= siaiaestieseet gs chgracest styles gseitgs : . Saeeeeet eel > bak - * my eR peer e —aAet Rp mein Nene hel ee eee, aie a t i ye er PY ! ; ene Pees to Se 33 leis eee te si eehees — i ; t “ eee it acegen * + | bawwes eee Ll eweees PT 1 meses joa + ferwece- mn ; ts ‘j——- =a instar =~. + |S aeoee + 3 | rete —— rs pe oeonte - 7 pone om ii tas tans * H 7 : laren a = cas] 1 ispeote ———* bie — i ete i ~wrw 4 oA ail “i yermat PATE ATE ATE A UTSLER LEACAL SD Gopright NO COPYRIGHT DEPOSIT: ' ae ak ne. YW i bi h Fae. THE WILEY TECHNICAL SERIES FOR VOCATIONAL AND INDUSTRIAL SCHOOLS EDITED BY J. M. JAMESON GIRARD COLLEGE THE WILEY TECHNICAL SERIES EDITED BY JOSEPH M. JAMESON TEXT BOOKS IN AGRICULTURE NOW READY Market Gardening. By }. L. YEaw, Manager, Oasis Farm and Orchard Company, Roswell, N. M. Formerly Professor of Market Gardening, Mas- sachusetts Agricultural College. vi+120 pages, 5 by 7. 36 figures. Cloth, 75 cents net. Studies of Trees: Their Diseases and Care. By J. J. Levison, Department of Parks, Brooklyn, N. Y. 54 by 8. x+253 pages, 156 half-tone illustrations. Cloth, $1.60 net. (Also 8 by 10%, loose leaf.) Agricultural Drafting. By Cuartes B. Hows, Bush- wick Evening High School, Borough of Brooklyn, New York, N. Y. viii +63 pages, 8 by 1034. 465 figures, 26 plates. Cloth, $1.25 net. Exercises in Farm Dairying. By Professor C. LARSEN, Department of Dairy Husbandry, South Dakota State College. Loose leaf, 8 by 10/4. 69 Exercises. Single Exercises two cents each. Com- plete, $1.00 net. Field and Laboratory Studies of Soils. By Pro- fessor A. G. McCatt, Department of Agronomy, Ohio State University. viii+ 77 pages, 5 by 74. Cloth, 60 cents net. READY IN FALL, 1916 Field and Laboratory Studies of Crops. By Pro- fessor A. G. McCauu, Department of Agronomy, Ohio State University. Agricultural Chemistry. By Professor T. E Kerrrt, Clemson Agricultural College. Injurious Insects. By Dan E. D. SanpERson and Professor L. M. Prarrs, West Virginia University. For full announcement see list following index. 1M. 9/1/15 Solid Rock fal i d iel in any F il So r the Unde ) (Adapted from Hall isptece. Front FIELD AND LABORATORY STUDIES OF SOILS AN ELEMENTARY MANUAL FOR STUDENTS OF AGRICULTURE Di Ae GY McCALL Professor of Agronomy, Ohio State University FLEAS T cH DLT LON FIRST THOUSAND NEW YORK JOHN WILEY & SONS, Inc. Lonpon: CHAPMAN & HALL, LimiTEp 1915 COPYRIGHT, 1915, BY A. G@. McCALL A , oe Sf ie —™ - 4 THE SCIENTIFIC PRESS ROBERT DRUMMOND AND COMPANY BROOKLYN, N. Y. ©ca416181 NOY 2 1915 “Y-. a ‘ SUGGESTIONS TO TEACHERS Tus little book of soil experiments has been prepared in response to the demand for a brief laboratory and field course in elementary soils, which may be given without the purchase of expensive equipment. With a few tools and the aid of the pupils, the teacher should be able to construct all of the apparatus necessary for many of the ex- ercises. Such cooperation on the part of the students will stimulate a keener interest in the work than can be secured by the exclusive use of purchased materials. However, as funds become available, it is advised that special equip- ment be purchased and substituted for the less satisfac- tory, home-made apparatus. In many schools apparatus from the chemical and botanical laboratories will be available for the soil work. For example, a good balance may be purchased for the joint use of the chemical and soils laboratories, and the compound microscope may serve for both botany and soils. The first purchase of equipment should include the following: 1. Gasoline or kerosene stove with oven. 2. Balance similar to the one shown in Exercise A-7. 3. Soil auger and spade. 4. Small equipment, such as sample cans, glass tumblers, tin cans, wrapping paper, cheese cloth and twine. Vv vi SUGGESTIONS TO TEACHERS A supply of clean sand, and also some loam, clay and muck soil should be secured in the fall. This material should be dried, pulverized, and passed through a sieve with one- eighth-inch mesh, to remove stones and sticks. The exercises are intended to furnish sufficient material for one period per week throughout the year or two periods per week for a half year. Although they are arranged in logical order, it is not necessary that the exercises should be taken up in the exact sequence in which they occur in the text. Indeed, it will be necessary for the teacher to vary the arrangement in order to adapt the study to the season and to the facilities of the school. A small working library should form a part of the equipment. For a study of soils this library should include several elementary books on soils, a collection of Farmers’ Bulletins from the United States Department of Agriculture and the publications of the State Experiment Station. While much of the material in the text is original, the writer has drawn freely from all sources for suggestions and illustrative material. Some of the illustrations have been adapted from the text-books and much material has been taken from the publications of the Agricultural Extension Department. The author wishes to make espe- cial acknowledgment of the helpful suggestions of former Superintendent A. B. Graham and Mr. Clark 8. Wheeler of the Agricultural Extension Department of the Ohio State University. A. G. McCatt. DEPARTMENT OF AGRONOMY, Onto STATE UNIVERSITY. June, 1915. CONTENTS EXERCISE AT. A 2. AS: A 4. A 5. A 6. / Ney (2 A 8. ACO: AAO, Acid: Momdy oF the Kormation.of Soils..0 o:.. 2.4.2. 25 asc a fo study the Composition of Soils: .. 20.4 22.5... es To Study the Groups of Individual Soil Particles.......... To Compare the Surface Soil with the Subsoil............ To Study the Relative Productiveness of Soil and Subsoil. . To Study the Individual Soil Particles................... To Determine the Amount of Organic Matter in Different To Determine the Pore Space in Soils... ...5.........--- To Determine the Weight of Soil per Cubic Foot.......... hoe hry. onl Cnt aman) 2-30. aon. es ee oa aloes Aka To Study the Effect of Freezing and Thawing upon Soil (SETS TL STO TAN Sa ee a i a NR Me eet 8 QE PN a . To Show That Some Soils Can Hold More Water Than TE Es Sd SS OR th I A RAI ca ee ee aa en ee PEE SEE d . To Show That Plants Give Off Moisture through Their Rete ee ee ax ne Rien ve SE PE ee Do Se . To Show the Effect of Soil Air upon Plant Growth........ . To Show How the Temperature of the Soil is Affected by the . To Study the Necessity for Soil Drainage................ An piaoy ot Warh-and Cold Soils... 0 22% ocec. ois S28 eat = lo Study- the Operation of Vile Drains... os)... 03.6. oe. PAmciivent mom Pemperature <7. sched. Cobos wae ees tek . To Demonstrate the Movement of Water in the Soil. ..... . To Show the Effect of a Loose Surface upon the Rate at which the Rain Will Soak into the Soil................. , Lo ptudy the Korms/of Soil-Moistire.. 2.20.2... .5) 0-46 02 vu viii CONTENTS EXERCISE A 24. A 25. A 26. A 27. A 28. A 29. A 30. A 3l. A 32. A 33. A 34. A 35. To Study the Capillary Movement of Soil Moisture....... To Show the Effect of Plowing Under Coarse Material such as Manure, Green Cover Crops or Cleds. . Me To Show the Effect of a Mulch in Preventing aie Lee ae Moisture, 2) oes ee oes ene cae Ge one To Study the Water Loss from Cultivated, Uncultivated and. Miulched: Soil Surfaces... 1.04. 2 sos ess a ae To Show the Effect of Drainage upon Soil Temperature. . To Show the Influence of Color upon Soil ‘l'emperature. . To Show the Effect of Lime upon the Soil................ To Study. the: Need:of the Soiltor Time:<+ yes. en eee To Study the Adaptability of Soils to Crops:.....5:....7% wo, study the Plow +s,.44 00 oS Bee Sa eee To Study Plant Roots and Their Relation to Soil Manage- FIELD AND LABORATORY STUDIES OF SOILS EXERCISE A-1. A STUDY OF THE FORMATION OF SOILS. Equipment: This exercise is based upon the pupil’s own observations rather than upon laboratory work. Any es a t es Fic, 1.—The Rock may Lie but a Few Inches below the Surface. natural formations in the neighborhood, which are illus- trative of soil-making processes, should be visited by the class. Each pupil should write an account of the trip, including a discussion of the questions given below. 2 FIELD AND LABORATORY STUDIES OF SOILS Questions: 1. Does solid rock come to the surface at your home? 2. Name a place where you know the depth at which solid rock is found. 3. Does your home well reach the rock? 4, At what depth? 5. Compare the shape of stones found in streams with that of crushed stone. How do you account for any difference? | Discussion: Under the soil in any field is solid rock. Sometimes this rock is very deep and again it may lie but a few inches below the surface. The soil also was once large rocks. It was made fine as we see it by natural agencies working through millions of years. These agencies are still at work and may often be observed. Water fills the crack in a large stone, freezes and bursts the stone apart. Exposed ledges of stone heated during the day and cooled at night for several years finally crumble. The roots of trees force themselves between the layers of rock and split them apart. Every little stream rolls and wears pebbles, grinding them finer and finer, finally forming soil. An examination of almost any soil shows that it con- tains not only fine rock particles, but also plant and animal remains. This organic matter may be found in the soil in all stages of decay, and constitutes the most important body of material present in the soil. It furnishes nitrogen, which is an important plant nutrient, and enables the soil to absorb and retain moisture. 3 BP THE HORMATION OF SOILS Q) A STUDY ‘OOBTT 0} OV] Y WIOIJ [IOG BSuLIAOJY AT[VNUTUOD STI 1o}V AA BUIMO]Y—'Z “DIV _ EXERCISE A-2. TO STUDY THE COMPOSITION OF SOILS. Equipment: Spade or soil auger; two pieces of oil- cloth or heavy wrapping paper sixteen inches square; two slender bottles; tablespoon. Method: By means of the spade or soil auger, secure a sample each of a sandy soil and a heavy clay. Place a tablespoonful of each soil in separate bottles and fill each about two-thirds full with clear water. Shake each bottle Sandy Soil. Heavy Clay Soil. for one minute and allow to settle for five minutes. Ob- serve carefully the layers in each bottle, the large particles at the bottom and the finest material at the top. Use the bottles shown above to indicate what you see. Discussion: Soils are composed of fine rock particles 4 TO STUDY THE COMPOSITION OF SOILS a that have resulted from the breaking and grinding of large rocks, to which has been added some organic material which has been formed by the decay of plant and animal remains. All of the light-colored rock particles in the bottles are quite similar except as to size. The dark material at the surface or floating in the water is organic matter which may be removed from the soil by burning. Both classes of material are essential to the growth of plants, the rock particles furnishing the mineral food elements and the organic matter the nitrogen. The organic matter also increases the moisture-holding capacity of the soil. EXERCISE A-3. TO STUDY THE GROUPS OF INDI- VIDUAL SOIL PARTICLES. Equipment: Four beakers or tumblers; samples of clay and sandy soil. Method: Make fine and dry a small quantity of each of the two kinds of soil. Put three tablespoonfuls of the clay soil in one tumbler or beaker, and a like amount of the sandy soil in the other. Fill each one half full with water. Taking the tumblers or beakers one at a time, proceed as follows: shake gently for four minutes, let stand one minute and pour off into another tumbler all the water possible without losing the settlings. The settlings are the sand. Allow the water poured off to stand one hour until a distinct layer of settlings can be seen at the bottom. Now pour off and discard the clouded water. This muddy water contains clay so fine that it will not settle. The material which has settled in the second glass is silt. Questions: (1) About what proportion of the sandy soil is silt? (2) About what proportion of the clay soil is silt? Discussion: Soils are classified according to the fine- ness of the rock particles which they contain. A _ soil which contains a large proportion of coarse particles is called a sandy soil. One which contains a large propor- tion of fine particles is called a clay soil. No soil is made 6 GROUPS OF INDIVIDUAL SOIL PARTICLES a up wholly of clay or of sand particles. All soils contain a certain per cent of each of these groups of fine particles. The coarser sandy soil drains more rapidly, warms up More quickly in the spring and is, therefore, better suited to early garden or truck crops. Clay soil dries out more . slowly, and for this reason it is capable of furnishing water to the crop during the hot dry summer months, especially if it contains a large amount of organic matter, EXERCISE A-4. TO COMPARE THE SURFACE SOIL WITH THE SUBSOIL. Equipment: Soil auger or spade; piece of oilcloth or heavy paper sixteen inches square. Method: With a spade dig a narrow trench a foot deep. Make one side of the trench smooth and note the line at the bottom of plow depth. Examine a handful of soil above and below the line and fill out the following table, comparing the two: Firmness. Color. Moisture. Surface soil. Subsoil..... Observe the line between the Fic. 3.—Soil Auger Made surface soil and the subsoil wherever by Welding a Three-foot the earth has been cut into, either 7 ACE rer at by a stream or an artificial grade. of a 13-inch Wood Au- There is usually a distinct difference ger. Additional lengths in color between the surface soil and may be added as desired. the subsoil. Discussion: If the soil contained nothing more than 8 SURFACE SOIL AND SUBSOIL 9 fine particles of rock there would be little difference between the surface soil and the subsoil. After the rocks were made fine, plants began to grow and by their death and ~ decay they have added to the soil the dark-colored material ‘which we call organic matter or humus. As the stems and leaves of plants fall on the ground and decay they are worked into the soil. Thus the surface soil is made to contain large quantities of decaying plants, while the subsoil contains but little of this material. This is the chief difference between the two. These decaying plants are an important addition to the soil. They add nitrogen and make the soil capable of holding more moisture. EXERCISE A-5. TO STUDY THE RELATIVE PRODUC- TIVENESS OF SOIL AND SUBSOIL. Equipment: Two flower pots or quart cans; wheat seed; soil and subsoil from the same place. Method: Fill one pot with moist surface soil, the other with moist subsoil, and plant six grains of wheat in each. Keep the pots watered and compare the growth of plants from time to time. Discussion: Why are washed hillsides and the high points in the fields usually less productive than the level land and the lower levels? Steep land should be cultivated across the slopes and should be kept covered with some crop in order to prevent the washing away of the surface soil. Deep plowing is often desirable to increase the depth of the surface soil. If the soil has always been plowed shallow it will be better to plow only an inch or two deeper each year until the desired depth is reached, than to plow deep the first year. Why? Observe the growth of corn or wheat in the “‘ dead furrow ”’ between the lands. While the plowing up of the subsoil in the humid regions frequently results in a decreased productiveness, the soil and the deeper layers in the arid regions may be mixed without injury. In these dry sections good crops are fre-— quently grown where the top soil has been entirely removed in the preparation of the land for irrigation. 10 PRODUCTIVENESS OF SOIL AND SUBSOIL 11 Fic. 4.—A Convenient Soil Bin, Mounted upon a Cupboard. The bins are filled from the top, the soil being removed from the open throat at the bottom. A sloping board just above the opening directs the soil back and prevents it from escaping faster that it is used. EXERCISE A-6. TO STUDY THE INDIVIDUAL SOIL PARTICLES. Equipment: Two tumblers; tablespoon; three large beakers or quart cans; samples of sand and clay soils. Method: (a) Puta tablespoonful of sand in one tumbler and the same quantity of clay in the other. Fill each with water and after thorough shaking, allow the soils to settle. Which settles the more rapidly? When a swiftly flowing stream carrying material in sus- pension is checked, which particles are first deposited? Find an example of the sorting power of flowing water in your neighborhood. (b) A day or two before the class is to meet put three or four tablespoonfuls of sandy loam soil in a beaker or can and nearly fill the vessel with water. Shake at inter- vals for one day and finally after thorough shaking allow to settle one hour and pour off into another beaker (or can) the muddy water down to within one inch of the bottom. Allow to stand for one minute, again pour off the muddy water and evaporate each separation to dry- ness on a stove. When dry, examine the material in each can; the last residue is sand, the second is silt, and the first separation is clay. Moisten a little of each and rub between the thumb and finger. Which ones are sticky and which fall apart easily? 12 LO STUDY THE INDIVIDUAL SOIL PARTICLES: “13 If a compound microscope is available, examine each separation and make a drawing of a few grains from each. Note that the soil consists of fine rock particles and dark humus or organic material. EXERCISE A-7. TO DETERMINE THE AMOUNT OF ORGANIC MATTER IN DIFFERENT SOILS. Equipment: Balance; small porcelain or tin dishes; soil samples; gas burner or alcohol stove. Method: Place a teaspoonful of fine dry soil in a dish. Put the dish on the left-hand pan of the balance Glass or Metal Tube Cork : Fria. 5.—Small Alcohol Stove Made from an Ink Bottle or Oil Can. and add weights to balance it. Now heat the sample over the flame until all the organic matter has been consumed. Take care that the same weights are on the right-hand pan of the balances and return the dish containing the soil to the left-hand pan. How does this weight of the sample compare with its previous weight? How do you account for this difference? Add dry leaves or cut straw until the pans are again in balance. What does this added material represent? Discussion: Soils vary greatly in the amount of or- 14 ORGANIC MATTER IN DIFFERENT SOILS 15 Fig. 6.—Two Types of Alcohol Stoves, which may be Made to Take the Place of Gas Burners. Fig. 7.—A Good Balance Costing about $12.00. 16 FIELD AND LABORATORY STUDIES OF SOILS ganic matter which they contain. Muck soils are composed almost entirely of organic matter, while some sandy soils contain comparatively little dead plant and animal remains. Whenever the supply of organic matter in a soil is low the crop yields are small. Applying manure and plowing under clover are good ways of increasing the amount of organic matter in the soil. Notre.—A very good balance can be purchased for about $12.00. Small dishes should be about two or three inches in diameter. If tin, they must be without soldered seams. Gas or alcohol stoves may be purchased at a small cost, or a very good alcohol lamp may be constructed in the laboratory without cost, by following the diagram shown on page 14. EXERCISE. A-8. TO DETERMINE THE PORE SPACE IN SOILS. Equipment: Dry samples of sandy soil and clay soil; graduated bottle or cylinder; a quart can or milk bottle. Method: (1) Fill the can or bottle to within one-half inch of the top with the dry sand and compact by tapping ---- O sca in ii if % Srole s30Nno fF menses =F SY — = S Hui o = uo ut 3 > ui Soe Cae ao S | | = =o 3g Il ' iste ti [ ft il a = Hh ln Thies i “FF i il Ng Fee | | i Fig. 8—A Graduated Bottle or Cylinder is a Necessary Part of the Laboratory Equipment. the can lightly on the desk top three times; (2) fill the graduated bottle or cylinder to the top mark with water; (3) carefully pour the water from the graduated vessel onto the top of the soil in the can and continue to do so until the water stands level with the top of the sand; (4) record 1 18 FIELD AND LABORATORY STUDIES OF SOILS the amount of water used. This represents the amount of water necessary to fill all of the open space in the sand. Repeat the above operations, using the sample of clay soil. Report your observations in the following table: Cu. Centimeters Cu. Centimeters of Soil Used. of Water Used. Per Cent of Pore Space. andy Soule erie s Wlayasoml fe ca. Fic. 9.—Spring-board Compactor Used to Secure Uniform Packing of the Soil. The can or tube of soil is placed at the middle of the board and the weight on the standard to the left is dropped a definite number of times from a fixed point. Discussion: The large amount of water which a can will hold after it is already filled with dry soil serves to bring out the fact that only about half of the soil is occu- TO DETERMINE THE PORE SPACE IN SOILS 19 pied by the soil particles, the remainder being occupied by water when the soil is very wet or by air when it is per- fectly dry. For the best growth of crops the space not occupied by the soil particles should be divided about ~ equally between water and air. If the space becomes entirely filled with water, crops will not thrive, since their roots will not be able to get the air necessary for their growth. Sandy soil has larger spaces between the indi- vidual soil particles, but the total amount of pore space is less in the sandy soil than in the clay soil. EXERCISE A-9. TO DETERMINE THE WEIGHT OF SOIL PER CUBIC FOOT. Equipment: Balance; brass cylinder* or quart can; samples of sandy loam and clay soils. Method: Fill the quart can with the dry sandy loam and compact by tapping it lightly on the desk four times. aa— Fig. 10.—A very good Balance of this Type can be Purchased for about $8.00. Stroke off the soil level with the top of the can and weigh. Subtract the weight of the empty can. Calculate the capacity of the can in cubic inches and from the weight of the dry soil determine the weight of one cubic foot. * Brass cylinders for this exercise may be purchased from labora- tory supply houses at a cost of about $1.00 each. 20 WEIGHT OF SOIL PER CUBIC FOOT 21 Calculate the weight of an acre of this soil to the depth of one foot. This will give the weight of an acre-foot. Repeat the determination for the clay soil and record - the results in both cases in the following table: Weight of Can |Capacity of Can of Soil in in Cubic Weight of a Weight of an Grams or Centimeters Cubic Foot. Acre Foot. Ounces. or Inches. Sandy loam.. Discussion: The weight of a given volume of soil depends very largely upon the amount of organic matter present—the greater the proportion of organic matter the lighter the weight of the soil. The extent to which the soil is compacted also influences the volume weight. EXERCISE A-10. TO STUDY SOIL GRANULATION. Equipment: Three shallow pans; sample of heavy clay soil. Method: Fill each of three pans nearly level full with dry clay soil. To the first pan add all the water which it will hold, continuing to pour on water as it soaks in, while working the soil with the fingers or with a stick. Over the second pan sprinkle one-half cup of water. Leave the third pan untreated. Place all three pans near a stove or in the sun, and dry thoroughly. Compare the size of the lumps of soil in the pans to which water was added. Which crumbles more easily between the fingers? Which is more like a field in good tilth? What happened to the first pan? ) Discussion: The fine rock particles in a pile of clean sand always remain separate, but the very, very fine par- ticles of rock which form the soil stick together to form crumbs or granules. When these granules are comparatively small and easily crushed, the soil is said to be well granulated. Large hard granules are called clods.. When a large amount of water is added to a clay soil, the soil becomes “‘ puddled ”’ or “run together,” and clods are formed. Similarly, if a wet clay soil is compacted by the feet of men or horses, or if it is plowed when too wet, hard clods are formed. 22 EXERCISE A-11. TO STUDY THE EFFECT OF FREEZING AND THAWING UPON SOIL GRANULATION. Equipment: Shallow pans; some clay soil. Method: Using heavy clay, make up two mud balls to about the consistency of putty. Place one on a shelf Fic. 11.—Running Water, Freezing and Thawing, and the Roots of Trees are Powerful Agencies in the Breaking Down of Rock to Form Soil. to dry and the other outside on the window sill where it will be frozen. Arrange to have the latter alternately freeze and thaw each day for a week or longer. When both are dry crush them with the hands. Which breaks the more easily? 23 24 FIELD AND LABORATORY STUDIES OF SOILS Discussion: The freezing of water is one of the natural agencies which plays an important part in the breaking up of the rocks to make soil. This same force can be utilized to good advantage every year by the farmer through the practice of fall and winter plowing. Heavy clay soils by this practice can be made more loose and friable. Ex- posure of the plowed land to the action of freezing and thawing is especially desirable where the soil has become hard and cloddy, as the result of plowing it too wet, or by the trampling of livestock. The hard clods absorb water which, on freezing, expands and bursts them apart. EXERCISE A-12. TO SHOW THAT SOME SOILS CAN HOLD MORE WATER THAN OTHERS. Equipment: Four funnels; muslin or cheese cloth; scissors; well rotted manure; four graduated cylinders or bottles; funnel holder; sand; loam, and clay soil. Method: Plug each funnel lightly on the inside with a piece of cotton or cloth. Fill the funnels as follows: (1) sand, (2) loam, (3) clay, (4) one-half sand and one-half manure. Arrange the funnels in the rack with their stems in the mouths of the bottles. Very slowly pour over each funnel exactly eight ounces (one-half pint) of water. Allow to stand till the drip ceases and read the amount of water in each bottle. Record these readings and subtract them from the amount poured into each funnel. What do these differences represent? Mixture mumber.; ......... 1 2 3 4 Amount poured in........ Ampont.im bottles... 2... Amount held in ‘soil. - ..: ... Discussion: The capacity of soils to hold water depends upon the size of the particles and the amount of organic matter. In clay soils it is increased by granulation. Clay 25 26 FIELD AND LABORATORY STUDIES OF SOILS soils can hold more water because the individual spaces between the particles are smaller and the total amount of space is larger, than in other soils. Muck and clay soils will hold the largest amount of water and sandy soils the ss Cylinder Used to ated Bottles Used to Show Measure the Water-holding Ca- that Some Soils can Retain pacity of Soils. more Water than Others. least. The supply of water is the most important single factor in the growth of plants. Consequently, the extent to which different soils retain moisture deserves careful study. EXERCISE A-13. TO SHOW THAT PLANTS GIVE OFF MOISTURE THROUGH THEIR LEAVES. Equipment: piece of cardboard; wax.* Method: Use a plant which is at least three or four inches high and grow- ing in a flower pot or tomato can. Cut a slit in the cardboard from the middle of one side to the center, and place the card- board around the plant: Seal up the slit in the card- board with wax. Now in- vert the glass jar over the plant and place in a sunny window. How do the drops of water get into the glass jar? Discussion: Plants are constantly giving off water from their The evap- leaves. largest amount is * Beeswax, paraffin, or graft- ing wax will be found quite satis- factory. Small potted plant; wide-mouthed jar; Fig. 14.—Potted Plant Arranged to 27 Show that Plants Give off Moist- ure through their Leaves. If placed in a sunny window, drops of moisture soon collect on the in- side of the can. 98 FIELD AND LABORATORY STUDIES OF SOILS orated in the hot sun and when an abundance of water is supplied to the roots. Sometimes in a drouth more water is evaporated from the leaves than is being taken in by the roots. If this is continued for some time the plant wilts. This reminds us that the water in plants gives the soft stems and leaves their stiffness. All the food which the plant takes from the soil must first be dissolved in water. It is estimated that 900 tons of water are evap- orated by each acre of corn plants during the growing season. EXERCISE A-14. TO SHOW THE EFFECT OF SOIL AIR UPON PLANT GROWTH. Equipment: Two tumblers, or quart cans; _ several grains of corn. | Method: Fill two tumblers within a half inch of the top with rich soil. Plant in each three kernels of corn. Water tumbler No. 1 only enough each day to keep the soil moist. Keep water in the second tumbler so that it stands a little above the surface of the soil. Fill in the following blanks: De ED ANGLIN 28 5 ore! ss, Sts Ses Sale e PS PO pe Minish fl LING WD oso cheaiicts: Geeuseers sie a § ato mates Ave. height 1 wk. after coming up........... What kept the corn in one tumbler from growing as well as that in the other? What became of the air in the soil in tumbler No. 2? Discussion: For the best growth of crops the space not occupied by soil particles should be divided equally between air and water. If this space becomes entirely filled with water, crops will not thrive, since their roots will not be able to get the air necessary for plant growth. 29 30 FIELD AND LABORATORY STUDIES OF SOILS Some plants, such as the cypress and the water lily, have special structures which enable them to obtain ‘air from the water while their roots are entirely submerged,- but our common field plants do not have this ability. EXERCISE A-15. TO SHOW HOW THE TEMPERATURE OF THE SOIL IS AFFECTED BY THE SLOPE. Equipment: Three boxes, 6’’12’’12’; three ther- mometers;* soil sample. Method: Number the boxes 1, 2, and 3, fill with the same kind of soil and set them in the sunlight, side by Fig. 15.—Arrangement of Boxes to Show the Effect of Slope upon the Temperature of the Soil. side. Arrange the boxes so that No. 1 will stand level, No. 2 slope toward the south (four inches slope to the foot) and No. 3 slope toward the north at the same angle. * The thermometers should be tested by placing the three side by side in a tumbler of water and after stirring the water for a few minutes compare the readings on the thermometer scales. If they do not read the same a suitable correction must be applied. 31 32 FIELD AND LABORATORY STUDIES OF SOILS Place a thermometer in each with the bulb covered with soil. Take readings every two hours during the day. TEMPERATURE RECORD List the three surfaces in the order of their temperature. What location would you seek for an early garden plot? Discussion: The temperature of the soil is affected by the slope, because in one case a given amount of the sun’s heat must warm a larger area of soil than in another. When the slope is towards the sun the soil stands more nearly at right angles to the sun’s rays, but when the sur- face is level or slopes away from the sun, it is inclined away from the direct rays. The same amount of heat must then warm a larger area. This increase in area may be shown by sawing off a board at right angles and then at an obtuse angle, and measuring the cross-section each time, EXERCISE A-16. TO STUDY THE NECESSITY FOR SOIL DRAINAGE. Equipment: Two one-quart tin cans; a graduated cylinder or bottle; a one-foot rule; several grains of corn; a sample of loam soil. Method: Make eight holes in one can by driving a nail through the bottom. Stand this can on blocks in a saucer. Fill both cans with loam to within one inch of the top and plant three grains of corn in each. Each day, pour water upon the surface of the soil in the tight can until it stands at the surface, noting the amount used each time. At the same time add the same amount of water to the other can, using the graduated bottle to determine the amount added. As soon as the corn appears above the surface measure its height every other day, recording the average height of the three plants in each can. The height may be regarded as the distance from the surface of the soil to the tip of the uppermost leaf. Average Height of Plants on the Following Dates: Can with holes... . From this exercise what do you conclude as to the 33 34 FIELD AND LABORATORY STUDIES OF SOILS relative length of time which would be required for corn to come up in a drained and in an undrained field? > Fic. 16.—Corn Planted the Same Day. Tumbler of soil to the left kept saturated while the one to the right is only about half-saturated with water, What effect does drainage have upon the air in the soil? Discussion: The rain which falls on the fields would TO STUDY THE NECESSITY FOR SOIL DRAINAGE 35 in time completely saturate the soil if no drainage were possible. The more nearly level the land the more readily does the rain pass into it. During a long-continued rain the water soaks into the soil until, like a blotter or a sponge, it can hold no more. Then the excess of water will flow over the surface to the lowest points in the field and finally join the creeks and rivers which are a part of Nature’s great drainage system. The water which has soaked into the soil gradually passes into the subsoil and eventually finds its way to the streams. If the soil is a loam with an open subsoil, this natural drainage will be sufficient. However, in heavy loams and in clay soils Nature does her work too slowly to be of immediate benefit. Then it is that we should supply artificial drainage in the form of tile to carry away the surplus water more promptly and thus assist Nature. EXERCISE A-17. A STUDY OF “WARM” AND “COLD” SOILS. Equipment: Dry loam soil; two thermometers; two flower pots or quart cans; a beaker or tumbler. Method: (a) Tie a piece of muslin cloth around the bulb of one thermometer and suspend it over a tumbler with the lower end of the cloth dipping into the water, but the bulb one inch above the surface. Suspend the other thermometer in the air near the tumbler. At the end of ten minutes read both thermometers and take the temperature of the water. Record as follows: Degrees. Temperature of the AEN,