BASIC FACTORS AFFECTING THE ENERGY REQUIRED FOR EMERGENCE OF PLANT $EEDLENG$ The“: for the Degree 0? M. 5. MICHIGAN STATE UNEVERSET‘Z Carl Thomas Morton 1959 gauze mm ‘1 rm W! W 31293 3009 947494 BASIC FACTORS AFFECTING THE ENERGY REQUIRED FOR EMERGENCE OF PLANT SEEDLINGS by CARL THOMAS MORTON AN ABSTRACT Submitted to the College of Agriculture of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SC IENCE Department of Agricultural Engineering Year 1959 1" Approved fi/éfirffifi% ABSTRACT Planting seeds to a uniform stand is of primary im- portance in the mechanization of practically every crop that is grown today. Research and field tests show more variation in seedling emergence than can be attributed to the performance of the planter. This indicates that the physical factors of the seed environment may be influencing seedling emergence. Mechanical impedance of the soil, depth of planting, surface profile, etc., affect the amount of energy expended by the emerging seedling and play an important role in the success or failure of a crop. Experiments, therefore, were. designed to study the effect of soil compaction, position of applying compacting pressure, soil moisture content, and length of drying time on the amount of energy and force which would be expended by an emerging seedling. The work was done in the laboratory under controlled conditions. A penetrometer was designed, fabricated and developed to give a relative measure of the energy required for emer- gence of plant seedlings. The instrument consisted of a mechanical seedling which was forced upward through a soil formation. A continuous record of the force and position of the mechanical seedling was recorded by Brush strain gage equipment. SR-h strain gages were used as force and position sensing elements. A Brookston sandy loam soil was screened and moistened to the desired moisture content. Various compaction pres- sures were applied to the soil surface or at the one-inch depth. The emergence energy was recorded on specific days as the samples were drying under uniform conditions. The energy required for emergence increased with soil compaction pressure, soil moisture content, depth of planting and amount of surface drying. As the diameter of the me- chanical seedling increased, the emergence energy increased. Applying the compacting pressure at the seed level and pre- venting evaporation from the soil surface reduced the energy required for emergence. These results indicate that planters should be designed to press the seed into moist soil and then cover with loose soil for maximum emergence. Methods for reducing the energy required for emergence of plant seedlings were suggested. BASIC FACTORS AFFECTING THE ENERGY REQUIRED FOR EMERGENCE OF PLANT SEEDLINGS by CARL THOMAS MORTON A THESIS Submitted to the College of Agriculture of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Agricultural Engineering Year 1959 . ' ,."- /,’ . / -. , , k - t I ACKNOWLEDGMENTS The author wishes to express his sincere thanks to Dr. w. F. Buchele, under whose supervision and creative guidance this study was conducted. Sincere thanks is extended to Dr. B. A. Stout and Dr. F. w. Snyder for their assistance and many helpful suggestions. Acknowledgment is also due Mr. John Koepele and Mr. George Keller for their assistance in gathering the data. Special thanks is extended to Mr. James Cawood and Mr. Glen Shiffer for their helpful suggestions in the con- struction of the apparatus. The author is indebted to Dr. A. w. Farrell, Head of the Agricultural Engineering Department. for his support of the project and providing the assistantship for the final phase of this study. The writer appreciates the support of the Farmers and Manufacturers Beet Sugar Association of Saginaw, Michigan, for the research grant which made this work possible. The faith, support, and assistance in preparing the manuscript of the authors wife Mary, is gratefully acknow- ledged. 0 TABLE OF 0 5—) TTENTS _ Page INTRODUCTION 0 O O O O O 0 O O O O O O O O O O O O O O l REVIENOFLITERA’IURE.................3 THRORETICAL CONSIDRRATIONS . . . . . . . . . . . . . . 15 MATERIALS AND APPARATUS. . . . . . . . . . . . . . . . 16 METHODORPROOEDURE..................2b. PRRSRITATIOR AND DISCUSSION OF EXPERIMRRTAL RESULTS. . 30 Effect of Mechanical Seedling Diameter on Emergence Energy and Force. . . . . . . . . . . 30 Effect of Soil Moisture Content, Compaction Pressure and Drying Time on the Energence EnerfgyandForCeutoooooooocococo37 Effect of Soil Aging on the Ehergence Energy andFOI'ce.o.oo..............53 Effect of Compaction Pressure Applied at Seed Level on the Emergence Energy and Force . . . . . 59 APPLICATION OR RESULTS . . . . . . . . . . . . . . . stmRI.. .. . .. .. .. . .. .. .. . CONCLUSIONS. . . . . . . . . . . . . . . . PROPOSED FUTURE INVESTIGATIONS . . . . . . . . . . . . 7h APPENDIX . . . . . . . . . . . . . . . . . . . . . REFERENCIBQOOOOO00000000000000oo83 Figure 10 11 12 13 LIST OF FIGURES Diagram of soil Penetrometer used in the Study. 0 O C O O O O O C O O O O O O O O O O 0 Wiring diagram for simply supported beam (Force measurement). . . . . . . . . . . . . Wiring diagram for cantilever beam (Displacement measurement) . . . . . . . . . Gage blocks used for calibration of the cantilever beam (Position measurement) . . . . Calibration curve for position measurement (Cantiliver beam). . . . . . . .,. . . 3 . . Vertical shaft and linear ball bearings used to eliminate cycling of the carrying platform. Over-all view of the penetrometer showing the rigid support for the simply supported beam and aligning mirror . . . . . . . . . . . Moisture tension curve for the Brookston sandy 10am soil used in this study . . . . . . Calibrated proof ring and hydraulic press used to apply compaction pressure to soil samples... 0 e e e e e o e e e e e e o e e e e Constant temperature room. . . . . . . . . . . Mechanical seedlings having various tip diameters used in the study. . . . . . . . . . Corn, bean and sugar beet seedlings that were measured to determine mechanical Seedling diameters e e e e e e e o e e e e o o Emergence eneray versus mechanical seedling diameter for surface compaction pressures of 1/2, 2 1/2, S and 10 ps1 . . . . . . . . . . . Shearing position versus surface compaction pressure for mechanical seedling tip diameters of 0.078, 0.162 and 0.2M? inches . . . . . . . _17 18 18 2O 22 23 23 25 27 27 28 23. 31 32 Figure 15 16 17 18 19 20 21 22 23 R) 4: iv Photograph of the soil cone sheared by various size mechanical seedlings. . . . . . A soil cone being pushed aside by the meChanical SCBdlinge e e e e e e e e o e e 0 Maximum emergence force versus mechanical seedling diameter for surface compaction pressures of 1/2, 2 1/2, S and 10 psi. . . . Emergence energy versus drying time for surface compaction pressures of 1/2, 1, 2, h, 8, and 16 psi. Initial soil moisture content - 12% dry basis . . . . . . Emergence energy versus drying time for surface compaction pressures of 1/2, 1, 2, h, 8, and 16 psi. Initial soil moisture content - 16% dry basis . . . . . . Emergence energy versus drying time for surface compaction pressures of 1/2, 1, 2, h, 8, and 16 psi. Initial soil moisture content “ 20% dry b88130 e e e e e e e e e 0 Soil samples compacted to the indicated pressures. e e e e e e e e e o o e e e e o e Emergence energy versus drying time for a surface compaction pressure of 8 psi and initial soil moisture contents of 12, 16, and 20%. e e e e e o e e e e e e e 0 Average emergence force versus drying time for various compaction pressures. Initial soil moisture content - 16%. . . . . . . . . Maximum.emergence force versus drying time for various compaction pressures. Initial 8011 moisture - 16¢. e e e e e o e e e e e e Logarithmic plot of emergence energy versus surface compaction pressure for various days of drying. Initial soil moisture content - l‘)% I O 0 O O O O C O O O O O O O O O O O O O Page ‘Bh 3h 36 39 to h1 h3 uh hS h? Figure 26 27 28 29 30 Shearing position versus compaction pressure for a Brookston sandy loam after 8 days drying. Initial soil moisture contents were 12, 16, and 20%. . . . Emergence energy versus aging time for surface compaction pressures of 1/2, 1, 2, h, 8, and 16 psi. Soil moisture content maintained at 16% . . . . . . . . . . Emergence energy versus aging time for compaction pressures of 8 and 16 psi. Solid line - initial soil moisture content l6%-drying conditions. Broken line - non-drying conditions. . . . . . . . . Emergence energy versus drying time for compaction pressures of 1/2, 1, 2, h, 8, and 16 psi applied one inch below soil surface followed by 1/2 psi applied at the surface. Initial soil moisture COntent ’ 16% e e e e e o e e e e e e e e e e Emergence energy versus drying time for compaction pressure of 8 and 16 psi. Solid line - pressure applied at surface. Broken line -- pressure applied one inch below surface. Initial soil moisture content - 16% Force versus depth diagrams for the conditions Stated e e e e e e e e e e e e e o Emergence energy required for various planting depths for a compaction pressure of 8 psi and a drying or aging period of 8 days. . . . . . . . . . . . . . . . . . . . Page h9 Sh SS 60 61 63 65 Table 10 LIST OF TABLES / Mechanical analysis of the Brookston sandy loam soil used in this study. . . . . . . . . Emergence energy, maximum emergence force and shearing position data for various surface compaction pressures and mechanical Seedling diameters. . o o o o o o o o e o e o Constants for the solution of Equation (2). . Emergence energy, maximum force, average force and shearing position data for various initial soil moisture contents and surface compaction pressures for a drying period of Bdayseoooelooeeeeeeeeeee. Moisture lost from soil surface at various initial moisture contents and compaction .pressures during a drying period of 8 days. . Bulk densities for Brookston sandy loam soil at various moisture contents and compaction preSSLI-res O C O O O O O O O O O O O O O O O O Emergence energy, average emergence force, maximum emergence force and shearing position for various days of aging at a condition of constant soil moisture. . . . . . . . . . . . Moisture lost by evaporation from the soil surface for various compaction pressures applied at a one-inch depth. Initial soil 1710131311136 content " 16%. e e e o e e e e e o o ' Emergence energy for various planting depths and seedbad conditions 0 e e e e e e e e o e Emergence energy, average emergence force, arnd maximum emergence force for various compaction pressures applied l-inch below 3011 surface. One-half psi applied at surface.0.0000000000000000 Page 35 AB 50 51 57 62 66 68 Table 11 12 13 1h 15 16 17 18 vii Emergence energy, maximum force, average force, and shearing position data for various initial soil moisture contents and surface compaction pressures for a non-drying con- dition. (Drying period = 0 days). . . . . . Emergence energy, maximum force, average force, and shearing position data for various initial soil moisture contents and surface compaction pressures. (Drying period = 1 day). 0 e e e e e e o o e e e e e Emergence energy, maximum force, average force, and shearing position data for various initial soil moisture contents and surface compaction pressures. (Drying pePIOd . 2 day3) e e e e e e e e e e e e e e Emergence energy, maximum force, average force, and shearing position data for various initial soil moisture contents and surface compaction pressures. (Drying period = u dayS) . . . . . . . . . . . . . . Emergence energy, maximum force, average force, and shearing position data for various initial soil moisture contents and surface compaction pressures. (Drying .pfiPiOd = 16 dayS)o e e e e o e e e e e e e 0 Moisture lost from soil surface initially at various moisture contents and compaction pressures for a drying period of 1 day . . . Moisture lost from soil surface initially at various moisture contents and compaction pressures for a drying psriod of 2 days. . . Moisture lost from soil surface initially at various moisture contents and compaction pressures for a drying period of h days. . . Moisture lost from soil surface initially at various moisture contents and compaction pressures for a drying period of 16 days . . Page 76 77 78 79 81 81 82 INTRODUCTION The existence of the human race depends upon man's ability to emerge and grow plants. The factors that retard or reduce the emergence of plant seedlings indirectly affect agriculture by limiting the income a farmer realizes from his crop. iflflle laboratory germination tests of a given seed lot range between 90 - 100%, the total emergence in the field may vary between 0 and 95%. Total emergence, therefore, de- termines the ultimate success or failure of a given crop. As a young seedling forces its way upward through a soil formation, mechanical work is done in pushing upward and/ or thrusting aside soil particles. Breaking crust that may be present on the soil surface also requires the expenditure of energy. When soils are seriously incrusted and compacted, more force may be required for emergence than the seedling can muster. As a result they perish in the effort! . Although the physical properties of the soil conducive to plant growth can be recognized by the experienced observer, these have not been defined satisfactorily in mathematical or physical terms. No single value or group of values ex- presses the Optimum conditions for germination and seedling emergence. At the present time, the design of precision planters is hampered by the lack of adequate basic information con- cerning the ideal environment for rapid emergence of the seedling. Factors such as soil moisture content, seedbed tillage, depth of planting, amount and position of compacting pressure, aeration, and mechanical impedance to emergence must be accurately described in physical terms so they can be translated into a functionally designed unit. A method of measuring the force and energy exerted by a mechanical seedling (a steel probe simulating a seedling) as it moves upward through a soil profile under different levels of soil compaction and soil moisture is presented. Basic factors that affect the energy required for emergence of plant seedlings will be presented, along with suggestions for reducing the energy. REVIEW OF LITERATURE The physical factors affecting the emergence and growth of plant seedlings has been recognized by many re- search workers. A considerable amount of effort has been exerted in the evaluation of the following factors on seedling emergence from soil: moisture, aeration, temper- ature, effect of the chemical nature of the soil, effort of seed characteristics, light, time, depth of planting, disease, etc. Stout (1957, 1959) has conducted an extensive review of literature on several of the above physical factors. To eliminate repetition of work the writer will limit this literature survey to tOpics related to the effect of me- chanical iapedance of the soil on seedling emergence and emergence force exerted by the seedling. This literature survey revealed little work where the forces exerted by plants or the mechanical impedance of the soil to emergence were measured in precise physical units. These factors have been in some cases related to soil bulk density and soil crust strength. The first work concerning the force exerted by plants on their surroundings was conducted by Pfeffer in 1893 as translated by Gill and Bolt (1955). Pfeffer studied the force exerted by plants on soils by encasing the root of a seedling plant in a plaster of paris block and the shoot h in a second block. Movement of the second block compressed a calibrated spring providing a measure of root elongation and the pressure exerted by a growing root. He observed that significant growth occurred with axial counter pressures up to about 10 atmospheres and with radial dounter pressures up to about 6.5 atmospheres with roots of varibuS species. Pfeffer also measured the external work performed by a growing plant. To measure work performance, root growth was followed in a homogeneous plastic medium of clay or gelatin in which external resistance was made possible by variation of the moisture content. Resistance of the medium was evalu- ated by a penetrometer with a tip similar in shape to the root. In a BM hour period at a moisture content of 18.3%, the work performed by a corn root was found to be 1290 gm. mm, He reported that when a root was grown against a re- sistance, the rate of growth was found to be zero until the cellular tugor pressure increased sufficiently to overcome the resistance. After this point, the growth rate in general was found to be constant and up to a certain point inde- nendent of the magnitude of the external resistance. Pfeffer reported that since the root has plastic properties, its path of growth would generally be along the line of least resistance indicating that the pressure exerted by'a root generally would be less than the pressure measured with a penetrometer. High values of axial pressures were encountered 5 only when the POOtiflE sufficiently confined in its radial direction. The observation was made that wrinkling or folding of the cell walls of the root tcnflc place when the root encounters large external resistance. Gill and Miller (1956) devised a rubber diaphragm cell that offered mechanical impedance to root growth and con- trolled soil atmosphere. Compressed gas acted on a rubber diaphragm which was placed against a simulated granular soil of glass beads. A corn seedling was placed in the simulated soil and grew against the rubber diaphragm. Different de- grees of mechanical impedance was measured with the roots bathed in atmospheres of identical composition. The compo- sition of the soil atmosphere was determined by the compo- sition of the gas used in the pressure chamber. The gas diffused at a predetermined rate across the rubber membrane into the simulated soil. He reported that the rate of growth fell to zero at relatively small levels of impedance if the oxygen content was low. The first increment of chamber pressure was more effective than the second in re- ducing the rate of elongation of the roots. Root cells were examined microscopicially and were found to be some- what flattened in the deformed roots, but the folded walls mentioned by Pfeffer were not observed. As the chamber pressure was increased and oxygen content of the soil atmos- phere decreased, the root growth decreased. Hudspeth and Jones (l95h) studied the effect of planting depth on the rate of emergence and total emergence of cotton. Although the final emergence was not affected by depth of planting, significantly higher yields were harvested from the l-to 2-inch than from the h-inch planting depths. Carnes (193h) used a suspended weight on a spring which was gradually lowered on a section of soil placed on two knife edges a known distance apart. When the section of crust broke, the amount of take-up in the spring indi- cated the weight required to break the crust. He reported that reducing the rate of drying increased the strength of the crust. An inverse relationship between the breaking strength and moisture content of the crust was found. The chemical nature of the soil also affected the breaking strength of the crust. In cotton fields, the modulus of rupture of the soil crust was greater in the middles than on the ridges. The relationship between rainfall and the force of breaking for each soil followed a general law whose form is R = aebx where; R is the modulus of rupture, a the intercept constant, b the slope constant, e the base of the Napierian logarithm = 2.71828, and x the amount of rain in inches. Hanks and Thorp (1956, 1957) reported that the modulus of rupture is a good measure of crust strength as related to seedling emergence of wheat and similar plants. They found that the limiting crust strength was between 200 and 500 millibars* for wheat seedling emergence and appeared to decrease as the amount of available moisture decreased. ' The rate of wheat seedling emergence was directly related to soil moisture content. Bulk density was related indi- rectly to seedling emergence in that any change in bulk density changed other factors such as oxygen diffusion rate and soil crust strength. Wheat seedling emergence was not influenced by seed spacing or crust thickness for a range of crust strength as measured by the modulus of rupture. The force required to break a l/2winch soil crust was 1.83 times greater than for a 3/8-inch thickness. Their data indicated that emergence of a wheat seedling through a crustwas influenced by the strength of the crust immedi- ately around the growing tip and not by the strength of the entire crust. Bowen (1959) measured the physical restraint en- countered by a seed by planting (like a seed) an eXpandable balloon in the soil. A measurable hydraulic pressure was applied to the balloon using a hypodermic syringe. This device gave the pressure in psi required to cause eXpansion of balloon in soil without cracking the soil surface and pressure required to rupture soil. He reported that ‘— * A unit of pressure, lOOO dynes per square centimeter or OoOluS p310 physical impedance to seedling emergence varies with the soil type, soil surface compaction, and with moisture content of the soil. The minimum impedance occurred when the soil was saturated with water and increases as soil moisturemum reduced by drying. The maximum impedance occurred after the soil had dried out following a soaking rain. Average maximum values for the various soils were as follows: (a) Cecil clay, 15 psi, (b) Norfolk sandy loam 120 psi. He reported that cotton seedlings emerged quickest when physical impedancevmm less than 10 psi, (other factors being equal) but can usually emerge if the impedance remained below 30 psi. Those seedlings that emerged against a high physical impedance, required 25% more time to emerge than seedlings planted in soil with less than 10 psi physical impedance. At greater than 30 psi physical impedance in the soil, the germination percentage was greatly reduced and the seedlings that do emerge were often damaged. Stout (1959) obtained evidence, in the laboratory, that planters for sugar beets, corn and beans should be designed to (a) pack the soil at seed level, (b) place the seeds prior to compaction or press the seeds in the compacted soil, and (c) cover the seed with loose soil. He reported that for each set of soil conditions there was a range of packing pressures which induced maximum seedling emergence, while insufficient or excessive pressures reduced emergence. Packing the soil surface caused sugar beet seeds to absorb water at a greater rate for a period of two to five hours, however, after that period, seeds absorbed more water from uncompacted soil. Packing the soil may improve seedling emergence if adequate moisturevnm available below the seed. If not, packing the soil was found to be of no ‘benefit and may even suppress emergence. In a hand-planted field ex- periment, surface pressures of five and ten psi seriously suppressed emergence of sugar beet seedling as compared to a pressure of one-half psi. Trouse (1958) studied root behavior as correlated with soil density in various Hawaiian soils. He found that when denseness alone is considered, one soil series may stop root growth at a different dry bulk density from another, although the real density values are similar i.e., Hilo silty clay - critical value = 1.0, while Honouliuli clay 4 critical value = 1.8. He reported that the low humic latosolic subsoils will not permit root penetration at a dry bulk density of 1.3 (real density 3.0), while low humic latosolic surface soils will not permit root penetration at a dry bulk density of about 1.5 (real density 2.9). He concluded that differences in pore size and continuity of pores might account for the difference in values. Torterfield, gt‘gl.,(1959) reported that the plateau profile for cotton planting has given satisfactory stands 10 81 percent of the time as compared to 36 percent obtained with the shallow furrow or conventional listing methods of planting. This planter removes the dry surface soil, forms a bed of moist soil, places the seed in the moist soil, applies the compaction pressure directly above the seed, and then covers the seed with loose soil. The major factors accounting for the large difference seem to be in the method and position of applying compaction pressure, placing the seed in contact with moist soil, and the shape of the seed- bed profile. Gill (1959) studied the effects of drying on the tensile strength of Lloyd clay. He reported that drying (moisture loss)is the most important factor contributing to the in- crease in mechanical strength during aging of the soil. Conditions favoring low moisture losses over a period of 2h0 days increased the mechanical strength 1h0%. However, this strength was approximately one-fifth that attained with larger moisture losses during a period of 3 hours. The mechanical strength of the soil appears to be related directly to the moisture loss regardless of the length of the drying period. The results of this study indicate that the action of the soil moisture films during drying influ- ences the strength of a recently manipulated soil. Differ- ences in moisture content alone are not enough to account for the differences in strength. The intra-aggregate bonds 11 were considerably stronger when the soil was dried after compaction to a specific density then when dry loose soil was brought to the same moisture content after which the soil was compressed into a condition of equal density. Samples which were compacted at increasingly higher moisture contents, attained increasingly higher mechanical strengths as measured by the modulus of rupture, even though they were dried at the same temperature. Richards (1953) measured the force required to break a soil briquet and determined the modulus of rupture as an index of soil crusting. He found that an increase in crust strength from 108 to 273 millibars resulted in a decrease in emergence of been seedlings from 100 to 0 percent. The increase in crust strength was attributed to artificially increasing the exchangeable sodium percentage to 37. Lemos and Lutz (1957) reported that the modulus of rupture increased as the moisture content of soil briquets decreased. In uncompacted soils the modulus of rupture decreased as the water content increased up to h0%. The modulus of rupture was increased about 15 times by compacting the soil briquets at high moistures, indicating that soil manipulation and degree of compaction of wetted soils are important factors causing very high modulus of rupture. The modulus of rupture decreased as the temperature of drying increased. The data indicated that harder soil crust resulted from slow drying. A decrease in the modulus of 12 rupture with successive cycles of wetting and drying was measured. This decrease was accompanied by a 12% increase in volume of the briquets. Each time the soil was wetted the rapid intake of water caused unequal swelling of the soil mass. The differential swelling, associated with the cementation-of the clay particles when the soil mass shrinks by drying, caused planes of weakness which account for the lower modulus of rupture. The compacting effect of rain- fall on soil briquets caused an increase in the modulus of rupture. Puddling or manipulation of the soil at high moisture tremendously increased the modulus of rupture. The modulus of rupture increased directly with clay and silt content of the soil. Allison and Moore (1956) investigated the use of VAMA and HPAN to reduce soil crusting. Both types of conditioners were effective in ameliorating the crusting tendency of high sodium soils. Hyder and Sneva (1956) reported that heavy rolling above the seed for range reseeding was undesirable in terms of mechanical restriction to emergence and soil aeration. Swanson and Jacobson (1956) measured the hardness of the soil surface in field plots with a modified Proctor soil- plasticity needle. They reported that corn yields varied inversely with the force required to penetrate the soil. Penetrometer readings revealed that the strength of the soil 13 crusts increased during the season innoncultivated plots, while in the cultivated plots, loosening of the soil by culti- vation increases penetration of the needle. Corn plots side-dressed with nitrogen generally showed less compaction than non-sidedressed plots because of the increased root growth and bacteriological activity. Bruce (1955) constructed a soil compacter which he used to measure the compactibility of soils. The instrument consisted of a steel compacting plate, a weight falling from a given height and a steel cylinder used for holding the scil sample. The amount of compaction energy applied to the sample was adjusted by varying the distance the weight fell, varying the number of blows, or changing the weight. He reported that as the compaction energy increased, the maximum bulk density increased and the moisture content at which it occurs decreased. The importance of soil crust formation on tilled land as a mecnanical impedance to emergence has been recognized by many researcners. (This is evident from the work reported in this survey.) This survey does not comprise all the work that has been accomplished in the field, but rather represents an attempt to present only the material directly related to the problem. Considerable worx has been done by Kasperov (l9u0), Gorbunov and Bekarevitch (1951) and Isiumov (1938) developing 11; theories of crust formation and measures to combat the formation of soil crust on the heavy clay soils in Russia. The need for instrumentation to measure the soil forces in terms of plant capabilities is evidence from the literature survey. THEORETICAL COm‘SIDEdA'T‘IONS An explicit mathematical equation discribing the energy expended during tne emergence of a plant seedling has not been developed. The energy expended during the germination and emergence process is expressed as a general relation by equation 1. Et=fiEe+Er+Eg+U) (1) Where: Et = Total energy expended 38 = Energy expended during emergence to over- come mecnanical impedance Er = Energy of respiration Eg = Energy used in cell reproduction and growth U = All other processes using energy. Only E6 (energy of emergence) will be considered in this thesis. It is hypothesized that as He is minimized the rate of cellular growth snould increase and the total Er -(energy of reSpiration) should decrease. The energy saved by minimizing Be and Er is then available to the plant for cell growth. The task of determining the interrelation of all the variables effecting the germination and emergence of a plant is beyond the scope of this thesis. The mathematical expression, equation 1, was presented to provide the neces- sary link between the expenditure of energies by the major . physiological and physical processes. MATERIALS AND AfPAfiATUS An instrument*, Figure l, was designed, developed and fabricated for measuring the energy expended during the emergence of a mechanical seedling. The mechanical seedling was forced upward through a soil formation in a manner simi- lar to an emerging seedling. The instrument consists of a simply supported beam employing a four-arm SR-h strain gage bridge for sensing the force being exerted by the mechanical seedling. A holder for the mechanical seedling was located in the center of the beam. A cantilever beam with a four arm strain gage bridge was used to indicate the position of the mechanical seedling tip in the soil. The wiring diagrams for the force and position measuring transducers are shown in Figures 2 and 3. The four-arm bridge arrangement resulted in maximum sensitivity and temnerature compensation. The lifting and lowering mechanism consisted of a plexi- glass platform and a gearing arrangement attached to two 15- inch long Acme screws. A 1/3 horsepower electric motor operated the Acme screws and lowered the soil sample onto the mechanical seedling at a constant rate. A variable speed Grahm Transmission varied the speed of the lifting and lowering mechanism from l/h to 6 inches per minute. The * Original design by B. A. Stout, Agricultural Engineering Department, Michigan State University. l7 .mcsum esp ca pew: Lonesoapmcmm Hfiom ho Ewammfim .H magmas hzuluznmdus moron (on _ _ 8100 ouhcoaaam >4m2.m 1’ ;/ r. .M; “1%.“ -I: .5 v J. m a r I a; . . ”no t a! .. ; . am aw.m a. a win twat 1w... 0 HMJA. . © M a. m. g. & F D \\ . y; o O I, 02-Jawmm fl ., It: . . 1’6 ddo.z<:om2 53.. © H”, o a a New. 1 . JOChZOO ouumm .\ Q a .u f o b N~ . . O 52.03: 1 2.32324 2Lu.:._.2mmnso cowpmabfiado zo_.—.om._mwo muz... .5310 O? on ON 0. .m casuah SBHONI - NOIJJSOd 3808c! 23 Muummw L «Wm Figure 6. Vertical shaft and linear ball bearings used to eliminate cycling of the carrying platform. Figure 79 Overall view of the penetrometer showing the rigid support for the simply supported beam and aligning mirror. METHOD 0? PROCEDURE Air dried Brookston sandy loam soil was screened through a US. No. 16 screen to obtain a uniform soil. The moisture content was adjusted by placing 2500 grams of soil in gallon containers and adding the amount of water calcu- lated to adjust moisture contsnts of the soil to 12, 16, and 20%. '(All soil moisture contents are expressed as per— cent dry weight basis.) The container was sealed an the mixture of soil and water was allowed to equalize for a period of 3 days. The container was shaken for a few minutes each day. The soil was avain screened through a US. 16 screen to break clods formed during wetting of the soil and to insure a uniform moisture distribution. The soil was placed in the container, rescaled and at least one more day was allowed for the soil to reach moisture equilibium. The mechanical analysis of the soil as determined by Stout (1959) is shown in Table 1. Table 1. Mechanical analysis of the Brookston sandy loam soil used in this study. - Percent by fleight n..- m _§rookston Sandy Loam : Sand : Silt : C1ay_ g“ : 63 : kflgg : 1h 4_g The moisture tension curve for this soil, as determined f—Io \ by Stout (19.9), s snown in Figure 8. .mpzpm mficu CH ram: Hwom smoa prnmm Cowmxooad on» Low o>p5c rcfimccp cazumwo: .m assume m_mmo o\o HZMHZOU mmDHQO—z |__Om mm ON m. 0. K P _. O. 00. SBHBHdSOWlV ‘NOISNBJ. BHfllSlOW "HOS 26‘ The soil was transferred to plastic boxes 7 inches long, 5 inches wide and h inches deep. Previously, nine holes, 3/8-inches in diameter, had been drilled in the bottom of each box for passage of the mechanical seedling. The holes were covered from the bottom with masking tape. A soil depth of 3 inches after compaction was used in all experiments. Compaction pressures of 1/2, 1, 2, h, 8, and 16 psi were applied either to the soil surface or at a l-inch depth. A calibrated proof ring and a hydraulic press was used to apply the compaction pressures (Figure 9). The mechanical seedling was forced through the soil samples immediately after they were prepared and l, 2, h, 8 and 16 days later. The plastic boxes containing the soil samples were stored or aged in a constant temperature room (Figure 10) maintained at 70 degrees Fahrenheit except when the emergence tests were being performed. In one experiment, fine tops of the boxes were sealed to prevent loss of soil moisture. In all other experiments the tops were removed and the soil allowed to dry. Mechanical seedlings, shown in Figure 11, with tip diame- ters of 0.078, 0.106, 0.162, and 0.271; inches were fabricated. The tip of the mechanical seedling was larger than the stem diameter to reduce frictional forces while passing through a soil profile. The 0.078-inch mecnanical seedling is approxi- mately the diameter of a corn seedling shoot. The average 'diameter of a protruding Michelite bean crook was 0.27h inches. These values were determined by planting corn and bean seedStnui then measuring the diameter of the shoots that emerged. kamel2 27 ' '-“~ .." Figure 9. Calibrated proof ring and hydraulic press used to apply compaction pressure to soil samples. The soil sample box is shown in the figure. Figure 10. Constant temperature room. A 1/2 ton air conditioning unit was used to control temperature. 28 Figure 11. Mechanical seedlings having various tip diameters used in the study. Figure 12. Corn, bean and sugar beet seedlings that were measured to determine mechanical seedling diameters . 29 shows corn, bean and sugar beet seedlings that were removed from soil for measuring. In one experiment, energy and force relationships for the various mechanical seed ing diameters were determined using a soil moisture content of 16% and compaction pressures of 1/2, 2 1/2, S and 10 psi. The remainder of the experi- ments were conducted with a 0.078-inch diameter mechanical seedling. The velocity of the mechanical seedling was held constant at 6 inches per minute while moving through the soil profile. A test was conducted to determine the effect of mechanical seedling emergence speed on the emergence force. For a speed range of 1/2 to 6 inches/min. no change in the value of the emergence force was noted. All treatments were replicated at least four times. Each value for the graphs and tables is an average of h individual measurements. The area under the force versus depth curve recorded by the oscillograph was determined with a planimeter and reduced to inch-pound units. These values represented the energy exerted by the mechanical seedling during the emergence process. The term "emergence energy" when used in this study refers to the energy required for emergence of the mechanical seedling. PRESENTATION AND DISCUSSIOW CF T"EU: .JJ TAI RTSULTS Four individual laboratory experiments were conducted in this study. They are presented in chronological order. B ct of Mechanical Seedli #Diameter on Emergence Energy and Force In this experiment, mechanical seedlings were forced upward through a 3-inch depth of soil (16% moisture) which had received compaction pressures of 1/2, 2 1/2, S and 10 psi at the surface. Non-drying conditions were maintained by kee eping the boy es covered except during test. Mechani- cal seedlings of 0.078, 0.106, 0.162 and 0.27h inches in diameter were used. The emergence eners y (Figure 13) increased directly with seedling diameter and compaction pressure. The larger increments of increase occurred at the higher compaction pressure and with the larger see M.lin diameters. The rela ionship between shearing position (the depth below the surface of soil where an inverted cone of soil shears from the main body of soil due to the force of the mechanical seedling), mechanical seedling diameter and com- paction pressure for 16? soil moisture is shown in Figure 1h. The position of shear remained relatively constant as the compaction pressure increased. It appears that the EMERGENCE EN ERGY- | N LB. l6 -— L _ '4 ‘H 2 Va PS' ..__.-__.#_,- IOF ‘" _/fl/ 0 .05 .l .15 .2 .25 MECHANICAL SEEDLING DIA.-IN. Figure 13. Emergence nnorcy versus mechanical seedling dianetcr nor surfcce conrficfion nressurns of 1/2, 2 1/2, 5 an? 1C: 7‘81. SHEARING POSITION- INCHES ‘3’? ,1... SOIL SURFACE O '/ , f’/' '9"’/"’/\ '71 "/\"' \ ’1’ x4" \M/I‘V'a/J'V ' I/ 1. 3. 5% — O T ' PROBE DIAMETER-INCHES .078 .I06 H .IGZ 0—0 .274 3o 2 4 6 8 IO COM PACTI ON PRESSURE- PSI 15 Fiidzs 14. Lqui * F'”i‘ on van* -ur:“"e co QCt' on _ .. I . " ‘v o 3):.nqnufio r~vs — n1 ' " .y-.,—~. {~— I" 3: -,«“-‘«L.L>,“ of C .07’, 0.106, 0:162, ani 0. 27h inches. b: be depth of shearing position for a condition of no evaporation from the soil surface, is independent of compaction pres- sure. The depth of shearing position depends upon the diameter of the mechanical seedling. The weight of soil cone sheared by the seedling tip also increased with diame- ter. The cone sheared from the soil by the mechanical seedling was similar in appearance to the cones produced during the emergence of plant seedlings. This is evident from the relative sizes of the inverted soil cones shown in Figure 15. In Figure 16, the mechanical seedling is thrusting aside the soil cone while emerging. Table 2 presents maximum force, emergence energy, and shearing position data. Figure 17 indicates that the maxi- mum emergence force also increased with seedling diameter and compaction pressure. The curves are similar in shape to the curves shown in Figure 13. 3h Figure 15. Photograph of the soil cones sheared by various size mechanical seedlings. (Numbers below cones refer to mechanical seedling tip diameters.) Figure 16. A soil cone being pushed aside by the mechanical seedling. 3S 0N...” :m.0 02.0.5 ww.H m0.m 8.0..“ mm.N Nd...“ 00.0 dim 00.0 :1: 0H wo.H o.~ Hm.~ m~.H :s.a os.m HA.N :mqa :m.m mm.m om.o em.m m 2.413% TIme ~1ij aloofi 3am; emé dm mad was E; New , wmé flmd miles: 3199:” SJ. :10 dawdmmJ 3.0. o A m .9H .9H .9H .9H OHHH 09H IOGH .QH OQHA FOAM.“ OHM-H ODH sets.“ OGH ODH IIOHHH Hag as Jim dS.dM .Es JR dS am mm mm mm“; mm mm 3 3 mm mm mm mm TB OI. dd 1.8 OI. dd 1.8 0.... dd 1.8 01.. JJ n+a an“ on?“ qsd emu flags 4;“ 9.m 9:3 q+J 9mm as? II m £9 11 n £9 11 n £9 1:: n K9 neu u 0%w w u onu m u nvu mm u Had . m u W Hos W uoa W mm W W m. magmmonm Am J a a cofipowQEoo e w w Aw mommasm u u u u o o o o e e e s .LJMN.O meH.o eoa.o mwo.o memocH an pcpesmao mcflapeom HmoHCm£ooz .mpmpeSQHc mcHHpmom Hmowcasoofi Tam measmmeam coHromafioo coamASm mscflae> you when QoHpHmom wcHAeQSm and coach eoceuaeSo SSEHKQE .huaoco monomaeam .N magma 36 BROOKSTON SANDY LOAM SOIL MOISTURE CONTENT-46% 6 M IO PSI J 3 ' /z§ /@ é __{9 MAXIMUM EMERGENCE FORCE— POUNDS o .05 . .I. ,I5 .2 .25 MECHANICAL SEEDLING DIAMETER-INCHES Figure 17- Maximum FNCPFCHC“ Tcrcc versus mechanical seedlinfi diflmcter For surface compaction pressures of l/S, 2 1/2, w and 10 p81. Effect 35 Soil Moisture Content, Compaction Pressure and Drying Time on the Emergence Energy and I7'orce Initial soil moisture contents of 12, 16 and 20% dr basis were used. Compaction pressures 0’ 1/2, 1, 2, a, 8 and 16 psi were applied to the soil surface. The depth of soil after compaction was 3 inches. A mechanical seedling (tip diameter 0.078 inches) was forced upward through the soil samples immediately after they were prepared and l, 2, h, 8 and 16 days later. The emergence energy increased directly with drying time, compaction pressure, initial moisture content, and indirectly with moisture content at time of sampling Edgures 15, 19 and 20). 1e rate of increase in the emergence energy with respect to drying time was the largest for the high compaction pressures. At initial soil moisture contents of 12 and 16%, and low surface compaction pressures, the emergence energy tended to decrease after a drying period of 8 days (See Figures 13 and 19). This can be explained by cracking and breaking of the soil surface due to compaction pressure and drying. The mechanical seedling emerged through these cracks resulting in low values for the emergence energy. Figure 21 shows the soil samples compacted to the pressures indicated. At the 1/2 and 1 psi pressure severe soil surface 8 5.) .mmmwn map gm 1 psopzoo masumfiofi Hwom HmeHcH .Hma ea 0cm .m .3 .m H .m\H mo meadmmeaa Cofiaowchoo mommasm Lea ohm; ucwmaw mamaq> masons eczemaesw m><0 Imsz... oz_>mo e. e. N. o. e v N .mfl ohfiuwh O a _m _m N a a N-§ d m INNI I.III.I..I.. Iwa - . . as if _ . I... I LLIi Q \ _Ea\\ O. N. '8—I NI-AOHBNE BONBSHEWE e .1 .3. a. . J. J h... _.. .. I, )_ u. .1. V...“ V- .. "DIWIVwU‘Fa' Diff”. {Yrulfl I. 4r.r\'u {Ct (grid ("ryrg HHom HeHanH .mep 0H woe .p .q .m .H .m\~ co acaxpacac a ; ... .f a I a .1“ .II .. a u a Cowpomafioo chcLSu Lot «awn mcwmpr m3axc> >thcco corctpcffi CH dadtfir m><0 Imzfi oz_>mo m. o. e w my MW ..om assess nu H DV\ a a l \ \ . \ £2 \ \ . O N .mae. . _ _.s—e 0 r0 O V 'B‘I NI-ASHBNB BONBSHBWB Figure 21s Soil samples compacted to the indicated pressures. Soil surface cracking due to compaction pressure and drying is shown in the figure. 'ihe soil cones for the various compaction pressures can be seen. M2 cracking is indicated. The soil cone sheared by the me- chanical seedling for various compaction pressures are 1. I\) shown in Figure In Figure 22, the relationship between emergence energy and drying time is given for a surface compaction pressure of 8 psi applied at initial soil moisture contents of 12, 16 and 20%. These curves indicate that for a given compaction pressure under drying conditions, the emergence energy increased as the initial soil moisture content increased. One explanation.is that, in the soil moisture range used,the moist soils under a given pressure compacted to a greater bulk density and developed greater strength than soils at lower moisture contents. Greater mechanical strength was also produced in the surface layer when these moist soils were subjected to drying conditions. Curves of the same general shape were obtained fo: surface compaction pressures of 1/2, 1, 2, h, and 16 psi. The average and maximum emergence force increased directly 0 0‘ with drying time, compaction pressure, nitial soil moisture (1’ content, and indirectly with moisture con ent at time of sampling. Figure 23 and 2h are representative plots of the average and maximum force data versus drying time for an initial soil moisture content of 16%. Curves of the same general shape were obtained for initial soil moisture IN LB. EMERGENCE ENERGY .7. 25 35 MI 20% M. c. Hevmc. / I2 °/oM I I . A: 7 l/I l5 fir‘ I I I I I I I I i /' 1 / I " VI BPSI #95 8 PSI 246 8 IO l2 I4 I6 DRYING TIME — DAYS Ii'T‘LU"C (_¢-. .‘L‘méy‘qp ' .I '11" f:';"fl.1 AIL “1-. . .1 “ Jr's“ 5 ._ - /\ w It~ . - r -,r 's‘ . .. 1 ‘ i ' - "‘7‘71 I‘C:l“*iitw“- urn“ - 1 it . = A 1 / W 4'} 1‘ " 1 ) O l‘ V’ VI ‘ in , i 'u , i .. . x M4 . a.‘ 4| \I 4 xl. \. . _ I ‘1‘... I c. \ .4 ‘lq. p . I. .ed .- \:\r&r ' #cel’fleog A\¢.IHH\_I~IWM.;\IL “WW-(VG In: THC 0L4....LIH_.(.7U.0M..\H£ r? CWIHO mr.I.MCO “do-"CHMWNr rHOC.’ mL.M.I.~ .19 “1.6”...“ PPM." URI—mgr: \r armav Hog .Qr. .fixpfi.» .rHQI.’ .0 1\ .NUPMF..M....1~ 0 mm O.NSMI.WHRWQ m>mo e. S m. o. m e e N o N 81-30803 30N3983W3 SAV I 5mm” [’0 ¢ an. e. 4 IO . “\J ' “3.1%... r..Q_I_. . .I . .. . . . . 4. l .. .. 4 .. 1. .I . . 2.! \H \rt.._l— Cw]... a. FHOU fiLW+Hr>F orflvrhjnuumfrrh rerHJOCrrHLiuo AIDL 14. 4. . l..q, J. naiw . n. 2 . \I . a- .,.. . .J.'|A..... .Ieao: u... rv “(PINNV frog C3. «J. 75‘“ arr...” mSCLCLr QQnHOC. ,k Ufi»aWL..fo...L-Hw «(xfinfnwlrlsxk :0 \Id err.._..L.Hrffi m>:._. 02_>mo m. S N. O. m 0 ¢ N O \. — . .ma N 51 v m_.IHI J— W Eden 7 f/ 5a2%\\\ '8']- 30803 EONBDHBWE 'XVIN he contents of 12 and 20%. The emergence energy, maximum emergence force, and average emergence force versus drying time curves all have the characteristic shape shown in Figures 18, 19, 20, 23 and 2h. A logarithmic plot of emergence energy versus surface I compaction pressure for the various drying times is shown in Figure 25. A linear relationship was obtained between surface compaction pressures of 2 and 16 psi. At low com- paction pressures greater variation in the value of the emergence energy was encountered, because the surface com- paction pressures did not collapse all the soil voids, thus resulting in a soil of non-uniform density. This is suggested as the factor responsible for the non-linear rela‘ion below 2 psi. Under field conditions air pockets and soil voids are present, therefore, the curves of Figures 19, 20 and 21 more nearly represent actual conditions and were used to present the data. Equation 2 is a mathematical expression of the curves shown in Figure 25: Be = CPX (2) 'J‘ -— 10- ”nere Ee — Ehergence enezgy C = The value of the emergence energy where the compaction pressure = 1 psi P = Compaction pressure X = Slope of the line Table 3 setsforth the constants shown in Enuation 2. EMERGENCE ENERGY IN LB. 147 BROOKSTON SANDY LOAM SOIL SOIL MOISTURE CONTENT—I6°/o 4o 30 25 . . IGDAYS 20L I | y A QDAYS I '0 4. ‘ll 4 DAYS Ar ‘0 2 DAYS .. 1° '10“ 0' ‘ o /I': ODAYS I 2 4 68l0 l520 SURFACE COMPACTION PRESSURE" ~PS| Figure 25. Logarithmic plot'of emergence energy versus surface compaction pressure For various days of drying. Initial soil moisture content — 16¢. Table 3 - Constants for AS the solution of Equation (2) _~_ Days : C i X 0 i 0.800 g 0.773 1 i 1.175 g 0.727 2 i 1.300 g 0.682 g i 1.600 g 0.636 8 1.800 g 0.636 16 2.600 g 0.636 The depth of the shearing position (Figure 26) of the cone under drying conditions only changed slightly with compaction pressure and length of drying time, and decreased as the initial soil moisture content increased. Table A gives the values for emergence energy, maximum emergence force, average emergence force, and shearing positions for the various compaction pressures for a drying period of 8 days. The data for drying periods of 0, 1, 2, h and 16 days are recorded in the appendix (Tables 11, 12, 13, lb and 15). SHEARING POSITION-INCHES SOIL SURFACE 07W" ' '9 //v\'.://'/ / / / W” I/ ‘ I AA A .___.‘. . c SOIL MOISTURE CONTENT ' A—A 20% H '6 0’0 H '2 0lo 2 4 6 8 I0 I2 l4 l6 COMPACTION PRESSURE PSI. vunp 2/ (Bhpnhinf‘ “,Qc'i‘ioq vanun Cf‘w mm +' '4‘. ~~wru~n~ n , . L .. - k -«l ..- o . 1 be 0.. i .L A.‘ e.) \.' '1 AC L . A -s\ s-Jur‘- for a ircwtstnn sandf loan ther 9 dsvs qT‘UI—IV'. Ili'iLlSI 5‘01]. :misture crwwfisnts warp w _ , ~ M ' J.’T, :(l , \ mi: 20. Suwanee megawaos Haom HerHeH Hm.m 00.: 00.5 0H.0 0:.N :0.m 0:.m m0.m 0m.0 0wI m0.m m:.m ms.0 ea.0m 0:.m ~0.H 0m.m Hm.H 00.: 0 ee.m Hm.m me.s 00.:H m:.m 00.0 mo.m 0m.0 Hm.m : 0m.m 0m.e 0m.m m:.e om.m 0m.0 0m.a mm.0 em.a m H0.m 00.0 00.m 0:.m mm.m Hm.0 H:.0 0H.0 0m.0 H em.m m:.0 00.0 mm.m mm.m 00.0 0H.0 00.0 maqq, m\fl .na .na .00 .0H .0H -.ea .00 .0H .na .sa . .na -.ca “m0 d..0GV d H dS.a Van”? .08 Vsfinm E swim ewe MM 30mins? m 3. m“ 0%“ a. 1.8 OJJ 0J1. dd 1.? Odd 0&1. J 139 JJO.JT.. JJ as She efiw 88 .1u930.03w on QJ 8? 93m 83 E... 90.. f,“ m... 2. mm a m... me am 5e m% we w mu u% we a nu u% o a o 9 a 9 9 9 9 9 9 9 sow woe ewe .mmmw m mo reason mmfihaw a how monummmpg coHpomLEoo moQMLSm Una muzopCOQ ennumwoa HHOw Hefiuficw mseflae> gem spew newpfimon wcwaemSm @ce meson eueao>m .eoaom Ssfiflxme .mmeece oonemaesm .0 cases 51 The amount of moisture lost from the soil surface at moisture contents of 12, 16 and 20% for a drying period of 8 days is recorded in Table 5. Table 5. Moisture lost from soil surface at various initial moisture contents and compaction pressures during a drying period of 8 days. (Egflgzgilon : Initial Soil Moisture Content We 5 12% E 16% L 20:: psi ; gms.. ; gms. ; gms. 1/2 3 113.8* 3 113.5 f 23h.0 1 E 117.5 2 123.5 2 268.3 2 2 118.0 : 132.0 § 260.8 a : 119.3 : 136.0 § 290.8 8 3 120.0 3 135.5 3 308.8 16 E 126.3 2 156.5 2 323.0 .. I. Moisture lost by evaporation from soil surface. The moisture loss data tor drying periods of l, 2, h, and 16 days are recorded in the appendix (Tables 16, 17, 18, and 19). These data indicate that the largest moisture loss occurred at a compaction pressure of 16 psi for initial soil moisture contents of 12, 16, and 20%. The maximum emergence energy was obtained for a moisture content of 20%, drying time of 16 days, and surface compaction pressure of 16 psi. Under these conditions the surface layer developed the greatest mechanical strength. This test provides evidence that the drying of the surdace soil is one of the factors \R R) r esycn sible for the development of mechanical strength. I)evc lo ment of mechanical strenwth also 10 spends upon soil ID ’\ r“ I>-’ compaction, Lype and initial moisI ure content at time of compaction. Eulk density of the soil at moisture contents of 12, 16 and 205 incr ased with compaction pressure as shown in CD / - . .. ,'.,. i. - ~ - :9" I Table 0. The Hahlmum vaiue was oatainel for a moi.ture ~ fit M A“ v ' n f ‘r\ . ‘ \ ' content C1 205 and compaction sressure o. la {81. Energen energy of the mechanical seedlinr increased with bulL hens Table 6. Bulk dens i ies for Trcokston sandy loam so various “c st “ i ure con ants and compaction yr L II o .1. Bulk Densities of Soil at Initial Soil Moisture Content 12% 16% 20% gm/cc 0.886 0.981 Surface Compaction Pressure gm/cc 0.893 0.938 0.998 psi 1.020 1.120 1.110 CD 1.230 . .. .. .. .. .. .. .. .. .. .. .. .I .. .. .. .. 16 ' 1.116 1.300 09 00 .0 O. 00 0. 00 00 0. O, Q. o. 00 000. O O \O D 4T0. DJ I. O. O. O. o. 00 o. a. o. O. o, o. o. 000. Effect of Soil Aging on the Emer ence Fherav and Force —————‘_—.* N A laboratory experiment was conducted at a soil moisture content of 16% in which the soil samples were sealed to pre- vent loss of moisture. Compaction pressures of 1/2, 1, 2, h, 8 and 16 psi were applied to the soil surface. A mecnani- cal seedling (tip diameter 0.078 inches) was forced upward through the boxes on 0, 1, 2, 8, 16 and 32 days. In contrast to tne marked increase in energy required for emergence as tne soil dries, Figure 27 indicates that tne emergence energy increased very little with aging when tne moisture content was held constant. The emergence energy tended to increase with aging at tne higher compaction pressures. “he increase in emergence energy might be ex- plained by a small loss of moisture from tne test boxes. Che theory nas been advocated by Carnes (l93h), that soils behave like concrete, the longer they age, tne stronger they become. The results of this experiment indicate that any increase in hardness of the soil under non-drying conditions may be due to a slight moisture loss and/or aging of the soil. (Final moisture content of the samples were not determined for tnis experiment.) Figure 28 compares the emergence energy under drying and non-drying (sealed boxes) conditions. The large increases in emergence energy were due to the drying of the surface layer of soil. For 16 days aging,the ratio of emergence energies on non-drying to drying conditions was .iza rm mocmcicway .Hmo 1*. a. 4. Q.) Q . . 4 s); ‘ .. m..l L. park .0 A: Ow n4. QN\H i0 UCESWUCrHrr CO.¢UJ.C.:CO Lou «Ham mcwuc mzmawp numecm monotheafl was ImsE ozaq Numiom mm mm vw Nu ON m. m. S N. o. rscpsoe eggpmHoE amol dame. A awn. _ N in Na a t a ._m& .v __ w 4 JT : d? IIIE.) at _ in A _ ozcéo 029 l o\o @_ u 0.2 Q‘I" 'BTNl-ASHBNE EONBOHBWEI \f t0 .mCOapamcoo .uchHaIco: I mafia Coio,r i .ucoHpHLcoo ccw>h.! 0H +ccuCOQ magpmaoa HHOm. Hwfipacfi I ccwa Ufiaom .Hme :4 code m e0 mcpsmmeap Cofiuomcsoo Lon 0E“; L:Him mswso> panama cocooamaw .mN casuam $93 lmzfi 02.2 o. e. m. o. m m V ._mm m — Ilt|lfilll.|l%fllleHWH|I-mln .m [6%. NW“! |.rl I. \a\ . \\ \\. \ . oxo m. «0.5. oz_>mo 02 I'll] u», ._mm m N.\ O. “2 O '81 “NT-Assam BONaaaawa “3 OJ an. m. . 625.5 I_|I 56 S to 1. This suggests that a metnod of covering tne seed- bed after planting snould be developed as a means of reducing the emergence energy required of seedling plants. Table 7 gives the data for emergence energy, average emergence force, maximum emergence force and snearing position for soil aged under a condition of nearly constant soil moisture. The average and maximum emergence force increased very little with aging. Whe depth of shearing position remained relatively constant. 57 00d 00.0 00.08.: 00.100; 05.0 3.: 00.0000 00.0T0é 0.0.20.0 00.00 10 2 mm.m mod 0m.0 m0.m 0m.wmb.0 0m.0om.m 0:.Nmo.0 Hm.000.n Hm.m0o.0 0m.0_.0.m m mm.m 9.0 dm.0 N0.N 0m.m0m.0 mm.000.m +3.Nm:.0 mm.0fi 0.0” mm.m0:.0 $3000; : mz.m 0N0 HN.0MN.H mm.m0m.0 nN.0An.H wn.mom.0 Hm.0mm.H o:.mmm.0 010010” N 0m.m :0 91000.0 0m.mflm.0 3000.0 om.NwH.0 31005.0 0m.mwa.0 03.050. 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OJJ JJ 1.9 OJIOJJ JJ Ia OJIOJJ JJ madmmmhm 1...“ 905m 9003 COCO aid 93m 9009 008 07.4 98 9003 800 HHOHpOQnHa—HOO .0... 00 00 0. 0.... .0 0.. .0 0.. .m .0 .2 uw 0 0 w How w 0 9. 9 UAW w m w GONMHDM e a e e .0 e e e e 00 mmwn I 0800 wc0w¢ 5.030.000... H000 pampmcoo 00 c0000vcoo 0 00 mQwa no 0000 000000> 000 CO0pHmoa wc000o£m 0am @0000 mocmmaoSo A.uzoov SSEHNwE .moaom oozmwp¢Em omwao>0 .mwamcm monomaoem .0 00009 Effect of Compaction Pressure Applied 3: Seed Level on the Emergence Energy and Force Compaction pressures of 1/2, 1, 2, h, 8 and 16 psi were applied at a l-inch depth in the sample boxes. One- half psi compaction pressure was applied to the soil surface. The initial soil moisture content was 16%. A mechanical seedling (tip diameter 0.078 inches) was forced upward through the test samples immediately after they were prepared and l, 2, h, 8 and 16 days later. The emergence enersy increased with drying time and compaction pressure but the maximum increase was less in this treatment than when similar compaction pressures were "5 appliec at the surface (Figure 29). (See compariso. in Fifiure 30.) When the pressure was applied at seed level, a considerably snaller increase in rate and total energy was required for eherjence with drying of the soil. Stout (1959) obtained greater seedling e ergence of corn, beans an“: ".7.I.;.'~=.l" tents 77;; fp‘t'lyill‘j the compacting pressure at seed level thsf 7:? ogjlying the same “rcr‘ire at the soil and loose scil ccverin; tfie 3e d, tie deve cpment of me- chanical impedance in the surface layer was retarded and less enerfiy was required for emergence. 6O PRESSURE APPLIED AT SEED LEVE L I2 MUG: ISO/o I I I I I | I 5 i / / I? IS PSI / OD .___- - - .___-.-_._.......___. __.__..._.__..__ --.4;_- a..._..__........__--._-_. bu... ".0 fif BPSI . 45 03f 4PSI 2 PSI - I PSI . . . . __ Vi . - + l_ EMERGENCE ENERGY- IN LB. ‘T VQFDEBI CD 2 4 6 8 IOI2 l4 I6 DRYING TIME —DAYS Firuro 29. Emergence enerry versus drying time for ’ Pu compaction pressures of 1/2, 1, 2, L, :, and 16 psi applied one inch below soil surface followed by 1/2 psi an lied at the surface. Initial soil moisture content - 16%. 61 ——— PRESSURE APPLIED 'AT SEED LEVEL DO (fl PRESSURE APPLIED AT SURFACE PI. h) (D GI i seen. |6PS|. 5 \\ \ \______ 0 \ \L \ I ’ I) 4 L. ~8PSI. EMERGENCE ENERGY- IN. LB. ail/59’ "I we' I o 2 4 6 8 IO l2 I4 l6 DRYING TIME— DAYS Fifijur'e 300 Emergence enerry versus drying time for compaction pressure of 8 and 16 psi. Solid line - pressure apjlied at surface. Broken line -- pressure applied one inch below surface. Initial soil moisture content - 165. 62 The moisture lost by evaporation during this experiment is recorded in Table 8. At low compaction pressures and short periods of drying, greater moisture loss occurred for pressure applied at a one-inch depth then when the pressure was applied at the surface (Table 5, 16, 17, 18 and 19), however, at the higher compaction pressure and longer drying periods, the amount of moisture loss was about the same for the two conditions. rFable 8. Moisture lost by evaporation from the soil surface for various compaction pressures applied at a one-inch depth. Initial soil moisture content - 16%. _ ___.- Compaction E 1 Drying Period Pressure _: <1 3 2 g h __i, 8 : IE ~—— psi ; days 3 days f days 3 days 3 days 1/2 = u5.5* ; 65.0 § 93.8 2 13h.0 E 18h.5 1 E h3.3 E 6u.o f 9h.o 3 136.3 3 189.0 2- § u6.a 3 67.8 3 97.5 3' 1ho.3 3 195.3 u f u8.o E 69.0 E 98.8 E 1h6.0 2 202.3 8 = A9.o ; 70.0 E 99.5 E 1hé.3 E 205.3 16 2 u9.3 70.8 § 100.8 i 1h9.3 § 212.3 Grams of moisture lost. Figure 31 is an actual size drawing of the force versus depth curves traced on.the oscillograph as the mechanical seedling emerged through a 3-inch depth of soil for the conditions listed below each graph. A detailed analysis of 4— FORCE-LB. 63 DEPTH— IN. _>\\\\\\\ \\ \:\\““‘q 8 PSI. APPLIED TO SURFACE AGED FOR 8 DAYS WITH DRYING EMERGENCE ENERGY= 9.58 IN.LB. 8 PSI. APPLIED AT SEED LEVEL AGED'FOR 8 DAYS WITH DRYING EMERGENCE ENERGY= 4.I4 IN.LB. ‘ \ \\\ \\\\\‘ \\§\\\\ \\ 8PSI.APPLIED TO SURFACE AGED FOR‘B DAYS WITH No DRYING EMERGENCE ENERGY = 2.96 IN.LB. Figure 31. Force versus depth diagrams for the conditions 3 t3 ted. 61+ the oscillograph charts shown in Figure 31 follows: 1. 2. Compaction pressure applied at the surface ---- as the mechanical seedling enters the soil, the force increases rapidly at first and then tends to remain constant until a depth of 2 inches is reached. At this point, the force tends to increase gradually until the l-inch depth is reached. Between a depth of l and 0 inches, the emergence force approximately doubled due to the hard compacted layer caused by surface drying. Compaction pressure applied at seed level ---- the emergence force approached a maximum at a depth of approximately 2 1/2 inches and remained constant until a depth of l-inch was reached. At this point the emergence force decreased rapidly to a constant value between 1- and 0-inch depth. A large decrease in emergence energy is evident. Pressure applied at the surface with no drying ---- the emergence force increased to a maximum value and re- mained essentially constant to the point of shear. Figure 32 is a representive plot of the emergence energy required for various planting depths for when an 8 psi pressure was applied at the surface and aged 8 days with drying, 8 psi applied at a l-inch depth below the soil surface and aged for 8 days with drying, and 8 psi applied to soil surface and aged 8 days with no drying. 65 [II—El PRESSURE APPLIED AT 69 9 SURFACE _ V—V PRESSURE APPLIED AT SEED LEVEL H PRESSURE APPLIED AT SURFACE NON-DRYING CONDITION OD N \ C” I / 0. at . EMERGENCE ENERGY- IN. LB. P0 (fl \ / 2 3 PLANTING DEPTH- IN. Figure 32. Emergence energy required for various planting depths for a compaction pres- sure of 8 psi and a drying or aging period of 8 days. 66 Table 9 presents representive values of the emergence energy for the 1-, 2-, and 3-inch planting depths. The percent reduction figures are presented for compaction _ pressure applied at the surface under non-drying conditions, and compaction pressure applied at seed level under drying conditions. These are compared to compaction pressure applied at the surfaCe under drying conditions (conventional method of planting). A considerable reduction in the energy required for emergence of the mechanical seedling was realized by applying the compaction pressure at seed level and preventing drying of the soil surface. A much greater reduction in the emergence energy for the 1- and 2-inch planting depths is evident, as compared to a 3-inch planting depth. Table 9. Emergence energy for various planting depths and seedbed conditions. Emergence Energy 4: Percent; Reduction* P1 tin . Surface : Surface :Seed Levelx_§urface gseed Level an g ‘Compaction:Compaction:Compaction:Compaction3Compaction _ Depth 3 Dr in :Non-dr in : Dr 1 :Non-d i 3 Dr 1 fi‘in. E in. lb. f in. 1b. 3 in. lb. 3 .% . g .% 1 f 3.71 E 0.82 E 0.02 E 78 . 99 2 g 6.80 g 2.02 : 2.0h i 70 i 70 3 ; 9.58 f .96 f 1.1u f 69 f 57 ‘31- Percent reduction as compared to Surface compaction pressure under a drying condition. 67 The maximum and average emergence force increased with compaction pressure applied at seed level but the maximum values were considerably less then when similar pressures were applied at the surface (Table 10). 68 Q40 00.1060 om.m 3.30. 00400.0 000 Buqmlgwoé 3.0 m0.m 00.0 00.0mm...” 00 3...... 00.0 03 00.0 43 004 3.0 0.0.30.0 00.0 00.0 00.0 3.0 tum 0m.0 00.0 00.0 0 004 mm.0 00.0 +3.0 00.N 00.0 00.0 0m.m 0.2.0 HQJ N0...“ 0.....0 N05 004 00.0 mm.0 omen : 0.0.0 00.0 00.0 00.003 00.0 8.0 00.0 00.0 00.0 00.0 00.0 8.0— mm; 00.0 2.0 00.0 m 00.0 :10 00.0 3000.0 3.03.0 00.0 3.0 S. 3.0 00.0 0101.0 3.0 00.0 as H W 040 0000 3.0 040310.110 00.0 00.0 0.0.03.0 20100.0 :00 000 00.0 00.0 m} A: .0; .0...“ .0...” .02“ .0...“ .na .0: .oh In“ .0: .0H :5 .90” .05” In“ .0: .oh A: .0; .00.. :5 000 4.00. .000de ,LVd-.aV3&w.aV.dEHJV 00.. mm“ 0.000%... $0.00..“ mm??? 0mmmmmma $0000? mm 4010.3 0.010.: a J odioaq aa caloaa 010,010.00 as a 0.3 04 0am e009 000m 0000 00 00 000m 9003 00.00 000m 0000 0000 08m 0003 Sfimameae 0000 9 us u as u u no u u ue u u ue u u as u U 0 O 0 O O O O O O 0 O O O O 0 0 QOapowQEOO W 9 8 3 9 9 9 9 8 9 9 9 9 8 9 9 9 0H 0 0 m H 0 06000.08; madman .0000030 #0 voafig :90 «mm 01227020 000.0950 .300 3309 £097..” 003350 00.30.0003 0830.09.30 0062000 no.“ 00.3.“ 020009080 088.3008 0:0 .098...” 08000080 0000050 $090000 0ocowaoem .0." 0Hnwa “APPLICATION OF RESULTS Since the energy required for emergence increased markedly with increasing compaction pressure at the soil surface and with.1ength of drying period, several methods for reducing the emergence energy required of plant seedlings are visualized as follows: 1. 2. 5. Decrease or eliminate compaction pressure at the soil surface but apply the pressure at seed level. This will reduce the mechanical strength of the surface layer of soil. A shallow depth of planting will require less energy for emergence and shorten the period of time between planting and emergence of a seedling. The faster the emergence, the lower the energy requirement.. Prevent the soil surface from developing mechanical strength by covering the seedbed. ‘Design a soil profile to eliminate the crusting problem and reduce emergence energy. This might be some form of a ridge. Provide a firm underfooting for the seedling to prevent the seedling from shearing from the roots while de- veloping the force necessary to overcome the mechanical impedance of the soil. Prevent soils from developing mechanical strength when 70 they dry by adding some type of chemical additive. 7. Develop means of keeping the soil surface moist thus preventing the soil from drying out and increasing the energy required for emergence. 8. Plant soaked seeds that have taken up sufficient mois- ture for germination,to thus increase the speed of emergence. 9._ Different types of soil structure might reduce the energy required for emergence. The above methais of reducing the emergence energy can be applied to planter design, seedbed preparation and seed treatment and should result in a uniform and adequate stand of plants. SUMI‘G‘ARY A penetrometer was designed, developed and fabricated that gave a relative measure of the energy required for emergence of plant seedlings. Basic information concerning fine seed enviroment for maximum emergence of plant seedlings was collected in a series of laboratory experiments. Data obtained in this study shows that the emergence energy requirements in- creased directly with soil compaction pressure, initial soil moisture content, depth of planting, amount of surface drying and indirectly with moisture content at time of measurement. As the seedling diameter increased, the emergence energy requirements increased. Thus, a bean seedling would require more energy for emergence than a corn seedling. Applying the compaction pressure at seed level and preventing evaporation from the soil surface reduced the emergence energy. The results of this study indicate that planters for corn, bean, sugar beets, etc., should be designed to press the seed into moist soil and then cover with loose soil for maximum seedling emergence. Several methods of reducing the energy required for emergence of plant seedlings are suggested. 1. 3. C ONCLUS I ONS The energy required for emergence increased directly with compaction pressure, initial soil moisture content, amount of soil surface drying, and indirectly with moisture content at time of measurement. When the soil was permitted to dry for 8 days, a marked reduction in the emergence energy was realized for vari- ous planting depths by applying the compaction pressure at seed level as compared to applying the compacting pressure at the soil surface. When the soil moisture was held constant, the mechanical strength of the soil surface increased only slightly. For various planting depths, the energy required for emergence of the mechanical seedling was reduced markedly as compared to a drying condition. Depth of shearing position of the inverted cone below the soil surface was independent of surface compaction pressure at constant soil meisture and tended to increase slightly when the surface was subjected to drying. Energy required for emergence and depth of shearing below the soil surface increases with the mechanical seedling diameter. Development of mechanical strength in the surface layer of a Brookston sandy loam soil is dependent upon com- paction pressure and soil moisture content. 7. 73 The increase in mechanical strength of the Brookston sandy loam soil under non-drying conditions depended on aging time and/or uncontrollable loss of soil moisture. PROPOSED FUTURE INVESTIGATIONS This investigation revealed advantages of applying the compaction pressure at seed level rather than at the surface to minimize the emergence energy required of plant seedlings. An experimental planter employing this principle should be developed and field tested to verify the results. The tests conducted in this investigation should be repeated on various soil types and at very slow mechanical seedling speeds. (1 inch per day or less.) A direct method of measuring the amount of energy a seed has for emergence should be developed. A study should be conducted to determine the combi- nation of compaction pressure, position of compaction pressure, and soil moisture content that would result in the maximum emergence of corn, sugar beets, beans, etc., using the penetrometer developed in this study. APPENDIX 76 oe.m No.0 mm.o :0.m mm.m ee.o oo.o $3.: m:.m we.o om.o mo.: ea mo.m o:.o mo.o oo.~ Hm.m o:.o om.o as.m o:.m ~:.o em.o om.m m om.m mm.o N:.o mm.a m:.m mm.o N:.o o~.H N:.N mN.o mm.o mo.H : mm.m :m.o mm.o m:.H m:.m :m.o Nm.o m:.e m:.m mH.o om.o mo.H m oo.m om.o mm.o ca.a N:.N mH.o om.o mm.o m:.N NH.o pH.o HN.O H oe.w ma.o mH.o He.o m:.m oa.o mH.o No.0 ::.m No.0 eo.o H:.o N\H .9H .9H .9H .m« .9H .na I.CH .GH .9H .3H l.ca .CH .na .na I.aa «ma deEVJH de-VdW E deVdN a...“ mm... mm mam? mm“ m. mm mm“ mm“ mm 1.8 OJJ 0J1. dd 1.8 Odd OJ... JJ TB OJJOJI. 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TI TI . mammogm m... 5..“ .2... a... m... .3 a... a...” 3...; 3...... a...” .333... qu we mm m uqu we mm m wuw we mm m mommasm 9 0 9 9 9 9 9 9 G mom a H amH a... 00 unau.noz Hnom H.0pscH Ammwp m u poHaoQ mchhQV .mennmmeam :oHpommEoo mowMHSm paw mucepzoo megawaos HHOm HwHuHcH msoprp Lou dump coHpHmom mcHammsm - 0cm .eoaou emmae>w .eopou ESEHKQS .thQCo oocowmesm .MH eases 79 ww.0 Mm.m.fiquw 00.Mg00.0 00.H mm.mfim0.0fi 00.0 HH.H 0H.0 mm.0 0H 00.0 00.0 00.: 00.0. 0.0 0H.H 00.0 00.0 00.0 00.0 m0.H 0H.: 0 mm.0 m0.H m0.0 00.0 00.0 m0.0 0m.H mm.m 00.0 00.0 mm.0 HH.0 0 :m.0 00.H me.H 00.0 00.0 00.0 00.0 00.0 m0.0 00.0 00.0 H:.H 0 00.0 00.0 0m.H 0m.: 0m.0 0H.0 00.0 0H.H 00.0 0H.0 0H.0 He.0 H 0m.0 sm«0 00.0 qumanaMIimmqm.10H.0 00.0 00.0 00.0 00.0 0 0 0\ OQH .DH 03..” .nH .0H .0H -.cH.,.aH .0H .0H -.nH .aH .0H .0H ..aa 0.0 JSdVdH. .de.uv.dW JSdVdN .0 mm... 0...... .0... 000m... 0... mm 00...... mm. mm It ea... 0...... .JJ 1.90.... ea... JJ 1.9 added... dd omsmmoam SJ 9008 efim 0000 Qdefie 900m 00.... 3a 9009000 0000 m... .0 .0. .3 m... 5. a. .2 0... .0 .m f. 5.555. up 0 o w ufim we a w U0w w w o cowhasm 9 9 9 O 9 9 +0 9 9 mom m0H 00H 0.. .00 .....002 H000 H.0000H Amzwp : u poanen wchaQV .meASmmean :oHuomnEoo commasm 0mm musercoo oaspmHoS HHOm HprHcH msoHa0> mom made coHpHmom wanwenm 0cm .eoaom ewwpe>0 .eoaom ESEHNdB .hmamne oosewaegw .JH 0Hnwa. 80 00.0 mm... 0.0.0.0000 00.0 00... 00.0 00.: £003.0950008 pH 0» named 00» coach , 0~.0 00.m 00.0H 00.0. 00.0 00.0 00.0 00.nH 00.0 00.H 00.H 00.0 0 00.0 00.0 m0.0 m0.00 00.0 H0.0 00.0.0H.0 0H.0 00.0 00.0 00.0 0 00.0 00.0 0H.0 00.mH 00.0 00.0 00.H H:.: 00.0 ww.0 00.0 0H.H 0 00.0 00.H 00.0 00.0 00.0 00.0 00.0 00.H mm.H 00.0 0H.0 0m.0 H 00.0 00.0 00.H 00.: 00.0 00.0 0H.0 0m.0 00.H 00.0 10.0 0H.0 0\H .0H .0H .0H . .00 .0H .0H ..00 .0. .0H .0H -.00 .0. .0H .0H -.00 0.0 708.0.de deflVJN deVJuwuN .0 0.00.00 .00. .0... .00 .00. 00.000 0.0 .00. 1:3 OJJOJI. dd 1.8 OJJ 0J1: JJ 1.80.4.4 0&1: JJ .. 0... 900.0... 00 00.0.0 .00 00 0.0.00 .00 00 500.00.00.00 0.0 0. 0.. 0 0.0 0. 0 0 0.... 0. 0 0 3...... 0 9 9 9 8 0 9 9 8 000 00H 00H 000 000 00000002 H000 H00000H Ammmp 0H u pegged wafimaav .mendmmeam cofipowmsoo mommasm 0:0 museunoo manpmfio: H000 Hwfipficw 0:00a00 now 0000 CoHuHmon unwawesm use .eoaom 0&00000 .moaom Esswxma .muaoae eocemaeem .ma 0H000 81 Table 16. Moisture lost from soil surface initially at various moisture contents and compaction pressures for a drying period of 1 day. Cimggzggon Initial Soil Moisture Content _£ressure 12% 10% 20% psi ems. ems. ems. 1/2 36.3“ 18.0 89,3 1 37.5 18.0 95.0 2 37.8 23.0 81.5 u 38.0 21.5 92.3 8 37.8 20.0 116.3 10 no.7 2h.5 9h.3 Moisture lost by evaporation from soil surface. Table 1?. Moisture lost from soil surface initially at various moisture contents and compaction pressures for a drying period of 2 days. _—§urface Compaction Initial Soil Moisture Content Pressure 12% wl6% 20% psi gms. ng. ng. 1/2 53.8* 32.5 158.3 1 3h.8 39.0 172.3 2 55.0 M7.o 160.8 0 55.8 h7.o 183.5 8 57.5 01.5 195.7 16 63.0 00.5 187.0 e ’l 1. Moisture lost by evaporation from soil surface. 82 Table 18. Moisture lost from soil surface initiall at various moisture contents and compact on pressures for a drying period of h days. r. Ciigaiifon Initial 3011 Moisture Content Pressure 12%? 16% 20% psi ems. gms. gms. 1/2 71.0“ 75.5 189.0 1 71.3 75.0 217.7 2 73.5 87.5 207.5 u 7u.8 90.0 235.5 8 75.3 90.5 250.3 16 77.0 99.5 256.0 * Moisture lost by evaporation from soil surface. Table 19. Moisture lost from soil surface initially at various moisture contents and compaction pressures for a drying period of 16 days. Surface Compaction Initial Soil Moisture Content Pressure 12% 16% 20% psi gms. gms. gms. 1/2 158.5* 151.5 308.3 162.8 171.5 3u1.0 2 163.0 18h.0 333.3 A 162.5 189.0 365.3 8 166.8 '192.0 385.7 16 171.7 212.5 399.0 * Moisture lost by evaporation from soil surface. R EF‘E’RENC ES Allison, L. E. and D. C..Moore (1956). Effect of VAMA and HPAN soil conditioners on aggregation, surface crusting, and moisture retention in alkali soils. Soil Sci. Soc. Amer. Proc. 20:103-lh6. Bowen, H. D. (1956). Unpublished material on basic planting studies. North Carolina State College. Bruce, R. R. (1955). An instrument for the determination of soil compactibility. Soil Sci. Soc. Amer. Proc. 193253'570 Carnes, A. (193u). Soil crusts - methods of study, their strength and a method of overcoming their injury to cotton stands. Agr. Engr. 15.167-171. Gill, W. R. (1959). The effect of drying on the mechanical strength of Lloyd clay. Proc. Soil Sci. Soc. Amer. 233255-570 Gill, w. R. and G. H. Bolt (1955). Pfeffer's studies of the root growth pressures exerted by plants. Agron. Gill, W. R. and R. D. Miller (1956). A mefiaod for study of the influence of mechanical impedance and aeration on the growth of seedling roots. -Soil Sci. Soc. Amer. Proc. 20:15h-7. Gorbunov, N. I. and N. E. Bekarevitch (1951). The nature of the formation of soil crusts and measures for com- batting them. Pochvovedence No. 0:1936200. Trans- lated by Marten D. Derdenian ARS. USDA. Beltsville, Maryland. Hanks, R. J. and F. C. Thorp (1956). 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