THE BIFLEX BINDER NOTEBOOK Span the slight inward opened archt position by p: Number Size 21 8 41 SVa 61 4% 22 8 42 554 62 VA Class c Book ir'.k+MO COPYRIGHT DEPOSIT. them by a ted on the ocked into the paper. Style le opening WITH i 09) 23 43 8 x \OVz 5K x 8 150 sheets 150 $0.45 .40 Side opening *Such paper as that furnished in (linn and Company fillers Fillers of plain or ruled paper for additional notes, 15 cents per half pound Printed fillers for the various special notebooks published in the Biflex Binder differ in price. For list and prices see Ginn and Company's Catalogues GINN AND COMPANY BOSTON :: NEW YORK :: CHICAGO :: LONDON : A MANUAL OP SOIL PHYSICS BY PERCY Bj BARKER, M.A. PROFESSOR OF AGRONOMY IN THE UNIVERSITY OF NEBRASKA AN J) HORACE J. YOUNG, B.Sc. ASSISTANT PROFESSOR OF AGRONOMY IN THE UNIVERSITY OF NEBRASKA GINN AND COMPANY BOSTON • NEW YORK • CHICAGO • LONDON ATLANTA • DALLAS - COLUMBUS • SAN FRANCISCO S52A <§* ft- COPYRIGHT, 1915, BY PERCY B. BARKER AND HORACE J. YOUNG ALL RIGHTS RESERVED 315.9 <$0; uC G1NN AND COMPANY- PRO- PRIETORS • BOSTON • U.S.A. ©CI.A416192 m -2 1915 PREFACE The exercises described on the following pages are intended to give the student an understanding of the origin, composition, and physical properties of soils and to show the relations of these properties to methods of soil management. The work outlined in the manual is sufficient for two semestprs, but may be completed in less time if more than two laboratory periods are held per week. While these exercises are the outcome of ten years' experience in teaching the important physical properties of soils, they are not all original with the authors. Material has been drawn from many sources and arranged to give the best applications to important principles of soil management. In connection with each exercise, references have been given and questions asked. It is hoped that this method of study will enable the student to obtain a great amount of information relative to the application of each exercise. THE AUTHORS University of Nebraska, College of Agriculture Lincoln, Nebraska [iii] 3. CONTENTS PAGE Introduction 1 KXERCISE I. A Study of Soils in the Field 3 II. Soil Kegions and Precipitation 5 III. Geological Map and Vertical Section of State . . 7 IV. Soil Classification 9 V. Examination of Soil Particles 11 VI. Soil-forming Minerals 13 VII. Soil-forming Rocks 15 VIII. Volume Density and Porosity 17 IX. Number and Surface Area of Soil Particles ... 21 X. Flow of Air through Soils 23 XI. Percolation of Water 25 XII. Determination of Hygroscopic Moisture .... 27 XIII. Capillary Rise of Water in Soils 29 XIV. Effect of Organic Matter and Dry Clods upon Capillarity 33 XV. Power of Soils to retain Water against Percolation 35 XVI. The Effectiveness of Mulches 39 XVII. Effect of Water upon Soil Volume 43 XVIII. Loss on Ignition 45 XIX. Soil Acidity and Basicity 47 XX Determination of Humus 49 XXI. Leaching of Soils 51 XXII. Power of Soils to absorb Salts 53 XXIII. Absorption of Gases by Soils 55 XXIV. Absorption of Moisture by Soils 57 XXV. Flocculation of Clay 59 XXVI. Effect of Lime on Soil Structure ....... 61 [v] MANUAL OF SOIL PHYSICS EXERCISE PAGE XXVII. Effect of Sand and Organic Matter on Soil Structure 63 XXVIII. Effect of Alternate Wetting and Drying on Soil Structure 65 XXIX. Effect of Alternate Freezing and Thawing on Soil Structure 67 XXX. Effect of Color on Soil Temperature .... 69 XXXI. Effect of Water on Soil Temperature .... 71 XXXII. Effect of Vegetation and Topography <>n Soil Temperature 73 XXXIII. Effect of Cultivation on Soil Temperature . . 75 XXXIV. Soil Tenacity 77 XXXV. Transference of Heat in Soils 79 XXXVI. Absolute Specific Gravity of Soil 81 XXXVII. Apparent Specific Gravity of Field Soils . . 83 XXXVIII. Specific Heat of Soils 85 XXXIX. Evaporation of Water 87 XL. Moisture Determinations of Field Soils . . 89 XLI. Standardization of the Eyepiece Micrometer . 91 XLII. Mechanical Analysis of Soils 93 XLIII. Soil Examination 97 XLIV. Examination of Soil Samples 99 Weights and Measures 101 «•< [vi] MANUAL OF SOIL PHYSICS INTRODUCTION SOIL SAMPLING In collecting samples of soil for study in the laboratory, great care should be taken to obtain samples that are repre- sentative of the soils in the area from which they are taken. Avoid taking samples in places where conditions are unusual, such as gopher mounds, squirrel holes, footpaths, cattle trails, old roadways, depressions, and other places showing abnormal plant growth. After selecting a place which represents the soil and field conditions, scrape away from the surface all foreign matter and plant remains. The underground parts of plants, as well as insects and other animal life in the soil, are considered as a part of it. The tools commonly used in taking samples are augers and soil tubes (Fig. 14). In sampling by the auger method, two augers, one 3 and one 6 feet long, are usually employed. By using a smaller bit on the 6-foot auger, samples may be procured which are less contaminated with soil from the upper three feet. Marks are made upon the shanks of the augers so that the depth from which the sample is being taken may be easily ascertained. The soil obtained from each foot is placed in a separate bag or container and labeled ac- curately as to the location and depth. After the sample from one foot has been obtained, work the auger up and down in the hole several times and discard the soil which sticks to the [1] MANUAL OF SOIL PHYSICS bit. This helps to keep the soil from the next foot from being contaminated with that above. In this manner continue the sampling to the desired depth. The soil tube has a cutting edge somewhat smaller than the bore. It is simply driven into the soil to the depth of one foot at a time, and a core of soil taken throughout the foot. For convenience, two or more tubes of different lengths are used. If the samples are being taken for determining the total moisture in the field, precautious should be taken to prevent evaporation. For this purpose tight metal boxes or glass jars are usually employed. The making of detailed studies of the soil sometimes calls for inch samples. A convenient method of procuring Buch samples is by means of the Nebraska Soil Anger < Fig. 13). This auger is also useful in obtaining a known volume of soil for determining the apparent specific gravity and porosity of field soil. Since the composition and physical characters of soils of the same type (especially soils of glacial origin) vary somewhat, it is the practice to take what is known as a composite sample. This means the taking of several samples in the same type and uniting them. The larger the number of places from which soil is taken, the more representative the sample. A composite sample made up of soils from three different loca- tions will usually be fairly representative of areas of less than ten acres. [2] EXERCISE I A STUDY OF SOILS IN THE FIELD Object. The object of the exercise is to make a thorough study of soils under field conditions. Materials needed. Four-foot auger; 6-foot auger; drawing paper ; notebook. Procedure. Examine several types of soil to the depth of 6 feet, with special reference to the following points: 1. Depth of the surface soil at different locations. 2. Texture and structure at different depths. 3. Amount and distribution of the organic matter at vari- ous depths and locations. 4. Variations in color. The soil types should be selected so as to give a variation in the depth of the surface soil and in the topography. In each type ascertain accurately the depth of the surface soil. Describe each of the soil types examined, giving due em- phasis to depth of surface soil, distribution and amount of organic matter, texture, structure, color, and topographic effects. Draw a section of each type examined, using a scale of 1 inch to the foot, showing the depth of the surface soil, the location of lime concretions, etc. In drawing the sections, use the following legend : li! ■HI WiMiWiiiii Subsoil Hard-pan (gumbo) Lime concretions Iron concretions Fig. 1. Legend used in drawing sections [3] MANUAL OF SOIL PHYSICS References : Widtsoe : Dry-Farming, pp. 59-73. Wiley: Principles and Practices of Agricultural Analysis, Vol. I, pp. 59-60. Hilgard : Soils, pp. 120-187. Lyon and Fippin : Soils, pp. 68-69. Questions : 1. State briefly what is understood by the following terms : (a) surface soil; (b) subsoil. 2. Explain briefly (a) the difference between the surface soil in arid and in humid regions ; (ft) the difference between the subsoil in arid and in humid regions. 3. Account in as many ways as possible for the even distri- bution of the organic matter in the surface soil. *- [4] EXERCISE II SOIL REGIONS AND PRECIPITATION Object. The object of the exercise is to make a study of the soil regions of the state or county, together with the distribution of rainfall. Materials needed. Ruler; hard pencil; base map of state or county ; guide map. Procedure. Draw upon the base map all the regions of main types of soil indicated on the guide map, and the lines repre- senting the annual precipitation. Use the same legend as has been used on the guide map ; also place this legend at the bottom of the map. References : Condra : Geography of Nebraska, pp. 72-113. Annual Report of the Nebraska Slate Board of Agriculture (1909), pp. 271-311 In other states the experiment station bulletins and the sxirveys of the United States Bureau of Soils will give valuable information. Questions : 1. How many square miles are there in each region ? 2. What is the origin of the soil in each region : (a) residual ? (b) glacial? (c) loess? (d) alluvial? 3. What is the average annual precipitation in the state or county ? 4. In which soil region is your home farm located ? 5. What is the annual precipitation on your home farm ? 6. Name two crops that are profitably raised in each soil region. [5] t , EXERCISE III GEOLOGICAL MAP AND VERTICAL SECTION <>K STATE Object. The objecl of the exercise is to make si study of the Important geologic formations of the state, with reference to their part in soil making. Materials needed. Ruler; hard pencil; base map of state or county; drawing paper ; guide maps. Procedure. Draw a map of the State <>r county, showing the geologic formations as they are exposed <>n the surface. Usr the same legend as is used on i\w guide map; also place the Legend in the margin of the map. Draw, according to scale, b vertical-section profile map, showing the underlying forma- tions of the state or oounty. Label each formation carefully. References : Annual Report of the Nebraska State Board of Agric.uUurc (l'.xxs L907), pp. 826 844. The bulletins of the State Agricultural Experiment Station or of the State Geological Survey will give valuable Information for this exercise. Questions : 1. N aim* in order, commencing with the oldest exposed, all the underlying Formations In the state or oounty. 2. What is the surface geologic formation of y borne farm? :i. How many formations underlie your home farm hi- place? NTame them. I. \\ iiiiii formations give rise to good productive .soils? 5. W'IihIi formations furnish a good watei supply? Which a poor water supply ? [7] c- EXERCISE IV SOIL CLASSIFICATION Object. The object of the exercise is to become familiar, first, with the different soil types, and, second, with the scheme of soil classification. Materials needed. Three-foot auger; notebook. Procedure : Classification as to Origin Physical Classification 1. Sedentary a. Residual 1. 2. Structure Class b. Cumulose 3. Organic matter 2. Transported a. Colluvial 4. 5. Origin Color b. Water (1) Marine (2) Lacustrine (3) Alluvial 3. Glacial 4. iEolian 6. 7. 8. 9. 10. Depth Drainage Topography Native vegetation Natural productiveness . Series Type The field selected for study should contain as many differ- ent soil types as can be found together. In this exercise the following points must be kept in mind: texture, structure, organic matter, origin, color, depth, drainage, topography, native vegetation, and natural productiveness. Also the meaning of the following terms should be well understood: soil province, soil series, soil class, and soil type. [9] MANUAL OF SOIL PHYSICS Write a full description of each soil type that you have studied, giving due emphasis to the ten points mentioned above. References : Lyon and Fippin : Soils, pp. 69-80. Hopkins: Soil Fertility and Permanent Agriculture, pp. 114-136. " Soils of the United States," in Bulletin No. 96 of the United States Department of Agriculture, Bureau of Soils, pp. 109-165, SOS- SSI, 465-495. Questions : 1. What is understood by a soil province, soil series, soil class, and soil type ? Give one example of each. 2. Describe the following classes of soils as used by the United States Bureau of Soils : («) fine sandy loam ; (b) silt loam ; (c) loam ; (<7) clay loam ; (e) clay. 3. How deep are soils sampled in establishing soil types ? [10] EXERCISE V EXAMINATION OF SOIL PARTICLES Object. The object of the exercise is to study soil particles, with and without the microscope, in order to become familiar with the general composition of soils. Materials needed. Microscope ; sand ; surface soil ; subsoil ; clay ; drawing paper ; pen or hard pencil. Procedure. Examine, without the aid of the microscope, a small amount of sand, noting the color and adhesion of the particles. Examine a small amount of sand with the micro- scope, noting the color, shape of the particles, and any cohe- sion. While the mount of sand is under the microscope, make a drawing of several particles to show their comparative sizes and shapes. In the same manner examine some of the surface soil, the subsoil, and the clay, placing the drawings on the same piece of paper with the drawings of the sand particles. In studying the surface soil, note the structure of the crumbs, comparing it with the same structure in the subsoil and in the clay. References : Snyder : Soils and Fertilizers, pp. 11-20, 326. Lyon and Fippin : Soils, pp. 69-79. Wiley : Principles and Practices of Agricultural Analysis, Vol. I, pp. 282-290. "The Mineral Composition of Soil Particles," in Bulletin No. 54 of the United States Department of Agriculture, Bureau of Soils. [11] MANUAL OF SOIL PHYSICS Questions : 1. What are the colors of the particles that compose the sand? 2. What is the difference in the color of the particles that compose the sand, the surface soil, the subsoil, and the clay ? Why are soil particles so similar in their mineral content ? 3. What is the range, in millimeters, in the size of sand parti- cles ? silt particles ? clay particles ? 4. AVhat is the structure of the surface-soil particles ? How do you account for such a structure ? 5. By what means can you distinguish the organic matter in the different soils while under the microscope ? 6. Define sand, silt, clay, and loam. [12] EXERCISE VI SOIL-FORMING MINERALS Object. The object of the exercise is to become familiar with the most important soil-forming minerals. Materials needed. Specimens of qnartz, feldspar, mica, talc, hornblende, calcite, gypsum, dolomite, iron ores, serpentine ; gravel ; microscope ; mortar and pestle ; hydrochloric acid. Fig. 2. Common soil-forming minerals Procedure. Study the above-named minerals, describing each according to the following outline : 1. Name. 2. Crystalline or amorphous. 3. Cleavage (number of planes). 4. Fracture (conchoidal or irregular). 5. Colors. 6. Luster. 7. Hardness. 8. Effect of hydrochloric acid. [13] MANUAL OF SOIL PHYSICS 9. Composition. 10. Kind of soil formed. 11. Per cent in earth's crust. 12. Miscellaneous. After describing each mineral select about half a dozen pebbles of the mineral from the gravel. Place them in the mortar and pulverize them, examining the broken pieces from time to time, noting the constancy of the cleavage and fracture characteristics. After they are pulverized examine some of the particles with the microscope, noting the same characteristics. References : Lyon and Fippin : Soils, pp. 4-9. Snyder: Soils and Fertilizers, pp. 64-67. Crosby: Common Minerals and Rocks, pp. 35-122. Questions : 1. Write out the scale of hardness you have used in determin- ing the hardness of the different minerals. 2. What is a plane of cleavage ? 3. Does the number of cleavage planes influence the weather- ing qualities of a mineral ? 4. Which minerals are found most abundantly in sand? in clay ? 5. Define a mineral. 6. Why is mica the most difficult to pulverize? 7. Do the number of cleavage planes and the fractures remain true in the pulverized material ? [14] EXERCISE VII SOIL FORMING ROCKS Object. The object of the exercise is '<» become familiar with ili<' most important soil-forming rocl Materials needed. Sj>eeimeiiH of granite, linn lone, quartz- ite, shale, gravel, phosphate rock, sandstone; microscope; mortar and pestle ; hydrochloric acid. Procedure. Si mly the above-named rocks, describing each according to the following outline: 1. Nihiic. 2. Kind (igneous, sedimentary, or metamorphio). ;{. Crystalline or amorphous. •I. ( lleavage ( number of planes). 5. Fracture (conchoidal or irregular). (i. ( lolors. 7. Luster. 8. Hardness. '.». Effect of hydrochloric acid. I o. Composition. II. K ind of soil formed. L2. Miscellaneous. Alter describing each rock pulverize a small ai int in the mortar, noting the manner in which it bn down. Aiter it is pulverized examine it under the mien ope, noting the oleavage planes and other characteristics due to the mineral composition. MANUAL OF SOIL PHYSICS References : Lyon and Fippin : Soils, pp. 9-15. Crosby: Common Minerals and Rocks, pp. 35-122. Merrill : Rocks, Rock Weathering, and Soils, pp. 150-195. Questions : 1. What is a rock ? 2. What minerals are the most abundant in granite ? 3. When a rock or a mineral effervesces with hydrochloric acid, what does this denote as to its composition ? 4. Define igneous, sedimentary, and metamorphic rocks. 5. Name one igneous, one sedimentary, and one metamorphic rock found in the state or county. [16] EXERCISE VIII VOLUME DENSITY AND POROSITY Object. The object of the exercise is to determine the vol- ume weight, apparent specific gravity, and pore space of soils. Materials needed. Three tubes; soils; balance ; graduate. Procedure. After weighing the tubes, fill one with sand, another with sur- face soil, and the third with subsoil, to within 1 inch of the top of the tube. Use compact- ing machine No. 1 in filling the tubes, allowing the weight to fall eight times from the 12-inch mark for each small measure of soil added to the tube. Determine the vol- ume space occupied by each soil by measurements or by filling the tube to the same height with water and measuring the number of cubic centimeters. If the [17] II No. 1 No. Fig. 3. The two designs of compacting machines used in these exercises MANUAL OF SOIL PHYSICS hygroscopic moisture content is not known, it must be deter- mined with a separate sample (see Exercise XII). Calculation. To obtain the apparent specific gravity of the soil, divide the weight of the water-free soil by the weight of the same volume of distilled water. Per cent pore spaee = 100 - Apparent specific gravity x m Absolute specific gravity Tabulate the results in a form similar to the following : Soil Weight of Empty Tube Weight of Filled Tube Weight of Soil Weight of Hygroscopic Water Weight of Water-free Soil in Tube Sand Surface soil Subsoil Grams Grams Grams Grams Grams Volume of Cylinder Weight of lcc. Water- free Soil Apparent Specific Gravity Absolute Specific Gravity 1 Per Cent Soil Space Per Cent Pore Space Sand Surface soil Subsoil cc. Grams From results obtained in this exercise, compute in pounds the weight per cubic foot and weight per acre foot of each soil. Soil Weight per Cubic Foot in Pounds Pounds per Acre Foot Sand Surface soil Subsoil 1 The average absolute specific gravity of most soils is 2.65. [18] VOLUME DENSITY AND POROSITY References : King: Physics of Agriculture, pp. 108-117. Lyon and Fippin : Soils, pp. 88-97. Wiley : Principles and Practices of Agricultural Analysis, Vol. I, pp. 95-99. Hall : The Soil, pp. 60-67. Questions : 1. Explain the difference between absolute specific gravity and apparent specific gravity. 2. Given a soil having an apparent specific gravity of 1.1 and a pore space of 58.5 per cent, what is the absolute specific gravity ? 3. Given three soils, having pore spaces of 65, 55, and 45 per cent respectively and an absolute specific gravity of 2.65 each, what is the apparent specific gravity of each soil? 4. The apparent specific gravity of soils in the field may be taken as an approximate indication of the tilth of the soil, Explain. 5. What factors influence the apparent specific gravity of soils ? [19] a EXERCISE IX NUMBER AND SURFACE AREA OF SOIL PARTICLES Object. The object of the exercise is to ascertain the num- ber and surface area of the particles in a given volume of different soil separates. Procedure. Considering the particles in each separate to be perfect spheres and arranged in a simple columnar structure, find the average number and surface area of the particles in a cubic foot of each of the soil separates, from coarse sand to clay inclusive. In obtaining the average diameter of a sepa- rate, use the average of the largest and smallest diameters. Indicate the method used in making the computation and tabulate your results in a form similar to the following: Soil Separate Number of Particles per Surface Area per Cubic Cubic Foot, in Millions Foot, in Acres Coarse sand Medium sand Fine sand Very fine sand Silt Clay References : Lyon and Fippin : Soils, pp. 80-84. King: Physics of Agriculture, pp. 109, 117-122. King : Soil Management, pp. 161-187. Widtsoe : Principles of Irrigation Practice, pp. 8-13. [21] MANUAL OF SOIL PHYSICS Questions : 1. What are the difficulties in determining the surface area of soil particles accurately ? 2. Would the number of soil particles per cubic foot be in creased or decreased if the soil had a single, or com- posite, structure? Explain. 3. What relation exists between the number of soil particles and the total surface area of all soil particles in equal volumes of different soil classes ? 4. Is there any relation between the total surface area of all soil x>articles per volume of soil and the water-retaining capacity? Explain. 5. Is there any relation between the total surface area of all soil particles per volume of soil and the rate of chemical solution by which the plant-food constituents contained in the mineral particles become available for plant use ? Explain. 6. What influence does the total surface area of all soil par- ticles per volume of soil have upon the quantity of food materials retained therein in a semiavailable form ? Explain. [22] EXERCISE X FLOW OF AIR THROUGH SOILS Object. The object of the exercise is to study the flow of air through different classes of soil. Materials needed. Three percolation tubes ; aspirator; large bottle ; graduate ; sand ; surface soil ; subsoil. Procedure. Fill the three percolation tubes, one with each class of soil, using the compacting machine in filling the tube, allowing the weight to fall three times from the 12-inch mark for each small meas- ure of soil that is added to the tube. After filling the bottle of the aspirator with water, attach the tube that ends near the top of the bottle to the tube containing the sand. By means of the other tube, siphon the water from the aspirator into the large bottle, which should be placed on the floor. Record the number of cubic centi- meters of air that will flow through the sand in a given time. The amount of water, in cubic centimeters, that flows from the bottle is equal to the amount of air that is drawn through the soil. [23] Fig. 4. Bottle aspirators, and apparatus for studying flow of air through soils MANUAL OF SOIL PHYSICS In a similar manner, determine how many cubic centimeters of air will flow through the surface soil and through the subsoil in the same length of time. Record your results in a form similar to the following : Sul L Sand Surface soil Subsoil Cubic Centimeters of Air in 10 Minutes References : Lyon and Fippin : Soils, pp. 432-447. King : The Soil, pp. 229-232. King: Physics of Agriculture, pp. 125-137. Questions : 1. How do you account for the air flowing through the sand so much faster than through the subsoil ? 2. What kinds of soils are naturally well aerated? 3. What kinds of soils are naturally poorly aerated? 4. Name several methods by which aeration of soils that are naturally well aerated may be reduced. 5. Name several methods of increasing aeration in compact, fine-textured soils. 6. What relation does aeration have to growth of organisms in the soil ? [24] EXERCISE XI PERCOLATION OF WATER Part I Object. The object of the exercise is to note the rate of flow of water through different classes of soil. Materials needed. Three percolation tubes; three beakers; graduate ; rubber tubing ; sand ; surface soil ; subsoil. Procedure. Fill the percolation tubes to within 3 inches of the top, one with each class of soil. In filling the tubes, use compacting machine No. 1, allowing the weight to fall three times from the 8-inch mark for each small measure of soil added to the tube. Place about an inch of gravel on the top of each soil, to prevent puddling. Connect the tubes by means of short pieces of rubber tubing, and, by means of a longer piece, connect to the water cock. Arrange the tubes so that the water will flow over the top of the soil in each tube, the surplus being conveyed into the drain. Before taking the readings, allow the water to percolate through each soil a week. Determine the number of cubic centimeters of water that will flow through each soil in one half hour. [25] 1 I m 1 m 1 i ! I l^w w m m w~* Fig. 5. Apparatus for studying perco- lation of water through soils MANUAL OF SOIL PHYSICS Reduce the results of Exercise X to a ratio and compare with the ratio of water movement. Tabulate your results in a form similar to the following : M Kind of Soil Sand Surface soil Subsoil Cubic Centimeters in 30 Minutes Relative Ratio of Water Movement Relative Ratio of Air Movement Part II Materials needed. Three 8-foot percolation tubes ; plotting paper ; loam ; silt loam ; clay. (The tubes should be prepared by the laboratory assistant.) Procedure. Take readings, every period, of the rate of percolation in each tube, recording your results in a conven- ient form. After the water has percolated through the entire column, take readings on the amount of water that percolates through each soil in twenty-four hours. After all the data have been collected, plot curves showing the rate of water movement through each soil. References : Hilgard : Soils, pp. 221-228. Widtsoe: Dry Farming, pp. 111-116. Hall : The Soil, pp. 75-79. King: The Soil, pp. 170-173. Questions : 1. What factors influence the flow of water through soils ? 2. What objections to a sandy subsoil does this exercise show ? 3. In what practical way may a clay subsoil be improved ? 4. Will water percolate most rapidly through a dry, a moist, or a wet soil ? Explain your answer in full. [26] EXERCISE XII DETERMINATION OF HYGROSCOPIC MOISTURE Object. The object of the exercise is to make a determina- tion of the amount of hygroscopic moisture in air-dry soil. Materials needed. Three tin boxes; balance; drying oven; sand ; surface soil ; subsoil. Procedure. Put a 20- or 30-grain sample of each air-dry soil into a weighed tin box, and heat in a drying oven at 110° C. until a constant weight is reached. (Constant weight is usually reached, with most air-dry soils, in two and one-half hours.) The loss in weight is due to the loss of hygroscopic water. Determine the per cent of hygroscopic moisture in each sample of soil, using water-free soil as the basis of calculation. Tabulate the results in a form similar to the following : Weight of Can WeightofCan and Soil Weight ok Hygro- scopic Water Weight of Water- free Soil Per Cent of Hygro- scopic Water Soil Before heating After heating Sand Surface soil Subsoil Grams Grams Grams Grams Grams (iniins References : Hall : The Soil, pp. 84-88. Hilgard: Soils, pp. 195-201. Lyon and Fippin : Soils, pp. 143-145. [27] MANUAL OF SOIL PHYSICS Questions : 1. Define hygroscopic water. 2. Name the soil and climatic factors that influence the hygro- scopic capacity of soils. 3. What influence does the porous condition of the various soil materials have upon the amount of hygroscopic water in a soil? 4. Is hygroscopic moisture of utility to planl growth? l)i- at length. [28] EXERCISE XIII CAPILLARY RISE OF WATER IN SOILS Object. The object of the exercise is to make a detailed study of the upward movement of the water in different classes of soil when in different conditions. Part I Capillary Rise of Water in Loose Soils Materials needed. Three 6-foot sections of 2-inch tubing; sand ; surface soil ; subsoil ; ruler ; muslin ; plotting paper. Procedure. Fill three tubes, one with each class of soil, exercising care to compact the soils as little as possible. After placing the tubes in the tube rack and adding water, take readings every half hour during the period. Also take read- ings every day for a week and then once a week until the end of the exercise. Part II Capillary Rise of Water in Compact Soils Materials needed. Three 6-foot sections of 2-inch tubing; sand ; surface soil ; subsoil ; ruler ; muslin ; plotting paper. Procedure. Fill three tubes, one with each soil. Compact the tubes by tapping the sides of the tube six times after each measure of soil has been added. The water should be added to these tubes at the same time it is added to the tubes in Part I. Take all readings as directed hi Part I. [29] MANUAL OF SOIL PHYSICS Part III Determination of the per cent of Capillary Water Materials needed. Soil containers ; balance ; drying oven. Procedure. When the capillary water has risen as high as it will by capillarity or has reached the top of the tube, obtain samples from each tube representative of each six inches from the top of the water table to the top of the moist column. Determine the per cent of moisture in all six tubes for every 6-inch section. Part IV Capillary Rise of Water in Loam, Silt Loam, and Clay Materials needed. Three 8-foot tubes; loam; silt loam; clay; plotting paper. (The tubes should be prepared by the laboratory assistant.) Procedure. Take readings, every period, of the rate at which the water rises in the three classes of soil, recording your results in a convenient form. After all the data for Parts I, II, and IV have been collected and tabulated in a convenient form, plot curves showing the capillary movement of the water as observed in each part. References : Hilgard : Soils, pp. 201-216. Widtsoe : Dry-Farming, pp. 106-111. Hall : The Soil, pp. 97-102. Lyon and Fippin : Soils, pp. 169-189. Questions : 1. In which soil was the water rising most rapidly at the end of the first hour ? the 48th hour? the 112th hour? Explain. 2. What effect does compacting a soil have upon the capillary movement of the water ? [30] CAPILLARY RISE OF WATER IN SOILS 8. What factors influence the amount of water drawn up in soils ? 4. What factors influence the rise of capillary water in soils? 5. What is the effect on capillarity if wet from the top as in rains? Explain in full. 6. Is the quantity of water in the moist column uniformly distributed? Explain in full. 7. Why is the daily rise of water not uniform ? [31] EXERCISE XIV EFFECT OF ORGANIC MATTER AND DRY CLODS UPON CAPILLARITY Object. The object of the exercise is to note the effect of organic matter and dry clods upon the capillary rise of water in soils. Materials needed. Stand with three glass tubes ; three beak- ers ; ruler ; muslin ; surface soil ; clods ; compost ; sawdust. Procedure. Tie a piece of muslin over the bottom of each tube and fill each with 12 inches of surface soil. Place a 1-inch layer of clods in one tube, a 1-inch layer of compost in another, and a 1-inch layer of sawdust in the third ; then fill the remainder of each tube with surface soil. Place the tubes in the stand and fill the beakers about half full with water. Every thirty minutes for the remainder of the period take accu- rate readings of the rate at which the water rises in each tube. Tabulate your results in a form similar to the following: Horns Snl LS 2 1 n o 24 48 Surface soil and compost . . . Surface soil and sawdust . . . Inches [ncht s Inches Inches Inches fitches References : Fletcher: Soils, pp. 89-96. Lyon and Fippin : Soils, pp. 144-160. - [ 33 ] MANUAL OF SOIL PHYSICS Questions : 1. What effect does a layer of coarse organic matter have upon the capillary rise of water? 2. What may be the effect of plowing under coarse organic matter just prior to planting corn ? 3. What may be the effects upon capillarity if land which is to be planted to corn is plowed the previous fall ? 4. Is there any reason suggested in the exercise for plowing the wheat land several weeks before sowing the Beed? Explain. * [34] EXERCISE XV POWER OF SOILS TO RETAIN WATER AGAINST PERCOLATION Object. The object of the exercise is to study the water- retaining power of soils in different degrees of compactness and containing various amounts of organic matter. Materials needed. Two stands of six tubes each ; sand ; sur- face soil ; subsoil ; compost or sawdust ; 4-gallon jar ; scales. Part I Power of Loose Soils to retain Water against Percolation Procedure. Weigh three tubes and record the weights in the proper blanks. Fill the tubes to within two inches of the top, one with each class of soil, exercising care not to com- pact the soil more than is necessary. Weigh and label the filled tubes. (A very convenient method of labeling is to place a small piece of paper on the top of the soil in the tube.) Determine the per cent of hygroscopic moisture in each sample, and the apparent specific gravity. Part II Power of Comtact Soils to retain Water against Percolation Procedure. Weigh three other tubes as indicated in Part I. Fill one tube with each class of soil. Compact the soil with compactor No. 2 if possible ; otherwise use machine No. 1, [35] MANUAL OF SOIL PHYSICS allowing the weight to fall four times from the 12-inch mark for each measure of soil that is added. Weigh and label as directed in Part I. Also r.ake all determinations as in Part I. Part III Power of Organic Matter to retain Water against Percolation- Procedure. Repeat Parts I and II, using the remaining six tubes. The soil, however, should be mixed with one fourth its volume of compost. Procedure in general. After filling and weighing all the tubes, place them in the jar and fill it with water, so thai the water level is a little above the level of the soil in the tubes. Allow them to remain in the water until the soil is thoroughly saturated. After saturation remove them and weigh as soon as possible ; then place them in the stands and allow to drain for two weeks. Place two inches of cotton in the tops of the tubes to reduce evaporation. Weigh the tubes every period during the two weeks and note the rate of loss in each. It is difficult to determine the time when the soils are thoroughly saturated if the water is allowed to run into the tubes from the top. By submerging the tubes below the level of the soil and allowing the water to flow up from the bot- tom the time of complete saturation will be indicated when the water appears on top of the soil. Calculate the weight of water, the per cent of water, the pounds per cubic foot, and the inches of water retained again si percolation in each soil. In making these calculations the student will find it necessary to know the apparent specific gravities of the samples. It is not required that a special determination be made at this point, provided the student has already obtained the figures from a previous exercise. [36] POWER TO RETAIN WATER AGAINST PERCOLATION Tabulate your results in a form similar to the following : Power of to retain Water against Percolation Kind of Soil Weight of Tube Weight of Weight of Tcbe and Air-dry Soil Soil Weight of Water- free Soil Apparent Specific Gravity Sand .... Surface soil . Subsoil . . . Grams Grams Grams Grams Kind of Soil Weights of Tubes and Soils after Saturation ] >ate Date Date Date Surface soil Grams Grams Grams Grams Grams Kind of Soil Maximum Weight of Water retained against Percolation Water retained against Percola- tion Water retained per Cubic Foot Surface soil . . Subsoil .... Grams Pi r cent Po mul 's Indies References : King: Physics of Agriculture, pp. 131-141. Hilgard : Soils, pp. 207-214. Questions : 1. Why is it important to know the water-retaining power of soils? Explain. 2. Explain why the compact surface soil and subsoil will not hold as much water against percolation as they do when loose. 3. Why does the addition of organic matter increase the water-holding capacity ? [37] • EXERCISE XVI THE EFFECTIVENESS OF MULCHES Object. The object of the exercise is to study the effect of mulches to retard evaporation of moisture from the soil. Materials needed. Eight evaporimeters ; scales; surface soil; mulching materials. It is advisable that the instructor start this exercise, so that the student may begin at once to make weighings of the evaporimeters. Procedure. Fill the evaporimeters to within three inches of the top with surface soil. Over the surface of the soil in each evaporimeter place a 3-inch mulch in the following order: 1. No mulch ; soil compact. 2. No mulch ; soil compact (check). 3. Soil mulch, cultivated three inches deep. 4. Soil mulch, cultivated three inches deep (check). 5. Gravel mulch. 6. Sand mulch. 7. Sawdust mulch. 8. Cut-straw mulch. Weigh the evaporimeters every period for two or three weeks, and at the end of that time determine the amount of water that has evaporated from each evaporimeter. Calculate in terms of tons per acre and in inches of rain- fall the amount of water that has been evaporated from each evaporimeter. [39] MANUAL OF Soil, PHYSICS Tabulate your results in a form similar to the following: Tube No. Date Date Date Date 1) \TE Date DAT] Toi \ i. K\ U'.'l; ITIOK 1 Grama Grams Grams Grams Grams Grams Grams llrt tins 2 3 4 5 6 7 8 Ti BE NO. Average Amount hi Water evapo- rated in One Day WATEH 1 \ AI'ii- RATED IN One Day per ACRE Water i-.\ \ po- RATED IN One Time ri to EVAPOB \ti 1 >M IM'II 1 Grams Tons 1 IK III s l)inis 2 3 4 5 6 7 8 References : King: Physics of Agriculture, pp. 185-195. Lyon and Fippin : Soils, pp. 199-210. "Soil Mulch" in Twenty-fifth Annual Report of Nebraska Agri- cultural Experiment Station, pp. 124-128. Widtsoe : Dry-Farming, pp. 152-156. Questions : 1. What climatic factors influence the evaporation of moisture from the soil? 2. What constitutes a mulch ? [40] THE EFFECTIVENESS OF MULCHES Under what conditions may a hard, dry layer of soil be as effective as a loose, dry layer of soil in retarding the evaporation of moisture? Explain. Why is sand, gravel, or straw more, effective as a mulch than the loose soil? When is it practical to use the following materials as mulches : travel ? sand ? straw ? [41] EXERCISE XVII EFFECT OF WATER UPON SOIL VOLUME Object. The object of the exercise is to determine the per cent of expansion and the per cent volume shrinkage of soils. Materials needed. Four cans ; ruler ; sand ; surface soil ; subsoil ; clay. Procedure. Place exactly three centimeters of soil in each can, using one can for each class of soil. Slowly add water to each can until the soil is thoroughly saturated ; then measure the number of centimeters of expansion. Place the cans in a warm place and allow them to dry. When dry, take measure- ments of the volume occupied by each soil. Calculate the number of cubic centimeters of expansion and shrinkage, and the per cent of expansion and volume shrink- age based upon the original volume of the soil. Tabulate the results in a form similar to the following : Soil Cubic Centimeters Expansion on Basis of Original Volume Shrinkage on Basis Expansion Shrinkage of Original Volume Sand Surface soil Subsoil Clay cc. cc. Per cent Per cent References : Warrington : Physical Properties of the Soil, pp. 35-42. Hall : The Soil, pp. 34-35. Lyon and Fippin : Soils, pp. 97-99. [43] MANUAL OF SOIL PHYSICS Questions : 1. What is the per cent of linear shrinkage of clay? the per cent of volume shrinkage ? 2. Name the factors that influence the degree of shrinkage in soils. 3. Explain the effect of shrinkage on crop growth. 4. Give three good methods of retarding the checking of clay soils. [44] EXERCISE XVIII LOSS ON IGNITION Object. The object of the exercise is to determine the amount of organic matter in the soil when the total volatile matter is considered as or- ganic matter. Materials needed. Three crucibles ; three burners ; three tripods ; soils ; desic- cators ; balance. Procedure. Put about 1 grams of each soil in sepa- rately weighed crucibles and ignite at a slow red heat. Stir the soil from time to time, noting the change in color. The stirring of a hot soil should never be attempted with a glass rod, as it is apt to chip off and cause trouble. After complete ignition place the crucible contain- ing the soil in a desiccator to cool, and then weigh. Note 1. A very convenient method of working the exercise is to use the water-free soil. If air-dry soil is used, the hygroscopic moisture content must be determined with a separate sample. Note 2. It will be frequently noticed during the process of ignition that the soil surface becomes darker in color. In some instances this is partially due to the water movement from the soil, but usually it is caused by the breaking up of carbon compounds and the temporary deposit of carbon on the surface of the soil. This temporary deposit is soon oxidized and lost as a gas. [45] Fig. 6. Apparatus for determining the loss on ignition MANUAL OF SOIL PHYSICS Tabulate your results in a form similar to the following ; Weight of Cruci- bles Weight of Crucible and Soil Loss BY Igni- tion Weight OF Water- free Soil Loss in Or- ganic Mat- ter Organic Matter Calculated in Soil Before igni- tion After igni- tion Per cent Pounds per cubic foot Tons per acre foot Sand Surface soil Subsoil Grams Grams Grams Grams Grams Grams References : Lyon and Fippin : Soils, pp. 124-127. Hall : The Soil, pp. 42-47. "Changes in the Composition of the Loess Soil," in Bulletin No. Ill of the Nebraska Agricultural Experiment Station. Questions : 1. Why do soils change color upon ignition? 2. What is organic matter ? 3. Distinguish between organic matter and humus. 4. What essential plant-food elements are removed from the soil by ignition? [46] EXERCISE XIX SOIL ACIDITY AND BASICITY Object. The object of the exercise is to study the method of determining whether a soil is acid or basic. Materials needed. Blue and red litmus paper; two evapo- rating dishes ; distilled water ; soils. Procedure. In testing a soil with litmus paper the greatest care must be exercised. All apparatus must be clean, and the paper must not be handled with sweaty fingers. Fill one of the evaporat- ing dishes nearly full with soil and moisten with dis- tilled water. Place a piece of the red litmus paper on the soil ; press it down with a clean knife blade, so that it is well in contact with the soil. In a similar man- ner place a piece of blue litmus paper on the same soil on the opposite side of the dish from the red paper ; allow it to stand for ten min- utes, and then observe results. Care must be taken not to confuse the two pieces of paper. After making one determination procure unknown samples from the instructor, and determine whether they are acid or basic. Report your results to the instructor. [47] Fig. 7. Testing soils with litmus paper for acidity MANUAL OF SOIL PHYSICS References : "Acid Soils," in Bulletin No. 90 of the Oregon Agricultural Experiment Station. Fletcher : Soils, p. 401. Van Slyke : Fertilizers and Crops, pp. 140-144. "Soil Acidity and Liming," in Bulletin No. 230 of the Wisconsin Agricultural Experiment Station. [48] EXERCISE XX DETERMINATION OF HUMUS Object. The object of the exercise is to determine the amount of humus in soils. Materials needed. Two 250-cc. Erlenmeyer flasks ; balance ; distilled water ; hydrochloric acid (4 per cent solution) ; am- monium hydroxide (5 per cent solution) ; two glass funnels ; filter paper ; two beakers ; graduate ; burner ; tripod ; two evaporating dishes ; water bath ; water-free surface soil. Procedure. 1. Weigh two samples of from 10 to 15 grams of water- free surface soil and place in separate flasks. 2. Add to each flask 100 cc. of 4 per cent hydrochloric acid and allow to digest for at least twenty-four hours. 3. Transfer the soil to a filter in a funnel, and filter off all the acid, discarding the filtrate. Wash the soil thoroughly with distilled water. 4. After the soil has been thoroughly washed, pass 5 per cent ammonium hydroxide through the soil until the filtrate is entirely clear or does not give a precipitate when treated with hydrochloric acid. 5. Transfer the filtrate to an evaporating dish and evapo- rate to dryness ; then dry for one hour at 100° C. 6. When dry, weigh and ignite at a red heat ; thenreweigh. The loss in weight is humus. 7. Calculate the per cent of humus in the sample and in terms of pounds per acre foot. [49] MANUAL OF SOIL PHYSICS Record your results in a form similar to the following Weight of Evaporating Dish and Residue Weight of Humus Per Cent of Humus Pounds per Before ignition After ignition Acre Foot First sample Second sample Grams Grams Grams References : Hilgard : Soils, p. 132. Wiley : Principles and Practices of Agricultural Analysis, pp. 357- 366. Widtsoe : Dry-Farming, pp. 58-59. Snyder: Soils and Fertilizers, pp. 103-116. Questions : 1. What is the material left in the evaporating dish after the humus has been driven off by ignition ? 2. What are some of the defects of the Grandeau method of humus determination? 3. Describe the formation of humus in the soil. 4. Discuss the relative plant-food values of humus found in humid and in arid regions. [50] EXERCISE XXI LEACHING OF SOILS Object. The object of the exercise is to study the leaching of soils. Materials needed. Three glass tubes in stand ; muslin ; three beakers ; distilled water ; graduate ; sand ; surface soil ; subsoil. Procedure. Tie a piece of muslin over the small end of the tubes and place 6 inches of sand in one tube, 6 inches of surface soil in a second, and 6 inches of subsoil in the third. Place the filled tubes in the stand and pour 50 cc. of distilled water into each. Allow the water to perco- late into the beakers, which are placed under the tubes. Observe the color of the water after it has perco- lated through each soil. The first two or three drops should be compared with the last few drops as to their color. Write a brief summary of your observations and conclusions. References : Hilgard : Soils, pp. 22-28. Widtsoe : Dry-Farming, pp. 65-66. Hopkins: Soil Fertility and Permanent Agriculture, pp. 556-561. King : Physics of Agriculture, pp. 77-79. [51] Fig. 8. Apparatus for studying leaching of soils MANUAL OF SOIL PHYSICS Questions : 1. Why does the water become colored in passing through the soil? 4— 2. What undesirable effects of heavy rains are suggested in this exercise? Explain. 3. Can leaching be retarded ? Explain the methods. 4. What salts are least liable to be leached from the soil ? 5. The humid soils contain 15 per cent less soluble material than arid soils and, as compared with the semiarid re- gion, 9 per cent less soluble material. 1 Is this condition due to the power of the soil to retard leaching or to cli- matic factors . ; Explain. 1 Lyon and Fippin : Soils, p. 66. ; [52] EXERCISE XXII POWER OF SOILS TO ABSORB SALTS Object. The object of the exercise is to study the absorp- tive power of different classes of soil. Materials needed. Three glass tubes in stand ; three beakers ; muslin ; graduate ; eosin solution ; sand ; surface soil ; subsoil. Procedure. Tie a piece of muslin over the small end of each tube and place 6 inches of sand in one tube, 6 inches of surface soil in another, and 6 inches of subsoil in a third. Place the filled tubes in the stand and pour two inches of the solution over each soil. Place beakers under the tubes to catch the solution that percolates through the soil. Note carefully the color of the first two or three drops that percolate through each soil, and compare it with the last drops that percolate through. Write a brief summary of your observations and conclusions. References : Snyder : Soils and Fertilizers, pp. 191-197. Hopkins : Soil Fertility and Permanent Agriculture, pp. 562-564. Hall : The Soil, pp. 211-232. Fraps : Principles of Agricultural Chemistry, pp. 234-243. Questions : 1. Do all soils have some power to absorb salts ? 2. Make a comparison of the color of the solutions that drip from each class of soil. 3. What salts do not undergo fixation ? 4. Why is it important that soils have the power of absorption ? 5. What factors influence the power of absorption? [53] ■\ EXERCISE XXIII ABSORPTION OF GASES BY SOILS Object. The object of the exercise is to study the power of soils to absorb gases. Materials needed. Four air-tight containers ; four watch glasses ; sand ; surface soil ; subsoil ; ammonia water. Procedure. In one of the containers place about 50 grams of sand ; in the second, 50 grams of surface soil ; and in the third, 50 grams of subsoil. No soil is placed in the fourth container. Pour a few drops of ammonia water on each of the watch glasses and place one in each container. Cover the container so that none of the ammonia gas can escape. Put the containers away until the next period. At the next labor- atory period open and try to detect the odor of ammonia in each container. References : Hall : The Soil, pp. 214-216. Hilgard : Soils, pp. 272-276. "Absorption of Vapor and Gases by Soils," in Bulletin No. 51 of the United States Department of Agriculture, Bureau of Soils. Questions : 1. What differences can you notice in the odor of the four containers after letting them stand from one period to the next? Name the soils in the order of their greatest apparent absorptive power. 2. Is absorption a physical or a chemical process? 3. What is absorption ? 4. How is this exercise related to the application of organic matter ? [55] EXERCISE XXIV ABSORPTION OF MOISTURE BY SOILS Object. The object of the exercise is to study the power of soils to absorb moisture when placed in a saturated atmosphere. Materials needed. Six tin boxes ; plotting paper ; thermom- eter; water-free soils; compost; balance; moist-air chamber. Procedure. "Weigh 20 grams of water-free sand, surface soil, subsoil, clay, and compost in separately weighed boxes. Place them, with the covers removed, in the moist-air chamber. Place the empty can in the moist-air chamber, to determine the amount of moisture that collects on it. Ascertain the weight of each can at the end of 24, 48, 72, and 96 hours, recording each time the temperature of the air in the chamber. Note. In making the weighings do not leave the lid of the moist-air chamber open any longer than necessary, as it causes a change in the humidity of the atmosphere. Make all weighings as rapidly as possible, in order that the loss by evaporation may be reduced to a minimum. Tabulate your results in a form similar to the following Soil Tempera- ture Water absorbed during 1st 24 hrs. 2d 24 hrs. 3d 24 hrs. 4th 24 hrs. Total Sand . . . Surface soil . Subsoil . . Clay. . . . Compost . . Degrees Per cent Per cent Per cent Pi r -lit Per cent [57] MANUAL OF SOIL PHYSICS Plot curves showing the amount of absorption by each soil as indicated by the data. References : Hilgard : Soils, pp. 196-200. Hall : The Soil, pp. 84-89. "The Wilting Coefficient for Different Plants and its Indirect Determination," in Bulletin No. 230 of the United States De- partment of Agriculture, Bureau of Plant Industry. Questions : 1. What is meant by the maximum hygroscopic coefficient of soil? 2. What relation exists between the maximum hygroscopic coefficient and the wilting coefficient of soils? 3. What practical applications may be made of the determina- tions for the maximum hygroscopic coefficient of soils ? 4. What factors influence the absorption of moisture from the air? 5. Why should the temperature be kept as nearly constant as possible? [58] EXERCISE XXV FLOCCULATION OF CLAY Object. The object of the exercise is to study the flocculat- ing effect of various materials on clay particles in suspension. Fig. 9. Apparatus for studying flocculation Materials needed. Four glass cylinders ; clay ; distilled water; 1 per cent ammonia solution; alum; limewater; pipette ; microscope. Procedure. Place 20 grams of clay in one of the cylin- ders and fill with distilled water. Stir thoroughly the con- tents of the cylinder, and after five minutes of sedimentation decant the turbid liquid into a second cylinder, rejecting all the sediment. Divide the turbid liquid into four equal por- tions. To one of the cylinders add 20 cc. of limewater ; to the second, 10 cc. of ammonia water ; and to the third, 0.1 grams [59] MANUAL OF SOIL PHYSICS of alum. Fill all four cylinders with distilled water, stir, and set aside, observing the results. After twenty-four to forty- eight hours examine, with the aid of a microscope, some of the particles in each cylinder. Procure a sample for the mount from the bottom of the cylinder by the use of the pipette. Care should be taken not to destroy the structure of the floccules. Take careful notes on the rate of flocculation in the four cylinders, as well as the time required for the water to be- come comparatively clear. Write a brief summary of your observations. References : Hall : The Soil, pp. 38-41. Van Slyke : Fertilizers and Crops, pp. 103-104. " The Effect of Soluble Salts on the Physical Properties of Soil," in Bulletin No. 82 of the United States Department of Agricul- ture, Bureau of Soils. Questions : 1. In which cylinder does the turbid water first become clear? 2. What is the physical effect of liming clay soils? Explain. 3. Define flocculation. 4. What materials will cause flocculation? 5. What materials will cause deflocculation ? [60] EXERCISE XXVI EFFECT OF LIME ON SOIL STRUCTURE Object. The object of the exercise is to study the crumbling or granulating effect of lime on clay soils. Materials needed. Three pans ; air-slaked lime ; clay. Procedure. Place about half an inch of clay in each of the three pans. Add to one of the pans one eighth as much air- slaked lime as there is soil in the pan ; to a second pan add one fourth as much lime as there is soil ; leave the third pure clay. Mix the lime thoroughly with the soil in the two pans, taking care that no lumps remain. Add to each pan enough water to saturate it ; then place all three pans where they will dry. Do not stir the soil after adding the water. As soon as the soils are dry, make drawings of each soil, showing the cracks that have been formed. Afterwards ex- amine each soil carefully, noting the physical condition and comparative hardness. References : Lyon and Fippin : Soils, pp. 116-118. Hall : Fertilizers and Manures, pp. 253-257. Hopkins : Soil Fertility and Permanent Agriculture, pp. 160-182. Questions : 1. What is the effect of lime on the cohesiveness of the soil particles ? 2. In what form and in what amounts should lime be applied to a clay soil to change the structure ? 3. In which pan is the soil the hardest? the softest? Why? [61] EXERCISE XXVII EFFECT OF SAND AND ORGANIC MATTER ON SOIL STRUCTURE Object. The object of the exercise is to study the effect of sand and organic matter upon the texture and structure of soils. Materials needed. Three pans ; sand ; sawdust ; clay. Procedure. Place one half inch of clay in one of the pans and add to it one eighth as much sand, mixing it thoroughly. In a similar manner, place as much clay in another pan and add one eighth as much sawdust, mixing it well with the soil. Fill the third pan with an equal amount of clay, then add sufficient water to make the contents of each pan in a slushy condition, and put them away to dry. When dry, make drawings of the soils, showing the cracks. Work over the material in each pan, noting carefully the structure and hardness of each soil. References : Lyon and Fippin : Soils, pp. 113-116. Van Slyke : Fertilizers and Crops, pp. 134-140. Questions : 1. In which pan is the soil the hardest? the softest? Why? 2. From the results of the exercise, is it advisable to add organic matter to the fine-textured soils to alter their physical condition? 3. When is it practical to add sand to a soil in order to change the texture and the structure? 4. What are the most important physical properties of soils that are modified by the addition of sand or organic matter? [63] • EXERCISE XXVIII EFFECT OF ALTERNATE WETTING AND DRYING ON SOIL STRUCTURE Object. The object of the exercise is to study the effect of alternate wetting and drying on the structure of soils. Materials needed. Six pans ; spatula ; surface soil ; clay. Procedure. Place 150 grams of surface soil in each of three pans and mix to a pasty mass. Use the spatula in mixing the soil, destroying any crumb structure that may exist. Put the pans in a warm place and allow the soils to dry. When dry, add a sufficient amount of water to two of the pans to saturate the soil, but do not stir it. Allow them to dry, and again wet one of the pans and again allow it to dry. In each of the other three pans mix 150 grams of subsoil to a pasty mass and treat in the same manner as the surface soil. After the soils are thoroughly dried, make a comparative study of the soils in each pan, noting the compactness and friability. Crumble a little of the soil from each pan between the thumb and finger, noting its relative hardness. Write a brief discussion of your observations, accounting for the dif- ferences in the soils. References : Lyon and Fippin : Soils, pp. 105-108. "Moisture Content and Physical Condition of Soils," in Bulletin No. 50 of the United States Department of Agriculture, Bureau of Soils. [65] MANUAL OF SOIL PHYSICS Questions : 1. Why does alternate wetting and drying change the struc- ture of soils? 2. From the results of this exercise, may there be any benefit — derived from plowing clayey soils before the fall rains ? 3. Why are soils that have been wetted more than once, more granular in structure than soils that have been wetted only once? 4. Would a sandy soil (75 per cent sand) show the same effect of wetting and drying? [66] EXERCISE XXIX EFFECT OF ALTERNATE FREEZING AND THAWING ON SOIL STRUCTURE Object. The object of the exercise is to study the effect of alternate freezing and thawing on soil structure- Materials needed. Four pans ; surface soil ; clay. Procedure. Mix to a pasty mass 150 grams of surface soil in each of two pans and 150 grams of clay in each of the other two pans. Place one of the surface-soil pans and one of the subsoil pans where they will freeze, and the other pan of each soil where they will dry out slowly. After the soils in the two pans are frozen, put them in a warm place until they thaw out, and again allow them to freeze. Repeat this process of freezing and thawing twice ; then dry the soils out slowly. When the soils are dry, determine the relative hardness of each, noting any differences that may exist hi the structure of the soils. References : Lyon and Fippin: Soils, pp. 108-111. Hilgard : Soils, pp. 118-119. "Physical Improvement of Soils," in Circular No. 82 of the Illinois Experiment Station. Questions : 1. From the results of the exercise, would it be advisable to hold water in the surface soil in the fall of the year, so that the soil would be subject to a greater freezing and thawing ? [67] MANUAL OF SOIL PHYSICS 2. Which is the most effective in producing a desirable struc- ture, alternate freezing and thawing or alternate wetting and drying ? 3. Why does the alternate freezing and thawing change the fPB structure of the soil ? 1. Why are the clay soils of some Southern states in pc>" tilth in the spring than similar soils in the Northern states ? 5. Give illustrations showing the same effects of freezing and thawing on materials other than soil. [68] EXERCISE XXX EFFECT OF COLOR ON SOIL TEMPERATURE Object. The object of the exercise is to study the effect of color on soil temperature. Materials needed. Two thermometers ; black and white cloths ; five flower pots, three white and two black ; sand ; surface soil; subsoil. Procedure. Fill one of the black pots with surface soil, and fill one of the white pots with sand and one with subsoil. After taking temperature readings in all of the pots at depths of 1, 2, and 3 inches, place them in the full sunlight. Fill the other black pot with surface soil, covering the top with 1 inch of char- coal. Fill the remaining white pot with surface soil and cover with i inch of Fig. 10. Method of studying soil temperature lime. After taking readings at depths of 1, 2, and 3 inches, place them in the full sunlight. Hang the two colored cloths in the full sunlight and at the end of fifteen minutes take temperature readings 1 inch from the back of the cloths. If the thermometer is held against the cloth or too far back from it, the reading taken will be useless for this exercise. [69] MANUAL OF SOIL PHYSICS Take readings every half hour during the period, recording the results in a form similar to the following : Sand Surface Soil Subsoil Depth Original Hours Original Hours Original Hours i 1 li i 1 11 i 1 li L inch . . . 2 inches . . 3 inches . . Light Covering Dark Covebing Depth Original Hours i tariginal Hours i 1 1J 1 1 U 1 inch 2 inches 3 inches White cloth Black cloth References : Hall : The Soil, pp. 126-128. King: Physics of Agriculture, p. 217. Questions : 1. How does color affect the temperature of the soil? 2. How does the color of a soil affect its heat-retaining power ? 3. Mention the soil factors to be taken into account in con- sidering the effect of color on the temperature of field soils. 4. How much difference is there in the temperature of the three classes of soils at the end of the period ? [70] EXERCISE XXXI EFFECT OF WATER ON SOIL TEMPERATURE Object. The object of the exercise is to study the effect of water on soil temperature. Materials needed. Six flower pots ; two thermometers ; sand ; surface soil ; subsoil. Procedure. Prepare wet and dry samples of each class of soil in the flower pots. Take accurate temperature readings at the immediate surface, 1 inch deep, and 2 inches deep ; then place them in the full sunlight. Take temperature readings every half hour during the period. Record the results of each class of soil in a form similar to the following: : Time Temperature of Dry Sand Temperature of Wet Sand Surface lin. 2 in. Surface lin. 2 in. Original .... £ hour 1 hour 1£ hours .... 2 hours .... References Snyder : Soils and Fertilizers, pp. 46-47. King : The Soil, pp. 225-228. "An Investigation of Soil Temperature and Some of the Most Important Factors Influencing It," in Michigan Technical Bul- letin No. 17, 1913. [71] MANUAL OF SOIL PHYSICS Questions : 1. How does evaporation affect the temperature of the soil ? 2. Why is a drained soil warmer than an undrained soil ? 3. What are the chief causes which make undrained clayey soils cooler than well-drained sandy soils? 4. At what time of the year is there the greatest difference between the temperature of the drained soil and that of the undrained soil? the least? Why? 5. The temperature of the air 9 inches above the drained soil is higher than the temperature 9 inches above the undrained soil. Why? 6. What is the specific heat of soil as compared with the specific heat of water? [72] EXERCISE XXXII EFFECT OF VEGETATION AND TOPOGRAPHY ON SOIL TEMPERATURE Object. The object of the exercise is to study the effect of vegetation and topography on soil temperature. Materials needed. Three-foot auger; two thermometers. Procedure. In taking soil temperatures the following points must be kept in mind : 1. The temperature of the atmosphere. 2. The direction and velocity of the wind. By means of the auger make a hole 18 inches in depth and immediately place a thermometer in the bottom and press the bulb into the soil. At the same time insert the bulb of the second thermometer into the soil to a depth of 3 inches. Make all final temperature readings an average of three readings taken within a radius of 2 feet. In this manner study the temperature of the soils on dif- ferent slopes, comparing them also with the temperatures of level land. Make a study of the temperatures of soil covered Avith green vegetation, trees, and grass, comparing them with the temperatures of bare land. Tabulate your results in a form similar to the following : SUMMARY OF READINGS Depth in Inches Exposure of Slope Kind of Vegetation Level South North Trees Grass 3 18 [73] MANUAL OF SOIL PHYSICS References : Hall : The Soil, pp. 120-126 ; 133-135. Lyon and Fippin : Soils, pp. 448-464. Questions : 1. Which slope has the highest temperature ? Why ? 2. AVhy is the ujiper 3 inches of the soil warmer than the soil 18 inches down? 3. Why does growing vegetation keep the temperature of the soil more uniform ? 4. Explain why the exposure of the slope affects the tempera- ture of the soil. ^ [74] EXERCISE XXXIII EFFFCT OF CULTIVATION ON SOIL TEMPERATURE Object. The object of the exercise is to study the effect of cultivation on soil temperatures. Materials needed. Three-foot auger ; two thermometers. Procedure. By means of the auger make a hole 18 inches deep in a field that has been recently plowed. As soon as possible place a thermometer in the hole, pressing the bulb into the soil. At the same time insert the bulb of the second thermometer in the soil to a depth of 3 inches, and after it has become constant, record the temperature. Make all final temperature readings an average of three read- ings taken within a radius of 2 feet. In this manner study the temperatures of soils that have received no cultivation. Also take careful notes on the weather conditions, slope, and vegetation. Tabulate your results in a form similar to the following : SUMMARY OF READINGS Depth in Inches Cultivated Uncultivated Cultivated Vegetation Uncultivated Vegetation 3 18 References : Snyder : Soils and Fertilizers, pp. 46-51. Hilgard : Soils, pp. 301-310. [75] MANUAL OF SOIL PHYSICS Questions : 1. What effect does the loose structure have on the tempera- ture of the soil ? 2. How can a farmer aid in warming up the soil in the spring ? 3. What factors influence the temperature of soils ? 4. Why is the temperature of the upper three inches of the cultivated soil warmer than the upper three inches of the uncultivated soil? 5. From what sources does the soil receive its heat? [76] EXERCISE XXXIV SOIL TENACITY Object. The object of the exercise is to determine the tensile strength of different classes of soils. Materials needed. Tenacity apparatus ; pan ; graduate ; spatula ; scales ; surface soil ; subsoil ; clay. Procedure. 1. Weigh 300 grams of soil and add water until you consider the greatest degree of stickiness reached, keeping a record of the amount of the water. Mix well. 2. Place the two parts of the soil container together on a level surface and lock firmly. 3. Fill the con- tainer level full with the moistened soil, leaving no air spaces along the sides. 4. Attach the filled container directly underneath the beam of the apparatus. 5. Unlock the container, exercising care not to jar or break the soil column. 6. Through a small funnel add sand to the other side of the beam until its weight is sufficient to break the soil column. [77] Fig. 11. Method of studying soil tenacity MANUAL OF SOIL PHYSICS 7. Weigh the sand. 8. Weigh the movable part of the container with the soil it contains. 9. Determine the tensile strength by subtracting the weight of the container, plus the soil it contains, from the weight of the sand. 10. To another 300-gram sample of the same soil add 15 cc. more water than was added to the first sample, and to a third 300-gram sample add 15 cc. less water than was added to the first sample, and in like manner determine their degree of tenacity. Record results in a form similar to the following : Surface Soil Subsoil (LAV 1st 2d 3d 1st 2d 3d 1st 2d 3d Amount of water added . Weight required to break soil column Weight of soil and mov- able container .... Tenacity References : Lyon and Fippin : Soils, pp. 97-99. Warington : Physical Properties of the Soil, pp. 23-25. Questions : 1. What is meant by tenacity of soils? 2. What factors determine the tenacity of soils ? 3. About what per cent of water gives the greatest degree of tenacity in each soil ? 4. Explain the relation between tenacity and the expansion and contraction of soils upon wetting and drying. 5. Give your opinion as to the desirability of the property of tenacity in field soils. [78] EXERCISE XXXV TRANSFERENCE OF HEAT IN SOILS Object. The object of the exercise is to study the heat- transferring power of soils. Materials needed. Heat-transference apparatus ; seven ther- mometers ; flask ; ruler ; burner and tripod ; asbestos gauze ; distilled water ; sand ; surface soil ; subsoil. Fig. 12. Apparatus for studying transference of heat in soils Procedure. 1. Place 950 cc. of distilled water in the flask and heat to boiling. 2. While the water is heating, fill the transference apparatus with sand, packing it as uniformly as possible. Place thermom- eters in the sand with the bulbs 2 inches below the surface at distances of 1, 2, 3, 4, 5, and 6 inches from the tank. As soon as they have become constant, record the temperature indicated by each. [79] MANUAL OF SOIL PHYSICS 3. On a piece of notebook paper rule a form similar to the one indicated below, in which to record your readings. 4. As soon as the water is boiling and the thermometers have reached a constant temperature, pour the boiling water into the tank, recording the exact time at which this is done. Immediately, by means of tubing, conduct a current of steam from the steam pipe into the water, in order to maintain a constant temperature. 5. Use the seventh thermometer to ascertain the temper- ature of the water. The cork may be removed from the opening from time to time in taking these readings. 6. Record the temperature indicated by each thermometer at the end of every 5-minute period for at least an hour and a half. 7. In the same manner determine the heat-transferring power of the surface soil and the subsoil. After obtaining the results, plot curves showing the rate of heat-transference in each soil. (A convenient method of plot- ting the curves is to use one sheet for each soil.) Tabulate the results in a form similar to the following : Time Temperature of Water Distance from the Heat Source 1 in. 2 in. 3 in. 4 in. 5 in. 6 in. Min. Degrees Degrees Degrees Degrees Degrees Degrees Degrees References : " Heat Transference in Soils," in Bulletin No. 59 of the United States Department of Agriculture, Bureau of Soils. Technical Bulletin No. 17 of the Michigan Agricultural Experi- ment Station. Questions : 1. What factors influence the heat transference of soils? 2. Summarize the conclusions as set forth in the first reference. [80] EXERCISE XXXVI ABSOLUTE SPECIFIC GRAVITY OF SOIL Object. The object of the exercise is to make determinations of the absolute specific gravity of soils. Materials needed. Pycnometer; balance; distilled water; thermometer ; water bath ; water-free soil. Procedure. 1. Fill a pycnometer bottle to the upper end of the capillary tube with distilled water. Wipe dry and weigh to three decimal places. Note the temperature of the water used. 2. Empty the water and again weigh. Add about ten grams of water-free soil and again weigh. The difference in the two weights represents the exact amount of soil used. 3. Fill the bottle about half full with water and place it in a shallow water bath, heating it until all the air is expelled from around the particles. 4. Reduce the temperature of the water in the pycnometer to the original temperature, completely fill with distilled water, and weigh. Calculation. To the weight of the water-free soil, add the weight of the flask filled with water, and deduct the weight of the flask filled with the soil and water. The difference expresses the weight of the volume of water equal to the quantity of soil used. The specific gravity can therefore be determined by dividing the weight of the soil used by the weight of the water it has displaced. [81] MANUAL OF SOIL PHYSICS Record your results in a form similar to the following : Soil Weight of Flask filled with Water Weight of Dry Soil taken Weight of Flask filled with Water and Soil Weight of Water dis- placed nv Soil Specific Gb wity Sand Surface soil Subsoil Grams (Irams Grams Grams drains References : Lyon and Fippin : Soils, pp. 94-97. Merrill : Rocks, Rock Weathering, and Soils, pp. 40-42. Questions : 1. Define absolute specific gravity. 2. Why is it necessary to use water-free soil for the deter- mination of the absolute specific gravity? 3. Why must all the air be driven out before the last weight is taken ? 4. What factors influence the absolute specific gravity of soils ? 5. How do you account for the small differences between the absolute specific gravities of the different soils ? [82] EXERCISE XXXVII APPARENT SPECIFIC GRAVITY OF FIELD SOILS Object. The object of the exercise is to determine the appar- ent specific gravity and pore space of soils under field conditions. Materials needed. Sampling auger; mallet; six sacks; bal- ance ; three cans ; drying oven. Procedure. By means of the auger secure a foot sample of the first foot of soil from three fields: an alfalfa field, a pasture, and a recently plowed field. In using the auger the tube is driven into the soil to such a depth that when the auger blade is just resting on the surface of the soil, the gauge may be set in the first notch and at the same time rest on the top of the tube. Raise the gauge one notch, and by turning the auger remove the first inch of soil, placing it in one of the sacks. In the same manner remove the soil from the first foot, placing it all in one sack if possible. It is best not to attempt to remove more than 1 inch of soil at a time, and under no consideration should more than 2 inches be [83] Fig. 13. Nebraska Soil Auger and sample boxes MANUAL OF SOIL PHYSICS -emoved at a time. After weighing the entire amount of soil amoved, take a small sample of about 100 grams and deter- nine the moisture content ; then calculate the weight of water- :ree soil. In calculating the volume of soil removed, use the liameter of the auger bit as the diameter of the boring. From the data collected determine the apparent specific gravity, per cent pore space, weight per cubic foot, and veight per acre foot for each field. Tabulate your results in a form similar to the following : Kind of Field Apparent Specific Gravity Porosity \\ i u, in ii B < i arc Foot Ul h.HT PEE \. be Poor \lfalfa .... *asture .... lecently plowed Per cent /'mi in Is Tons References : Exercise No. 8 (for method of calculation). King: Physics of Agriculture, pp. 110-117. Hall : The Soil, pp. 60-67. Lyon and Fippin : Soils, pp. 88-97. Questions : 1. Define apparent specific gravity. 2. What factors influence the apparent specific gravity of soils under field conditions? 3. Does the per cent porosity vary as the apparent specific gravity ? 4. From the standpoint of crop production, what is the impor- tance of soil porosity? [84] EXERCISE XXXVIII SPECIFIC HEAT OF SOILS Object. The object of the exercise is to determine the specific heat of soils. Materials needed. Specific-heat apparatus ; two thermom- eters ; three crystal dishes ; graduate (200-cc.) ; distilled water ; drying oven ; balance ; water-free soils. Procedure. 1. Fill the three crystal dishes, one with each type of soil, and weigh to three decimal places. 2. Place one crystal dish, filled with soil, on the upper shelf of the oven. 3. Through the opening in the top of the oven insert one of the thermometers, extending it down into the soil in the dish. 4. Heat until the thermometer reads between 100° and 110° C. While the soil is heating weigh the calorimeter cup and stirring rod and determine their water equivalent in calories (weight times specific heat). 5. Measure into the calorimeter cup 200 cc. of distilled water and place it in the jacket. 6. With the other thermometer determine the exact tem- perature of the water in the calorimeter ; immediately take the exact temperature of the soil in the oven. 7. Quickly transfer the soil from the oven into the calo- rimeter, covering it as soon as possible. 8. Insert the thermometer and stir for three or four min- utes, until a constant temperature is obtained throughout the mixture. [85] MANUAL OF SOIL PHYSICS 9. Put the crystal dish back into the oven and let it stand there until it can be weighed to determine the exact amount of soil in the calorimeter. 10. Repeat the above operation for each soil. Tabulation and calculation : 1. Specific heat of calorimeter cup, 2. Specific heat of water, 1.00. Kind of soil used Weight of calorimeter cup Weight of dish and water-free soil .... Weight of dish M — Weight of water-free soil T — Temperature of soil t — Temperature of water and calorimeter before adding soil C — Constant temperature of water and soil mixed in calorimeter W — Weight of water used plus water equiv- alent of calorimeter iS' — Specific heat Sand Surface Soil Subsoil Formula : References : Coleman : Elements of Physics, pp. 182-185. King : Physics of Agriculture, pp. 29, 215-217. Hall : The Soil, pp. 128-129. Lyon and Fippin : Soils, pp. 455-456. Hilgard: Soils, p. 301. Questions : 1. Derive the above formula (Coleman). 2. What is specific heat? 3. What factors influence the specific heat of soils? 4. Does a knowledge of the specific heat of a moist soil aid in determining whether it is a " late " or an " early " soil ? [86] EXERCISE XXXIX EVAPORATION OF WATER Object. The object of the exercise is to study the rate of evaporation from soils as compared with the evaporation from a free-water surface. Materials needed. Two evaporating pans ; surface soil ; balance; plotting paper. Procedure. Place in one of the pans a layer of surface soil 2 inches deep and add water until the moisture content is about 25 per cent. Fill the second with water to a depth of 2 inches. The water used in both pans should be at about room temperature. Weigh, place in full sunlight, and note the loss from each by weighing every twenty minutes for two hours. Plot two curves showing the rate of evaporation from the two pans and tabulate your results in a form similar to the following : Grams of Water evaporated diking Each Ten Minutes 1st 2d 3d 4th 5th 6th 7th 8th Total Free-water surface . . Soil surface References : Fletcher : Soils, pp. 88-89. Bulletin No. 188 of the United States Department of Agriculture, Bureau of Plant Industry, pp. 16-30. Twenty-fourth Annual Report of the Nebraska Agricultural Ex- periment Station, pp. 97-101. [87] MANUAL OF SOIL PHYSICS Questions : 1. Account for the fact that evaporation from a free-water sur- face is slow at first and faster at the end of the period. 2. What factors influence the rate of evaporation ? % 3. According to the references, about how much water will be evaporated from the free-water surface in six months ? 4. Compare the rate of evaporation from the soil with that from the leaves of plants. [88] EXERCISE XL MOISTURE DETERMINATIONS OF FIELD SOILS Object. The object of the exercise is to determine the moisture content of soils under field conditions. Materials needed. Two augers or tubes (one 6-foot and one 3-foot) ; eighteen tin boxes (in case) ; dry- ing oven ; balance. Procedure. 1. Weigh the tin boxes, being sure that each is prop- erly labeled. 2. Take composite samples from each foot of soil to a depth of 6 feet in an alfalfa field, a cornfield, and a pasture. Take notes regard- ing topography, vegetation, etc. (Care should be taken in securing the samples to put the covers on the boxes as soon as the soil is placed in them, to prevent loss from evaporation.) 3. Weigh the samples carefully. 4. Place the boxes in an oven with the lids removed, and heat at a temperature of 110° C. until the samples are water-free, 5. Weigh samples again. [89] Fig. 14. Soil augers, tubes, and other apparatus for mak- ing moisture determinations MANUAL OF SOIL PHYSICS 6. Compute the per cent of moisture in the samples, using the water-free soil as a basis. Record your results in a form similar to the following : Field. Date. Depth Weight of Box Weight of Box and Soil Loss IN Water Weight of Water-free Soil Amount of Water in Soil Feet Before heating After heating Per cent Inches of rainfall Grams Grams Grams Grams Grams Note. In computing the inches of rainfall, assume the soil to have an apparent specific gravity of 1.3. References : Lyon and Fippin : Soils, pp. 135-165. Twenty-fifth Annual Report of the Nebraska Agricultural Experi- ment Station, pp. 71-73, 106-110. Widtsoe : Dry-Farming, pp. 94-129. Hall : The Soil, pp. 64-67. Hopkins : Soil Fertility and Permanent Agriculture, pp. 577-583. Questions : 1. Comparing the moisture content of the three fields, in which foot do you find the greatest variation of moisture ? 2. How do you account for the fact that the three fields differ in moisture content? Explain. 3. What factors influence the amount of moisture found in field soils? 4. Rainfall is disposed of in what way? 5. What practical methods may be employed which will favor the storing of moisture in the soil ? [90] EXERCISE XLI STANDARDIZATION OF THE EYEPIECE MICROMETER Object. The object of the exercise is to standardize the micrometer scale of the microscope and learn the value of each division. Materials needed. Microscope ; stage micrometer. Procedure. Place the micrometer scale on the microscope stage and, using the No. 10 eyepiece, determine for each of the objectives the number of divisions or spaces of the eyepiece micrometer that correspond to 1, 0.5, 0.1, 0.05, and 0.005 mm. of the stage micrometer. Tabulate in a form similar to the following the number of spaces of the eyepiece micrometer that correspond to the size of the various classes of soil particles. Microscopk No. Soil Class Diameter in Number of Spaces Nitmber or Spaces Millimeters in 16mm. Objective in 4 mm. Objective Coarse sand 1.0 to 0.5 Medium sand 0.5 to 0.25 Fine sand 0.25 to 0.1 Very fine sand 0.1 to 0.05 Silt 0.05 to 0.005 Clay 0.005 and less [91] EXERCISE XLII MECHANICAL ANALYSIS OF SOILS Object. The object of the exercise is to make a partial mechanical analysis of and to become acquainted with the texture of various soils. Materials needed. Microscope (standardized) ; four beakers; burner ; evaporating dish ; crucibles ; sieves ; pipette ; wash bottle ; balance ; mortar and pestle (rubber-tipped) : soils. Procedure. Read the entire exercise very carefully before attempting to work it. In making a mechanical analysis of soils it is very important that all composite or crumb struc- tures be destroyed and that the entire sample be in a single- grain condition. This is accomplished by gently rubbing the sample of soil in a mortar with a rubber-tipped pestle. In rubbing there should be just enough pressure to detach adhering particles — not enough to break them. Add just enough water to make the soil into a pasty mass, and pestle for a little while. Fill the mortar about half full of water and allow to settle about live minutes, or until all particles larger than 0.05 mm. have settled; then pour into a beaker the water which contains only silt and clay. Again pestle the soil particles for a time, add water, and allow to settle, again pouring off the silt and clay into the beaker which already contains some silt and clay particles. Continue this operation until all the particles are completely disintegrated. When disintegration is complete, the particles show sharp out- lines under the microscope and are glassy in appearance. [93] MANUAL OF SOIL PHYSICS When disintegration is complete, transfer all the soil to the beaker already containing silt and clay and probably some sand. For convenience this beaker is called A. Fill the beaker A with water and stir thoroughly. Allow the parti- cles to settle until an examination with the microscope shows that all particles larger than 0.05 mm. have settled ; then pour the turbid liquid into a second beaker B. Examine the sediment in the bottom of beaker B, to make sure that no par- ticles larger than 0.05 mm. have been poured off. In case sand particles have been poured off, stir the contents of beaker B and allow all the sand particles to settle, pouring the liquid containing silt and clay into a third beaker C. Return the sand in beaker B to beaker A. Examine the sediment in beaker C, and if no sand particles are found, the liquid may be discarded. Again fill beaker A with water and stir. As soon as all the sand particles have settled, pour the turbid liquid into beaker B. In the same manner as above examine the sediment in beaker B, returning any sand particles to beaker A. Continue this process until all silt and clay particles have been removed from beaker A and it contains only sand or particles larger than 0.05 mm. in diameter. Transfer the contents of beaker A to an evaporating dish and evaporate to dryness ; then weigh. After weighing, trans- fer the particles to the sieves and shake until a thorough separation has been made. Place each separate in a weighed crucible and ignite to burn off the organic matter, then weigh and determine the exact weight of each. By means of a separate sample of the original soil deter- mine the per cent of volatile matter that it contains (Exer- cise XVIII). To determine the combined weight of silt and clay which the sample contained, add the weights of all the separates and the volatile matter, and substract from the weight of the original sample. (A complete mechanical analysis may be made by separating the silt from the clay, [94] MECHANICAL ANALYSIS OF SOILS using the materials that are discarded in the separation of the sand and gravel classes.) In order to obtain a check on the amounts of particles lost, analyze all samples in duplicate. By the above method determine the per cent (water-free basis) of coarse gravel, fine gravel, coarse sand, medium sand, fine sand, very fine sand, silt, and clay, together with the per cent of organic matter, in the samples given out at the storeroom. Tabulate your results in a suitable form, and report as soon as the separation is completed. References : Bulletin No. 4 of the United States Department of Agriculture, Bureau of Soils. Bulletin No. 24 of the United States Department of Agriculture, Bureau of Soils. Questions : 1. Name five methods of mechanical analysis. 2. Discuss briefly the force or forces used in each of the above methods. [95] EXERCISE XLIII SOIL EXAMINATION Object. The object of the exercise is to give practice in estimating approximately the texture and physical composition of soils. Materials needed. Graduate ; soil samples. Procedure. Procure samples of soil from the storeroom and study them according to the following outline: Dry soil Color Pulverent, crumbly, or cloddy Moist soil Color Floury, mealy, or gritty Pliable or plastic Composition (estimated) Supply of carbonates Organic matter (per cent) Gravel (per cent) Coarse and medium sand (per cent) Fine sand (per cent) Very fine sand (per cent) Silt and clay (per cent) Do the work rapidly, using only a few pieces of apparatus. In estimating the physical composition of a soil a graduate is sometimes of considerable help. Place 10 cc. of the soil in the graduated cylinder with from 60 to 80 cc. of water; shake and allow to settle. The amount of sand may be read very [97] MANUAL OF SOIL PHYSICS roughly after the soil has settled. The cylinder is of little aid in studying a heavy type of soil. In testing for carbonates place several drops of hydrochloric acid on a small portion of the sample. In case the soil con- tains about normal amounts, effervescence will not be readily observed ; large amounts will be easily detected. [98] EXERCISE XLIV EXAMINATION OF SOIL SAMPLES Object. The object of the exercise is to study samples of soil taken from the student's home farm, or some place of interest, in order to become more familiar with them. Materials needed. Samples of soil (first, second, and third foot of each type) ; apparatus necessary for the exercises named below. Procedure. Study each type of soil that has been procured, using 1 the following exercises as an outline : Exercise IV, Soil Classification (Origin). Exercise XVIII, Loss on Ignition. Exercise XIX, Soil Acidity and Basicity. Exercise XX, Determination of Humus. Exercise XLII, Mechanical Analysis of Soils. Exercise XLIII, Soil Examination. Tabulate your results in a suitable form. [99] WEIGHTS AND MEASURES 1 kilogram = 2.2 pounds avoirdupois. 1 liter = 1.056 quarts. 1 inch = "J.").:!!)!) millimeters. 1 pound 153.59 grams. 1 cubic fool "t' water weighs approximately 62.5 pounds. 1 inch of water over 1 Bquare fool weighs approximately 5.2 pounds. 1 acre inch of water = 113.3475 tons. 1 acre 13560 square feet. 1 acre foot contains 4-3560 cubic feet. 2 7T/- or ttD — circumference of circle. irr- — area of circle. I m 3 or 7r/>- = area of Bphere. \/'-\ 7n -:t or I/O 7r/> :! = volume of sphere. ■nr-h = volume of cylinder (h = altitude). [101] =« =1 =* =1 fc L