inal chalky con- 
dition to that plastic and adhesi%'e 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 hme- or soda- 
liine feldsfiars 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 

Hornblende (Amphibole) and Pyroxene f Augite), These 
are two vcrj^ widely diffused minerals, differing but little in 
composition though somewhat differently crystallized, mostly 
in 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) OEid of iron ; the mineral 
as a whole may be considered as a silicate of lime, magnesia, alumina 
and jfon, vmiying greatly in their absolute proportions ; alumina and 
Iron being sometimes almost absent* When iron is kcking the mineraJ 
may be aJmosi white (tremolite, asbestos), and its weathering b then 
much retarded, since the oxygen of the air cannot take part In the pro- 
\ €l disiniegratioru 

The black variety of hornblende is not only the most abun* 



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- 


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 

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, but 
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. i8). 

The Zeolites, — Zeolites may be defined as hydro-silicates 
containing as bases chiefly lime and alumina, commonly to- 



gether with more or less of potash and soda, more rarely 
magnesia and barj'ta. The water is easily expelled by heat- 
ings btit is present in the basic form, not merely as water of 
crystallization. AH zeolites are readily decomposed by chlor- 
hydric and otlier stronger acids* 

The zeolites proper are not original rock mgredients, but are formed 
in ihe course of rock decomposiibn by atmospheric agencies, heated 
water, and other processes not fully understood. They are therefore 
Wttally found in the cavities and crevices of rocks that have been sub- 
ject to the influence of atmospheric or thermal waters, most frequently 
in emptive rocks, particularly in the vesicular cavities characterizing 
what is known as amygdaioids. They are also found in the crevices of 
Mndstoncs and shales percolated by water^ as well as in nodules of 
isiJIltfation (geodes), in which they are frequently associated with quartz. 
Tboie found in the cavities of rocks are usually well cryitallized wherever 
room is afforded, and are readily recognized by their crystalline form ; 
Ibcjr 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- format ion 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 
£eoIific nature of the material to be inferred from its chemical 
behavior. Among these characters the ready decomposability 
by adds has already been mentioned ; another of special import- 
aiKe in the economy of soils is the fact that w^hen 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 
^eolitic powder, while corresponding amounts of the bases 
originally present will pass into solution. 

Thus when a hydrDsilicate of soda and alumina is digested with a 
•olution of potassic cblorid 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 time 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 
&rther 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 


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.^ 


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 

^ A reoUtic mass, at first ^latinous and then becoming granular^rystalline 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 the 
crevices of natural sandstones. 



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 SoiUformers, — 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 oflf-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 



or " heavy " soils are always calcareous. On the other hand, 
the blue-grass region of Ken lucky » and most of tlie lands of the 
arid regions are prominent examples of '* light " calcareous 

C^'fSt Sinkhoks^ Sitiia^tiies, — Perhaps the most striking exempli- 
licaiion of the solvent power of carbonated water h seen in the form- 
atiom of limestone caves. As a matter of fact, the vast majority of ail 
existing caves Is found in limestone formations ; and such formations, 
as will be more fully discussed hereafter, nearly always bear a luxuriant 
f^getatlon* The water filtering through the vegetable mold, in which 
carbonic acid is eonstantly being formed, becomes charged wnth it, and 
Oil 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 fivsi are almost 
always the bed of a stream, the mechanical action of which accelerates 
the process of enlargement, until after souie time the water is perhaps 
drained off through some crevice to a lower level, where the same pro- 
cess b 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 
care, instead of dropping down, evaporates there and eventually forms 
kiclclike ** iiaiachiti '* out of the dissolved substance ; while when 
dropping on the floor and thus growing upwards, the corresponding 
formation is called *^ tfa/agmif^.** These caves, subterranean rivers, 
sinkholes, natural bridges and tuimels, etc*, mostly owe their origin to 
this solvent action of carbonated water on limestone formations*' 

The same occurs on a small scale, when calcareous land is 
underdrained; the Hme 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, If. Re^€ I in his treatise on Chcmied Denudation in Rela^on to Ge^logicvl 
Tim«) calculates that 143.5 tons of lime carbonate are annually retiioved by solu* 
tion fft»m each tquare mile of land in England and Wale^^ and that the average 
amotini thus removed aiif;yaUf from each square mile of the eartti'a surface 
b abotit Mty torn. 



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 ^ 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 

* Bull. No. I, U. S. Dept. Agr. Veg. Path, and Physiol. Investig. 



p. 26), more rarely of the tmnsformation 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 
til in 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). 

G>psum 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. U may be said in general that few naturally g>^pseous 
soils are very productive. This is largely because of the very 
heavy clays which commonly accompany it, as the compound it- 
sdf is not only not hostile to plant life but is in extended use as 
a \*aluable fertilizer ("land 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, tt also specially favors nitrification in 
soils* In the arid region it renders important service in the 
netttralization of *' black alkali '* or carbonate of soda in alkali 
soils. Being soluble in 400 parts of w^ater, 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 agrkultural use the rock g}'psum 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 yellow ochre. It makes a rust-colored streak 
on biscuit porcelain or unglazed queensware. // is the coloring 
material of all yellow 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 



nature by Itmonite 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 tbe soils of some 
regions, is 

iltagm'tiie or magnetic iron ore, also known as lodestone. 
This mineral, the oxygenHTompound 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 

But while the ore is of tittle interest to the farmer, it is quite 
otherwise with the comp45und 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 heate<l by 
the formation of red ferric oxid; while when exposed to damp 
air, they assume the rust color of ferric hydrate* 

Reduciion of ferric hydrate in ill-drained soils. — When such 
oxidized, rust-colored clays or soils are excised 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 

The importance of this reaction to farming practice ties 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 


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. 


Rocks may be broadly classified into three cat^ories, viz: 

1. Sedimentary rocks, formed by deposition in water and 
hence more or less distinctly stratified. 

2. Metamorphic rocks, formed from rocks originally sedi- 
mentary, by subterranean heat in presence of water. Usually 


48 SOILS. 

crystalline, that is, composed of more or less distinct (large or 
minute) crystals of one or several of the minerals mentioned 

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 clay racks form the most varied products under the in- 
fiucfice of (aqueo^igneous) metamorphism ; granites, gneiss, 
syenite and hornblendic schist are among the most common. 
The great variations in the composition of clayey materiab 
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 
quarts (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 
rardy in hornblende). 

Of the latter class are the dark " basaltic " rocks constituting the 
IIU9S of the enormous eruptive sheet of the Pacific Northitvest, covering 
the greater part of Washington, Oregon and northeastern Califoniia. 
Tbt lavas of the Hawaiian islands are of the same class and even more 
basic ; while the emptives of Nevada, middle and southern Califomiap 
and eastward to the Rocky Mountains, are mostly of the light -co bred, 
acidic type. The same is largely tnie 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 cliemical analysis. The same is sometimes 
true of metamorphic rodcs; 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, chrysoUte, leucite and other silicates require considera- 

Ceneralities 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 ahovc^ 



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 tfie 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 



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 
ire largely occupied by a rock containing, besides quarti;, chiefly sodar 
lime feldspai and some hornblende^ and scarcely any mica. It is more 
properly a dioriie (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 
diorjtes), th^e soOs are light- colored (not " red '* ), and bear a growth 
of small pine instead of the usual oak growth of the lower Siena 

What is said of granite soils is also generally true of those 
formed from 

Gneiss, whidi is composed of the same minerals as granite, 
but has a slaty cleavage and on that account when upturned ou 
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 ocair, the proverbial 
barrenness of mining districts is very frequently traceable to 
tiiese rocks. The same may be said of some of the related 
rocks, such as gabbro, minette and others. 

Normal dtorite consists of hornblende and sod a- 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 
Slates 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-gjained 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 arc 
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 soils derived from trachytes and trachytic lavas are 
getierally 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 tlie 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 quarts 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 Calif ornia* 
Such *' volcanic ash '' soils are usually very unthrifty, and bear 
a growth of small pines. 

SoUs from sedimeniary racks. — 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 
htxuriant vegetation that usually flourishes on soils rich in 
lime. The popular adage that " a limestone country is a rich 
countr}','* is of almost universal application and stamps lime, 
from the purely practical standpoint, as one of the most im- 
portant soil ingredients. 

Residual Limeshme Soils, — Striking examples of the forma- 
tion of large, fertile soil areas by the leaching out of limestones 
arc 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 



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 


Fine Earth. 
Chemical analysis of fine earth. 

Insoluble matter 

Soluble silica 

Potash (K.O) 


lime (CaO) 

Magnesia (MgO) 

Br. Ox., of Manganese (MngO^) . 

Peroxide of Iron (FeO) 

Alumina ( A1,0.) 

Phosphoric Acid (P,0,) 

Sulfuric Acid (SO,) 

Carbonic Add (CO,) 

Waterand Organic matter . . . . . 

Humus . 


Hygroscopic moisture, 
absorbed at *»C 

" Rotten 

Depth.. 12 ft 











2-3 ft. 






15 ms. 











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 

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- 
rugifious, 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 by 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 


Sandstones with purely zeolitic cement are on the whole not 
of frequent occurrence, the zeolites forming, more commonly, 
the hard portion of a day-sandstone cement, which disinte- 
grates by tlieir weathering-out. 

In regions where the tufaceous rocks of eruptives prevail, we not 
uncommonly find the " volcantc ash '* solidly cemented by a zeolitjc 
mass, which is then usually apparent in cavities or crevices in the form 
of cnists or crystals. Such tiiffs are commonly rich in alkalies and 
lime, but mostly poor in phosphates, and in disintegration form soils of 
« coriesponding nature, 'rhey are largely represented in the valleys 
off Piiget Sound, as well as in portions of centrml Montana, and north*- 

Clay-Sandsi(mes (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, 
ever)* 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 
cLiyey 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- 
days, in which little if any mineral p)ant*food remains, and which are 
best used for other purposes than agriculturep unless under special con* 
dttions 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- 
nion life* Such are porcelain clay, pipe-clay, fire-clay, potters' 

58 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 

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. 



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 permanenlly, 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^ probably consists (as 
has been slated above) of silica and alumina in the proportion 
of nearly 46 to 40, the rest ( 14/fc) being water of hydration, 
whidi 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 kaolintte, 
it is readily mistaken for chalk, (and is sometimes used as 
such)« being powdery to the touch and entirely devoid of plas* 
tictty ' when wetted and kneaded. The microscope shows this 

* TbU Icnn was &rat eniployed by Th* Schloestng, in commtintcations to Ihe 
French Acadeu]^ of Sciences, and reported in the Comptea Kendus of tha^t body ; 
fint ui 1870. Unaware of Schloesing's work, Ibe writer began a full mvestiga* 
lh» of the subject of mechajiical soil analysis m tSji, and pubUslied the resulu 
ia 187 J (Am. Jotir. Sci-» Oct. 1373). XJp to that time the limited n^outces of the 
Sbnuy of the Unjvcoity of Mississippi had not given him an opportunity to s«« 
ScMoesing *s publication. The two Independent investigations* choiigh conducled 
<N| tooicwhat different Un^, gave of course practically the tame feaulta, and com- 
plement each othcT- 

* There h still some dl^uAmoti as to the chemical identity of colloidal day with 
ICaolinite ; but the objections are not convincing. 

> It has of late been attempted to extend the meaning of thb word to the be- 
hmrivr of aU powdfin when wetted with water. But the adhesive ptaaLticity of 
day atands almost akme% in that (aside from contraction} it preserves in drying 
the fonn into which it nay have been molded while wet, ever) when struck^ 
whccreiis other powdeiy substatkce* iimliarly treated ai once colUp^ back into the 
oi^gfiial powder. The eEclnaifi mm of day lit mwitlt^g offers the typical example 
of piMlicity ^ generatly understood. The additlozi of any powdery Bubatanc«» 
bowevBf iac, diminishes the plastidty of day. 

6o 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 ^ 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.^ Such turbid " clay water " may 

1 American Journal of Science, 2d Ser., Vol. 43, p. 357. 

* 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, 
vtM, 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 ozids fail to 
replace clay in its adhesive functions. 



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 

Stparais&H &/ CoHaidai Ciay. — ^This property of the pbstic clay 
9ut>5tant-e, of ill-using in pure water, furnishes the means of sepaTating 
from it the coarser, sandy and silty portions of soils and natur^il ctays, 
ADcl observing its characterLitic properties, so far as the almost un- 
avoidable admixture of some otlier substancesj presently to be considered^ 

Id natural soils the clay particles usually incrust the powdery itigredi- 
eats, cementing them together ; or themselves form complex aggregates 
(flocoiles) 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- 
iog) in hot water, or more expeditiously, by lively boiling with water. 
The boiling should not, however, be prolonged beyond the time actually 
required for diiintegration, since (as Osborne * has shown) long- pro- 
tected boiling tends to render the clay permanently less diffusible. 

From the lurbid 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 
impension by the action of certain substances which possess the prop* 
erty of curdling (coagulating) the clay substaiice into flocculcnt masses 
that settle quickly* Of all known substances, lime, in the form of 
lime-water, acts luost energetically in producing this change ; but other 
solutions of lime^ as well as most salts and mineral acids, produce the 
nme effects when used in su^cient quantity. Common salt is among 
tiie most convenient, because it can most readily be leached out of the 
clay precipitate thus thrown down* This when white» resembles boiled 
ttarch, but being usually colored by iron might be easily mistaken for 
the mixed precipitate of fentc hydrate and alumina so commonly 
obtained by chemists in soil analysis. When separated from the water 
and dried, the jelly-like substance ( *' colloidal day " ) shrinks as 
extravagantly as would so much boiled starch, into hard, shiny crusts or 
fiakes, which when struck in mass are sometimes even resonant, and 
l>ear 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. CoQn. Agr. Expt. Stn.i ]SS6^ 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 

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. 




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 (g^nites, " 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 re\'ealed the presence of 
phosphate rock in numerous localities, chiefly where limestone 


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 

" Thomas S/ag." — -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 PjO^ such as is contained in the 
*' Thomas slag " of the basic process of steel manufacture, is nearly or 
in some cases ( '* sour " soils) ^ui/e 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 
k>w-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- 



ture of superphosphate. The bone-earth consists in the main 
of tri*calcic phosphate with from one to two per cent, of cal- 
cimn 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 pliosphoric acid 
and nitrogen, and the presence of the latter has been largely 
the cause of a material overestimate of its efficacy as a fertil- 
iser 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 b(y\h 
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 fanning or gBrdening, 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 

riviamie and Dufrettite, 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 

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 


the pans ; the nitrate is afterward farther purified by crystaHization. 
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% 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- 

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 vicufias 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 com- 
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 

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 



time, almost the entire demand for alkalies for industrial uses 
bore upon the same product, until the invention, toward the end 
of the last ccntur>\ or LeB lanes 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. LeB lane's invention was most timely in that it very 
quickly diminished materially the production of potashes 
which, in view of the increased demand for alkahes for in- 
dustrial uses, seriously threatened the depletion of agricultural 
lands, and of woodlands as well, of one of its most essential 
ingredienis. 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 evajjoration of sea %vater for the manu- 
facture of common suit, was on too small a scale to influence 
materially the manufacture of potashes, ^ 

Discovery of Siassfurf 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 
lo the fact that the saline deposits 0%'erlyi ng certain large 
rock-salt beds that bad been developed by barings 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 industr>^ developed rapidly in that 
region as well as in the adjacent portions of Saxony^ where the 
same forraatioir 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 dev^elopment, the manufacture of potashes 
from plant ash has almost ceased, outside of Canada and 
Hungary ; and the production of potash salts tn the Stassfurt 



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 l^uminous 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 
80on 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. 



In the manulacture of sea-salt by evaporation m shore lagoons oi 
"saltpan;;,'* the solution retnaining after the salt hm been deposited 
(kiiowti m " mother-waters/' or " bittern '* ), of course remains on the 
9urfiice o! the salt unless allowed to drain off, as is done in the process 
of manufacture* VVhen not drained off, the water gradually evaporates, 
and there remains a salme crust of a composition ejcactly 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 
Tock'salt deposit in the worlds the answer is that in a great many cases 
the concentrated mother-waters have had an opporiunity 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. 

Naiure of ihi 5ii//i,— The potash is present in the Stassfurt salts in 
the form of compleit sulfates and chlorids containing, besides, sodium, 
calcium and magnesium in various proportions and modes of com- 
bination. The most abundant of the potassic chiorid minenils is car- 
Dallite, a hydrous chiorid of potassium and magnesium. The chlorids 
chancterite chiefly the upper portions of the deposit, the sulfates 
the lower* 

Kainit. — Of the products derived from the Stassfurt salt 
industry for a^icultural use, the two requiring special con- 
sideration are " kainit/' a natural mixture of the several chio- 
rid minerals in varying proportions; and ''high-grade sul- 
fate/' Being a natural product, " katnit " is the cheapest 
soiu*ce of potash available to the farmer: but on account of 
its variability tn 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 e\Tn those not visi- 
biy 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 ts somewhat higher in 
price for the same amotmt of potash* The potash content of 

^2 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 con- 
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 hot only with different animals but 



also with the different feeds consumed by them ; but tlie aver- 
age composition of farmyard manure is approximately given 
thus by Wolff and others : 


Water , 

DiT Matter.,,,.. 
Asa ifigfedknts. . 


Limt *. 

Plioiphoric add 
Ammonia. ...... 

Total Nilrogen., 





71 00 





35.00 ' 















a 18 










ay 8 





t. Average compoiition of fre^h fa^m manure (Wolff). 

t. Avenge compoflitlon of modetatelj rotted f^rm manure (Wolff). 

3. At^rage compoaition of vety tharoughly rolled farm manure (Wolff). 

4^ Uhttd cow and horse manure from a bed two feet lbick» accumulated during 
^e wuiter in a large covered yard, and packed solid by the tramping of cattle fThe 
unlT^ hf F. £, Forry). 

Si *Boi If^nure^** contuting &i mixed manure of hullocka, horses, and pigs 
(Wttft Royal Agfk. Soc Joum^ tSjo^ 11^ 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 utiHzed 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 sliown 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* 
propnate food for those normally existing in the soil (see 

> And todA. 


74 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 — 3, " 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. 

(m.) MUTBAALs uKKssHNTiAi* 0% oTjtnaous to mtts^ 

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 unf requently affect soils desirable for culture 
to such extent as to make them unavailable for general farming 

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 
^used 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). 

ii€€0gniiion 4>f Iron pyriUi, — ^Thc mineral is easily recogtiiied by its 
golden or bra^-yeUow tint ; the latter color being the one most com* 
monly shown in the *^ sulphur balls " occurring in marls or soft lime- 
itofics. A very easy test is to pulverize it and then heat it on a shovd 
over a fire, when it will soon itself take fire, burning with a blue sulphur 
Same, and upon more complete roasting, leaving behind a red powder^ 
vii.f *' Venetian red " or red ochre ; that is, ferric oxid. In clays it 
commonly occurs in large, weU-defined cubes, which do Dot readily 
form copperas but rather become eoirered with a crust of Mmonite 
or brown iron ore. 


76 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, magnesia 
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- 


trailed in any way, it can be gotten rid ol only by leach ing-out Thm 
process is ustiaHy accomplished in seashore lands by the action of lain, 
Of 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 

Mirabilitc, (Glauber's salt) or sulfate of soda, exists not 
tin frequently in the soils of the arid region and sometimes en- 
cnists 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, w^hen w^afted by the wind, it is 
reduced to a fine white tlust, which constitutes a gfX)dly pro- 
portion and sometimes the entire mass of the " alkali dust " 
that t$ 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 witli 
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 
iSt however, much less injurious to plant growth than common 
salt^ according to experience in Caltfomia 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 Eg>'pt, 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 

78 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. 

Injury 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 


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-boratc 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. 




As has already been stated (chapt. i, p. lo), 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 
physical 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 
lof)se tilth would be impossible. Sand drifts illustrate this 

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 

When to these essential physical properties of clay, there is 
added the fact that usually the clay-substance as it exists in 


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 

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 pnly 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 " y)lastic 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 5 to 3 % clay 

Ordinary sandy lands . . . 3.0 to 10% '* 

Sandy loams lo.o to 15% " 

Clay loams 15.0 to 25-% " 

Clay soils 25.0 to 35% " 

Heavy clay soils .... 35.0 to 45% and over. 



It must be distinctly understoadp howevcrj that these figures make no 
tkim to nccurar^ or invariability. For, the tilling qualities of a soil 
containing one and the same amount of such "clay" may be very 
matetially modi0ed according to the k:md and amount of each of the 
teveral grain- si^es of rock powder or sand they contain. 

Inffitcnce of fine poicdcrs on (elasticity and adhesiventss. — An 
admixture uf a large amount of fine powders diniinishes mater- 
ially the adhesivetiess of a clay soil, even though it may render 
it even mure ** heavy '* in tillage; while the admixture of coarse 
sand» even in very considerable proportions, does not greatly 
influence the adhesiveness of the clay. 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; 
amung which ferric hydrate or iron rust is especially apt to 
acaimulate predominantly in the clay, considerably increasing' 
its apparent weight ant I greatly diminishing its adhesiveness,^ 
In strongly ferruginous soils, therefore, it becomes necessary 
to take into special consideration the amount of the ferric 
hydrate or rust whic4i 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 methnd descn!)ed, although most of 
it remains with the finer pjwdery sediments or grain- sizes. 
There are, besides, other colloidal or at least amorphous sub- 
stances present in all soils, sudi as silicic, alumintc and zeolitic 
hyilrates. 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 takai into consideration in judging of a soifs tilling 
qualities by its clay content), the figures given in the above 
table approximate much more nearly to a tangible basis for 
such estimate, tlian 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 

* ThklactemphftxifeA the impoitibUity cif oipt^mg the plaiiiclty »ndadli«dv» 
f of cIjij wnjily as a ftinction of fineneai oi 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. 


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 northeastem 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- 


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 Statue of 
Mississippi, representing a very large land area in that State as well as 
in Tennessee and Ix)uisiana. 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). 


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. 



The fine particles flock together» forming littk pellets, which refuse to 
be se 1*3 rated by the sieve. This difficiiky can, of course, be partly 
overcome by previousiy separating the clay from the sand by means of 
wmier, as detailed above ; but even then it mil be found that so 
tooti as the grain-sizes fall much below ^ of an inch (^ millimeter) 
tlie same ditRculty is experienced, so long as the sand is dry* By 
playing a small stream of water u|>on the sieve» however^ all the parti- 
cles t>eyond the 3^ of an inch may be successfully separated from the 
coarser portion ; and for many practical purposes the separation need 
be carrictl no farther. 

Us€ ^f Water far Sefamiing ^ntii Grmm-Sius* — 'ITie scientific 
in%'estig3itor» however* must of necessity proceed to separate the finer 
gram-sizeH 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 sm^ll amount of soil is 
stirred up in water, and is afterward allowed to stand for some 
time, the diflfererit grain-sizes will settle consecuti%'ely in ac- 
cordanci! 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 sus|>ended in the water, the latter is not only denser 
but especially more viscid than if the clay w^ere absent. In 
order therefore to obtain correct results by any method in- 
volving the use of water, it is necessary t<i remove the clay l>e- 
fore proceeding 10 the separation of the granular sediments. 
This, as has lieen already statetl, is approximately accom- 
plished by allowing the soil, when diffused in water after 
proper disintegration, to settle for 24 hours from a column of 
welter 200 mm. high, wherehy all grain-sizes, of and alxive .01 
mm, diameter are removed from the turbid liquid. This 
sedimentation is then repeated until after 24 hours the water 
liecomes clear. The clay is then determined in the ** clay 
water" by evaporation or precipitation: the granular sedi- 
ments may then he successfully separated by sedimentation* 

The U, S. I^ureau of Soils uses for the separation of clay, 
insiead of subsidence for 24 hours, the more expeditious pro* 
ces* of contnfugin^ the turbid soil water in appropriate glass 
cylinders, by the aid of an electric motor; and thus in a rel- 



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. 

I*" Hydraulic Elutriation, — The sedimentation (or 
/\ I ** beaker'*) method, long practiced in the arts is, 
^ 1 \|^ however, quite tedious, requiring the constant 
^T ^ 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. 

I 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- 

y responding to the prevailing velocity will be car- 

r ried away. It is of course easy to ascertain to 
c what grain-sizes certain velocities of the upward 

Eiutri^tor.^"*' currcnt (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; 





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 
tnlet*Uibe is readily clogged by the soil mass at the lower 
velocities, which are thereby changed, so that, nnless 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- 


Fiej. 7. -The Churti El^irslaf ^HOptrd'i) btr the pJiyiicil anil>^if ot »oilt 

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 Elutriaiar ivith Cylindrka! Tube. — The errors just 
alluded to are obviated by an arrangemem devised by the 
writer, in which a rapidly-revolving i>tirrer, placed at the base 
of a cylindrical tube in which the washing process is conducted 



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 chum 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,^ 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. 

Voder'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. Hureau 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. 



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 

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. 

Xumbcr of Scdinioifs. — 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 l)etween one-fourth and one-half of a millimeter. 
But l:)eIow 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) 
eflfects 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- 



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. 


Designation of materials. 

Velocity per sec- 

Maximum dia- 

ond, or hydraulic 

meter of quartz 

















2- 4 


1.0- 2 


•5- > 







<3 0.0023 




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. ^ 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 : 

^ 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. 




K0l4«^^^a^K^ - i^> 

Wta, lL — IUi»tnti4Ht ai Revile M Elf dnttlk Otttfiatidti, ihowinis cxifcoi^ of toil tei|ja», vid 




S * 1 t ft ' S 4 n 4 * I 

Tuctt V.'JlluaLir.tiiuii uf KmuJii ol HydrauUc Elutriitioii* ihawlisg Alluvial 5ilia mm^ Pm^Womt 

PhysiiitI coiitfiosidon carresponding to popular designations 
of Soil quality. — Hie subjoined table illustrates the physical 
composition of a number of soils from tlie State of Mississippi, 



selected for their representative character, in order to deduce 
therefrom approximate definitions of physical character corre- 
sponding to popular desi^ations* This table, published in 
1873 in accordance with results obtained during the two pre- 
ceding years, does not require any material modification 00 
account of subsequent investigations. It lacks, however, a 
characteristic representative of the predominant soils of the arid 
region, \Hz., 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 w-e 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 
eondition, 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^ 
cnt 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 'Mighicn*' soils, but even to render them more intractable 
(" putty soils' '), white coarser ones gradually change the dense clay- 
teiture into the " loamy/' it Is dear that in between there must be a 
neutral point, some grain sixes 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-sixc lies at or near the diameter of .025 mm,, or 
.5 mm* hydraulic value. In correlating the results of analysis wiih the 
tilling qualities of the soil as to ** heaviness and lightness/' ihereforei 
that grain- size may usually be left out of consideration* 











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Number of soil grains per gram. — It is of some interest to 
consider die number of grains of different sizes that may be 
contained in, r. 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 graiivsi^es, assuming the density to be that of 
quartz (2.65), with the result that while with a diameter of one 
millimeter (T-25 inch) the number of grains would he 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-sij^es. — 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 
gi\'en 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 ; w^hile 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 footp 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. Mitschcrlidi (Bodenkunds ftir Land-und-ForstwJrtlie j Berlmp 
1905) attributes to the surface offered by the soil particles supreme 
Importance in detennining the productiveness of soils* Accordiog 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 mean^ of the heat produced in wetting the soi! ( " BeDel- 


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. i8, p. 225, 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^ more clay than the former. 



and 7 % more than the latter. But No. 346 is a highly ferruginotis 
chy, in which the ferric hydrate is in a very finely diirided condition, 
and materially influences the physical qualities of the clay substance. 
Were tt all accumulated in the ** clay," it would diminish the percen- 
tage of true clay by 11.75%, reducing the clay-percentage to tS.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, w4iich themselves act as sand 
grains; and a^ain, 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 substanfes. — 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 1^ 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 hydraie; since 
no zeolitic mass can contain as much alumina as does kaolinite, 
Wliether the aluminic hydrate be in the form of gibbsite. 


bauxite, disapore,^ 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 : 

^ 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 2fl^i Uiat of ^aspore being nearly 15° ^^ 
gibbsite about 35^/9. 








.50 mm. 

•y> " 

.16 " 
.12 " 

x>72 - 

.047 •• 
.036 " 
.025 " 
J016 " 











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- 



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 : 








.50 mm. 

•30 - 
.16 " 
.12 " 

Xfjl " 

x)47 " 
.036 •• 
.025 " 
X)i6 " 





It would seem the best and almost only remedy to be afH 
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 

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, g^ven in the table be- 
low, will convey some idea of their peculiarities in this respect. 




Hydi. Value, 


No 17. 

No. 57^ 

No 7^ 

"■' J 

*!,ooa3. mm, 
<.i5 mm. 

.25 to s 

.5 to 2.0 

z^ to $.0 
S^to 64^ 


XJ2S— ,047 
.047-— ,120 

.11-. SO 



. 3^ J9 


49-S7 1 


Sand.,, .,..»: 

37 SI 

3-97 _ 





Slow penetration of IVater, — 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 ver>' cl( ise 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, wMth a sudden downward 
break of the curve before the coarser grain-sizes are reached. 
It would seem as thou^ 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 



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 ^ has shown, of a fairly definite com- 
position of sufficiently wide range of grain-sizes for the pur- 

The effects of humus in modifying soil texture are discussed 
farther on. 

^ The Mechanical Composition of Wind Depoeita, Bull. No. i, Augustana Libraiy 
Publications; 1898. 


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-lV eight, — 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 J4 
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,^ 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, 3J4 

^ This remarkable soil seems to haye been derived from the finest *'slickens ** of 
the hydraulic gold mines. 




millions; for humus or garden land and woods earth, about 3 
millions of pounds; for reedy swamp and peaty lands, 2 to 2j4 

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 " " " " 

Arable land, first do. do 89.4 " " " " 

Same, fourth do. do 101.4 " " " " 

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 P^^ cent of the soil 
volume.^ If the same globular particles 
were packed as loosely as possible, *. 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 

Fig. io.-Variou« powible , . / , / . f J r 

arrangemenu of sou particle*, obviously bc greatly mcrcascd, to au ex- 

^ King, Physics of Agriculture, p. 116, ff« 



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 iit 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 cultivatioa 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 tilih, and it results from the formation of 
relatively large, complex crumbs ^ or flocculcs, 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 aggr^ates or floccules, loosely piled upon 
one another and separated by large interspaces. The increase 

1 The word crufxilie, which Is generally understood as meaning a relative! f large, 
loose aggregale, se«mi prcferalt^e lo the word kernels, suggested for the ^aine by 
Kiflf (Physici of the Soi), p. no). Kernels are undjcrstood to be bodies rather 
I t^d thAn (hi» surroynding mass, end do not convej the idea of loose aggre- 
Tlie word ** Kriimeistniclur*Mcniinb^$tnjcture)i adopted bj WolLnj for 
^b phenomenon. 1i» both fitiie» md priority In Its favor. 

no SOILS. 

in volume from consolidated clay to crumb-structure is given by 

It-/-- '-,'■. ;^^?^\^ ■ ■■■-r-"-V ! r ■' , :■ ^. >"'. ■ Ar '.- ' ' ^'■■".' v-. ' 

Fig. I i.^Land before and after plowing. The compectaeae of the aoQ b Indicated bj the deiwily 
of dotting. Before plowing there it a compact surface crust (s), below which the soil becomes lose 
and less compact as we go deeper. After plowing we find the soO (fs, furrow-slice) converted into a 
looee mass of cnimbe (floccules), with increase of balk. Compa c ted plow-sole at pi. 

WoUny (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- 
ever the water-films evaporate, un- 
less some cementing substance was 
dissolved or suspended in the 
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, gfripping 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 

Clay is most frequently the substance which imparts at least 
temporary stability to the crumbs and crumb-structure; this is 

Fig. ia.~A soil<cmmb, magnified to 
show the particles of which it is com- 
posed. The particles are held together by 
the water-menisci, jostasare the hairs ot 
a brush when wetted. The white spaces 
between the particles represent air. 



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, wilt 
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 (jdly-Iike) 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. 

Haw Nature Tills. — When we examine the undisturbed soil 
of woods or prairie in the humid region, w^e will as a rule find 
the natural surface soil in a very good condition of tilth; the 
ob\nous 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 titled- 

Crusting of Soils. — ^In some soils, especially of the Gulf 
States, the beating of rain followed by wami 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 crtist 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; 


112 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 sufiiciently 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 bark, 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. 


In the arid region it wilt frequently happen that such soils 
when not tilled to a sufficient depth, will during the later part 
of the summer so shrink and crack hcneath 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 U> bestow upon theni, to the fullest ex- 
tent, the deep and thorough tillage which is absolutely essential 
in the utilization of their usually high productive power, 

Ex^nt 0/ Shnnka^* — The extent ol this shrinkage in drying, and 
sotisequent exp;uis(on in wetting, have been measured by the writer by 
thruse of the sieve cylinder described below (chapt* 11, p, 209), as 
Irving lor the determination of the water capacity of soils* When a 
soil of the kind above referred to is placed in the sie^^e cylinder in the 
tilled (flocculated) condition, then allowed to absorb its maximum of 
water and then dried at too degrees C, the contraction In drying can 
lie ve^ strikingly seen^ and its amount measured by fiiiing 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 2 S to as much as 40 per cent, of the original 
bulk.* 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 sod which has been rained upon. 

Tile 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 nf water-holding power (see chapt. 1 1, p. 2og). 
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-lKJx 
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- ft is easily seen that these 
variations in volume ma>' bring al>out very marked results in 

> WdUtiy *F<Jr«h. Vol, 20, p. tj flf, 1897) record* limilaily high shriiikage« In 
\ experinieftts. 




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. 

RtiiiCtAV Soit, Black '* Ak^^jkb " Ulav Soil* 

F^G. ti,— Expiindtiu on Wettiaf and Coatractiflii on DryiriK ot lieavy cUy »Ui. 

Contraction on IVetting. — In the case of alkali soils contain- 
ing mucli carbonate of soda, a very notable font taction occurs 
in iccfiifig 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'7valloivs/' — In the field the ^vetting of cracked clay 
soils produces some very curious effects. The effect of tlie 
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 by 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,*' ^ 

' A totally different kind of ** hog-wallows,*' occurring in California and the arid 
region generally, have l>een described in a previous chapter under the head of 
Aeolian soils (See chapt. t, p. 9^ 



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 of such extreme character as to be 
almost uncultivatable will serve to exemplify their physical 


No 242 MUs. No. 643 CaL 



Jasper Co. 


Black Adobe. 

Cootra Costa 



Weight of gravel over 1.2 mm. diameter. 

** ** between 1.2 and I mm. . 

** ** between i and 0.6 mm. . 
Fine earth 


Hydr. Value. 



} 35.18 







^.0023 mm 








r '<'o.25 mm 

0.25 mm 


0.5 mm 




ijo mm 

2.0 mm 

4tO mm. T , , » T . - 

1 80 mm. ... ..... .... 

16.0 mmT .... .--,-,., 



12.0 mm 

64.0 mm 

100 JOO 


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 


few hours of sunshine become of stony hardness and will resist 
all efforts at pulverization or the production of tilth. ^ 

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- 

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. 

* Schiibler (Grandsatze d.Agrikulturchemie, 1838) 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. 



Loamy and Sandy SoUs. — It is larg^dy 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- 

The subjoined physical analyses of two soils from the Brown-Loam 
region of Northern Mississippi (see chap. 34), shows the composi- 
tion of lands excellent in every respect other than the tendency to 
crust after each rain : 




Coarse materials . 




X — 

3 mm. 



.02 J 

Hydr. Value. 

64 mm. 

32 " 
x6 " 

8 ** 

A " 
2 " 
I " 




No. 219. 







No. 197. 



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 



capillary water, or otherwise flocculated or cemented. Freez- 
ing of the soil is therefore of matenal 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, MO). 
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*ctit '* of grain, result- 
ing from the upward expansion of the surface soil in freezing, 
that may readily mpture 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 cHmates, 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 thetr lower ends, and the expaDsion 
occurring in freeEing^ 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 wiuds occur in winter. 



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. 


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- 




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 acctimulation 
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 rcfer^ in individual eases, 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, 

Cmises 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 tlie process of soil- format ion. 

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 arc bacteria. But the antiseptic nature 
of the compounds thus formed ^ 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, CH^), the 
former predominating in the early stages ; while later, the car- 
buretted hydrogen predominates, rendering the gas readily in- 

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.^ 

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 

^ The antiseptic properties of sour humus are well exemplified in the perfect 
ttate of preservation in which the remains of animals, wood implements, etc, are 
found in bogs into which they have sunk in prehistoric times. 

* See Miiller. Natiirliche Humusformen. 



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 vegcta^ 
tioo, in these lands. 

It has been long known that after long-contiiitied cultiYatiODt soils 
origioally of neutral or slightly basic reactioa become acid : and the 
Ijmmg of such lands is an ancient practice in Europe. The matter^ 
however, received but scrant attention until Wheeler and Hartwellp of 
the Rhode Island Experiment Station, demonstmted the almost untTer* 
ni acid coodition of the older lands of that State, and the excellent 
effect produced by neutral Nation with lime, or even with the alkali 
carbonates.' The current neutralization of the humus-acids is unques* 
tionably one of the cardinal advantages of calcareous lands ; for such as 
cofitain only small amounts of Umc carbonate will of course become acid 
quickly under cultivatioa. 

Humin 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 neutrahze them as formed, the normal process 
of humificatton 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 arc markedly richer in 
nitrogen and carbon than the substance of the higher plants 
from which they were derived (see chapt. g). Com- 
parative analyses show that in the normal process of humifica- 
tion of vegetable substances^ oxygen and hydrogen are climi- 

1 Report* of tli« Rhode Utftod £xp*t St^uon, 1S91, and E. 



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 

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- 


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 * below, for the substances 
moderately and uniformly packed : 




Quartz Sand. 




When saturated with water, the same substances gave the 
following figures : 

Air-dry. Saturated Increase, 

with water. ^j^ 

Hamas* 3565 ^-^^H ^^' 

Clay ix>39j 1.6268 55.9 

Quartz sand., i^sca 1^270 25.9 

These data show strikingly the effects produced by the sev- 
eral physical soil constituents upon some of its physical prop- 

Chemical Nature, — While humus artificially produced by the 
action of caustic alkalies upon sugar or cellulose is free from 
nitrogen, all naturally occurring humus tontains 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 doiltd 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 WoUny, Zersetzung der Organischen Stoffe, pp. 242,243. 
' Peat pulverized and extracted with alcohol and ether to remcTe resinoos sal> 

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 coimection 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 HumiHcation. — The progressive changes in- 
volved in the process of humification of vegetable matter are 
illustrated in the table below,^ 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. 

> Data recalculated, omittiDg ash. 





(^k Wood. 








40 in. 







*9 4ton>-7 
1 *' it.7 

1.16 4,10 

69. SO 

J. 10 


The steady increase of carbon and nitrogen, together with 
a corresponding decrease of oxygen, arc 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.j2% 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, CH^). 

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 undistinguishablc 
from Hgnite 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 coak arc and have 
been fantned under the conjoined actioti of submergence and pressure, 
sometimes also aided by heat ; and thus they cannot perfonn the func« 
tion of soil-humtis, any more than the frre-clays or shales underlying 

1 Detni«r, La»dw. Versuchitt Vol 14, 1S71, 




them can resume their original soil-functions without prolonged weather- 

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- 

Fio. 14.— Section of Ugnitised log showing contrmctioQ into solid lignita on diyingi 

tent at i^), 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 

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 



m drying into a small sheet of lignitized wood ; the original tmn^ 
projecting from a bed of sand some forty feet below the surface, being 
lo 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 I 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, ft thus seems impossible, as fn ibe case of humus, 
to assign any definite proportion as between woody matter and coal 
formed from iL 

N&mtal humificatian takes place only under the influence of 
inodcrate temperature* When the temperature is too low, bac^ 
tcriat and fungous growth are repressed or arrested; when too 
high, the fungous vegetation assutnes a diflFerent 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,* 

Eremacausis^ — In the absence of a sufficietit 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 ** lire- 
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 humas-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 

^ A itdkldg niustfation of thb \m ftlforded hj Nacgeirs experiment of enclo^ng 
•ev«ml loft^e^ of br?acl In a loo^el^ closed tin-box. After eighteen months tKer« 
rvmi^ned only »«venEeca per cent of ajf^drf mouldy matter, totmUj deititufe of 




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 ^ 
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 giveis for each six 
inches the following data as found in the tchernozem, taking as 
ICG the root-content of the surface layer: 















6 inches. 




8.1 1 



12 " 







i8 " 






24 •• 







30 " 
36 " 



2.1 1 



^l " 






48 " 



54 " 



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 /^ss 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. 

* Abstract in Ann. dc la Science Agronomique, Tome 2, 1887. 



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 Cultk^ation and FaUamng. — ^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,^ who determined 
the loss both of humus and of nitrogen suflFered 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 pi ant- 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 

I BiiU, No. 70 Wmn. Ejcp'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.' 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 : Matiere 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 

' The humus determinations thus made, which include nearly all those made by 
German chemists, give the humus-content from 40 to 50°/^, too high. The French 
determinations are mostly made by the method of Grandeau. 



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 
frt*m time to time replaced l^ 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** 

Humates and Uhnates. — 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 die quantitative determination 
of humus according to Grandeau ; since these bases are almost 
always extracted by the weak acid. When the brown solution 
of alkali humatc 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 aciflity. 
The brown tint of certain subsoils in the northern humid re- 

I The decresiM* of humtis from wheat culture In the soikof Miooctota md North 
Dakota hiA be«n Rtudied hy IL Snyder aiid E. F. l^dd, tie$pectivefy. In the 
firaiiie Undft of the Utter St«te the torjil orgamc matter in the 6rst six Inches of 
■oil mjig«« ft9m 15 to as much u 2^'''^ and Iht hnmus tdone froni 4 to 7^v 


134 SOILS. 

gions have been shown by ToUens 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 

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 : * 


Insoluble matter^ 61.97 

Potash (KiO) 7.50 

Soda(NaiO) 8.13 

Lime (CaO) 0.09 

Magnesia (MgO) 0.30 

Peroxid of Iron (Fe,Og) 3.12 

Alumina ( Al,Oi) 3.48 

Phosphoric acid (P,Oj) 12.37 

Sulfuric acid (SO,) 98 

Carbonic acid (COt) 1.64 

^ Precipitation with an excess of acid does not greatly change the results. 
* In California soils this is mostly silica soluble in carbonate of soda. 



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. 

Funciwns 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 
soiUdecomposition ; 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-nit rogen^ 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,^ 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 Miigmrd mmd/sffa, Oti the Nitrogen-content of SolMiumui ia the Humid auid 
Arid regions. Hep. Ca). £xp*t Station fof 1891^ ; Agric^ Sdencet Aprils 1894 1 
WoUnf 's Foracb. Geb, Agr. Ph/s., i^^^ 





Soils arranged in order of nitrogen percentages in 

Soils of the Arid Region (California). ' 

S061 Dark clay loam, Arroyo Grande Valley, San Luis Obispo 


3291 Red soil, Orland, Glenn Co 

1904 Sediment Soil, Porterville, Tulare Co 

1 901 Sandy soil near Ceres, Stanislaus Co 

704 Sandy soil of plains, near Fresno, Fresno Co 

6 Black adobe soil, Stockton, San Joaquin Co 

1679 Black adobe soil, Berkeley, Alameda Co 

2324 Clay soil of desert, Impenal, San Diego Co 

1167 Black clay loam soil, near Tulare, Tulare Co 

1 536 Brown loam soil, Windsor Tract, Riverside, Riverside 


1 1 26 Sand V loam soil, Paso Robles, San Luis Obispo Co . . 

2301 Red fiill soil. Upper Lake, Lake Co 

1007 Plateau soil of desert, Lancaster, Los Angeles Co. . , 

1 1 59 Sandy plains soil, Tulare, Tulare Co 

1900 Sandy soil, near Modesto, Stanislaus Co 

11x3 Clay loam soil (slate), Jackson, Amador Co 

1 149 Adobe clay soil, near Paso Robles, San Luis Obispo 


1538 Mesa soil, Chino, San Bernardino Co , 

11-^7 Sandy loam soil, Paso Robles, San Luis Obispo Co. , 

2403 Vallev Soil, Wheatland, Yuba Co 

1 28 1 Red Mesa soil, Pomona, San Bernardino Co 

1 1 17 Sandy granitic soil, near Jackson, Amador Co 

1406 Red loam soil, Arlington Heights, Riverside, Riverside 


117 2 Red clay loam soil, east of Tulare, Tulare Co 

1958 Sandy Mesa soil, Nipomo, San Luis Obispo Co. . . . 
1423 Chocolate-red soil, Carisa plain, San Luis Obispo 


1 291 Sandy hill land, near Jackson, Amador Co 

W5 Wire-^rass loam soil, Visalia, Tulare Co 

863 Red ndge loam soil. Grass Valley, Nevada Co 

1907 Dark loam soil, near Chino, San Bernardino Co. . . . 
Ill 5 Sandy granitic soil, near Jackson, Amador Co 

332 Plateau desert soil, Mojave, Los Angeles Co 

2126 Gravelly soil. East Highlands, San Bernardino Co.. 

1910 Ojai Valley soil, Nordhoff, Ventura Co 

2 1 87 Sandy loam soil, Soledad, Monterey Co 

1759 Sandv soil, Perris Valley, Riverside Co 

774 Bencn slope soil, Ontario, San Bernardino Co 

1984 Red soil, East Highlands " " " 

232 j Silt soil of desert. Imperial, San Diego Co 

1906 Light sandy soil, Pomona, San Bernardino Co 

2430 Hmside adobe, Berkeley, Alameda Co 

Arerage of arid uplands. 
























II. 21 
II. 10 






















Soils arranged in order of nitrogen percentages in 

a ft 




SuB-iRRiGATBD ARID SoiLS (California). 

586 Sandy plains soil, Tulare, Tulare Co.... 

1466 Loam soil, Miramonte, Kern Co 

1384 Moist land loam soil, Chino, San Bernardino Co. . . , 
1 1 48 Swale soil, near Paso Robles, San Luis Obispo Co... 
17 14 Bench soil, Santa Clara River, Piru, Ventura Co. .... 

77 Alluvial soil, Tulare Lake bed, Tulare Co 

1800 Creek bench soil. Niles, Alameda Co 

1901 Sediment soil, Porterville, Tulare Co 

168 Alluvial soil, Santa Clara river, Santa Paula, Ventura Co 
1760 Green-sage land, Perris Valley, Riverside Co 

506 Alluvial soil, Colorado River, Yuma, San Diego Co . 

1636 Red soil, Manton, Tehama Co 

17 58 Alkali soil, Perris Valley, Riverside Co 

1963 Sandy loam soil, Willows, Glenn Co 

2080 Sandy soil, Santa Maria Valley, Santa Barbara Co . . 


1. 16 



1. 12 






Average of sub4rrigated arid soils . 








Eel River Alluvial soil, Femdale, Humboldt Co. . 

Alluvial soil, Hupa Valley, Humboldt Co 

Marsh soil, Novato, Meadows, Marin Co 

Valley soil, HoUister, San Benito Co 

Tule soil, Upper Lake, Lake Co 

Alluvial soil, Putah Creek, Dixon, Solano Co. . . 
Redwood Valley soil, Pescadero, San Mateo Co. 



Average for California . 


26 Bog soil, Michigan 

Back-land clay loam, Houma, Louisiana. 

Duff soil, Oregon 

Sandy prairie soil, Harris Co., Texas. . . . 

Average for other States. . 


» 33.02 





Qed soil, Oahu Island, Hawaii (maximum). 

Guava soil, Hawaii Island (minimum) 

Average of 5 soils, Oahu Island 

Average of 2 soils, Maui Island 

Average of 4 soils, Hawaii Island 



Average for Hawaiian Islands.. 
Total for Humid soils, average. 


























a- 54 








* Introduced only for comparison of the nitrogen percentage in Humos 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 Nitrogen- Content 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. 



Depth in feet. 

Percent Humot in 

Per cent Nitrogen in 

Per cent Humus- 
Nitrogen in soiL 


1. 21 




1. 16 





































1. 81 


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/ 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 



































While it may be questioned whether the process of htunifica- 
tion had in these materials really reached the point of sensible 
completion in all cases (notably in those of sawdust and cow 

> Bull. No. 53, Minn. Exp't Station, p. 12, Chem. of Soils and FertHixers, p. 94. 

'The figures for cow manure are so far out of range with any others thus far 
observed, that it seems reasonable to suppose that thej are influenrftd by un- 
changed substances present in the excreta. 


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- 

Humus from meat scraps 10.96 ^ Nitrogen. 

" " green clover 8.24 

" " cow manure 6.16 

" " wheat flour 5.05 

" " oat straw 2.50 

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. 



Correspondingly, Ladd ^ 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 Bailn S. Dakote Station, Nm. 24-32, 35, 47. 

SOIL AND SUBSOIL {Continuid). 


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 g^am 
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 Hohl at the bacteriological 



station at Liebcfeld, near Bertip 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 
Ijebefcld 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 i, p, 461, 1905), 

Mayo and Kinsley (Rep* Kansas E^cp't Station for t903'5) 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 theif figures exceed considerably 
those given by European observers, as they often reach high into the 
111 ill ions, in one case to over fifty millions, per cubic centimeter*^ 

Five fields with diflerent soils were investigated ; the land being 
described as follows: ''Field No. i is a bbck loam containing con- 
siderable humus ; field No. z is similar to field i but contains more 
humus ; field No. j is a thin soil with clay gumbo subsoil ; fields Nos. 4 
and 5 are btack loams, but not as rich in humus as either No. i or 

No. tr 
The average bacterial contents of the several fields are given as 


Field No, i , * , , 33i93^ j747 per cubic centimeter, 

^ No* ^ 53,596,060 " " « 

" No^j.,., 7S,S34 " " 

** 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 
die bacteria) 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- 
munlcated ; but at the request of the writer samples of the soils of the 

1 The mode of ftt^tement in the paper Is tiot always quite clear as to the manner 
In which the averages given were calctitated. It muAt be remembered that iheae 
data refer to cubic centimeters of soil, or about twiee the amount {t gram} used 
bjr Earopesn obserren. 



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% " " 

" No. 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. i, 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 



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 combipwd 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 efi"ects 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- format ion and plant growth, there 
are several kinds whose acti\ity has been proved to be of the 
utmost importance in one or lx>th directions; it having been 
shown that when the soil is sterilized cither 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 arc those connected with 
the processes of nitriiication and denitri£cation. 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- 





ditions of their activity have been largely developed by R. 
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 
Fio. 16— Nitrobacterium. (Winogndsky). f rom a supply of the nitrifiablc 
substance, a fairly high temperature (24° C. or 75° 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- 


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, 
he 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: 

(} ypsum 1 00 

Sodic Sulfate 47.9 

Potassic Sulfate . . 35.8 

Calcic Carbonate 1 3.3 

Magnesic Carbonate 12.5 

The above estimates are markedly confirmeti 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 carl)onate 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 S(m1 was left unmoved for 
several m^jnths, 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 i 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- 



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. 

UnhumiHed Organic Matter does 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 
Fig. 17— Bacillus dcnitri- has scrvcd cxtcnsivcly for the production 
ficansi. (Burri.) of saltpctcr in the " niter- plantations " for 

the industrial purposes; the material of which was loose 


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 mycoidcs, 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 '' (5. 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 



Ftg. i8.— liactUus subtilis. 

(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- 
zer (Landw. Presse, 1904, No. 
11) 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 
(Woiiny, after 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- 

FiG. 19. — Bacteria producing ammoniacal 
fermentation : A, C. mycoidts : B, B. si ut- 
ter i. (Frum Conn, Agr. Bacteriology.) 

Fir.. 20. — Bacillus 

magaterium. (From 



phcre through the ammonia in rain water. This was then 
shown to be wholly inadequate ; and Boussingault proved con^ 
clusively that plants do not take tip nitrogen gas from the air, 
Tlvis was subsequently denied by Ville; but investigation at 
the Rothamsleatl agricuhural station by Lawes and Gilbert 
definitely confinned Bou5singault*s results. At the same time 
they also proved very definitely tliat while grass and root crops 
deplete the soil of nitrogen, clover and other leguminous crop^ 
leave in tlie soil more nitrogen than was pre\*ioush* 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 
l>ecome a practical maxim ; but the cause was not underslotid 
until, in 1888, Hellriegel and Wilfarth announced that the 
variously-shaped excre^icences or tuliercles which had long l)een 
observed as frequently deforming the roots of legimies, are 
caused by the attacks of bacilli capable of absorbing the free 
nitrogen * »f 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-shai^ed 
organism was named Bacillus radkicola by Beyerinck; Rhho- 
hium kgumiiwsiiniffK by A. Frank, who has published an ex- 
tensive treatise on the subject,* 

Microscopic examination of the nodules shows their tissues 
to contain partly motile, free 
baaeria. partly others ( l>acte- 
rrnds), which Inve assumed a 
quiescent conditii-n, and are 
of much greater ilirnensions 
than those of the motile form. 
These relatively thick, and 
sometimes forked* forms* dif- 
fering somewhat in each of 
the gronp adaptations men- 
tioned l>elow, constitute ihe 
bulk of the ccll-crmtents of the 
nodules, and ullimcitely serve 
for the nutrition of the host- 
plant witli nitrogen. When 

* VhcT dic r0«yiftbco4<* der r^|*ijmii*<>s<fn» Berlin, tSrp, 
^ Otigtml ^g^Tc frciOj df^t^kiig \f\' O, Butler. A»»t* In 

Ft&. fi.— Mtcmttopic «rcttMi of c«11 (imuc, 
filled «ilh Klili(ibU.> 

Agr. D«ii*t Uftiv. of 

152 SOILS, 

the growth of the excrescence is completed, the swollen, quies- 
cent bacteroids gradually collapse and become depleled 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 acti\'e bacteria again* The nodules 
are thus Umm] mainly on the actively-growing roots, and at 
the time when vegetation and assimilation are mtjst active in 
the plant, In autumn, or when the plants are in fruit, the roots 
may be wholly destitute of nodules. 

Flo. M$. — SquATc^pod pe4,--Tciragoaa1obiii purpuneus. Fm. 16.— White Lupin.— LupLuui «Ibuj, 

The adliesion of the nodules to the roots is mostly very 
loose, and tlieir falling-off when the seedlings are carelessly 
transplanted, doubtless accounts for much of the difficulty 
generally found in transplanting legumes when once es- 

The figures annexed show the various forms assumed b}^ the 
nodules in different plants, and with them also the correspond- 
ing forms of the bacteroids of each. The latterj here shown 



154 SOILS. 

magnified about looo times, are taken from the inaugural dis- 
sertation of D. Brock on this subject, published at Leipzig in 
1 89 1. 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^ with each of several 
groups of the legumes in order to exert their most beneficial 
eflfects. 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.^ 

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 harrozving 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. (ieo. 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. 

•^ 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 



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 

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.^ 



Hairy vetch, not inoculated. . . 

do. do. inoculated 

Crimson clover not inoculated. 

do. do. inoculated 






lbs. Value. 











$ 105 



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 heir 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 flon. 

The distinctive agricultural function of supplying nitrogen 
to the soils on which they grow, renders inexcusable the per- 
sistence <^f some writers and teachers in designating all forage 
plants as ** grasses." Whatever excuse there may have l^een 
for this practice so long as the nitrogen-gathering function of 
the legimies was unknown, disappears with this discover}', 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 algae 
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 
chroococcum) 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 chroococcum 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 
inflasksof 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 bacilhis. 

It was thus clearly proved that A, vinelandii at least does not need 
symbiosis with algae to fix atmospheric nitrogen ;.l)ut 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. 



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-fall 
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.^ 

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- 

* Ko^ticheff, Formation and Properties of Humus; in abstract Jour. Chem. Soc, 
1891, p. 6ri. 

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 

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 (Luvibricus) 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 l^etween it and 
the surface soil. Briefly stated, the earthworm nourishes itself 
by 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 fairly 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 tlie 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 



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 

Wollny (Forsch, Agr., 1890, p. 382), has shown by direct experimental 
cultures in boxes, with and without earthworms, sur])rising differences 
between the cultural results obtained, and this has l>een fully confirmed 
by the subsequent researches of Djeniil (Her. 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 i*^ ^^^^ ^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 inc reased looseness, and per\'iousness 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 regicMis. 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 
K. 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 efTectuallv. 

l6o 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. 



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,) 

Chetfiical effects of Water-Percolation. — The accumulation 
of plant-food in the subsoil is not, however, due only to the 
mechanically-carried particles, but 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 by the carbonic acid formed chiefly 
II 161 

1 62 SOILS. 

within the humic surface soil, and is often carried oflF 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 

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 Hardpaus. — 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. 

'' Razcness" 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 


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 otic 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, 

1 64 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. ^^ ^^e 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, ^., 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-ploiving 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 der)ends 
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 hann 
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). 



rvrR iif ItASTBRM SCHtS 



Tm(l 4f.— Soil Prd^am lUn^tntlof dittertcttet in bi.ii]i ••! rtu'^uj ^nd Aitd Regioa. 

i66 SOILS. 

It must not be forgotten that there are in the lowlands of 
the arid region (river swamps or tules, 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-grozvth 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 

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 


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, m a gravelly clay loam varj-ing but little the 
entire distance. In a similarly uniform and pervious material, the 
loess of Nebraska, Aughey^ 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 rains are found to be dependent uix>n 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 iceeks 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 \\\\\ contain 
practically no feeding-roots, the paralysis or death of which 
by heat and drought would influence sensibly the welfare of 
the growing plant. 

* See Merrill, Rocks and Rockweathering. 



Raoi'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 tliere 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 



f \v- J-" I. 

Fiq. *S.— Rpoloran Kaitem (Wisconiin^ Ffult Tnrc 

.13. h l:.y JVijI r \K Kin|; } 

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 w^eeks' 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 


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 harb<:irs, Under the same weather-conditions an 
adjoining field, properly plowed, may almost wholly escape 

Comf^arison of root dei'clopmcnt in the arid and humid 
rr^ioi!^.— Figures iS, 29 ^'i^en here show the differences as 





\ ('r 2 s - VtuSic fret tn F'*»rh Rowit, at Nilri, t -d 

actually seen in the case of fruit trees as grown in Wisconsin 
anrl California, respectively, both in the absence of artificial 

Adaptation of humid species to arid conditions. — Figtires, 
in No. 30, show the nx)t systems respectively of the riverside 
grape ( yitisriparia) as grown in the Mississippri Valley states, 
and the natural development as found in the Rock grape of 



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 

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. 



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 extending to 8 
feet depth, but where broken oflF 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 jn sandy 
lands descend to from 4 to 7 feet even in the case of annual 
fibrous- rcx)te(l plants like wheat and barley.^ 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 

' Shaler r'^)rigin and Nature of Soils; 12th Rcpt. 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. 


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 ornicum) and the figwort (Scrophularia cali- 
fornica), 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 was 
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 
fig^vort, 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; 







S ' 






s ^ 

{ 2- 

K Pi trclUC ^f, 

.1 8 





Fic. 34.— Califprda Mabc, GremrD Wllhottt JUinor InifiUliML 


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 soc n 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 necessar>', 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. c, 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 

No. I 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 Ixith 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 

The case of So. 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 





c _ 










useless for cultivation. It is naturally covered with low, 
stunt eel shrubs or chai>arral ; only here and there, where a cleft 
has been caused hy earthquakes or subsidence, a large pine tree 
indicates lliat nourishment and moisture exists wnthin the 
refractory clay stratum, and suggests blasting as a means of 
rendering ihe Innd fit for trees at least. 

K* J, 3 is a case similar to that of No, 2, only there is here a 
dense un stratified mass of red clay^ of good native fertility. It 
is here that the expedient of blasting the tree holes with dy- 
namite was tirst successfully employed, in central California, 
For lack of this, extensive tracts of simitar land in southern 
California, planted to orchards, have completely failed of useful 
results after three years of culture. 

Xo. 4 shows a typical case of calcareous hard pan obstruct- 
ing the penetration of roots, even though usually interrupted at 
intervals, because of the fr)rmation 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 uixm the depth to which the annual rainfall pene- 
trates, (Sec below, page 183). 

Nos. 4, 5, and 6 alt illustrate cases of intrinsically fertile, 
very deep soils, shallow efl by obstructions which in the case of 
No. 4 are hardpan sheets, white in No. 5 the intervention of 
bottom water limits root penetration, hence restricts the use of 
the land to relatively shallow -nxjted 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 w iihin reach of most plants, but is 
prevented from being utilized by the intervention of layers of 
coarse sand or gravel, through wliich the water will not rise: 
and the roots, while they would be alile to penetrate* are not 
near enough to feel the presence of w^ter underneath and there- 
fore spread on the surface of the gTavel. suffering from drought 
within easy reach of abundance of water. The "going- 
back '* of large portions of orange orchards in the San Ber- 

I So 



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 Impcrz'ious 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 l)est accomplished by 
moderate charges ( 5^ to »}4 pounds) of *' Xo. 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 projx^rtioned the charge will hardly disturb 
the surface: hut if this be desired, from iJ/2to 2y2 pounds of 
black powder placed above the dynamite will throw out suffi- 

1 82 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- 

"" 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 


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 of 
the substrata, and especially of the deeper roots ; in the diseased or 
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. 

Hardpan. — 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 tlie 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, vear after vear. Finallv there is 

1 84 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 Miiller and Tuxen ^, 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, Moorbedpan, 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 

^ See '• Studien iiber die natiirlichen Ilumusformen," by Dr. P. E. Miiller. 


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 catise 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 oi time destroy the hardpan layer. This is the more 
desirable as in such cases the surface soil is usually completely 

1 86 SOILS. 

leached of its lime content, and is consequently extremely un- 

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. 

" Plowsolc'* — 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 

Marly Substrata. — Among the causes of failure occasionally 
found in the case of the '* going-back " of orchards, is the 


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. 




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. 



Capillary ascent in glass tubes 
of one mm. diameter. 

Water 14 mm. 

Alcohol 6 mm. 

Olive oil ... I mm. 

Heat Relations. 

Water at 0° C. (freezing 

Pt.) 99988 

Water at 4 (Maximum 

density) i. 00000 

Water at 15° C. (ordi- 
nary temperature) . . . .990 
Ice at o^ (freezing pt.). .92800 

Specific Heats. 


Ice 502 

Steam. ... .475 

Clay, Glass. . . .180-.200 

Charcoal 241 

Wood 032 

Gold, Lead 0^2-jo^ i 

Zinc 096 

Steel 119 

Heat of fusion. 

Water (Ice). . . 80 Cal. 

Metals 5-28 " 

Salts, (incl. sili- 
cates) 40-63 " 

Heat of Evaporation. 

Water at 20° C. 61 3 Cal. 
" 100° 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 



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 tempera.ture 
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* 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 diflferences 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 

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 diflFerences are 

* 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. 

igo SOILS. 

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 
4° C. (49^.2 Fahr), and expands as it grows colder, until at 
o° C. (32° 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., i 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 powerfully, 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 



from 60% to 90% of liquid water, the temperature of which 
can only be raised or lowered slowly; aiid the presence of the 
sea tempers the cHmates of coasts and islands as compared with 
tlie heal or cold occurring in the interior of the continents. 

Ice. — Again, it is shown in the table that the heat reqtiired 
to melt ice is g-reater than in the case of any other substance, 
especially die metals; which when once heated to the fusing 
|}oint. require only a very little more heat to become liquid. 
The fusion of salts (inclutling silicate rorks) requires more 
heat than does that of the [>urc metals* 

Vaporization, — In the amount of heat re<jutred for its XHipor- 
isaiian water is also especially pre-eminent, and potent in its 
influence upon organic life. The table shows that the cvaijor- 
alion of water requires six hundred heat units * as compared 
with alcohol, requiring only two hundred; while spirits of 
turpentine, the representative of a large proportion <if vegetable 
fluids, needs hut sixty-seven. 

The practical result is that evaporation of water from the 
surface of animals and the leaves of plants, is exceedingly 
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 temperaturCp 
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 fie 
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 I^juisiana when the therm* mieter stands 
at 95^ F. will experience no inconvenience under the same con- 
ditions in the dry atmosphere of the Great Valley of California, 

Sah^rni Fotver. — ^To tlie exceptional properties of water ilis- 
cussed above, should be added another hardly less important 
one, viz., that of being an almost universal solvent especially of 

* A heat unit, or " calofte," b the amount of heat required to raA&e the tevnpef^ 
Im of a tintl-weight (pound, kilogfmfa,or graint of water one thermoiaetric degr^s. 
Accordiitg to the unil^wdght and thertnoneiric *cale used, the 6guri» will varj. 
tiiit m Ihm text the baiia ii utidentood to be kUogums and the centigrade »caie» 

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, 
VVollny 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 



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 bctu'ccn Evaporation and Plant-grozvth. — 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 zinthin limits varying for different soils 
and crops, production is almost directly proportional to the 
zvater supply during the period of active vegetation. 

On the basis of Hellriegers 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 i :i.5, King calculates the 
following table of probable production under different moisture 
conditions ( Physics of Agriculture, page 140) : 


Number of 

Weight of Grain. 

Weight of Straw. 

Total Weight. 

Water used. • 





































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 

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:^ 

"In e X p e r i m enting 
with barley last winter 
the natural rainfall, 
which amounted to 4^ 
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.'' 

Fig. 37.— Experiments on Cereal production with 
various amounts of water (Fortier, Report Mont. 
Expt St a., 1903). 

* " Water and Forest," January, 1905. " The Use of Water," by S. Fortier, 



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 (Balletin 22, Bureau of Soib^ U*S. Dept. Agr,), has carried 
this rule so far as to claim that in all sotk, the moisture supply is the 
0nfy important factor, and that so long as this is provided for, soil 
fertility coniinaes 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 WoUny as requiring 
over three times as much w^ater 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 tn dry climates (see this chapt. p. 212). 

It is therefore impossible to assign a definite figure for the 
amount of water required by vegetation al large; and even for 
one and the same plant, only approximations conditioned upon 
climatic factors can be given* We can in many cases, hnw- 
cver, 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 SoU'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 S«e WoUnj*! eiperiixieiits, Fofidi. Agr^ Pbys. Vol* jq^ p^ jS^ 



3. Liquid water seeking its level ; bottom, ground or hydro- 
static 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 15° Cent., is called the coef- 
Hcient 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. 


lly^r. Moisture.,,.* .*.. 


Ferric Hydrate * , * * * . . 


FiTieiit Silts <oi-.0350 mm^y. . , 
Sandal f and c. (<)25&-.50 ram.) 






*^'= o 














4 70 


be ^ 
t >. 

i 3 








33 W 






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 the 
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 

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. Schiibler, 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,^ so that these determinations are marred by ineliminablc 

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 d 
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 toil 

198 SOILS. 

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 of 
absorption with rise of temperature not only is not true iox 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 temperature rises^ at least between 
15 and 35 degrees Cent. Thus, fine sandy soil which at 15^ absorbed 
2% of moisture, took up 4% at 34^^ ; while loam soil absorbing 7 % at 
15^, showed nearly 9% at 35^ ; an increase of 2% in each case. But 
in partially saturated air ' 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 15^, 
it was found that in air three-fourths saturated, \ 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 it 
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 ^/^ more than the uppermost one. 

' 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 Wiillner (Pogg. Ann.). These solutions were placed in a wide, 
flat dish, over which a layer of soil i mm. in thickness was exposed, all being 
covered with a bell glass lined inside with the same solution, so as to insure equal 



unden&luiated air. Since air thus undersatumted occurs not uncom* 
monly in the arid regions of the world, the tact that the ioil cannot be 
lafther dried by such air of the same tempcniture, is of some practicil 

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, alumtnic 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). 

Utitity of Hygroscopic Moisture to Plant-grou*ih. — 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. r3i). Yet Mayer himself concedes the cogency of the 
experiments made by Sachs^ which proved that diy soil im- 

t £. A. MltBcheHicb (Bodenkunde fat Li^d-und Foristwirthc, p. 156 et ml^ 
dums th&t all detcnninfiCiCins of sail bygroscopldtj Ihiis far made ar« gTO^]f 
incorrect cm ftccoiuit of the dew liable to be condensed on the soU la^er from 
fully saturated air, am the r^ult of sright changes of cemperaturv. He therefore 
would hftve ^ aucfa determinadon made either in m air^vacuum, or over a lo^/^ 
iolution of sulfuric ad<L 

Such dew-forntatioTi| bowereTT c*nnot bappen to any appreciable extent under 
lbs conditioiu makitained in the write r*s work, vit^ absorption within a thick> 
vailed (two-inch) wooden box of the dtroensions given above^ and lunk in the 
ground in a cetlar m which the temperature varies only a few tenths of a degree 
diuing 34 hoiin. The soil layer of one mil 11 meter thickness being put down in 
tlia morning, the 7 hour absorption period falls at the time of slightly rising tem* 
perature, as an addjiional precaution against dew-deposition. MitscberUch fails, 
moreoYer^ to show that this source of error produces any wide or serious dis* 
Cfwpandes £;a.cept under such long absorption periods as he 6nd« it necessary lo 
use because of the gr«at thickness of his soil layers. It is doubtful whether the 
limits of erroni in soil sanipUug do not greatly exceed any of those involved in 
the writerV method, and whether such accuracy as is attempted by MitscherUch la 
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 Joum., 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: 

I. Soils of high hygroscopic power can withdraw from 
moist air enough moisture to be of material help in sustaining 



the life of vegetation in rainless summers, or in time of 
drought. It cannot, however, maintain normal growth, save 
in the case of &omc desert plants. 

2, High moisture-absorption prevents the rapid and undue 
heating of the surface soil to the danger point, and thus often 
saves crops that are lost in soils of low hygroscopic power. 

Capillahy Water. 

The liquid water held in Uie 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 h^t 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,^ 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 

> Simple fts 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 great accuracy. 



months* reaches a maximum height beyond which the hquid 
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 smalt propor- 
tion of clay. The maximum height of capillary rise 
thus far observed, viz, 10,17 f^^^* ^*^s 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, wiiich, like clay, 
remain almost indefinitely suspended in water* But it must be 
remembered that while pure gi^ins 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 

These facts are exemplified and graphically illustrated below. 

The soils selected for this illustration, from California lo- 
calities, are the following: 

No. 2^ J. 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^ 119/. 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 

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 

No. i6gf. Black adobe or clay soil, from the experiment 
station pounds, 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. 









<.2S to 

.5 mm. h.v. 


.5 to 2. mm. 

h. V. 

2.0 to 
64 mm. 

No. 233. Morano sandy soil 

No. 1 197. Gila bottom soU 

No. 198. Ventura silty soil 

No. 1697. Berkeley adobe soil 











The most striking feature in this diagram is the very rapid ^ 
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, i6y2 inches, 
within six days, when the silty Gila soil stood at about double 
that height. 

Ascent of Water in uniform * Sediments, — ^Loughridge has 
ascertained the rate of ascent of uniform sediments of differ- 
ent grain-diameters, with the results shown in the diagram 

^ 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- 

' I. e., uniform between the narrow limits given. 



nter wQI rfw br oi^lkHlf l» 
















'*'/ #f/ 

■tan?.; ; ; ! !^'i ; a t., 

2 ? 

J-w^L -L-L- 'i>/Jr; 1. — ■t:..'J,..,^.J..;^.:..ljil 

! ! i ! ! 

' ^ ■ ■ ' 

., i ;v'^i-{v\j.:7i. 

! Ill { I i l^ll: "^21 >-.'*=,f;^ 

riV fO> 






subjoined, together with the maximum height reached by each. 
The diagram is very eloquently ilhistrative 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 ver>^ great extent the results deduciblc 
from such calculations ; hence the data conveyed by the observ- 
ations of Loughridge must be constdcrcd 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 jMinimum 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.* 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 

> Ad. Mayer (Agficulturchemie z, p. 141) designates Ihks mimmum content of 
liquid water as the " absolute '" water ca)>aintf of the »aine ; but tc b not obviotit 
wherem this factor b better entitled to thb name tban would be the Eoaximum 
(see Wollny's Forsdu, 189^, P» »-)- M. Whitney (Rep. Proceedings Ass*n Agi. Coll* 
ft £xp*t Sl^9^ Hot. 1904} giwee as a new obsenration the fact that In soils ap- 
proaching the drought condition water ** does not obey the ordinary physical laws 
as we recognise them in capillariry." Thii evidently refers simply to the well- 
known phenomenon me:nlJoned above. 



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 

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. 


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. 






Height above Water 

Sandy Soil, 

Sandy Alluvium, 

Adobe, Berkeley. 

47 inches 

42 inches 

36 inches 

30 inches 

24 inches 

18 inches 

12 inches 

6 inches 

3 inches 

X inch 







Since gravity limits the capillary ascent in a progressive ratio, as 
shown in diagram 39, it is obvious that the true maximum saturation 

^ This figure represents only a temporary condition ; the full height of 46 inches 
was not reached until the 195th day. 



can exist only in a very short (strictly speaking, an infinitesimally 
short) vertical column. The least practicable height for experimental 
work being about i cm. (| in.), the writer has adopted for the purpose 
of rapid determination of this factor, the use of a brass cylinder i 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 has 
been struck level, and weighing, it is immersed to i 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 amoimt 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% (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 (WoUny'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 


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.^ 

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 eflfect 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 

^ 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 
maadma given for the same. This discrepancy I am unable to account for. 



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, al the limit of 
a cold zone resulting from the penetration of unseasonable tem- 
perature C^cold snap'') from abo%T, 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- 
laiy movement has ceased. It is^ as it were, dew within the 

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^ 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: 



First 11 inches, day loam , . . ^,* , ., , , , 
Second 1 1 Inches, reddish day . . ,.,,*. 
Z4 to 30 inches, smnd]r day* ........,** 





40 to 43 inches, «and * * 

It is plainly shown here that the roots of clover and corn 
were unable to utilize the higher moisturenrontent 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 Pbjiics 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 fof 
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 

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 ^ 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. X897H58, pp. 65-96. 



Loughridgc 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 crc^ 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. 




Kind of Crop. 

Wh«at . 


Barley.. . ..,. 
Sugar Beet*. 
Vines.. ,., ... 


Apples* >. 


Apricots . I 



OUve». ... 
Peach«9* - 

PruQcs. . .... . 


Citma fruits. 

Kind of Soil. 

Very s^^ndy. , . . 
Sandy loutci , « , 


Clay adobe. ^ . . 
^andy loam. . . 
Black adobe. . 
BUck toam.. . . 

Loam ....*.... 

Sandy loam .. . 
Loam. .... . . . 

Same ^eld. . . . 

Loam , 

Gravelly loam. 
Red loam. . .. . 
H«avy loam... 
Red loa.m. . , , , 
Sandy loam. . . 
Red loam 

Gray loam. 

Sandy loam. 
Sandy soil . . . 

Condition of 



Good ..... 


Very good 


flood * . . . 




Su^Fering. . 
E^xcellcnt. . 
Poor ..... 

Excellent . . 

Poor . » 


Good ..... 

Suffering. . 


Hxceltent. . 
Poor ..... 

Good. ... 

Leafless. .. 

Per cent Mokture in four feet. 














ft. 2 























3-5 ' 














































Free ¥rater in four 
feet of 80U. 

Crops that did well in lowest 
amount of moisture men- 

Crops that suffered in highest 
amount of moisture men- 

Per cent. 

per acre. 

tioned in first column. 

tioned in first column. 

to X.0 

80 { 

Apricots, Olives, Grapes, 

Peaches, Soy-bean. 

Citrus, Pears, Plums, Acacia. 

1.0 to 1.5 


Citrus, Figs. 

Almonds, Apples. 

1.5 to 2. 


Almonds, Plums, Saltbush. 


( 176 
( 200 


2 to 2.5 

Walnuts, Eucalyptus. 


2.5 to 3 



3 to 3-5 



3 to 4 


Hairy Vetch. 


4 to 5 

5 to D 


Wheat, Maize. 


Sugar beets, Sorghum. 

Sugar beeto. 




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- 


2i6 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 loo 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 ^t 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 seepage ^ into the streams and rivers ; or by evaporation. 
The latter agpin 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.^ 

^ 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. 

« 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° ^ in forested areas, against only 60° ^ in the non-forested ; but 


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 oflF 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. 

Washing-away 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 

When these lands were taken into cultivation little or no attention 
was paid to the direction of the furrows and rows of com and cotton ; 

that later, after the soil had been partially saturated, 60% only was absorbed in 
the forested land, against 5° ^ 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 



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 rainsj 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 furrow's, and the 
frir, 40— Tsriismtj ii» Mia»itHf>i« r.vbie Land*, latter Were quicklv deepened and 

cauiifiit tit.'«t ruction nf »erkeilm,ia! \iiluc tmth o[ ^- * » ^ *** ,^ * t t* 

iT,u.a...idV.Jkyv af.Gcc,„th A«^ Repi. Widened mtogulhes^^red washes 
U a, i8<|o^fj — whose presence rendered any 

resumption of cultivation diflficult. 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 

Fici. iQ^.^-Ercraion jti ^flt.%Usippi Tdble Lands, causing destruction of afticuhufaJ Tilue both of 
LfplamdB itid Villey*. ;McG«, uth Ann. Kept. U, S. G. S.» iB(}o-9t j 

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^ 



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 flnding 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 sheep; 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.^ California, eastern Oregon and Washington, and Mon- 
tana, offer 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-off of the water from the 
bare and hard-baked mountain slopes, and then running dry 

1 open Range and Irrigation Fanning. R. H Forbes, in Forester, Nos. 7, 9b 

220 SOILS. 

within a short time, so as not even to afford drinking water to 
pasturing cattle in snmmer. 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 front 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," t. 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 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-sixes; because measurably in- 
dependent of the physical changes that almost unavoidably ac- 
company I he percolation of water from alwve downward ; 
whether such water comes in the form of rain, or irrigation, 
or even when applied w ith the utmost precautions in the labor- 
atory. The ** lieating** 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 

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, — ^Wlien water is al- 

1 Thti effect U wdl lU nitrated by the behai^or of a dry brick bud upon ft irel 
tpcpnge. Tt win qtikkly absorb all the liquid molstttre conuiixed in the latter, 
while Ehe apongc will be wboUf uttmble to lake anj moist u/e from a fully-soaked 

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 g^ven below, which embodies the observations made by 
Mr. A. V. Stubenrauch ^ in connection with a more extended 

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 lOO 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 i^ 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 eflfect of hy- 
^ Kep't Calif. Exp't Station for 1898 to 1901, p. 165. 



BlMk Adobe, 



Sandy Soil, 









d J ^'. 

t\ 80 

as 5 

30 )0»e^ 14 

49 84 



95 35 18 '.i^-yV^ 




31 ik 


61 53 

81 ^^'!^«^A*L^ 
HI 30 88 

ff3 42 


10 45 
13 54 

18 13 ^ '^t *• 

44 41 18 

5ri8^ iQ 18 
58 30 30 

85 Ol--^ 31 

-^k 8 



85 ^^i^ 78 59 





I a 

8 38 
5 48 

5 15 

II 7 
13 55 
n 7 
10 85 
15 Jl 

38 88 
41 85 

48 55 


81 15 
61 81 

56 15 

Jte 4i.^DiMgnun aborning Affereoott In ntes ol pcttcAaAiQA tVittraiiXv 

vAii&A^ 4% 




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 : 


Diameter of Uniform Sand 

30 minutes 

30 minutes. 

in one hour. 

.475 mm. 
.083 " 









First 21- 
23 hours. 

First 10 


Second lo 


Total in 


505 hours. 

Sandv loam 


2.1 X 



Clay ' loam 




This table is very instructive in showing the great difference 
in the rapidity of percolation in materials of uniform, evcn- 
sized g^rains, as compared with such as contain particles of 
many different sizes, in which tlie interspaces of the larger ones 
are filled more or less closely by the smaller sizes of particles 
(see chapter y, 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 artifidal 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 sue- 


226 SOILS. 

cessive intervals, as derived from the observation of the water 
levels in the several holes.^ 

Fig. 4a.— Percolation in clay land after heavyrain. 

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 leveb 
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 i ; 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 imdersaturation 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. 

* The exact record of these observations was unfortunately destroyed by fire 
the soil was a heavy day, and it took ten days before the water disappeared from 
the lowest hole. 



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." ^ 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 arc 
frequent or much prolonged, one half and even more may 
finally reach the permanent level ; runoff and evaporation dis- 
posing of the balance. 

LysimeUrs, — For the determiiiation 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 

> In contradistinction to other levels or " streams *• of water which may usuatly 
be found lower down, separated from the first water by some impenrious stratum 
of clay, hardpan or rock, and very commonly under sufficient pressure to rise 
s -unewhat higher than the point at which it was struck, owing to connection with 
V.ichcr-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 

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 ^ 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 
II, 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 

* Physics of Agriculture, p. 270. 



depths are only exceptionally used, partly because the laying^ 
of drains then becomes too expensive, 

A mass of four feet of cby*loani 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 samly 
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 extraordinar}^ 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, 

Rfsen^e of Capillary IVater. — It must be remembered that it 
is not only, nor usually, the bottom water that supplies 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 uix)n the moisture within their immediate reach for 
the purpose of leaf evaporation. This fact can be plainly ob- 



served in the arid r^ion, 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 

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 oflf 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, 6i, 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 df the gradual rise of the seepage water in the 



substrata, until finally it may come to within a few feet of, or 
actually to the surface. 

Consequences of the Swamping 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 fomiation 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- 
burettcd 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 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. 

WATER OF SOILS (Continued). 


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 

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: 



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 

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, 

236 SOILS. 

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 
Aood-waters to saturate the land is therefore in many cases the 
saving clause for a dry season. 


The manner in which irrigfation 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 

The following methods are in use to a greater or less ex- 

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 gf 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. 



Surface Sprinkling. — This method seems to be the closest 
tmttation of the natural rainfall; and yet it is in practice about 
the most wasteful and least satisfactory of all It is difficult of 
appHcation 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 spent 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 
w^ater 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 w^ater, 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 flooding 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 tillagt? 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 ^ shows the manner in which water 
sinks and spreads from furrows of various depths and widths, 

1 Published by pennission of the Department. 




fyrrow9 6 jud^a dlm^ m 








te / 


















































f / 





























































e^^ "^^Z ^-cww ^<^^ 





^-±g.-% Mf iij'^ J^^_ ^^J 


I n 














^— F 





.«i, J 










-^ ^ 



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 



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 fertili2ation 
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 side wise 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 mare pronounced than in the shallow fur- 
row alongside. 

Distance Between Furrows and Ditches. — The distance be- 

tw^een 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 



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 ^ 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. 

^ 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. )I77. 



Basin IrrigaliofL — ^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 tiody 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, 
arc made to supply themselves with moisture, without irri ga- 
llon, by opening around them large, funnel-shaped pits, which 
remain open in winter so as to catch the rain, causing it to 
penetrate downw^ard 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 
w^ells, 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 sticcessfully grown 
excellent fruit for years, on land that would originally grow 
nothing but cactus* SuVirrigation from pipes has been applied 
in a similar manner. 

A combination of the furrow- and basin-trrigation 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.^ 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 g^ven 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 
com 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 

^ See below, chap. 17. 


the proper exercise of the root-functions, and that the roots 
existing there are either inactive or diseased. That in such 
cases freciuent 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-focnl. 
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 *' citnis 
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 by 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 pii)es, as compared with earth 
ditches, if additionally combined with its application to in- 
dividual trees or vines, presents the maximum of economy 
that can l>e effected. The actual use of this method is unf<:)r- 
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 ami orchard, whatever may 
be the material used for the main conduits. 'ITie use of concrete and 
tile in small size?» proves in the end very- expensive, l)ecause <>f frecpient 

246 SOILS. 

breakage, and leakage due to varying pressure in the supply pipes or 
reser\oirs ; 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 reich 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. 


Saline J Voters. — 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 eflfects of the use of saline irrigation water (containing 
in this case about 100 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. 

Liinits of Salijiity. — It is not easy to assign a definite limit 
of mineral content beyond which water should be considered 
unfit for irrigation purjK>ses: ])artly because of the differences 
in the kind of the mineral salts, pnrtly because the nature of 
the soil and the amount of water at command, materially in- 
fluence its availabilitv. 










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 ^ 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 R^oin^ as hi^li as 8000 parts 
per million, or 214 grains per gallon. The cultivat(^rs arc 
said to he 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 Hull. No. 21, Bureau of Soils ; also circular N'o. lo, \\y\i\. 



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 ezvporation. It is clear that when such waters are used 
sparingly, ^o 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 

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. When this is not the case, c. g,, 
in clay or adobe soils, or in those underlaid by hardpan, waters 
wliich 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 diflFicultly permeable ones, 
their use may be either wholly impracticable, or subject to 
very close limitation. 

Sranetimes the alternate use of pure and salt-charged water 
serves to eke out a too scant supply of the former. But in 



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. 
Ai^ain, 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 Bull. Ariz. Exp't Sta. No. 44. 



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.^ 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 regpions, 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, 58. 

252 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. 10, 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 ; ^2 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 irri^^^ator 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, /. c, 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. 



That this will not happen when the head ditches are nearer 
together^ is shown in the lower diagram. 


FiOh ^ 4 j«-*DUcmDi aHowIcix \om by percoktiDii when had dSiclwt^ ate t«» br apftit. 

The means of avoiding the mechanical losses have already 
been discussed, and may be siummarized thus: tightening of 
leaky ditches; use of water in deep furrows; and ascertaining 
Uie rapidity of percolation (see p. 242) so as to obtain a 
proper gauge for the time during which water ifihould run, and 
for the distances at which head ditches or furrows should be 

The importance of thus diminishing the losses of water is 
obvious when it is considered that if the duty of water can l>e 
reduced to twenty instead of forty or fifty acre-inches, twice 
the area can he irrigated with the same amount of water, or 
the cost of water correspontlingly reduced. It should be noted 
that when the land is leachy it may be pure waste to continue 
the Row beyond a few hours; hut tlie irrigation must then be 
more frequently repeated. 


Alongside of and supplementary to the best possible utiliza- 
tion of the rainfall anrl irrigarion water, the prevention of un- 
necessary' evap<^>ration has to be considered. Evaporation 
from the soil's surface implies not only unnecessary loss of 
w atcr 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 ^ 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 




Temperature of water. 

Degrees Fahrenheit 










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) : 














Totals for year. . . 

Aug. 1903 
Feb. 1904 



July 1903 
Jan. 1904 


July 1903 
Jan. 1904 


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 13^ Fahr. 
in winter to 120® 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 



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. 



Rothamsted, England 

London, " 

Oxford, " 

Munich, Germany 

Emdrup, Denmark 

Cambridge, Massachusetts 

Syracuse, New York 

Logan, Utah 

Tucson, Arizona 

Fort Collins, Colorado 

Fort Bliss, Texas 

San Francisco, California. . . 

Sweetwater Reservoir, San Diego, California. 

Peking, China 

Deiiierara, South America 

Bombay, Fast India 

Petro-Alexandrowsk, West Turkestan 

Kimberley, South AJfrica 

Alice Springs, South Australia 

This table, the data for which are taken from various 
sources, exhibits clearly the enormous variations in evapora- 
tion in (Hffcrent countries, and even in localities not very re- 
mote from each other. Tlie 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 witli Oxford. Tropical Demerara stands nearest to 
Oxford in its evaporation ; Bombay indicates its location on 



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 Resenvtrs 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 by 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 60°, was found 
to be ^)i 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. 

Prei'cntion 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 

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. ii). 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 

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 



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. Loughridge* 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 : 




Depth in soil 

Per cent 

Tons per 

Per cent. 

Tons per 

First toot 










Second foot 

Third foot 



Fourth foot 

Fifth foot 


Sixth foot 

Total for six foot 



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. Su. for 1897-98, p. 65. 







' JjU 



H^^^Ph w 






^1^^ J^H^^^ * ^^^^£ ^L 



*^^^^B i^^ii ^^^^B* ^^^V^_^ 



^^^^U^^I^H ^l^^^^l^k 





. w 



trm. n^Hcw Gcmtli and irritft M Tw**, CnJiiwud 

Cr»^ Bead] Laud 


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. 


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, ii) 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 

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 


field crops, to correspond most nearly so the observationB 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 looo 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 ofT 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 iii) 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 tlie dry season begins. The 
same objection holds against the growing of summer crops 
between the orchard-rows. 


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 sliallowness of tlie 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; 


and where surface roots are few or absent it may readily hap- 
pen that the surface soil is moister than the subsoil. 

Thm was very strikingly showa by the iftvestigations of Ototzky in 
tiie South- Russian steppes, in com paring both the moisture contents and 
the depth of bottom water as between forest land and the open plains. 
Ofi the steppe near Chipoff, Government of Voronej, he found the 
ground water at from 3 to 5 meters (to-t6 feet) depth ; under the forest 
in the sarae re^on and in identical underground formations, the water 
level stood at 15 meters* In the Black Forest near ChersoUi the water 
is found at about 15 feet beneath the surface ; under the steppe and in 
cultivated ground it stood at lo 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 i under which, moreovcri 
there were few shallow rooted plants to draw upon the moisture of the 
surface soil. 

The great evaporation froin 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 lari^e scale, e. ^,, in 
the use of the eucalyptus in the Pontine Marshes of Italy, and 
of the maritime pine in the t^ndes 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 
dilFence 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 re<luce 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. 




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.* 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 arc 
often required to remove all the soluble matter thus "ad- 
sorbed." „ 

Decolorizing 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- 

^ In mamy cases this decrease of salinity is probably doe to a slow influx of frsih 
water from landward ; bat very often it cannot be thus explained. 


268 SOILS. 

ever, by the extraction of these earthy particles (calcic carbon- 
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 

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- 

Thus when a very dilute (^ 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 



aitDeml ingredients from sclutiafi, and retaming them In such manner 
AS to be readily available to plant growtk (See chap. B, p. 1 34.} 

In view of the almost in variable conjunction of physical and 
chemical effects, it may be fairly said that no soUition, at least 
of mineral salts, can pass through the soil without being 
changed in its concentration and chemical composition. It is 
sometimes difhcult to decide to wirich 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 
decolorizalion 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 ]mss 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 wdls from 
the surface-drainage from barnyard or house refuse. Even if 
fissures or layers of sand or gravel should not inter^^ene 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, 

IVasie of Feriilizers. — The same, of course, holds true iii 
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 
waslied through into the country drainage by the rains. More- 

270 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 

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 



and ammonia among the bases, and phosphoric actd among the 

Thus (as stated above) when a weak (one or two per cent) 
solution of potassic chtorid 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 ingre<li- 
ents will be retained* A solution of g>'psum (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 «irth-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- 
d rains, 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 

272 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. 


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 



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 
t^ absorption and oxidation, ammonia and carbonic gas alone 
tiltimately 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 lodid) solution. 

274 SOILS. 

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. (2 i8°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. 



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.— Abaorption of Carbonic and Amraoab Cues 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- 

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. 


In 1864 and 1865 Reichardt and Blumtritt ^ 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 : 

^ Journal fiir praktische Chemie, Vol. 98, p. 167. 



Ckuee«], coii&f«rou» air dry .,...».. ^ .,, , 

" inoutci»<| wnd ^r-dffwL «..*.,,..« ^^ , 

" Lciabafdy Pophkr.**,.^ , 

Peat ..,>.,..,.,.„,„., , 

G»rdcD Etnh, inout , 


ttiwwT Silt, atr^ried 

" " •IwhUr moJ4t«i»d ,,..., 

" ■Irdritrd ,.....< 

Clay* loni fxpoKd . . « ^ . ^ ^ , ^ »..,.,, , 

*' iJiWntljr >TtDi>ren«d. «>.,,< ..^^ir.. 

Ftfrk: Hydnie, cam menial,, ^,« .* ....*.***, 
"^ " frcihljT pradpilitcd, alr-drM 

Oud, Jftilu^ ,...., 

Alvminic Hydnic, air-dried '..*...,........, 

'' diiftdaliw^ .,„,,= 

Preparad ChaLlit t3^-6s. . , , 

iKj - 

C^de Cmrbonau, prcdpiuted. 1864-4] ....... 

" 1B61-66 

Harnciik Carbonate -..,*. ^ . h ..»., h 

GfpBum, iiDtly powdCtW. .i.. ........ .......d 








41 4M 



■9} 4 




Si a 



iw tol^t fat co«ula*d 

44 44 

64 ?* 



74 4^ 
Bo 8i 
77 57 
*J *» 

■ «| 

a 04 

* p» 
4 7* 
6. 14 


l| ♦<» 
19 f9 



il Ai 
^ 5^ 

14 M 

«9 ^ 
1 7> 







Discussion of the Table, — It will be obscnrcd 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 
soib (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 soib. It 
will, however, be noted that in the garden soil, also, the proportion of 
carbonic gas is very large, while diat 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 

278 SOILS. 

charcoal and of calcic carbonate (whiting), the gas was foond 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 



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; ^ 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 

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 compotition of atmospheric air is giren on p. 16, chap. 2. 

28o 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 sulfids; 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 

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 



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* 
St rated 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 cart)onic gas, besides 
what may be contained in the condensed form* we may con- 
clude that this gas is formed within them with considerable 
rapidity i for otherw^ise, 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 Activiiym 
— It has been fully demonstrated by the researches of Koch, 
MiqueU Adametz, Fuellcs, WoUny and others, that tlie 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). 



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 diarac- 
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- 


284 S^^^- 

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. 

WoUny (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 



will generally show that from some cause, such white lands 
have been subjected to the watery macerattoti 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 prevaiK 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 feldspathie 
rocks (sec chap, 3, p. 32), although they may be poorer in 
potash than the latter 

But the red lint 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." 

IVhite soils, or more properly those having very light gray 
tints, are not usually looked upon with fav^or, especially in the 
humid region. The causes of the unfavorable judgment cur- 
rent among farmers in respect to white soils has already l>een 
partially explained in the discussion of the black and red tints. 
The light color means the scarcity or absence of lH>th 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. io» 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. 
^3S)> ^he 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- 

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). 



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 l>een 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 studieSp it becomes necessary to introduce^ 
first, a summary* consideration of the subject of chmate. 

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 slates 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 


288 SOILS. 

the result of heat conditions, it is proper to discuss from the 
outset the origin and mode of action of heat. 


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 low 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-Conditions, 
— 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 ? 



The Annual Mean Temperature not a Good Criteriim. — 
Since one and the same figure may result equally from the 
averapng 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 temi>erature of 60^ F. might re- 
stiU; 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 diflferent. 

Extremes of Temperature are Most Important, — It is, on 
the contrar)% 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, 
tliat 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 conipari' 
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. 

Scasanat 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* 
dcrstanding, 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 Catifomia, it becomes neces- 
sary for practical purposes to regard the ** season," and not 


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 arc 
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. 


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 oflF 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. 
Hence grain is always sown there in spring only. 

These examples may suffice to show that summary state- 



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. 


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,* 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 

I 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 
idr 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 breeies 
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. 



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, arc 
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 " ^ 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. 



of a clock, and commonly produce rain in their east portion, 
A high-pressure wave or center, from which the atr naturally 
flows toward the ouiside, 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- 
cast (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 appH- 
cation of the general rules. 

In the southern hemisphere, the air*movements substantially 
correspond to those obser\'ed in the northern, so far as not 
modified by mountain chains; as is especially the case in South 


Rains to Windward 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 tlie 
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. Tlie 



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 

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 

Fio. 5a.~Coniposite Cunre showing distribution of Rainfall in Europe, Africa and America pro- 
jected on too 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," ^ 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 

^ " The Evolution of Climates"; by Manden Manson, July, 1903; also j4mtr 
Geologist^ Aug.-Oct. 1897. 



dO^EiL.; the west coasts of Europe and Africa; the 30th 
mefidian WX*, in the Atlantic Ocean; and the west coasts of 
North and South America, projected on the plane of the looth 
meridian WX. Tlie latter curve corresponds with remarkable 
closeness to the mean curve here g^iven. ** 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 cast 
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 ratn-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-bclts. 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 genera! above. But as water 
warms so much more slowly than air, its ciroilation would he 
comparatively insensible were tt 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 airrent 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 

296 SOILS. 

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 diflfer- 
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 oflF 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 oflf 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 diflfer by only a few 
degrees, viz., 15.5 and 13.0° C. (60 and 56^ R); so that a 
change of clothing from season to season is hardly called for. 
The Alaska Current leaves the immediate coast of California 



off Pt. Conception near Santa Barbara, gradually losing it- 
self south westward^ 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 loo*^ 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 cloud s, 
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- 

298 SOILS. 

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 v^etation 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 

CUMATE. 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. J 

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- 

Utilisation 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- 



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 

' See Rept. of the U. S. Commissioner of Agriculture for 1878, pp. 486-488 ; 
Bull. Nos. t6 and 42, Wjoming Expt. Station ; Bull. No. 150 Calif. Expt Station; 
Ball. No. 51. Nevada Expt. Station ; South Dakota Station Bulletins Not. 40^ 69^ 
70,74; Kansas Expt. Station, Bulletin No. 102; New Mexico Expt Station, 
Bulletin No. 18 ; Montana Expt Station, Bulletin No. jo ; and otheis. 



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 d^ree 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. 

Water 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 at>out 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 soiMemperature is largely 
dependent upon the control of the water-content of the same, 
which has been discussed in a former chapter^ Even in the 




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 be as great 
as that of the entire soil mass. This consideration emphasizes 
the importance of such control. 

Cold and Warm Rains, — 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 v^etative 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 Sun's 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, 



reach to greater depths; while the annual variations do not 
disappear in the temperate zone, e. g., 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 : Ayermge temperature. Annual range. 

3.25 7.2**C. lo.^'C. 

15.6 iSi'C. 4'fC, 

30^ 16.4 C. i.3**C. 

75^ 17X) C. ao®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. (19° F.) ; at 145 feet— 5** Cent. (23 ** 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 
ICG. 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 Low 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 



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 soiU 
whose smooth surface wouJd waste less of the heat received 
by radiation. 

King has caHed special attention to the dtiTerence of temperatuft 
existing between soils smoothed and compacted by a roller^ and the 
ynrolled soil having a loose surface. He found that the former at a 
depth of one and a half inches was as much as 5.5^0* (lo^F,) warmer 
than the loose soil, and that even at a depth of three inches a difference 
as high as 5.5 °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 
dilferences observed in the soit itself. But at night the heat is given 
out more rapidly from the rolled than from the unrolled suriace, the 
latter acting as a non-cotiductor and keeping the soil wanner than that 
of the more compact rolled landi King gives as the average di^erence 
observed between rolled and unrolled land on eight Wisconsin fanns^ 
i.6°C. (3**F.) in favor of the rolled land between i 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 Uie 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. 

InAuence of a Covering of Vegeiaiion, and of Mukhes. — 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 (i-5 degrees ¥.), 
and are mostly lielow .50° C. (i^ F.), btit during different 
parts of the day they may rise to 2,2 to 2.5** C (4 to 4.5® F.), 
at 4 inches depth, Tn 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 

3o6 SOILS. 

the greatest cooling influence upon the soil, and next to these 
the dense herbaceous crops, such as clover, and the legumes 

InAuence 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. 



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 stunmary 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 Dew. — ^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 ^ 
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 SoUs," pp. 175-189^ 

308 SOILS. 

Dew 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 tnie 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. 

Dew within 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 



the soil, e. g., at night, dew must be deposited within the $oU 
down to the depth to which the nightly variation reaches, in* 
creasing at that depth as the vapor from the wanner 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*con tents, 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 captllartty in 
effecting a measurably uniform vertical distribution of mois- 
ture. (See also page 207, chapter 11), 

Plant'development under different Temperature — Condi- 
Hans, — 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 v^etable functions, 
in ground soaked with water practically ice^rold* 

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- 



low which most cultivated plants may be considered as remain- 
ing practically inactive lies between 4.4 and 7.2^ C. (40 and 
45° R). Few tropical plants will germinate much below 
23.8° (75** F.) and in some cases not below 35** Cent. (95® 
F.). Even maize and pumpkins, according to Haberlandt, 
germinate most rapidly between 35 and 38.3° C. (95 and loi® 
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 17.5° C. (63® to 63.5®), 
it took a full week for germination when the temperature was 
only 5° C (41° 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 

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 23.8^0. 
(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. (55° 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 





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. 


While the obvious importance of the physical soil-conditions 
has long ago rendered them subjects of close study by Schiib- 
ler ^ 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 phjrsics, published at Leipzig in i8j8 
under the title of " Gnindsatze der Agrikulturchemie "and now almost inaccessible 
outside of old libraries, b remarkable as baring anticipated very definitely much 
that has since been brought forward and elaborated anew. He b really the father 
of agricultural physics. 




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 long-leaf pine uplands of the Cotton States, the scattered 
settlements have fully demonstrated that after two or three years crop- 
ping with com, 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 superadded, 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 



recognize the causes oi 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 
saHent 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 fanners and settlers, should not be 
traceable to definite physical and chemical diff'erences 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 " 



as xeroph)rtic, 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. ^ 

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 
r^arded 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 

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. 



virgin soils were ^sily 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 
v^etation 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 geoktgical 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 
w*ith others that have already fallen under cultural experience, 



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 Soil- 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 



kqit in view. The former interests vitally the permanent 
settler or farmer; the latter concerns the immediate outlook 
far crop production, the ** Diingerjsustand '* 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. 


While it is true that plants cannot form their substance or 
develop heahhy 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 3ind 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 be ghen to the ascertainmeni of the proper phy- 
sical conditions in the soil, subsoil and substrata. Without 
these, oftentimes, no amount of cultivation, fertilization and 
irrigation is eflfective 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 nfater*soluhle 
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 tatter in saline and alkali 
lands. Furthermore, substances in that form would be verv 



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 znrtually 
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 reserve food-store may then be placed under the fol- 
lowing heads: 

Hydrous or *' seolitic " silicates, from which dilute acids 
can take up the bases potash, soda, lime and mag^nesia. These 
silicates may be in either the gelatinous or powdery form; in 
the former case they may also occlude water-soluble sub* 

Carbonates of lime and magnesia, which are readily dis- 
solved by carbonated water as well as by the vegetable acids* 

Pkosphates 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.* 

> Whitnej (Bull. t% U. S, Buresiu of SotU| dmims «n the ba^u of a Urge it amber 
of (three- minute) extr^ictioni of toils made with dUtiUed water, that these s^Iutiofia 
are eaaentiallj of the iame compost don in all ftoilj ^ that all Hoili contain enough 
plant-food to produce crops inde&mtely i and thai the difiefeocci m production 




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 r^ions 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.^ 

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 b the active solvent surrounding the plant root. 
1 See Appendix B. 



IS that of the reaction of the soil on litmus or other test paper, 
to ascertain its acid, neutral or alkaline reaction. Shoulil 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, 
pag« 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, vii*, 
the insotuble or unavailable, wholly undecomposed rock fnine- 
rals; the *' reserve^'* consisting of compounds not soluble in 
water but soluble in or decomposable by w^eak acids; and the 
water-solubU 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 immetliately 
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.* 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 
tlie plant 'food in the soil-material upon which these processes 

1 The Invesdgatioiii of Kinf (On the Influence of Soil M.anftge£nent upon the 
Water Sottible Solu in Soib and the Yield of Crops, MAdUon^ 1903) mhow that frofn 
iome iolU ftt tesist, a sufilclenei' of plant -food mgredienta for a season's crop tnajr 
be dts^toWed by db lilted water alone^ if the sol] be repeatedly leeched and dried 
ft! I to^, W^b ether such « supply caa b« expected under field co&dilioiUf remalat 
to be tctled. 



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 water- 
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 

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 



arc partly or wholly due to other causes than those purposely 
supplied by the experimenter. 

Anafysu 0/ CulHvakd S^ih. — It is also clear that in view of the in* 
evilable 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 allj viz., the investi- 
gation of soih long cultivated and manured ; lands which, having been 
subject peihaps for centuries to a great and wholly indefinite variety of 
crops and cultural practices, had thereby t>ecome so beset with artificial 
conditions that without a previous knowledge of what constitutes the 
normal rdginie in natural soils, the conelation of their chemical const!- 
tion, as ascertainable by our present methods, with their productioo 
iin let 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- (ood ingredients withdrawn from soils by cultivation could not be 
detected by quantitative analysis, numerous examples have shown thai 
with our present more delicate methods this can in most cases be done, 
though not always after a single year's crop. 

Mith^ds of S&ii 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, WTien 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 xeolitic '* reserve," 
and the water-soluble portion- It was early recognised that the results 
of such analyses bear no intelligible relation to the productive capacity 
of soils ; for pulverised 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 car 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* 

326 SOILS. 

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 



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 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: 



Potash (KiO) 

Soda (Na»0) 

Lime (CaO) 

Magnesia (MgO) 

Peroxid of Iron (FeiOi)... 

Alumina (AliOi) 

Phosphoric acid (PtO») . . . . 

Sulfuric acid (SO») 

Chlorid of Sodium (NaO) 







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 ^ and by Schultze;* their general con- 
clusions have quite lately been corroborated by King,' 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. 


Total matter 

Organic and 



First extract 










Second do. ... 

Third do 

Fourth do 


Fifth do 

Sixth do 




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. • Ibid. VI. p. 411. 

• Proc. Ass'n Prom. Agr. Sci. 1904. 


^m general to these from the Bonn soil, in the previous table. ^^| 
^M From a poorer soil similarly treated by Ulbricht, described by ^^M 
^B him as a ferruginous sand from Dahme, the leaching of which ^^H 
^M was continued for thirty days in periods of three days each. ^^H 
^1 with a total of forty times its weight of water, the results ^^M 
^m were as follows : ^^| 







Sbclh H 

^^H pjntf^^l*! 















■ Soda 

^M 1 tmt 

^H M^gn^jA........ 

^H Phosphoric acid.... „.., . 
H Total! 

^m It will be seen that there is a considerable dtflference both in ^H 
^m the total amounts of matters dissolved and in the phosphoric ^H 
^1 acid taken out by the water, as compared with the rich soil ^^| 
^M treated by Schultze, The uniformity of the amounts of ^^M 
^M potash removed at the successive leachings is remarkable. ^^| 

^M King^s Results. — The same general features are again strik- ^^H 
^B ingly illustrated by King's results, as given in the following ^^| 
^1 table. King s first leachings were always made by shaking up ^^| 
^m the soil with ten times its dry weight of water for three ^^H 
^1 minutes, then after subsidence BItering the solutions through ^^| 
^m a Chamberland (porcelain biscuit) filter, and then (without ^^H 
^M evaporation) determining the ingredients dissolved, by very ^^H 
^1 delicate, mostly colorimetric methods* Subsequent leachings ^^| 
^M were made by packing the soil around the Alters and washing ^^| 
^ft with five times the weight of water, taking about fifteen ^^| 
^M minutes each time; but drying the soil at 120 degrees C ^^| 
^B between successive teachings, ^^M 



By F. H. ring. 















Sassafras sandy j i eztractioB 
soil. ( II extractions 

Norfolk, North j i extraction 
CaroUnasandYSoil( ii extractions 









































JaaesvUle, Wis.( 1 extraction 

Hacerst^wn, Pa. ( 1 extraction 
Clay loam. ( 1 1 extractions 






5$. 10 






1 ISO. 30 

































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.^ 
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 

t Bulletin No. 22. Bureau of Soils, U. S. D. A. 


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 JaneszHUe 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. 

Z4?am Soil from JanewiUe^ Wisconsin; 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 1 10^ C, consisted of 


Insoluble matter ^35 

Soluble silica. loSo 

Potash (KO.) CO 

Soda (Na«0) J04 

Lime (CaO) ^3 

Magnesia (MgO) 51 

Br. ox. of Manganese (MnaO«) xA 

Peroxid of Iron (FeiOa 3.60 

Alumina (AUOa) 5.26 

Phosphoric add (PtO,) X)6 

Sulfuric acid (SOt) 10 

Water and organic matter 8.72 

Total I0(X03 

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. 199 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 compariaoQ 
for 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.^ He found in the case of a num- 
ber of soils investigated by him that the amount of phosphoric 
acid P2OS 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 

^ Ann. de U Sd. Agron., 2de serie tome i, pp. 41^349; iS99> 



is assuined to be thus demonstrable by many French chemists. 
Moreover, a number of King's resuhs, tabulated in curves^ 
exhibit a remarkable general parallelism of the curves showing 
totals of plant-food extracted by water, and actual crop prL*- 
duct ion. 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 soiUsolution 
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* 




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 product iveness, 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 pi ant- food so small as to be beyond the 1 units 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 arc 
not absolute. Thus a dressing of 150 lbs. of Chile saltpeter, 
containing only ab*3ut 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 
ivould have been harvested; provided, that all the other re- 
quisite ingredients w^ere 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 add actually 



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 




Chite Saltpeter. 

P + N 



P + K 

Super plM lepiiate 

aiMl sulfate of 


P + N-hK 


Chile Saltpeter and 

SttlfMa ol Potash. 

K + N 

Salfate of Potash 
aod Nilrogea. 


Thoasaa Pho^hate 

Scheme for Plot-tests of Fertilixers. 

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 far 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- 


suits tlius obtained arc 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 I he 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 catried to an extreme by the LT. 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 siie, 
in which the soil to be tested is sown with seeds which are allowed to 
develop only for three to iive weeks ; it being claimed th^t the devel- 
opment occurring during that time is quite sufficient to indicate what 
will be the ultimate outcome in crop production. But pntctical ex- 
pericncc 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 gi?e 
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. 


Testing chemical saU'Ckaracter by crop analysis, — Another 
method for the determination of immediate soil requirements 
has been elaborated by E. Godlewski** 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 
I Zdtschn Ixddw* Vtn, O&tvn^ 1901. 

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 

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 


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. 



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 '* Diingerzustand " 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, 

Loughridge's Investigation, — Systematic work on these 
points was undertaken, at his suggestion, by Dr. R. H. Lough- 
ridge in 1 87 1 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 



H^ valley of the Mississippi river, and known locally as the ^^M 
^M ** Table lands : '' a noted cotton-producing upland region. The ^^H 
^M brown or yellow, moderately clayey loam is of great uni- ^^H 
^M formity throughout its region of occurrence, and is evidently ^^H 
^1 derived from such widely-spread sources that it represents no ^^H 
^M special rock or complex of rocks. Its natural growth is a mix- ^^H 
^M ture of oaks and hickories, strong and well-developed trees, ^^| 
^M such as any land*secker would at once approve for settlement. ^^B 
^1 Its cotton product when fresh was a 4CN>poutid bale of cotton ^^M 
^m lint per acre. It may therefore well be considered a typical ^^| 
^M generalized soil of the humid upland of the Mississippi valley. ^^M 
^M Its physical analysis is given in chapter 6, it being No. 219 ^H 
^1 of the table on p. 98* ^H 
^m Sirengih of Acid used, — Three different strengths of acid ^^| 
^m were simultaneously employed, viz., chlorhydric of, ^^H 
H I.I 15 and L160 density. With these the soil was digested at ^^M 
^M steam heat in porcelain beakers covered with watch glasses for ^^| 
^m five days each, then evaporated and analyzed as usual The ^^| 
^M results were as follows: ^^| 


^^ lAgfe4i«nts. 

Sp. G. of Add ^^M 

1. 10 



IiuioEtihle rcstdue* . .....<-...,...*»... 









^!ti^i! sain. ...,...*....,.. 

Potoih....- ,-...„- ..,„ 

Soda... » 


MagntBia .,. 

Ferric Chiid..... ...,.,.,.-.... .--... 

Alumitw..... ..g.... ..,..***«•. 

SitH uric add *........ • * • * 

Volidl« nijitier* ............... i....» - . 

Amottfil of tolublt matter. ...•.■.*.«»» 

Amount of ftolubJe bases . ........*...# 

It will be noted that the strongest add produced the smallest ^^H 
amount of decomposition of the soil silicates, e, g. the silica ^^H 
soluble in carlwnate of soda solution being 3% less than in the ^^H 

~— 1 



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.I 15 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- 



No. of Days' Digestion. 


Insoluble Residue 

Soluble Silica 





Br. Ox. Manganese 

Ferric Oxid 


Phosphoric acid 

Sulfuric acid 

Votatile matter 


Amount of soluble matter 
Amount of soluble bases.. 






5.1 5 






II. 18 


































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 



writer for his work; and it. together with the arid 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>extra€lion suggested by Kedzie and since adopted by the 
Association of Official Agricuhural 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,^ 

yirgin Soils with High Plant-food Percentages are Always 
Productiir. — 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 shonnng high ffercentages of ^/fltii- 
food as ascertained by extraction unih 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. 

Disttission of Table^ — It will be noted in this table that while 
the total of the matters soluble in adds (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 

* While fcgretting to t!iu» *■ cec^e " ftom the fellowship af hi* coUeafueA^ th« 
writer cannot but regret eqiully their volunta^ry decision to do over ftgun, or 
Ggfatli reject, mlX that h*d beeft done befon: in correcting soil composition »a4 
pUnt^rowth. He still thinks thai it is idle to expect mny unilicatiom natiofiAl or 
InCema^donaifOf methods of soU analytis based upon purely arbitrmry prescriptioii«, 
snleai prcTiou^ly sihown to be definitely correUted with natural aikd cdlu^ coih 
ditlont ; la U measurably tlie ease witb Dyer*t method. 













o e . 

g.p> 8>, 

S 6 S 2:5 I 

>s o <« a ^ 



a S c o 

i -9a 8 

•A O M OO O C" JftOO 00 lA >• 00 O 

• irt •• M (« <o m 

oo«p romrtoe M O minw 
•^K o - r>o5 Q >: ^ *: (<! 

<> K •■ m roO ■• 00 tn ro q 

i 1 


: : : :iSS^t^5 



a— ® . 



thousands of crop years. For, one*lenth of one per cent in 
the case of the clayey soils of the preceding table would atnoimt 
to abiiut 3500 pounds per acre- foot, and to 4000 in the case of 
ilic sandy ones. Hence the amount of phosphoric acid in c. g., 
the Mississippi delta soil from Houma would suflfice 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 
nmis of grain easily i>cnetrate to twice and half and three 
times that depth even in the humid region, the number might 
Ik tripled. As a matter of fact, however, that soil has prcH 
duced full cn>ps for from forty to fifty years only; yet this is 
considered an exceptionally long duration of profitable pro- 
duction without fertilization* 

The firat aad last soils in the above list represent probably the highest 
tyf^»es of productiveness known. The Yanoo bottom soil has produced 
up to oae thousand pounds of cotton lint per acre when £resh, and li 
still pro<^Jucing from four to five hundred pounds after thirty years' 
culiurc. The Arroyo Grande soil of California with its extraordinary 
percentages of phosphoric acid and nitrogen, as well as exceptionally 
high projjortion 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 
priies 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 limeHrontent. The remarkably high 
content of acid-soluble silica, indicating the presence of much easily 
available rcolitic matter, is doubtless connected with the exceptional 

Experience, then, proves that lands showing such high 
plant'food percentages will yield profitable harvests for a long 
time without fertilisation, or with only such partial returns 
as arc afforded by the offal of crops. Also that when fertiliza- 
tion comes to he required, instead of supplying all the ingre- 
dients usually constituting fertilizers, only one or two of these 
wnll as a rule be actually neetled, and even these in smaller 

^The Rio Gimnde and Colomdo bottom ftoU» conl^n amoiinls of lime carbonate 
Uf]ge1y in excess of reqmrenienu» 2 to f\<j/l that compoufid being all that h 
needed to instira all the advantageou* effects of !ii)ae to any »otl (see f bis chapter, 

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 


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. Oa 
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. 

5*017 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- 



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. 





ficult to preserve intact the extreme circumferential rootlets 
and hairs; yet the general development is correctly shown. 




Fig, 5S,^-^SciiMIIalioa Experiment: Fhatogmph ftbowing Matare Plants. 

The following table shows the percentage composition of 
the original as welt as the diluted soils, while the photographs 
show the development of the plants in their siiccessi%^e stages, 


Chemical analysis of fine earth. 

Insoluble matler<« *..... 

Soluble silica** .„„,,.,,, ., , 

Pi>Ush (K,0) „,, 

Sr)da(NafO),„** - -*..** 

Lime iCaOj...... 

Magnesia MgO}* ,„.- 

Br, ox* of Manganese iMniO^V., 
Peroxid of Iron ( FCsOj ),„.„..,. . 

Alumina (AltO»)...... »,,..,,.. 

Phosphoric acid iPjO^J,** ..,», 

Sulfuric acid ( SO| J* ...... ,..^. 

Carbonic acid |C0,K. ....,.,,. 

Water and organic matter,-..., 
Loi» in analysis^,.* .«.,,,....,..*...«. 


Humus . 


A?h .„. ....*...., 

Nitrogeiii p.ccnL in Humus 
** p, cenL in BiiiL*.. . 










1-3 i : 4 




























t 'S 












SO far as these could be observed; the continued attacks of 
mildew and plant hce preventing full maturity being attained- 

The restricted volume of soil occupied by the roots in the undtiuted 
adobe soilp together with the very abundant development of root -hairs, 
is very striking. A marked change in these respects is manliest in the 
Unt dilution, and increasinglf so as dilution increases ; the paucity of 
root-hairs is very marked in the last (greatest) dihition, in which » as 
the photograph of the plants showsj 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 
senes of testa 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 tliat in the undiluted 
soil the roots 51 led the entire soil mass, instead of remaining near the 
surface, as in the pure adobe. It ts possible that the latter was too wet 
when given the full half of its water-capacity, althoughi as the figures 
show, the water was slowly introchiced from below by means of glass 
tubeSi ending within a shield to prevent puddling* 

Limitation of Root Action, — These results, representing five 
soils of different i>ercentage-composition and physical char- 
acter, but identical chemical composition and ratios l^etwcen 
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 soirs productiveness from f^er- 
emtages of chemical ingredients alone. It is clear that the 
physical diaractcrs of the land as well as its depth, must be 
essentially taken into account* But there is ob\'iously a cer- 
tain limit beyond which greater perviousncss and root-i)enet ra- 
tion cannot make up for deficiency in the absolute amounts of 
plant-food w ithin p<3ssible reach of the plant : for in the case of 
excess! %'e dilution these are rendered partially inaccessible 
within the time*limits of a season's gn>wth. 

It is hardly necessary to say that these experiments require 
repetition w ith 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 



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. 

Lowest 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. 

Pine Lands. 



Number of Sample. 



Insoluble matter 

Soluble silica . . . . 

Potash (K,0) 

Soda (Na-0) 

Lime (CaO) 

MagncsU (MgO) 

Br. ox. of Manganese ( Mns04 ) . 

Peroxid of Iron ( FejO, ) 

Alumina (AljOa) 

Phosphoric acid ( PjOj ) 

Sulfuric acid ( SO, ) 

Carbonic acid ( C( )2'> 

Water and organic matter 


1. 18 










Total icx>. 19 


2 33 







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 


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 behveen soils of similar 
character and origin, the production and durability are 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 are the lowest percentage limits of 
each of the more important plant-food ingredients compatible 
with profitable production. 



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 

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 

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 ^ 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 adecjuate ; thus in the laterite soils of India and Samoa, 

1 I'ntersuchun^en uber die Hestimmung des Diingerbediirfnisses der Ackerboden 
und Kulturpflanzen, von G. Liebscher; Journal fiir Landwirtschaft 43 (1895), 
Nos. I c^ 2, pp. 48-216. 



according to Wohltmann, in the soils of Jamaica according to Fawcett, 
and in those of Madagascar according to Mtintz and Rousseaux.' 
There, potash-percentages over .10% seem to be high, and in Mada- 
gascar some lands in fair production range as low as .01%. 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%) 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 decomp>osing ( " 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 P^O*; 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 VaJeur AgricoU des Torres de Madagascar, Ann. de la Science Agrono- 
mique, 2*me serie, tome I, 1901. 



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 r^ards ferric 


(Rept. Cal. Exp. Sta. 1894-5, page 27.) 

Number of Sample. 

Coarse Materials> 0.55" 
Fine Earth 


Insoluble matter 

Soluble Silica 

Potash (K,0) 

Soda (Na,0) 

Lime (CaO) 

Magnesia (MgO) 

Br. ox. of Manganese (Mns04).. 

Peroxid of Iron (Fe«0>; 

Alumina ( AlaO») 

rhosphoric acid ( PaOj) 

Sulfuric acid (SOs) 

Carbonic acid (COj) 

Water and organic matter 



" Ash 

" Nitrogen, p. c. in Humus. 

" ** , p. c. in soil 

Phosph. acid in humus ash 

Soluble in 2 °'o Citric acid. . . 

in Nitric acid, 1.20 sp. g 

in Chlorhydric acid i.i 1 5 sp. g 
Hygroscopic moisture 1 5° C. . 


No. 21. 





No. 22. 































No. 24. 















No. 26. 














No. 27. 












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 



of phosphoric acid in soUs and doubtless also in ferUUiers. The very 
unusually high content of phosphoric acid in the Hawaiian soils, ex- 
ceeding all others on record^ so far as known to the writeri 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) raethod for the determination 
of avaibbfe phosphoric acid which in soils Nos. zi to 16 yielded results 
taigely in excess of the established limit in European soils, cannot be 
successfully applied to these highly ferruginous soils* It should also be 
lioted that the amounts of phosphoric acid found in the humus extracled 
by the Grandean method is in the first two Hawaiian soils over ten 
times the amount extracted] by citric acid, but that while they rise and 
Call together, no de5nite 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 alumiiiic 

Nitrogen, — In determining the nitrogen-content of the soil, 
a great variety of methods has been followed. Some include 
all that can l^e 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 detennination of the humus 
by the method of Grandeau, and of the nitrogen contained in 
it, should be the standartl; 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 I>een 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 Z2%), the amount of the latter 

358 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 1 200 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 : 


Coarse Materials > 0.55™™ i.oo 

Fine Earth 99-oo 



Insoluble matter ^ 62.62 \ 

Soluble silica 8.30 ( ^O'^* 

Potash (KaO) .95 

Soda (Na,C)) 50 

Lime (CaO) 5.07 

Magnesia (MgO) .84 

Br. ox. of Manganese ( Mni04 ) .06 

Peroxid of I ron (FeaOi) 6.43 

Alumina ( A1,0») 3.88 

Phosphoric acid (PsOft) .21 

Sulfuric acid (SO,) 06 

Carbonic acid (COa) 3.66 

Water and organic matter D.02 

Total 99.70 

Water-soluble matter, per cent .137 

Sodic nitrate, per cent .020 

Humus 1 .99 

Ash 1. 13 

." Nitrogen, per cent, in Humus 10.30 

** " , per cent, in soil -.203 

Total Nitrogen in soil .330 

" " in unhumified matter .127 

Available Potash ( citric \ 

Available Phosphoric acid ( method J * ^ 

Hygroscopic Moisture 5.81 

absorbed at 1 5** C. 



It will be noticed that this is a rather strongly calcareous soil, (nearly 
g% oi 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 fiat 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 opj)osite 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 
kx>se condition by stirring. The whole was placed so as to nuuntain, 
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 yeara. 

f /Cached natural soil x x - 





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 (i : 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 itselL 

36o 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 

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? 
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 data extant on this subject are rather scanty, and thus 
far have all been obtained at the California Experiment Sta- 
tion.^ 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 (Xo. 52 below), illustrate this point. 



Per cent. 

Per cent. 

Per cent. 


Kind of 




Humus in 





in Humus- 

in SoU.^ 


Black Adobe. 

Near Stockton, San Joaquin 







Vir«zin Soil, Tniversity 

(; rounds, Berkeley 






Ramie plot, Univ. (Grounds, 

10 years cultivated 

I. So 





(Iniss plot, Univ. Grounds, 

10 years cultivated 





Dark loam. 

Sii'xar-cane land, Maui, H. 






Dark loam. 

(iuava-land hills, near Hilo, 

Hawaii IsPd 




Nos. 6 and 1679 show the usual humus- and nitrogen-percentages in 
the "black a(lol>e " or " prairie " soils of California. Nos. 1842 and 
1 84 1 represent the same soil as 1679, upon which, however, ramie and 
ray grass had respectively been growing, without fertilization, for about 
ten years : showinj; that while the humus-content of the soil has increasedy 
the nitroi^en-content of the humus has decreased in the case of ramie by 
72.78';;, in that of the grass by tO.-jS^/c ; 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 TA^ Stt/'/'.y 0/ Sot/ Xitroi^eny Rep. Cal. Expt. Station, 1892-95, page 68; ibid., 
1S94-95, page 2S : T7i^ /Ceco:^nition of Nitroge9t Hungrittessin Soils^ in Bull. 47, Div. 
of Chemistry, V . S. Department of Agriculture, 1895; Landw. Presse, No. 55, July 
18S5. See al-o for detailed data chapter 8, page 135. 

2 Calculated upon the true humus substance (matiere noire), not by determining 
total (incl. unhumified) nitrogen in the soil. 



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 


Chile T 

Fici. 59.— Growtli 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 experiment could not be carried to full completion on ac* 
count of the overwhelming invasion of mildew; but the figtires 
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 u ^ 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 i» ike nitrogen-percentage of sail-humus, con- 
sidered in connection with other chemical cmd physical condi- 
tiims and soil derivaHons, we have a means of ascertaining the 
needs of plants with respect to nitrogen-fertiH2ation, if proper 
study be given to the subject. Broadly speaking, it appears to 
be necessary io 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 tchemozem 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 
Prol 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 Uke some of 
the dark alluvial soils of Louisiana and CaHfomia, and ap- 
proach them very nearly in the essentials of composition^ as 
will be seen from the table below : 







No. 24a 

Black clay lands. 

No. 1 167. 




(No coarse material in soils.) 

Insoluble matter 

Soluble silica 

Potash ( K,0) 

Soda (Na,0 

Lime (CaO) 

Magnesia (MgO) 

Br. ox. of Manganese (Mn^OJ 

Peroxid of Iron (Fe,Ot) 

Alumina ( AUO.) 

Phosphoric acid (P,0») 

Sulfuric add (SO,) 

Carbonic add (COi) 

Water and organic matter 



Ash ... 

" Nitrogen, per cent, in Humus . 
" " per cent, in soil . . . . 

Available Potash ( citric acid ) 

Available Phosph. acid ( method ) 

Hygroscopic Moisture 

aibsorbed at 





















































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 tchemozem 
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. 



'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 This statement appears contradictory of the observations of Schloesing iOt 
upon the solubility of phosphoric add in presence of lime carbonate (Am. ScL 
Agron., tome i, x9^)» but the natural conditions seem to justify fuUy the above 
















{1 f*Me M oiM 9^t^g 

8 "^ff 





(u o 

V o 

•^8 w ! 

^ ' '•^" *^? * ' <^ 8: :" 



Nos* 1 59 and 171 are heavy black prairie mils of high productive capa- 
city, whose prodtictioti had, at the time of sampling, lasted almost un- 
diminished for over twenty years. Nearly the same is true of the two 
California ^ils, Nos, 499 and 11x5; which| however, are ferruginous 
loams of only moderate clay-content. Id all, the percentage of phos- 
phoric acid shown hy the analysis is at or below the recogniEed limit 
of deficiency, white 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. 1115. 

Passing to the soils of low lime*content, we And the two Mississippi 
soils, poor in both potash, lime and phosphoric acid, so low in produc- 
tion as to be wholly an profitable in cultivation without previous ferti- 
lifation ; No. 559, from California, produced two fair crops of barley 
and then no more. No. 307, 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 lew years* culture ot 
clover or alfalfa (which di^w 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 miiitatea 
against the success of culture plants, and more especially against those 
of the leguminous relationship. 

What are Adequate Lime Percentages^ — We have in the 
presence or absence of the natural vegetation peculiar to cal- 
careous soils (** calciphilc") an excellent index of the pres- 
ence or absence of such amounts of lime carbonate as fulfil tlie 
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 
tw^enty or thirty minutes turns to a blue alkaUne 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 bdow 
in the <^se of the last three soils; while the first. No. 220, ex- 




emplifics 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. 


No. Sample.. 


Insoluble matter 1 

Soluble silica J 

Potash (KiO) 


Lime (CaO) 

Magnesia MgO 

Br. ox. of Manganese (MntOi).. 

Peroxid of Iron (FetOt) 

Alumina (AltOt) 

Phosphoric acid ( PsOi) 

Sulfuric acid (SOi) 

Carbonic acid (CO,) 

Water and organic matter 


Hydroscopic Moisture 

absorbed at **C 





low, Jasper 















Smith Co. 









ridge, Ala- 
meda Co. 






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-pn> 
duction was good and even high. 



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 .io9J> 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 i % ; 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 valae of soils corresponding to chemical composition 
as ascertained by analysis with strong acids, substantially in accordance 
with the methods adopted by the writer. 











Bdow 0.0S 
0.0S — ais 

Abort a4o 

Btlow 0.05 
.05— .10 
.10- .15 
.15- .a$ 

Abovt .as 

Btlow .lo 
.10— .as 
.as- .so 
.JO— 1.00 

Abovt 1.00 

Btlow .OS 
.10 -.1$ 
.to— .JO 

Abovt .fo 

Btlow .OS 
.OS - .10 
.10 — .IS 
.«5 - .»5 

Abovt .as 

M •dl«ai . . . . r . T 




" " Arid Reg... 
" *« HumidlUg. 






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. In this respect, 
and almost throughout, Maercker's ratings are in remarkable agreement 
with those made by the writer as far back as i860.* 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. 




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). 


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 Two 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 i6), 
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 r^on 
govern largely the vegetative changes. For we there find the 
timber growth of the lowlands ascending into the uplands so 

1 In the discussion in this chapter the ** humid region " referred to is alwmjs that 
of the temperate zones, unless expressly otherwise stated. The moat humid regioo 
of aO— the tropica — is treated under a special head. 
















5*^ ' '21J ' 2 




00^ mti* 


w> n ^ r^oo N o O m oO 


s a 

M M «o « * o *ao r*oo 00 O I 1^ 


-< 8 










^5 I * 












45 ?.?T?y?2r25:^|^ ^^ ^; 


«r9 I 

jwmp5|5|| 3= n 




< 1 




374 SOILS. 

soon as the latter becomes decidedly calcareous; as is abun- 
dantly exemplified in the loess or " bluflf " 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, 



and the varied black rocks of the great lava sheet of the Pacific 
Northwest, all alike produce soils of high lime 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 hme-content, however, it will be noted in the 
preceding table that the potash-conttnt 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.^ — 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 
i883» under the auspices of the Northern Pacific Railroad » in 
Washington and Montana. The published data are derived 
partly from the records of State survey s, 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 Oi^cial 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- 

I AbitT^t^ and reviied from BuUetiii No, ^ V. S. Weather Bureau, tS^^ 

376 SOILS, 

meter size also creates an unfortunate and ineliminable dis- 

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. These averages arc 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, 

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. 





m 6 


9t| % 5^7 

^ ^ 



s^^syrs^s's^rf *£ r« ^?8 tf-^i^'1 -^^& 



«» « « «^ f* #^ f* o 


« »^ * ■+ "- •• ■•■■* 1^ •» •n , ♦ 


« ■« A c^ « 4 <iH<$ 

•PI"* -"a 

?^?n^.*«s??: f?S 

ai ; !?^:^t %: '. ? 


^r^safs:^??^! Kt^ :?^ s^ 'fez^^Mt^a c^ 5^ ? 

?S^&^,?^:rs^'S? ffi?s ^5.R ^;?&?fcSs|r ??^^ 

^I^^S'&irtS? rZZ ffna frtr?-? 

^ n It ^» B^ ■ 

^s-w^triii ?^^ &1S ^^^js^s;^ 2^^^ 



V *^ nwT vtaT «q A 

J ? 

tf« t^ ft 

-ag.42s.&s^j 5j 55% s;s^rt^is| --J 5 

1 8 "1^ 


lllKlillb Ir 'm f|i|i1| hr 

378 SOILS. 

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. 


Deposited on on land by irri^atioa 

Insoluble matter 63.70 

Potash (K.O) 1.06 

SodaNtaO) 22 

lime (CaO) 4.97 

Magnesia f MgO) 243 

Br. ox. of Manganese (Mn904) 14 

Peroxid of Iron (Fe,0,) 5.80 

Alumina (A1«0.) 8.86 

Phosphoric acicl (PsOt) 16 

Sulfuric acid ( SOa) 13 

Carbonic acid (CO,) 74J5 

Water and organic matter 9.98 

Humus 1. 17 

** Nitrogen ii.ii 

** " per cent, in soil 13 

Hygroscopic Moisture 2.63 

absorbed at ^ .... 


Lime, — Considering in this table, first, lime, a glance at the 
columns for the two regions shows a surprising and evidently 
intrinsic and material diflFerence, approximating in the average 
by totals to the proportion of i to 11 ; in the average by states, 
I to 14 5^. This diflFerence 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 diflferences 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 


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 o{ 
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 Sails. — ^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 

Physically, even a small amount of lime carbonate^ by its 
solubility in the carbonated soiUwater, will act most beneficially 
in musing 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 : — 
K 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 w tth the proper degrees 
of moisture and warmth, of the conditions of abundant bac- 
lerial life (see above, chapter 9, p. 146) ; more especially those 
of nitriftcatton, 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 A^otnbacter fibid. 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, 



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 Lpew,^ 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.* 

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,* no one who 
has observed the characteristic dark black tint of our calcareous 

1 Bull. No. I, Div. Veget. Physiol, and Plant Pathol. U. S. Dept. Agr.; et al. 

' Loeb (Publications of the Spreckers Physiological Laboratory of the Univer^ 
sity of California, has shown a similar protective influence of the lime salts in 
tea-water, against the other salts, in the case of the lower marine organisms. 

• •« Black Soils ; " Agric. Science, January, 1892. 



*' prairie ^iU " can qtieslion the fact ; which moreover is perfectly ex- 
plicable upon the analogy already alluded to^ with caustic limef which, 
together with caustic alkalies ^tash aad soda), is known to act power- 
fully in the coovenion of vegetable matter into humus. That instead 
of libera ting the nitrogen in the form of ammonia, as do the caustic 
bydfates^ the milder carbonate should only cause the formalion of humic 
amideSi is quite intelligible* That such is really the case, has beea 
conclusively proved by the investigations oC the writer made conjointly 
with M* E. Jaffa (Rep. Sta. Cal. Agr. ExpL 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 ^^ soils are calcareous) that percentage rises as high as 22,0%^ 
with a general average of between 15 and i6%. 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 
nitrificatjon known to take place in the arid regions cvenrwhere. 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 activei 
points stmngly 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, ma^esia, 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, Wc 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,^ 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 I :i, while others require, that that ratio should be as 2 or 3 
is to I, 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 algse perished in a solution containing i per 1000 of magnesium 
nitrate, but remained alive when ,3 per 1000 of calcium nitrate was 

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. 



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, Funita and Katayama (Bull, ColU Agi, 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 Hud 
for nee and oats i : t, for cabbage 1 ; i , for buckwheat ^: i ; there being 
apparently a connection between the extent of leaf-surface and lime 
requirement, since leaves contain predominantly lime, while in the fruit, 
magnesia predotni nates. 

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, c, g,, the leaves of the long-leaved pine of the 
cotton states.* But no definite data showing the importance of 
this element to crops were available until Loew and his co- 
workers at Tokyo ' established its stimulating action in a num- 
ber of oises, in which crop production was materially increased 
by the use of protoxid salts of manganese. A so * applied man- 
ganous chlorid to an experimental plot of thirty square meters^ 
at the rate of twenty-five kilos of Mn^O^ 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 

^ R^p. Agr. and Geotogf of Mtssutalppi, iS6ch p. j60k 

• Bull. AfT. CcilL Tokyo, Vol V., Nos. 1 and 4. i Ibid* Vol, ^ 

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 


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* 
nion 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 : 


Insoluble matter 1 5.96 

Soluble silica 33*io 

Potash KaO) 1.47 

Soda (Na«0) 1.70 

Lime (CaO) .09 

Magnesia (MgO) 1.33 

Br. ox. of Manganese (MnsOi) 30 

Peroxid of iron (FetOi 18.76 

Alumina (AUOs^ 18.10 

Phosphoric add (PaO») 18 

Sulfuric acid (SO») 06 

Carbonic acid (COt) xxy 

Water and organic matter 9.00 

Total ioai4 

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 (i 2.17) 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- 

386 SOILS. 

bixiations 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 

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 eflfect and hence the sand grains 
remain incrusted 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 diflference, 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 b plainly a predominance of complex hydrous 
silicates in the soils, as compared with humid regions. 



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 
toil in the humid States. 



MlMkllMlP ......,,. 

CaUfofnU ijti Cliino^ >,.. 
d<>. Jsckidff* ^ . . . . < 

Silt ^v^r^^tubmnk, di4fD,... 

MluuftipfiL . ^ ^ , H, . » ^ * ^ , 

CiltfoniU ^Oiinoi....... 

Silt Ji»i6 — ,«} nio. diuB. . 

MisliwjppI, ^ , ^ , 

CaliloRiu, Chino* ^ «..*..« < 

*" Jlckion ^ * . 

Silt jTiK — .oj(7 Biift. dim^, 


CalifOifmi, ChinQ ~ < 

•* jA^k»0', , 

SUt jojMi-^,D47 Dim. dti^m,. 


OJifofiujii Chino- ... ». 


€<Hrke Sill 0+*— jct^i turn. 

•' Jjckwn 

Fiat und .P?i -.11 mni. dl 
QtUriffULft, ChJDa — ^ < - , - 

StnA tt—.y^mm. dum..^'. 
CililorWA, Citinn .,..,.... 





10. IQ 















a. II 









■ .70 




It thus appears that while in the Mississippi soil, solubility of 
plant-food practically ceased at grain-diameter of .036 mm, in 

* Analjiesby L. ILTohnaii. •Analyietby 

1 Analyses by R. H. Loughridge. 
£. 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. 


In the analjTsia 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 
toils 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* 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 

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;* and the visible 
occurrence of " gibbsite " and " bauxite '* in modern forma- 

> Report of the Tenth Centos, Vols. 5 & 6 ; see especiaHy the analyses of soils 
from Mississippi and Alabama. Also the Reports of the California Experiment 

< Excepting the relattrely rare minerals of the Allophane, Kollyrite, and 
MUoshite group. 



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.* 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. 




Name of SolL 



Total iotu 



Lof to 








Dirk Lt>,\m 

FLitwood^i Clijr -...,< 
Rtd VulcJnic,.,*, ...^ 
Moiare Mesert. .**... 


Red Ctuparral.. K . ^ **, 
*' " Subsoil.. 

TuUre Plajni 

Drv Boge r , « . . , 


BmvmiTih Loam. .,», 

Ellack Loi.m,, , 

^mmcnlo Alluviam. 
R«i FfMZhihJll 


Lakt ... 

Kem ... 
MertcdrH ^ 




Butte . . . . 

Nevada . 

■ r 


10,3 J 



37. iq 

13.1 J 

19 .So 


a J. 46 








JO 4 



6. 10 









4' 4 J 


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 

^ Since any complex zeolite would contain /ess alumina than kaolinite, this 
assumption more than covers the possible zeolitic alumina. 



which EO other form ot combination can be aligned. Since some ol 
the alumina tindoubiedly takes part in the formation of stich zeolites, 
the lilica must to that extent be irithdrawn from the estimate made for 
kaolin] te> While it is impossible to make any definite mi me ri cat al'* 
lowance for this fact, it clearly will tend in many cases to increase 
matenalty the amount of alumina that must be assigned to the hydimte 
condition. It will be noted that in most cases given» the alumina pet 
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 arc rather pre- 
dominant, while the reverse is the case in the humid region.* 
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 ihe localities where some of the most 
striking mstances of excess of alumina over soluble silica have 
been found* 

Thus Noa, 86 1 and B$^ from the neighborhood of Gi^s VaJlcyp 
which show this excess most strikingly, occur within t$ miles of locaW 
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 whole, that the excess of alumina occurs most frequently in con- 
nection with soils fomied fmm eruptive rocks ; in the case referred to, 
from volcanic ash* It will require more detailed study to detect the 
causes of these marked differences. 

Rrtenti&n of S^iubk Si^ca in AUkoM Soiit. — It ii somewhat stirpnsifig 
that^ contrary to the expectation one would naturally entertain, the 
a]kali lands, so frequently rich in the carbonates of the alkalies that 
would dissolve free silica^ on the contrary, show most frequently an 
fiuress 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 zeoUtic 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 

^ See for compa^rison the data ^vea to volt, 5 and 6 of Che report of the Tentli 
Cenaus of the United Sta^tea, 



of both alkaline and earthy bases in acid-solable silicate combinationi. 
But much farther research is needed to explain fully the marked dis- 
crepancies observed !n 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- 

Phosphoric Acid, — As regards that highly important soil 



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 arc 
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 arc 
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 

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.,* by Bottcher and Kellner* and 
Nagaoka,* 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 wann 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. ScL Agronomiqoe* tome i, 1S99. 

* Landw. Presse, 1900, No. 52 ; ibid. 1901, Not. 23 and 24. 

' Bull. UniT. Tokyo, VoU 6, No. 3. Production wms diminished to lets than one 
half when lime was used with bone meal, and actual assimulation of phoqihoric 
acid to one fifth. 



derived from these rocks, up to nearly two per cent.' But almost the 
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 

^ See table, chapter 19, p. 256. 



two, or somewhat less, is maintained in the average propor- 
tion of soda to potash in both rcgiotis ; 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. ( Sec chapter 3, p, 38 ) . 

The process of " kaoUnizQiion" being that by which clays 
are formed out of feldspatliie 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 (zei>lites). 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 notahle amount of soluble 
salts exists, and is kept in circulation by the alternation of rain- 
fall and evaporation, the latter causing the salts 10 accumulate 
at the surface and to manifest themselves in the form of saline 
crusts or efflorescenses. Alkali lands arc a ch.iracteristic 
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 ffowtng 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 iirst sub- 

396 SOILS. 

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 wtU 
alone hold out for many years under the demands of cultiva- 
tion,* 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 cultiu-e, 
e^. 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°/o*t equal to 38,000 pounds per acre-foot. 



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 l)eets. 
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 ivith 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. 



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 




of the soirs 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, Qyartzose, 
magnesian, and other soils resulting from the decomposition 
of ** simple " rocks will, of necessity, be poor in plant- food 

Humus in Tropical soils, — Another inference from the cli- 
matic conditions of the tropics is that the properly tropical 
soils arc 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 
tn the arid regions, must also take place. A good example 
illustrating the intertropical regime as regards humus is given 
in the table in chapL 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 tan, consistently with productiveness, range 
lower than has thus far been observed tn temperate climates. 
This again forms a striking contrast with the soils of the arid 

It is greatly to be r^retted 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 referriblc 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 kaoHnite 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 pho^hate 
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 iropical 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 



ircgetation. Nitrificatioo must likewise, of courae» be very active udder 
the cotiUnual heat and moistuie, and the humus farmed under tliefle 
circumstances is likely to be quite poor in nitrogen* On this Utter 
point, however^ deitnite data are alttiost 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 ;^ and by 
Miintz 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 climateSp 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 inteirening 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 
xerophjiic { arid-land )vcgetation^ 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-trc^ical 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 rg, 
p. 352), it must be remembered that those mentioned as being 
productive arc so by virtue of great depth and relatively high 

) Samoft ErkuaduQg, by F. Wohltmai^n, Kolont^-VVlrthstk, Komieee, Berlin, 




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 Miintz 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. 


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 i^ 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." * 

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 muck as five 
times more than the cold ; but no such case appears in his reports on Samoa and 



Koas in thb volume have been based. The tigures for nitrogen and 
phosphoric acid may be assumed to be fully comparable i that of Ume will 
in general represent fully only that which is preseni in the forms of 
carbonate, sulfate and humate, and a part ol that eicisting in ^eolitic or 
hydrous silicate form. Of the two potash determinations only the one 
made in hot extraction will be even remotely comparable, being pro* 
babfy at least ^o ^ lower than would have been obtained by the writet'i 

Even thus, however, Wohltmann's results are highly in- 
structive. He gives the following summary of his mode of 
interpreting such analyses: 

Very rich. 



Potssh , * *...,.♦... 




linie and Mvfncnm. , . « . 

Phosphoric Add ,,.,.-....-, 

Kitrogtn .,*♦,,,...,,-.,.-, 


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 add being placed in par- 
entheses after the other. 

Smk ^f Sampan liiands. — A discussion of these analyses shows, frooi 
ihe writer's poiot of view, a very low content of potash and lime, with 
the peculiarity that both are somewhat higher at Ihe 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 htimus 
reaches to the lowest depths examined, is clear from the nitrogen*coa- 
tent given for these samples* Wohltmann^ whose estimate of these 
soib 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 




g - 


g " 

H s 


< y 

81 I 









.£ E-. 


i^^^% ? «'^% ^ 


l|ili|l5l fe 


f, m 4 t/> >. (AM rs,oo ♦ 
OOm^Onoo ••»>- «1 
' ' ' & -i ti ' « to 





he has not determmed either the true humus or its nitTogeii-conteiiti it 
remains uncertain whether or not a sutficiency b in an availabic 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 tie nitrogen-hungry. Agaiup 
as regards the phosphoric acid, which Wohltmann considers satisfactory 
to highj it is questionable to what eitent 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 ihey cease to 
produce we!! on these soils. 

&i& #/ Kamerun. — In the soib of Kamerun, also analysed by 
Wohltmannp and of which two are placed alongside ot 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 arc also very rich in organic 
matter^ evidently down to the depth of a meter, a^ are those of Samoa. 
It is probably due to the high humus^ con lent that these soils, washed 
as they have been by tht 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 ]tme; a fact 
readily intelligible from the more ready solubility of lime in 
carbonated water. It is hardly doubtful that this dispropor* 
lion will in many cases explain a lack of thriftiness, which 
could be effectually remedied by a simple application of Umc 
or marl, without resorting to the more costly fertilizers. 


The soils of the island of Madagascar have been analyEcd to 
the number of about 500 by Miintz and Rousseaux, under the 
auspices of the French government.* So large a number of 

1 Aiittale» da la Sdeoot Agrononikiye, tome leri 1901, fukuloi li 3, 3. 

4o6 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 oflf 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 



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 dcnuflation 
of the mountain slopes. This is especially the case in the 
Imerina province (in which the capital, Tananarive^ 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 arc not usually 
very hea\^, 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 vallej'S 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 














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form available lands. It seems to the writer that, in view of 
their own expressed opinion that tropical soils arc not to be 
gauged on the same perceiitage*basis of soil-ingredients as 
lliose of temperate regions. Miintz and Rousseaux rather un- 
dcrestim-ite the productive value of many of these lands; re- 
garding which the field notes report good pnxiuction, 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 

Be that as it may, the influence of the tropical climate and 
rainfall upon the composition of these soils is certainly veiy 
marked. While giieiss 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- 
fnation. 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 add, 
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 Imcrina the valleys and lower 
slopes show a fair content of both lime and potash: but in the 
province of Betslleo, 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- 


SItlai. .«. ..... 15.J 

Fotisli.... ««•«.«., .^, ••..•.. .... .3 

Lime .. ** tn£« 

Mafn«iiA.>»..»....t •*.».■....«•. 1.1 

Ferni: oxkl.* •«.»*»•« a «*..4. lou6 


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 diflferent 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 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.^ 

According" to Dr. Leather, " the four main types of soils to 

1 On the Composition of Indian Soils. Agr. Ledger, 1898, No. 2. 



be dealt with, and which certainly occupy by far the larger of 
the Indian cuhivaled area/' are : The Indo-Gangetic alluvium^ 
cnvering the chief cuUivable areas of the Indo-Gangetic plain; 
iJie 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 met amorphic 
rocks of Madras; and the '' laterite " soils which are met with 
in many parts of India. To these should be added the alltwial 
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 Inda-Gangetic Plain. — ^The general rain-map of India 
shows the Pandjab and Rajputana to be arid throughout; 
thence eastward the rainfall increases to 2$ and 30 inches on 
the Ganges; notwithstanding which, silkali (reh) is abundant 
about Aligarh^ Meerut and Agra. Thence tow*ard Calcutta 
there is a steady increase of rainfall until^ at the head of the 
Bay of Bengal, 70 inches is reached. 

I f 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 ixcurs very generally in India, 
and as stated above (chapters 9 and rg), this ocairrence of 
calcarc<]us hardpan, nf vanting hardness, is almost universal in 
tlie arid r^ions* 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 o! an arid 


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. 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»tablc 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 
Inclo-Gangetic soils. In the latter, potash ranges between .65 
and ./oVf ; 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- 



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 Rcgur 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.^ 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 s(m1 is thus partly inverted by the surface 
soil falling into the cracks. To the latter fact Leather as- 

^ 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 j)rocess in originally very rich soils. The present product of cotton on the 
rcgur lands does nf)t seem to be on record; judging by the wheat product it 
should not be over one hundred pounds of lint per acre. 



cribes, in part, the long duration of fertility in the rtgxir 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 otlier examples are however also given in tlie table. 

It will be noted that while the cnnlcnls 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 fain 

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, 
iheir high lime-con tent causes a copious crop of leguminous 
weeds, constantly replacing the nitrogen supply,^ Unfor- 
tunately we have no determinations of humus or of its nitrogen- 
conient. Leather attributes the black color of the rcgur to 
some mineral substance rather than to humus; but his argu- 
ments are not rjuite convincing* so long as the Grandeau test 
has not been made, Tn 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 l>e underlaid over the greater 
part of its area by a basaltic eruptive sheet (not by meta- 
morphic rocks, as stated by Leather K and it is not easy tn con- 
ceive how such a soil stratum can have been formed from such 
rocks as a sedentary formation* Elsewhere such soils arc 
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- 
ptysit; 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 " lanrls, which appear to !)c 
sedentary soils formed from underlying dark colored, mostly 
eruptive rocks. Some of these are very rich in lime and pot- 
ash, others vtry poor, and it seems impossible to classify them 

^ S«e %*0elclcer, Re|iort on the Impmvement of Indian A grictilture^ 1892, p, ^4 
|nr. Go. 

4i6 SOILS. 

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 

" 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. \Vohltniann\s definition of laterite soils seems best rep- 
resented by the ** terra roxa " of Brazil, which as he states has 
.02 to .087^ of potash, .02 to .io7<? 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 



1^ of mgU rdlnfaU dh the Malab^t t^estWti) toafet of the 

- The^roHoctiveneiis brthe laterife ^oiir^eetris tlirougflifint tn 
b6 oTily mo<lerate, yet muth hig^her ihan %%'otild be expected of 
sdth of similar 'Wrriikisit tort nt th^ lempciraie zones. %vhefe the 
riife 51 soil-format ibn is m mucli sI6tvci^ tlian in the tropics* 

''Ft^orii thr analyses of ** coffee soill" from Yarcahd in the 
S1t^^^r6y hfll< noHh of Madras, we learn tliaircoffee doe5 well 
iSith a* fairly liberal supply of lime ( '30' to ^44%) s"*l phos- 
pHdric acid, biit is satisfied with a rrtiich smaHer amount b( 
pdtash'ihin is fdiin'd in the tea soils of Assam.' 

X farther systerhatic investigation of the soils of India, with 
rfmuttantous accrtrate observations on their depth, sidisoit, 
gii^bTogical derivation, topograpliical location and relations to 
riirtfill. coilld n6t fail to yield very iiriportant practical results 
The examinaiion'of sampled collected and sent in by persons 
unfamiliar with the proper mode of talcing soil specimens, and 
the information WTiidi should accompany them, always in- 
Solves a great rf^aTbf uhtertairily and waste of labor^ and in- 
diifinifeness of results. ' - ^ 

^lill i»{i In 1 fin 

ijfFLiiifl^cE Ai^ ARrtirrt'WdN civilization. 


In connection with the facts given and discus&cd above, as 
tt*: the relative prmluctive cajiacity of lands of the humid and 
arid regions, it becomes of interest to consider what mfluence, 
if any, these differences may have had in determining the 
choice of the majority of the atKient civilizations in favor of 
countries where nature imposes upon the husbandman, who 
su])plies the prime necessaries of life, the onerous condition of 
artilidal irrigation,* 

' Prefcraice' of Ancieni Cmlhatioks for Arid Cdunfru^s. — A 
bHef revie^v suffices to Establish the fact of such choice: Aside 
from Egypt, the perrnanent fertility of which is ascribed to the 
ii^undattom of the Kile, we find to westward the oases of the 
Eitoyan and^^^^fa'desterts, the hJgfi fertlRty of which Has 
become proverb?^! and' Itai caused therrt^b bd cnltiv^nted from 
ancient times to the presetit. Similarly/ on both sides df the 

* V«rKaiidlungen tier Deutvchcn ThpilotogiflcKtn Geselljiclijtft m Ueilxtu Decern. 
Lei; i$g2i Korth Ainerieiii KeTtew, September. 19&2. ^ ' ' 



41 8 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 tlie bountifully productive ficrra calicntc, 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 Algonciuin race. From time 
immemorial they have practiced irrii^ation in connection with 
cultivation, maintaining a comparatively dense population on 
very limited areas. 



It might be thought that the desire to avoid the lal>or of 
clearing the forest ground was the motive which guided the 
choice of the ancient nations toward the cheerlcss*looking, tree- 
less regions. 

But if we consider the cost and labor of establishing and 
maintaining irrigatinn 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 any 
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 

Irrigation nfctssitatt*s Co-operation, — Irrigation enterprises 
can be accomplished in a ver/ limited degree only by individ- 
uals or even families. Its permanently successful execution re- 
quires the co-ojieration 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 
orgam^alioQ quite diflcrcnt from and far in advance of that neces- 
sary in humid countries. And such organisation is mani- 
festly conducive to the preservation and development of the 
arts of peace, wdiich means civilization* The most ancient 
systematic code of laws know*n to us is that of Hammurabi, the 
king of arid Assyria, 

The high and permanent pradnctirrness of arid soils induces 
permanence of civil organhaiion. — In humid countries, as is 
well known, cultivation can only in excei>tional cases be con- 
tinued profitably for many years without fertilization. But 
fertilisation requires a somewhat protracted development of 
agriculture to be ratirmally and successfully api)lieil in the 
humid regions, and the Germanic tribes, like the North- Ameri- 
can Indians, seem to imvt shifted their culture grounds fre* 



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 



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 modem 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." 


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 

While sea-shore lands are by no means always of high fer- 
tility even when freed from their salts, especially w^hen 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 arc 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- 




sist. Where the rainfall is abundant, that portion of the salts 
corresponding to " sea salts " is leached out into the Ixitloni 
water, and with this passes through springs and rivulets into 
the countf)^ drainage, to be finally carried to the ocean*' An- 
other portion of the salts formed by weathering, however, is 
partially or wholly retained by the soil ; it is that portion cliiefly 
useful as plant food* 

It follows that %vhcn, 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, hut 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 ihe above salts are in part at least derived from the 
leaching of adjacent or subjacent geological deposits impregnated wilh 
them at the lime of their formation. Stich is the case in portions of 
Wyoming, Colorado and New Mexico, in the Coiorado 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 ]ot:)king over 
a rainfall map of the gloljc* we see that a very considerable 
portion of the earth's surface, fomvitig two belts to poleward 
of the two tropics, has deficient rainfall; the latter term being 
commonly meant to imply any annual average Ies«* than 20 
inches (500 millimeters), Tlie 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 

i S«e Cbapter 2, p. *6. 

* Sc« aboVB, chApter f/s 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 b}^ 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,** ^ 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 

* St'C Chapter 23. 














.1.1 fl]ffiyii| 


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426 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 w^e 
examine plants that have been injured by alkali, we will mostly 
find tliat the visible damage has been done near the base of the 
trunk, or root crozm; 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 tinge for half an inch 
or more, so as to be soft and easily peeled off. In the case of 
trees, tlie 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 \)q\\v^ 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 



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- 


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- 

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 margpln 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 



after irrigation,^ 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 

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 of 
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 9J;), 
and it was within these 1 5 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 ^ 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 surfac e ; their roots kej)t above the strongly-charged 
subsoil, and through them and the stems r.nd 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 Ililgard and Loughridge, Bulletin No. 128, California Experiment Station; R©. 
port California Kxperiment Station. i.S94-<)5, p. 37 ; Bulletin No. 30, Office ot 
Kxperiment Stations ; Wollny's Forsch. Geb. Agr. Thys., 1896. 




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It is thus that the luxuriant vegetation of the San Joaquin 
plains^ dotted with occasional alkali spots, is maintaineil ; tlie 
spots themselves being almost always depressions in which 
the rain water may gather, and where, in din sequence of the in- 
creased evaporation, the noxious salts have risen to the surface 
and render impt^ssible all but the most resistant saline growth; 
particularly wheoi in conseijuence 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* 

Upti'ard Transiocation from Irrigatioft. — *Fig. 65 sliovvs 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 w^as harvested 
the same year, without irrigation. Investigation proved that 
here the condition of the soil was intermediate between the two 
precetling diagrams. The irrigation \vater had dissolved the 
alkali of the subsoil, and the more abundant evaporation had 
brought it nearer the surface; hut 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 gj^^sum, moreover, the 
injuriousness of the alkali had been somew^hat 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 ** w hite " only, the tendency to accumu- 









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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- 

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Fk.. ^.— Dittribution of Alkali 5alt» in 5andy I^ands. 

ness of ** wliite alkali." An illustration of the distribution of 
the salts in very sandy lands, from the Tulare substation, is 
ji^iven in V\^. (>(). Here we see that the maximum is not at, 
but some distance below the surface, the entire saline mass is 

436 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. 

Saltan 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 15 feet, below which there is a second decrease; 








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below thiSp at to feet, there is a final very heavy mcrease, not only oi 
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 otiserv- 
able elsewhere, /. g~ near White Plains, Nev,, whose name is derived 
from the copious surface accumulation of the sulfate. It seems as 
though this must have been formed in some way from the common 

Horizontal Distribution of Alkali Salts in Arid Lands. — TIte 
constant occurrence of " alkali spots ** in arid lands shows at 
once the great inequality of horizontal distributton of alkali 
impregnation. This is as prominent in level lands as on slopes, 
and in cxtrenaely arid regions it is mostly not possible to recog- 
nize even very considerable differences without close examina- 
tion. Thus in lands appearing exactly alike on the surface, 
on the edge of the Sal ton basin in California, on t!ie 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, esi>eciaMy in irrigated land, as might be ex- 
pected. Those cultivating alkali lands have therefore to exer- 
cise constant watch ftiln ess, unless the sails have been defi- 
nitively eliminated by underdratnage 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 lamls themselves are 
remarkably free from alkali, even in the arid regions; except 
when water is gathered in depressions, where strongly saline 
waters may be foutid in Washington, Montana and elsewhere, 
But on level plateau lands, where drainage is slow or imjierfect, 
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 
wc find alkali salts incrusting the surface in the valleys of the 
streams, as e. 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. 



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.^ Subsequently, a more elaborate investigation 
of the subject w^as made by Dr. J. W. Leather, Agricultural 
Chemist to the Government of India.^ 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 
tisar 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 w^e 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 

* An alxstract of the report of this commission is given in the Report of the 
California Experiment Station for 1890. 

* See Agricultural Ledger, 1897, No. 13; ibid. 1901, No. 13. 


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 the investigations made by other Russian observers on the 
saline lands of the steppes of European Russia. 


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 carbonate* 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 ; * while the other 
salts, often together with Epsom salt and bittern ( Magnesium 
chlorid), constitute " white alkali," which is known to be very 
much mil3er 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 nonnal (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 add 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 monoKrarbonate, which unfortunately, in the nature of the case, alwa3rs 
predominates near the surface, and thus injures the root-crown. 

* 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 b tenaciously retained by the chlorids of 
calcium and magnesium impregnating the land, thus contrasting strongly with th« 
gray tint of the general dry soil. 







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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 (t. 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 i 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-' 



tive ingredients — ^potash, phosphoric add and nitrates — present 
in the land in the water*solub1c form. 

As has been shown in the preceding discussion, the analysis 
at the surface foot alone, which has frequently been alono 
made, gives no definite clew whatever to the tolat 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 aj, page 467). 

Composition of Alkali Soils as a Whole. — As may be im- 
agined, the presence of the alkali salts 6nds expression in the 
anal>^t€al 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 acnimulation 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 sarpristng when it is considered that the cooiinacd presence of 
the salts resulting from roc k dcromposition a^fTotds opportunity for the 
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448 SOILS. 

in soils by the formation of complex zeolitic silicates. In most cases 
the potash-percentage exceeds .75%, and rises as high as a.o^ ; 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,* 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 Ezp't St*n for 1892-^ p. 141. 




Mineral Salts. 

Potassium sulfate . . 
Sodium sulfate . . . . 
Magnesium sulfate . 
Sooium chlorid .... 
Sodium carbonate. . 
Sodium phosphate . , 
Sodium nitrate 


Organic matter 

Total soluble in soil 
Mineral salts 









of spot. 















































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^ Chiorids and Sulfates of AOtalus 
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 1 824 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 



and later with Jaffa, investigated it quantitatively.^ 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 100^ C. 

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Fig. 6q.— Progreuive Tnmsformation of Alkali Solfatct 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 1 ^™- J°*"^- S^*' August 1896. 



the solid state. The calcmm chlorid not uncommonly found in 
some alkali regions is undoubtedly the product of the above re- 

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 when 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 cltapter pp, 431 and 432), we always 
find the sodic carbonate relatively decreasiftg 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 tlie *' 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 
w*e should often find an apparent inverse ratio Ijetween 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 ^ipparent 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 diying north winds; 







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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 

Again» it not infrequently haf^ens that in sloping valleys or 
basinSr 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, arc 
usually quite limited, and are at present scarcely reclaimabic 
without excessive expenditure; t