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I 4 "a: ...‘.1,,.”1‘_‘ C ”I "-1-.‘3’ .'u:‘p If ”“1”- la,--1v'.I-{Au,....f" I I .. -1..': sW-J ~11 {tactfqy . . la. I}. n V v ‘ . - ‘ XI» 36??" )1; .1?) ~ 2M3“? MICHIGAN STATE EUNI VRE H H H H H ”HHHHHHH 31293 00542 0124 LIBRARY Michigan State University H This is to certify that the dissertation entitled GENOTYPIC RESPONSES OF BARLEY AND OATS TO SOIL COMPACTION presented by Rex Benedicto Alocilja has been accepted towards fulfillment of the requirements for Ph. D. degreein Crop Science Qumqu/M/LMJW Mam professor 2/94/8’? M5 U i: an Affirmative Action/Equal Opportunity Institution 0- 12771 ___—_______# ___ _. 1V1531_J RETURNING MATERIALS: P1ace in book drop to LIBRARJES remove this checkout from ”- your record. FINES will be charged if book is returned after the date stamped beiow. GENOTYPIC RESPONSES OF BARLEY AND OATS TO SOIL COMPACTION BY Rex Benedicto Alocilja A DISSERTATION Submitted to Michigan State University . in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1989 6554902 ABSTRACT GENOTYPIC RESPONSES OF BARLEY AND OATS TO SOIL COMPACTION BY Rex Benedicto Alocilja Field and greenhouse studies were conducted to determine, through quantitative root analyses, the response of barley and oat genotypes to mechanically compacted soils. Genotypes of barley and oats used in both experiments were selected through a preliminary experiment. A randomized complete block, two factor factorial experiment was conducted with compaction as the main plot and genotypes as the subplot. Soils in the field experiment were compacted using a tractor. In the greenhouse experiment, a specific quantity of soil calibrated to 18% gravimetric soil moisture content was compressed in polyvinyl chloride cylinders using a hydraulic press to obtain the calculated bulk densities of 1.3, 1.6, and 1.9 Mg m”. High soil bulk density significantly reduced plant .height, root length density, root growth rate, root penetration ratio, shoot dry weight, test weight, and grain yield. Barley cultivar W7222 and oat cultivar Korwood were n~ found to be tolerant to soil compaction. Compaction tolerance indicators were the higher root length densities and root penetration ratios. In highly compacted soils, barley genotypes had significantly higher root length densities and significantly higher root penetration ratios than oats. Barley showed a greater propensity than oats to resume normal root growth after its roots penetrated soils layers with a high bulk density. The stepwise regression analysis showed that barley and oats differ in root growth patterns in response to increasing soil bulk density. Tractor wheels compaction significantly increased soil bulk density. Compacted soils significantly reduced yields and root length densities of barley and oats. Barley yields were reduced by 35% and root length densities by 34%. Similarly, oat yields and root length densities were reduced by 17% and 23%. In both studies root length densities were reduced by soil compaction. Root length densities of barley were reduced by 33% and 34%, of oats by 27% and 21% in the greenhouse and field study, respectively. The seedling core screening procedure was shown to be as effective as the field method for evaluating tolerance of genotypes to soil compaction. To Evangelyn, my beloved wife, cheerer and loyal supporter as I ran the race for the prize and Domingo (posthumously) and Carmen, dearly loved parents, who modeled persistence, perseverance, and a firm faith in God. iv ACKNOWLEDGMENTS I am indebted to many people who have contributed to the completion of this work. I appreciate and sincerely thank the chairperson and guidance committee members from the Crop and Soil Sciences and Horticulture departments. Dr. Russell D. Freed, my major Professor, took me into his mentorship, generously supported my studies financially, and my research experiments physically beyond his working hours. He patiently helped me untangle the knotted presentation of results. As Director of MSTAT, he allowed judicious use of the microcomputers for word processing and data analysis. Dr. Everett E. Everson, my first professor ever in a plant breeding and genetics course who devotedly and deliberately taught me the fundamentals and the skills of this particular discipline. He permitted the use of the growth chamber and several times dispatched his crew during root sampling and harvesting. Dr. Alvin J. M. Smucker, provided technical advice and countless hours of consultation on the soil biophysics component of my experiment, and initial criticisms of the manuscript. He expedited the use of the soil core sampler and the hydropneumatic elutriation root washer. His visits to the greenhouse were valuable interactions. Dr. Ronald Perry, for his valuable suggestions on the methodology of this research and input through follow-up consultations with him on some of the anatomical and morphological component of root research which gave an added impetus to this study. His enthusiastic support and interest in my research encouraged me greatly. Dr. Joe T. Ritchie, for his prayers and deep concern for the progress of my manuscript. He gave me access to the microcomputers and printers. Brad, Brian and Scott taught me how to use PlotIt. Dimon Wolfe, Beth Burnett, Dave Livingston and Mark van Koevering made the work bearable with their help and sympathetic support. Dr. Max Mortland and Govindaraj allowed the use of hydraulic press. Hossain Asady taught me the intricacies of the seedling core technique. Nasrat Wassimi encouraged me with great perception and sympathy. Dave Glenn provided logistic support and uplifting words. Betsy Bricker patiently taught me the nuances of the MSTAT software which I used for experimental design and analysis of data. A very good friend, Riad Baalbaki, served as a bouncing board for some farfetched ideas which became important components of the discussion. George Acquaah gave valuable suggestions on the stepwise regression analysis. vi My beloved wife, Vangie, infused into me her determination and enthusiasm during an uphill climb. Fellow believers in Jesus Christ empathized with me and sustained me with their intercessions. Extended family members supported and sympathized with my academic struggles. To the only Sovereign God, the Creator of heaven and earth, the source of wisdom, revealer of knowledge and of great and unsearchable things . . .the LORD is His name. I prayed to the LORD for the success of my research. Without Him this dissertation research would have come to naught. To Him, I am continually grateful for the wondrous things He has established for me. All that I have accomplished He made it possible because He strengthened me. CHAPTER I CHAPTER II CHAPTER III CHAPTER IV TABLE OF CONTENTS INTRODUCTION 1.1 Objectives REVIEW OF LITERATURE 2.1 The confounding effects of soil compaction 2.2 Root growth and proliferation in compacted soils 2.3 Penetration and root growth in plowpans 2.4 Plant response to soil compaction 2.5 Effects of soil compaction in some field crops 2.6 Genotype response to compaction 2.7 Measurements of soil compaction MATERIALS AND METHODS 3.1 Preliminary experiment 3.2 Greenhouse experiment 3.3 Field experiment RESULTS AND DISCUSSION 4.1 Greenhouse experiment 10 12 15 17 19 21 21 22 25 29’ 29 4.1.1 Greenhouse experiment with barley 29 viii CHAPTER V 4.1.2 Greenhouse experiment with oats 4.1.3 Comparison of the effects of the different bulk densities on barley and oats 4.1.4 Stepwise regression analysis procedure 4.1.5 Stepwise regression analysis of greenhouse experiment with barley 4.1.6 Stepwise regression analysis of greenhouse experiment with oats 4.2 Field experiment 4.2.1 Effect of tractor wheel compaction 4.2.2 Field experiment with barley 4.2.3 Field experiment with oats 4.2.4 Stepwise regression analysis for field experiment 4.2.5 Stepwise regression analysis for field experiment with barley 4.2.6 Stepwise regression analysis for field experiment with cats SUMMARY AND CONCLUSIONS 5.1 Greenhouse experiment 5.1.1 Barley 5.1.2 Oats 5.1.3 Barley and oats ix 35 40 51 53 54 57 57 59 64 67 7O 72 74 75 75 75 76 5.2 Field experiment 5.3 Greenhouse and field experiments 5.4 Final comments APPENDICES BIBLIOGRAPHY 77 77 78 79 94 Table Table Table Table Table Table Table 6. LIST OF TABLES The effects of soil compaction on plant height, total dry matter (TDM), root penetration ratio (RPR), root length density (RLD), and root growth rate (RGR) of four barley cultivars 14 days after seedling emergence. Greenhouse experiment, 1987 30 Root length density of four barley cultivars within the whole core assembly, top, middle, and bottom layers when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987 32 Root length density (RLD) of four barley cultivars within whole core, top, middle, and bottom layers when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987 33 Total and relative (%) root lengths of four barley cultivars within the top, middle and bottom layers of the core when the middle layer was compacted to bulk three densities. Greenhouse experiment, 1987 34 Effects of soil compaction on plant height, total dry matter (TDM), root penetration ratio (RPR), root length density (RLD), and root growth rate (RGR) of four oat cultivars 14 days after emergence. Greenhouse experiment, 1987 36 Root length density of four oat cultivars within the whole core, top, middle, and bottom layers when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987 37 Root length density of four oat cultivars within whole core, top, middle, and bottom layers of the core when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987 39 xi Table Table Table Table Table Table Table Table Table Table 10. 11. 12. 13. 16. 17. Total and relative root lengths (%) of four oat cultivars within the top, middle and bottom layers of the core when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987 Mean root penetration ratio (RPR) and root length density (RLD) of four barley and four oat cultivars 14 days after emergence as affected by soil bulk densities. Greenhouse experiment, 1987 Mean root penetration ratio (RPR) and root length density (RLD) (cm cmfi) of four barley and four oat cultivars in 3 soil densities 14 days after emergence. Greenhouse experiment, 1987 Partial regression coefficients (%) of four barley cultivars' root length density in different layers selected by the stepwise regression procedure with the total d matter as the dependent variable. Greenhouse experiment, 1987 Partial regression coefficients (%) of four oat cultivars' root length density in different layers selected by the stepwise regression procedure with the total dry matter as the dependent variable. Greenhouse experiment, 1987 Effect of tractor wheel compaction on the bulk density of soils at 0-10 cm, upper 0-23 cm, and lower 23-46 cm layers. Field experiments, 1983-84 Analysis of variance summary for yield, test weight, total dry matter (TDM), height and root length density of four barley cultivars evaluated with and without compaction. Field experiments, 1983-1985 Mean grain yield and root length density of four barley cultivars across years of study as affected by soil compaction. Field experiments, 1983-1985 Mean grain yield and root length density of four oat cultivars across years of study as affected by soil compaction. Field experiments, 1983-1985 Analysis of variance summary for yield, test weight, total dry matter (TDM), xii 41 42 44 55 56 58 60 62 65 Table Table Table Table Table Table Table Table Table Table 18 19. 20. A.1. A02. AI3. A.4. A.5. A06. AI7. height and root length density of four oat cultivars evaluated with and without compaction. Field experiments, 1983-1985 Compaction by cultivar interaction on mean root length density of four oat cultivars at the upper 0-23 cm layer of the soil core. Field experiments, 1984 Partial regression coefficients (%) of three barley cultivars' root length density in different layers selected by the stepwise regression procedure with the yield and total dry matter as the dependent variable. Field experiments, 1984 Partial regression coefficients (%) of four oat cultivars' root length density in different layers selected by the stepwise regression procedure with the yield and total dry matter as the dependent variable. Field experiment, 1984 Analysis of variance table for top layer root length density per plant of 4 barley cultivars as affected by three compaction levels. 1987 Analysis of variance table for middle layer root length density per plant of 4 barley cultivars as affected by three compaction levels. 1987 Analysis of variance table for bottom layer root length density per plant of 4 barley cultivars as affected by three compaction levels. 1987 Analysis of variance table for whole core root length density per plant of 4 barley cultivars as affected by three compaction levels. 1987 Analysis of variance table for total dry matter per plant of 4 barley cultivars 14 days after emergence as affected by three compaction levels. 1987 Analysis of variance table for root penetration ratio of 4 barley cultivars as affected by three compaction levels. 1987 Analysis of variance table for plant height of 4 barley cultivars 14 days after emergence as affected by three compaction levels. 1987 xiii 66 68 71 73 79 79 80 80 81 81 82 Table Table Table Table Table Table Table Table Table Table Table Table A.8. A.9. A010. A.11. A.12. A.13. A.14. A.15. A.16. A.17. A.18. A.19. Analysis of variance table for total root length per plant in whole core assembly of 4 barley cultivars 14 days after emergence as affected by three compaction levels. 1987 Analysis of variance table for total dry matter of 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Analysis of variance table for middle layer root length density of 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Analysis of variance table for root penetration ratio of 4 cat cultivars 14 days after emergence as affected by compaction levels. 1987 Analysis of variance table for the top layer root length density of 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Analysis of variance table for the bottom layer root length density of 4 oat cultivars 14 days after emergence as affected by compaction levels. 1987 Analysis of variance table for total root length of 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Analysis of variance table for root penetration ratio as average of 4 barley and 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Analysis of variance table for root length density as average of 4 barley and 4 cat cultivars 14 days after emergence as affected by three compaction levels. 1987 Analysis of variance table for grain yield of 2 barley cultivars as affected by compaction levels. 1983 Analysis of variance table for grain yield of 4 barley cultivars as affected by compaction levels. 1985 Analysis of variance table for the whole xiv 82 83 83 84 84 85 85 86 86 87 87 Table Table Table Table Table Table Table Table Table Table Table A.20. A.21. A.22. A.23. A.24. AOZSI A.26 A.27. A.28. A.29. A.30. core root length density of 2 barley cultivars as affected by compaction levels. 1983 Analysis of variance table for the upper 0-23 cm root length density of 2 barley cultivars as affected by compaction levels. 1983 Analysis of variance table for the lower 23-46 cm root length density of 2 barley cultivars as affected by compaction levels. 1983 Analysis of variance table for the upper 0-23 on root length density of 3 barley cultivars as affected by compaction levels. 1984 Analysis of variance table for the lower 23-46 cm root length density of 3 barley cultivars as affected by compaction levels. 1984 Analysis of variance table for grain yield of 4 oat cultivars as affected by compaction levels. 1985 Analysis of variance table for the whole core root length density of 2 oat cultivars as affected by compaction levels. 1983 Analysis of variance table for the upper 0-23 cm root length density of 2 cat cultivars as affected by compaction levels. 1983 Analysis of variance table for the lower 23-46 cm root length density of 2 oat cultivars as affected by compaction levels. 1983 Analysis of variance table for the whole core root length density of 4 oat cultivars as affected by compaction levels. 1984 Analysis of variance table for the lower 0-23 on root length density of 4 oat cultivars as affected by compaction levels. 1984 Analysis of variance table for the upper 23-46 on root length density of 4 cat cultivars as affected by compaction levels. 1984 88 88 89 89 90 90 91 91 92 92 93 93 Figure Figure Figure Figure Figure Figure Figure Figure 10 LIST OF FIGURES Relationships between (a) compaction and root length density (RLD) and (b) compaction and root penetration ratio (RPR) of barley and oats 14 days after emergence. 1987 Effects of the middle layer high in bulk density (1.9 Mg ma) on the root length density (RLD) of 4 oat cultivars within the top and bottom core segments 14 days after emergence. 1987 Effects of the middle layer high in bulk density (1.9 Mg m”) on the root length density (RLD) of 4 barley cultivars within the top and bottom core segments 14 days after emergence. 1987 Effects of bulk density on (a,c), root length density (RLD) and (b,d), root penetration ratio (RPR) of 4 barley (a,b) and 4 cat cultivars (c,d) 14 days after emergence. 1987 Root length density (RLD) and total dry matter (TDM) of 4 barley cultivars in response to soil bulk density. 1987 Root length density (RLD) and total dry matter (TDM) of 4 oat cultivars in response to soil bulk density. 1987 Grain yield and root length density (RLD) of 3 barley cultivars in response to soil compaction. 1984 Grain yield and root length density (RLD) of 4 cat cultivars in response to soil compaction. 1984 xvi 45 47 48 49 50 52 63 69 CHAPTER 1 INTRODUCTION Compaction has become a significant problem in many soils because of changes in crop management that have occurred within the past two or three decades. The development of specialized management has led to continuous cropping with repetition of the same tillage often under less than optimum conditions. Another problem is that the increase in tractor size and capability has led to the tillage of soils when moisture content is very high, thus leading to greater compaction (Mckibben, 1971). Soane (1981) inferred that farming practices such as heavier field machines, higher tire pressures and the tendency of field traffic to be controlled by time rather than soil conditions, damage the soil structure and increase the incidence of soil compaction. Many agricultural soils have been compacted by years of intensive tillage. Also the soil organic matter has been depleted and the soil structure has been destroyed as fields are worked and re-worked (USDA, 1979). Compaction is defined as the moving of soil particles closer together by external forces exerted by humans, 2 animals, equipment, and/or the impact of water droplets, freezing and thawing and other climatic factors. Packing of soil particles together results in the loss of pore space within the soil which lead to poorer internal drainage and aeration. In many soils, compaction leads to slower water infiltration, which results in greater runoff and soil loss from both rainfall and irrigation (Dickey, et al.,1965). Ghaderi, et al., (1984) believed that it was expensive to select crop cultivars having some tolerance to certain compacted soils using the conventional plant breeding field programs. In addition, it is an arduous task to quantify root morphological responses of plant populations grown in the field. Asady, et al., (1985) contends that more quantitative information relating specific root responses to compacted soils must be available before improved selection programs can be established. 1.1 Objectives This study attempted to measure quantitatively root tolerances of different barley and oat genotypes to soil compaction that may provide useful information for the development of cultivars tolerant to compaction through breeding and selection. Specifically, in barley and oats, no previous study has established a quantitatively based root analysis component of the plant as an indicator of the cultivar's response to soil compaction. Hence this study was conducted to: 1) determine the genotype responses to mechanically compacted soils based on quantitative root analysis both in the greenhouse and field studies. 2) determine the effects of soil compaction by tractor wheels on the growth and yield of barley and oat cultivars. 3) test a soil core screening procedure for evaluating genotypic tolerances to soil compaction at the seedling stage for barley and oats. CHAPTER II REVIEW OF LITERATURE 2.1 The confounding effects of soil compaction Excessive soil strength, sometimes called physical impedance or mechanical impedance, can severely distort normal root growth patterns. This excessive soil strength can be caused by a high bulk density, high soil cohesion, and drying of a consolidated or cohesive soil mass. The excessive soil strength sometimes occurs as a result of natural conditions but often is accelerated by plowing or soil compaction with tractor tires (Taylor, et al., 1983). The net result of soil compaction is a reduction in crop yield. Yields are reduced because compaction affects root growth, their distribution, and the supply of nutrient ions and water to the absorbing root surface. Soil compaction reduced both plant populations and performances of sugar beet and pea (Hebblethwaite and McGowan, 1980). Compaction has a detrimental effect on root growth and development (Gooderham and Fisher, 1975). This was affirmed by Asady, et al. (1985) which showed that soil compaction severely limited the growth and penetration of drybean 5 roots. They further observed that root penetration was significantly reduced by more compact soil or soils with higher densities. Brereton, et al. (1986) contends however, that it is not known how far reduced root growth is a consequence, rather than a cause of poor shoot growth. Compaction reduces the size of soil pores, especially those of relatively large diameter. The reduced pore size can cause mechanical impedance to root extension, inhibit gas exchange between the soil and the atmosphere, and decrease the amount of moisture available to the roots. All these effects modify root growth and as they can be simultaneous when soil is compacted, it is often difficult to delineate them. Further uncertainty in studying the response of roots to mechanical impedance in soil comes from the fact that the magnitude of the forces which oppose their elongation cannot be directly measured (Russell, 1977). Russell and Goss (1974) contend that the measurement of the external pressures on roots in soil is subject to considerable uncertainty and indirect procedures. For example, penetrometers must be used. Even if they are made to resemble roots in shape, three basic characteristics of the growing root cannot be simulated, namely, a) the capacity of its apex for deformation in response to external pressure, b) the curving of the root around obstacles, and c) the possible lubricating effect of the mucigel sheath which typically develop on the root cap. Some investigators (Stolzy and Barley, 1968; Eavis and Payne, 1969) have 6 attempted to compare the axial pressures roots experience when penetrating soil with those measured by penetrometers of comparable size. The pressure experienced by root hairs within a few millimeters of their apices makes such comparisons of doubtful significance. A further reason for regarding penetrometers as only a quantitative guide comes from work with devices equal in diameter to roots but with tips of contrasting form. Greacen et a1. (1968) considered that the manner in which soil particles are displaced by penetrometers with tips similar in shape to that of a root differed considerably from the pattern of displacement shown by roots themselves. The displacement produced by root apices was judged to be more closely simulated by 'needle' penetrometers, with a 10° cone at the apex, a shape markedly in contrast with that of a root. Previous compaction studies on barley, oats and wheat have shown inconsistent results. In barley, Kruger (1970) observed decreased yield due to compaction. However, some workers obtained yield increases as soil bulk density increased (Homolka, 1971; Krausko and Ockay, 1978). Separate studies by Cheng et a1. and Schuurman (1971) showed a decrease in oat yields in more compact soils. Wheat appears to tolerate sowing and spring postsowing compaction. Two simultaneously published studies (Jaggi and Gorantiwar; Singh and Gupta,1970) showed increased germination percentage up to a certain degree of compaction. Pilat (1974) reported more tillers, faster rate of dry 7 matter increase and higher grain yield with compaction. 2.2 Root growth and proliferation in compacted soils As measured by root density or weight, the amount of roots observed at different growth stages and soil layers tended to be lower on compacted soil (Cannel et al., 1973). This difference in root mass was accompanied by shallow rooting in compacted soil, especially during the early vegetative growth phases. The extension of the seminal root system was restricted on compacted soil. Reduced axial growth of roots was compensated for by greater radial growth and enhanced by a larger diameter of the seminal root axes of barley (Yuerver, 1972 as cited by Baeumer and Bakermans, 1973). Compaction is often hastened by seed drilling machines used in direct seeding. Compaction due to seed drillers reduced the growth of seminal roots and shortened the root axes (Elliot et al. (1977), restricted the lateral spread of roots and thickened the roots (Russell and Goss (1974). Elliot et al. (1977) observed that in compacted soils, after direct-drilling, root extension was restricted and the root system remained superficial at the tillering stage. At flowering, however, the same number of roots was obtained per unit area in both compacted and noncompacted soils. Plant roots must exert a root growth pressure greater than the resistance of the soil through which it is growing 8 in order to penetrate that soil mass (Taylor and Gardner, 1963). Pfeffer's experiment done in 1893 had shown that when growing roots were rigidly confined by encasing them in gypsum block they were capable of exerting pressures in the range of 5-12 bars. Gill and Bolt (1955) and Gill and Miller (1956), citing Pfeffer's work (1893), have emphasized that conditions affecting plant vigor will alter the growth pressure of a plant. Taylor and Gardner (1960) argue that adequate anchorage is necessary before a root can transmit maximum root growth pressure to the resisting soil mass. They also contend that root penetration is influenced by three classes of variables, namely, those affecting (a) root growth pressure, (b) root anchorage, and (c) strength of the soil. Voorhees, et al. (1971) concurs that root proliferation is influenced not only by the average properties of the soil mass, but also by the properties of the individual soil structural units. Root elongation rates of cotton (Ggssypigm hirsutgm) and peanut (Araghis hypogaea) decreased with increasing soil strength as measured with a penetrometer (Taylor and Ratliff, 1969). Larger roots of corn (Zea mays) were confined to the larger voids between peds in a silt loam, whereas the smaller roots penetrated into peds in the B horizon if the ped density was less than 1.8 Mg m"3 as reported by Edwards, et al. (1969). This was attested to earlier by Fehrenbacher et al. (1965) who observed the absence of corn root penetration into peds having a density 9 of 1.8 Mg m”. These results suggest 1.8 Mg m"3 as the upper limit of soil density for plant root penetration. Earlier work of Viehmeyer and Hendrickson (1948) found that maximum bulk density which permitted root penetration could vary from 1.46 Mg m"3 in clays to about 1.75 Mg m"3 in sandy soils. Reviewing previous researches, Schuurman (1965) inferred a "critical soil density" values ranging from 1.3 to 1.8 Mg m’3 for root growth in loam soil. His observations showed that roots grew into soil packed at 1.52 Mg In-3 only if they first grew into and through a layer of soil packed to a lower density. The cessation of root elongation is affected by texture, bulk density, soil water suction, and plant species interacting over a wide range of soil physical conditions (Greacen, et a1. (1968). Both pore size and bulk density determine root penetration (Veihmeyer and Hendrickson, 1948). A study by Wiersum (1957) on oats grown in cylinders of various diameters containing sand, confirmed the effects of pore size and pore rigidity on root penetration. Wiersum's study (1957) showed that in larger cylinders, the individual sand grains were not confined, and were easily displaced as roots elongated. The effect of mechanical resistance on root elongation is a continuous phenomenon affecting root elongation rates even at low mechanical stresses (Barley, 1963). The initial angle of root-soil contact as well as the density difference affects the 10 ability of the root to penetrate a structurally layered soil (Greacen, et al., 1968). The probability that root hairs may elongate only in existing voids was suggested by Barley (1968). As such, growth of root hairs may be affected more by pore diameter than soil strength. 2.3 Penetration and root growth in plowpans A concept has been advanced that soil pans (also referred to in literature as hardpans, plowpans, tillage pans, plow soles, tillage sole) are either genetic in origin or that they develop as a result of man's manipulation of the soil. However, Taylor et al., (1963) theorized that the root-restricting pans are caused by excessive soil strength that occurs largely as a result of soil drying. They suggested two general ways pans affect plant root systems. First, plant roots may penetrate the soil pan but do not expand their diameter later in the growing season. These pans cause girdled tap roots in which the transport of water and nutrients is restricted. Second, all vertical growth of roots may be prevented from further penetrating a horizontal soil pan. Compaction by tillage machinery and traffic by heavy equipment has formed "plowpans" in some soils. These layers, as well as naturally-formed dense or slowly permeable layers, impede water infiltration and root penetration (Arkin and Taylor, 1981). Taylor and Gardner 11 (1981) showed that soil strength, not soil bulk density or any other physical feature of the soil, controls the penetration of roots through sandy soil pans. Both soil water and bulk density affect soil strength, but strength is the determining factor. Plowpans are most likely to occur on fine sandy loans or other soils that do not swell and shrink while wetting and drying. Pans divert roots and reduce rooting intensity below the pans. Initially, young roots grow downward through soil loosened by tillage. When roots encounter a soil pan, some of the roots enter the pan and some are diverted horizontally. Roots that penetrate the pan exhibit a reduced elongation rate as the soil strength increases. The roots that are diverted laterally may later encounter a vertical crack through which they can penetrate the pan (Taylor and Burnett, 1964). If no crack is encountered, the roots continue to grow horizontally along the pan surface until growth conditions change. Mechanical inhibition of rooting depth will reduce the quantity of water available for plant growth (Lowry et al., 1970). Pan penetration by various plants such as alfalfa, sweet clover (Melilotus alba) and guar (Cyamopsis tetraggnglgba) has been reported in the literature. These crops, when grown in soils with hardpans, promote favorable conditions that cause increased root penetration, nitrogen supply, aeration, and infiltration for succeeding crops. The previous reports are not clear as to the exact mechanism attributable to the yield increases. Elkins et al. (1977) 12 reported that roots of bahiagrass (Paspalum notatum Flugge 'Pensacola') will penetrate soil layers that mechanically impede cotton roots. They found that bahiagrass increased the number of pores greater than 1.0 mm in diameter and thus increased cotton rooting densities to a depth of at least 60 cm. Cotton grown where bahiagrass sod had been plowed under 3 years before still yielded more than cotton grown where the soil had been chiseled to 35 cm deep. C. M. Peterson (quoted by Elkins et al., 1977) found that bahiagrass roots possess a fibrous sheath beneath the epidermis. This sheath, absent in most plants, is probably responsible for the additional penetration of bahiagrass roots. 2.4 Plant response to compaction Barley (1962) drew attention to the ample chemical energy present in the form of readily oxidizable material in the root to meet the work expenditure needed even for rapid growth against high resistances. He conceived that this energy was utilized in cell extension and therefore sought to explain the response of roots in terms of osmoregulation in expanding cells. In subsequent discussions (e.g. Barley et al., 1965; Barley and Greacen, 1967; Greacen and Ch, 1972) the same basic approach was adopted. Some responses to mechanical stress can be readily explained in terms of osmoregulation: the maximum pressures roots appear capable 13 of exerting are comparable with the osmotic pressure of their expanding cells. However, many aspects of the response of roots, especially to low pressures, cannot be explained in this way. As Barley (1962) recognized, the rate of enlargement and the final volume of root cells would be smaller if their response depended on osmoregulation. However, there is evidence that external pressures which considerably restrict root extension do not reduce cell volume (Barley, 1965; Russell and Goss, 1974); increased cross-sectional area can counter-balance reduced cell length. Several authors suggested that the extension of cell walls depends on complex metabolic processes which are under hormonal control (Cleland, 1967; Ridge and Osborne, 1970; Davies, 1973). The involvement of growth control mechanisms in the response of roots to a number of stresses in the soil environment, for example anaerobiosis, salinity and water shortage, has been strongly suggested by Vaadia and Itai (1969). Information on the effect of mechanical stress on endogenous growth substances is at present limited to indications that the evolution of ethylene can increase when roots encounter a mechanical barrier but a number of considerations suggest that a study of the effects of external pressures on growth regulatory mechanisms may be tenable (Russell and Goss, 1974). The apical tissues of roots, including the root cap, which can be particularly subject to distortion by mechanical forces, are major sites 14 where growth control substances are synthesized (Pratt and Goeschl, 1969; Weiss and Vaadia, 1965; Scott, 1972). Moreover, when roots have been grown against an external applied pressure which is subsequently relieved, their rate of extension does not return to that in unimpeded roots until 2 or 3 days later, that is to say after the cells formed since the pressure was removed, have reached the stage of rapid expansion (Russell and Goss, 1974). This 'lag' is readily compatible with the postulate that the response to mechanical impedance is initiated within the apical meristematic tissues. An observation made by Snow (1905) and recently repeated (Goss and Drew, 1972) is again suggestive that mechanical restraint affects the growth regulatory process in roots; when root axes are forced to bend, lateral initials typically develop on the convex side. Since their initiation is believed to be closely controlled by growth substances it appears likely that mechanical stress may influence the production or action of these substances. Russell (1977) stated that no full interpretation is yet possible for the manner in which low external pressures reduce root extension. Simple physical explanations are inadequate. Additional evidence of this has been provided by the observation of Goss and Ward (1975) that when the root cap of extending roots comes into contact with a fixed solid object its rate of extension can be significantly reduced within thirty minutes; however, if the root displaces the 15 obstruction it can soon resume its original rate of extension. The results of further physiological studies must be awaited before the detailed manner in which roots respond to mechanical forces can be explained. 2.5 Effects of compaction in some field crops Soil compaction has a qualitative effect on the growth, maturity, and general physiological behavior of plants. However, yield response to compaction is rarely predictable. Cannell (1977) concurs that losses due to compaction are difficult to assess because yield reduction varies with the crop, soil type and weather. Hubbel and Staten (1951) obtained increased yields of field-grown cotton with increasing compaction. Flocker and co-workers (1958, 1959a, 1959b, 1960) reported greenhouse and field studies in which yields of certain winter cover crops, potatoes and tomatoes have been reduced by compaction. Physiological responses have been related to soil compaction, but evidence is contradictory. Heath (1937) reported that compaction hastened maturation of field-grown cotton plants, while Phillips (1959) observed that compaction delayed silking and tasseling dates for field corn. Brereton and Dawkins (1986) assessed the differential sensitivities of field beans (yigia_fabg), spring barley and 16 sugarbeet crops to soil compaction. Their findings showed that topsoil compaction imposed by one pass of a tractor reduced the total amounts of roots down to 100 cm depth in sugarbeet and field beans. Compaction reduced both the depth and lateral growth of roots in all crops, with barley being least affected. Compaction reduced leaf area in sugarbeets resulting in lower water use, but in field beans water use was unaffected by compaction despite a reduction in leaf area. In barley, compaction delayed senescence. Dry matter production was reduced by compaction in sugarbeet and field beans but not barley. Yields of sugarbeet roots and field beans were reduced by 60% and 26% respectively. Compaction also affects germination and emergence of seedlings. On coarse to medium-textured soils with a friable soil surface, more emerged plants were observed in compacted than in noncompacted soil (Baeumer and Bakermans, 1973). This likely happens when a lack of available soil moisture restricts seedling emergence on tilled noncompacted soil. Baeumer and Bakermans (1973) suggested that a difference of 1-2° C between compacted and noncompacted soil may be decisive for germination and subsequent growth if minimum temperature requirements are not met. A study by Elliot et al. (1977) comparing direct drilling (heavily compacted soil), reduced cultivation (slightly compacted), and plowing (noncompacted), showed no differences in speed of emergence and the time of full emergence of barley seedlings. Kropecky (1970), however, 17 found increased germination and emergence at higher soil bulk density. Elliot et a1. (1977) found that barley plants growing in compacted soil yielded significantly less dry matter than plants in noncompacted soil. As time progressed the crop dry matter weight in compacted soil became progressively less than that in non-compacted soil. Plants in noncompacted soil had 85% more dry matter at 42 days after sowing and 58% more dry matter at harvest than those in compacted soil. They suggested that compaction caused a continuous growth restriction rather than a temporary set-back in the early stages. Barley from plots in noncompacted soil had more leaves per plant than those in compacted plots. Tillering was not delayed but the total number of tillers per plant and the number of tillers with heads per square meter was reduced by soil compaction (Kopecky, 1970). No difference in either lOOO-grain weight or the number of grains per head was observed between compacted and noncompacted soil. Compaction had more adverse effects on straw than on grain yield. Compacted plots had shorter plants hence, less straw than noncompacted plots (Elliot et al. 1977). 2.6 Genotype response to compaction The genetic system which controls the root growth in cereals has not been studied as much as the above-ground 18 organs. Troughton and Whittington (1969) and Zobel (1975) presented empirical evidences supporting the existence of genotypic differences in root systems of several crops such as, maize (Spencer, 1940), wheat (Hurd, 1968; Yu, et al., 1969), barley (Hackett, 1968), rice (Chang, et al., 1972, and tomatoes and beans (Zobel, 1975). Russell (1977) contends that even with the existence of appreciable genetic variation, rooting characteristics were not established as a major consideration in plant breeding programs because of the considerable variability commonly induced by environmental factors under field conditions. Some of these factors are the compensatory growth which occurs in variable environments, the concentration and distribution of nutrients in the soil, gradients in soil water potential and mechanical forces. The magnitude of these environmental effects suggests that in practice they may often mask genetically controlled variability. Lupton et al., (1974) showed that under field conditions there were no consistent differences in root formation between conventional European varieties of wheat and semi-dwarf varieties derived from Norin 10, even though small differences were shown in individual experiments. Comparing the response of two cultivars of barley, Impala and Julia, Elliot et a1. (1977) did not obtain differences due to compaction on the germination and emergence, vegetative growth, dry matter yield and grain yield. Bobeck et al. (1970) noted an increase in grain yield -.‘\ 19 of 18 cultivars of spring barley with increasing bulk density, but yield among cultivars did not differ. Using long-stemmed and short-stemmed barley cultivars, Kopecky (1970) observed that compaction decreased lodging of tall cultivars. His findings also show that compaction increased the malting quality of all cultivars used. 2.7 Measurements of soil compaction There are two methods commonly used to measure compaction by researchers according to Dickey, et. al.,(1985). One is soil bulk density and the other is taken with a soil penetrometer. Bulk density is simply the dry weight of a known volume of soil. Bulk densities of clay soils normally range from 1.2 to 1.5 Mg Ira, and sandy soils from 1.6 to 1.8 Mg 1M3. The cone penetrometer index (or simply cone index) is an indirect measurement. Researchers measure the amount of force it takes to push a rod with a cone-shaped point through the soil. These measurements are generally reported in pressure per unit surface area. This type of measurement is not unlike judging the soil by noting how much force it takes to push a spade or soil sampling probe into it. A version of the penetrometer, the needle penetrometer is smaller in diameter than the standard cone and is sometimes used to evaluate the actual resistance a root would encounter in the soil. The cone index is a function of both 20 soil strength and soil moisture. Different soil textures have different strengths, just as they have different weights. The strength of a soil at a given time depends on both compaction and moisture. For a given soil moisture and soil type, a larger cone index number means more compaction (Dickey, et. al., 1985). Increasing soil density is generally associated with decreasing mean pore size which is usually associated with high penetration resistance (Barley and Greacen, 1967). In both greenhouse and field experiments, the level of soil compaction was determined by calculating the bulk density of the soil cores. CHAPTER III MATERIALS AND METHODS 3.1 Preliminary experiment A two factor factorial experiment with split plots was established in a randomized complete block design with compaction as the main plot and cultivars as the subplot. Fifteen cultivars each were used for both barley and oats. Seeds of thirty cultivars were sown in flats, 35 cm wide, 56 cm long and 8.5 cm deep. The soils were compacted to about 1.4 Mg 111'3 immediately after sowing. Fourteen days after ememrgence, root and shoot dry weights were obtained. The root-shoot ratios were calculated for all cultivars, values were analyzed statistically and means compared using the Duncan's Multiple Range Test to determine the cultivar response to compaction. Cultivars for the main trial were selected based on high, intermediate and low root and shoot weights and root-shoot ratios. 21 22 3.2 Greenhouse experiment Four cultivars of barley and oats were used in the experiments. The barley cultivars were Bowers (x 969- 3*2/B130), Morex (Cree/Bonanza), Robust (Morex/Manker) and W7222 (Thompson Seed Co., Canada) while the oat cultivars were Heritage (Mi 56-22-1689/*2 Marino), Korwood (Beaver/Garry//Clintland/CI 15163), Mariner (Garry/ Mi56-22-1493), and Ogle (Brave/2/Tyler/Egdolon 23). All the barley and cat varieties are commercial cultivars grown in Michigan except W7222 which is an experimental line from Wisconsin. These cultivars were selected from the preliminary compaction experiment outlined above. Cores were made from polyvinyl chloride cylinders (PVC), schedule 40, with 7.6 on inside diameter and a circular wall thickness of 0.64 cm. One experimental unit was made up of a layered soil column which consisted of the top 2.5 cm layer compacted to constant bulk density, the middle 2.5 cm layer compacted to variable densities corresponding to the compaction treatments, and the 7.6 on bottom layer which had the same bulk density as the top layer. The cores were filled with the soil taken from the Crop and Soil Science Research Farm described according to the Ingham County Soil Survey (1979) as belonging to the Capac series (aeric ochraqualfs, fine-loamy, mixed mesic). The Capac series consists of somewhat poorly drained, moderately slowly permeable soils on till plains and 23 moraines or glacial deposits. These soils were formed in medium and moderately fine textured deposits. The texture is dominantly loam, but the range includes sandy loam or fine sandy loam. It has an average of 26% clay. A composite soil sample from 10 sites of the experimental area were collected, sun-dried in the greenhouse and sieved. Aggregate sizes ranging from 0.25 to 2.0 mm were equilibrated to a constant gravimetric soil moisture content of 18% and uniformly compacted to the desired bulk densities. The soil was compressed into 2.5-cm and 7.5 cm high cores by a piston (7.6 cm diameter) attached to a hydraulic press (Carver type, Model 20505-11). Initial bulk density levels of 1.3, 1.6, and 1.9 Mg m'3 (referred to as low, medium and high) were established by pressing a specific quantity of soil into the middle 2.5 on core. The compacted cores were sandwiched between the top and the bottom cores that had the same calculated bulk densities of 1.3 Mg m”. The three cores were joined together by wrapping them with a 5-cm wide plastic-impregnated tape. Each soil container was saturated for 36 h, to develop water continuity between the soil layers, drained for 16 h and seeds were planted on the surface soil. After sowing, the initial weights of each soil core at its drained moisture content were taken. The soil moisture content in the cores was maintained by weighing the same cores twice daily (in the morning and at noon) and adding a quantity of water sufficient to its initial weight. Each experimental unit consisted of three- 24 layered soil core assembly containing three seedlings. Six seeds treated with Vitavax 200 wettable powder at the rate of 0.0025% volume per weight (4 oz/loo lbs) were sown in each core and were thinned down to three seedlings two days after emergence. They were allowed to grow for 14 days in a greenhouse with a constant humidity of 65 :5%, day/night temperatures of 24/18 ° C and a 16 h photoperiod with a light intensity of 640 umol m'2 s”, which is approximately one-half full sunlight. The experiment was a two factor factorial with a split laid out in randomized complete block design with four replications. A duplicate trial was made for both barley and oats and the analysis of variance was computed for the combined data for eight replicates. Data were taken for height, shoot dry weight (also referred to as the TDM, total dry matter), total root length, relative root growth rate, and root penetration ratios. The relative root growth rate was obtained by dividing the total root length by 14 days after emergence, the time in which the seedlings were allowed to grow. The root penetration ratio (RPR) is defined by Asady et al. (1985), as a ratio of the number of root tips that exit the compacted middle core divided by the number of roots that penetrate the same core. Root counts for RPR calculations were obtained from a 20.3 cm? central area of the container assembly to exclude any influence the soil and container interface could have on root growth. RPR was determined only in the middle 2.54 cm core which was 25 compacted to various bulk densities according to treatments. Root measurements in each layer of the soil container assembly were determined by cutting the soil core system into its three primary components and washing the roots from the soil of each layer using the hydropneumatic elutriation method developed by Smucker, et al., (1982). Root length for each layer was approximated by the line intercept method of Newman (1966) as modified by Tennant (1972). The amount of roots within each layer of the core assembly which were estimated by the line intercept method is referred to as the total root length. The root length density is the amount of roots per unit volume of soil. 3.3 Field Experiment The trial was conducted for three seasons (1983, 1984, and 1985) at the Crop and Soil Sciences Research Farm in East Lansing, Michigan. The same soil type, previously described in the procedure for the greenhouse experiment was used for the field experiment. Cultivars of barley and oats were selected from those already grown by farmers in Michigan. The barley cultivars used were, namely: Morex (Cree/Bonanza), ND4242, Robust (Morex/Manker), and W7222 (Thompson Seed Co., Canada). Oat cultivars used were as follows: Heritage (Mi 56-22-1689/2* Marino), Korwood (Beaver/Garry//Clintland/CI 15163), Mariner (Garry/Mi56-22-1493), and SD78-0304. All barley and oat 26 cultivars were included in the yield trials of the Barley and Oats Breeding Program of the Department of Crop and Soil Sciences, Michigan State University. The experiment was a two factor factorial with the split arranged in randomized complete block design with four replications. The two factors were compaction, the main plot and cultivars, the subplots. Seeds were tractor-drilled at the row spacing of 25 cm between rows. Each plot consisted of five rows with initial dimension of 5.5 m long and 1.25 m wide. Because root sampling was destructive, duplicate plots were established for (1) soil core samples and dry matter weights and, (2) yield information. The plots sampled for root length and dry matter were not used for grain yield determination. For grain yield, all five rows were trimmed back and the remainder, after the alleys were removed, was 4 m long and 1.25 m wide or a total of 5 m2 harvested area. The heads were harvested using a Hege small plot combine. Soil compaction was achieved by one pass across the plots with a Ford 3600 tractor, having a wheelbase weight of 3600 kg and a tire inflation pressure of 0.86 kg cm}, and speed of approximately 5 miles per hour. The tractor was made to pass over the compaction treatment plots including the spaces in between rows and plots. Compaction was done within 7 to 14 days after seedling emergence at field capacity moisture content. Bulk densities were calculated from core samples taken a day after tractor wheel compaction 27 using the procedure as illustrated by Foth (1977) and during root sampling using the method developed by Srivastava et al.(1982). A total of 8 cores were taken tractor compaction for each treatment field core samples were taken for each experimental plot. Soil core samples for quantitative root analysis were taken at the early grain-filling stage (soft-dough) for both barley and oats. Soil cores were taken only during the 1983 and 1984 trials because the core sampler was not available in 1985. Portions, 22.9 cm long, within the three middle rows of the plots were randomly chosen and marked off before the soil cores were taken. Plant parts above the soil surface were cut off and oven-dried for total dry matter (TDM) measurements. Then the steelcased, tractor mounted core sampler (Srivastava et al., 1982) was placed on the spot where the plants were cut off and then driven into the soil by the pneumatic hammer until the desired depth was reached. The core sampler was pulled out of the soil by the hydraulic lift. The core samples were 7.62 cm wide, 22.9 cm long and trimmed to 45.7 cm deep. The whole core was subdivided into 18 subsamples, each having a volume of 443 cm3, using a steel fractionator and a hydraulic jack. The roots in the subsamples were washed free of soil using the hydropneumatic elutriation method developed by Smucker et al. (1982). Washed roots were preserved in 10% formaldehyde solution and stored at.49 C in a growth chamber. Root lengths were estimated using a procedure developed by Newman 28 (1966) and modified by Tennant (1972). Data such as height at maturity, total dry matter, grain yield, and test weight were also taken. Heights were measured from 5 plants selected randomly within the three innermost rows of each plot. A microcomputer statistical package, MSTAT, was used to design and analyze data for both the greenhouse and field experiments. Data were analyzed by the analysis of variance and differences among means were determined by using the Duncan's Multiple Range Test (DMRT) at the 5% level of probability. In field experiment, compaction treatment mean differences were determined at the 10% level of probability. Dyer (1982) and Dyer and Brown (1983) observed a characteristic of roots which complicates the interpretation of results. Root data are not normally distributed and their statistical distribution may not be constant across experiments through time. The impact of this non-normal distribution is to modify the significance level associated with various tests. Because of the high variability of root growth within the soil layer in field experiment, it was appropriate that a 10% level of probability was used. CHAPTER IV RESULTS AND DISCUSSION 4.1 Greenhouse experiment 4.1.1 Greenhouse experiment with barley The effects of soil compaction on four barley cultivars after 14 days are presented in Table 1. A high soil bulk density reduced the root growth rate (RGR) by 32-38% and the root length density (RLD) by 35-41%. The same RGR and RLD was obtained at low and medium bulk densities. The root penetration (RPR) values were significantly different (P>0.01) in all three bulk densities with 0.82, 0.62, and 0.50 at the low, medium and high bulk densities, respectively. There was a significant reduction in total dry matter (TDM) at the high bulk density. Plant height was not significantly reduced and there was a significant compaction x cultivar interaction in both plant height and TDM showing that height and TDM of only some cultivars were significantly reduced by high bulk density. The effects of the middle layer compacted at different bulk densities on the RLD of barley cultivars within the whole core, the top and bottom layers of the core are shown 29 30 Table 1. The effects of soil compaction on plant height, total dry matter (TDM), root penetration ratio (RPR), root length density (RLD), and root growth rate (RGR) of four barley cultivars 14 days after seedling emergence. Greenhouse experiment, 1987. Bulk density Plant ht. TDM RPR RLD RGR (Mg m‘a) (cm) (mg plt") (cm cm“) (cm day") 1.3 32.0 a 147 a 0.82 a 2.2 a 17.8 a 1.6 32.4 a 147 a 0.61 b 2.0 a 16.4 a 1.9 31.9 a 140 b 0.50 c 1.3 b 11.1 b Comp x Cult * ** n.s. n.s. n.s. In each column, values followed by the same letter are not significantly different at 1% level of probability by DMRT. Mean of 8 replications. *-significant differences at 5% level: **-highly significant differences at 1% level n.s.-no significant differences 31 in Table 2. The RLD was the same within the layers above the middle layer with different bulk densities. The RLD within the bottom layers followed the same magnitude of significant differences as that of the whole core (Table 2). The same RLD was obtained among cultivars within the whole core as well as the bottom layers when the middle layer had low and medium bulk densities. W7222 had significantly higher RLD than Bowers and Morex in all segments when the middle layer had high bulk density. At the low bulk density, the RLD within the whole core of all cultivars were the same but at high bulk density, the magnitude of reduction in RLD for W7222 was significantly lower (2.7-2.5) compared with Bowers (2.1-1.7) and Morex (2.4-1.6) (Table 3). At the bottom layer, between the the low and high bulk densities, the RLD of Bowers and Morex were significantly lower than W7222. The RLD of W7222 quantitatively increased from 2.4 cm cm'3 at the low bulk density to 2.5 cm cm'3 in the bottom layer of the high bulk density. The amount of roots within the whole core assembly estimated linearly is referred to as total root length. The relative root length is the proportion (%) of the total root length within each layer of the core relative to the total length of roots within the whole core. The total root length among cultivars was the same within the soil core with the middle layer low and medium in bulk density (Table 4). W7222 had significantly longer total root length than Bowers and 32 Table 2. Root length density of four barley cultivars within the whole soil core assembly, top, middle, and bottom layers when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987. Bulk density Whole core' Top Middle Bottom (Mg m'a) ----------- cm cm"3 -------------- 1.3 2.4 a 2.8 a 2.2 a 2.3 a 1.6 2.2 ab 2.8 a 2.0 a 2.1 ab 1.9 2.0 b 2.7 a 1.3 b 2.0 b In each column, values designated by the same letter are not significantly different at 5% level of probability by DMRT. Mean of 8 replications. ' Volume of whole core is different from those of the top, middle and bottom layers of the core. 33 Table 3. Root length density (RLD) of four barley cultivars within whole core, top, middle, and bottom layers when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987. Bulk densigy Cultivars Whole' Top Middle Bottom (Mg m" ) -------------- cm cm’3 ---------------- 1.3 Bowers 2.1 abcd 2.1 d 1.8 bcd 2.3 ab Morex 2.4 abc 3.0 abc 2.2 ab 2.3 ab Robust 2.3 abc 2.7 bcd 2.0 abc 2.3 ab W7222 2.7 a 3.5 a 2.6 a 2.4 ab 1.6 Bowers 1.9 cd 2.2 d 1.7 bcd 1.9 abc Morex 1.9 cd 2.6 cd 1.9 had 1.8 bc Robust 2.4 abc 3.0 abc 2.1 ab 2.3 ab W7222 2.5 abc 3.2 abc 2.3 ab 2.3 ab 1.9 Bowers 1.7 d 2.1 d 0.9 e 1.8 bc Morex 1.6 d 2.7 bcd 1.3 de 1.4 c Robust 2.1 bod 2.6 cd 1.4 cde 2.1 ab W7222 2.5 ab 3.3 ab 1.7 bcd 2.5 a In each column, values designated by the same letter are not significantly different at 5% level of probability by DMRT. Mean of 8 replications. ' Volume of the whole core is different from those of the top, middle and bottom layers of the core assembly. 34 Table 4. Total and relative (%) root lengths of four barley cultivars within the top, middle and bottom layers of the core when the middle layer was compacted to bulk three densities. Greenhouse experiment, 1987. Bulk Total root Relative root length density Cultivars length Top Middle Bottom Mg m'a) (cm) ---------- % ----------- 1.3 Bowers 1236 abcd 18.9 c 17.0 abcd 64.1 ab Morex 1397 abc 25.2 b 19.2 ab 55.6 cdef Robust 1350 abc 23.4 bc 17.9 abc 58.7 abcde W7222 1532 a 26.8 b 20.0 ab 53.2 def 1.6 Bowers 1110 cd 23.4 bc 19.4 ab 57.2 bcdef Morex 1120 cd 27.2 b 21.0 a 51.8 ef Robust 1391 abc 24.8 b 18.5 ab 56.7 cdef W7222 1427 abc 25.3 b 18.7 ab 56.0 cdef 1.9 Bowers 992 d 24.4 b 11.1 e 64.5 a Morex 943 d 32.9 a 16.6 bcd 50.5 f Robust 1196 cd 25.0 b 13.4 de 61.6 abc W7222 1466 ab 26.0 b 14.0 cde 60.0 abcd In each column, values designated by the same letter are not significantly different at 5% level of probability by DMRT. Mean of 8 replications. 35 Morex at high bulk density. Among the cultivars, Morex had the lowest regrowth after its roots penetrated the middle layer high in bulk density resulting in a significantly lower total root length within the bottom layer. Taylor and Burnett (1964) and Russell and Goss (1974) reported a decrease in root elongation rates, of both the main axes and laterals, with greater soil compaction. 4.1.2 Greenhouse experiment with cats The root length density (RLD) and root growth rates (RGR) of oats were significantly reduced only at the high bulk density (Table 5). The RPR was significantly different in all three soil bulk densities. The RPR was reduced from 0.84 at low bulk density to 0.67 and 0.31 in the medium and high bulk densities respectively. The high bulk density significantly reduced plant height. The total dry matter were significantly different in all three bulk densities. There was no compaction by cultivar interaction for height, total dry matter, root penetration ratio, root length density and root growth rates. The root length density of oats within the whole core decreased significantly as the bulk density of the middle layer increased. The RLD values decreased from 1.2 cm cm'3 (100%) for low bulk density, to 1.1 (92%) and 1.0 (83%) for the medium and high bulk densities (Table 6). The RLD was the same within the top layer of the core with the middle 36 Table 5. Effects of soil compaction on plant height, total dry matter (TDM), root penetration ratio (RPR), root length density (RLD), and root growth rate (RGR) of four oat cultivars 14 days after emergence. Greenhouse experiment, 1987. Bulk density Plant ht. TDM RPR RLD RGR (Mg m'a) (cm) (mg plt’l) (cm cm'a) (cm day“) 1.3 28.3'a 120*‘a 0.84**a 1.3'a 10.4 a 1.6 28.9 a 113 b 0.67 b 1.2 a 10.0 a 1.9 26.8 b 101 c 0.31 c 1.1 b 8.8 b In each column, values followed by the same letter are not significantly different at 1% level (**) and 5% level (*) of probability by DMRT. Mean of 8 replications. 37 Table 6. Root length density of four oat cultivars within the whole core, top, middle, and bottom layers when the middle layer was compacted to three different bulk densities. Greenhouse experiment, 1987. Bulk density Whole core Top Middle Bottom (Mg m'a) ---------------- cm cm'3 ------------- 1.3 1.2 a 1.1 b 1.3 a 1.1 a 1.6 1.1 b 1.1 b 1.2 a 1.0 b 1.9 1.0 c 1.4 a 1.1 b 0.8 c In each column, values designated by the same letter are not significantly different at 5% level of probability by DMRT. 38 layer low and medium bulk densities but both RLD's were significantly lower than the RLD of the core with the middle layer high in bulk density. The middle layer high in bulk density caused the RLD at the layer above it to increase significantly (Table 6). Table 6 also shows a significantly lower recovery by oat roots which had penetrated the middle layers medium and high in bulk densities. Results of a study on oats by Wiersum (1957), showed that when soil strengths are great, roots can enter the soil volume if the diameter of soil pores are larger than the root tips. Schuurman (1965) observed that roots of cats grew into soil compacted at 1.52 Mg cm'3 only if they first grew into and through a layer of soil compacted to a lower density. According to Barley and Greacen (1967), increasing soil density is generally associated with decreasing mean pore diameter, which in turn, is usually associated with lesser root penetration. Because of the high bulk density of the middle layer, the pore diameters of the soil were too small for most of the roots of oats to penetrate. The root main axes and laterals were largely confined within the top layer of the soil core with a middle layer high in bulk density, hence a significant increase in RLD within the top layer. The same RLD was obtained from within the whole core, the top and bottom layers when the middle layer had high bulk density (Table 7). The compacted middle layer reduced the top layer RLD in all cultivars by 23-31%. The RLD of oats within the whole core were significantly different 39 Table 7. Root length density of four oat cultivars within whole core, top, middle, and bottom layers of the core when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987. Bulk densigy Cultivars Whole Top Middle Bottom (Mg m') -------------- cm cm’ ------------ 1.3 Heritage 1.1 be 1.1 cd 1.2 bc 1.1 ab Korwood 1.3 a 1.4 abc 1.5 a 1.3 a Mariner 1.1 bcd 1.2 bcd 1.2 be 1.0 bc Ogle 1.0 bcde 0.9 d 1.2 bc 1.0 bc 1.6 Heritage 1.0 cde 1.0 d 1.2 bc 0.9 bcd Korwood 1.2 ab 1.3 abc 1.3 ab 1.1 ab Mariner 1.1 bcde 1.2 bcd 1.2 bc 1.0 bcd Ogle 1.0 cde 1.1 cd 1.2 be 0.9 bcde 1.9 Heritage 1.0 cde 1.5 ab 1.0 c 0.8 def Korwood 1.1 bcde 1.6 a 1.2 be 0.9 cdef Mariner 0.9 e 1.4 abc 1.0 c 0.7 ef Ogle 0.9 de 1.3 abc 1.0 c 0.7 ef In each column, values designated by the same letter are not significantly different at 5% level of probability by DMRT. 40 among cultivars in both the low and medium bulk densities. At the low bulk density, Korwood had a significantly higher RLD than all cultivars. The same cultivar, Korwood, had significantly higher RLD than Heritage and Ogle at the medium bulk densities. The RLD of oat cultivars within the bottom layers were the same when the middle layer had medium and high bulk densities (Table 7). The RLD values in Table 7 also shows that significant genotypic differences in root length density obtained at low soil bulk density is nullified at medium and high soil bulk densities. The total root length of Korwood was significantly higher than Heritage and Ogle in soil cores with middle layers low and medium in bulk densities (Table 8). All the oat cultivars had the same total root length in cores with middle layers high in bulk density. Significant differences in relative root lengths were observed among cultivars only at the soil core with the middle layer low in bulk density. Table 8 shows no resumption of normal root growth in all oat cultivars after the roots had penetrated the layer high in bulk density. 4.1.3 Comparison of the effects of the different bulk densities on barley and oats The RLD of cats were significantly reduced by soil compaction more than barley (Table 9). The mean RLD of oats (1.2 cm cm”) was 33% lower than barley (1.8). Both crops 41 Table 8. Total and relative root lengths (%) of four oat cultivars within the top, middle and bottom layers of the core when the middle layer was compacted to three bulk densities. Greenhouse experiment, 1987. Bulk density Cultivars Total root Relative root length (Mg ma) length Top Middle Bottom (cm) ---------- % -------------- 1.3 Heritage 662 bc 19.8 be 21.8 a 58.4 a Korwood 772 a 19.8 bc 22.1 a 58.1 a Mariner 631 bed 22.5 a 21.6 a 55.9 a Ogle 597 bcde 18.0 c 22.8 a 59.2 a 1.6 Heritage 573 cde 21.1 be 23.9 a 55.0 a Korwood 692 ab 22.4 b 22.3 a 55.3 a Mariner 606 bcde 22.5 b 22.3 a 55.2 a Ogle 574 cde 21.6 bc 23.4 a 55.0 a 1.9 Heritage 563 cde 31.7 a 21.3 a 45.0 b Korwood 623 bcde 30.7 a 21.5 a 47.8 b Mariner 519 e 30.9 a 23.2 a 45.9 b Ogle 527 de 30.6 a 23.1 a 46.3 b In each column, values designated by the same letter are not significantly different at 5% level of probability by DMRT. 42 Table 9. Mean root penetration ratio (RPR) and root length density (RLD) of four barley and four oat cultivars taken from the middle layer 14 days after emergence as affected by different soil bulk densities. Greenhouse experiment, 1987. Crop RPR RLD (cm cm'3) Barley 0.64 a 1.8 a Oats 0.61 a 1.2 b In each column, values designated by the same letter are not significantly different at 5% level of probability by the LSD. Mean of 8 replications. 43 had the same RLD when the soil core had a middle layer with 1.9 Mg mfl’ bulk density. Barley had a significantly higher RLD than oats within the soil core with middle layers low and medium in bulk densities. There was a significant (P>0.05) compaction x crop RLD interaction (Table 10). The same RPR for both barley and oats was obtained when the middle layers had low and medium bulk densities, but barley had a significantly higher RPR when the middle layer had a high bulk density. Highly significant ( P>0.01 ) compaction x crop RPR interaction was observed for both barley and oats (Table 10). Figure 1 shows a steadily declining RLD of barley as the bulk density of the middle layer increased compared to an almost constant RLD of oats. The same figure indicates that the RPR's of both the oats and barley were similarly reduced from low to medium bulk density. The RPR of cats however, significantly decreased with higher bulk density while that of barley remained the same. These results suggest that when oats grow in a soil layer high in bulk density, its roots tend to proliferate above the layer high in bulk density rather than penetrate through it. Previous data (Table 5) attests that oats have a significantly lower root penetration ratio at high soil bulk density. Barley roots, as the result indicates, would penetrate a layer with a high bulk density better than oats. Russell and Goss (1974) disclosed that crop species reacted differently in their elongation rates at specific soil strengths. The difference between barley and oats in their 44 Table 10. Root penetration ratio (RPR) and root length density (RLD) of four barley and four oat cultivars 14 days after emergence as affected by different soil bulk densities. Greenhouse experiment, 1987. Bulk densigy Crop RPR RLD (Mg m' ) (cm cm'a) 1.3 Barley 0.82 a 2.1 a Oats 0.84 a 1.3 b 1.6 Barley 0.61 bc 2.0 a Oats 0.67 b 1.2 b 1.9 Barley 0.50 c 1.3 b Oats 0.31 d 1.1 b Bulk density x Crop 0.01 0.05 In each column, values designated by the same letter are not significantly different at 5% level of probability by the LSD. Mean of 8 replications. 45 2.4 A 4 O F? 2.0-1 \0 S 1.6- \ E i D O \O/ 1.2'4 KER-“D O . g 08‘ B—a Oats [60605) O 4‘ 0—0 Barley ' 1.3 1.6 1.9 (0) Bulk density (Mg m‘3) 0.9 0'8“ \ ILSDLOS) 0.7- a: 0.6‘ ‘ C1. 0: 0.5“ A 0.4»4 0.3. H Oats O 2 H Barley ' 1.3 1.6 1.9 Bulk density (Mg I'D—3) (b) Figure 1. Relationships between (a) compaction and root length density (RLD) and (b) compaction and root penetration ratio (RPR) of barley and oats 14 days after emergence. 1987 46 response to high soil bulk density was also evidenced by a resurgence of root growth after barley roots penetrated the layer high in bulk density which was not observed in oats. Among the oat cultivars used none showed resurgence of root growth (Figure 2), but all barley cultivars except Morex showed a resurgence of root growth (Figure 3). Hence, a significant increase in the RLD in soil layers below the highly compacted middle layer. It was observed that the magnitude of the RPR of the crop cultivar is not always associated with its RLD. A barley cultivar W7222 had a significantly higher RLD as well as RPR. Oat cultivar Korwood, which had a significantly higher RLD, did not consistently show a significantly higher RPR than the other oat cultivars (Figure 4). Barley and oat cultivars differ quantitatively in their root length density (RLD) and total dry matter (TDM) as a result of compaction. In barley, two cultivars showed contrasting responses to compaction. Bowers had a steadily decreasing RLD with increasing levels of compaction while the magnitude of TDM remained the same. In contrast, W7222 had a higher magnitude of RLD and lower TDM relative to that of Bowers but both RLD and TDM remained the same even when the compaction level increased from low to high (Figure 5). The mean RLD of W7222 was significantly higher than that of Bowers while the mean TDM of Bowers was significantly higher than that of W7222 (Table 1). In oats, Heritage had the same RLD as Ogle while the 1.9 1.7. RLD (cm cm—s) 0.7« 0.5 47 1.5- 1.3‘ 1.11 0.9« LSD(.05) \\\\\\\\\\\\\U \\\\\\\\l To p« \\\\\\\.\\\\\\\\\\‘l Middle « T0 p . \\\\\\\R\\\\\\l Middle - Top. Middle 1.\\\\\\\\‘ Bottom lk\\V Top . Middle . Bottom .._\\\\‘ Bottom «mm Bottom «m Korwood Mariner Ogle I (D I. H- 0 L0 (D Figure 2. Effects of the mi dle layer high in bulk density (1.9 Mg m’ ) 0n the root length density of 4 oat cultivars within the top and bottom core segments 14 days after emergence. 1987 48 RLD (cm cm—Z’) 3.6 3. 2 . ILsoms) 2.8- 2.43 2.0- 1.6« 1.24 0.8— 0.4: $.85 3% 3% fig 2003 2:8 20% 208 Bowers Morex Robust W7222 Figure 3. Effects of the middle layer high in bulk density (1.9 Mg m‘s) on the root length density of 4 barley cultivars within the top and bottom core segments 14 days after emergence. 1987 [150(05) H i A r RLD (cm cm-3) ow llsocos) 0.7- 0.5. RPR 0.54 Bowers Morex Robust W7222 (b) Barley Cultiva rs 49 LSD(.05) ill]— Heritage.m Korwoodim Manner\\\\\\V Ogle-1m (d) Oct cultivars Figure 4. Effects of bulk density on (a,c) root length density (RLD) and (b,d) root penetration ratio (RPR) of 4 barley (a,b) and 4 oat cultivars (c,d) 14 days after emergence. 1987 SO Wm D 3.0. rmoflobwvuobo Mo E 3:. 508.8738 Na Na ML. NM NO mm #0 me RN #0 RLD (cm cm—s) fu :w Eb A...“ fa To A...“ 1.01.0 fa fa Mb @0558 710sz moocw» EVNNN 1.16:8 w. woos rm: :5 amzwmq 36V one 8.8. a? do. 333.. 3?; or. 1? U013 8:?me 3 «88:8 8 mo: cc; magma? 5mm 100 Mac 3.0 Moo 100 3.0 Lao LNG :0 400 (L_1ld 6w) WCll 51 TDM of Ogle was significantly higher than that of Heritage. Korwood, with intermediate TDM, had significantly higher RLD than Heritage and Ogle (Table 5). All three cultivars show a decreasing magnitude of RLD and TDM as the level of compaction increased (Figure 6). 4.1.4 Stepwise regression analysis procedure The response of crops and cultivars to soil compaction was analyzed using the stepwise regression procedure. The stepwise regression procedure as reviewed and elucidated by Acquaah (1988), is only one of the four general procedures in multiple regression analysis which are used for model- fitting. This procedure was used to determine if changes in the dependent variable, Y (total dry matter for the greenhouse experiment; yield and total dry matter for the field experiment), is associated with unit changes in the independent variables (root length density in the different layers of the core for greenhouse; and root length density in upper 0-23 cm and lower 23-46 cm of the core sample for the field experiment). The stepwise regression procedure of the statistical analysis system (SAS, 1985) package was on an IBM Microcomputer used for model-fitting. According to the procedure, a variable, once selected is not guaranteed a place in the model since the subsequent addition of a new variable may render its contribution to variance, as 52 RLD (cm cm"3) flm flu. N 4.0 om U 3.0. rwomobwvnogm E 40:. rmonobwvumoum flu flu flo flu flm flo flu flm flo flu flm fl© Imwzooo xoozooa 73139. 090 30:8 m. moo.” _ms 9 Q0390. 3:8 and 3?: 3. 9% 3048.. 320 9. a. on: 05:38 3 xmwposwm 3 ac? amazon 5mm :0 Euo END :0 .50 00 mo (L_1ld 6w) WCll 53 determined by the partial F-statistic, non-significant at a specified level. For this study, all variables that met the 0.1500 significance level were entered into the model. The general form of the multiple regression equation is as follows: Y = a + bIJQ + ... + bn)g where: a = the intercept on the Y axis r5 = the partial regression coefficient of variables, and )9 = individual variables to be included in a model 4.1.5 Stepwise regression analysis of greenhouse experiment with barley For the greenhouse experiment with three independent variables, the regression equation is: where: Y= an estimate of the total dry matter )q= RLD within the top layer )Q= RLD within the middle layer )g= RLD within the bottom layer 54 Generally, for each of the specified bulk densities, roots in a particular core segment or region of the soil was most important in influencing the TDM (Table 11). Furthermore, there were cultivar differences in the region (Xn ) involved and two classes were usually observed. At 1.3 Mg m'a, cultivars Bowers and Morex depended on X3 while Robust and W7222 depended on X1. However, at 1.6 Mg m’a, Bowers and Morex depended on,X5'while Robust depended on X3, a reversal in roles of the effects of core segment roots on TDM. For all cultivars, X5 roots did not have a significant influence on TDM at 1.6 Mg m“. At the highest bulk density, 1.9 Mg m”, the effect of X3 on the TDM was not significant in any cultivar. Because the middle layer (X5) had a high bulk density, the pore space may have been too small to permit penetration, hence less amount of root growth in X3. Barley cultivars respond to levels of compaction by growing roots in the different core segments. The root system at the bottom of the highly compacted core segment appears to be inhibited. 4.1.6 Stepwise regression analysis of greenhouse experiment with oats Table 12 shows that oat cultivars had a different pattern of response to compaction as those of barley. Generally, in all three bulk densities, X5 is the most 55 Table 11. Partial regression coefficients (%) of four barley cultivars' root length density in different layers selected by the stepwise regression procedure with the total dry matter as the dependent variable. Greenhouse experiment, 1987. Independent variables (rfi Bulk density (Mg m”) Cultivars Top(XQ 1Middle(xg Bottom(Xg 1.3 Bower - - 51.8** Morex - - 40.2* Robust 90.8*** 7.9*** - W7222 94.0*** - - 1.6 Bowers 67.5*** - — Morex 62.3** - 22,7** Robust - - 57,1** W7222 - — - 1.9 Bowers - 38.6* - Morex 79.3*** - - Robust 42.6* - - W7222 - 45.2* - All independent variables entered in the model(with partial F-values) are significant at the 0.15 level. In each column, missing values are not significant at the 0.15 level. *** - significant at the 0.01 level of probability. ** - significant at the 0.05 level * - significant at the 0.10 level 56 Table 12. Partial regression coefficients (%) of four oat cultivars' root length density in different layers selected by the stepwise regression procedure with the total dry matter as the dependent variable. Greenhouse experiment, 1987. Bulk density (Mg m'a) Cultivars Top (X1) Middle (X2) Bottom (X3) 1.3 Heritage 90.7*** 7.5*** 1.8*** Korwood 94.2*** 3.3** 2.5*** Mariner - 78.0*** _ Ogle 84.0*** 11.1** 4.9*** 1.6 Heritage - 94.1*** - Korwood 89.7*** 6.1** 4.2*** Mariner 78.1*** 11.7* 10.2*** Ogle 85.6*** 12.0*** 2.4*** 1.9 Heritage 39.6* 29.2* 31.2*** Korwood 80.3*** 16.7*** 3.0*** Mariner 66.9*** 22.8** 10.3*** Ogle 41.6* 25.9* 32.5*** Independent variables (r3) All independent variables entered in the model(with partial F-values) are significant at the 0.15 level. In each column, missing values are not significant at the 0.15 level. *** - significant at the 0.01 level of probability. ** * - significant at the 0.05 level - significant at the 0.10 level 57 important variable affecting the TDM. As compaction increases, X2 and then X3 becomes increasingly important as the effect of x, progressively decreases. The response of oats differs from that of barley where the variables were selectively important at different levels of compaction. 4.2 Field experiment 4.2.1 Effect of tractor wheel compaction The bulk densities of the soil in Table 13 were calculated from the core samples taken a day after tractor compaction and during root sampling. Bulk densities values from the soil cores in compacted soil were significantly higher (P>0.10) than the noncompacted soil, indicating that tractor wheels caused the soil bulk density to increase significantly even with a single pass. Table 13 also shows that a fairly uniform compaction was achieved in both soils planted with barley and oats. Bulk density values from soil cores taken during root sampling at soft dough stage showed that the compacted soil had a significantly higher bulk density within the 0-23 cm layer compared with the same layer of the noncompacted soil. The same bulk densities were obtained from the 23-46 cm layer of the two compaction treatments. Soil cores were taken only during the 1983 and 1984 experiments because the core sampler was not available in 1985. Froehlick (1974) reported that a small crawler tractor and load of 58 Table 13. Effect of tractor wheel compaction on the bulk density of soils at 0-10 cm (taken a day after compaction), upper 0-23 cm, and lower 23-46 cm layers (taken at crop's soft-dough stage). Field experiments, 1983-84. Treatments Sources . Soil Layers ** of soil 10 cm 0-23 cm 23-46 cm cores --------- Mg m’3 ------------ No compaction Barley 1.52 b Oats 1.56 b Whole plot 1.51 b 1.60 a With compaction Barley 1.65 a Oats 1.62 a Whole plot 1.61 a 1.63 a Bulk density values are mean of 8 soil core samples for each compaction treatment. " Bulk density values are mean of 36 soil core samples for each layer and compaction treatment. In each column, values designated by the same letter are not significantly different at 10% level of probability by the LSD. 59 Douglas fir logs caused an increase in soil bulk density and the impacts of compaction were evident to a depth of 15 to 23 cm. Mckyes, et al., (1980) suggested that most compaction (usually less than 25 cm) from surface operation of agricultural equipment is not deep enough, to require subsoiling, but the higher pressure equipment used for right-of-way construction may compact the soil to such depths that deep tillage is needed. 4.2.2 Field experiment with barley In all three years of the field experiment, barley yields were significantly reduced by compaction (Table 14). The cultivars responded differently only once in three years of the study. In the 1985 experiment, the grain yield was significantly different among cultivars within the compacted treatment, and the yields of some cultivars were significantly reduced due to compaction more than others. The test weights were reduced by compaction in all trials. In all three years, test weights among cultivars were equally reduced by compaction. Significant reduction in total dry matter and plant height was not consistent (Table 14). The root length density was consistently reduced due compaction within the whole core and within the top 0-23 cm of the soil. The root length density of cultivars was similarly reduced by compaction (Table 14). These results 60 Table 14. Analysis of variance summary for yield, test weight, total dry matter (TDM), height and root length density of four barley cultivars evaluated with and without compaction. Field experiments, 1983-1985. Year experiment was conducted Variables Treatments 1983 1984 1985 Yield Compaction *_1/ * * (gtmfi) Cultivars n.s. n.s. * Comp x Cult. n.s. n.s. * Test weight Compaction * * * (g l”) Cultivars n.s. * * Comp x Cult. n.s. n.s. n.s. TDM Compaction n.s. * - (g‘mfl) Cultivars nus. n.s. - Comp x Cult. n.s. n.s. - Height Compaction n.s. - * (cm) Cultivars n.s. - * Comp x Cult n.s. - n.s. Root length density (cm cm“)_1/ Whole core Compaction * * - Cultivars n.s. * - Comp x Cult. n.s. n.s. - 0-23 cm Compaction * * - Cultivars n.s. n.s. - comp X C1111: n08. nos. - 24-46 cm Compaction n.s. * - Cultivars n.s. * - Comp x Cult. n.s. n.s. - Note: * - significantly different at the 5% level of probability by Duncan's Multiple Range Test (DMRT). n.s. not significantly different at the 5% level by DMRT. _1/ Significantly different at 10% level of probability by DMRT. 61 show that the reduction in the RLD of barley due to tractor wheel compaction was confined mainly to the upper 0-23 cm of the soil. Evidence shows significant differences in the RLD within the top 0-23 cm layer of the soil Core but the same root length densities were obtained within the lower 23-46 cm. Although the RLD's were reduced only at the upper 0-23 cm and the RLD's at the 23-46 cm layer were not, the tractor wheel compaction caused significant reduction in the RLD of the whole core. This effect could be more obvious in barley because barley roots often grow nearer the surface, especially in soils with poor aeration, such as a compacted soil (Weaver, 1926). In this study, the soil compaction by tractor wheels may have caused the roots of barley to grow superficially, and the underdeveloped main and lateral axes resulted in a significantly lower root length densities within the tractor wheel compacted treatments. The yield and root length density of the four barley cultivars were significantly reduced by compaction. Mean reduction for yield was 35% and that of RLD for the whole core was 34% (Table 15). Cultivars, however, varied in magnitude of reduction of both yield and RLD. With compaction, the yield of Robust and ND4242 decreased along with the RLD while the RLD of W7222 increased relative to yield of the two cultivars (Figure 7). 62 Table 15. Mean grain yield and root length density of four barley cultivars across years of study as affected by soil compaction. Field experiments, 1983-1985. Treatments Without compaction With compaction % reduction P>F (DMRT) Whole sample Without compaction With compaction % reduction P>F (DMRT) Upper 0-23 cm Without compaction With compaction % reduction P>F (DMRT) Lower 24-46 cm Without compaction With compaction % reduction P>F (DMRT) Yield (9 m4 ) across years Mean % 1983 1984 1985 decrease 250 a 198 a 426 a 146 b 131 b 304 b 41.6 33.8 28.6 35 0.10 0.02 0.01 Root length density (cm cm“) 0.5 a 0.7 a 0.3 b 0.5 b 40.0 28.6 34 0.06 0.01 0.8 a 1.0 a 0.4 b 0.7 b 50.0 30.0 40 0.01 0.01 0.3 a 0.5 a 0.2 a 0.4 b 33.3 20.0 27 n.s. 0.03 63 240 0.9 zzz: Yield; LSD(0.10)=24.1 [:1 RLD; LSD(0.10)=0.2 2204 ~O.8 7200 a 2 - E 6 6 7 ~07 s ‘80 f g 2 2 2 /‘ 2 _ £160 2 2 2 c r a r 'é a 4 ¢ 0 140* ¢ ¢ ¢ 7 4 ? ~06 120« 6 Z 6 a a 100 N N / 0.4 1;; e (\l 4,7; <1» N j (\l N 3 N N D 5* S -8 a R 00: z 3 cr 2 3 No compaction Figure 7. Grain yield and root length density With compaction (RLD) of 3 barley cultivars in response to soil compaction. 1984 (,L._uJo LUO) (1'13 64 4.2.3 Field experiment with cats Results of the three year field study on oats showed that yields were consistently reduced by compaction, on the average by 17%. There were no consistent significant differences in yield among cultivars, and yields of all cultivars were equally reduced by compaction (Table 16). Test weights in two out of three years of data were significantly reduced by soil compaction. In all three years of the study, cultivars had significantly different test weights, but the test weights of all cultivars were equally reduced by compaction. The effect of compaction on the total dry matter and height of oats was not consistent over the three year period. The significant differences in root length density of oats within the top 0-23 cm and the whole care were sporadic over the two years, but the compaction treatment had a consistently and significantly lower RLD than no compaction at the 23-46 cm layer (Table 17). The shallow soil compaction by tractor wheels severely limits the elongation rates of main axes and lateral within the top 0-23 cm, thus significantly reducing the root length density within the lower 23-46 cm of the core. Russell and Goss (1974) concluded that if the pores are too small for the main root axes to enter, but does not restrict the laterals, the laterals proliferate resulting to a root system with more branches. When the soil pore sizes are too small for the 65 Table 16. Mean grain yield and root length density of four oat cultivars across years of study as affected by soil compaction. Field experiments, 1983-1985. Treatments Without compaction With compaction % reduction P>F (DMRT) Whole sample Without compaction With compaction % reduction P>F (DMRT) Upper 0-23 cm Without compaction With compaction % reduction P>F (DMRT) Lower 24-46 cm Without compaction With compaction % reduction P>F (DMRT) Yield (g m"2 ) across years Mean % 1983 1984 1985 decrease 307 a 234 a 375 a 268 b 169 b 337 b 12.7 27.8 10.1 17 0.01 0.01 0.01 Root length density (cm cm”) 0.6 a 0.7 a 0.5 a 0.5 b 16.6 28.6 23 n.s. 0.02 0.8 a 1.0 a 0.7 a 0.6 b 12.5 40.0 21 n.s. 0.02 0.4 a 0.5 a 0.3 b 0.4 b 25.0 20.0 23 0.06 0.05 66 Table 17. Analysis of variance summary for yield, test weight, total dry matter (TDM), height and root length density of four oat cultivars evaluated with and without compaction. Field experiments, 1983-1985. Year experiment was conducted Variables Treatments 1983 1984 1985 Yield Compaction * * * (g‘mq) Cultivars n.s. n.s. * Comp x Cult n. . n.s. n.s. Test weight Compaction n.s. * * (g 1") Cultivars * * * Comp x Cult n.s. n.s. n.s. TDM Compaction n.s. * - (g‘mfi) Cultivars n.s. n.s. - Comp x Cult n.s. n.s. - Height Compaction n.s. - * (cm) Cultivars n.s. - * Comp x Cult n.s. - n.s. Root length density (cm cm”)_1/ Whole sample Compaction n.s. * - Cultivars * * - Comp x Cult n.s. n.s. - 0-23 cm Compaction n.s. * - Cultivars n.s. n.s. - Comp x Cult n.s. * - 24-46 cm Compaction * * - Cultivars * n.s. - Comp x Cult n.s. n.s. - Note: * - significantly different at the 5% level of probability by Duncan's Multiple Range Test (DMRT). n.s.not significantly different at the 5% level by DMRT. _1/Significantly different at the 10% level of probability by DMRT. 67 laterals to enter, the entire root system is stunted. This could be the reason why the root length densities of oats in the tractor compacted soils were significantly lower than those of the noncompacted soils at the 23-46 cm layer of the soil care. In noncompacted soils, significant differences in root length densities was obtained among oat cultivars, but tractor wheel compaction nullified the significant differences in RLD among cultivars. Without compaction, the RLD of heritage was significantly than other cultivars but with tractor compaction, the same RLD was obtained among oat cultivars (Table 18). Figure 8 shows that both the grain yield and whole core RLD of oat cultivars were significantly reduced with compaction. Moreover, there was a varied response to compaction as indicated by the magnitude of RLD relative to the differences in yield. Without compaction, the RLD's were the same but with compaction, Korwood had significantly higher RLD than Heritage and Mariner. The greenhouse data in Table 8 showed that Korwood had significantly higher RLD than Heritage but not with Mariner at similar bulk density (1.6 Mg m”, in greenhouse compared with 1.61 Mg m”, field experiment, Table 13). 4.2.4 Stepwise regression analysis for field experiment For the field experiment with two independent variables, the regression equation is: 68 Table 18. Compaction by cultivar interaction on mean root length density of four oat cultivars at the upper 0-23 cm layer of the soil core. Field experiment, 1984. Cultivars No With Comp x Cult compaction compaction P>F ------- cm cm”------- SD 78-0304 1.0 b 0.6 c 0.1 Heritage 1.1 a 0.6 c Mariner 0.9 b 0.6 c Korwood 0.9 b 0.7 c In each column, values designated by the same letter are not significantly different at the 5% level of probability by the DMRT. Grain yield (9 m—Z) 520 69 0.9 480~ 440- 400 ~ 360i 3204 2804 240* 200- - Yield; LSD(0.05)=23.5 [:1 RLD; Lso(o.os)=o.13 ~0.8 ~O.7 .05 0.4 Vt I o o a) p o -o '8 a» 3 O "7 a) 5 O O c O O a r: o l .4: ._ s I .4: ... 3 co 8 8 a co 8 s a '\ I 2 x '\ :1: 2 x o Q in w No compaction With compaction Figure 8. Grain yield and root length density (RLD). of 4 oat cultivars in response to soul compaction. 1984 (94.03 we) O‘ltl 70 Y = a + blx1 + bzx2 where: Y = an estimate of the yield; total dry matter )0 = RLD within the upper 0-23 cm of the core RLD within the lower 23-46 cm of X N II the core 4.2.5 Stepwise regression analysis of field experiment with barley Table 19 shows varying patterns of response to compaction treatments by barley cultivars. Without compaction, X1 was important to the yield of Robust while it was X, in with compaction. Earlier data (Table 11) indicates a reversal in roles of variables for the same cultivar between the low and medium bulk densities. However, X2 was important to the TDM of Robust in both compaction treatments. With compaction, both the yield and TDM of Robust depended upon X2 but were not significant to the same parameters of cultivars ND4242 and W7222. In the same treatment, only the yield of W7222 was dependent upon Xltnn: the same variable was not important to both the yield and TDM of other cultivars. In two cultivars, W7222 (no compaction) and ND4242 71 Table 19. Partial regression coefficients (%) of three barley cultivars' root length density in different layers selected by the stepwise regression procedure with the yield and total dry matter as the dependent variable. Field experiment, 1984. Treatments Cultivars Dependent Independent variables(r2) variables Upper Lower 0-23 cm 23-46 cm x1 x2 No compaction Robust Yield 91.6** - TDM - 82.5* ND4242 Yield - - TDM - 93.0** W7222 Yield - - TDM - - With compaction Robust Yield - 98.9*** TDM - 98.1*** ND4242 Yield - - TDM - - W7222 Yield 96.0** - TDM - - All independent variables entered in the model(with partial F-values) are significant at the 0.15 level. In each column, missing values are not significant at the 0.15 level. *** - significant at the 0.01 level of probability. ** - significant at the 0.05 level * - significant at the 0.10 level 72 (with compaction), variables X1 and X2 did not have an effect on both the yield and TDM. 4.2.6 Stepwise regression analysis of field experiment with oats Without compaction, X1 was particularly important to the yield of SD78-0304 but had no effect on the same parameter of other cultivars (Table 20). Variable X2 had a significant influence on both the yield and TDM of Korwood only. The yield and TDM of cultivars Heritage and Mariner did not depend upon the RLD in X1 and X2. With compaction, X, was significant to both the yield and TDM of SD78-0304 but did not affect the same parameters of other oat cultivars. Both X1 and X2 were not important to the yield and TDM of Mariner and Korwood (Table 20). The two variables, X1 and X2 did not affect both yield and TDM of Mariner in all compaction treatments. With compaction, the response of oat cultivar SD78-0304 (Table 20) was similar to that of barley cultivar Robust (Table 19) where the yield and TDM of both cultivars were dependent upon the RLD in.X§.‘Without compaction, the yields of the two cultivars were dependent upon X1 and on X2 when the soil was compacted. 73 Table 20. Partial regression coefficients (%) of four oat cultivars' root length density in different layers selected by the stepwise regression procedure with the yield and total dry matter as the dependent variable. Field experiment, 1984. Treatments Cultivars Dependent Independent variables (rfi Variables Upper Lower 0-23 cm 23-46 cm x1 x2 No compaction SD78-0304 Yield 86.8* - TDM - - Heritage Yield - - TDM - - Mariner Yield - - TDM - - Korwood Yield - 98.6*** TDM - 75.5 With compaction SD78-0304 Yield - 90.5** TDM - 98.2*** Heritage Yield - - TDM 97.5*** - Mariner Yield - - TDM - - Korwood Yield - - TDM - - All independent variables entered in the model(with partial F-values) are significant at the 0.15 level. In each column, missing values are not significant at the 0.15 level. *** - significant at the 0.01 level of probability. ** - significant at the 0.05 level * - significant at the 0.10 level CHAPTER V SUMMARY AND CONCLUSIONS Evidence of differences in root growth in cereals has been documented but has not been studied in much detail. In fact, even with the existence of appreciable genetic variation, root characteristics are not given a major consideration in plant breeding programs. The subterranean nature of root research makes it a tedious undertaking to determine and analyze roots quantitatively. A genotype may have the inherent capability to tolerate soil compaction but high bulk density can obscure this genetic trait. Considerable variability is commonly induced by environmental factors, which often masks genetically controlled variability. However, these efforts could potentially result in greater knowledge of the genotype x environment interactions which leads to a greater understanding of the process mechanisms which are limiting crop yields. This study was conducted to determine the 1) genotype response to mechanically compacted soils both in greenhouse and field, 2) effects of tractor wheel compaction on the growth and yield of barley and oat cultivars, and 3) 74 75 validity of a soil core screening procedure to evaluate tolerances to soil compaction at the seedling stage of barley and cats. The following conclusions were drawn from this study: 5.1 Greenhouse experiment 5.1.1 Barley The root length density and root growth rate of all barley genotypes studied were significantly reduced by high soil bulk density. A layer high in bulk density significantly reduced the root length density within the soil core due to the lower root penetration ratio which was significantly reduced even at a medium soil bulk density. A barley genotype, W7222, was found to have a significantly higher root penetration ratio among the barley genotypes studied. The total root length of a cultivar is directly related to its resumption of normal root growth after its roots had penetrated the layer high in bulk density. High bulk density reduced the total dry matter and reduced plant height of only some barley genotypes. 5.1.2 Oats A high soil bulk density significantly reduced the root length density and root growth rate of oats. As the soil bulk density increased, the root penetration ratio of oat 76 genotypes significantly decreased. Roots of oats accumulated above the layer high in bulk density and had a significantly lower penetration and significantly lower recovery after its penetrated soil layers medium and high in bulk densities. None of the cat genotypes studied showed a significant resumption of its normal root growth after the penetration of the soil layers medium and high in bulk densities. 5.1.3 Barley and oats Compaction significantly reduced the root length density of both crops, but oats had a 35% lower root length density than barley. Barley had a higher root length density than oats when the middle layers had a low and medium bulk densities. Both crops had the same RLD's within the whole core when the middle layer had a high bulk density. The same root penetration ratio was obtained in both crops at low and medium bulk density. Barley had a significantly higher root penetration ratio at high bulk density indicating that barley roots can penetrate a highly compacted soil better than oats. Not all barley genotypes used in this study showed both significantly higher root length density and root penetration ratio. A barley genotype, W7222, had a high root length density as well as a high root penetration ratio. The oat genotype Korwood had a high root length density but had a low root penetration ratio. A high root length density, high root penetration ratio along with its 77 ability to resume normal root growth after the roots had penetrated the layer high in bulk density are good indicators of the genotype tolerance to high bulk density. The stepwise regression analysis showed that the two crops had different patterns of root growth in response to the increasing soil bulk density. 5.2 Field experiment Tractor wheel compaction significantly increased soil bulk density. Soils compacted by tractor wheels significantly reduced the root length density of barley within the 0-23 cm layer as well as the root length density of the whole care. In all three years of study, yeilds and test weights of barley were significantly reduced due to soil compaction by tractor wheels. Tractor wheel compaction did not significantly reduce consistently plant height, test weights, and total dry matter of oats. Compacted soils significantly reduced oat yields in all three years on the average of 17%. 5.3 Greenhouse and field experiments Both experiments showed that a compacted soil reduced the root length density. The greenhouse compaction study showed that the root length density of barley was reduced by 33% while a 34% reduction was obtained from the field study. 78 The root length density of oats was reduced by 27% and 21% for greenhouse and field experiments respectively. The seedling core screening procedure proved to be an effective technique for evaluating genotypic tolerances to soil compaction. 5.4 Final comments More investigation is needed to better understand the genotype x soil compaction interaction especially at the process mechanism level. It is evident that several of the barley and oat genotypes studied showed promise for a breeding and genetics research. One area for further investigation could be the heritability of root characteristics on both barley and oats which showed tolerance to soil compaction. There is a potential extraneous variation that is inherent in the investigations on root characteristics of genotypes. This study confirms that a very high soil bulk density could confound the genetic expressions of tolerances to soil compaction. APPENDICES ANALYSIS OF VARIANCE TABLES 79 Table A.1. Analysis of variance table for top layer root length density per plant of 4 barley cultivars as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 81.47 11.639 30.72 .000 Compaction 2 0.35 0.175 0.46 Error (8) 14 5.30 0.379 Cultivars 3 17.79 5.930 15.58 .000 Comp x Cult 6 1.94 0.323 0.85 Error (b) 63 23.98 0.381 c.v. (%) = 22.43 Table A.2. Analysis of variance table for middle layer root length density per plant of 4 barley cultivars as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 9.22 1.318 7.42 .000 Compaction 2 11.64 5.822 32.79 .000 Error (a) 14 2.49 0.178 Cultivars 3 6.67 2.225 6.73 .000 Comp x Cult 6 0.65 0.109 0.33 Error (b) 63 20.82 0.331 c.v. (%) = 31.57 80 Table A.3. Analysis of variance table for bottom layer root length density per plant of 4 barley cultivars as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 30.78 4.397 9.40 .000 Compaction 2 2.01 1.007 2.15 .153 Error (a) 14 6.55 0.468 Cultivars 3 5.04 1.679 4.77 .004 Comp x Cult 6 2.58 0.431 1.23 .305 Error (b) 63 22.15 0.352 c.v. (%) = 28.07 Table A.4. Analysis of variance table for whole core root length density per plant of 4 barley cultivars as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 32.28 4.611 19.74 .000 Compaction 2 2.52 1.258 5.39 .018 Error (a) 14 3.27 0.234 Cultivars 3 5.87 1.955 8.20 .004 Comp x Cult 6 1.33 0.222 0.93 Error (b) 63 15.02 0.238 c.v. (%) = 22.38 81 Table A.5. Analysis of variance table for total dry matter per plant of 4 barley cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 11695.58 1670.797 5.96 .002 Compaction 2 985.22 492.608 1.76 .208 Error (a) 14 3926.75 280.482 Cultivars 3 11106.30 3702.099 17.61 .000 Comp x Cult 6 4707.68 784.614 3.73 .003 Error (b) 63 13243.86 210.220 c.v. (%) = 10.01 Table A.6. Analysis of variance table for root penetration ratio of 4 barley cultivars as affected by three compaction levels. 1987 Source d.f. 88 MS F-value Prob. Blocks 7 0.66 0.094 1.62 .208 Compaction 2 1.69 0.845 14.62 .000 Error (a) 14 0.81 0.058 Cultivars 3 0.28 0.092 4.11 .010 Comp x Cult 6 0.14 0.023 1.05 .404 Error (b) 63 1.41 0.022 c.v. (%) = 23.29 82 Table A.7. Analysis of variance table for plant height of 4 barley cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 877.00 125.286 9.44 .000 Compaction 2 4.37 2.183 0.16 .000 Error (a) 14 185.77 13.269 Cultivars 3 253.87 84.622 13.43 .000 Comp x Cult 6 91.86 15.310 2.43 .035 Error (b) 63 396.87 6.299 c.v. (%) = 7.82 Table A.8. Analysis of variance table for total root length per plant in whole core assembly of 4 barley cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 10820115.07 1545730.724 19.74 .000 Compaction 2 843489.69 421744.844 5.39 .018 Error (a) 14 1096261.76 78304.411 Cultivars 3 1966546.98 655515.659 8.20 .000 Comp x Cult 6 447021.78 74503.631 0.93 Error (b) 63 5036905.75 79950.885 c.v. (%) = 22.38 83 Table A.9. Analysis of variance table for total dry matter of 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 44131.71 6304.530 31.57 .000 Compaction 2 5442.81 2721.405 13.63 .000 Error (a) 14 2795.85 199.703 Cultivars 3 8865.10 2955.035 26.73 .000 Comp x Cult 6 936.07 156.011 1.41 .224 Error (b) 63 6964.45 110.547 c.v. (%) = 9.45 Table A.10. Analysis of variance table for middle layer root length density of 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 2.18 0.311 4.53 .000 Compaction 2 0.68 0.342 4.98 .000 Error (a) 14 0.96 0.069 Cultivars 3 0.67 0.224 4.79 .000 Comp x Cult 6 0.12 0.021 0.44 Error (b) 63 2.94 0.047 c.v. (%) = 18.45 84 Table A.11. Analysis of variance table for root penetration ratio of 4 cat cultivars 14 days after emergence as affected by compaction levels. 1987 Source d.f. 88 MS F-value Prob. Blocks 7 0.93 0.133 3.77 .016 Compaction 2 4.72 2.359 67.17 .000 Error (a) 14 0.49 0.035 Cultivars 3 0.06 0.021 1.53 .215 Comp x Cult 6 0.04 0.006 0.48 Error (b) 63 0.86 0.014 c.v. (%) = 19.24 Table A.12. Analysis of variance table for the top layer root length density of 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 13.23 1.889 10.72 .000 Compaction 2 1.94 0.969 5.50 .017 Error (a) 14 2.47 0.176 Cultivars 3 1.39 0.464 6.25 .000 Comp x Cult 6 0.37 0.062 0.84 Error (b) 63 4.68 0.074 c.v. (%) = 22.00 85 Table A.13. Analysis of variance table for the bottom layer root length density of 4 oat cultivars 14 days after emergence as affected by compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 6.19 0.885 27.87 .000 Compaction 2 1.90 0.952 29.99 .000 Error (a) 14 0.44 0.032 Cultivars 3 0.59 0.198 6.52 .000 Comp x Cult 6 0.06 0.010 0.33 Error (b) 63 1.92 0.030 c.v. (%) = 18.24 Table A.14. Analysis of variance table for total root length of 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 328442.69 46920.384 3.72 .017 Compaction 2 184558.79 92279.394 7.32 .006 Error (a) 14 176413.51 12600.965 Cultivars 3 240841.29 80280.430 9.65 .000 Comp x Cult 6 26710.50 4451.751 0.54 Error (b) 63 524038.88 8318.077 c.v. (%) = 14.91 86 Table A.15. Analysis of variance table for root penetration ratio as average of 4 barley and 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 0.37 0.053 8.29 .000 Compaction 2 1.46 0.730 114.92 .000 Error (a) 14 0.09 0.006 Crop Species 1 0.01 0.015 1.14 .297 Comp x Crop 2 0.14 0.071 5.54 .011 Error (b) 21 0.27 0.013 c.v. (%) = 18.15 Table A.16. Analysis of variance table for root length density as average of 4 barley and 4 oat cultivars 14 days after emergence as affected by three compaction levels. 1987 Source d.f. SS MS F-value Prob. Blocks 7 0.60 0.086 3.55 .020 Compaction 2 2.09 1.044 43.17 .000 Error (a) 14 0.34 0.024 Crop Species 1 4.83 4.826 37.21 .000 Comp x Crop 2 0.94 0.468 3.61 .045 Error (b) 21 2.72 0.130 c.v. (%) = 23.98 87 Table A.17. Analysis of variance table for grain yield of 2 barley cultivars as affected by compaction levels. 1983 Source d.f. SS MS F-value Prob. Blocks 2 793.52 396.760 0.07 Compaction 1 32614.61 32614.615 6.06 .132 Error (a) 2 10761.79 5380.893 Cultivars 1 1935.48 1935.481 5.11 .086 Comp x Cult 1 136.01 136.013 0.36 Error (b) 4 1514.19 378.547 c.v. (%) = 9.83 Table A.18. Analysis of variance table for grain yield of 4 barley cultivars as affected by compaction levels. 1985 Source d.f. SS MS F-value Prob. Blocks 3 4969.05 1656.349 1.33 .409 Compaction 1 120393.24 120393.240 98.86 .002 Error (a) 3 3728.84 1242.946 Cultivars 3 9047.38 3015.792 20.75 .000 Comp x Cult 3 1668.89 556.298 3.83 .027 Error (b) 18 2615.75 145.320 c.v. (%) = 3.30 88 Table A.19. Analysis of variance table for the whole core root length density of 2 barley cultivars as affected by compaction levels. 1983 Source d.f. SS MS F-value Prob. Blocks 2 0.04 0.021 2.73 .268 Compaction 1 0.11 0.113 14.76 .061 Error (a) 2 0.02 0.008 Cultivars 1 0.01 0.014 2.10 .220 Comp x Cult 1 0.01 0.008 1.22 .330 Error (b) 4 0.03 0.007 c.v. (%) = 20.22 Table A.20. Analysis of variance table for the upper 0-23 cm root length density of 2 barley cultivars as affected by compaction levels. 1983 Source d.f. SS MS F-value Prob. Blocks 2 0.02 0.010 2.57 .279 Compaction 1 0.36 0.359 91.95 .010 Error (a) 2 0.01 0.004 Cultivars 1 0.02 0.023 0.92 Comp x Cult 1 0.02 0.020 0.80 Error (b) 4 0.10 0.025 c.v. (%) = 25.84 Table A.21. Analysis of variance table for the lower 24- 46 on root length density of 2 barley cultivars as affected by compaction levels. 1983 Source d.f. SS MS F-value Prob. Blocks 2 0.10 0.050 2.00 .333 Compaction 1 0.01 0.005 0.21 Error (a) 2 0.05 0.025 Cultivars 1 0.01 0.008 1.57 .278 Comp x Cult 1 0.00 0.002 0.35 Error (b) 4 0.02 0.005 c.v. (%) = 34.20 Table A.22. Analysis of variance table for the upper 0-23 cm root length density of 3 barley cultivars as affected by compaction levels. 1984 Source d.f. SS MS F-value Prob. Blocks 3 0.79 0.263 11.80 .036 Compaction 1 0.60 0.601 26.91 .013 Error (a) 3 0.07 0.022 Cultivars 2 0.11 0.055 1.27 .316 Comp x Cult 2 0.01 0.007 0.15 Error (b) 12 0.52 0.044 c.v. (%) - 25.01 90 Table A.23. Analysis of variance table for the lower 24- 46 cm root length density of 3 barley cultivars as affected by compaction levels. 1984 Source d.f. SS MS F-value Prob. Blocks 3 0.31 0.104 29.52 .009 Compaction 1 0.06 0.060 16.99 .025 Error (a) 3 0.01 0.004 Cultivars 2 0.15 0.074 6.80 .010 Comp x Cult 2 0.05 0.023 2.12 .162 Error (b) 12 0.13 0.011 c.v. (%) = 27.75 Table A.24. Analysis of variance table for grain yield of 4 oat cultivars as affected by compaction levels. 1985 Source d.f. SS MS F-value Prob. Blocks 3 27836.43 9278.812 27.72 .010 Compaction 1 11927.40 11927.402 35.63 .009 Error (a) 3 1004.22 334.739 Cultivars 3 5450.96 1816.987 2.43 .098 Comp x Cult 3 1177.45 392.484 0.53 Error (b) 18 13447.80 747.100 c.v. (%) = 7.68 91 Table A.25. Analysis of variance table for the whole core root length density of 2 oat cultivars as affected by compaction levels. 1983 Source d.f. SS MS F-value Prob. Blocks 1 0.02 0.023 18.84 .144 Compaction 1 0.01 0.011 9.17 .203 Error (a) 1 0.00 0.001 Cultivars 1 0.07 0.074 9.02 .095 Comp x Cult 1 0.00 0.001 0.09 Error (b) 2 0.02 0.008 c.v. (%) = 16.78 Table A.26. Analysis of variance table for the upper 0-23 cm root length density of 2 oat cultivars as affected by compaction levels. 1983 Source d.f. SS MS F-value Prob. Blocks 1 0.14 0.145 47.18 .092 Compaction 1 0.00 0.002 0.59 Error (a) 1 0.00 0.003 Cultivars 1 0.13 0.127 4.53 .166 Comp x Cult 1 0.00 0.002 0.07 Error (b) 2 0.06 0.028 c.v. (%) = 22.79 92 Table A.27. Analysis of variance table for the lower 24- 46 on root length density of 2 oat cultivars as affected by compaction levels. 1983 Source d.f. SS MS F-value Prob. Blocks 1 0.01 0.006 24.42 .127 Compaction 1 0.03 0.029 128.36 .056 Error (a) 1 0.00 0.000 Cultivars 1 0.03 0.035 128.27 .007 Comp x Cult 1 0.00 0.000 0.30 Error (b) 2 0.00 0.000 c.v. (%) = 4.81 Table A.28. Analysis of variance table for the whole core root length density of 4 oat cultivars as affected by compaction levels. 1984 Source d.f. SS MS F-value Prob. Blocks 3 0.51 0.170 12.88 .032 Compaction 1 0.33 0.326 24.74 .015 Error (a) 3 0.04 0.013 Cultivars 3 0.01 0.004 0.48 Comp x Cult 3 0.04 0.013 1.54 .237 Error (b) 18 0.15 0.008 c.v. (%) = 14.50 93 Table A.29. Analysis of variance table for the lower 0-23 on root length density of 4 oat cultivars as affected by compaction levels. 1984 Source d.f. SS MS F-value Prob. Blocks 3 0.55 0.185 4.39 .127 Compaction 1 0.92 0.917 21.79 .018 Error (a) 3 0.13 0.042 Cultivars 3 0.02 0.007 0.78 Comp x Cult 3 0.08 0.028 2.99 .058 Error (b) 18 0.17 0.009 c.v. (%) = 11.91 Table A.30. Analysis of variance table for the upper 24- 46 cm root length density of 4 cat cultivars as affected by compaction levels. 1984 Source d.f. SS MS F-value Prob. 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