UC-NRLF SOIL PHYSICS LABORATORY MANUAL HOSIER AND GUSTAFSON • . * THIS 800K ISJ&J GIFT OF Agricultural Educ.Div MAIN SOIL PHYSICS LABORATORY MANUAL BY J. G. MOSIER, B.S. PROFESSOR OF SOIL PHYSICS, UNIVERSITY OF ILLINOIS AND A. F. GUSTAFSON, M.S. ASSOCIATE IN SOIL PHYSICS, UNIVERSITY OF ILLINOIS GINN AND COMPANY BOSTON • NEW YORK • CHICAGO • LONDON ' ••••%•' PREFACE These practices are the result of ten years' experience in teaching soil physics, and are designed for one semester's work, during which it is hoped to give the student a knowledge of the principles that underlie many common agricultural operations. In a number of practices students may work together in groups, not so large, however, but that each one may have a distinct problem to work out in each practice. This plan will enable the class to complete the work in one semester, which otherwise might not be possible. Questions are asked and references given to enable the stu- dent to get the greatest amount of information possible out of each practice. An appendix of additional practices is added for students who wish to pursue the subject further. THE AUTHORS UNIVERSITY OF ILLINOIS, COLLEGE OF AGRICULTURE URBANA, ILLINOIS COPYRIGHT, 1912, BY GINN AND COMPANY 212.9 CONTENTS PAGE List of Apparatus for Each Student v Weights and Measures . . . . vi Stock Soils and their Preparation 1 Collecting Soil Samples . 1 Determination of Capillary Moisture in Soils 4 Determination of Hygroscopic Moisture in Soils 6 Effect of Drainage on Temperature of a Soil 8 Effect of Color on Temperature of a Soil 10 Determination of Total Moisture in the Same Soil under Different Conditions , 12 Determination of the Variation in the Hygroscopic Moisture of Soils 14 Flocculating Effect of Lime 16 Determination of the Effect of Lime on Plastic Soils 18 Testing the Tenacity of Moist Soils 20 Determination of Shrinkage in Soils 22 Determination of the Apparent Specific Gravity of Soils 23 Determination of Apparent Specific Gravity of Surface Soil under Field Conditions 26 Determination of Real Specific Gravity of Soils 28 Determination of Porosity (First Method) 30 Determination of Porosity (Second Method) 32 Determination of Loss on Ignition 34 Determination of Humus in Soils 36 Determination of Conductivity of Heat in Soils 38 Determination of Specific Heat of Soils 40 The Power of Loose Soils to retain Capillary Water ....;. 42 The Power of Compact Soils to retain Capillary Water 44 Effect of Organic Matter on Retention of Capillary Water .... 46 Determination of the Rate of Percolation of Air through Soils . . 48 Determination of the Rate of Percolation of Water through Soils . 50 Effect of a Layer of Organic Matter on Rise of Capillary Water . . 52 A Study of the Capillary Power of Different Grades of Sand ... 54 A Study of the Capillary Power of Soils 56 iii 674626 PAGE Effect of Organic Matter on Rise of Capillary Water 58 Effect of Varied Quantities of Salts in Solution on Rapidity and Height of Rise of Capillary Water 60 Determination of Per Cent of Capillary Water at Different Heights above the Water Table 62 A Study of the Physical Composition of Soils 64 Standardization of the Eyepiece Micrometer 65 Mechanical Analysis 66 Determination of the Effect of Cultivation and Mulches upon Tem- perature and Moisture Content 69 Effect of Soluble Salts on Retention of Capillary Water 70 Determination of Coefficient of Evaporation 71 IV APPARATUS FOR EACH STUDENT 1 Asbestos mat, 10 cm. square 4 Beakers, assorted sizes 1 Blue pencil, wax for marking on glass 1 Brush, camel's-hair 1 Bunsen burner 1 Capsule, horn, 10 cm. long 1 Cheesecloth, one yard 4 Corks, same size as No. 8 rubber stopper 6 Crucibles, 25 cc. 6 Crucibles, 50 cc. 1 Desiccator, 15 cm. in diameter 4 Erlenmeyer flasks, 250 to 500 cc. 1 Forceps, brass, 10 cm. long 4 Funnels, 10 cm. in diameter 1 Graduated cylinder, 100 cc. 1 Box of gummed labels 6 Jars, Mason's pint 1 Vial of litmus paper, blue 1 Box of matches 1 Mortar and pestle, 12.5 cm. in diameter 1 Ring stand, small, medium, and large rings 1 Rubber policeman on glass' rod 20-22 cm. long 4 Rubber stoppers, No. 8 1 Ruler, 30 cm., 12 inch 4 Shaker bottles, 375 to 400 cc. 12 Soil pans, 10 cm. square, 5 cm. deep 2 Soil pans, 10 x 22 cm., 5 cm. deep 1 Spatula, 15 cm. blade 1 Spoon, horn, 10 cm. long 2 Test tubes 1 Tongs, crucible, 20 to 25 cm. long 2 Towels 1 Triangle, pipestem flanged, medium 1 Wash bottle, 500 to 750 cc. 5 Watch glasses 56 mm., 2^ inches in diameter 4 Watch glasses 106 mm., 4| inches in diameter 8 Weighing bottles, 30 mm. in height and diameter WEIGHTS AND MEASURES 1 Meter = 39.37 inches = 3.28 feet 1 Centimeter = .3937 inches 1 Kilogram = 2.2 pounds avoirdupois f 1.056 quarts 1 Liter = •{ i. 61.02 cubic inches . T , f 25.399 millimeters 1 Inch = •< I 2.5399 centimeters 1 Pound = 453.59 grams 1 Cubic foot of water weighs 62.42 pounds 1 Square foot inch of water weighs 5.201 pounds 1 Acre inch of water = 226,000 pounds (approximately) 1 Acre = 43,560 square feet Circumference of a circle = 2 rrr or irD Area of circle = Trr2 Area of a sphere = 4 Trr2 or TrD2 Volume of a sphere = ^trr* or ^TrZ)8 Volume of a cylinder = 7rr2A ; h= altitude VI SOIL PHYSICS LABORATORY MANUAL STOCK SOILS AND THEIR PREPARATION The soils commonly used are (1) a sand or sandy loam, (2) a gray silt or gray silt loam, (3) a brown silt loam, (4) a clay or clay loam, and (5) peat. Any other soils may be used. The selection of soils for class use should depend largely on the locality. The prevailing types in the vicinity should be used. These soils should be thoroughly air-dried, and ground suffi- ciently fine to pass through a 2-mm. sieve. COLLECTING SOIL SAMPLES In collecting samples of soil a one and one-half or a two-inch auger with an extension, making it 40 inches long, should be used. Select the place for sampling and remove any vegetation. Collect the surface soil to a depth of approximately 6J inches, or to the plow line. Enlarge the hole by reaming out with the auger so that the subsurface soil may be removed without coming in contact with the surface soil. Take the subsurface sample to the depth of 20 inches. This gives the subsurface 13^ inches, or twice that of the surface. It may be desirable in some cases to take the subsurface to the natural subsoil line, as indicated by the change in color and physical ( opposition, oi^ir ally from 15 to 20 inches in depth. Enlarge and .clean out tlie hole as before and collect the subsoil to" ti depth (»f 4P -i^cj^sj It may be convenient to divide the subsoil into two equal parts of 10 inches each. In collecting samples for moisture determi- nations, expose the soil to the air as little as possible before putting in jars. FIG. 1. SOIL SAMPLERS A, one-inch field auger ; B, one and one-half to two-inch sampling auger ; C, exten- sion rods; D, King's soil-sampling tube; E, hammer for forcing D into soil. PRACTICE I DETEKMINATION OF CAPILLARY MOISTURE IN SOILS The moisture content in these exercises will always be ex- pressed as per cent of the water-free soil. Use the soil collected according to method given on a previ- ous page and make the determinations in duplicate for surface, subsurface, and subsoil. Record all data on the opposite page. Weigh carefully six soil pans. Place in each pan 200 g. of the soil and weigh quickly to avoid loss of moisture by evapo- ration. Dry at room temperature for 72 hours, after which .weigh at intervals of 24 hours until a practically constant weight is obtained. The loss in weight is the capillary moisture. Express results in grams, and after completing the next exercise express results in per cent of water-free soil. Use these air-dry soils for Practice II. REFERENCES. " Soils," Lyon and Fippin, pp. 141-148. "The Soil," Hall, A. D., pp. 27-28 and 71-75. "Soils," Hilgard, E. W., p. 195. Bulletin No. 123, Illinois Agricultural Experiment Station, pp. 193-195. Date of sampling PRACTICE I (CONTINUED) STRATUM SURFACE SUBSURFACE SUBSOIL 1 2 1 2 1 2 \Veight of pan . Weight of pan and soil as it came from field Weight of pan and air-dry soil Weight of soil as it came from field . . . ^Veiffht of air-dry soil - Loss in weight = capillary water .... Average per cent of hygroscopic water as found in Practice No II . . Weight water-free soil calculated, using above per cent of hygroscopic water Capillary water in per cent based on weight, of water-free soil PRACTICE II DETERMINATION OF HYGROSCOPIC MOISTURE IN SOILS Use air-dry soils from Practice I after grinding thoroughly in a mortar. Weigh the necessary weighing bottles or crucibles which have been made water-free by drying in an oven at 100° C. for five hours. Crucibles may be made water-free in a blast flame. Cool in a desiccator before weighing. It is best to weigh out all of the duplicate samples at the same time, so as to have them under the same moisture conditions. The hygroscopic moisture of soil varies with the temperature and relative humidity of the atmosphere. Dry in an oven at 100° to 105° C. for at least eight hours. Cool in a desiccator. Weigh rapidly to avoid the absorption of much moisture from the air. The loss in weight is the hygro- scopic moisture. Express in tabular form on the opposite page the hygroscopic water in grams and in per cent of water-free soil; also the total moisture in the samples in per cent of water-free soil. « REFERENCES. " Soils," Lyon and Fippin, pp. 141-144. "The Soil," Hall, A. D., pp. 84-88. " Physical Properties of Soil," Warington, Robt., pp. 57-60. "The Soil," King, F. H., p. 252. PRACTICE II (CONTINUED) STRATUM SURFACE SUBSURFACE SUBSOIL 1 2 1 2 1 2 Weight of wei^hin0" bottle Weight of weighing bottle and air-dry soil . Weight of weighing bottle and water-free soil Weight of air-dry soil Weight of water-free soil . .... Loss in weight = hygroscopic water . . Hygroscopic water in per cent, based on weight of water-free soil Per cent of capillary water as found in Practice No I Total water in per cent PRACTICE III EFFECT OF DRAINAGE ON TEMPERATURE OF A SOIL* Two wooden trays 2 three by four feet and eight inches deep, without legs, the bottom resting on the ground, one lined with zinc to prevent drainage and the other made so as to allow drain- age, are filled with the same kind of soil. Water is added to each until drainage begins in the latter. Each tray should be divided into plots of equal size. After the soil is dry enough to work properly, wheat, corn, water- melons, etc. should be planted in their respective plots in each tray, the same number of seeds in each plot. It is convenient to plant 50 or 100 seeds of each kind in this and the following practice. Each student may look after the planting of a single plot, but should make observations morning and evening on all plots in both trays, and keep accurate records of the number of plants that have come up. After the plants begin to come up the temperature in each tray at one, two, and four inches in depth is read and recorded hourly on a clear day from 6 A.M. to 6 P.M. Explain differences in temperature. Why is clay land so often cold ? Why are these seeds used ? REFERENCES. "Soils," Lyon and Fippin, pp. 163, 242-244, and 463. "The Soil," Hall, pp. 130-132. " Physical Properties of Soil," Warington, pp. 174-178. "The Soil," King, pp. 225-227 and 237-238. " Soils," Hilgard, pp. 301 and 307. 1 This and the following practice logically come later in the course, but the season here makes it necessary to give them early in the first semester, but later in the sec- ond semester. Best results may be obtained by conducting these practices before the weather gets too cold in the fall or too hot in the spring. 2 Where it is possible it may be better to conduct this and the following practice in the field, where the conditions of soil and temperature will be more nearly normal. Instead of the undrained tray a zinc box may be put into the ground. It will then be well to place in this box the soil removed to make room for it. Some frames will be needed to mark the limits of the plots, Date of readings PRACTICE III (CONTINUED) TIME THERMOMETER 1 INCH BELOW SURFACE THERMOMETER 2 INCHES BELOW SURFACE THERMOMETER 4 INCHES BELOW SURFACE Drained Undrained Drained Undrained Drained Undrained 6 A.M 7 A.M 8 A.M 9 A.M 10 A.M 11 \ M . . - 12 M 1 P.M 2 P.M 3 P M 4 P AI 5 P.M 6 P.M. GERMINATION TEST TIME AFTER PLANTING WHEAT CORN WATERMELONS Drained Undrained Drained Undrained Drained Undrained days .... days .... days .... days .... days .... days .... days .... PRACTICE IV EFFECT OF COLOR ON TEMPERATURE OF A SOIL Fill a wooden tray three by six feet and eight inches deep with a very light-colored 1 gray silt loam, well pulverized. Divide the tray lengthwise into halves. Divide each half into five or six plots, and plant the same kind of seed — wheat, oats, corn, soy beans, watermelons, etc. — in opposite plots, planting the same number in each. Cover those in one half of the tray three fourths of an inch deep and in the other one half inch deep. Then cover the latter with one fourth inch of black soil so that all of the light-colored soil is covered. Keep all parts of tray equally moist. The planting, observing, and recording the number of plants up each morning and evening may be done the same as in Practice III. Place thermometers with bulbs at one, two, and four inches be- low the surface and one with bulb one inch above the surface, supported in a way that will not affect the temperature. Read and record the temperature hourly from 6 A.M. to 6 P.M. Which soil shows the higher temperature ? Why ? Why can you see the corn rows on low black land sooner after planting than upon the higher lighter colored land ? REFERENCES. " Soils," Lyon and Fippin, pp. 130 and 456-458. "The Soil," Hall, pp. 127-128. "Physical Properties of Soil," Warington, pp. 161-164. M The Soil," King, pp. 230. 1 We may get the same results by filling the tray with dark soil, a brown or black silt loam, and by covering the one half with a very light gray silt loam. 10 of readings PRACTICE IV (CONTINUED) TIME THERMOMETER 1 INCH ABOVE SOIL THERMOMETER 1 INCH BELOW SURFACE THERMOMETER 2 INCHES BELOW SURFACE THERMOMETER 4 INCHES BELOW SURFACE Dark Light Dark Light Dark Light Dark Light 6 A.M 7 \.M 8 A.M 9 A.M 10 A M ... 11 A.M i. 12 M 1 P.M. . . 2 P.M 3 P.M 4 P.M. . . . 5 P.M 6 P.M GERMINATION TEST TIME AFTER PLANTING WHEAT OATS CORN SOY BEANS MELONS Dark Light Dark Light Dark Light Dark Light Dark Light Dark Light days days days days days days days 11 PRACTICE V DETERMINATION OF TOTAL MOISTURE IN THE SAME SOIL UNDER DIFFERENT CONDITIONS Three students may work together, one taking the surface, an- other the subsurface, and the third the subsoil. These results may be compared. Collect samples of surface, subsurface, and subsoil 1 from the following places : (1) sod, (2) tilled field, (3) forest. In col- lecting these samples care should be taken to secure them from as small an area as possible, so that the mineral composition of the soil may be uniform. It is essential, also, that the topography, in so far as it affects drainage, should be uniform. Expose the samples to the air as little as possible while taking them. After taking them to the laboratory the soil should be thor- oughly mixed by shaking. The condition of the weather at the time the samples are taken, and also the amount of rainfall within the week previous, should be noted. Make the determinations in duplicate. Weigh six soil pans and use 100 g. of each soil. Weigh rapidly to avoid loss by evaporation. Dry at room temperature for forty-eight hours; then place in an oven at 100° C. for at least ten hours. Cool to room temperature and weigh at once. The loss in weight represents the total water content. Explain differences in moisture content of the soils. REFERENCES. " Soils," Lyon and Fippin, pp. 144-148. "The Soil," Hall, pp. 71-75. 1 In collecting the subsoil for moisture determination it is sometimes well to divide it into two equal parts as to depth. 12 Date of sampling .... PRACTICE V (CONTINUED) NAME OF STUDENT SURFACE SUBSURFACE SUBSOIL Sod 1 2 1 2 1 2 Weight of pan .... Weight of pan and. soil Weight of pan and water-free soil .... Weight of moist soil Loss of water in grams Per cent of moisture on water-free basis . . Tilled field "Wei^ht of pan . AVeight of pan and soil Weight of pan and water-free soil .... Weight of moist soil W'eight of water-free soil Loss of water in grams Per cent of moisture on water-free basis . . Forest Weight of pan Weight of pan and soil Weight of pan and water-free soil .... Weight of moist soil .... Weight of water-free soil Loss of water in grams . . ... Per cent of moisture on water-free basis . . 13 PRACTICE VI DETERMINATION OF THE VARIATION IN THE HYGROSCOPIC MOISTURE OF SOILS In this exercise each student will use air-dry soils provided for the regular class work. These are sand or sandy loam, gray silt or gray silt loam, brown silt loam, clay or clay loam, and peat. Determine the weight of moisture lost when heated for eight hours in an oven at 100 to 105° C. This loss is the hygroscopic moisture. Express in per cent based on the weight of water- free soil. All samples, especially duplicates, should be weighed out at the same time to avoid any change in the amount of mois- ture due to a change in relative humidity or temperature. For directions in detail see Practice II. Explain differences between clay or clay loam and sand or sandy loam ; between peat and sand or sandy loam. REFERENCES. "Soils," Lyon and Fippin, pp. 141-144. " The Soil," Hall, pp. 84-88. " Physical Properties of Soil," Warington, pp. 57-60. "The Soil," King, p. 252. "Soils," Hilgard, pp. 196-200. 14 PRACTICE VI (CONTINUED) SOILS SAXD OR SAXDY LOAM GRAY SILT OR GRAY SILT LOAM BROWN SILT LOAM BLACK CLAY LOAM PEAT 1 2 1 2 1 2 1 2 1 2 Weight of weighing bottle Weight of weighing bottle and air-dry soil . . . Weight of weighing bottle and water-free soil . . Weight of air-dry soil . T » Weight of water-free soil . Loss in grams = Wt. of hy- groscopic water . . . Hygroscopic water in per cent on water-free basis 15 PRACTICE VII FLOCCULATING EFFECT OF LIME Use four shaker bottles with rubber stoppers. In the first put 200 cc. distilled water as a check, in the second 200 cc. of a 0.025 per cent solution 1 of quicklime (CaO, preferably C.P.), in the third 200 cc. of a 0.05 per cent solution, and in the fourth 200 cc. of a 0.1 per cent solution. Add to each 3 g. of a heavy clay finely ground in a mortar. Agitate for one hour in the mechanical shaker. After shaking take out a drop from the check and 0.1 per cent solution and examine under a microscope with a high power. Make sketches on data sheet of the arrangement of soil particles. Then pour some of the contents of the bottles into tubes and whirl in a centrifuge, stopping every two or three minutes to note the effect upon clearness. Whirl for at least ten minutes. Then pour the contents of the tubes back into their respective bottles, shake thoroughly, and set aside. Observe regularly to determine the time required for complete sedimentation in each case. Which becomes clear first in the centrifuge ? Why ? What application of this principle is made in farm practice ? REFERENCES. " Soils," Lyon and Fippin, pp. 116 and 352. "The Soil," Hall, pp. 38-41. "Physical Properties of Soil," Warington, pp. 25-35, especially 30-32. " The Soil," King, p. 30. 1 These solutions will be made by the instructor. 16 Date run in centrifuge PRACTICE VII (CONTINUED) TIME TO BECOME CLEAR IN CENTRIFUGE TIME FOR SEDIMENTATION Check — distilled water 0.025 per cent solution 0.05 per cent solution 0 1 per cent solution . Make sketches of arrangement of soil particles. Distilled water 0.1 per cent lime solution 17 PRACTICE VIII DETERMINATION OF THE EFFECT OF LIME ON PLASTIC SOILS Two students may work together on this experiment. Weigh out six 300-g. samples of a clay soil. To sample No. 1, check, add no lime. To No. 2 add 0.1 per cent, 0.3 g. of powdered quicklime. To No. 3 add 0.5 per cent, 1.5 g. of powdered quicklime. To No. 4 add 1.0 per cent, 3.0 g. of powdered quicklime. To No. 5 add 2.0 per cent, 6.0 g. of powdered quicklime. To No. 6 add 3£ per cent, 10.0 g. of sand. Mix the clay and lime thoroughly in a soil pan and add just enough water for maximum plasticity. Cover with a glass plate to reduce loss by evaporation. Set aside to let the lime act for at least twenty-four hours. Make a test of tenacity, as directed in Practice IX. After making the tenacity test fill the mold, first placing in it a piece of damp cheesecloth to facilitate the removal of the clay. Make duplicate bricks of each mixture, being careful to com- press each to the same degree. Place the bricks on a cloth in a soil pan and dry in an oven for five hours at 100° C. Test the strength of each brick by supporting the ends so as to allow just 3 inches between the points of support. Suspend weight bag in the middle of brick and determine the weight necessary to break each by pouring shot into the bag. Explain the effect of lime. Why does the sand not have as much effect as lime on the breaking strength ? How many tons of lime per acre do the above percentages rep- resent, the surface 6| inches of soil weighing 2,000,000 pounds? REFERENCES. " Soils," Lyon and Fippin, pp. 116-117. " The Soil," Hall, pp. 40-41. " Physical Properties of Soils," Warington, pp. 25-35, especially p. 33. " The Soil," King, p. 30. " Soils," Hilgard, pp. 59-60. 18 PRACTICE VIII (CONTINUED) TEST OF STRENGTH OF BRICKS First trial Second trial Average Check — no lime 0.1 per cent 0.3 g. of lime 0.5 per cent 1.5 g. of lime 1 0 per cent 3 0 & of lime . . 2 0 per cent 6 0 °° of lime 3^ per cent, 10.0 g. of sand COMPARISON OF TENACITY MIXTURE CHECK 0.3 GRAM LIME 1.5 GRAMS LIME 3 GRAMS LIME 6 GRAMS LIME 10 GRAMS SAND 1 2 Average of trials Weight to overcome friction Tenacity 19 PRACTICE IX TESTING THE TENACITY OF MOIST SOILS Two students may work together. Use the gray silt or gray silt loam, brown silt loam, and the clay or clay loam. Weigh out three 200-g. samples of each soil in a pan, and mix by hand enough water with the first to bring it to a maximum adhesiveness, as near as you can judge. Carefully measure and record the amount of water used. To the second sample add 10 cc. more water, and to the third 20 cc. more than to the first sample. Fasten the cages together firmly, pack the moist soil into them, and scrape off level with top of cage. Attach the weight bag, release the movable cage, and pour fine shot into the bag slowly until the soil column breaks. Weigh the bag and shot. Put the movable cage in place, but not having ends of the soil columns in contact with each other, and determine the weight necessary to overcome friction. Subtract this from the previous weight. The result represents the tenacity of a column of moist soil 1 square inch in cross section. Make a duplicate test. Sample No. 1 made up to maximum tenacity should be used immediately in Practice X. How does fineness of grain affect tenacity ? What effect has undecomposed organic matter on tenacity ? What term is applied to very tenacious soils ? What are the differences in the working of these soils ? REFERENCES. w Soils," Lyon and Fippin, pp. 97-99 and 129. "Physical Properties of Soil," Warington, pp. 23-25. 20 PRACTICE IX (CONTINUED) SOILS GRAY SILT OK GRAY SILT LOAM BROWN SILT LOAM CLAY OR CLAY LOAM 1 2 3 1 2 3 1 2 3 Amount of water used .... Weight to overcome tenacity . 1 2 Average of trials . Weight to overcome friction . . Tenacity - FIG. 2. TENACITY-TEST APPARATUS 21 PRACTICE X DETERMINATION OF SHRINKAGE IN SOILS Two students may work together. Weigh out in a small soil pan 200 g. of sand or sandy loam, gray silt or gray silt loam, brown silt loam, clay or clay loam, and peat. The soil with the quantity of water representing maximum tenacity in Practice IX may be used here if put into the pan while it is still moist. Mix each sample thoroughly by hand with the right quantity of water to bring about maximum adhesiveness. Place cheesecloth in the bottom of a pan 3 inches, or 76 mm., square and ^ inch deep. Pack in the soil and scrape it off even with the top of pan. Take out the block of soil on cheesecloth and dry at room temperature for 'a day or two before placing in the oven at 100° C. for twenty-four hours. Measure and record the size of the block of dry soil. Cal- culate the shrinkage and express in per cent of the original area of the block of wet soil. SOILS AREA OF SOIL BLOCKS AFTER" DRYING AVERAGE AREA OF PAN BOTTOM SHRINKAGE DUE TO DRYING PER CENT OF SHRINKAGE Sand 1 2 Silt 1 2 1 2 Black clay loam 1 2 Drab clay 1 2 Peat 1 2 • 99 PRACTICE X (CONTINUED) What relation exists between size of particles and shrinkage ? What effect has clay and organic matter on shrinkage ? REFERENCES. " Soils," Lyon and Fippin, pp. 98-99. " Physical Properties of Soil," Warington, pp. 35-36. "Soils," Hilgard, pp. 112-114. PRACTICE XI DETERMINATION OF THE APPARENT SPECIFIC GRAVITY OF SOILS In determining apparent specific gravity the pore space is not taken into account. Then apparent specific gravity is much less, numerically, than real specific gravity. Find the apparent specific gravity of sand or sandy loam, gray silt or gray silt loam, brown silt loam, clay or clay loam, and peat. Weigh a clean empty soil tube.1 Fill the tube with one of the soils by simply pouring it in loosely until it reaches the crease near the top, being careful not to compact it by jarring or jolt- ing. Weigh, empty, and then fill again with the same soil in the same way, using the average of the two weights to determine the apparent specific gravity. Treat each soil in the same way. Calculate the weight of water-free soil taken in each case by using the average per cent of hygroscopic moisture found in Practice VI. These average figures will be given to the class by the instructor. Find the volume of the soil tube by filling with water and weighing. The weight in grams will give the volume of the tube in cubic centimeters, since 1 cc. of water weighs approxi- mately 1 g. The weight of the soil divided by the volume of the tube gives the weight of 1 cc. of soil, or the volume weight of the soil. Numerically this is the apparent specific gravity. Repeat the above process with each soil, but compact the soil. Lift the base on which the tube stands to the 6-inch mark and let it drop. Do this six times. Repeat, refilling each time until tube is full to the crease. 1 A brass tube 2 inches in diameter and 12 inches long, closed at one end. 23 PRACTICE XI (CONTINUED) The apparent specific gravity of soils varies with the degree of compaction. A freshly plowed field is much lighter per cubic foot than one compacted by rains, tramping, or by means of the roller. FIG. 3. SOIL COMPACTOR A, movable interior to be lifted, which, by dropping, compacts the soil; 5, soil tube in place on base of A ; C, rubber stopper closing tube ; D, felt or rubber cushion Why is the apparent specific gravity of a sandy soil higher than that of a silt loam ? Why is the apparent specific gravity of peat so low ? 24 PRACTICE XI (CONTINUED) Sandy soils have less pore space than clay or clay loams. How will this affect the apparent specific gravity ? Calculate the weight of a cubic foot of each soil, loose and compact. REFERENCES. w Soils," Lyon and Fippin, pp. 94-96 and 128. "The Soil," Hall, pp. 63-64. " Physical Properties of Soil," Warington, pp. 42-44. " The Soil," King, p. 85. " Soils," Hilgard, pp. 107-108. SOILS SAND OR SANDY LOAM GRAY SILT OR GRAY SILT LOAM BROWN SILT LOAM CLAY OR CLAY LOAM PEAT L* C1 L C L C L C L C Weight of tube and air- dry soil 1 2 Average of trials . . . Weight of tube .... Weight of air-dry soil . Per cent of hygroscopic moisture Weight of water-free soil No. cc. water to fill tube . Apparent specific gravity Weight of a cubic foot pounds in 1 L = Loose ; C = Compact. 25 PRACTICE XII -3*6- DETERMINATION OF APPARENT SPECIFIC GRAVITY OF SURFACE SOIL UNDER FIELD CONDITIONS Two students may work together, one taking plowed ground, the other sod near by. Take a tube 1 similar to Fig. 4 and force it into the ground to the depth of 6 inches. Remove the soil to a weighed pan. Collect another sample of the same soil under identical con- ditions, using every precaution to have the duplicate similar. Dry at room temperature for a day or two before placing in the oven at 100° C. to dry for twenty -four hours. Calculate the volume of soil taken and divide the weight of water- free soil by this. The result is the apparent specific gravity. The apparent specific gravity of soils in the field may be taken as an approximate indication of their tilth, since the better the tilth the lower the apparent specific gravity for the same kind of soil. This is due to the fact that soils in good tilth are looser on account of the presence of a larger proportion of organic matter and better granu- lation. The apparent specific gravity of a continuously cropped soil is higher than that of one on which proper rotations have been , n practiced. Why ? if It will be well to collect samples under varied conditions and have each student secure the results from a number of others and tabulate in his guide for purposes of comparison. -8*- 1 An iron or brass tube 2 or 3 inches in diameter, with a cutting edge. 26 PRACTICE XII (CONTINUED) What is the weight of a cubic foot of soil under the -above conditions ? REFERENCES. " Soils," Lyon and Fippin, pp. 94-96. " The Soil," Hall, pp. 64-65. " Physical Properties of Soil," Warington, pp. 44-49. " Soils," Hilgard, pp. 107-108. Soil STUDENT CONDITION OF SOIL, * 1 2 1 2 Weight of pan and water-free soil Weight of pan . . . W^eio'ht of water-free soil Capacity of tube in cc. — volume of soil Apparent sp. gr. based on wt. of water-free soil . . . \Veifirht of a cubic foot of soil in pounds 27 PRACTICE XIII DETERMINATION OF REAL SPECIFIC GRAVITY OF SOILS Each student will use a light and dark soil provided by the instructor. First determine the hygroscopic moisture as in Practice VI and tabulate on opposite page. Fill a 50-cc. pycnometer to the top of capillary tube in glass stopper with freshly boiled and cooled distilled water whose temperature is known. Wipe pyc- nometer dry and weigh. Pour out about half of the water and weigh. Add about 5 g. of soil (about half as much in case of peat) and weigh again ; the difference is the soil added. In this case the soil need not be weighed accurately beforehand. Boil gently for a few minutes in a water bath, sand bath, or on an asbestos mat to drive out the air from the soil. Refill with distilled water, bring to the same temperature as before, and weigh. From the per cent of hygroscopic water as deter- mined calculate the weight of water-free soil used. The weight of the pycnometer full of water plus the weight of water-free soil added, minus the weight of the full pycnometer containing the soil gives the weight of water displaced by the •i rr^i weight of water-free soil soil. 1 hen — -P- — = specific gravity, weight 01 water displaced Compare real with apparent specific gravity. Why is the real specific gravity higher ? REFERENCES. " Soils," Lyon and Fippin, pp. 94-96. " The Soil," Hall, p. 63. "Physical Properties of Soils," Warington, pp. 41-42. 28 PRACTICE XIII (CONTINUED) SOILS 1 2 1 2 1 2 1 2 Weight of air-dry soil . .... Per cent of hygroscopic water .... Weight of water-free soil Weight of pycnometer filled with water *. Weight of pycnometer filled with water + water-free soil Weight of pycnometer and soil + water, Weight of water displaced Specific gravity HYGROSCOPIC WATER SOILS 1 2 1 2 1 2 1 2 ^V^eight of air-dry soil Weight of water-free soil Loss in weight = hygroscopic water . . Per cent of hygroscopic water .... 29 PRACTICE XIV DETERMINATION OF POROSITY (FIRST METHOD) Use sand or sandy loam, gray silt or gray silt loam, brown silt loam, clay or clay loam, and peat. The weight of soil and volume of tube as found in Prac- tice XI may be used here, or one may weigh a Nessler jar or graduated cylinder and fill to the 100-cc. mark with soil not compacted, and weigh. Compute the amount of water-free soil, using the average per cent of hygroscopic moisture from Practice VI which was given for Practice XI. The real specific gravity will be deter- mined or furnished by the instructor. (Volume of soil x real specific gravity) — weight of water-free soil ^ _ Volume of soil x real specific gravity per cent of pore space or porosity. What effect does size of particles have on total amount of pore space ? Does the amount of pore space increase or decrease with the amount of organic matter ? Which of the soils have the largest pores ? Does this mean the greatest amount of pore space ? REFERENCES. " Soils," Lyon and Fippin, pp. 84-94. " The Soil," Hall, pp. 60-63. " Soils," Hilgard, pp. 108-109. 30 PRACTICE XIV (CONTINUED) SOILS SAND OR SANDY LOAM GRAY SILT OR GRAY SILT LOAM BROWN SILT LOAM CLAY OR CLAY LOAM PEAT H C1 L C L C L C L C Weight of cylinder . . . Weight of cylinder and air-dry soil .... 1 2 Average of trials . . . •i Average weight of air-dry soil ....... Weight of water-free soil Per cent of hygroscopic water Real specific gravity . . Per cent of pore space 1 L = Loose ; C = Compact. 31 PRACTICE XV DETERMINATION OF POROSITY (SECOND METHOD) Find what per cent the apparent specific gravity is of the real specific gravity and subtract this from 100 per cent. The re- mainder expresses the per cent of pore space in the soil, or its porosity. Use the real specific gravity and the average figures for apparent specific gravity from Practice XI, as given you by the instructor. Determine the porosity of the stock soils, loose and compact, and express the results in tabular form. What relation exists between porosity and apparent specific gravity? Why? REFERENCES. " Soils," Lyon and Fippin, pp. 92-93. " The Soil," Hall, pp. 60-63. 32 PRACTICE XV (CONTINUED) SOILS SAND OR SANDY LOAM GRAY SILT OR GRAY SILT LOAM BROWN SILT LOAM CLAY OR CLAY LOAM PEAT LI C1 L C L C L C L C Apparent specific gravity . Heal specific gravity . . Per cent of pore space . 1 L = Loose ; C = Compact. 33 PRACTICE XVI DETERMINATION OF LOSS ON IGNITION The loss that a soil suffers when it is ignited is often taken as a measure of its organic matter, but it can be only a very rough approximation at best for most soils. For some subsurface and nearly all subsoils it gives little or no idea of the amount of or- ganic matter. By igniting, the organic matter, volatile salts, car- bon dioxide of carbonates present, and water of hydration will be driven off. In heavy clay soils and all fine-grained ones water of hydration forms a very large part of the loss. Subsoils with little or no organic matter may lose as much as surface soils, due to the larger amount of clay and consequently a larger amount of water of hydration which is driven off by the heat. The more organic matter present in a soil or the greater the sand content, the nearer the loss on ignition will correspond to the actual organic content, so that for sandy and peat soils ignition may give a close approximation to the amount of organic matter present. Use the same soils as used in Practice XIII. Bring four small crucibles (25 cc.) to a constant weight by igniting in a blast flame. Weigh out 5-g. duplicate samples of each soil and ignite in the crucibles at a low red heat for one hour in a muffle furnace. Cool in a desiccator and weigh. Calculate the weight of water-free soil used. Express the loss due to ignition in per cent of the water-free soil. Which soil loses more ? Why ? If a coarse- and a fine-grained soil have the same organic con- tent, which will lose more on ignition ? REFERENCES. " Soils," Lyon and Fippin, pp. 124-126. w The Soil," Hall, p. 43. 34 PRACTICE XVI (CONTINUED) SOILS 1 2 1 2 1 2 1 2 Weight of crucible and air-dry soil . . Weight of air-dry soil Weight of crucible and water-free soil . Hygroscopic moisture in per cent . . . Weight of water-free soil Weight of soil after ignition .... - Loss in grams due to ignition .... Percent loss on ignition on water-free basis 35 PRACTICE XVII DETERMINATION OF HUMUS IN SOILS Weigh out 5-g. or 10-g. samples of the air-dry soils used in Practices XIII and XVI. Place on a filter in a funnel and leach out the lime and magnesia with dilute hydrochloric acid.1 When the lime and magnesia are all leached out as shown by testing the filtrate by collecting a few cubic centimeters of the acid filtrate in a test tube direct from the funnel and adding dilute ammonia drop by drop until the solution is slightly alkaline, the addition of a few drops of ammonium oxalate will produce no pre- cipitate. If lime is present, a white opaque crystalline precipitate is formed. Wash out the hydrochloric acid with distilled water. Dry the soil and filter at room temperature for a day, then in the oven at 100°C. for 8 hours. Place soil and filter in a shaker bottle. Add 150 cc. of dilute ammonia2 for light soils and 250 cc. for dark soils, the amount depending on the quantity of humus in the soil. Shake for 3 hours. Filter. If evaporation, which would concentrate the filtrate, can be prevented, evaporate 100 cc. of the humus filtrate to dryness and calculate total humus ; otherwise evaporate all of the fil- trate. In this case care should be taken to wash out with am- monia any humus that may be held mechanically in the soil or filter paper. Dry the evaporated humus at 100°C. for 5 hours. Weigh, ignite, and weigh again. The loss in weight is the humus. Cal- culate from the weight of air-dry soil the weight of water-free soil used, and express the humus in per cent of water-free soil. Of what benefit is a large amount of humus in a soil ? If an acre of soil, 6| inches deep, weighs 2,000,000 pounds, how many tons of humus in the surface of the above soils ? REFERENCES. " Soils," Lyon and Fippin, p. 127. "The Soil," Hall, pp. 42-47. " The Soil," King, pp. 94-96. " Soils," Hilgard, pp. 125-140, especially p. 132. Circular No. 82, Illinois Agricultural Experiment Station. 1 For dilute hydrochloric acid use 25 cc. hydrochloric acid, sp. gr. 1.19, with 808 cc. of distilled water. 2 For the ammonia 178 cc. saturated ammonia with 422 cc. of distilled water. These solutions will be prepared by the instructor. 36 PRACTICE XVII (CONTINUED) SOILS ... 1 Weight of crucible Weight of crucible and air-dry soil . . Weight of air-dry soil Per cent of hygroscopic water (if needed) Weight of water-free soil (calculated) . Weight of evaporated filtrate before ignition Weight of evaporated filtrate after ignition Loss in weight = humus (approximately) Total humus of sample Per cent of humus Average per cent Tons of humus per acre Pounds of nitrogen per acre in humus 37 PRACTICE XVIII DETERMINATION OF CONDUCTIVITY OF HEAT IN SOILS The five regular stock soils are used. In one end of the tray place the copper vessel for the water and put asbestos board on all sides except the one in contact with the soil. Place the same quantity of water in each copper vessel. Fill the trays with soil. Place thermometers, which read uni- formly, with the bulb at a depth of 2^ inches and 1, 2, 3, 4, 5, and 6 inches from the vessel of water. Heat the water with a Bunsen burner through the opening in the bottom of the tray. Remove the burner when the water reaches a temperature of 95° C. and record the temperature of the soil. Record the tem- perature reached at the end of each five- or ten-minute period for about an hour. Students may work in sets of five, each taking the tempera- ture in one soil and exchanging with each of the other four for comparison. Is there any relation between porosity and conductivity ? REFERENCES. " Soils," Lyon and Fippin, pp. 459-460. " Physical Properties of Soil," Warington, pp. 168-174. FIG. 5. APPARATUS FOR DETERMINING CONDUCTIVITY OF HEAT 38 H «J N OH CLAY OR CLAY LOAM -i. BROWN SILT LOAM GRAY SILT OR GRAY SILT LOAM SAND OR SANDY LOAM STUDENT a I 0 § H Temperature at 1 inch . 1 o