ABSTRACT THE INFLUENCE OF DEEP MIXING A KALAMAZOO SANDY LOAM ON SEVERAL PHYSICAL SOIL FACTORS AND CORN ROOT DEVELOPMENT AND YIELD by Curtis Dean Piper A research project was conducted over an eight year period to determine the feasibility of using a deep-mixing process to alter the physical properties of a dense soil layer that acted as a barrier to root development and reduced yields. The deep-mixing did improve the physical properties of the dense soil layer, by redistributing the soil separates. Increases were obtained in the total pore space and macro- pores, with a corresponding decrease in the density of this soil layer. These improvements were of short duration as they soon reverted back to, or in most cases beyond their original state. The deep-mixing increased the oxygen diffusion re— covery rate and also improved the soil water utilization. The over-all influence of the deep-mixing was to increase the corn grain yields every year but one (1962) and resulted in an eight year average increase of 30.4 bushels per acre. For this particular soil the increase in yields were suf- ficient to warrant the expense of the deep-mixing operation. Curtis Dean Piper Supplemental organic matter in the form of chopped alfalfa hay, used as a stabilizing agent in the soil, in— creased the water retention capacity of the soil, as indicated by the neutron moisture probe. It also increased the phos— phorus, potassium, calcium and magnesium content of the soil. The alfalfa treatment decreased the amount of root develop— ment, however, it did increase the corn grain yields every year but one. THE INFLUENCE OF DEEP MIXING A KALAMAZOO SANDY LOAM ON SEVERAL PHYSICAL SOIL FACTORS AND CORN ROOT DEVELOPMENT AND YIELD BY Curtis Dean Piper A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Soil Science 1967 ACKNOWLEDGMENTS The author wishes to express his sincere appreciation to: His major professor, Dr. A. E. Erickson, for his personal interest and support throughout the author's doctoral program. Dr. R. L. Cook, Head of the Soil Science Department for his moral support and personal interest in helping to direct the author's study program. Professors, H. D. Foth and L. S. Robertson for their in- valuable assistance throughout the course of the author's research and study program. His wife, Helen, for her devotion, encouragement and under— standing, throughout the entire time the author was involved in the doctoral program. ii TABLE OF CONTENTS INTRODUCTION . . . . . . . . . . . . . . . . . . . REVIEW OF LITERATURE . . . . . . . . . . . . . . . I. II. III. IV. V. Mechanical Impedance and Root Development. Oxygen Diffusion in the Soil System and Root Growth. . . . . . . . . . . . . . . . Soil Water Use by th Plant Roots as Influ— enced by Soil Compaction . . . . . . . . . Soil Modification and Root Growth. . . . . Soil Modification and Water Infiltration Rates. . . . . . . . . . . . . . . . . . . DESCRIPTION OF FIELD EXPERIMENT. . . . . . . . . . I. II. METHODS I. II. RESULTS Description of Soil. . . . . . . . . . . . Description of Field Plots and Treatments. OF STUDYING SOIL PHYSICAL PROPERTIES . . . Methods of Analysis. . . . . . . . . . . . 1. Soil Nutrient Status. . . . . . . . . . 2. Soil Particle Size Analysis . . . . . . 5. Porosity and Bulk Density Measurements. 4. Infiltration Studies. . . . . . . . . . 5. Soil Moisture Measurements. . . . . . . 6. Oxygen Diffusion. . . . . . . . . . . . 7. Root Studies. . . . . . . . . . . . . . Methods of Statistical Analysis of Data. . AND DISCUSSION . . . . . . . . . . . . . . Soil Test Results. . . . . . . . . . . . . Particle Size Composition of the Soil. . . Laboratory Analysis of Soil Cores. . . . . iii 11 12 14 17 17 17 25 25 25 24 25 26 29 5O 5O 52 54 54 57 59 TABLE OF CONTENTS - Continued 1. 2. Water Soil Moisture Contents—-Measured with Changes in Soil Properties at the to 15 Inch Depth. . . . . . . . . Changes in the Soil Properties at 18-21 Inch Depth. . . . . . . . Infiltration Rates. . . . . . . . Neutron Moisture Probe. . . . . . . . . Oxygen Diffusion Rates. . . . . . . Corn Root Development . . . . . . . . . Corn Grain Yields as Influenced by: 1. 2. Plowing Depth . . . . . . . . . . Organic Matter. . . . . . . . . . 5. Plowdown Fertilizer . . . . . . . 4. Variety . . . . . . . . . . . . . CONCLUSIONS. General Summary in Retrospect . . . . . BIBLIOGRAPHY iv Page 40 41 SO 54 85 9O 96 99 100 100 107 112 119 TABLE 1. 10. 11. 12. 15. 14. 15. LIST OF TABLES Soil test results for 1956 and 1961. . . . . Particle size analysis of the Kalamazoo sandy loam soil. . . . . . . . . . . . . . . . . . Summary of soil core data for alfalfa treat- ment . . . . . . . . . . . . . . . . . . . . . Summary of soil core data for crop residue treatment. . . . . . . . . . . . . . . . . . . Analysis of variance of the 1959 soil core data . . . . . . . . . . . . . . . . . . . . Analysis of variance of the 1960 soil core data . . . . . . . . . . . . . . . . . . . . . Analysis of variance of the 1962 soil core data . . . . . . . . . . . . . . . . . . . . . Analysis of variance of the 1965 soil core data . . . . . . . . . . . . . . . . . . . . . Infiltration rates obtained through the use of the double-ring infiltrometer. . . . . . . . . Infiltration rates obtained through the use of the FA type infiltrometer. . . . . . . . . . . Soil moisture data for 1959. . . . . . . Analysis of variance of the 1959 soil moisture data . . . . . . . . . . . . . . . . . . . . . Soil moisture data for 19600 . . . . . . . . . Analysis of variance of the 1960 soil moisture data . . . . . . . . . . . . . . . . . Soil moisture data for 1961. . . . . Page 55 58 44 45 46 47 48 49 55 55 59 6O 65 64 67 LIST OF TABLES - Continued TABLE 16. Analysis of variance of 1961 soil moisture 17. 18. 19. 20. 21. 22. 25. 24. 25. 26. 27. 28. 29. 50. 51. 52. data . . . . . . . . . . . Soil moisture data for 1962. . . Analysis of variance of the 1962 data . . . . . . . . . . Soil moisture data for 1965. . . Analysis of variance of the 1965 data . . . . . . . . . . . . Soil moisture data for 1964. . . Analysis of variance of the 1964 data . . . . . . . . . . . . . . soil moisture soil moisture Oxygen diffusion rates obtained in spring of 1959 . . . . . . . . . . . . . . Oxygen diffusion rates obtained in fall of 1959 . . . . . . . . . . . . . . Oxygen diffusion rates obtained in spring of 1961 . . . . . . . . . . . . . . Weights of corn roots obtained from each treat- ment C O C O O O O O O O O C O O O O O O O O 0 Analysis of variance of the corn root weights. Weights of corn roots obtained for the 1965 growing season . . . . . . . . . Corn grain yields obtained from respective treatments . . . . . . . . . Corn grain yields for the 1965 and 1964 grow- ing seasons. . . . . . . . . . . Analysis of variance of the corn grain yields. Analysis of error variance for pooled testing of interactions. . . . . . . vi Page 68 71 72 75 76 79 80 87 88 89 94 94 95 102 105 104 104 LIST OF TABLES - Continued TABLE Page 55. Corn plant and ear count for 1964 . . . . . . . 105 54. Analysis of variance of the 1964 corn plant and ear count . . . . . --. . . . . . . . . . . . . 105 55. Rainfall data for the plot area . . . . . . . . 106 vii FIGURE 1. 2. 5. 10. 11. 12. 15. 14. LIST OF FIGURES Plot diagram for 1956 Plot diagram for 1965 Soil moisture content depth for 1959. . . . Soil moisture content depth for 1959. . . . Soil moisture content depth for 1960. . . Soil moisture content depth for 1960. . . Soil moisture content inch depth for 1961 . Soil moisture content depth for 1961. . . . Soil moisture content inch depth for 1962 . Soil moisture content depth for 1962. . . . Soil moisture content ment in 1965. . . . Soil moisture content treatment in 1965 . . Soil moisture content ment in 1964. . . . . Soil moisture content treatment in 1964 . . through 1962. . . and 1964. . . . . . . at the 6 to 18 inch at the 24 to 56 inch 0 O O O O O O C O O O at the 6 to 18 inch at the 24 to 56 inch at the surface to 18 at the 24 to 56 inch at the surface to 18 at the 24 to 56 inch for the alfalfa treat— for the crop residue for the alfalfa treat- the for crop residue viii Page 21 22 61 62 65 66 69 70 75 74 77 78 81 82 INTRODUCT ION Many soils are agriculturally unproductive because they have natural barriers which restrict plant root development. These soils produce inferior crop yields, yet many of them can be mechanically manipulated so as to improve their physi- cal properties and increase the yields of crops. The root system of a plant bears the characteristics of the species but is greatly influenced in its development by the prevailing soil physical conditions, such as moisture, aeration, compaction (bulk density), and temperature, as well as the soil chemical properties, such as pH, fertility and salinity. Bonner and Galston (8) aptly describe the soil-plant relationship in their discussion of, "The soil as a medium for plant growth," as follows: The mineral and water resources of the soil are tapped by the plant through a prodigiously ramified system of roots and root hairs, which bring the plant into inti- mate contact with many of the soil particles beneath it. This thorough exploitation of the soil is achieved not only by repeated branching of the root as it penetrates downward, but also by the production of the root hairs which develop in enormous numbers in the roots of many species. If then the plant is depending on such a complete rami- fication of the soil by the root system, to supply its needed water and nutrients, any restriction placed on root development will tend to be followed by a reduction in vege- tative growth and eventually a reduction in crop yield. With the powerful equipment available today, it is pos— sible to modify soils that are presenting difficulties to the rooting of certain plants. This modification should allow a suitable depth of root penetration and total proliferation within the soil mass. The modification procedure used in this research to break up the barrier layer existing below normal plow depth, was to thoroughly mix the surface soil to the depth of 22 inches with a disc plow that had been adjusted for maximum mixing. This study includes both laboratory and field measure— ments to determine the following: A. The influence of a deep-soil-mixing process on the physical properties of specific soils. B. The effects of the alteration of the soil physical properties on the development of plant roots within the given area. C. The duration of the alteration of the soil physical properties, brought about by the deep-soil-mixing process. D. The effects of supplemental organic matter as a stabilizing agent, on the physical properties of the soil. E. The influence of supplemental plowdown fertilizer, incorporated into the soil by the soil-mixing process, on crop yield response. The feasibility of using deep-soil-mixing to modify problem soils as a means of increasing crop produc- tion. REVIEW OF LITERATURE In the past few years a considerable number of investi- gations have been carried out to determine the effects of the soil physical properties on plant root deve10pment. Various methods of soil modification have been tried in order to increase the productive capacities of certain soils that limit normal root development. I. Mechanical Impedance and Root DevelOpment Soils having high bulk densities have been observed to restrict root growth. For this reason the effect of mechani— cal impedance of dense soil layers have received much atten- tion. Veihmeyer and Hendrickson (87) observed that plants growing on soils with a dense subsoil layer, tended to be as shallow rooted as those growing on hardpan soils. In their investigations to determine the threshold density for root penetration, they concluded that it was not necessarily the same for all soils, but instead covered a wide range, from 1.46 grams per c.c. to 1.9 grams per c.c., depending on the soil texture. It was their impression that roots failed to penetrate compact soil layers due to the small pore size, rather than from the lack of oxygen (87). Wiersum et al. (90) in an experiment to determine the effect of size and rigidity of pores on root penetration, found that young growing roots would only pass through pore sizes exceeding the diameter of the root tip. They were also able to demonstrate that the rigidity of the pore struc- ture influenced root penetration. One may ask the question as to the amount of pressure a young growing root does exert in forcing its way through the soil? Pfeffer in his "Studies of Root Growth Pressures Exerted by Plants," as reviewed by Gill et al. (52) has provided the answer to this question. This review indicates that Pfeffer was able to demonstrate that plants vary as to the root pressures exerted, according to the species. However, using one species for an example, Pfeffer determined that Zea Maise roots could exert an axial pressure varying from 9.55 atm. to 24.94 atm. depending on the distance from the root tip. The radial pressure was found to be 6.59 atm. Needless to say, the total force ex- erted by the radial pressure was much greater than for the axial pressure. Fehrenbacher and Snider (21) were able to determine that for a Cisne soil, corn roots were highly developed throughout the compact claypan, due to the well developed prismatic structure which permitted corn roots to penetrate. However, they found the A 2—2 horizon, having a dense platy structure, to be most limiting to root branching. Fehrenbacher et al. (22L reporting on further studies, state that the Cisne soil showed that with proper fertilization and liming the amount of root penetration into the "claypan" B horizon, was very good for all crops. In an experiment to determine the influence of soil compaction on root penetration, Meredith and Patrick (58) were able to show that as artificial soil compaction increas- ed bulk density, there was a decrease in non-capillary por- osity, water permeability and root penetration. They also obtained a linear relationship between soil root penetration and bulk density, emphasizing the fact that there appears to be no critical bulk density stopping root penetration. However, Edwards, et al. (17) found a bulk density of about 1.80 grams per c.c. to be a threshold density above which discrete soil peds are not penetrated by corn roots. Phillips and Kirkham (65) also working with artificially compacted soils, obtained a definite correlation between, (1) root penetration and bulk density, and (2) between the amount of root penetration and corn yields. They concluded that probably the mechanical impedance set up by the high bulk density soil was more restrictive to root penetration than any other factor. Tackett and Pearson (80) also assumes that mechanical impedance is more detrimental to root growth than are low oxygen concentrations in subsoils with bulk densities above 1.5 grams per c.c. Taylor and Gardner (81) found a highly significant negative correlation to exist be— tween the relationship of soil strength and root penetration. Their conclusion was that soil strength, not bulk density was the critical impedance factor controlling root penetration. In a study of the effect of mechanical stress on the growth of roots, Barley (2) found that a stress of 1.1 to 1.8 atm. would greatly reduce the length of growth of corn radicles. He was also able to show an interaction between mechanical stress and oxygen supply on root growth. Cannon and Free (12) were the first to conclude that a certain level of oxygen must be maintained within the soil atmosphere for proper root development. Using a device to adjust mechanical impedance and oxygen concentrations on a root system, Gill and Miller (55) were able to show that a mechanical impedance would restrict root growth, even at optimum oxygen concentrations. They also demonstrated that the ability of the root to enlarge in spite of the mechanical resistance is greatly impaired by modest reductions in oxygen concentrations. II. Oxygen Diffusion in the Soil System and Root Growth In 1955 Lemon and Erickson (47) introduced the platinum microelectrode method for the measurement of oxygen diffusing through the soil solution to the plant roots. These research- ers concluded that the concentration of oxygen in the soil atmosphere was not the controlling factor in the supplying of oxygen for root growth, but that the rate of diffusion of oxygen across the soil solution phase surrounding each plant root was much more critical. Their findings have stimulated a considerable volume of research in the area of soil aera— tion and mechanical impedance on root growth. Bertrand and Kohnke (5) found that corn roots did not penetrate subsoils compacted to a bulk density of 1.5 grams per c.c., but that they grew profusely in a subsoil having a bulk density of 1.2 grams per c.c. They also determined that the oxygen diffusion rate was much slower for the more dense subsoil than for the looser subsoil, and that high moisture contenusintensified the restricting effect of the dense subsoil on both the oxygen diffusion rate and root growth. They suggested that an oxygen diffusion rate of less than 20 to 50 x 10'8 g.cm-‘°".min"1 would limit root growth. Erickson and VanDoren (18) have shown that oxygen defi— ciencies for a one day period can have a great influence on the yield of the plants. The magnitude of the influence will be determined by the specie and variety of the plant, its stage of development, soil fertility as well as some other factors. Birkle et al. (6), Letey et al. (48,49,50,51,52 and 55) and Stolzy et al. (76) have conducted a considerable number of experiments applying the platinum microelectrode method of measuring the oxygen diffusion rate to root response. Their work has centered around the use of a controlled and varied oxygen supply and its influence on diffusion rates, and has further substantiated the initial findings of Lemon and Erickson (47). Their investigations could be summarized briefly as follows: (1) Oxygen diffusion rather than oxygen concentration of the soil atmosphere is the more critical factor in root growth, (2) The shoot growth responses of many plants are influenced by the oxygen supply in the root zone, (5) Plant species vary in their limiting value of oxy- gen diffusion rate and root response, (4) The concentration of potassium, nitrogen and phosphorus increases in the plant tissue as the oxygen supply to the plant root increases, where as the sodium concentration decreases, (5) Water con- sumption by the growing plant is reduced under low oxygen supply, (6) Corn roots can show restricted growth where the J. 2.min’ , oxygen diffusion rate is greater than 10’8g.cm’ while a rate of 40 x 10"‘3’g.cm""‘3-min"l provides for a maximum growth. Jensen et al. (40) and Jensen and Kirkham (59) indicate that the reason corn roots are able to continue growing at such low oxygen diffusion rates, is that there is apparently a self-diffusion of oxygen from the shoot down through to the root, thereby supplying the corn roots with a portion of their required oxygen supply. Birkle et al. (6) and Wadding- ton and Baker (88) have also shown that other members of the grass family can produce as well under conditions of lower oxygen diffusion rates, probably because they too have self- diffusion of oxygen within their root systems. The conclusions of Letey and his associates seem to bear out the findings of HOpkins et al. (56), in that the accumu- lation of the major plant nutrients, with the exception of 10 magnesium, was dependent upon the oxygen supplied to the roots and that the sodium content decreased as the oxygen supply increased. Van Diest (85) found that the oxygen dif— fusion rates were greatly depressed in compacted soils and that the ability of the plant roots to absorb nutrients supplied by fertilizers, varies more with compacted soils than with the more normal aerated soils. Wiersum (91) has found a good correlation to exist be- tween measurements of oxygen diffusion rates and soil char- acteristics also with root penetration. Scott and Erickson (72) have also shown that there is a definite interaction between oxygen availability and root penetration brought about by high bulk density layers. Kristensen and Lemon (44) explain that the rate of oxygen diffusion is governed by the “apparent diffusion path length," that the oxygen must move across to enter the plant root. This would substantiate the findings of the other researchers whereby oxygen diffusion rates have decreased as bulk densities have increased. This would be accounted for by the increase in the capillary poros— ity, lengthening the mean diffusion path of oxygen through the soil solution. Williamson (92) using lysimeters installed in the field, was able to show a direct relationship between the oxygen diffusion rate and a controlled water table. He was also 11 able to obtain a very good relationship between the relative yields of corn and the rates of oxygen diffusion. The interaction of reduction of diffusion rates due to increase in moisture content of the soil has stirred some controversy about the possibility of increased CO2 concen- trations reducing root growth due to the toxicity of the CO2, rather than the lack of oxygen causing the reduction. Geisler (50) using solution cultures found that CO2 concen- trations such as those found in the soil system stimulated root growth in the pot cultures. However, Tackett and Pearson (80) were able to show that at low bulk densities the root elongation rate decreased progressively with in- creasing CO2 concentrations, although moderate to good growth did occur even at 24% CO2 concentrations. At high subsoil density, CO2 concentrations had little effect on root penetration. III. Soil Water Use by the Plant Root Systems as Influenced by Soil Compaction Gardner and Ehlig (28) found that any impedance to water movement in the soil limits water availability in dry soils and is greater than the impedance to water movement into the plant roots, even in the relatively moist soils. Gardner (27) also indicates that the relative distribution of roots with depth and the water retaining and transmitting properties of the soil determine the main features of the water uptake \‘O‘ U6 by U- B. () (I) U) I). ti.) “1 12 pattern and that the total number of roots were relatively unimportant. However, Stevenson and Boersma (75) concluded that the water absorption process, which appears to be related to the water content of the soil, should be interpreted in terms of amount of root growth as affected by the water content of the soil. Russell and Danielson (71) were able to determine that corn can utilize water to a depth of five feet or more in a deep Brunizem soil and that the total water used was proportional to grain yields. The effect of soil moisture stresses at different stages of growth on the development and yield of corn have been shown by Denmead and Shaw (14). A moisture stress prior to silking reduced grain yields as much as 25%, while a moisture stress at silking time reduced grain yields by 50%, and moisture stresses after silking reduced grain yields by only 21%. They assume that the early stress may reduce the total root assimilation surface, while a later stress reduces direct assimilation of essential nutrients. IV. Soil Modification and Root Growth Kohnke and Bertrand (42) found an increase in corn root growth due to subsoil fertilization, while subsoiling alone increased root growth only slightly. The subsoil fertilized area maintained a higher porosity for over two years, result- ing in a greater water supply for the growing crop. 15 Linscott et al. (54) determined that moisture use was related to corn root growth and that the efficiency of the moisture use, as measured by grain production, was increased by the application of nitrogen fertilizers. It was assumed that the increased root production, due to the fertilization, in— creased subsequent moisture utilization during a critical period of plant development prior to and during tasseling, resulting in higher yields. Woodruff and Smith (95) found that only in a few cases did the increased yields pay for the power requirement for subsoil shattering and liming on a Putnum silt loam. Patrick et al. (62) were able to demonstrate an increased corn root development in the subsoil due to deep plowing, sub- soiling and deep placement of fertilizers, on soils having a traffic pan. They found that the increased root growth en- abled the crop to better withstand dry periods. Fehrenbacher et al. (22) ascertained that deep-soil-mixing alone did not increase corn root penetration. However, when fertilizer was placed throughout the entire tilled zone, root penetration did increase. Harper and Brensing (55) summarized their findings on "Deep Plowing to Improve Sandy Land," as follows: (1) experi- ments have shown that on some types of loose, sandy soil deep plowing will; (a) increase crOp yields and (b) reduce wind erosion, (2) the research has also shown that deep plow- ing will not; (a) improve the physical conditions of all 14 types of land, nor (b) improve crop yields permanently unless followed by proper use of rotations, fertilizers, and soil- improving crops. They further explain that their increased yields were obtained on loose sandy soils which had sub- soils containing 10% to 25% clay lying near enough to the surface to be reached by the special plows used. They also stipulated that the method would not be satisfactory for soils having a sandy subsurface. These researchers assume the effects of the deep-plowing operation to be permanent, that is for a period of at least 50 to 100 years. V. Soil Modification and Water Infiltration Rates The water infiltration rate of a soil has been defined by Richards (68) as the maximum rate at which a soil, in a given time, can absorb rain. It has also been defined by Parr and Bertrand (61) as the maximum rate at which a soil will absorb water impounded on the surface at a shallow depth when adequate precautions are taken regarding border or fringe effects. The double-ring infiltrometer has been used extensively to study the movement of water into the soil. Haise et al. (54) have presented general information as to selection of site, equipment, installation, operation, computations and plotting of data obtained from the use of the ring infil— trometers to determine the intake characteristics of soils. 15 Marshall and Stirk (57) have studied the effects of buffered and unbuffered rings on the lateral movement of water in soil. They found the buffered rings do yield more consistent results. However, Burgy and Luthin (11) were not able to determine any appreciable differences in the values obtained from the buffered and unbuffered ring infiltrometers. The differences in the observations of Marshall and Stirk and those of Burgy and Luthin comes from the use of two dif- ferent types of soil profiles. The former group were studying the effects of water movement into a well developed soil pro- file, which presented an impedance to water movement, result- ing in a considerable amount of lateral movement. The soil studied by Burgy and Luthin showed no profile development and was freely permeable, hence a minimum amount of lateral movement of water. Swartzendruber and Olsen (78) have made extensive studies in the use of the double-ring infiltrometer as affected by size of rings and soil texture. They recommended the use of larger rings than were generally accepted as sufficient for most studies. They suggested an inner ring of 20 inches in diameter and an outer ring of 24 inches in diameter, to mini- mize the influence of the double-ring flow system. However, Aronovici (1) concluded from his studies on the influence of ring size on the infiltration rate, that the decrease in flow velocity was only 0.05 centimeters per hour for each inch of increase in ring diameter beyond four inches, while the rate ICW f). '1 16 of change was 1.5 centimeters per hour for every inch in- crease from one-half inch up to four inches in diameter. Slater (75) has suggested using 15 replications of the double ring infiltrometers to insure an accuracy within 20% of the true mean, while Burgy and Luthin (11) found that an average of six replications came within 50% of the true mean, for a soil having no restricting layers. The FA infiltrometers or rain simulators have also re- ceived considerable use in determining the amount of infil- tration and runoff from research plots. Wilm (95) has used this method to determine the effect of and measurement of artificial rainfall on the water intake rates of soil. Where— as the double ring infiltrometer employs a constant head of water imponded on the surface of the soil, the FA type infil- trometer employs the use of a sprinkler system spraying the water into the air in such a fashion as to simulate water droplet sizes close to the size of rain drops. The FA type infiltrometer also uses a wetted buffer zone around the area of actual measurement. In comparing the infiltration veloci— ties of the two types of infiltrometers, Slater (75) found that the unbuffered ring velocities exceeded that of the sprinkler velocities by a factor of four. Swartzendruber and Olsen (77) using rings of considerably larger diameters than Slater used, obtained a ring velocity that exceeded the sprinkler velocities by a factor of only three. DESCRIPTION OF FIELD EXPERIMENTS I. Description of Soil Indications from previous studies on the Kalamazoo sandy loam soil had shown slight increases in crop yields due to subsoiling or subsoil fertilization treatments. One of the characteristics of this soil is the dense B 2 horizon, having a sandy loam texture. This horizon is 15 to 15 inches thick and lies 11 to 12 inches below the surface, which is just be— low the depth ordinarily reached by a conventional moldboard plow. It has a high bulk density and has a consistency some— what plastic when wet, firm when moist and hard when dry. The Kalamazoo sandy loam is a Gray—Brown Podzolic soil developed on a coarse textured outwash material underlain by acid sands and gravel at depths of 24 to 66 inches. It is well drained and is one of the more droughty agricultural soils in the southern part of Michigan. The mechanical analysis and the bulk density measurements of this soil are shown in Tables 2, 5 and 4. II. Description of Field Plots and Treatments Field plots were established in the fall of 1956 on a uniform area of this soil type, located on the Ewald Pick 17 'C) '(J (I, o; 'rt ’(1 I 18 farm, approximately four miles south and three miles east of Battle Creek, Michigan. The total area, measuring 244 by 520 feet, was divided into four main blocks, each measuring 61 by 520 feet. Two of these blocks were plowed with the conventional moldboard plow to a depth of 9 to 10 inches. The remaining two blocks were tilled to a depth of 20 to 22 inches using a giant disc plow that had been adjusted for maximum soil mixing. Prior to the deep mixing, four additional treatments were superimposed at right angles to the direction of plowing. These treatments were replicated two times on each plowed area and were as follows: (1) control or crop residue treat- ment, (2) five tons per acre of chopped alfalfa hay, (5) five tons per acre of a partially decomposed oak sawdust, and (4) subsoiling to a depth of 27 to 28 inches. Each of the areas originally designated for depth of tillage, were again subdivided for three rates of plowdown fertilizer, to be applied along with the plowing operation. These rates were: (1) no fertilizer, (2) 500 pounds per acre of a 12-5.22-10 (12-12-12) granulated fertilizer, and (5) 1000 pounds per acre of the same grade of fertilizer. An early maturing variety of hybrid corn, M-250 was planted in the spring of 1957, using minimum tillage. All of the plots received 500 pounds per acre of the same grade of fertilizer at planting time as that used for plowing down. The corn also received supplemental nitrogen applied as a ~pA‘ J 5A -\I PAY "v. I“... 5.3.. l..\ to side—dressing at the rate of 150 pounds of N per acre, when the corn was cultivated. All of the above treatments were repeated for the springs of 1958 and 1959. However, during the 1958-60 seasons each of the plowdown fertilizer treatment areas were further sub— divided for two varieties of corn. One was the early matur- ing hybrid M-250. The other was a late maturing hybrid variety, M—480. The late maturing M-480 was the only variety grown during the 1961 and 1962 growing seasons. In 1960, 1961 and 1962 the entire plot area was plowed to a depth of 9 to 10 inches with the conventional moldboard Iplow. During these three years, no further additions of sup- ;plemental organic matter or plowdown fertilizer were made, Iuor was the subsoiling operation performed. In the spring of 1965 it was decided to alter the tillage treatments to determine the influence of a one time, three 'time and four time deep—soil-mixing process, on the physical Iproperties of the soil. The previously shallow plowed and the deep tilled areas were split in half by another deep till- age operation. This resulted in one-fourth of the total plot area remaining as a control area, receiving only the tillage operation of the conventional moldboard plow, to a depth of nine to ten inches. One-fourth of the area was deep-tilled 'to a depth of 22 to 24 inches for the first time, while ano- tflaer fourth of the area received the fourth deep tillage treat- Inent. The remaining one-fourth of the plot area which had [‘0 0 previously been deep tilled three times was plowed with the conventional moldboard plow. The giant disc plow was again used to accomplish the deep-tillage operation and was set to operate to a depth of 20 to 22 inches. Prior to the tillage operations in 1965, the supplemental organic matter and subsoiling treatments were repeated as they were in the previous years. A blanket application of 500 pounds per acre of the 12-5.22-10 (12-12-12) granulated ferti- lizer was applied to the entire area for a plowdown treatment. In 1964 the entire area was plowed with the conventional moldboard plow to a depth of 9 to 10 inches. Two moderately early maturing hybrid varieties, M-250 and M-500 were grown during the 1965 and the M-500 only for the 1964 seasons. Each year the following procedures were follow on all plots: (1) planting time fertilizer was applied at the rate of 500 pounds per acre, using the 12-5.22-10 (12-12-12) granu— lated fertilizer, (2) supplemental nitrogen was applied at the rate of 150 pounds of N per acre, (5) corn was planted accord— ing to the minimum tillage principle, (4) the previous years crop residue was returned to its respective area, (5) all plots received a pre—emmerge weed spray treatment and were culti— vated only once during the growing season, and (6) grain yields were taken and recorded in bushels of shelled corn per acre. With the above experimental design all treatments were replicated four times each year. 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Methods of Analysis 1. Soil Nutrient Status Before the deep tillage operation was performed in 1956, composite soil samples were taken at the 0 to 9 inch depth and at the 27 to 28 inch depth, to determine the nutrient status of the soil. The soil was again sampled in 1961 on both the shallow plowed and the deep-tilled areas that had re- ceived a total of 500 pounds of fertilizer per year. The depth of sampling in 1961 was 0 to 9 inches. A routine soil analysis was carried out by the Michigan State University Soil Testing Laboratory using the following methods of analysis: (a) in 1956 the phosphorus and potassium was determined by the Spurway reserve test using an extracting solution of 0.15 N HCl, and the calcium and magnesium were determined by the Spurway active test employing an extracting solution of 0.018 N HAc. (b) The 1961 phosphorus was determined by the Bray P1 test, which employs a 0.25 N HCl plus a 0.05 N NH4F extracting solu— tion in a 1 to 8 soil to solution ratio. The exchangeable potassium, calcium and magnesium were determined by using a 1 N NH4Ac extracting solution buffered at a pH of 7.0. The results of the soil test analysis are reported in Table 1. 25 24 2. Soil Particle Size Analysis To determine the extent of the change in soil texture brought about by the deep-soil-mixing process, soil samples were taken from the shallow plowed and from the deep tilled areas, at four depths in the profile. A particle size analy- sis was made of each sample to determine the percent sand, silt and clay within each layer sampled. The pipette method was used to analyze the soil samples taken in 1959. This method is widely used and is considered to be the most accurate yet devised for the particle size analysis of soils. This method was developed independently by Krauss in Germany (45), Robinson in Wales (70), and Jennings et al. in the United States (58). The accepted pro- cedure for making a pipette analysis is described in the "Methods of Soil Analysis”' (7). The results of the pipette analysis are presented in Table 2. After the deep-soil-mixing process in 1965, soil samples were again obtained from three depths of the soil profile, for a particle size analysis to determine the effect of the soil-mixing process on the textural makeup of this soil. The hydrometer method developed by Bouyoucos (9) was used to obtain the clay fraction of each sample. This procedure con- sisted of weighing a 100 gram sample of soil, treating with a dispersing reagent, a sodium hexametaphosphate solution, and stirring 10 minutes with a modified malted milk blender. The sample was then transferred to a sedimentation cylinder 25 and brought to volume and then allowed to reach a constant temperature of 200C. The soil solution was agitated thor- oughly to bring the soil particles into suspension, then it was allowed to sediment. Two hours after the solution was agitated the hydrometer was inserted to determine the amount of clay particles remaining in suspension. The soil solution was then washed through a 500 mesh sieve which retained all of the sand fraction. The sand particles were then trans- ferred to a drying dish and placed in an oven set at 1050C. After drying, each sand fraction was weighed to determine its percentage of the soil sample weight. The silt size compo- nents of the soil sample were then obtained by subtraCting the sum of the clay and sand fractions from the original weight of the soil sample. Table 2 shows the results of the 1965 particle size analysis. 5. Porosity and Bulk Density Measurements The Uhland type core sampler (85) was used to obtain undisturbed soil samples from each plot area, at three speci— fic depths in the soil profile, for the years 1959, 1960, 1962, and 1965. The soil cores measured three inches in di— ameter and three inches in length. After their removal from the field_plots the soil cores were further prepared in the laboratory for total and non-capillary porosity and for bulk density measurements. The soil cores were saturated with water, weighed, then placed on tension tables, constructed after the method 26 described by Leamer and Shaw (46). The soil cores were al- lowed to reach equilibrium to a tension of 60 cm. of water, over a 48 hour period. They were removed from the tension tables, reweighed and placed in an oven adjusted to 1050C. After drying for 48 hours the cores were removed from the oven, cooled and again reweighed. From the weights of water lost from the cores between saturation and 60 cm. of water tension and from saturation and oven dry weight, the volume of the non-capillary or macro pore spaces and total porosity of the respective soil cores were determined. A total of 10 soil cores were taken at each depth, for each plot area. The values expressed in Tables 5 and 4 are the averages of four repli- cations for each treatment. 4. Infiltration Studies In 1958 and 1959 studies were undertaken to determine the effect of tillage processes and organic matter treatments on the infiltration rate of water through this soil. Two types of infiltrometers were used to obtain the infiltration rates. One type, the double—ring infiltrometer, consists of two six inch long, concentrically placed cylinders, measuring five inches and nine inches in diameter respectively, were driven two or three inches into the soil with the least amount of soil disturbance as possible. Water was then im- ponded to a shallow depth in the inner compartment through the use of a reservoir system, which enabled the maintaining 27 of a constant head of water and also provided a means of measuring the volume of water delivered over a period of time. Water was also imponded to a one inch depth in the outer com- partment by manual application, to buffer the lateral flow of water from the inner compartment. Ten of the double—ring infiltrometers were used on each replication of each plot area in this study in an effort to obtain a value as close to the mean as possible. The infil- tration rates were obtained for the soil at the existing soil moisture content by applying water to the soil for a period of about two to three hours, or until the rate of water in- take remained the same over a period of one hour. The rings were allowed to remain in the soil after this series of read- ings and the soil was allowed to drain for twenty-four hours and the process was repeated. The data presented in Table 9 are the equilibrium infiltration values. The FA type infiltrometer or rain simulator was the second type of infiltrometer used to obtain the infiltration rates for this soil. This method has also been used to a considerable extent to determine both the infiltration and runoff rates for research plots. Wilm (95). Fischback and Duley (25), Duley and Domingo (16) and others have used the FA infiltrometer to determine the water intake rates of various soils. This method consists of driving a seven inch high metal frame, measuring one foot in width by two and one- half feet in length, three inches into the soil, again with 28 the minimum amount of disturbance to the natural soil struc- ture. The entire area bounded by the metal frame and also a border area of one and one-half feet were wetted by a sprinkler system. The wetted border area provided moisture for buffering the lateral flow from the pan area. The sim- ulated rainfall was applied by a spray nozzle positioned so that the water was sprayed up into the air and would then fall back to the soil similarly to rain drops. The drops of water produced by these nozzles were relatively large sized. The entire mechanism of the sprinkler and metal frame were enclosed by a tent, to reduce the amount of wind disturb— ance on the falling water. The water was supplied to the sprinkler at a constant pressure of 15 p.s.i. by a centrifugal pump from a large mobile water supply tank. Rainfall intensities were determined from a 10 to 15 minute calibration run made either prior to or after each soil infiltration determination. The amount of runoff water was measured volumetrically and the difference between the applied rainfall and the amount of runoff was assumed to be the infiltration rate for that soil. After the initial runs were made under the prevailing soil moisture conditions the Inetal frames were allowed to remain in the same location and a second determination was made at the end of 24 hours which was called the wet run. The application of water to these areas continued until the runoff rate remained constant for 29 a period of thirty to forty—five minutes. The values pre- sented in Table 10 are the infiltration rates obtained under the above described conditions. 5. Soil Moisture Measurements With the introduction of the neutron scattering probe "i situ, for measuring soil moisture a relatively large number of measurements can be made over a short period of time. The theory and application of this method for use in soil moisture measurements have been presented by Gardner and Kirkham (29), Van Bavel (84), McHenry (58) and others. The use of the Nuclear Chicago P-19 depth probe to de— termine soil moisture on this project began in 1959 and was used each successive year through the 1964 season. Each spring after the corn was planted, two aluminum access tubes, measuring two inches in diameter and 45 inches in length were placed in the corn row within each plot area. Placing of the access tubes in the corn row allowed for cultivation with- out disruption of the tubes. Each tube was inserted into the soil by augering out a hole the size of the tube with the minimum amount of disturbance of the soil around the hole. The tubes were stoppered to prevent evaporation and possible plugging by foreign objects. Moisture measurements were taken within each tube at six inch intervals to a depth of 56 inches, periodically during each growing season, to trace the moisture depletion by the corn crop. The access tubes were removed from the plot area each fall and reused the following year. 50 The P-21 Surface Moisture Probe was used to obtain the moisture content of the top 12 inches of soil during the 1961 to 1964 growing seasons. The compiled moisture data are presented in Tables 11, 15, 15, 17, 19, and 21, and are averages of eight determin- ations for each treatment. 6. Oxygen Diffusion The use of the platinum microelectrode as a method to determine the rate that oxygen diffuses through the water film surrounding the plant roots was first introduced by Lemon and Erickson (47). In the years following its introduction, this method has become very pOpular for characterizing the soil aeration status. Oxygen diffusion readings were taken at varying depths on both the shallow plowed and the deep tilled areas to de- termine the effect of depth of tillage on the rate of oxygen diffusion to the plant root system within the depth sampled for the 1959 and 1961 growing seasons. Tables 25, 24, and 25, show the results of these determinations. 7. Root Studies Preliminary studies were undertaken in 1960 to determine the effect of depth of tillage on the penetration and prolif— eration of the corn root system within the soil profile. A metal frame, measuring 4 inches by 21 inches by 24 inches was constructed to remove a slice of soil from the 51 wall of a pit dug perpendicular to the corn row. The metal frame was adjusted so that one side split the corn stalk in half and the other side extended into the center of a 42 inch row spacing. The top of the frame was placed directly at the soil surface and the bottom extended to a depth of 24 inches, which was just below the depth attained by the giant disc plow. It is assumed that inasmuch as the corn plants were spaced at 8 inch intervals, the samples obtained repre- sented one-fourth of the total root system to a depth of 24 inches. Each slice of soil was sectioned vertically at 5, 9, and 15 inches from the center of the corn stalk. It was then sectioned laterally at 6, 12 and 18 inches from the soil surface. Each individual soil section of the total slice was then placed in a wire screen basket and washed free of all soil particles. The corn roots remained on the screen during the washing process and were then removed, oven-dried and then weighed. The same procedure was used in 1961 to obtain root sample weights from the respective treatments. A modified procedure employing the same method used by Foth (26) was used in 1962 and 1965 to obtain the root samples. This method employs the use of a smaller steel frame, measuring four inches by 12 inches by 24 inches. The slice of soil was taken from the wall of a pit dug between two rows of corn. The metal frame was centered between the two adjacent corn plants to assure an even distribution of 52 roots within the sampling area. After removing the block of soil and roots from the pit, the slice of soil was sec- tioned vertically in half and laterally at 6, 12 and 18 inches. Each section of soil was then washed free of soil, the roots were removed and oven—dried then weighed. This method of sampling reduced the total number of samples to be washed, however, it did give sufficient information to char- acterize the effect of the tillage operations on the amount of root proliferation into each soil layer sampled. The root samples were taken after the corn plants had reached the tasseling stage. According to Foth (25), the density of corn roots in the lower soil depths sampled did not increase to any extent after the corn plant had reached this state of maturity. II. Methods of Statistical Analysis of Data Over the period of years that this research was conduct- ed, a considerable volume of data was obtained that was influenced by many variables. The data were therefore sub- jected to analysis of variance to determine if any significant differences existed due to the various treatments. The analysis of variance was done by the Control Data Corporations 5600 computer in the Michigan State University Computer Laboratory. Each analysis was made on the basis of a split plot design. The number of splits ranged from a one— way split up to a three-way split according to the number of 55 treatments and samplings involved. Inasmuch as the plowing depths were of primary interest, they were always considered as the main plots. The supplemental organic matter treat- ments were usually considered as the first sub-treatment, with the depth of sampling or fertilizer treatment acting as the second split of the main plot area. The third split of the main treatments usually entered in the number of determin- ations obtained for each second sub areas. The analysis of variance is given in table form for all determinations as F—values and the values for least signifi- cant differences are given where applicable. Additional analysis of variance analyses were made on the yield data, after close observation of these yields gave indication that the depth of plowing did increase crop yields, though not verified by the analysis of variance using the split plot technique. Error variance within years was pooled for testing interactions between plowing depth and years. The plowing depth by year interaction mean square was used to test effects of years and the long term effects of plowing depth, as described in Snedecor (74). The results of this analysis are included with the other results in their re— Spective tables. RESULTS AND DISCUSS ION Soil Test Results as Influenced by the Tillage Depth, Supple— mental Organic Matter and Rate of Plow Down Fertilizer Before the first deep—mixing operation was performed in 1956, soil samples were obtained at the 0-9 inch and 27-28 inch depth to determine the nutrient status. The analysis were made in the Michigan State University Soil Testing Lab- oratory using the following extracting procedures: (1) phos- phorous and potassium were extracted by the Spurway Reserve test, using a 0.15 N HCl extracting solution, (2) calcium and magnesium were extracted with the Spurway Active Test, employing a 0.018 N HAc extracting solution. The results of the 1956 soil test are presented in Table 1 as pounds per acre. The pH values are also presented in the same table. In 1961 the soil was again sampled at the 0-9 inch depth to determine if the various treatments had influenced the nutrient status of the soil. The analyses were again made in the Michigan State University Soil Testing Laboratory, however, the extracting procedures were changed as follows: (1) phos— phorus was determined by the Bray P1 test, employing a 0.25 N HCl plus a 0.05 N NH4F extracting solution, in a 1:8 soil to water ratio, and (2) potassium, calcium and magnesium were determined with an extraction solution of 1.0 N NH4AC buf- fered at a pH of 7.0. The results of the 1961 soil test are presented in Table 1. 54 55 Table 1. The 1956 and 1961 soil test results for the Kalamazoo sandy loam soil, showing the effects of plowing depth, organic matter treatment and plowdown fertilizer rates. All values are averages of four determinations for each treatment. Plow Organic Fert. Pounds per acre of available Depth Matter Rate P K Ca Mg pH (lbs/A) 1956 Soil Test* 0-9 inches 48 84 (520 16 6.1 28 inches 50 64 (520 0 5.0 1961 Soil Test** (0-9 inch soil depth) Alfalfa 0 104 516 1824 104 5.9 Crop Residue 0 99 '182 1716 96 5.9 Shallow Alfalfa 500 122 558 1644 92 5.7 Crop Residue 500 110 250 1644 98 5.6 Alfalfa 1000 159 414 1812 68 5.6 Crop Residue 1000 151 526 1751 60 5.6 Alfalfa 0 71 220 1872 120 5.7 Crop Residue 0 68 152 1691 107 5.5 Alfalfa 500 75 246 1908 127 5.7 Deep Crop Residue 500 75 184 1716 127 5.6 Alfalfa 1000 101 520 1788 115 5.5 Crop Residue 1000 89 248 1648 107 5.4 *1956 Soil Test P and K determined by Spurway reserve (0.15 N HCl extract- ing solution). Mg and Ca determined by Spurway active (0.018 N HAc tracting solution). **1961 Soil Test P determined by "Bray P1 test" (0.25 N HCl plus 0.05 N EX" NH4F extracting solution in a 1:8 soil to solution ratio). K, Ca and Mg determined using a 1.0 N NH4Ac solution buffered at a pH of 7.0. extracting 56 The deep mixing process decreased the concentration of phosphorus and potassium in the surface soil and influenced the amount of calcium and magnesium very little. However, the mixing process did decrease the pH values slightly. The decrease in the phosphorus, potassium and pH were brought about by a dilution effect, through the mixing of the subsoil and the surface soil. The addition of a total of 15 tons of chopped alfalfa hay per acre for the most part increased the amount of phos- phorus, potassium, calcium and magnesium in the soil and at the same time increased the pH values slightly, especially on the deep-tilled areas. The amount of nutrients contained in alfalfa hay have been listed in Millar, Turk and Foth (60) as: 2.45% nitrogen, 0.5% phosphorus, 2.1% potassium, 1.59% caléium and 0.555% magnesium, per ton of dry material. The total amount added to this soil on the acre basis by the alfalfa treatment would amount to: 755 pounds of nitrogen, 150 pounds of phosphorus, 650 pounds of potassium, 417 pounds of calcium and 106.5 pounds of magnesium. As the fertilizer rate increased, the amount of phos- phorus and potassium in the soil increased, and at the same time the pH values decreased. The fertilizer rate had little influence on the calcium content of the soil, however, it did have a considerable influence on the magnesium content in the soil. As the fertilizer rate increased the amount of magnesium in the soil decreased. This was especially true 57 where the high rates of fertilizer were applied to the surface soil on the shallow plowed areas, where it decreased the mag- nesium content as much as 57%. This decrease could have occurred due to two or more factors: (1) the additional potassium ions added to the soil by the fertilizer may have replaced the magnesium on the exchange sites of the clay and organic matter, allowing the magnesium to be leached from the soil, or (2) the magnesium could have been trapped as inter- layered material between the illite (n: montmorillonite crystals, as the potassium ions caused a collapsing of these structures, as the soils dried out. Inasmuch as the ferti- lizer added to the deep-tilled areas was incorporated through- out the entire mixing depth, the influence of the potassium in the fertilizer on the magnesium content was not as great. Effects of Deep—Soil-Mixing on the Particle Size Composition of the Soil In 1959 the plowing treatments were sampled at four depths. These soil samples were then subjected to a pipette particle size analysis in the laboratory to determine how ef- fective the soil-mixing process had been in developing a uni- form soil mixture. Table 2 presents these data for the 1959 (and also includes the 1965 results) pipette analysis indi- cating the effectiveness of the soil-mixing procedure. The natural soil had a nearly uniform texture to the eight inch depth, due to the yearly manipulation of this soil layer for agricultural purposes. The clay content of this 58 Table 2. Summary of the particle size analysis of the Kalama— zoo sandy loam soil. Each value given is an average of four determinations for the shallow and deep—mixed treatments. Plow Depth of Percent Depth Year Sample Sand Silt Clay (inches) 1959* 0-5 60.4 28.5 10.9 5-8 59.5 29.6 10.9 11-14 65.7 21.9 14.4 Shallow 18-21 76.1 11.2 12.6 Plowed 1965** 5-6 55.2 51.7 15.1 12-15 59.8 24.7 15.5 18-21 72.8 15.9 15.5 1959* 0-5 60.2 26.5 15.1 5-8 60.5 26.2 15.5 11-14 62.5 24.5 12.8 Deep 18-21 69.2 19.1 11.7 Mlxed 1965** 5-6 56.9 29.1 14.0 12-15 59.5 25.8 14.7 18-21 65.4 22.5 14.5 *1959 Data are averages of four determinations using the pipette method of analysis. **1955 Data are averages of four determinations using the modified Hydrometer method of analysis. 59 soil increased 5.5% below the normal tillage depth. The deep- soil-mixing, which was repeated three times was successful in obtaining a nearly uniform textural composition throughout the tilled portion of the soil. After the deep-soil-mixing process was repeated in 1965, the soil was again sampled at three depths for a laboratory analysis of their particle size composition. The analysis employed a modification of the Bouyoucous Hydrometer Method of soil analysis as described in the experimental procedure. The results of the 1965 particle size analysis are pre- sented in Table 2 and again indicate that the deep-mixing process was able to obtain a nearly uniform texture through- out the depth of mixing. Effects of Deep-Soil-Mixing and Supplemental Organic Matter Treatments On the Laboratory Analysis of Soil Cores for Soil Moisture Holding Capacities, Pore Space Relationships and the Soil Bulk Density Soil core samples (three inches in diameter and three inches high) were obtained from three depths in the soil pro- file during the 1959, 1960, 1962 and 1965 growing seasons. These cores were then subjected to laboratory analyses to de— termine the amount of macro, micro and total porosity and the bulk density of the soil. The summaries of all of these data obtained from these soil cores are presented in Tables 5 and 4. The results of the analysis of variance of each year's data are presented in Tables 5, 6, 7, and 8, respec- tively. 40 Although there were considerable variations in the data obtained from the soil cores, these variations were not sig- nificantly related to treatment until 1962 when the analysis showed significance for all determinations except on the amount of water held in the soil at 60 cm. of water suction. Only the bulk density determinations were statistically sig— nificantly different in 1965. With the exception of the 1962 data the variability was so great between cores taken within a treatment that small differences due to treatment could not be detected. The influence of the depth of tillage on the pore space relationships, water holding capacities and bulk density measurements varied considerably from year to year and with sampling depth. As the primary interest of this research was to determine the influence of deep mixing on the dense B horizon, the major portion of the discussion will deal with the 12 to 15 and 18 to 21 inch sampling depths. Changes in Soil Properties at the 12 to 15 Inch Depth The 1959 soil mixing process increased the macro pore space 59% by volume, which showed high significance, and at the same time increased the amount of total pore space by 10.0% and decreased the bulk density of the soil, although neither of the latter two changes were statistically signifi- cant. However, in 1960 the bulk density measurements of this soil indicated a slight increase due to the deep tillage and in 1962 there was a significant increase of 0.1 g/cc 41 over that of the same depth on the shallow plowed area. During these two years the tillage treatments had little or no influence on the pore space relationships. After the 1965 revision in the tillage treatments, the 1X and 4X deep tilled areas were found to have: (1) significantly increased, (a) the total pore space by 9.0% over that of the shallow plowed areas, and by 15.9% over the 5X deep tilled areas, (b) the macro pore space by 56.0% over the shallow plowed area and 66.0% over the 5X deep tilled areas, and (2) sig- nificantly decreased the bulk density of this soil by 0.17 g/cc from those obtained on the shallow plowed areas and by 0-22 g/cc in comparison to the 5X deep tilled areas. Although the shallow plowed areas did contain the highest amount of micro pore spaces, followed by the 5X deep tilled area then by the 4X and the 1X deep tilled areas, the differ- ences were not significant. Changes in Soil Properties at the 18 to 21 Inch Depth In 1959 the deep tillage showed no consistent influence on the pore space relationships and even though the bulk density was reduced by 0.1 g/cc it was not a statistically significant reduction. In 1960 the deep tilled areas con- tained 2.7% and 14.0% more total and micro pore spaces re- spectively than did the corresponding shallow plowed areas. There was little or no influence on the macro pore spaces and bulk density values. In 1962 the deep tillage increased the micro pore space by 9.8% and significantly increased the 42 (1) total pore space by 4.0% and (2) the bulk density of the soil by 0.04 g/cc, resulting in a corresponding decrease of 8.0% in the macro pore spaces. The 1965 results indicated that the total pore space was significantly increased by 5.4% on all of the deep tillage treatments to that in the shallow plowed treatment. The 4X deep tilled area contained 4.4% more micro pore spaces than did the 1X deep tilled area and 11.0% more micro pore spaces than both the 5X deep tilled and shallow plowed areas. All treatments contained approxi- mately the same amount of macro pore spaces. The bulk den- sity determinations prove to be the same for the 1X and 4X deep tilled areas and both were 0.04 and 0.08 g/cc less than those obtained on the 5X deep tilled and shallow plowed areas, respectively. Although the supplemental organic matter treatment showed trends of increasing the total pore spaces in the soil, these increases were only significant for 1960. The organic matter treatment did however increase the amount of micro pore spaces and the water held in the soil under 60 cm of water suction for the years 1960 and 1965. There were indications that these increases were existing during the other two years, however, they were not statistically significant. The al- falfa treatment did show less macro pore spaces than the control area in 1962 and the indications were the same for the other years, especially for the 18 to 21 inch sampling depth. The organic matter treatments did not have any influ- ence on the bulk density measurements of the soil. 45 The depth at which the soil cores were obtained proved to display a significant influence on all determinations for each year except in 1965 when the amount of macro pore spaces were not significantly influenced by sampling depth. In general the amount of total and micro pore spaces de- creased with increasing depth of sampling as did the moisture holding capacities of the soil. The macro pore spaces were usually lower in the 12 to 15 inch depth of sampling than in the 18 to 21 inch depth, with the 5 to 6 inch depth having the highest amount of macro pores of the three layers sampled. The bulk density of the soil displayed a definite in- crease as the depth of sampling increased to 12 to 15 inches and then decreased slightly at the 18 to 21 inch depth, in respect to that of the preceding layer. The immediate effect of the deep tillage operation in the lower portion of the soil was to increase the amount of total pore space as well as the macro pore space, and at the same time decrease the bulk density of the soil. However, the long term effect of this tillage process, resulted in a reduction of the total porosity, as well as the macro and micro porosity and also increased the bulk density of the soil, in comparison to the values obtained for the natural soil. The addition of the chopped alfalfa hay did not have too much influence on the porosity and bulk density of this soil. There were indications that the alfalfa was increasing the amount of micro pore spaces. 44 Table 5. Summary of the soil core data obtained for various years at various depths in the soil on the Alfalfa organic matter treatment. All values are averages of 40 cores taken at each depth, except for the year 1959, which are the averages of 20 cores. . Sample Plow Year H20 H20 Macro Micro TPS B.D. Depth Depth Sat. 60 cm P.S. P.S. (inches) gm/cc Percent 5-6 Shallow 1959 55.9 20.8 16.6 27.2 44.1 1.51 1960 51.5 19.4 15.6 26.9 42.5 1.59 1962 51.5 20.8 14.2 28.1 42.5 1.58 1965 29.2 18.5 15.8 27.5 45.1 1.48 Deep 1X 1965 29.6 18.5 16.5 27.6 44.0 1.49 Deep 5X 1959 24.9 16.8 14.9 24.9 59.8 1.49 1960 29.1 17.5 17.5 25.5 42.8 1.47 1962 29.7 18.7 15.9 27.2 45.1 1.46 1965 26.5 17.5 15.7 27.6 41.5 1.59 Deep 4X 1965 27.4 18.2 14.1 28.2 42.5 1.55 12-15 Shallow 1959 26.1 17.5 12.6 25.5 58.1 1.46 1960 24.8 16.9 12.5 26.6 58.9 1.58 1962 27.8 18.2 14.0 27.0 41.0 1.49 1965 24.4 16.9 12.2 28.7 40.9 1.65 Deep 1X 1965 29.6 17.5 18.2 25.6 45.8 1.48 Deep 5X 1959 27.9 18.1 14.4 26.9 41.5 1.48 1960 24.5 16.7 11.9 26.7 58.6 1.60 1962 24.5 17.0 12.6 26.7 59.5 1.60 1965 25.2 16.2 11.8 26.4 59.2 1.69 Deep 4X 1965 50.1 18.4 17.5 27.2 44.5 1.48 8—21 Shallow 1959 25.5 20.6 9.2 52.7 41.9 1.58 1960 25.1 16.2 15.8 25.4 59.2 1.57 1962 26.0 14.8 17.5 22.0 59.0 1.52 1965 22.5 15.0 12.5 25.5 57.8 1.68 Deep 1X 1965 25.7 15.9 15.4 25.5 40.7 1.58 Deep 5X 1959 55.4 20.8 17.5 25.4 40.9 1.45 1960 25.1 16.2 15.8 25.4 59.2 1.57 1962 26.7 16.1 16.1 24.8 40.9 1.54 1965 25.0 16.2 14.5 26.4 40.9 1.64 Deep 4X 1965 25.1 17.0 15.0 27.5 40.5 1.62 ..VI: I . ........ Table 4. 45 Summary of the soil core data obtained for various years at various depths in the soil on the Crop Residue organic matter treatment. All values are averages of 40 cores taken at each depth, except for the year 1959 which are the averages of 20 cores. Sample Plow Year H20 H20 Macro Micro TPS B-D. Depth Depth Sat. 60 cm P.S. P.S. ' (inches) gm/cc Percent 5—6 Shallow 1959 29.4 18.1 16.6 26.7 45.5 1.48 1960 29.4 18.5 15.5 26.5 41.8 1.45 1962 28.5 19.7 12.5 28.6 41.0 1.47 1965 50.5 17.8 18.5 25.8 44.5 1.45 Deep 1X 1965 29.5 16.7 17.6 26.2 45.6 1.49 Deep 3x 1959 29.0 15.9 17.9 24.5 42.5 1.46 1960 27.2 17.5 14.5 25.2 59.7 1.46 1962 28.7 17.6 16.4 25.9 42.5 1.47 1965 27.1 16.0 17.1 24.7 41.8 1.55 Deep 4X 1965 26.7 15.6 15.9 24.7 40.6 1.59 12-15 Shallow 1959 24.0 17.1 11.1 27.7 58.8 1.62 1960 25.4 15.2 12.7 24.0 56.7 1.58 1962 25.0 15.9 14.0 24.4 58.5 1.54 1965 24.5 15.6 14.5 25.5 59.7 1.65 Deep 1X 1965 50.4 17.4 19.1 25.4 44.5 1.46 Deep 5X 1959 50.4 17.6 18.5 25.5 45.8 1.46 1960 22.8 15.4 11.9 25.0 56.9 1.62 1962 24.5 15.9 15.4 25.2 58.6 1.65 1965 21.4 14.9 11.0 25.2 56.1 1.69 Deep 4X 1965 29.5 16.5 18.8 24.4 45.2 1.47 18-21 Shallow 1959 24.7 10.9 21.5 17.1 58.4 1.56 1960 25.8 9.4 25.4 15.1 56.5 1.54 1962 25.7 15.6 18.4 20.6 59.0 1.52 1965 22.8 12.5 17.0 20.7 57.7 1.66 Deep 1X 1965 25.2 1 .0 16.2 25.8 59.9 1.61 Deep 5X 1959 27.5 14.9 18.9 22.4 41.1 1.51 1960 25.8 15.4 19.1 20.4 59.5 1.55 1962 24.7 15.9 16.7 22.1 58.8 1.58 1965 25.8 15.6 16.4 22.1 58.5 1.62 Deep 4X 1965 26.1 1- 4 16.5 25.7 40.2 1.55 46 Table 5. Analysis of variance of the 1959 soil core data. F- Values Percent Treatments H2O at H2O at Macro Micro TPS B.D. Sat. 60 cm P.S. P.S. ALgm/cc) Plow 0.78 0.52 797* 1.06 1.65 0.95 Organic 1.8 2.19 1.42 1.27 5.88 10.7 P XOM 94.1* 7.77 0.05 4.59 51.2* 52.0* Depth 54.9** 10.1** 16.2** 6.9** 21.8** 29.5** P x D 7.1** 1.82 5.5* 1.01 5.56* 8.5** OM x D 0.62 2.29 2.09 5.42 0.65 0.92 P x OM x D 5.5* 0.52 5.2 2.44 1.28 4.8* Number 0.57 1.17 0.41 1.24 0.56 0.27 P x N 0.75 1.19 0.45 0.86 0.59 1.15 OM x N 1.21 1.48 0.97 0.85 1.54 1.18 P x OM x N 0.65 0.67 0.57 0.60 0.64 0.70 D x N 0.75 0.98 0.80 1.01 1.14 0.64 P x D x N 0.72 0.48 1.01 0.76 0.90 0.60 OM x D x N 0.68 0.85 0.90 1.17 1.01 0.74 PxOMxDxN 0.76 0.48 0.74 0.44 0.85 0.77 L S D values Plow 1.14 Organic 0.97 1.15 0.059 Depth 1.89 1.77 2.14 2.41 1.74 0.048 Plow = plowing depth; Organic = organic matter treatment; Depth = depth of samping, and Number = number of core samples taken at each depth, Sat. = saturation; 60 cm = 60 cm of water tension, Macro PS = macro pore spaces; Micro PS = micro pore spaces; TPS = total pore spaces, and B.D. = bulk density or weight/ volume of soil. 47 core sampling; Number depth; Sat. soil. saturation; P8 = macro pore spaces; Micro PS total pore space, and B.D. Table 6. Analysis of variance of the 1960 soil core data. F- Values Percent Treatments H20 at H2O at Macro Micro TPS B.D. Sat. 60 cm P.S. P.S. (gm/cc) Plow 1.41 0.00 4.97 1.54 0.21 4.68 Organic 5.61 18.9** 5.61 25.5** 14.0* 0.12 P x OM 0.05 0.72 2.22 0.70 0.15 0.14 Depth 77.6** 58.5** 19.9** 55.4** 57.4** 85.7** P x D 8.7* 10.5** 0.58 7.4** 10.4** 5.2* OM x D 1.82 5.46* 9.24** 6.6** 1.60 1.91 P x OM x D 0.17 0.41 0.07 0.67 0.92 0.55 Number 1.25 0.57 1.46 0.98 1.59 0.79 P x N 0.77 0.98 0.57 0.54 0.69 1.16 OM x N 1.98* 0.75 1.58 0.87 0.95 1.54 P x OM x N 0.64 1.22 1.49 1.60 0.79 0.67 D x N 0.89 1.05 0.97 0.74 0.87 1.10 P x D x N 1.61* 1.11 1.57 0.68 1.55 1.55* 10M x D x N 0.77 1.29 0.92 1.44 0.82 0.70 PxOMxDxN 1.57 0.77 1.10 0.92 1.05 1.11 L S D Values Organic 1.08 1.44 1.11 Depth 1.15 0.95 1.58 1.55 1.02 0.029 Plow = plow depth: Organic = organic matter; Depth = depth of = number of core samples taken at each 60 cm = 60 cm of water tension: = micro pore spaces, bulk density or weight/volume of Macro TPS'= 48 Table 7. Analysis of Variance of the 1962 soil core data. F- Values Percent Treatment H2O at H2O at Macro Micro TPS B.D. Sat. 60 cm 9.9. P.S. (gm/cc) Plow 1.74 1.28 0.01 0.02 0.05 11.4* Organic 2.55 1.59 0.08 0.81 1.65 5.74 P x OM 0.01 0.11 0.10 0.44 0.54 0.20 Depth 27.2** 21.0** 26.5** 16.5** 22.2** 55.8** P x D 0.54 1.80 2.57 2.47 0.49 0.59 OM x D 0.07 0.50 0.60 1.57 0.18 0.52 P x OM x D 0.76 1.00 0.29 1.02 1.56 0.42 Number 5.5** 0.91 2.54* 2.45* 2.09* 5.4* P x N 0.78 0.92 1.55 2.66** 0.46 1.59 OM x N 1.68 1.12 1.58 1.06 2.06 2.00 P x OM x N 1.66 1.66 1.17 1.25 1.47 1.54 D x N 1.15 1.00 1.56 0.94 1.17 1.15 P x D x N 1.25 1.54 1.50 1.44 1.05 1.92 OM x D x N 1.15 1.16 0.95 1.15 1.15 0.88 PxOMxDxN 1.14 0.96 0.95 0.94 1.08 1.56 L S D Values Plow 0.018 Depth 2.25 1.52 1.69 1.51 1.68 0.016 Number 0.80 0.74 0.57 0.55 0.006 Plow = plowing depth; Organic = organic matter; Depth = depth of core sampling; Number = number of core samples at each depth; Sat. = saturation; 60 cm = 60 cm water tension; Macro PS = macro pore space; Micro P8 = micro pore space; TPS = total pore space; and B.D. = bulk density or weight/volume of soil. 49 Table 8. Analysis of variance of the 1965 soil core data. F- Values Percent. Treatment H2O at H2O at Macro Micro TPS B.D. Sat. 60 cm P.S. P.S. (gm/cc) Plow 18.8** 4.1* 5.5* 0.50 14.5** 24.8** Organic 0.07 8.5* 14.5** 15.6** 1.12 1.50 P x OM 0.52 0.55 1.51 0.76 0.77 0.17 Depth 26.2** 26.0** 2.79 8.8** 24.9** 21.5** P x D 10.5** 2.55* 5.69** 1.09 8.57** 11.2** OM x D 0.15 0.50 0.69 1.06 0.57 0.55 P x OM x D 0.77 0.71 0.44 0.42 1.01 0.66 Number 1.96 1.02 0.97 0.59 1.89 2.0% P x N 1.02 0.77 1.06 0.71 1.14 0.92 OM x N 2.19* 0.58 2.54 1.10 2.12* 2.16* P x OM x N 1.12 1.00 1.00 0.88 0.98 1.14 D x N 1.05 0.59 1.46 0.52 0.78 0.86 P x D x N 1.14 1.25 1.15 1.45 1.52 1.00 OM x D x N 1.70* 1.71* 1.15 1.04 1.64 1.96* PxOMxDxN 1.27 0.92 1.11 0.59 1.26 1.10 L S D Values Plow 1.19 0.96 1.65 1.11 0.050 Organic 0.95 0.99 1.51 Depth 1.06 0.65 1.01 0.95 0.029 Number 0.018 Plow = plowing depth and number of times plowed deep; Organic = organic matter; Depth = depth of core sampling; Number = number of core samples taken at each depth; Sat. = saturation; 60 cm = 60 cm of water tension; Macro P8 = macro pore spaces; Micro PS = nucro pore spaces; TPS = total pore spaces; and B.D. = bulk . density or weight/volume of soil. 50 The porosity of the soil decreased with increasing soil depth and at the same time the bulk density showed a definite increase. The tillage treatment did show statistically sig- nificant interactions three of the four years between plowing depth and sampling depth. In some years there were increases in the porosity obtained and decreased in others depending on the length of time between sampling and deep tillage, while the reverse was holding true during the same years for the bulk density measurements. Water Infiltration Rate as Influenced by Deep—Soil—Mixing and Supplemental Organic Matter The rate at which water enters a soil is governed by the physical properties of that soil and any change in these properties, especially the pore space relationships, should reflect a change in the water infiltration rate. In 1958 and again'in 1959, studies were made to determine the influ- ence of the deep-soil-mixing and addition of chopped alfalfa hay on the water intake capacities of the Kalamazoo sandy loam soil. Two types of infiltrometers, the double-ring and FA type, were used each year in an attempt to characterize the water intake rate of this soil. The values shown in Tables 9 and 10 are averages of 10 double—ring infiltrometer units and two replications of the FA type infiltrometer respectively. The values presented under the "dry-run" heading for the double—ring units, were obtained under the existing soil 51 moisture conditions, which were well below field capacity. The "wet-runs" were obtained approximately 24 hours later, on the same locations of the "dry—runs." In 1958 a rain storm interrupted the crOp residue dry-run and therefore no data was obtained for either the double-ring or FA type in- filtrometers. In 1959 no datawere obtained for the double- ring wet-runs. In the comparison of these data obtained from the two methods it should be understood that there should be con- siderable differences in the infiltration rates obtained due to the methods of applying the water to the soil. The double— ring infiltrometers, of course, maintained a constant head of water, while the FA type is more closely associated to that of actual rainfall. Slater (75) found that the un- buffered ring velocities exceeded that of the sprinkler velocities by a factor of four, while Swartzendruber and Olsen (78) using rings of considerably larger diameters than Slater used, obtained a ring velocity that exceeded the sprinkler velocities by a factor of only three. An analysis of variance of the 1958 double-ring wet-run data indicates that although the deep tillage process did increase the water intake rate slightly, the increase was not significant. However, the chopped alfalfa hay increased the intake rate significantly on both the shallow and deep tilled areas, with a slightly larger increase existing on the latter of the two. Since the water movement through the 52 soil is governed by the amount of macro pore spaces, one would assume that the alfalfa treatment had increased the macro pore spaces of this soil. However, the information ob- tained from the 1959, 1960, 1962 and 1965 core data indicates that the reverse was true, in that the macro pore space was reduced, while the micro pore spaces were increased. There- fore the increase in water intake due to the alfalfa treatment ‘was obtained from some other factor than the influence of the alfalfa on the pore space relationships. Without a doubt the- greatest influence of the alfalfa treatment was on the stabil— ity of the soil aggregates due to the increased amount of ndcrobial gums which were acting as strong cementing agents. The increased soil aggregate stability allowed the water to enter the soil much more rapidly than did the crop residue treatments. As there were only two replications of the FA type infiltrometer and since the crop residue dry-run was rained out, no statistical analysis of the 1958 data was attempted. ‘The analysis of variance of the 1959 data gave no indications “that the water intake rates were being influenced by either 'the deep-tillage or alfalfa hay. However, the averages of tflne two determinations do indicate that the water intake Irate was greater for the alfalfa treatment than for the crop- :residue treatment. Had more replications been run on these 'treatments the indicated trends may have proven to be sig- nificant. 55 Table 9. Infiltration rates obtained on a Kalamazoo sandy loam soil through the use of double-ring infiltrometers. Each value is an average of 10 units replicated two times for each treatment. Plow Organic 1958 1959 Depth Matter Dry Run Wet Run Wet Run Inches per hour Alfalfa 5.6 4.8 12.6 Shallow Crop Residue 5.8 1.5 15.8 Alfalfa 10.1 5.5 10.2 Deep Crop Residue xxx 1.7 14.2 x XXCrop Residue dry run rained out. Table 10. Infiltration rates obtained on a Kalamazoo sandy loam soil, through the use of an FA type infiltrometer. Each value is an average of two replications for each treat- ment. Plow Organic 1958 1959 Depth Matter Dry Run Wet Run Dry Run Wet Run Inches per hour Alfalfa 1.79 1.49 2.16 1.68 Shallow Crop Residue 1.79 1.06 1.69 1.50 Dee Alfalfa 1.29 0.75 2.89 2.11 p Crop Residue xxx 1.52 2.02 1.44 x XXCrop Residue dry run rained out. 54 The Effect of Deep—Soil-Mixing and Supplemental Organic Matter on the Soil Moisture as Measured I§_§i£u Through the Use of the Neutron Moisture Probes In 1959, aluminum access tubes measuring 2 inches I.D. and 45 inches in length were inserted vertically into the soil within the existing corn rows. On seven dates during the growing season, soil moisture measurements were made at six inch intervals to a depth of thirty-six inches, using the P—19 Neutron Moisture probe. At the end of the growing season, the access tubes were pulled from the soil and were replaced within each treatment every year through the 1964 growing season. In 1961 and each year thereafrer the surface soil moisture (0-12 inches) was determined through the use of the P—21 Neutron Moisture probe in place of the P—19 probe. The summaries of the moisture measurements for the respective years are presented in Tables 11, 15, 15, 17, 19 and 21. The moisture data were subjected to an analysis of variance each year to test for significance of these data. The results of the analysis of variance are presented in Tables 12, 14, 16, 18, 20 and 22. These tables include both the F and LSD values obtained for each treatment. The depth of tillage displayed no significant influence on the soil moisture, except for one date in 1960, up until the year 1965 when the moisture readings showed significant differences on each date of that year. The analysis of var- iance of the 1965 data did indicate that both the depth of tillage and the number of times the soil was mixed deep were 55 exerting significant influences on the soil moisture. Figures 11a, 11b, 12a and 12b indicate that the influences of depth of plowing were somewhat varied for the surface and 12-inch moisture measurements. However, a general pattern did exist throughout these two depths of moisture measurements indicating that the 5X and 4X deep mixed areas were yielding higher moisture values than were the shallow and 1X deep mixed areas. The greatest influence of plowing depth existed at the 18-inch depth of measurement. At this depth, which is below that reached by the conventional moldboard plow, the shallow plowed area showed a considerably higher moisture content than the other areas and the 5X deep mixed area, for the most part, had a higher moisture content than the other two deep plowed areas. Even though the analysis of variance of the 1964 data gave no indications that the plowing depth was significantly influencing the soil moisture holding capacities, the same moisture pattern exists for this year as for 1965. This is especially true for the 18-inch depth of moisture measure- ments. From the 1965 and 1964 data, one can draw the conclusion that especially at the 18-inch depth of moisture measurement, the soil condition of the shallow plowed area was such that it restricted the removal of water by the growing plants. This also held true for the 5X deep mixed area, which had not been remixed to the 22—inch depth since 1959. These moisture 56 data along with the information gained from the soil cores obtained in 1965, would indicate that the soil physical con— dition had not been maintained as it was the first summer after the 1959 deep plowing treatment. In fact, the soil condition was such that plant root growth was restricted, as was the amount of water removed by the growing plants on this deep plowed area. The analysis of variance of the yearly moisture data in- dicated that the supplemental organic matter treatment of alfalfa hay increased the moisture holding capacities of the soil. Although these increases were not significant on every date of the moisture readings, for their respective years, these data for the most part showed significant increase in soil moisture due to the added alfalfa hay, especially at the 12-inch depth of moisture readings and lower. This increase due to the added alfalfa hay was also evident in the moisture holding capacities of the soil cores when placed under 60 cm. of water suction. It was also visible at the time of plowing each spring, inasmuch as the alfalfa treatments were much more moist than were the crop residue treatments and did present some problems in side slippage of the crawler tractor while deep-soil-mixing these areas. The depths of moisture measurements were highly signif- icant every year. These data indicate that the amount of soil moisture increased with increasing depth of moisture measurements up to the 18—inch depth and in some cases up to 57 the 24-inch depth, then the moisture content decreased with increasing depth of measurement beyond this point. As one considers these moisture readings and the information ob- tained from the particle size analysis (see Table 2), it is evident that the moisture content of the soil is closely associated with the clay content, as the clay content in- creased to a maximum around the 15 to 18-inch depth and below this depth the clay decreased with a corresponding increase in the amount of sand. Even though the particle size analy— sis did not extend below 21 inches, the texture of this soil was observed annually to a depth of 45 inches while augering out holes for inserting the tubing for the moisture measure— ments. It was very evident from these observations, that the sand content of this soil increased greatly below 22 to 24 inches and at the same time the clay and silt content de- creased. There were considerable amounts of interactions between the plowing depths and depth of moisture sampling as shown in the analysis of variance for the respective years. The 1959 soil moisture readings were consistently lower on the deep tilled plots at the 12 and 18—inch depth, than were the shallow plowed plots. However, the alfalfa deep tilled plots were giving higher moisture contents at the 24 and 50-inch depth than the shallow plowed plots. Assuming that the slope of the lines in Figures 5c and 4a are the result of a greater use of water by the plant root system due to the deep soil 58 mixing, then it also should indicate that the deep mixing has increased the amount of root growth in these areas to increase the water absorption area. The 1960 moisture data indicated very little interaction with plowing depth and sampling depth, however, there were considerable interactions between the organic matter treatr ment and sampling depths. These were especially noticeable in the 18 and 24—inch depth, where the alfalfa treatments had consistently higher moisture content on every data of moisture determinations. The 1961 soil moisture data did show tendencies for the deep-soil-mixing plots to give higher moisture readings than the shallow plowed plots at the 18 and 24-inch depth, however, the greatest influence at these depths was brought about by the alfalfa treatment, which increased the soil water holding capacity greatly. In 1962 the deep mixing process and organic matter showed a variety of influences at the different depths. The alfalfa deep tilled plots usually had higher moisture readings at the 12, 18 and 24-inch depths than the shallow plowed plots. At the same time the crop residue deep tilled treatments gave lower moisture readings on the 12 and 18—inch depths and higher moisture readings at the 24—inch depths than the shallow plowed plots. Again the alfalfa registered higher moisture values than the crop residue treatments. 59 Table 11. Percent soil moisture, on a volume basis, obtained on a Kalamazoo sandy loam soil, at 6 depths for 7 dates during the 1959 growing season, using the P 19 Neutron moisture probe Each value is an average of 8 observations at each depth for each treatment. = 1 Plow Organic’ Sample Dates of moisture readings Depth Matter Depth 6-17 7-1 7-20 7-29 8-10 8-24 9-15 (inches) 6 18.0 11.9 17.8 22.6 15.6 9.8 15.1 12 21.7 16.1 19.1 25.9 19.5 15.5 16.1 18 22.1 18.9 19.1 21.5 19.5 15.1 16.7 Alfalfa 24 17.6 15.8 15.5 16.1 15.5 15.2 15.5 50 15.5 12.1 12.5 12.2 12.2 10.1 10.8 56 12.2 11.4 11.4 11.2 11.7 11.0 10.7 Shallow 6 15.9 10.5 16.6 20.8 15.5 8.5 12.2 12 20.6 14.7 19.4 22.2 17.5 11.9 15.1 Crop 18 19.5 16.5 17.1 20.8 16.7 12.5 14.1 Residue 24 15.2 15.9 15.8 15.1 14.5 11.4 11.8 50 15.2 12.5 12.5 12.9 12.9 10.6 10.7 56 15.5 12.5 11.9 12.4 12.2 10.9 11.5 6 17.7 11.7 15.5 22.0 14.5 10.6 12.2 12 20.9 15.9 15.7 22.1 15.9 12.5 12.9 Alfalfa 18 21.8 15.4 12.7 20.8 16.7 12.9 15.2 24 21.6 16.1 15.6 18.9 17.2 15.7 15.6 50 16.4 14.2 12.4 15.8 15.5 12.7 12.2 56 15.5 12.2 11.4 11.6 11.6 11.9 11.0 Deep 6 16.7 11.1 17.4 20.6 15.7 9.9 12.5 12 18.8 11.8 14.9 20.1 14.1 10.5 12.1 Crop 18 18.9 12.1 12.6 18.7 15.9 10.5 11.2 Residue 24 15.8 12.0 11.8 16.2 15.5 10.5 10.8 50 12.4 10.5 10.6 12.4 11.0 9.7 9.6 56 11.8 10.7 10.1 11.1 10.6 9.9 9.9 60 Table 12. Statistical analysis of the 1959 soil moisture data, giving the results of the analysis of variance, by indicating the F and the LSD values for each treatment and the interac- tions. (**indicates significance at the 1% level and * indicates a significant difference in soil moisture at the 5% level.) F values Treatment‘ 6/17 7/1 7/20 7/29 8/10 8/24 Plow 0.21 2.49 9.26 0.26 2.90 1.64 Organic 28.1** 17.8** 1.04 4.64 9.7* 8.1* P x OM 4.45 5.80 0.56 1.24 0.86 0.40 Depth 88.7** 26.9** 16.0** 142.9** 58.4** 24.4** P x D 5.4** 6.0** 5.2** 5.0* 4.7** 5.8** OM x D 5.7** 2.56 1.54 1.97 1.76 2.05 PxOMxD 1.99 1.71 1.67 0.57 1.62 1.18 Number 1.51 0.72 0.15 0.50 5.56 1.47 P x N 2.17 1.06 0.91 1.04 7.99** 10.1** OM x N 0.01 1.54 2.42 4.06 2.85 5.01 PxOMxN 0.05 0.11 0.15 0.08 0.58 1.00 D x N 0.50 0.14 0.41 0.17 0.49 0.15 PxDxN 0.10 0.49 0.86 0.09 0.50 0.55 OMxDxN 0.16 0.15 0.72 0.14 0.10 0.59 PxOMxDxN 0.44 0.17 0.68 1.65 0.05 0.16 LSD values in percent Plow Depth Organic 0.96 0.68 1.26 1.05 Depth 0.99 0.95 1.81 1.07 0.99 0.87 Number 0.54 0.56 Plow = plowing depth; Organic = organic matter treatment; Depth = depth of moisture sampling; and Number = number of moisture determinations within each replication. 0030...... 0000 030.00". 09.0 II.II 0030.1 0000 3.9.4 I...|.| 826.1 26:95 323.... no.6 ..... I 0030.... 30:0...m 0:33. mkzm2h.mw._.wn_ FIG—m “.0 m0< 24 m. MEI—45 IU> 0mm3m>OmO mmmw MI... 02.130 mmhad zm>mm ZO 9......me mmth #4. .m_m >m mm:...m.02 4.0w hszmwn. MOE mafumom enema—z to .300 0550001 9.30.02 00 300 NNNNNNNNNN Nswswsssss \/ 580 6:. we 0.: ...... Econ 65 0 0.0 \\ Amy . . A3 .09 .09 .02 .0: -03 .8. . Om? 1.0m? . 0.0. .03 . 05 .09 .00. .00. .09 .05 . 08 1.09 .. 0.5 .09 .09 .08 .03 0.8 . ON .09 awnloA Kq aJnisgow waxed 62 0030.0 nova 03.0.00”. 00.0 I o In , 2.26.1 Q30 «:32. l.li 0030.0 30:05 03.0.3”. no.5 IIIIII 326... 26:95 2.22 mkzw2p< Z< m. w34<> IU>Om0 mmmw m1... OZEDO mmbqo 2w>wm ZO thmmO wwmI... ._.< .m_mm mmDhm.O.2 4.0m Pszmwn. mozzumom 0.3.3.02 .0 0.00 NNMNNNMNNM Egon cue. 1m 2. V .OE awnyoA Kq aqnisgow waxed Table 15. a Kalamazoo sandy loam soil, 1960 growing season, 65 Percent soil moisture, on a volume basis, obtained on at 6 depths on 9 dates during the using the P 19 Neutron moisture probe. Each value is an average of 8 determinations for each depth of each treatment. Plow Organic Sample Dates of moisture readings 1 Depth Matter Depth 4-5 6-20 7—5 ‘7-18 8—2 8-10 8-18 8-25 9 (inches) 6 24.3 14.8 13.8 9.1 11.7 9.3 7.5 8.1 12 25.5 25.6 23.4 17.5 16.0 15.3 14.6 15.0 1 Alfalfa 18 24.2 22.4 22.9 19.3 16.9 15.6 14.7 14.6 1 24 19.9 19.2 18.5 15.7 13.9 13.9 12.1 11.2 1 30 17.5 16.0 14.6 12.7 11.6 11.3 10.6 10.4 36 17.9 16.3 14.6 13.3 12.0 11.7 11.0 10.7 Shallow 6’ 23.6 14.2 13.3 8.5 11.2 7.8 9.1 '3 12 25.1 23.1 22.6 17.3 15.8 14.4 12.8 £2 1 Crop 18 22.4 20.9 19.4 15.6 13.6 12.8 11.9 13:; 1 Residue 24 19.2 19.1 16.7 14.5 12.7 11.8 10.9 ,3}; 30 18.5 18.2 14.7 12.9 11.6 11.0 10.4 0 36 19.1 18.2 14.9 13.6 12.1 11.4 11.1 g 6 22.5 14.6 11.5 15.7 10.6 9.2 10.1 12 24.3 23.5 18.3 17.1 15.9 14.7 15.6 1 18 23.8 T) 23.7 18.2 16.5 15.6 14.4 14.8 1 Alfalfa 24 23.0 a, 20.0 16.5 14.6 13.6 12.7 12.4 1 30 ~ 18.8 53 16.3 13.7 12.7 11.9 11.1 10.8 36 17.7 33 15.9 13.8 12.9 12.0 11.4 11.1 Deep Q 6 21.8 0 13.2 9.9 14.010.011.0 "g 12 21.8 :3 21.4 16.0 16.4 13.1 13.0 833 1 Crop 18 19.8 r0 18.7 15.0 14.7 12.1 11.7 .uru 1 Residue 24 17.8 ‘5 16.2 13.5 12.0 10.6 10.4 ,g;; 1 30 15.7 g 16.112.611.110.6 9.9 00 36 15.9 16.1 13.8 12.0 11.4 10.5 ,2 64 Table 14. Statistical analysis of the 1960 soil moisture data, showing the results of the analysis of variance, giving the F and LSD values for each treatment and the interactions. (**indicates a significance at the 1% level, and * indicates a significant dif- ference in soil moisture at the 5% level.) F values Treatment 7/5 7/18 8/2 8/10 8/18 9/18 Plow 0.46 0.18 11.9* 0.56 0.50 0.85 Organic 11.4* 8.2* 2.94 10.8* 4.60 1.62 P x OM 1.19 1.06 0.26 0.71 0.26 0.06 Depth 111.0** 85.8** 15.9** 45.0** 24.4** 56.9** P x D 1.55 2.58 2.05 1.95 0.84 0.18 OM x D 6.5** 4.5** 0.85 2.9* 5.9* 1.15 P x OM x D 0.51 0.56 0.40 0.82 0.40 0.14 Number 0.29 0.49 1.67 0.15 0.57 0.55 P x N 0.68 0.51 0.06 0.56 0.44 0.54 OM x N 0.10 0.45 5.5* 0.08 0.22 0.47 P x OM x N 2.75 2.22 0.57 4.2* 5.5* 2.54 D x N 0.97 0.72 0.75 0.54 0.10 0.54 P x D x N 0.54 0.67 1.17 0.25 0.55 0.12 OM x D x N 0.47 0.52 0.88 0.28 0.18 0.57 PxOMxDxN 1.45 1.12 1.11 0.72 0.47 0.25 L S D Values in percent Plow Depth 0.79 Organic 1.15 1.18 1.16 Depth 0.96 0.86 1.29 0.85 0.98 1.68 ZNumber 0.62 0.52 0.44 Plow = plowing depth; Organic depth of obtaining moisture determination; Number Inoisture determinations within each replication. organic matter treatment; Depth ‘ number of 0030.1 noon. 030.03. noLU l+ ll sz2~< 33213235323". no.6 ....... z< m. wDI.<> IU >m 95.0.02 I..Om hzwomma p.07. mmE000m 0.25202 .0 0.00 mmEumom 0.53.02 .0 .300 09:000.”. 0.5.0.02 .0 0.00 a. a 0n 8 0. m a m MmmodeAA mews wwwdwmmwuowowowowow wwwmwexwdomomoxwowfi 530 cue. 0. . Econ 65 N. face 55 0 1 G. o: as am. 2. 8 .09 .ON .03 10.0 d a .00.. .Od N a 00. 00. w. i ON? .O.—.—. .nle 00. .09 .1... m 00. .09 e . 00m .03 m 0.8 on. m 0mm 00. m a .QMN .OBF 0.5 00. 8m 00. 66 0030.1 0000 0307.0”. 020 lol Fzm2...< 003213265 0:23”. no.5 ...... z< m. wDI.<> IU> 6026:. 26:93 2.2.... (II Qmm3m >m mmaem_02 4.0m kzmummn. 0.0.“. mmEUmom 0...:um..02 .0 Oumo mmEUmom 0.35202 .0 Damn. mas—umvm 9:530: .0 wumo 88088 0000 80.88 m.m80.m 80.88 wwwdwwmmwmAamae wwdxwxwxoowaase ddxwxwxmomsAAxoxu Shoo SE 8 . Enos 6:. 8 £30 5:. 8 00 a. om a. 8 2. Om 0.0 0.0. 0.0. 0.9 0.: a. 0.: 0.: 8. u a 8. 8. .8. .u. 0.9 8. 0.3 m 03 0.3 on. m. 0.0. on. 0.0. a 0.0. 00. 0x. M 0k. 05 0.0. m 00. 00. 00. m a 00. 0.0. 08 08 08 08 0.8 08 08 67 Table 15. Percent soil moisture, on a volume basis, obtained on a Kalamazoo sandy loam soil, at 6 depths, on 8 dates during the 1961 growing season, using the P 19 and P 21 Neutron moisture probes. Each value is an average of 8 observations at each depth for each treatment. Plow Organic Sample Dates of moisture readings Depth Matter Depth 7-18 7—25 8-1 8-8 8-15 8-29 9-5 9-12 (inches) 0-12 9.7 13.6 15.8 13.3 7.6 20.7 18.8 17.0 12 17.2 15.2 14.6 19.4 16.9 21.8 22.4 21.1 18 17.0 16.7 15.1 16.4 16.2 18.3 19.2 18.3 Alfalfa 24 13.5 13.7 11.9 12.6 12.4 13.7 13.9 13.2 30 10.4 11.6 10.4 10.6 10.2 11.3 11.4 11.0 36 11.2 10.4 10.4 10.0 9.8 11.3 10.6 10.2 Shallow O-12 10.5 12.8 14.5 12.3 7.2 18.1 17.0 15.2 12 15.6 14.3 13.6 20.2 17.3 22.4 21.2 20.0 Crop 18 13.7 14.4 13.4 16.2 14.7 19.0 16.9 16.0 Residue 24 11.8 11.7 11.0 12.5 11.6 15.9 13.0 12.5 30 11.8 11.6 10.8 11.8 11.4 15.0 12.3 12.1 36 11.9 11.7 11.0 11.7 11.4 14.4 12.5 12.1 0-12 11.8 15.9 16.8 16.1 10.5 21.5 20.8 17.2 12 18.4 16.7 15.8 21.4 19.1 24.8 25.0 22.8 Alfalfa 18 18.8 17.1 16.3 19.4 18.4 23.7 25.0 22.1 24 17.1 17.1 16.0 17.3 17.0 21.7 21.9 19.6 30 13.8 15.3 13.3 13.7 13.3 18.6 16.6 15.6 36 12.3 12.7 11.7 11.6 11.5 15.8 14.7 13.9 Deep 0-12 11.1 15.3 16.4 14.4 9.5 20.1 18.7 15.5 12 15.9 14.6 13.8 19.9 17.4 22.0 21.9 20.0 Crop 18 14.9 14.4 13.1 16.9 15.8 19.4 19.2 18.0 Residue 24 12.6 12.6 11.4 13.1 12.6 15.6 14.8 14.0 30 11.0 11.1 10.4 11.6 11.2 14.4 13.0 12.3 36 11.5 11.0 10.4 11.2 11.1 14.6 13.1 12.3 68 Table 16. Statistical analysis of the 1961 soil moisture data showing the results of the analysis of variance, giving the F and LSD values for each treatment and the interactions. (**indicates a significance at the 1% level and‘* indicates a significant dif— ference in soil moisture at the 5% level.) F Values Treatment 7/18 7/25 8/1 8/8 8/15 8/29 9/5 9/12 Plow 1.95 3.19 1.65 3.75 4.71 2.49 8.69 6.16 Organic 35.7** 25.2** 13.5* 12.3* 18.6** 0.12 8.29* 7.8* P x OM 13.8** 6.9* 4.79 20.7** 22.8** 3.92 5.32 4.32 Depth 50.8** 26.5** 42.2** 81.7**108.3**111.2**128.5**102.9** P x D 0.85 1.94 1.30 1.01 1.56 2.5* 3.7** 4.0** OM x D 4.8** 3.1* 2.29 1.34 3.0* 2.7* 6.0** 3.4** P X OM x D 0.91 1.70 1.71 0.62 0.80 6.7** 2.5* 2.2 Number 1.64 1.49 0.07 0.55 0.62 1.04 0.97 0.08 P x N 0.16 0.18 4.4* 9.6* 2.59 4.3* 18.8* 21.8** OM x N 2.63 8.5** 6.6* 6.5* 2.48 0.00 7.4** 1.83 P x OM x N 0.10 2.00 0.01 5.1* 12.3** 1.70 1.73 6.0* D x N 0.82 0.34 0.89 1.10 1.11 0.80 1.34 2.25 P x D x N 0.57 0.43 0.45 0.53 0.59 1.08 0.82 0.48 OM x D x N 1.88 0.65 1.28 1.32 1.06 0.05 0.88 0.88 PxOMxDxN 1.15 0.09 0.26 1.11 0.91 0.38 0.11 0.45 L S D Values in percent Plow Organic 0.69 0.85 1.01 0.64 0.56 1.87 1.62 Depth 1.00 0.88 0.88 1.08 0.92 0.95 0.97 0.95 Number 0.52 0.49 0.57 0.49 0.99 0.74 0.57 Plow = plowing depth; Organic = organic matter; Depth = depth of obtaining moisture determination; Number = number of moisture determinations on each replication. 69 0030.0 0000 03200”. 00.5 I... 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Saou :2: Va 60 .0. am . 0 a. on /. 2. F . .. o.m \ II..\ \\.II / .09 d 9 .0: u 0 .09 m. .09 W .03 w m .00. a .00. .M a: m m .09 w G 6.9 .09 . .05 .00m 08 .600 .03 .03 .600 Table 19. a Kalamazoo sandy loam soil, 1963 growing season, probes. for each treatment. 75 Percent soil moisture. on a volume basis, at 3 depths on 9 dates during the obtained on using the P 19 and P 21 Neutron moisture Each value is an average of 8 observations at each depth Plow Organic Sample Depth Matter Depth 7-8 7—22 8-5 8-15 8-22 8-29 9—5 9-11 9-18 (inches) 0-12 '5.6 11.7 12.8 10.3 9.2 11.8 8.9 7.7 8.6 Alfalfa 12 11.6 18.0 18.1 16.0 14.2 14.9 13.6 12.2 12.4 18 18.5 20.2 20.5 19.7 18.6 18.9 17.8 17.4 17.1 Shallow 0-12 5.0 10.7 11.3 8.2 6.7 9.7 6.9 6.0 7.1 Crop 12 9.3 14.5 15.1 12.8 11.2 11.5 10.5 9 5 9.9 Residue 18 16.0 18.8 18.8 17.4 16.3 16.5 15.8 15.3 15.5 O-12 4.7 11.7 12.7 8.7 7.7 10.8 8.0 6.6 7.2 Alfalfa 12 9.2 14.3 14.8 12.3 11.4 12.2 10.7 10.0 9.9 18 12.4 14.3 14.5 14.3 13.8 13.4 13.0 12.5 12.5 Deep 1 X 0-12 4.6 10.8 12.1 8.1 7.0 9.8 7.4 6.2 6.9 Crop 12 9.0 14.5 15.1 12.1 10.9 11.9 10.6 9.5 9.6 Residue 18 12.1 13.5 14.3 13.4 12.6 12.8 12.2 11.5 11.4 O-12 6.1 13.6 14.5 11.4 10.4 12.7 9.6 8.4 9.3 Alfalfa 12 14.0 18.3 18.1 16.0 14.4 15.0 14.2 11.0 13.0 18 18.5 20.1 18.5 17.5 16.1 16.5 15.5 13.3 15.3 Deep 3 X 0-12 4.8 11.1 15.3 7.8 7.0 10.2 6.7 5.7 7.3 Crop 12 11.6 15.4 14.9 12.8 11.0 11.8 11.1 10.4 10.7 Residue 18 15.2 17.8 15.3 14.5 13.5 13.5 13.0 12.5 12.8 0-12 6.7 13.4 13.8 10.4 9.6 12.0 9.0 7.7 9.1 Alfalfa 12 13.3 18.2 17.5 14.4 13.2 14.3 13.1 12.5 12.8 18 16.6 18.1 16.3 15.1 14.6 14.4 14.0 13.7 13.8 Deep 4 X 0-12 5.4 11.5 11.8 8.2 7.6 10.5 7.3 6.3 7.7 Crop 12 13.6 16.9 16.8 13.5 11.9 14.2 12.2 11.6 11.3 Residue 18 13.7 16.8 15.8 13.7 12.8 13.9 12.9 12.4 12.5 76 Table 20. Statistical analysis of the 1963 soil moisture data, showing the results of the analysis of variance, giving the F and LSD values for each treatment and the interactions. (**indicates a significance at the 1% level, and * indicates a significant dif- ference in soil moiSture at the 5% level.) Treatment F Values 7/8 7/22 8/5 8/15 8/22 8/29 9/5 9/11 9/18 Plow 11.4**73.4** 76.6* 34.3** 27.4** 7.8** 9.5** 9.5** 14.3** Organic 8.3**21.2** 9.6** 14.4** 19.3** 12.4** 14.3**10.0** 14.8** P x OM 0.44 2.61 1.47 1.35 1.26 1.61 1.33 0.54 0.89 Depth 593** 463** 135** 422** 576** 181** 587** 511** 374** P x D 12.7**16.6** 11.7** 9.9** 14.0** 14.2** 16.4**14.0** 11.0** OM x D 4.0** 1.59 0.50 0.14 0.08 0.04 0.19 0.44 0.24 P x OM x D 0.94 2.05 0.54 0.75 0.56 1.12 0.92 1.57 0.37 Number 0.40 2.71 0.56 1.43 1.86 0.06 0.30 2.18 1.86 P x N 0.01 0.03 0.13 1.41 3.00* 5.2** 4.5** 5.2** 3.7* OM x N 0.31 0.06 0.82 0.16 0.10 2.41 0.17 1.73 1.13 P x OM x N 0.11 0.02 4.3** 2.57 1.05 3.5* 1.81 1.76 1.09 D x N 0.99 0.12 0.07 0.56 0.20 0.01 0.17 0.09 0.07 P x D x N 0.90 0.07 0.54 0.46 0.38 0.41 0.62 0.85 0.76 OM x D x N 0.20 1.82 2.18 0.46 0.48 0.47 0.26 0.14 0.19 PxOMxDxN 0.52 0.24 0.47 0.23 0.27 0.64 0.25 0.17 0.27 LSD Values in percent Plow 1.31 0.46 1.07 0.60 0.55 1.02 0.85 0.86 0.81 Organic 0.97 0.72 1.19 1.13 1.02 1.05 1.03 0.93 0.84 Depth 0.58 0.40 0.58 0.46 0.40 0.43 0.37 0.43 0.44 treatment; Depth = Number = number of Plow = plowing depth; Organic = organic matter depth of obtaining the moisture determination; moisture determinations taken per replication. 77 .5. 3:6: noon |..|. .szqummh xm 8265 ammo ||||| IU< z< m. x? 326E aooo ....... m:..<> IU>Om0 moor MI... 02350 mw._. >m 95.5.02 45m Fzmumma 3.9“. mmEomom 0.3362 .0 End mmEommm 0.25302 F0 oumo mmEomom 0.25302 .0 3.3 mt. wwmpagem 41.....th mommy... wwwfi 92$“. £98 :8: 9 . £30 55 m. . 323m .03 low :OM .Ilf xx. AUV Amy Ad; . 0.9 . .om .ov .03 5.9 do d 9 on; .0: too m a .09 5m. ox w 10.2 6.9 do w. : O.mr .O.VF . ow m .09 6.9 6.9 m 6.8 5.9 5.: m .08 .9: 69 m 5% .09 . 1.0.9 m /.\. 9 .08 6.9 .\ 6.3 .\ ..o.v~ ca .69 78 xv 326E aooo Ill. KM 0030:”. 0000 ||||| x. 0026.1 0000 U0>>o_n. 30. .95 030307.. no.0 ”2.szng mmEom0m 0.33.02 .0 0.00 m 80 000 wwawwWwwow 5.00.0 not. me .0. v v i. .v 4' _. . v A. 0.0.. 0. : ON... ON? QVF 0.9. .00F ONF 0.0? 0.09 0.0m 0am 0.NN m34<> IU< Z< m. .memm mm:...m.0.2 ZOthmz rmun. QZ< QTn. < If; 0mm3m>OmO mmmr NIH OZEDO mm... >m mm:...m.OZ 4.0m hszmma N707... mmfumém 0.23202 .0 03mm. .. ax m @omVon mhh emow 5.00.0 50:. N? Am. . 0.0.. .00.. mmEum0m 0.3.20.2 .0 03.00 m m or O Ow O www.0muww 000.com .3 0M— 1.0.3. .09. . 0.0.. eumloA Kq aJmspow waxed Table 21. a Kalamazoo sandy loam soil, 1964 growing season, 79 at 3 depths, Percent soil moisture on a volume basis, obtained on on 6 dates during the using the P 19 and P 21 Neutron moisture probes. Each value is an average of 8 observations at each depth. Plow Organic Sample Dates Depth Matter Depth 7/=O 7/27 8/3 8/10 8/17 8/24 (inches) 0-12 11.9 7.0 6.0 4.9 6.6 1.59 Alfalfa 12 18.2 14.3 15.1 12.6 14.3 35.4 18 22.9 20.3 18.2 18.2 20.4 38.9 Shallow 0-12 10.1 6.0 5.7 4.3 5.9 13.6 Crop 12 15.9 14.0 13.7 13.2 14.3 30.8 Residue 18 18.8 15.0 13.9 14.5 13.6 26.3 0-12 10.2 6.0 5.9 4.4 6.2 14.9 Alfalfa 12 18.8 14.4 14.1 12.1 13.7 28.3 18 19.5 17.9 15.9 14.9 15.3 27.5 Deep 1 X 0-12 10.0 5.4 5.8 4.2 6.1 14.3 Crop 12 18.4 14.1 14.1 12.5 13.9 30.8 Residue 18 18.5 15.6 14.1 14.5 14.0 29.2 0-12 12.8 7.3 7.8 5.2 8.4 17.2 Alfalfa 12 20.7 15.6 15.0 13.9 14.3 30.4 18 24.1 16.5 15.3 14.9 14.5 27.0 Deep 3 X 0-12 11.1 6.4 6.8 5.1 7.9 14.5 Crop 12 19.6 14.4 13.8 12.9 14.2 27.8 Residue 18 21.3 14.0 12.9 13.6 12.7 24.8 0-12 11.8 7.0 7.1 5.2 8.0 16.8 Alfalfa 12 19.4 15.5 14.5 13.3 14.2 33.5 18 21.8 16.0 14.7 14.2 14.3 31.0 Deep 4 X 0-12 11.8 6.9 7.0 5.0 7.6 14.0 Crop 12 19.5 14.7 13.8 13.2 14.2 29.8 Residue 18 21.0 14.7 13.3 13.4 13.5 25.6 Table 22. 80 LSD values for each treatment and the interactions. a significance at the 1% level, * indicates a significant differ- ence in soil moisture at the 5% level.) Statistical analysis of the 1964 soil moisture data showing the results of the analysis of variance giving the F and (**indicates Treatment F Values 7/10 7/27 8/3 8/10 8/17 8/24 Plow 4.90 0.18 0.47 1.10 0.92 1.92 Organic 1.16 7.89* 7.42* 3.79 5.70 1.82 P x OM 0.25 0.39 0.48 0.64 0.85 0.68 Depth 124.0** 485.0** 325.0** 1065.0** 272.0** 241.0** P x D 1.33 3.3** 2.7* 5.9** 5.5** 2.29 OM x D 0.29 7.8** 4.4* 6.2** 8.5** 2.44 P x OM x D 0.30 0.94 0.46 2.3* 2.2 1.69 Number 0.53 0.11 0.03 0.01 1.97 2.55 P x N 0.53 0.89 0.29 0.51 1.96 1.99 OM x N 0.26 2.20 0.55 0.84 0.47 6.0* P x OM x N 1.10 1.40 1.80 0.95 0.83 1.48 D x N 0.27 0.55 0.04 0.68 0.58 1.06 P x D x N 0.40 0.31 0.45 0.42 0.49 0.74 OM x D x N 0.26 0.61 0.75 0.03 0.12 1.84 PxOMxDxN 0.45 0.81 1.30 0.15 0.68 0.63 LSD Values in percent Plow Organic 1.15 0.99 Depth 1.27 0.68 0.80 0.41 0.47 1.01 Plow plowing depth; Organic organic matter treatment; Depth = depth of obtaining individual moisture determinations; Number = number of moisture determinations obtained per each replication. 81 Xv 0030.0 0000 Iloll .hzwihxxwmh xn 2.26... none IIIII 1040 “.0 Ihmwo 104m «0“. sz...< 2.4 m. x. 0026;. 930 ....... wD..<> 104m .memn. meHm_02 ZOmhnmz Run. 02.4 070 < I.._>> 326E 26:95 III omm3mmm zO m._m._ >m wmohm52 4.0m Pszmwn. 9.0.“. mmc_om0m 0.25302 .0 0500 mmEum0m 0.25202 .0 0500 mmc.um0m 0.25302 .0 0500 m m m a 0m 0m 0. m a 0m 0 m m .04.... wwwmwu. WM..000 Same 5:. m. . :33 5c. 9. .2. 032$ .09 . .09 .00 .0. I .m. .00. on. .00 .ON—. .O.V—. .ON MW .oo. .09 .00 w 0.: .00. 0.0 w. .09 .05 0.9 w. 6.9 Om. 0.: m J 6.8 0.9 .00. a G. .O._.N .OdN .Oflr K 0.8 .03 .03 m n 0.3. .08 .09 w .ovm .08 0.0. comm 0% of 08 0mm 09 xv 0030.0 0000 II.|I .FZNZHdflm... xm 0030.0 0000 lllll 1060 00 Ih0m0 1040 000 mZO_....mm._.mO HIO_w 00 w0< 24. m. x. 0030.0 0000 uuuuuuu w34<> 1060 .mem0 mm:...m.02 ZOKFDMZ .mun. OZ< GTO < I..._>> 0026.0 26:05 III Dmmam >m meHm.O.2 4.0m Pszmm0 3.0.0 22:000.... 0.25202 .0 0500 mmc_0000 0.25002 .0 0500 000.0000 0.25002 .0 0500 $0.00.... 7...... $0.... 00$... / 5000 5c. 0. 5000 rue. N. mumtam .77....\7.// 6. 0m. .. a. 0m. . . 2. om // 0.3 0.9 . .00 0.9 0.3 .0... d 9 0.0. 0.9 00 u. 2 w 8 40.5. .00. .00 1 00. 0N. 0.0. M .00. 0.0: 0.: m. .08 .00. .00. a _ .08 0.8 .0? m .ONN Oew .03 M .. n .Qmm .0.” . :00. w QVN . vQMN .00. _ _ 0.0m . 03 H. 0.: . . 83 The revision of the tillage treatments in 1963 resulted in considerable influence on the soil moisture holding capacities. In general the moisture readings at the 18-inch depths followed in the descending order, with the shallow plowed having the highest, then the 5X deep tilled plots, followed by the 4X deep tilled plots and the 1X deep tilled plots giving the lowest readings. The root weights obtained in 1963 at the 12 to 24-inch soil depth were greatly influenced by the moisture holding capacities of the soil. The total root development in these depths followed the reverse order of the moisture measure- ments, indicating that the total water use was greatest for the greater amount of root development. In 1964, the moisture measurements showed little influ- ence due to tillage except at the 18-inch depth, which followed the same pattern as the 1965 moisture measurements. Oxygen Diffusion Rate as Influenced by Deep—Soil-Mixing and Supplemental Organic Matter An active growing plant root system requires sufficient oxygen to maintain normal growth rates and any impedance to the oxygen supply for these roots will give a corresponding reduction in root growth. It has been substantiated that the amount of water held in the soil micr0pores will have a considerable influence on the rate at which oxygen reaches the plant root system. The controlling factors in the dif— fusion process is the diffusive properties of oxygen in water and the amount of water the oxygen must diffuse through 84 to reach the root system. Since the diffusive properties of oxygen cannot be governed, the only other possible chance of controlling the oxygen diffusion rate is to decrease the mean path of diffusion for the oxygen as rapidly as possible after the soil has been wetted. This could be accomplished by improving the macro—micro pore space relationships in the soil, allowing more air to diffuse into the soil more rapidly. The platinum micro-electrode oxygen diffusion equipment is widely used to determine the rate of oxygen diffusing through the soil solution to the plant roots. This equip- ment was used in this research to determine the influence of the tillage and organic matter treatments on the oxygen dif- fusion rates in this soil. In 1959 oxygen diffusion rates were obtained within the wetted plot area used for the FA type infiltration studies. The diffusion rates presented in Table 25 are averages of 10 electrodes taken on four separate days following the satur— ation of the soil by the FA infiltration studies. The oxygen diffusion rates obtained for the surface soil are well above the minimum amount of 40 x 10-8 g Og/cm2/min., established to maintain maximum root growth. The diffusion rates did de— crease on the fourth day of readings due to a heavy rainfall on the previous day. However, even these readings were only slightly below the minimum requirements for normal root growth. 85 On the first of September, 1959, additional diffusion rates were obtained from the 14 to 17—inch soil depth. This was accomplished by excavating a pit in the soil of suffi- cient size and depth for taking the required readings. After the pit was opened, water was ponded on the soil so as to saturate the soil. The first readings were obtained 24 hours after the last visible water had drained away. From the data presented in Table 24, at no timewere the plant roots under an oxygen stress of any extent, which would indicate that the dense B horizon of the natural soil was maintaining an oxygen diffusion rate sufficient for plant root growth. However, one must remember that under natural growing condi- tions the plant roots growing at this depth may be experienc- ing a lower supply of oxygen than is indicated by these determinations, due to the 14 to 17 inches of soil and water lying above these roots that the oxygen must diffuse through to reach the growing roots. The reduction of oxygen diffusion rates with each increasing depth of determinations has been well established by many researchers. From the information presented by Letey et al. (51) it would seem plausible that the plant roots are receiving less oxygen than the rates obtained indicate by these determinations. In 1961 additional oxygen diffusion rates were obtained at varying depths in the soil under the alfalfa treatment only. These data are presented in Table 25 and are averages of 10 micro-electrode readings for each replication. 86 The surface readings were replicated four times, while the others were replicated only two times. It is apparent from these data that the surface soil drained rapidly after saturation, allowing a sufficient amount of oxygen to diffuse into the soil for both tillage treatments. However, as the depth of determinations in- creased, the oxygen diffusion rates decreased on both till- age treatments. The oxygen diffusion rates for the 9-inch depths on the shallow plowed areas were always lower than the corresponding depths of the deep tilled areas, with both indicating an oxygen stress for several days. The recovery rate after saturation was much slower for the shallow plowed soil (10 days) than for the deep tilled areas which required a total of only 6 days to return to normal. These data also record a decrease in diffusion rates for the shallow plowed area on the 25rd of June, caused by a light rain shower on the previous day. The shower did not decrease the diffusion rates on the deep tilled areas, however. The effects of the rain shower were also noted in the soil moisture determin- ations for the same time period (see Table 35), however, they were only sufficiently heavy to moisten the surface layer and did not penetrate to the 12-inch depth. The differences in the two series of oxygen diffusion rates obtained at the lower soil depth probably were due to the time of the season in which they were obtained. The 1959 diffusion rates were obtained late in the season after the 87 Table 23. Oxygen diffusion rates obtained on the Kalamazoo sandy :3 loam soil, at a four inch depth, following the FA type infiltra- -? tion studies. (All values are expressed in grams of oxygen-cm‘g- " min-1, and are averages of 10 electrodes.) ----- Plow Organic Date Rep. Rep. Ave. . Depth Mater 1 2 . Alfalfa July 20 49.4 54.4 51.9 Crop Residue July 20 38.8 43.8 41.3 Alfalfa July 21 51.2 49.1 50.2 Crop Residue July 21 38.2 40.0 39.1 Shallow Plowed ..... Alfalfa July 22 58.8 41.8 50.1 Crop Residue July 22 43.8 48.2 45.9 Alfalfa July 24 39.5 43.9 41.7 Crop Residue July 24 32.6 38.1 35.3 Alfalfa July 20 46.7 50.0 48.4 Alfalfa July 21 42.7 39.4 41.1 Crop Residue July 21 41.5 33.9 37.7 Deep Plowed Alfalfa July 22 48.2 43.6 45.9 Crop Residue July 22 45.2 43.0 44.1 E Alfalfa July 24 37.5 37.7 37.6 Crop Residue July 24 31.5 40.7 35.9 88 Table 24. Oxygen diffusion rates obtained on the Kalamazoo sandy loam soil, taken on four consecutive days at 14 to 17 inch depths after a hole had been filled with water and allowed to drain away. (All values are given in grams of oxygen-cm‘a-min‘l, and are averages of 10 electrodes.) —1. J Plow Organic Date Rep. Rep. Rep. Rep. Ave. Depth Matter 1 2 3 4 Alfalfa Sept. 1 34.6 42.5 31.9 47.1 39.1 Crop Residue Sept. 1 47.1 44.4 65.9 39.3 49.2 Alfalfa Sept. 2 34.7 42.7 31.2 30.2 34.7 Crop Residue Sept. 2 45.9 31.9 44.7 58.8 45.6 Shallow Alfalfa Sept. 3 44.9 49.6 50.4 51.2 49.0 Crop Residue Sept. 3 75.4 54.4 61.7 48.2 60.2 Alfalfa Sept. 4 48.8 53.4 58.7 55.5 Crop Residue Sept. 4 50.5 47.9 52.0 50.2 Alfalfa Sept. 1 44.7 48.1 41.5 50.0 46.1 Crop Residue Sept. 1 55.0 38.8 43.7 38.9 44.1 Alfalfa Sept. 2 45.3 30.1 60.7 35.2 42.9 Crop Residue Sept. 2 47.0 42.6 43.3 45.4 44.6 Deep Alfalfa Sept. 3 47.9 37.1 30.5 37.9 38.3 Crop Residue Sept. 3 44.7 44.1 60.9 40.4 47.5 Alfalfa Sept. 4 42.9 45.2 46.7 44.9 Crop Residue Sept. 4 48.3 43.7 50.3 47.4 A: HHJ 89 Table 25. Oxygen diffusion rates obtained in 1961 on the Kalamazoo sandy loam soil taken at various soil depths and on various dates, after the soil had been saturated with water. (Each value for the 4 inch depth is an average of 4 replications while the other values are averages of 2 replications only, with each replication using 10 electrodes. Each value is expressed in grams of oxygen x 10‘ /cm2/min.) Depth (inches) Date Shallow Plowed Deep Mixed 4 9 12 4 9 18‘ June 15 50.6 29.5 24.1 52.5 29.5 30.1 June 16 41.6 44.0 June 20 46.4 28.3 42.4 51.2 35.6 52.5 June 21 42.8 38.4 43.4 48.8 39.8 47.6 June 23 45.2 33.2 43.4 47.0 42.8 47.6 June 24 43.4 35.6 53.7 50.1 43.4 47.6 June 27 59.1 45.2 56.1 59.7 50.0 57.9 90 soil had experienced a considerable amount of drying during the summer months, which improved the amount of structural development in this clay layer, improving the oxygen diffu— sion rates. The 1961 diffusion rates were obtained before the soil had an opportunity to dry and therefore the struc- tural arrangement was such that the oxygen diffusion rates were reduced to such a level as to place the growing roots under an oxygen stress, thereby reducing the root development in these soil depths. The Effect of Deep-Soil-Mixing and Supplemental Organic Matter on the Amount of Corn Root Development From 1960 to 1963 the root distribution of the corn plants was studied. The method of obtaining the corn root samples is presented in the experimental procedures and was modified somewhat in 1962 and 1963 (see details in the experi- mental procedures). The weight of corn roots obtained from both methods showed the amount of root develOpment at each sampling depth as they were influenced by the specific plow— ing and organic matter treatment. Although the data in Table 26 shows a greater total amount of roots developing in the deep tilled treatments than in the shallow plowed treatment, the increases obtained were not large enough to be statistically significant until 1963 (see Tables 27 and 28). In that year the combination of the deep soil mixing and the number of times the soil had been mixed deep proved to have a significant influence on the amount of root development. The 1X and 4X deep mixed areas 91 increased the amount of root development, especially within the 12 to 24-inch sampling depth. At the same time the 3X deep mixed area increased the root development only in the 18 to 24-inch sampling depth of the crop residue treatment. The amount of root development at each sampling depth was considerably influenced due to the addition of the chopped alfalfa hay in respect to that of the crop residue treatments. The general pattern was that the alfalfa decreased the amount of root development at all sampling depths, except for a very few instances in 1962 and 1963. However, the decrease was more noticeable in the lower sampling depths (12 to 24 inches) and ranged from a low of 1/6 in 1961 to a high of 1/4 decrease in root weights in 1962 on the shallow plowed areas, while the 1963 results indicated no differences. The decrease was even greater for the 3X deep tilled areas and averaged close to a 50% decrease in root development, except in 1962 when the alfalfa treatment showed a slight increase in root growth. In 1963 the 1X deep tilled areas also decreased the root growth in the 12 to 24-inch sampling depth by approximately 50% and at the same time the 4X deep tilled areas responded in a 2-fold increase in root development. The analysis of variance indicated that the supplemental organic matter had a highly significant influence every year but 1963, when the variabil- ity of the various plowing depths removed the significance. The amount of root growth decreased with increasing sampling depth as one would expect. However, the decrease in 92 root growth was considerably greater at the 12 to 18 and 18 to 24-inch sampling depths on the shallow plowed areas than on the deep tilled areas. The difference in root growth due to the deep mixing process ranged from 1/3 to a 2-fold in- crease in root growth at the 12 to 18-inch depth on the alfalfa treatment (except for a slight decrease at this depth in 1962), and up to a 3-fold increase in root growth on the crop residue deep mixed areas. At the 18 to 24-inch depth of sampling the increase was even greater. The alfalfa treatments ranged from a 2-fold increase to a 5-fold increase. The crop residue treatments averaged about a 9-fold increase for 1960, 1961 and 1963, due to the deep tillage process and registered a slight de- crease in 1962. The statistical analysis indicated that the decrease in root growth with increase of depth of sampling was highly significant every year. It also indicated that the interactions obtained between plowing depth and organic matter treatments and organic matter and depth of sampling was highly significant every year but 1963. The increase in root growth with depth of sampling due to the deep tillage process gave a significant response in 1960 and 1961. A three way interaction between plowing depth, organic matter treat- ment and depth of sampling gave significant increases in root development every year but 1961. In comparing the information obtained from the soil core data and the field moisture measurements with that of the corn 93 root weight data, there appears to be a very close relation- ship existing between the amount of root development and the amount of water held in the soil by the micr0pores. Inasmuch as the alfalfa treatments showed a definite increase in the micro pore spaces, resulting in a greater water holding capacity, it also showed a reduction in the amount of root development, especially at the 12 to 24—inch sampling depth, when compared to the same depth on the crop residue treatments. The increased water holding capacity of the alfalfa hay treatments should have increased the "mean diffusion path" for the oxygen within the soil system, especially at the 12 to 24-inch depths, and in turn would decrease the amount of root development in these depths of soil. However, the oxygen diffusion readings taken in 1959 (see Table 24) indicate that at the 14-inch soil depth there should only be a very short period of time after soil saturation that the corn roots are actually undergoing an oxygen stress. That is if one assumes the oxygen diffusion rate of 40 x 10'Bg/cm2/min to be suffi- cient for maximum root development. The diffusion rates given in Table 25 are showing the influence of having removed the surface 12 to 14-inches of top soil so that the diffusion readings for the 19-inch soil depth might be obtained. The removal of this surface soil would in itself increase the possibilities of obtaining a higher diffusion rate at the 14- inch soil depth than might be obtained had the soil been left on the surface and diffusion readings taken through the full depth of soil. 94 Table 26. Grams of corn roots obtained by year from various depths in the soil, representing one quarter of the total root system to depth sampled. All weights are given in grams per 504 in? and are averages of 4 replications for each treatment. Plow Organic Sample Years Depth Matter Depth 1960 1961 1962 1963 (in.) Grams of corn roots/504 in? 0-6 1.42 0.27 6-12 1.53 1.76 0.90 0.12 Alfalfa 12-18 0.55 0.55 0.38 0.08 ‘ 18-24 0.13 0.13 0.36 0.05 Total 2.19 2.42 3.06 0.52 Shallow 0-6 1.40 0.25 Crop 6-12 2.85 2.85 1.21 0.45 Residue 12-18 0.60 0.60 0.52 0.11 18—24 0.21 0.19 0.46 0.03 Total 3.66 3.64 3.59 0.84 0-6 0.80 0.07 6-12 1.44 1.39 0.64 0.42 Alfalfa 12-18 0.99 0.97 0.52 0.12 18-24 0.61 0.73 0.67 0.11 Total 3.04 3.09 2.43 0.72 Deep 0-6 1.75 0.28 Crop 6-12 2.53 2.53 1.93 0.35 Residue 12-18 1.85 1.85 0.54 0.18 18-24 1.64 1.73 0.29 0.31 Total 6.02 6.11 4.51 1.12 Table 27. Analysis of variance of the corn root weight yields by years. F-- Values 1960 1961 1962 1963 Plowing depth 4.74 5.3 0.5 7.7 ** Organic Matter 120.0** 83.0** 17.3** 0.1 P x OM 14.2** 14.9** 7.7* 0.5 Depth of sample 48.2** 115.9** 28.6** 5.4** P x D 26.1** 28.9** 0.6 1.5 OM x D 10.6** 6.3** 5.9** 0.7 P x OM x D 6.9** 2.9 4.7** 3.7** LSD values (grams) Plowing depth 0.04 Organic Matter 0.17 0.18 0.05 Depth of Sample 0.18 0.21 0.07 0.03 95 Table 28. Grams of corn roots obtained on the Kalamazoo sandy loam soil at four depths, taken from the center of the corn row (15 to 21 inches from the corn plant), for the year 1963, show- ing effects of depth of plowing number of times plowed deep and organic matter treatment. Each value is an average of 4 repli- cations for each treatment. Plow Organic Depth of Root Total Depth Matter Sample Weight Weight Ave. (inches) (gm/144 in?) 0-6 0.077 6-12 0.034 Alfalfa 12-18 0.025 18-24 0.014 0.148 Shallow 0-6 0.070 Crop 6-12 0.129 Residue 12-18 0.030 18-24 0.008 0.237 0.192 0-6 0.14 6-12 0.278 Alfalfa 12-18 0.099 ' 18-24 0.027 0.544 Deep 1 X 0-6 0.075 Crop 6—12 0.090 Residue 12-18 0.157 18—24 0.104 0.426 0.485 0—6 0.021 6-12 0.121 Alfalfa 12-18 0.055 18-24 0.030 0.207 Deep 3 X 0-6 0.080 Crop 6-12 0.100 Residue 12-18 0.052 18-24 0.088 0.320 0.263 0-6 0.015 6-12 0.046 Alfalfa 12-18 0.083 18-24 0.093 0.237 Deep 4 X 0-6 0.078 Crop 6-12 0.072 Residue 12-18 0.039 18-24 0.039 0.228 0.232 LSD values (see Table 27 for analysis of variance). Plowing depth Depth of sampling 0.038 grams 0.030 grams 96 The 1961 oxygen diffusion determinations do indicate that the corn root systems were undergoing oxygen stresses especially at the 9-inch depth and it also shows that the deep mixed areas made a much faster recovery after the soil had been saturated than were the shallow plowed treatments. It has been well established that the oxygen diffusion rates will decrease with increasing soil depth even though the soil structure is uniform and that the oxygen concen- tration above the soil is maintained at a constant high level. The decrease in root growth with respect to depth of sampling can also be explained through the same principle, that is the rate of oxygen diffusion in this soil is decreas- ing with depth and the root production is also decreasing accordingly with depth. It is interesting to note that the decrease in root growth is less at the lower depths under the deep plowing treatments than for the shallow plowing treatments during the 1960 and 1961 growing seasons, with the same trend still persisting in 1962 and 1963. Corn Grain Yields as Influenced by Depth of Plowing Supple- mental Organic Matter Treatment, Plowdown Fertilizer Rate and Variety of Corn Plowing Depth and Grain Yields The corn grain yields are presented in Tables 29 and 30 as averages of the four replications of each treatment each year. Inasmuch as the original plot areas were revised in 1963, Table 29 just records the results of the original 97 plowing depths over the 8-year period. Table 30 consists of the yields results for the complete revision during 1963 and 1964. Each year the yields were subjected to an analysis of variance to determine if the yield differences brought about by the respective treatments were significantly differ- ent from one another. The results of this analysis are pre- sented in Table 31. The yield response from the deep-tillage operation re— sulted in an increased yield every year except one, 1962, when the shallow plowed area did outyield the deep tilled areas, but only by 0.9 bushels per acre. The increases ob- tained from the deep-soil-mixing process proved to be signifi- cant in three of the years. In 1963 and 1964 the influence of the number of times the deep-tillage process had been performed were significantly different but were very low yields. The corn grain yields reached a maximum in 1958 and then maintained a somewhat lower although respectible yield over the next three years, after which they started to decline. The reduction of yields in 1962 were not too drastic, hoWever, the 1963 and 1964 yields were reduced to such an extent that there was a crop failure. The reduction in yields during these two years can be accounted for due to insufficient rainfall during the growing season, and especial- ly during the period of pollination. The rainfall data pre- sented in Table 35, along with the moisture data obtained 98 "in situ" with the neutron moisture probe (see tables 11 through 14) indicate that the growing plants were undergoing serious moisture stress both years during the latter part of July and early part of August. At the time of harvesting the corn in 1964 it was noted that the plants were quite short and a good percentage of these plants were barren, so a plant and ear count was made of each plot area. The averages of the four replications are presented in Table 33, as is the results of the analysis of variance of these data. As can be seen from these data, there was no significant differences in the plant stand count, although the alfalfa shallow plowed area did have some 2000 plants per acre less than the others. It is also evi- dent that the depth of plowing had a highly significant in- fluence on the number of ears of corn produced on each plot area. The differences between the shallow and 1X deep tilled areas were not significant nor were the differences between the 3 and 4X deep-tilled areas. However, the 3 and 4X deep- tilled areas yielded approximately 48% more than the shallow plowed areas and 38% more than the 1X deep-tilled area. From the neutron moisture measurements made in 1964 (see Figures 13 and 14), it is evident that the soil moisture content was very low and that the 1X deep plowed areas were registering less moisture than the others. The shallow plowed plots had more moisture than the others at 18 inches deep, which would indicate that the plant root system was not able 99 to penetrate this dense layer of soil sufficiently well to remove the moisture that was there in the soil. The yield increases from the deep-soil—mixing only averaged 11.8 bushels per acre for all other treatments in- volved. However, the 8-year average increase due to the deep mixing on the 500 pound per acre plowdown fertilizer rate for the early variety of corn was 30.4 bushels per acre. Organic Matter and Grain Yields The supplemental alfalfa hay treatments also produced significant increases in yields every year except 1J1 1962 and 1963, when all treatments are considered. However, if one again uses the yields for the 500 pound per acre plow- down fertilizer rate, the alfalfa increased the yields sig- nificantly each year. The 8-year average increase for the shallow plow and deep mixed treatments were 25.8 and 29.0 bushels per acre respectively. The increase in yields due to the alfalfa treatment can be accounted for in part by the increased amount of water held in the soil at field capacity and also in respect to that held by the crop residue treatments throughout the season. This increased the available water for plant use and was very evident in the 1964 season, when all treatments experienced a considerable shortage of moisture. During that year all treatments maintained the same number of plants (see Table 33), however, the alfalfa treatments produced a con- siderably larger number of ears of corn per acre than did the 100 crop residue treatments. These increases ranged from 21% on the 1X deep tilled treatments to 54% on the 3X deep tilled treatments. Another factor that may have helped in increasing the yields, was the additional amounts of available nutrients supplied to the soil through the decomposition of the alfalfa hay. Plowdown Fertilizer Rates and Corn Grain Yields The influence of the plowdown fertilizer rates on the corn grain yields was quite variable and showed statistical significance only twice in the first six years of the re- search project. For all practical purposes the 500 pound per acre fertilizer rate returned the most consistent high- est yields. Because of this consistency in providing higher yields, the 500 pound per acre rate was maintained over the entire plot area after the 1963 revision of the tillage treatments. Variety and Grain Yields The pollination of corn is greatly influenced by the amount of available moisture in the soil and since the avail- able moisture varies as the rainfall varies during the growing season, an early and a late maturing variety of corn was planted in 1958, 1959 and 1960, to determine if the maturing date and available water would influence the yields. The yield results proved to be significant each year, however, 101 there were interactions between the variety of corn and the plowing depth during 1958 and 1959 that added to the influ- ence on the yields. The early maturing variety returned higher yields on the shallow plowed areas in 1958 than did the late maturing variety, however, the late maturing variety outyielded the early variety on the deep-tilled area. The reverse of this was true for 1959. As no moisture data is available for 1958, little can be said as to the influence of the moisture on the yields, except that the late maturing variety of corn must have been able to utilize the soil moisture more effec- tively on the deep tilled areas than was the early variety. According to the moisture determinations in 1959 (see Table 11 and Figures 3 and 4), there was little or not rainfall during the period of the month of August while the corn plants were undergoing pollination, and therefore the plants were required to utilize the available water stored in the soil, with the result that the late variety made better uti- lization of the water on the shallow plowed areas, as did the early variety on the deep plowed areas. Table 29. 102 loam soil as affected by depth of plowing, down fertilizer and variety of corn. 4 replications of each treatment. Yearly corn grain yields obtained on a Kalamazoo sandy organic matter, plow- Each value is an average of Plow Organic Years Depth Matter Fert. Var. 57 58 59 60 61 62 63* 64* 0 250 60.7 69.0 69.7 67.9 480 61.6 86.5 61.7 78.1 55.0 Alfalfa 500 250 64.6 90.9 71.8 68.7 18.9 480 62.8 92.3 67.2 79.4 59.1 23.1 10.0 1000 250 64.1 83.0 68.5 70.8 Shallow 480 70.5 81.3 65.4 67.6 57.2 0 250 46.0 68.4 60.8 65.7 480 42.8 72.7 59.2 71.3 54.8 Crop 500 250 52.3 78.1 73.0 59.5 27.4 Residue 480 45.2 82.3 62.4 69.8 56.7 31.4 5.4 1000 250 51.1 57.4 74.6 67.5 480 46.8 78.1 57.4 59.9 54.4 0 250 71-2 134.8 98.3 81.4 480 133.5 90.0 78.5 89.3 55.3 Alfalfa 500 250 71.5 114.0 75.0 78.5 28.8 480 118.4 85.6 66.4 85.0 63.2 28.7 23.5 1000 250 72.0 113.7107.1 77.0 Deep 480 137.8102.0 71.2 93.0 58.0 Mixed 0 250 54.5 109.5 59.1 66.4 480 108.3 53.3 59.5 77.4 51.7 Crop 500 250 57.1 111.6 73.8 70.8 38.1 Residue 480 101.0 83.8 52.2 71.7 52.9 37.2 8.5 1000 250 54.2 92.3 89.4 61.3 480 93.3 81.4 54.4 83.1 48.4 LSD values in bushels per acre Plowing Depth 4.4 2.5 5 4 Organic Matter 7.5 12.4 3.9 3.9 2.4 2.9 4.3 Fertilizer 2.2 6.6 Variety 6.1 5.2 2.6 * The 1963 and 1964 yields are given for the Shallow and Deep 3X only and the variety was M—300 instead of the M-480. 103 Table 30. Corn grain yields obtained on a Kalamazoo sandy loam soil as affected by plowing depth, organic matter, variety of corn and number of times plowed deep. Each value is an average of 4 replications for each treatment. Plow Organic Depth Matter Variety 1963 Ave. 1964 Ave. Bushels per acre M—250 18.9 Alfalfa M-300 25.1 10.0 Shallow 21.0 Crop M—250 27.4 Residue M-300 31.4 5.4 29.4 Average 25.2 7.7 M-250 25.1 Alfalfa M-300 55.9 10.6 Deep 1 X 29.5 Crop M-250 25.3 Residue M-300 29.9 8.0 27.6 Average 28.5 9 3 M-250 28.8 Alfalfa M-300 28.7 25.5 Deep 3 X 28.7 Crop M-250 38.1 Residue M-300 37.2 8.5 37.6 Average 33.2 16.0 M-250 42.9 Alfalfa M-300 45.5 24.8 Deep 4 X 43.2 Crop M-250 38.2 Residue M—300 37.2 10.7 37.9 Average 40.5 17.7 Plowing depth Organic matter LSD values in bushels per acre 2.5 5.4 2.9 4.3 104 Table 31. Analysis of variance of the corn grain yields by year. Treatment 57 58 59 55 valuzi 62 63 64 Plow 7.5 270** 3.5 6.7 9.7 0.2 68.0** 6.4** Organic 23.3** 15.0**59.5** 15.6**107** 3.0 3.5 24.5** P x OM 0.2 0.4 21.2** 3.6 4.1 1.2 7.3** 2.3 Fert. 5.0* 0.4 6.6* 0.5 0 5 1.0 P x F 2.2 2.6 5.3* 1.6 5.9* 0.1 OM x F 0.8 1.9 6.1** 0.1 0.1 0.4 PxOMxF 0.3 0.7 2.9 0.9 0.1 0.8 Variety 7.3* 5.0* 28.8** 3.4 P x V 13.9** 7.1* 2.8 1.5 OM x V 2.8 0.7 0.6 0.4 F x V 0.3 0.6 0.6 0.1 PxOMxV 2.9 2.1 0.2 PxeV 0.4 0.9 5.0* OMxeV 0.1 0.1 0.1 PXOMXFXV 1.2 0.1 0.8 LSD values in buZacre Plow 4.4 2.5 5.4 Organic 7.5 12 4 3.9 3.9 2.4 2.9 4.3 Fert. 2.2 6.6 Variety 6.1 5.2 2.6 Plow = plowing depth; Organic = organic matter treatment; Fert. = plowdown fertilizer; Variety = variety of corn. Table 32. Analysis of error variance within years for pooled testing of interactions between plowing depth and years, treating each organic matter treatment separately. Treatment F-values LSD (5%) LSD (1%) Alfalfa Plowing depth 14.4** 5.32 bu/a 7.87 bu/a Years 78.5** 9.81 bu/a 15.78 bu/a Crop Residue Plowing depth 2.5 Years 10.5 19.7 bu/a 29.1 bu/a 105 Table 33. Corn plant stand and ear count at the time of harvest- ing corn on the Kalamazoo sandy loam soil in 1964. Each value given is an average of four samplings for each treatment. Plow Organic Plants Ears Depth Matter per Acre per Acre Alfalfa 16956 4637 Shallow Crop Residue 19980 2268 Ave. 3452 Alfalfa 19008 4731 Deep 1 X Crop Residue 19798 3672 Ave. 4201 Alfalfa 19116 9776 Deep 3 X Crop Residue 19009 3834 Ave. 6805 Alfalfa 19656 8370 Deep 4 X Crop Residue 18900 4914 Ave. 6692 Table 34. Analysis of variance of the 1964 corn plant and ear count at time of harvest, giving the F and LSD values for each. Treatment F value F values LSD (plants) (ears) (ears/a) Plowing 0.37 9.78** 1765 Organic 0.92 34.13** 1179 Px OM 1.38 3.65* 106 Table 35. Amount of rainfall received on the plot areas during the respective growing seasons as measured in inches per rain. Rainfall data for 1961 and 1962 are not available. 1959 1960 1963 1964 Date Rain Date Rain Date Rain Date Rain 7-1 .05 5-19 .38 6-28 .18 4-16 .63 7-10 .05 5-24 .30 7-8 1.36 5:1 .95 7-16 1.45 6-7 2.69 7-15 .86 5-8 .77 7-23 .97 6-16 .70 7-22 1.38 5-15 2.64 7—29 .32 6-20 .15 7-30 .76 5-22 .56 7—30 .20 6-27 .37 8-5 .30 5-29 .08 8-3 .30 7-1 2.28 8-14 .03 6-5 .05 8-6 .08 7-7 .43 8-21 .85 6-12 1.06 8-12 .67 7-21 2.08 6-19 .92 8-23 1.10 8—2 .55 6-26 .18 8-27 1.10 8-12 .38 6-30 .59 9-2 .78 8-19 .60 7-10 1.08 9-16 1.64 7-17 .99 9-20 2.40 7-24 .14 CONCLUSIONS The Kalamazoo sandy loam soil has a dense B horizon which restricts root growth and limits crop yields. A giant disc plow was used to break up this horizon and mixed it throughout the tillage zone. The effects of this tillage operation was observed through many types of measurements both "in situ" and in the laboratory. The following conclu- sions have been drawn in respect to the effect of the tillage operation on the crop yield response as well as the various physical and chemical properties of this soil. 1. Although the deep mixing operation did increase the corn grain yields for the overall treatments, they were not consistently statistically significant. However, after separating many of the variables included in this research, one finds that the deep-mixing7did give an average increase for the 8 years of 30.4 bushels per acre for the plowdown fertilizer rate of 500 pounds per acre, and for the early variety of corn. 2. The mixing of the soil with the giant disc plow did alter the mechanical composition of the soil, especially in the dense B horizon, distributing the soil separates evenly throughout the soil profile to a depth of 22 inches. 3. The tillage operation showed very little influence by itself on the water holding capacities of the soil, until 107 108 after the 1963 revision of the tillage treatments. At this time the deep tillage treatments increased the amount of water held in the soil at 60 cm. of water suction and also allowed the plant root systems to remove the soil moisture more effectively. 4. The pore space relationships were only slightly in- fluenced by the deep-mixing operation, until after the 1963 revision of treatments. At this time the deep-mixing in- creased the macro and total pore spaces in the soil, expecial- ly in the 12 to 21-inch depth of sampling the soil profile. 5. The deep-mixing usually resulted in an immediate reduction in the bulk density values in the 12 to 21-inch sampling depth. However, these reductions were of short duration, as the bulk density of this lower portion of the soil returned to the original or even higher values within one year after the tillage operation. At the end of four years these values were considerably higher. 6. Although the deep-mixing operation appeared to de- crease the water infiltration rate in 1958, it also in- creased the water intake rate in 1959. However, neither of these were statistically significant increases or decreases. 7. The 1961 oxygen diffusion rates gave indications that the deep-mixing allowed the oxygen diffusion rate to recover more rapidly in the lower portion of the soil, after the soil had been saturated, than was possible for the natural soil at the same depths. 109 8. The deep—mixing did reduce the concentration of phos- phorus and potassium in the 0-9 inch soil depth, and at the same time reduced the pH value of the soil. It also gave slight increases in the exchangeable magnesium concentrations of this same layer of soil. 9. The amount of corn root development was increased considerably, in some instances the increases were close to 10-fold, in the 12 to 24-inch sampling depth. The increases at these depths due to the deep-mixing were statistically significant. Supplemental organic matter in the form of chopped alfalfa hay was added to the soil at the time of the deep- mixing operation, to attempt to improve the stability of any changesin.the soil physical properties brought about by the deep-mixing process. The following conclusions are drawn in regards to the influence of the alfalfa hay on the crop yield response and on the physical and chemical properties of the soil. 1. The alfalfa hay increased the corn grain yields sig- nificantly every year, except in 1962 and 1963. 2. The alfalfa hay did increase the water holding capaci- ties of the soil when placed under 60 cm. of water suction. However, these increases were statistically significant in 1960 and 1963. It also increased the amount of moisture held in the soil as measured "in situ" with the neutron moisture probe. 110 3. The general trend was that the alfalfa hay decreased the amount of macro pore space and increased the micro pore space in the soil. However, the decreases and increases were statistically significant in 1960 and 1963 only. 4. The alfalfa hay treatment reduced the amount of corn root development considerably in 1960, 1961 and 1962, in comparison to that obtained in the crop residue treatment. 5. There was no influence on the bulk density values brought about by the alfalfa treatment. 6. The water intake rates of the soil, on the wet runs, were generally increased due to the alfalfa hay treatment. 7. The addition of a total of 15 T/A of chopped alfalfa hay to this soil resulted in general increases in the phos- phorus, potassium, calcium and magnesium content of the soil and at the same time increased the pH values by 0.1 to 0.2 points, especially on the deep mixed treatments. The deep mixing operation resulted in a thorough mixing of the soil to a depth of 22 inches and in so doing would tend to dilute the concentration of the essential plant nutrients in the surface soil. Supplemental fertilizer was added to the soil as a plowdown treatment to determine the quantity required for counteracting the dilution process. The following conclusions were obtained from the plowdown fertilizer treatments in respect to their influence on the corn grain yields and on certain chemical properties of the soil. 111 1. The addition of high rates of plowdown fertilizer to the shallow plowed treatments decreased the amount of magnesium available for plant use. 2. The addition of plowdown fertilizer did increase the acidity of this soil. 3. The 500 pound per acre rate of plowdown fertilizer gave the most consistent higher yields of corn grain, and was therefore maintained as the blanket application for the 1963 tillage revisions. Two varieties of hybrid corn were used in this research to determine if the maturity date of the corn showed any influence on the yields. They were observed to produce varied yield responses from year to year and were influenced somewhat by the deep—mixing process. In general the early maturing variety seemed to respond better on this soil than the late maturing variety. The results of this research indicate that the deep-soil- mixing Operation alone could increase the production capaci- ties of this soil. However, supplemental organic matter in the form of chopped alfalfa hay and supplemental plowdown fertilizer improved the yield capacities even more. The changes brought about in the soil structure by the deep mixing, were found to be of short duration, however, the increased yields continued even though the improved soil structure did not persist. 112 With the yield increases obtained due to the deep—soil- mixing, supplemental organic matter and plowdown fertilizer, one could economically afford to perform this operation on soils such as the Kalamazoo sandy loam to improve the pro- ductive capacities of these soils. General Summary in Retrospect The Kalamazoo sandy loam soil was chosen for this re- search project because it did possess a dense B horizon, also due to the fact that previous studies had indicated that any fracturing of this horizon could increase crop yields. Inasmuch as the dense B horizon seemed to act as a natural barrier to root penetration, the decision was made to till the soil to a depth of 22 inches with a giant disc plow, rather than to subsoil, with a chisel type tool, because the shattering of the dense layer with the chisel was known to quickly revert back to its natural condition. With the thorough mixing of the soil to a depth of 22 inches, the physical properties of the dense horizon should be improved. Therefore the amount of root proliferation in this area should also increase, thereby improving the total absorption area and possibly increase the crop yield. If the deep mixing process was found tq be successful for improving crop yields