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Text follows. y UMI ALLEVIATION OF COMPACTION ON FINE-TEXTURED MICHIGAN SOILS By Bradley Scott Johnson 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 1987 / ABSTRACT ALLEVIATION OF COMPACTION ON FINE-TEXTURED MICHIGAN SOILS By Bradley Scott Johnson Normal fall and spring tillage practices conditions for crop growth on Charity clay (fine, mesic Aerie Haplaquept). This soil conducted to poor illitic physical (calcareous), has an unstable surface and poor internal drainage due to its naturally dense were create subsoil. Tillage studies evaluate the potential for increasing crop yields by reducing the physical limitations of Charity clay and a second lake-plain soil, Parkhill Haplaquept). loam Both (fine-loamy, soils were mixed, nonacidic, subsoiled and subsequent controlled to avoid recompaction of the loosened soil. established during 1983 to mesic Mollic traffic was Experiments were 1985 on Charity clay at the Saginaw Valley Bean and Beet Research Farm, Swan Creek, MI. conducted in 1983 on Parkhill loam near An identical experiment was Ithaca, MI. Both sites were artificially drained and nearly level. Subsoiling improved the physical condition of Charity clay below the Ap Horizon. Physical one crop year. in the changes created by subsoiling persisted through only Compaction caused by preplant wheel traffic surface of was evident Charity clay and below the normal depth of plowing. Fall moldboard plowing plus conventional spring tillage produced the least favorable conditions for crop growth in terms of soil aeration. Subsoiling Controlled increased tended traffic dry to increase improved soybean and sugarbeet yields in 1983. seedling emergence most of the time, bean rooting in 1983, and tended to increase crop yields. Dry beans and sugarbeets were more sensitive to wheel induced than other crops included in the study. compaction Preplant wheel traffic decreased yields of these crops during two of three years. Soybeans were the least sensitive to soil compaction as preplant wheel traffic actually increased yields on Parkhill loam in 1983. each year. excesses Crop response depended on the climate Tillage effects were most evident in 1983 when soil water occured during the early part of the growing season followed by a dry June-to-August period. Tillage effects on aeration using the CERES-Maize model. because the soil water of Charity clay were evaluated further This simulation model proved to balance created by Simulated water contents resembled the measured values for two diverse tillage simulated water treatments. contents Air were each indices. The SDI was greatest for 1983 weather data suggest that corresponding the based to the basis for calculation of Deep tillage plus controlled soil most evident. year as improved were aeration porosities used cumulative stress day index (SDI). growth useful is calculated on daily basis and soil inputs can be altered to account for varying soil conditions tillage. be traffic on the cumulative stress day when tillage effects on crop Results of a long-term study using generated poor aeration under conventional fall and spring tillage may limit yields on this soil during at least one of three years. ACKNOWLEDGMENTS The author expresses sincere appreciation to his major professor, Dr. A. Earl Erickson, for encouragement to pursue this ' degree during completion of the degree program. K. L. Poff, J. and guidance The author wishes to thank Drs. T. Ritchie, A.J.M. Smucker, and R. Wilkinson for their participation as committee members. Special thanks is extended to F. J. Pierce for his role as a committee member during the later stages of this degree program. TABLE OF CONTENTS List of T a b l e s ........................................................... Ill List of F i g u r e s ...........................................................vli INTRODUCTION .............................................................. I Chapter 1: LITERATURE REVIEW ............................................ 4 Soil physical properties Influenced by compaction .................... 5 Measurement of soil c o m p a c t i o n ................... 5 Influence of soil conditions on root growth Mechanical Impedance ................................................. 8 Soil a e r a t i o n .........................................................10 Evaluation of soil aeration Soil air c o m p o s i t i o n .................................................. 10 Gaseous diffusion rates ............................................ 12 Air p o r o s i t y ........................................................... 14 Factors which Influence air porosity Soil c o m p a c t i o n ...................................................... 15 C l i m a t e ............................................................... 16 Causes of soil compaction in Michigan Naturally occurring compaction .......... . 18 Wheel induced c o m p a c t i o n ............... 19 Changing cropping systems .......................................... 22 Untimely field operations .......................................... 24 Alleviation of compaction Natural forces ....................................................... 25 S u b s o i l i n g ................. 29 Controlled traffic ................................................... 32 Persistence of tillage-induced changes ............................. 34 The role of simulation m o d e l s ......................................... 35 S u m m a r y ................. 37 List of R e f e r e n c e s ...................................................... 39 Chapter 2: PHYSICAL CONDITIONS OF CHARITY CLAY AS AFFECTED B Y DEEP TILLAGE AND CONTROLLED TRAFFIC I n t r o d u c t i o n ............... 48 Materials^ and M e t h o d s .................................................. 51 Results and Discussion Subsoil physical conditions ........................................ 56 Topsoil physical conditions ........................................ 68 C o n c l u s i o n s ............................................................. 75 List of R e f e r e n c e s ...................................................... 81 Chapter 3: INFLUENCE OF DEEP TILLAGE AND CONTROLLED TRAFFIC ON PROFILE WATER CONTENT OF TWO LAKE-PLAIN SOILS Introduction ........................................................... Materials and Methods ................................................ 84 86 Results and Discussion Site 1 .................................................................90 Site 2 ......................................... ................... 101 C o n c l u s i o n s ........................................................... 104 List of R e f e r e n c e s ............. .................................... 107 Chapter 4: SEEDLING EMERGENCE, ROOTING, AND CROP YIELDS AS AFFECTED B Y DEEP TILLAGE AND CONTROLLED TRAFFIC Introduction ......................................................... 108 Materials and Methods ............. . . . . . . Results and Discussion Corn r e s p o n s e ...................................................... 116 ................................................ 119 Sugarbeet response Soybean and dry bean plant r e s p o n s e .............................. 129 Yields on Parkhill l o a m ...................... ................... 137 Yields on Charity clay ................................... 139 Oat and wheat r e s p o n s e ........................................... 143 Location effects on yield responses In 1983 ...................... 145 Yearly variation of yield response on Charity clay ............. 148 C o n c l u s i o n s ........................................................... 150 List of R e f e r e n c e s .................................................. 151 Chapter 5: EVALUATION OF TILLAGE EFFECTS ON SOIL AERATION USING A SIMULATION MODEL AND THE STRESS DAY INDEX APPROACH I n t r o d u c t i o n ............... ............ ............................155 Materials and M e t h o d s ................................................ 159 Model m o d i f i c a t i o n s ................................................ 159 Model I n p u t s ........................................................ 161 Calculation of stress day index ...................... 164 Results and Discussion Evaluation of model modifications ................................. 166 Tillage effects on soil aeration during 1983 to 1985 ........... 166 Long-term study of tillage effects ............................... 177 C o n c l u s i o n s ............................................................ 181 List of R e f e r e n c e s .................................................. 183 Chapter 6: SUMMARY AND CONCLUSIONS ................................... 185 Recommendations ...................................................... 188 APPENDIX T A B L E S .........................................................189 APPENDIX FIGURES ...................................................... 221 Ill LIST OF TABLES Chapter 2: Table 1. Influence of primary and secondary tillage on bulk density and porosity of Charity clay at the 0.27 to 0.34 m depth during the first crop year........................... 57 Table 2. Influence of primary and secondary tillage on bulk density, porosity, and macroporosity of Charity clay at the 0.27 to 0.34 m depth during the first crop year................ 62 Table 3. Influence of primary and secondary tillage on bulk density, porosity, and saturated hydraulic conductivity (Ksat) of Charity clay at the 0.27 to 0.34 m depth during the second and third crop y e a r . ........................................................ 63 Table 4. Influence of primary and density, porosity, saturated hydraulic volumetric water content of Charity depth during the first and second crop secondary tillage on bulk conductivity (Ksat), and clay at the 0.30 to 0.10 m year............................69 Table 5. Influence of primary and density, porosity, saturated hydraulic volumetric water content of Charity depth during the first and second crop secondary tillage on bulk conductivity (Ksat), and clay at the 0.13 to 0.20 m year............................70 Chapter 4: Table 6. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on corn grain moisture, plant population, and grain yield during 1983 on Parkhill loam.............................. 120 Table 7. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on corn grain yield from 1983 to 1985 on Charity c lay ..................................................................... 121 Table 8. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on sugarbeet plant density, root yield, and recoverable sugar yield (RSY) during 1983 on Parkhill loam......... 124 Table 9. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on sugarbeet root yields from 1983to 1985 on Charity clay............................................................ 126 Table 10. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on recoverable sucrose yield of sugarbeets from 1983 to 1985 on Charity clay. . . . . . ........... . . . . . . . . 128 Table 11. Final soybean and dry bean stands on two soils (Parkhill loam and Charity clay) as affected by primary tillage (p), secondary tillage (S), and cultivar (C) during 1983................. 133 Table 12. Influence of and cultivar (C) on on Parkhill loam. primary tillage (P), secondary tillage (S), soybean seed moisture and yield during 1983 ............................................. 138 Table 13. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on dry bean seed moisture and yield during 1983 on Parkhill loam........................................................ 140 Table 14. Influence of primary tillage (P)t secondary tillage (S), and cultivar (C) on soybean seed yields from 1983 to 1985 on Charity clay.............................................................141 Table 15. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on dry bean seed yields from 1983 to 1985 on Charity clay............................................................ 142 Table 16. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on oat yields from 1983 to 1985 on Charity clay. . 144 Table 17. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on wheat yields from 1984 to 1985 on Charity clay.......... 146 Table 18. Mean squares from combined analysis of variance over locations for sugarbeet root yield (SRY), sugarbeet recoverable sugar yield (RSY), corn grain yield (CGY), soybean and dry bean seed yields in 1983.......................... 147 Table 19. Mean squares from combined analysis of variance over years for sugarbeet root yield (SRY), sugarbeet recoverable sugar yield (RSY), corn grain yield (CGY), soybean and dry bean seed yields on Charity clay at the Saginaw Valley Research Farm, Swan Creek, M I .......................................................... 149 Chapter 5: Table 20. Soil aeration stress on Charity clay during 1983 to 1985 as affected by t i l l a g e ................................................ 176 APPENDIX TABLES Table 1. Crop cultivars, planting dates, row spacings, seeding rates, and fertilizer application rates used at two study sites in 1983................................................................ 189 Table 190 2. Herbicide program used for 1983 viii Table 3. Crop cultivars, planting dates, row spaclngs, seeding rates, and fertilizer application rates used In 1984................ 191 Table 4. Herbicide program used for the experiment on Charity clay In 1984................................................................ 192 Table 5. Crop cultivars, planting dates, row spaclngs, seeding rates, and fertilizer application rates used in 1985................ 193 Table 6. Herbicide program used for the experiment on Charity clay in 1985................................................................ 194 Table 7. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on corn grain moisture at harvest from 1983 to 1985 on Charity clay....................................................196 Table 8. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on corn plant population from 1983 to 1985 on Charity clay............................................................ 197 Table 9. Mean squares from analysis of variance for two measures of root density of soybeans (SB), dry beans (DB), and corn grown on Charity clay from 1983 to 1985.................. .................. 198 Table 10. Influence of primary tillage (P), secondary tillage (S), and depth on root weight density of soybean (SB), dry bean (DB), and corn roots during 1983 to 1985 on Charity clay.................... 199 Table 11. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on sugarbeet sucrose content (SC), clear juice purity (CJP), recoverable sucrose content (RSC), and alpha-aminoN content (AAN) during 1983 on Parkhill loam.............. 200 Table 12. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on sugarbeet plant density from 1983 to 1985 on Charity clay............................................................ 201 Table 13. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on sucrose content of sugarbeets from 1983 to 1985 on Charity clay.................................................. 202 Table 14. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on clear juice purity of sugarbeets from 1983 to 1985 on Charity clay.................................................. 203 Table 15. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on recoverable sugar content of sugarbeets from 1983 to 1985 on Charity clay........................................... 204 Table 16. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on alpha-amino-N content of sugarbeets from 1983 to 1985 on Charity clay................................................ 205 ix Table 17. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on soybean grain moisture at harvest from 1983 to 1985 on Charity c l a y . .......................... .. ............... 206 Table 18. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on dry bean grain moisture at harvest from 1983 to 1985 on Charity c lay ................................................. 207 Table 19. Sample water balance output produced by the original version of CERES-Maize......................................... 208 Table 20. Sample water balance output produced by the modified version of CERES-Maize.................................................. 209 Table 21. CERES-Maize soil inputs for the 1983 simulations and the long term simulation runs using the generated weather data. . . 210 Table 22. CERES-Maize soil inputs for the 1984 simulations........... 211 Table 23. CERES-Maize inputs for the 1984 simulations.................212 Table 24. Model output produced by the original version of CERESM a i z e.......................... ........................................ 213 Table 25. Model output produced by the modified version of CERESM a i z e .....................................................................214 Table 26. tillage CERES-Maize output for the conventional fall and spring treatment (NDTMP-CST) using the 1983 weather data ...........215 Table 27. CERES-Maize output for traffic treatment (DTMP-NST) using the deep tillage - controlled the 1983 weather d ata ............. 216 Table 28. CERES-Maize output for theconventional fall and spring tillage treatment (NDTMP-CST) using the 1984weather data. . . . . Table 29. CERES-Maize output for traffic treatment (DTMP-NST) using Table 30. tillage 217 the deep tillage - controlled the 1984 weather d a t a ............. 218 CERES-Maize output for the conventional fall and spring treatment (NDTMP-CST) using the 1985 weather d ata ...........219 Table 31. CERES-Maize output for the deep tillage - controlled traffic treatment (DTMP-NST) using the 1985 weather data ............ 220 LIST OF FIGURES Chapter 2: Figure I. Air porosities (a) and soil water retention (b) at the 0.27 to 0.34 m depth during the first crop year as affected by primary and secondary tillage. . ..................................... 59 Figure 2. Fore size distribution of Charity clay at the 0.27 to 0.34 m depth during the first crop year as affected by primary and secondary tillage.................................................... 60 Figure 3. Air porosities of Charity clay at the 0.27 to 0.34 m depth during the second (a) and third (b) crop year as affected by secondary tillage..................................................... 66 Figure 4. Influence of primary and secondary tillage on the volume of large pores (i.e., > 150 x 10 m in diameter) at the 0.27 to 0.34 m depth during the first (YRl)t. second (YR2), and third (YR3) crop y ear .................................................... 67 Figure 5. Influence of secondary tillage on air porosity (a) and soil water retention (b) of Charity clay at the 0.03 to 0.10 m depth during the first crop y ear ....................................... 73 Figure 6. Influence of secondary tillage on air porosity (a) and soil water retention (b) of Charity clay at the 0.03 to 0.10 m depth during the second crop year. . . . . . . . . . ............... 74 Figure 7. Pore size distribution of Charity clay at the 0.03 to 0.10 m depth as affected by secondary tillage during the first (YR1) and second (YR2) crop y ear ....................................... 76 Figure 8. Influence of secondary tillage on air porosity (a) and soil water retention (b) of Charity clay at the 0*13 to 0.20 m depth during the first crop y ear....................................... 77 Figure 9. Influence of secondary tillage on air porosity (a) and soil water retention (b) of Charity clay at the 0.13 to 0.20 m depth during the second crop year...................................... 78 Figure 10. Pore size distribution of Charity clay at the 0.13 to 0.20 m depth as affected by secondary tillage during the first (YR1) and second (YR2) crop year....................................... 79 ,xi Chapter 3: Figure 11.Linear regression probe ratio at the 0.15 m of soil water content on neutrondepth............................... 88 Figure 12. Linear regression probe ratio at the 0.30 m of soil water content on neutrondepth............................... 88 Figure 13. Cumulative growing season precipitation (a) and monthly precipitation departures (b) during 1983 to 1985 at the Saginaw Valley Bean and Beet Research F a r m..................................... 91 Figure 14. Dally growing season precipitation during 1983 (a), 1984 (b), and 1985 (c) at theSaginaw Valley Bean and Beet Research Farm..................... 92 Figure 15. Hater content of Charity clay at three depths in plots planted to corn (a-c) and daily precipitation (d) during 1983. . . . 93 Figure 16. Hater content of Charity clay at three depths in plots planted to sugarbeets (a-c) and daily precipitation (d) during 198 3 ..................................................................... 94 Figure 17. Hater content of Charity clay at three depths in plots planted to corn (a-c) and daily precipitation (d) during 1984. . . . 96 Figure 18. Hater content of Charity clay at three depths in plots planted to sugarbeets (a-c) and daily precipitation (d) during 1984 ..................................................................... 97 Figure 19. Hater content of Charity clay at three depths in plots planted to corn (a-c) and daily precipitation (d) during 1985. . . . 98 Figure 20.Cumulative growing season precipitation (a) and monthly precipitation departures (b) during 1983 at Alma, M I ................ 102 Figure 21. Hater content of Parkhill loam at two depths in plots planted to corn (a-b) and daily precipitation (c) during 1983. . . 103 Figure 22. Hater content of Parkhill loam at the 0.46 (a), 0.61 (b), and 0.76 m (c) depths during 1983 in plots planted to corn. . 105 Chapter 4: Figure 23. Emergence of corn seedlings on Parkhill loam in 1983 (a) and on Charity clay during 1983 to 1985 (b-d) as affected by secondary tillage. Cultivars used were Great Lakes-422 (GL), Pioneer-3901 (3901), and Pioneer-3744 (3744). . . . . . . . . . . . 117 Figure 24. Corn root length density on Charity clay in 1983 as affected by secondary tillage.......................................... 118 xii Figure 25. Emergence of US-H23 (H23) and US-H20 (H20) sugarbeet seedlings during 1983 on Parkhill loam (a) and during 1983 to 1984 on Charity clay (b-c) as affected by secondary tillage. . . . Figure 26. Emergence of Hodgson-78 (H78) and Corsoy-79 (C79) soybean seedlings on Parkhill loam in 1983 (a)and on Charity clay in 1983 (b) and 1985 (c) as affected by secondary tillage. . . 130 Figure 27. Emergence of C20 and Swan Valley (SV) dry bean seedlings on Charity clay as affected by secondary tillage in 1983 (a), 1984 (b), and 1985 (c)....................................... 132 Figure 28. Soybean root length density on Charity clay during 1983 to 1985 (a-c) as affected by secondary tillage........................135 Figure 29. Dry bean root length density on Charity clay during 1983 to 1985 (a-c) as affected by secondary tillage.................. 136 Chapter 5: Figure 30. Comparison of simulated water contents at two depths under the NDTMP-CST treatment during 1983 using a version of the model that allows runoff and a modified version that suppresses runoff.................................................................... 167 Figure 31. Comparison of simulated water contents at four depths under the NDTMP-CST and DTMP-NST treatments for 1983............... 168 Figure 32. Comparison of simulated water contents at four depths under the NDTMP-CST and DTMP-NST treatments for 1984............... 169 Figure 33. Comparison of simulated water contents at four depths tinder the NDTMP-CST and DTMP-NST treatments for 1985............... 170 Figure 34. Comparison of simulated air porosities at three depths under the NDTMP-CST (solid line) and DTMP-NST (dashed line) treatments for 1983........................................ 172 Figure 35. Comparison of simulated air porosities at three depths under the NDTMP-CST (solid line) and DTMP-NST (dashed line) treatments for 1984 .................................................... 173 Figure 36. Comparison of simulated air porosities at three depths under the NDTMP-CST (solid line) and DTMP-NST (dashed line) treatments for 1985.................................................... 174 Figure 37. Frequency distribution for 100 years of predicted yields under two tillage treatments.................................... 178 Figure 38. Frequency distribution for the number of wet days under NDTMP-CST and DTMP-NST produced by 100-year simulations for each treatment.......................................................... . . . 1 7 9 xiii Figure 39. Frequency distribution for stress day index under NDTMP-CST and DTMP-NST produced by 100-year simulations for each treatment................................................................ 180 APPENDIX FIGURES Figure 1. Comparison of measured and simulated water contents at three depths under the NDTMP-CST treatment in1983.................. 221 Figure 2. Comparison of measured and simulated water contents at three depths under the NDTMP-CST treatment in 1984 . . 222 Figure 3. Comparison of measured and simulated water contents at three depths under the NDTMP-CST treatment in1985.................. 223 Figure 4. Comparison of measured water contents under the NDTMPCST and DTMP-NST treatments for 1983. . . . . . . . ............... 224 Figure 5. Comparison of measured water contents under the NDTMPCST and DTMP-NST treatments for 1984................................. 225 Figure 6. Comparison of measured water contents under the NDTMPCST and DTMP-NST treatments for 1985................................. 226 Figure 7. Variation of the stress day factor with soil air porosity (Pa)........................................................... 227 xiv INTRODUCTION Soil compaction is a major problem in the United States. Restricted root growth and possible reductions in yield are the obvious consequences of soil compaction. resulting from Gill (1971) estimated that the value of crop soil compaction amounted to 1.18 billion dollars in the United States based on 1964 figures. costs increased. More energy is required to soil associated with In production noncompacted losses addition management till of a to yield compacted compacted losses, soil soil are than a one and wear on tillage tools increases with density of the (Voorhees and Hendrick, 1977). Since tilling compacted soil produces greater clodiness (Johnson et al., 1979), an increased number of tillage operations may be required to produce an adequate seedbed. Remedial actions are costly on compacted soils as a result. Though wheels some of soils are agricultural contributed greatly to naturally dense, most compaction is caused by vehicles. the Changing incidence and cropping degree of systems wheel have induced compaction because of their influence on tillage intensity and the amount of residue returned to the soil. Crop rotations which include leguminous hay have been replaced by rotations in which an annual crop may be for several years in succession (Robertson, 1984). Michigan, the in On prime farmlands in percentage of field crop hectarage in row crops Increased from 45.8 to 71.7% during the period 1967 hectarage grown small to 1982 at the expense of grains and sod crops (Whiteside and Lumbert, 1986). Thus, soils depleted in organic matter are being worked more intensively. 1 Problems associated with wheel Induced compaction are worsened by the steadily Increasing size of agricultural wheel equipment. Most agricultural traffic can be attributed to the rear tires of tractors which have Increased In size as a necessary consequence of the more Intensive use of land, the Increase In size of farms, (Gill, 1971). and the scarcity of farm Tractors have Increased In weight from an average of 2.7 Mg in the late 1940's (Voorhees, 1977) to current weights of wheel drive units Which may large axle loads have four exceed 22.4 Mg (Carpenter et al., 1985). Contact pressures under tractor tires have been held relatively as labor increased by However, high axle loads result in constant increasing tire diameter and width. deeper compaction even though the weight may be distributed over a larger contact area. Natural weathering forces such as freezing and thawing ameliorate wheel induced subsoil compaction even where frost depth is substantial. result. to than Dense subsoils must be loosened mechanically as a compaction within the normal depth Furthermore, disruption of a dense layer or horizon which development may not not penetration Unfortunately, subsoil compaction is more difficult alleviate may always and of costly plowing. inhibits root improve yields depending on the prevailing climate and management practices. When deep tillage is deemed to be necessary to improve subsoil physical conditions, the most appropriate tillage operation should be selected and implemented at the proper time. For shattered most effectively by subsoiling Post subsoiling recompaction prevention of example, at low dense soil subsoils water are contents. traffic must be controlled or at least reduced to avoid soil loosened by deep tillage. Thus, compaction and occasional corrective procedures are essential components of a compaction management system. compaction under wheels are Even though techniques available, for reducing their adoption by farmers and manufacturers has been limited (Soane et al., 1982). The objectives of this study were to: (1) evaluate the potential for reducing the physical limitations of Charity clay (Aerie subsoiling in of changes brought controlled; (3) determine the secondary by the fall when it is dry; (2) determine the susceptibility of the loosened soil to recompaction during subsequent persistence Haplaquept) tillage traffic and the about by subsoiling where traffic is influence of subsoiling and subsequent operations on growth of crops that are typical of the dry bean and sugarbeet production areas in Michigan; (4) further evaluate crop response to tillage using a crop simulation model and the stress day index approach; and benefit from (5) subsoiling develop and probabilities of crop response and controlled traffic using simulations over long periods of time and soil aeration as the criterion for response. Chapter 1 LITERATURE REVIEW Soil compaction is a major problem in Michigan. Robertson and Erickson (1980) reported the occurrence of symptoms of excessively compact soil in every county of the state. Visual symptoms in soil may include soil crusts, shrinkage cracks in vehicle others. The authors also wheel identified displayed by Michigan crops including tracks, a standing variety distorted of water and visual symptoms stems, variable plant emergence and/or size, wilting plants, discolored leaves, malformed roots and lodging. Plants which exhibit the diversity of responses to compacted soil described in the preceding paragraph share one thing in common: all soil environments which subject several stresses simultaneously. common environmental stresses have their roots to at least one, possibly Water and nutrient accompanying soil deficiencies compaction. are Impeded aeration can result in oxygen deficiencies as well as the accumulation of carbon dioxide and other toxic substances in some compacted soils. Soil properties influenced by compaction and their influence on plant root growth (and productivity) will follows. be surveyed in the review which Soil aeration and interactions with the prevailing climate will emphasized. examined after Finally, the influence be of Approaches to considering possibility root zone amelioration causes of of using modification responses will be discussed. soil of compaction simulation (e.g., problem soils will be in Michigan. models to evaluate the deep tillage) on crop 5 Soil Physical Properties Influenced by Compaction Root growth and function are influenced by physical and chemical properties of soils but unfavorable physical conditions associated with compacted soils features of soil compaction. have this been review Increases soil (Barnes subsequent review by Byrnes et al. (1982). The authors et al, often 1971). Salient studies were summarized in a concluded that compaction bulk density and strength, decreases total porosity, but more importantly decreases the volume of large pores. of most Physical properties characteristic of reviewed and are Thus, resistance the soil to penetraition by roots and emerging seedlings is increased. Rates of water infiltration and internal drainage are reduced retention can be increased or decreased porosity and pore size distribution. and water depending on the changes in In addition, exchange of oxygen and carbon dioxide between the soil and atmosphere can be inhibited at times. Measurement Of Soil Compaction Soil compaction can be measured using a variety of techniques because there are so many soil properties Procedures used to measure that soil (1971) and Byrnes et al. (1982). are indicators compaction of compaction. were reviewed by Freitag Bulk density, the mass of dry soil per unit bulk volume, is the most frequently used measure of soil compaction. Soil bulk density (Db) can be determined using the core, coated clod, or radiation methods (Blake, 1965). characterization of Soil porosity is the simplest partial the soil pore system and can be calculated directly from Db if the density of the soil particles is known: P - 1 - Db/Dp where P (1) is the volume fraction of the total bulk not occupied by solids _3 and Dp is the particle density (usually about 2.65 Mg m ). Pore size distribution (PSD) is the volume of the various sizes of pores in a soil and is expressed as a fraction of the bulk volume* Since compaction affects the volume of larger pores more so than the volume of fine pores, PSD is an attractive measure of soil compaction. No single dimension of a pore can unambiguously be defined as its size (Klute, 1982). result. is Pore size must be defined by a method of measurement as a Vomocil (1965) described a procedure in which a capillary used torepresent soil pore space. Water is extracted initially saturated soil sample of known volume by a series h. The volume of of model from an suctions water extracted at each h is equal to the volume of pores having an effective radius greater than the corresponding value of r in the capillary rise equation: r - 2 y cos a 8 D1 h where y is the surface tension (dyne (2) cm *), « is the contact angle (usually assumed to be zero), g is the acceleration due to gravity (980.7 -2 cm s ), and D^ is the density of usually measured in cm of the water, liquid units appropriate for calculation of r in cm. this When -3 cm ). (g given PSD in is Since h paranthesis determined is are using procedure, one is essentially measuring the volume fraction of air- filled pores (airporosity) at the same h. Thus, results also be reported as air porosities over the range of applied can series of suctions suctions. Porosity and PSD influence the especially at high water potentials. tube is the Water flow of through soil a to water, cylindrical proportional to the fourth power of the radius according to the Poiseuille equation. when conductivity radius Thus, flow volume is decreased by a factor of the tube is reduced by a factor of two. of 16 Water flow through interconnecting soil macropores is affected just as by reductions in size based on the capillary model. dramatically Since most of the water is conducted through macropores at water contents near hydraulic conductivity of measure of soil compaction. laboratory procedures used soil at high water potentials is a sensitive Klute (1965) described the most prominent to measure saturated hydraulic conductivity (Ksat) of samples held in metal or plastic described saturation, containers. Boersma (1965) several field techniques which can be used to measure Ksat and Cassel (1975) demonstrated in situ measurement of unsaturated hydraulic conductivity at different depths in the soil profile. Soil strength, its resistance to penetration and displacement, can be determined in the field using penetrometers and laboratory techniques than any but other soil penetrometers device in shaped. also were historically Numerous been been used standardization. used. Penetrating circular or rectangular flat plates or cone For forced into the soil at a constant required more impedance studies. Techniques used to advance the penetrometer tips into lack pressure have mechanical Penetrometers of various sizes and shapes have elements vanes. also exist (e.g., unconfined compressive strength and modulus of rupture) extensively shear the soil example, moving-tip penetrometers are rate. Penetrometers which measure to push the tip a specific distance are called static tip penetrometers. Moving-tip cone index types are presently considered to be standard penetrometers (Anonymous, 1985). Penetrometer resistances (R), often reported as cone index, increase as soil bulk density Increases or as soil water content decreases. that R changes with penetrometer method. water The fact content is an important shortcoming of the Changes in R (e.g., with tillage or. compaction) may reflect variation in water content at sampling rather than changes in soil structure. The penetrometer method is also handicapped by the fact that changes in R with Db or soil water content are soil dependent. No single measurement or procedure is appropriate for all situations since each have advantages and limitations. Vomocil and Flocker (1961) suggest that PSD is a more sensitive indicator of soil compaction than is Db because PSD suffers greater relative change with compaction than Db. Voorhees (1983) and Voorhees et al. indicator volume. of soil compaction (1986) because Bulk density is insensitive to weakness in the soil both of Db that Db is a poor is sensitive mainly to pore pore which characteristics and root extension. agree structure relate and directly planes of to water flow The authors concluded that hydraulic conductivity and penetrometer resistance are probably better indices of compaction as a result. Hydraulic conductivity was also the measurement of choice in a study conducted by Allmaras et al. (1982) transmission systems characteristics were hydraulic compared. conductivity of Under was in a the a the silt Pacific weather measurement conditions, because internal drainage of these soils can influence water conservation through on runoff and evaporation. Hater loam under various management prevailing pertinent Northwest. effects Obviously, the procedures or measurements should be selected to provide the most effective results. Influence of Soil Conditions on Root Growth Mechanical Impedance In most situations, roots grow partly through existing pore space and partly by moving aside soil particles (Bowen, 1981). Because large pores are scarce in compacted soils, it becomes necessary for roots pores soil by exerting (Cannell, a 1977). to expand force greater than the mechanical strength of the Russell (1977) cited the work of several investigators who demonstrated that roots can exert longitudinal pressure of 0.9 to 1.3 MPa. However, relatively small external pressures (50 kPa) can drastically restrict root extension (Russell and Goss, 1974). Root growth layer exceeds soil is mechanically impeded when strength of a soil or soil the maximum force the root is capable of strength decreases as root growth when dry can growth wet. to encounter than are annuals. soil water tabacum L.) roots become nonrestrictive to annuals cannot. Perenials are Vepraskas et al. (1986) demonstrated the influence on soil more E-B of strength and growth of tobacco (Nicotiana roots in soils with dense tillage pans. the root the restrictive layer when the strength is reduced content below layer This explains why, in some situations, perenials can penetrate dense soil layers that likely Since soil water content increases, a soil that inhibits when exerting. horizon was The proportion of dependent on cumulative rainfall in addition to bulk density and sand content. Root responses to mechanical stress have been reviewed (Barley and Greacen, 1967; Taylor 1971,1974; Cannell, 1977). The usual effects of mechanical impedance are reduced availability of water and plant nutrient elements according to Bowen (1981) and may be attributed to one or more of the following factors Identified by Taylor (1971): (a.) of root development is restricted, (b.) explored volume is diminished, (c.) root is sufficiently reduced proliferation within the an extra quantity of photosynthate is utilized by roots growing in high-strength diameter maximum depth media, or (d.) taproot retarding transport functions of the root. The reader is cautioned that productivity of crops with mechanically impeded roots is not necessarily reduced (Russell, is influenced by additional factors such as 1977). Productivity climate and management 10 practices. usually Where water is not limiting not for example, plant growth is increased by disruption of a dense soil layer that inhibits root development (Weatherly and Dane, 1979). demonstrated that with Buxton and Zalewski (1983) proper irrigation management, potato yields are not adversely affected by restricted rooting in compacted subsoils. Soil Aeration Root growth and survival require metabolic energy which is generated by respiration of sugars under aerobic conditions. Respiration occurs in the mitochondria and Involves the transfer of electrons from sugars to a series of organic molecules and finally to oxygen, releasing energy along the way. Anaerobiosis will occur in soil whenever the demand for oxygen, determined by the respiratory requirements of roots and soil organisms, exceeds the rate at which it can enter the soil. Air porosity of the soil is its physical characteristic which has the greatest influence on gas exchange with the atmosphere Rates 1977). of gas exchange increase as the fractional volume of soil occupied by air increases. are (Russell, inversely anaerobiosis. almost Since fractional air porosity and soil proportional, excess soil Taylor and Arkin (1981) suggests always caused by water that is water the oxygen content cause of stress is excessive soil water contents in noncompacted soils as in the presence of a shallow water table. However, Blake and Page (1948) recognized that aeration can be impeded in compacted soils at certain 'critical times'. Soil and weather conditions that promote soil water excesses will be described in subsequent sections. Evaluation of Soil Aeration Soil Air Composition When gas exchange is restricted and anaerobic metabolism takes place, the composition of soil air changes towards lower concentrations of 11 oxygen and higher concentrations of carbon dioxide. High concentrations of COg can be toxic to plants but studies reviewed by Grable Kramer (1969) Indicate that compared to 0^ deficiencies. are produced during CO 2 metabolism other and toxic substances may affect roots which survive 0 ^ depletion Itself. Major groups of organic gases (e.g., ethylene), and sulfides. acids, hydrocarbon and Is a minor source of Injury to plants A wide variety of anaerobic (1966) conditions such as pH and the presence of toxic fresh substances organic Include debris Soil as an energy source for microorganisms dictate the relative Importance of these toxic substances. Oxygen concentrations which inhibit root growth or respiration vary considerably and have been estimated at values ranging from 14 percent to less than one percent in Jackson (1981). reviews by Russell (1977) and Cannell Russell (1977) attributes Such variation to differences in experimental conditions, especially temperature. Root growth may have been affected in some experiments by the production of toxic In the addition, supply rhizosphere the of O2 actually organisms not substances. concentration of the soil air is not equivalent to may available deplete surface of roots to an unknown extent. may and to the the partial root. For example, pressure of The aeration status of at the the soil be adequately assessed by measurement of 0^ concentration alone owing to these difficulties. soil aeration. Alternative methods can be used to measure Their usefulness will be evaluated following a discussion of mechanisms of gas exchange in the soil. Gaseous Diffusion Rates The most Important mechanism of gas exchange between the soil and atmosphere is diffusion which obeys Fick’s Law: q^ ■ -D dc/dx where is one dimensional flow of (3) gas, D is coefficient, and dc/dx is the concentration gradient. Typical units “2 q^, the gas diffusion -1 2 for -1 D, and dc/dx used in the literature are g cm min , cm min , and _3 g cm /cm, respectively. The gas diffusion coefficient is a property of both the medium and the gas but it is also influenced by atmospheric 4 pressure and temperature. Since diffuses 10 air than in water, diffusion of O 2 The gas diffusion coefficient times more rapidly occurs mainly in air filled pores. in soil (Ds) is smaller than the coefficient in free air (Do) because of the reduced cross sectional available for movement and increased path diffusion expressed as a diffusion via the gaseous fraction coefficient of Do. (Ds/Do) phase in Methods have various of area length resulting from the tortuosity of the interconnected air filled channels. of in To compare rates media Ds is usually measuring the relative been reported by Taylor (1949) and Raney (1949). Many functional relationships between Ds/Do and air porosity have been proposed (Hillel, 1980). Several equations are of the form: Ds/Do ■ e Pa where Fa is tortuosity. through the air porosity Penman (1940) measured the packed soil cores values of e equal to 0.66. values and e (4) is a constant which represents diffusion of carbon bisulfide in the range of 0.195 < Pa <0.676 and found Other investigators have reported different of e for different soils and ranges of air porosities. Blake and Page (1948) found that the ratio between Ds/Do and Pa varied between 0.62 13 and about 0.8. zero when Their most significant finding air attributed to porosity the fell below discontinuity of was that 3 10% (0.1 m air filled m -3 Ds approached ), an observation pores inside soil aggregates. Wesseling (1962) proposed another linear model: Ds/Do - 0.9Pa - 0.1 which suggests that (5) Ds becomes zero when air porosity falls below 11%. Grable (1971) endorsed these findings stating that the continuity of air filled pores to the soil surface is likely to be broken when air porosity is less than about 10%. Several nonlinear models have been proposed, some of which account for the influence of soil characteristics other than diffusion. Millington just air porosity on and Quirk (1961) considered the geometry of flow paths and the probability of pore continuity in dry porous media and derived the equation: Ds/Do - P a 10/3/P2 where P is total soil porosity. Sallam (6) et al. (1984) found best agreement between calculated and measured Ds at low air porosities (0.05, 0.10, and 0.15) using this model but with the Pa exponent reduced from 3.33 to 3.10. It is clear that a strong relationship between Ds/Do and Pa exists but that it is not constant for all soils. In addition, Currie (1984) showed that no single relationship between the Ds/Do and Pa fitted the results relative for even one diffusion coefficient soil (a clay loam) that was packed to varying levels of bulk density. Evaluation of the soil oxygen environment is further complicated by the existence path for of (>2 water films covering active root surfaces. The diffusion from the atmosphere to actively respiring cells of roots is 14 completed method via these water films. to measure microelectrodes oxygen to diffusion simulate based on the principle that producing Lemon and Erickson (1952) Introduced a rate (ODR) actively respiring roots. is 0^ reduced at the its surroundings. Stolzy and electrode surface (1964) reviewed The authors concluded roots of most plants do not grow in soils with ODR values less than 3.3x10 6.7x10 _o “8 kg m kg m —2 “2 8 -1 “1 most conditions. microelectrode (20x10 s relationship (40x10 —8 -8 exists —1 -2 g cm min -2 g cm min ~i ) and that ODR must exceed ) for optimum top growth. between ODR and air porosity of the soil under However, Lemon and Erickson (1952) used the platinum method to show that 0^ supply to plant roots may at times be controlled by water film thickness rather than and Their method is Letey studies of plant responses to measured ODR values. A platinum a current proportional to the rate at which Og diffuses to the electrode from that using air porosity. Letey Stolzy (1967) confirmed their results by calculating from theory the water film thickness corresponding to measured ODR values at various soil porosities. For concentration a of root which has a radius of 0.23 20% in the gas phase, and a porosity of 0.5 m the soil surrounding the root, a water film thickness of —2 „o limit the ODR to 3.3x10 pores was substantial. what conditions agreement by mm, water kg m researchers on 3 mm m 0^ -3 for would —1 s even if the volume of air filled Unfortunately, it is difficult to films 0.40 an restrict what predict under diffusion because there is poor water film thicknesses occur in practice. Air Porosity Several aspects of soil aeration have been considered up to this point: oxygen concentration of soil air, diffusion rates in gas filled pores and in water films, and air porosity. Erickson (1982) categorized these 15 Indicators of soil aeration as intensity, respectively. to rate, and capacity factors, Measurement of ODR in water films is the most reliable way evaluate the O2 environment of roots. The use of platinum microelectrodes simulate roots, eliminating the need to know the soil and water geometry surrounding them. commonly measured Nevertheless, air porosity is the soil aeration parameter and may be attributed in part to the fact that growth limiting levels of air porosity porosity of 10% most is frequently cited aeration should be adequate for plant as growth the exist. An air level above which soil (Wesseling and van Wyk, 1957; Vomocil and Flocker, 1961; Thomasson, 1978). Factors Which Influence Air Porosity Soil Compaction The relative abundance of air filled pores depends on soil pore size distribution and the prevailing soil water regime. Compaction influences pore size distribution, especially in the larger pore size range 1982). The (Klute, soil water characteristic, or the relationship between soil water content and soil water matric potential, is altered accordingly the result of soil compaction. as The soil water regime following a heavy rain or irrigation is determined by the soil water characteristic. Vomocil and Flocker (1961) suggest that the water potential at 'field capacity', the water content after free drainage is neglible, is -7.5 -20 kPa. at to Webster and Becket (1972) demonstrated that the water potential field capacity can be much higher in soils containing more than 30 to 40 percent clay and that only pores larger than 100 to 300 (Im in diameter are air filled. More recently, Cannell and Jackson (1981) suggested that water drains freely under gravity only from pores larger than 30 to 60 fim in diameter to a water potential no less than about -5 to -10 kPa in most soils. 16 At any rate, only large pores are air filled at field capacity, the volume of which Is diminished by compaction. compacted soils exhibit a greater Thus, in tendancy a given climate to become anaerobic than noncompacted ones and remain so for longer periods of time based on their altered drainage and water retention properties. Several investigators have demonstrated the influence of compaction on drainage and duration of anaerobiosis. Blake et al. (1976) calculated the time required for soil profiles in packed and nonpacked plots corresponding to to drain an air porosity of 10%. to matric In the absence of evaporation and plant water uptake, air porosity at the 0.30 to 0.40 reach potentials m depth would 10% after 10 days of free drainage in the nonpacked plots compared to more than 30 days in the packed plots. that ODR Agnew and Carrow (1985) found measured with platinum microelectrodes remained below critical levels for a longer period of time following irrigation in compacted pots compared to noncompacted pots. Climate Occurrence of aeration stress is dependent on weather conditions during the growing season just as water stress of plants with mechanically impeded roots may not occur depending on the distribution of rainfall and irrigation. primary Therefore, before aeration stress can be physical limitation occurrence must be considered. of problem soil, likelihood as the of its This prompted Greenwood (1968) to suggest that the aeration status of a soil probability a diagnosed must be defined in terms of the of occurrence of a particular set of weather conditions that are necessary to induce Oj deficiencies in soils having given drainage characteristics. When soil conditions and climate are such that excess soil water may exist at times, the extent of plant injury due to impeded aeration Is 17 Influenced stress. by plant species or cultivar, growth stage, and duration of For example, some species waterlogging tolerant (e.g., of grain Vicia Fabia legumes L.) are caused may also greatest when that O2 pea (Pisum sativum stages but plant Erickson and Van L.) yields (Zea mays) during early (Hiler and Clark, 1971; Singh and Ghlldyal, 1980). Thus, it may not be sufficient to examine the probability of occurrence stress were deficiency occurred just prior to blossoming. Soil water excesses seem most harmful to corn growth 1981). This may be consumption change during their life cycle. Doren (1960) demonstrated reduced Jackson, by excess moisture varies with growth stage. attributed in part to seasonal differences in Oj sensitivity as while others are very sensitive to short periods of waterlogging (Cannell and Injury regarded without considering the crop of O2 and stage of growth during which stress is likely to develop. The importance of duration of anaerobiosis may be attributed to the fact that soil air contains only a limited supply of O 2 at any one For the volumes of O 2 example, Cannell and Jackson (1981) contained in a sand and clay soil after were 0.03 and 0.003 m 3 m -3 compared draining freely. be large. volumes in the sand and clay, respectively. short term interruption of gas exchange between the soil can The time. harmful when the quantity of O 2 and Even atmosphere required for soil respiration is Hillel (1980) calculated that a soil with an effective root zone 3 depth m 2 of 0.6 m and 15% air porosity contained 0.09 m of soil surface. 20% (i.e., 0.03 m oxygen reserve 3 With an initial O 2 m -3 would probably begin earlier. effects of O 2 ) and an O 2 last only concentration in the gas phase of requirement of 2.5 of air under each days Erickson and Van Doren only one day of oxygen deficiency. but 10 g m -2 d -1 the stress symptoms would (1960) showed dramatic Yields of peas subjected 18 to one day of Og deficiency just prior to blossoming were reduced 30 percent. Causes of Soil Compaction in Michigan Naturally Occurring Compaction Many Michigan horizons. soils Some of of soil cementation dense soil layers lacustrine are these horizons particles formed deposits characterized may by naturally dense layers or be attributed or by under physical are more common. calcareous melt and phenomenon as texture is However, in till and For example, the parent materials glaciers water from glaciers (ablational till). its chemical as in fragipans and orsteins. of the soils in Huron County were deposited directly by till) to sandy loam, loam, (basal This till is or clay loam. Approximately 60 percent of the Huron County soils have naturally dense C -3 horizons with bulk and 62 percent of these C horizons occur within 1 m of the (Linsemier, _3 densities ranging from 1.70 to 2.13 Mg m 1980). Daddow and Warrington (1983) (g cm soil surface established relationship between growth-limiting bulk density and soil texture on their influence on mechanical resistance to root penetration. limiting bulk densities ) a based Growth- corresponding to textural classes found in the -3 Huron County subsoils range from 1.50 to 1.70 Mg m , well below the prevailing bulk densities. Some Michigan because they textured, soils are considered have high bulk densities, exhibit poor internal aeration for root growth at certain Charity clay (Aerie to be but naturally compacted not because they are drainage, and therefore lack adequate times during the growing season. Haplaquept) is an example of such a soil. It is a lake plain soil of lacustrine origin which has poor structure and dense fine is so that little rooting occurs below the plow zone except in shrinkage 19 cracks that occur late in the growing season (Erickson, clay Is part of 1982). Charity the expansive Erie-Huron Lake Plain which covers more than 1.7 million hectares (4.22 million acres) In Michigan's southern lower peninsula. Wheel Induced Compaction Compacted soil conditions induced by man are more extensive than those that occur naturally. compactive forces Agricultural vehicles are the (Cohron, 1971). Wheels of primary source of agricultural vehicles produce pressures at the soil surface and within the soil body. Vertical pressures are equivalent to normal stresses such as stresses exerted by a static load. especially Shearing when stresses wheel also slippage occurs. arise under rolling tires, When the combined stresses are sufficient to cause soil compaction, the major actions in the soil are rearragement of soil particles and reduction in pore space, especially of large pores (Harris, 1971). Tractors contribute most to total vehicle traffic but tillage implements, harvesting equipment, and hauling units may also lead to considerable amounts of vehicle traffic. The extent of vehicle traffic and vehicle weight are two of the most important factors influencing the degree of wheel-induced compaction. Excessive traffic is a problem wherever modern agricultural practices are employed. There are traffic. Gohlich concluded that season. several (1984) tractors examined travel of reporting the extent of vehicle farming practices in Europe and 30 to 60 km ha * on the average in one Another approach is to determine the size of the wheel tracks in relation to the soil surface. number ways of field operations, wheels can be determined. By multiplying this value by the total the wheel track surface caused by vehicle Voorhees (1977) calculated the amount of wheel traffic associated with a six-row operation covering a width of 4.6 m, 20 and using 0.46 m wide rear tractor tires. Assuming a total of six operations per growing season, half of them with dual wheels, the tractor tires make enough wheel tracks to cover every square meter of twice. and the field In Sweden, the total wheel track surface is commonly between four five times as great as the surface where small grains are the main crop but even higher with other crops such as sugarbeets and potatos (Eriksson et al., 1974). When every point on the soil surface is exposed to wheel traffic two times on the average, it is obvious that some points may be driven across several times while others not at all. particular However, the probability the randomly distributed field under normal farming operations (Voorhees et al., 1979). Exceptions are well defined areas planting, a point on the field will be affected by at least one pass of a tractor tire is high because most wheel traffic is over that cultivation of concentrated and harvest of row crops. random wheel traffic on freshly tilled soil wheel traffic from The adverse effects of become obvious when one considers the well documented phenomenon that most soil compaction occurs after one pass of a tire. For example, Taylor et al. (1982) showed that three fourths of the total change in bulk density and 90% of the sinkage on a silt loam occurred after the first of four passes. The second factor that influences the depth compaction is vehicle weight and weight distribution. (1985) reported the and degree Carpenter of soil et al. results of a University of Nebraska survey of U.S. tractor weights during the last 17 years. The average tractor weight has increased from 4.6 Mg in 1968 to an average of 6.8 Mg in 1985, with large four-wheel drive units exceeding 22.4 Mg. commercial fertilizer spreaders and products have also increased in size. Transport trucks vehicles such as used to haul agricultural Capacities of trucks used to haul 21 sugarbeets from fields to processing plants have Increased from 5.5 to 9.0 Mg over the last 40 years according to Anderson and Peterson (1985). Prior to the classic work by Soehne (1958), It was commonly believed that Increasing tire width or diameter as the result In load not Soehne (1958) disproved this notion by examining the theoretical distribution a will an Increase In compaction because tire Inflation pressure and soil contact pressure can be held constant. under Increases load applied normal of vertical to the soil surface. pressures Important findings were: (1) pressure in the upper soil layer is determined by the specific pressure at the soil surface which depends on tire inflation pressure and soil deformation, and (2) pressure determined by the magnitude of Blackwell and Soane (1981) vertical pressure (normal the in the load. verified Taylor the stress) within deeper et soil al. layers (1980) is and second finding by measuring the soil body under various loads. Subsoil compaction is an issue of great concern to agriculturalists because it is more difficult and coatly to within the normal depth of plowing. correct applied to the soil and permeability appeared of 6.0 heavier Mg. The may towards an larger compaction. sizes as the larger Measurable differences in loads pore volume axle loads speculated that the continuing trend towards cause a increasing gradual shift in equilibrium soil degree of subsoil compaction. Saini (1978) and Voorhees et al. (1978) have since cited machinery and in the upper part of the subsoil at authors machinery conditions surface. compaction Eriksson et al. (1974) measured actual changes in soil physical properties as were than is primary This claim may be reason especially for valid the ever persistence in increasing of northern subsoil climates 22 where the natural forces of freezing and thawing might otherwise decrease bulk density of the compacted subsoil. Changing Cropping Systems Soil compaction Is usually more prevelant under continuous or Intensive cropping systems than under rotations, especially those Including meadows or legumes. Several factors associated with crop rotations or cropping systems Influence the degree of compaction. and amount of Tillage Intensity, the residue returned to the soil are the primary factors but their effects on soil conditions are difficult to Allmaras, amount 1971). of associated wheel year traffic Is was rotation the dominant factor. Compaction the The authors concluded that a which included two years of alfalfa was superior to results traffic rows in continuous of Intensity bulk potatos. density Soil bulk was reduced. Saini (Db) measurement under density was directly to the number of years under continuous cropping and not organic matter levels indicating that the primary factor Influencing Many the rotation experiments have amount rotations retard of vehicle been conducted soil organic which show that matter levels. et al., 1986). 1979; Odell (1971) the the Crop summarized the et al., Products of biological decompostion of organic materials are required to stabilize soil structure. Allmaras was the decline of soil nitrogen and organic C compared to continuous cropping systems (Hageman and Shrader, Skidmoore traffic degree of compaction. degree of compaction is related to 198^; and with continuous corn culture in a 13 year rotation experiment reported related (Larson the continuous corn because overall tillage (1980) separate Results of some studies imply tillage intensity or on Brookston clay (Bolton et al., 1979). four kind Larson and results of numerous long term rotation experiments designed to evaluate the influence of cropping systems on 23 soil structure. Addition of crop residues or cropping systems that included legumes promoted low Db and the decreases in proportional to increases in organic matter content. stability of soil structure (e.g., water associated with various cropping systems Db roughly Further, changes in stability were were even of more aggregates) evident than changes in organic matter content. Recent studies have been conducted in which the Influence of organic matter on susceptibility to compaction is clearly the nonexistent effects of machinery travel were demonstrated because or accounted for. Howard et ai. (1981) evaluated the susceptibility of 14 California forest and range densities. soils to compaction The four most by measuring imposed maximum bulk susceptible soils were range soils, each of which was characterized by low organic C (1986) Proctor content. Pikul and Allmaras several residue management treatments on a winter wheat- fallow system in the Pacific Northwest. Soil bulk density and soil water desorption curves indicated that compaction was greatest where organic C addition was lowest. The trend towards intense crop rotations is recognized as a key factor contributing to Michigan's growing compaction problem (Robertson, Such rotations do not organic matter required include to 1984). leguminous hay, an important source of stabilize soil structure. Whiteside and Lumbert (1986) summarized the extent of this trend in their comparison of land use changes from 1967 to 1982. In the southern lower peninsula, where most of Michigan's farmland is located, there was increased percentage a shift an of field crop hectarage in row crops from (45.8 to 71.7) and decreased percentages in small grains (from 24.4 to sod to crops (from 29.8 to 12.0). 16.3) and These shifts in land uses have been most pronounced on the prime farmlands which were thought to have the least 24 limitations to use in terms of physical and chemical properties. Untimely Field Operations Soil texture and water content influence the susceptibility of a soil to compaction given a particular compactive effort. and Denton et al. (1986) showed that coarse those with a Larson et al. (1980) textured especially wide range of particle size, can be compacted to high Db. Larson et al. (1980) classified finer textured soils whose soils, compressibilities were into three groups dominated by the type of clay rather than particle size distribution. Producers are operations, Robertson if and unable to possible, Erickson control can soil reduce (1980) texture the risk but of timely soil compaction. attributed" deterioration of conditions of Michigan soils to inadequate drainage and field on wet soil in addition to causes of compaction field physical operations already cited. Inadequate drainage is a problem because it increases the likelihood that certain field operations will be conducted when the soil is wet and most susceptible to compaction. The relationship between soil water content and Db resulting from a given compactive effort has been described by Vanden Berg (1967), (1958), Harris (1971), and Saini et al. (1984). compactive effort, there is a soil moisture Soehne water content called content' at which the maximum Db is obtained. the Gill and For every 'optimum Dry soils resist compaction due to particle-to-particle bonding and frictional resistance. As water content increases, moisture films develop on which weaken interparticle lubricating the particles contents the above bonds (Hillel, optimum and 1980; reduce particle internal IJamdani, 1983). surfaces friction At by water moisture content, the fractional volume of expellable air is reduced and soil density can no longer be increased to 25 the same degree as before. As compactive effort increases, the maximum attainable Db increases and the optimum moisture content lover values because less moisture is shifted to is required to lubricate the soil particles• A laboratory test for the determination of the optimum moisture content and corresponding maximum attainable Db was developed by Proctor (1933). This test is routinely used by engineers who view soil as construction material and strive to manipulate it so that strength of a soil layer can be increased and permeability can be decreased. contrary to those of agriculturalists. the term 'optimum moisture content' attainable Db, should be Saini et al. (1984) proposed that which replaced These objectives are by corresponds to Field when is less than the critical soil water content operations should Unfortunately, rainfall probabilities increase during the to October in Michigan's major production unavoidably harvested during unfavorable soil This problem is maximum 'critical moisture content' to account for this contradiction. the the areas. be conducted water content. period Some conditions August crops as a are result. particularly acute in production of sugarbeets because the required harvest machinery and hauling equipment are so massive. Alleviation of Compaction Natural Forces Raney and Edminster (1961) density or degree of compaction soil. suggested that there is an equilibrium that is characteristic of each kind of Water content and temperature changes and biotic activity in soil bring about bulk density changes following loosening or compaction of soil and these changes will usually be toward this equilibrium Db (Larson and Allmaras, 1971). Two implications can be drawn from this statement: (1) natural forces can alleviate soil compaction under some conditions, 26 and (2) the ameliorative effects of tillage are probably transient. The influence of swelling and shrinking, freezing and thawing, and plant root activity on soil structure will be considered in this section. Swelling and Shrinking associated with wetting and drying cycles tend to decrease the Db of aggregated soil. of compacted soil and increase that a loose Blackwell et al. (1985) demonstrated beneficial effects alternate periods of wetting and drying on a swelling clay soil which was previously wheeled uniformly by a combine harvester Bulk density changes, tractor. In addition to Db drying. Bullock et al. attributed regeneration of structure to the development of planar voids as the result of wetting and drying. always reflect measurable These Detrimental effects shrinkage cracks may Db changes but they provide a recurring path for root penetration (Greacen et al., 1983). a vertical cracks may develop along planes of structural weakness as the soil volume changes during wetting and (1985) and decreased and porosity increased within the surface 0.15 m of soil where wetting and drying was most prevalent. not of of 1968; Taylor, 1974; Jones, wetting and drying on soil loosened by tillage will be discussed in a subsequent section. Freezing and Thawing has long been recognized effects on soil tilth when fine textured soils are (Baver, 1972). for its beneficial plowed in the fall The mellowing effect of freezing on free-lying clods can produce a favorable seed bed without further soil manipulation under some conditions. attributed The effect to disruption thawing and drying. depends on soil cooling), and the Apart from of its freezing by freezing and and thawing some on clods can be reaggregation during The structure formed (i.e., degree of aggregation) type, conditions of freezing and thawing (e.g., rate of water content at the time of freezing. effects on aggregation of surface soil, freezing and 27 thawing is expected to decrease Db In soli more packed than density and to natural state. subsoil are promotes the loosening the transition. of Thus, the physical 9% effect volume conditions on soil increase as of pores associated Migration of water to sites of dehydration. natural density of soil which is looser than its a naturally not expected to change with freezing and thawing. a accomodate sites Increase the become with ice dense Freezing enlarged to the water-to-ice formation can produce Thus, loosening effects of freezing and thawing are often difficult to distinguish from wetting and drying. Ameliorative potential in the literature. of freezing and thawing is often overestimated Krumbach and White (1964) compared Db of frozen to Db of soil in the same depth prior to freezing. that freezing The authors concluded can decrease Db of Michigan soils as the densities in all frozen depths (to a depth of 0.37 m) were lower than the freezing. soil However, subsequent studies have shown average that before substantial reconsolidation of soils can occur upon thawing. For example, Kay et al. (1985) demonstrated that Db of two Ontario soils decreased surface 0.15 40% in the m during freezing but quickly returned to near prefreezing Db's prior to spring planting. Gill (1971) assessed the magnitude of the compaction problem in the United States in terms of the area affected. used as the criterion to determine compaction. The soil profile the Frost penetration depth was distribution may not receive amelioration where frost penetration is less than added that, exceeds 0.25 soil m, 0.25 of 'perpetuating' adequate m. The natural author compaction can occur in areas where frost penetration but annual penetration of frost may diminish its persistance. In the same monograph, Larson and Allmaras (1971) stated that there was 28 no evidence of structural freezing and thawing. statement. In Numerous Sweden, Eriksson et al. (1974) subsoil compacted amelioration below a depth of 0.20 m due to where were two to investigators frost unable three have substantiated depth ranges from 0.60 to 0.80 m, to detect structural years earlier. changes thawing despite attempts to enhance in In Minnesota, subsoil compaction persisted for a nine-year period in the presence and this frost of freezing heaving with the application irrigation water prior to freezing (Blake et al., 1976). Voorhees et al. (1978) induced subsoil compaction forces in Minnesota. and was Voorhees (1983) demonstrated that wheel not alleviated by compaction applying modern equipment. axle Bulk conductivity loads density, typical of penetrometer on a harvest resistance, clay loam by and transport and hydraulic measurements showed that subsoil compaction persisted up to four years despite annual freezing to a depth of 0.90 m. cannot weathering In a more recent study conducted in the same area, Voorhees et al. (1986) imposed subsoil high natural Thus, farmers afford to depend on the natural weathering forces of freezing and thawing to alleviate compaction below the normal depth of plowing. Plant Roots impart structural changes that may be attributed largely to their influence products of cementation on aggregate microbial and formation. metabolism are Baver (1972) suggests that intimately stabilization of soil aggregates. plant roots and dead tissues from pre-existing involved in the Exudates from living roots are the primary energy sources for these microbial transformations (Russell, 1978). Larson and mechanisms of adjacent Allmaras aggregate (1971) and Raver formation (1972) involving plant described additional roots. Particles to roots may be reoriented and pressed together into aggregates as the result of pressures exerted by roots. Extraction of water from 29 the soil is another factor as greater shrinkage can occur near the root surface than at some initiation occur can distance was weathered soil reduced roots. Extensive aggregate The Influence of alfalfa roots on demonstrated of the within about five times the radius of the root as the result of this mechanism. aggregation from the by Radcliffe southeast. et Subsoil subsoil al. (1986) on a highly mechanical impedance was as aggregates larger than 4.0 mm in diameter were created at the expense of aggregates smaller than 0.5 m m in diameter. Roots can bring about structural changes by mechanisms other than their influence on aggregation. Decayed root channels can transmission of water through slowly permeable soils. more increase Since the roots can easily widen an existing channel than create its own, root channels provide a preferred path for root (Greacen et al., 1968). cotton roots. through high strength soils Bowen (1981) cited results of a study in which Pensacola bahiagrass roots were impeded growth shown to penetrate soil layers that Root length densities of subsequent cotton crops were increased because the volume of pores greater than 1.0 mm in diameter was increased by the rooting activity of the bahiagrass. Subsoiling Deep tillage is defined as a primary manipulates soil to a greater depth than Society of America, 1984). Deep tillage normal tillage plowing operation (Soil which Science can be accomplished with a variety of implements including a large heavy-duty moldboard or disk plow which inverts the soil, or with a heavy-duty chisel plow the soil. Thus, which shatters subsoiling consists of deep tillage without inversion and a minimal mixing of the soil. Deep tillage is a beneficial management practice only where a specific soil factor is limiting plant growth (Burnett and Hauser, 1968). Russel 30 (1956) demonstrated the Importance of this requirement by surveying the results of nearly 100 deep Deep tillage unaffected was or tillage beneficial sometimes on reduced experiments 50% of the by deep conducted fields tillage In England. but yields were In the remaining experiments. Recent studies have shown that even when soil strength Is thought to be the soil beneficial. factor limiting plant growth, deep tillage may not always be Since critical strength can be Identified for a particular plant grown on a given soil, Gerard et al. (1982) suggested that periodic evaluation of mechanical Impedance would be an excellent way to determine the need for deep tillage. Vepraskas et al. (1986) evaluated diagnostic soil properties and values that could be used subsoiling would Improve root growth. to The identify authors soils where showed that the success of subsoiling was dependent on Db and sand content of the subsoil in addition to soil strength (cone index). Excessive strength of soil layers such as fragipans, hardpans, clay pans, h i g h - d a y horizons, or plowpans is an which can limit plant growth. soils with such layers of a soil factor The objective of deep tillage conducted on is almost always allevation of water stress by increasing the effective depth within example the explored volume. of root growth or root proliferation Root-impeding layers are commonly disrupted by subsoiling. When subsoiling is carried out on dry soil, the maximum degree of shattering can be achieved (Cooper, 1971; Cannel, 1977; 1982). Cooper (1971) disturbed by subsoilers. soil water content and Bowen (1981) decribed Byrnes et al., patterns of soil These patterns of disturbance are influenced by during subsoiling and subsoller working depth. Subsoiling has been shown to reduce Db (Douglas et al., 1980; Ross, 1986) 31 and reduce penetrometer resistance (Buxton and Zalewski, 1983; Vepraskas and Miner, 1986) within the volume of soil disturbed. Since root-impeding layers are usually disrupted to alleviate water stress, subsoiling may or may not increase subsequent rainfall. it crop yields depending upon As the amount of growing season rainfall increases, is expected that the beneficial effect of subsoiling would be reduced (Weatherly and Dane, 1979). wet years in 1974; B o x and properties Subsoiling had no effect on yields during southeastern parts of the United States (Campbell et al., Langdale, 1984). In the Pacific Northwest, physical of a tillage pan were improved dramatically by subsoiling but potato yields were increased only at low irrigation rates (Ross, 1986). Few studies have been conducted in which the primary objective of deep tillage was improved soil aeration. the Woodruff and Smith (1946) evaluated potential for improvement of a claypan soil using subsoil shattering alone and with lime fertilizer mixed with the yields were attributed Black clay. aeration throughout Increased to improved aeration in the subsoil. Stewart (1983) reported results of a Houston subsoil. profile modification corn Unger and study on a Deep profile mixing caused greater and more uniform the profile, increased root proliferation, and increased cotton and grain sorghum yields. Cannell and Jackson (1981) stated that artificial drainage (i.e., subsurface system of pipes) is the principal method that can be alleviate poor aeration. However, the authors add drainage will only be useful if continuous transmission the topsoil and machinery in some pores as those subsoil and situations. which are these pores Greenland greater may (1977) than important to achieve rapid movement of water. 100 fim used to that artificial pores exist in have to be created by defined transmission in diameter and are Since it is the volume of 32 these large pores which is affected by tillage (Cassel and Nelson, 1985), tillage of a dense soil with poor aeration characteristics can correct temporarily the aeration problem (Burnett 1982). Hauser, 1968; Erickson, Salient points in this section were summarized in a statement by Cannell (1977) who suggested with and a definite hard that subsoiling is justified only pan or horizon impeding root in soils growth or water movement. Controlled Traffic Subsoil compaction can be corrected, if subsoiling or some other form of deep tillage. and frequently treats only Subsoiling any combination and of the subsoil) three. of minimized: (1) reduction (2) the using expensive probelm Except is wheel Wheel traffic can be random, excessive, untimely, or Soane et al. (1982) considered these possibilities and suggested three ways in which (surface is only the symtoms, not the basic problem. where subsoil compaction is naturally occurring, induced compaction. temporarily, field the overall compaction soils by agricultural vehicles can be of vehicle mass and contact pressure of wheels; reduction of the number of passes of conventional machinery; and (3) confinement of traffic to permanent controlled traffic). or temporary wheel tracks (i.e., Options two and three will be discussed at greater length in the remainder of this section. Advantages of reduced or minimim tillage systems became apparent as soils depleted in organic matter have been worked with increasingly massive machinery. al. (1953) compared minimum seedbed preparation tillage more and Recognizing these trends, Cook et with conventional on a Brookston loam in Michigan. and dry bean yields were obtained when the least tillage The intensively tillage during Highest sugarbeet was performed. authors concluded that farmers were working their soil more than was 33 necessary. fine Similarly, Glenn and Dotzenko (1978) demonstrated that on a montmorillinitic soil in Colorado, conventional and minimum tillage (field operations were reduced 40%) produced sugarbeet crops of comparable tonnage and quality. The controlled traffic concept was initiated 30 years ago as a method for increasing crop yields by reducing wheel Induced compaction 1983). The controlled traffic concept is based on the fact that conditions required by plants efficient operation of are exactly opposite those pneumatic tires. moist soil while firm, dry surfaces Williford (1980) (Taylor, described a are soil needed for Plants require uncompacted, needed for optimum traction. controlled traffic system in which zones planted to cotton and zones restricted to wheel traffic were referred to as production zones and traffic zones, respectively. Controlled traffic has gained greatest popularity where subsoiling is routinely used to disrupt traffic pans. which is easily recompacted and can become more dense than has been broken up it was susceptibility traffic. before of a tillage. clay loam The author found that the Cooper (1971) stated Trouse to that soil (1983) demonstrated compaction the during post-subsoiling edge ofa tractor tire must be at least 0.30 m from the subsoiled channel to prevent recompaction. Wheel traffic associated with field operations that follow subsoiling can be controlled to avoid recompaction of the loosened soil the need for annual subsoiling. under traffic was controlled with conventional tillage consisting of random wheel traffic. Recompaction levels were more severe and cotton with reduce Williford (1980) compared penetrometer profiles from areas where post-subsoiling profiles and conventional tillage. yields were diminished In California, Carter (1985) showed that the surface 0.30 m of a fine sandy loam was recompacted to an average Db of 34 1.69 Mg m no traffic. -3 In wheel trafficked Interrows compared to 1.61 Mg m Dumas et al. (1973) following deeper-than-normal demonstrated tillage compaction and cotton yields. that -3 controlled significantly under traffic affected soil Subsoiling was not beneficial under normal tractor traffic on a silty clay soil in Florida (Colwick et al., 1981). Soane et al. (1982) and Cooper et al. (1983) suggest that adoption of controlled traffic for commercial production has been lack of standardization obstacle must be overcome inhibited by of wheel widths on production machinery. because the success of controlled the This traffic depends on the ability of farmers to maintain traffic-free zones. Persistence of Tillage-Induced Changes Wheel traffic is one of several factors which persistence of changes brought about by deep tillage. can influence the As indicated in an earlier section, there is a tendency for the density of soil loosened tillage to change natural forces. towards an equilibrium value under the influence of Cassel and Nelson (1985) measured numerous soil physical properties at three depths during the first two months after tillage planting. Changes were greatest the 0 to 0.14 m depth of nontrafficked interrows where the difference between the post-tillage Db and the 'equilibrium Db' was greatest. et and All properties exhibited significant temporal variability and were attributed to alternate wetting and drying. in by al. (1986) demonstrated resulted in most of the properties following that temporal the first variability Mapa wetting and drying cycle of four soil hydraulic tillage which consisted of subsoiling at one site, moldboard plowing at another. Burnett and Hauser (1968) suggested that physical changes in the soil profile created by deep tillage are long lasting if: (1) fine textured throughout the profile; (2) the the soils are tillage operation is 35 drastic, such as tillage with large plows; and textured zones are essentially genetic. (3) the dense or fine The authors commented further on the third requirment indicating that physical changes in the soil brought about by deep tillage are transient if the compacted layers are Induced by machinery. This statement may have been based on the inability or unwillingness of farmers to Implement controlled traffic systems. Direct evidence showing the influence of soil persistence of changes brought about by deep tillage is literature. (1968) However, as a the requirement substantiated. texture .on the lacking in the second condition cited by Burnett and Hauser for lasting deep tillage changes can Hauser and Taylor (1964) showed that Db differences were apparent four years after deep disk plowing. The effects of hand digging on subsoil physical conditions were detected up to four years soil was loosened (Gooderham, 1977). et al., 1986). The after the B y contrast, hardpans loosened by paraplowing did not always remain loose during the first (Wilkins be growing season paraplow is the trade name for a slant- legged tillage tool which is similar to subsoilers in that it loosens the soil by lifting without inversion. Drastic deep tillage operations may in general produce results that are more persistent than those from subsoiling. operations require larger equipment, consume more soil layers with unfavorable chemical However, these tillage fuel, properties and can bring closer to the soil surface. The Role of Simulation Models Simulation models, a collection of quantitative relationships used to describe a system, can be used modifications. with to evaluate the impact of root zone Taylor and Arkin (1981) described difficulties associated more conventional approaches. First, root observations are costly, 36 time consuming, and destructive. modification factors. Second, crop responses to root zone are frequently masked by other environmental and management Computer distinguish simulations crop response confounding responses. derived to root from zone models may be modifications used from to other In addition, simulations for long periods of time (e.g., using generated weather data) can be used to develop probabilities of crop response and benefit (Arkin and Taylor, 1981). Relationships between water abundant in the literature. on these relationships. effects of soil use and production of various crops are Feddes (1981) reviewed numerous models based The author suggested that one can manipulation on attempts have been made to do so. inability to This may be explained in part predict physical changes brought about by tillage. (1982) have the production through water use but few advances by Linden (1979), Blackwell Larson consider and Soane (1981), and by our Recent Gupta and increased our ability to predict tillage effects on soil conditions. Models based on production system. water use describe only one part of the more complex The influence of tillage on soil physical is another part of the system. conditions Until recently, few models were available which described other components of the system such as those discussed in previous sections. Soil aeration is an Important component of Michigan because so many of the prevailing soils are prone to compaction. Whisler production systems in poorly cultivation and wheel traffic mechanical impedance, and (3) changes stress. The soil or et al. (1982) described a cotton growth simulation model (GOSSYM) which was modified to account for of drained on (1) in root hydraulic growth the effects properties, (2) due to low status is evaluated by calculating 0^ concentrations 37 due to one dimensional diffusion into the soil profile. Apparently, the influence of Og deficiency on cotton growth in their model is due only to reduced root elongation rates during anaerobiosis. Erickson (1982) suggested that a cumulative product representing some combination of deficiency duration and intensity (e.g., 0^ concentration) could be used as a measure of stress and that a further Improvement would be to consider Clark (1971) the type of crop and its growth stage. proposed the Hiler use of a stress day index (SDI) to account for the influence of soil water deficits and excesses on corn yields. for be each period during the growing season multiplying a stress day factor (SD) times a crop (CS). The and can The SDI calculated susceptibility by factor SD factor is a measure of the degree of water or 0^ deficit. The CS factor quantifies the plant susceptibility to a given stress. Its magnitude depends on the crop species and stage of development. The SDI concept was employed by Hardjoamidjojo et quantify the effect of excessive and deficient soil water corn yields. The 1974) was used SD factor to relationship management conditions to calculate the SDI for excessively wet conditions. 0.02 model 42 Crop days after during the period 81 to 120 days after planting. obtained was on originally defined by Sieben (Wesseling, susceptibility factors varied from 0.51 during the first planting al. (1982) to subsequently incorporated into the The water DRAINMOD to quantify the effect of soil water stresses (deficiencies and excesses) on corn during simulation of drainage system designs (Hardjoamidjojo and Skaggs, 1982). Sumary Poor physical conditions Valley Bean and Beet Research compacted because its pores of Charity clay limit yields at the Saginaw Farm. are This so soil small is considered to be that root penetration and 38 internal drainage are impeded. adequate aeration for root Soils with poor internal drainage lack growth at certain times during the growing season when rainfall is excessive. Normal fall and spring tillage problems associated with Charity clay. that the practices perpetuate Results of this the physical survey suggest following procedures may promote more favorable conditions for crop growth on this fine-textured soil: (1) deep tillage can be used to alleviate temporarily the aeration problem; (2) subsoiling is a practical deep tillage practice even though more drastic tillage procedures may create more persistent physical changes; and (3) subsequent traffic be controlled or at least must reduced to obtain the maximum benefit from subsoiling. Traditional soil and plant measurements can be used to evaluate the effectiveness of these approaches. demonstrate that Recent evidence in the literature crop simulation models can be used to distinguish crop response to tillage from other confounding responses and to evaluate probability of crop response and benefit. the LIST OF REFERENCES Agnew, M.L., and R.N. Carrow. 1985. 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Fundamentals of soil physics. Academic Press, Inc., New Howard, R.F., M.J. Singer, and 6.A. Frantz. 1981. Effects of soil properties, water content, and compactive effort on the compaction of selected California forest and range soils. Soil Sci. Soc. Am. J. 45:231-236. Jones, C.A. 1983. Effect of soil texture on critical bulk densities for root growth. Soil Sci. Soc. Am. J. 47:1208-1211. Johnson, C.B., J.V. Mannering, and W.C. Moldenhauer. 1979. Influence of surface roughness and clod size and stability on soil and water losses. Soil Sci. Soc. Am. J. 43:772-777. Kay, B.D., C.D. Grant, and P.H. Groenevelt. 1985. Significance of ground freezing on soil bulk density under zero tillage. Soil Sci. Soc. Am. J. 49:973-978. Klute, A. 1965. Laboratory measurement of hydraulic conductivity of saturated soil. In C.A. Black et al. (ed.) Methods of soil analysis. Agronomy 9:210-221. Klute, A. 1982. Tillage effects on the hydraulic properties of soil: A review, p. 29-44. In P.W. Unger and D.M. Van Doren (ed.) Predicting tillage effects on soil physical properties and processes. Spec. Pub. 44. Am. Soc. Agron., Madison, WI. Kramer, P.J. 1969. Plant and soil synthesis. McGraw-Hill, New York. water relationships: a modern Krumbach, A.W., and D.P. White. 1964. Moisture, pore space, and bulk density changes in frozen soil. Soil Sci. Soc. Am. Proc. 28:422-425. 44 Larson, W.E., and R.R. Allmaras. 1971. Management factors and natural forces as related to compaction p. 367-427. In K.K. Barnes et al. Compaction of agricultural soils. Am. Soc. Agr. Eng., St. Joseph, MI. Larson, W.E., S.C. Gupta, and R.A. Useche. 1980. Compression agricultural soils from eight soil orders. Soil Sci. Soc* Am. 44:450-457. of J. Lemon, E.R., and A.E. Erickson. 1952. The measurement of oxygen diffusion In the soil with a platinum microelectrode. Soil Sci. Soc. Am. Proc. 16:160-163. Letey, J., and L.H. Stolzy. 1967. Limiting distances between root and gas phase for adequate oxygen supply. 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Soil Sci. Soc. Am. J. 50:214-219. Proctor, P.R. 1933. Fundamental principles of soil compaction. Eng. News Record Vol. Ill, New York, NY. R a d d l f fe, D.E., R.L. Clark, and M.E. Sumner. 1986. Effect of gypsum and deep-rooting perennials on subsoil mechanical impedance. Soil Sci. Soc. Am. J. 50:1566-1570. Raney, W.A. 1949. Field measurement of oxygen diffusion through soil. Soil Sci. Soc. Am. Proc. 14:61-65. Raney, W.A., and T.W. Edminster. research. Trans. ASAE 4:246-248. 1961. Approaches to soil compaction Robertson, L.S., and A.E. Erickson* 1980. Compact soil-visual symptoms. Mich. State Univ. Ext. Bull. E-1460. 45 Robertson, L.S. 19844 Crop rotations affect compaction* Solutions. 28:2224. Ross, C.W. 1986. The effects of subsoiling and Irrigation on potato production. Soil Tillage Res. 7:315-325. Russell, E.W. 1956. The effect of very deep ploughing and of subsoiling on crop yields. J. Agric. Sci., Camb. 48:129-144. Russell, R.S., and M.J. Goss. 1974. Physical aspects of soil fertility the response of roots to mechanical impedance. Neth. J. Agric. Sci. 22:305-318. Russell, R.S. 1977. Plant root systems: their function and Interaction with the soil. McGraw-Hill, Berkshire, England. Russell, R.S. 1978. Cultivation, soil conditions and plant growth in temperate agriculture, p. 353-362. In W.W. Emerson et al. (ed.) Modification of soil structure. John Wiley & Sons, New York. Saini, G.R. 1978. Soil Soc. Am. J. 42:843-844. compaction and freezing and thawing. Soil Sci. Saini, G.R. 1980. Pedogenlc and induced compaction in agricultural soils. Tech. Bull., Agriculture Canada, Research Stations, Fredericton, New Brunswick No. 1, 32 pp. Saini, G.R., T.L. Chow, and I. Ghanem. 1984. Compactlbility Indexes of some agricultural soils of New Brunswick, Canada. Soil Sci. 137:33-38. Sallam, A., W.A. Jury, and J. Letey. 1984. Measurement of gas diffusion coefficients under relatively low air-filled porosity. Soil Sci. Soc. Am. J. 48:3-6. 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Whiteside, E.P., and P.J. Lumbert. 1986. Some soil-land use relationships in Michigan in 1967 and in 1982. Michigan State Univ. Res. Rep. No. 470. Wilkins, D.E., P.E. Rasmussen, and J.M. Kraft. 1986. Effect of paraplowing on wheat and fresh pea yields. ASAE paper No. 86-1516, Chicago, IL. 12 pp. Williford, J.R. 1980. A controlled-traffic system for cotton production. Trans. ASAE 23:65-70. Woodruff, C.M., and D.D. Smith. 1946. Subsoil shattering and subsoil liming for crop production on claypan soils. Soil Sci. Soc. Am. Proc. 11:539-542. Chapter 2 Physical Conditions of Charity Clay as Affected by Deep Tillage and Controlled Traffic INTRODUCTION Many Michigan soils are characterized by naturally dense layers or horizons formed under physical phenomenon deposits. of lacustrine origin are prevalent in the Lake plain soils Saginaw Valley, an important dry These fine bean as and in till sugarbeet and lacustrine production area. textured soils are considered to be compact not because they have high bulk densities, but because their pores are so small that penetration and internal drainage is impeded. Soils with poor internal drainage lack adequate aeration for root growth at certain the growing season when the root times during fractional volume of air-filled pores is diminished by the presence of excess water. Physical those problems that occur operations necessary cropping on wet caused naturally soil, consequence systems by have of farming (Robertson such as rainfall also practices are more common than and harvest patterns Erickson, 1980). of sugarbeets, are often a in Michigan. amounts 1971). to Intensity of plant residue returned to the soil (Larson and Allmaras, Levels of organic matter needed to stabilize soil difficult Changing contributed to the incidence and degree of wheel Induced compaction because of their influence on tillage and Field structure are maintain in crop production systems that include dry beans and sugarbeets because only small quantities 48 of residue are produced 49 (Lucas and Vitosh, 1978). Thus, soils depleted in organic matter are being worked more intensively. Subsoiling is a beneficial tillage operation on soils where root penetration is mechanically impeded by a high strength layer or The objective of subsoiling under these conditions is almost always alleviation of water stress by increasing the growth horizon. effective or root proliferation within the explored volume. depth of root Subsoiling has been shown to reduce bulk density (Douglas et al., 1980; Ross, 1986) reduce penetrometer resistance (Buxton and Zalewski, 1983; Vepraskas and Miner, 1986). (1985) and However, demonstrated Williford that (1980), Trouse (1983), and Carter post subsoiling traffic must be controlled to avoid recompaction of the loosened soil. Few studies have been conducted subsoiling, or deep tillage Subsoiling in in which the primary objective of general, was improved aeration. improved aeration and increased corn yields on a claypan soil (Woodruff and Smith, 1946). Unger and Stewart (1983) reported results of a profile modification study on Houston black clay. caused soil greater and more uniform Increased root proliferation, and aeration Increased Deep profile throughout cotton and the mixing profile, grain sorghum yields. Cannell and Jackson principle method that can authors (1981) be stated used to that artificial drainage is the alleviate poor aeration. stressed that artificial drainage is useful only when continuous transmission pores exist in the topsoil and subsoil and that these may have to be created by machinery. large pores which is effected tillage The of a by tillage pores Since it is the volume of these (Cassel and Nelson, 1985), dense soil with poor aeration characteristics can correct 50 temporarily the aeration problem (Burnett and Hauser, 1968; Erickson, 1982). The objectives of this portion of the study were to: (1) evaluate the potential for reducing the physical limitations of characterized by a a the loosened plain soil, naturally dense subsoil and an unstable surface, by subsoiling in the fall when it is dry; (2) determine of lake topsoil the susceptibility and subsoil to recompaction during subsequent traffic; and (3) determine the persistence of changes subsoiling where traffic is controlled. brought about by MATERIALS AND METHODS Field experiments were conducted from the fall of 1982 through 1985 on Charity clay (Aerie Haplaquept) at Research Farm, Swan Creek, MI. the Saginaw Valley Bean and Beet Charity clay has an unstable surface and poor internal drainage when wet but cracks moderately when dry. The site is level and artifically drained m. experimental design was with tiles spaced 10.1 The a split-plot with fall primary tillage as main plots and spring secondary tillage as subplots, complete at blocks and replicated four times. arranged in randomized The influence of primary and secondary tillage on the growth of several crops was tested and will be reported in a subsequent chapter. Main plot treatments, half of which included deep tillage, were applied each fall from 1982 through 1984 to areas previously cropped to alfalfa (Medicago sativa L.). The alfalfa crop was mowed periodically during the summer and sprayed with glyphosate a week or two before implemented. were Main plot treatments were: (1) deep tillage-moldboard plow (DTMP); (2) deep moldboard treatments plow tillage-chisel (NDTMP); and plow, (4) (DTCH); (3) no deep tillage- no deep tillage-chisel plow (NDTCH). During the fall of 1982, only the DTMP and NDTMP treatments were applied. Deep tillage was accomplished by subsoiling to a depth of about 0.35 to 0.45 m at right angles using a triple shanked susoiler with shanks spaced at 0.71 m. Moldboard plowing to a depth of 0.20 to 0.28 m and chiseling to a depth of 0.15 to 0.20 m was applied each fall after the surface of subsoiled areas was subjected to one or two wetting and drying cycles. Main plots were split to include secondary tillage variables consisting of conventional spring tillage and no spring tillage. Conventional spring tillage (CST) involved the normal amount of preplant wheel traffic and was implemented by applying wheel-to-wheel track 51 compaction with a 52 tractor weighing 4.2 Mg. tooth harrow A seedbed was prepared using a spring and spike after the entire plot surface was covered by one pass of a rear tractor tire. Under no spring tillage (NST) wheel traffic was restricted to interrows bordering the four-row plots and was accomplished by combining planting and herbicide application into a single operation. All plots were planted using a four-row minimum those planted 2.03 m. but to small grains. planter to 10 m in length during 1984 and 1985. enough to accomodate four 0.51-m rows. two planting. traffic rows of each restricted during 1983 Plots were wide Thus, interrows adjacent to the plot were unaffected by wheel traffic during When field operations was except Tractor and planter tire spacings were Plot dimensions were 2.03 m wide by 20 m in length reduced center tillage were required after planting, wheel to the interrows bordering the plots under both CST and NST. Sufficient crop from a numbers corn-dry combinations (four of plots bean-sugarbeet In addition, plots from was applied only once an so of that in all eight One crop rotation also 1983 and 1984 were restrictions: (1) deep possible residual effects of be determined. T hus, one the plots established for 1983 were subsoiled the previous fall but primary tillage operations in the fall of and during following changes brought about by deep tillage could half appeared oats-soybean established maintained through 1985 but with the tillage rotation in 1983) of primary and secondary tillage. from a soybean-wheat and one crop appeared. were established each year so that each 1983 (shallow chiseling) 1984 (moldboard plowing) were applied uniformly to all plots and did not include deep tillage; (2) the two secondary tillage applied without treatments were rerandomization each spring so that cumulative effects, 53 if any, of preplant Wheel traffic could be evaluated; and (3) crops rotated according to the crop sequences cited above. Soil physical changes properties were measured to determine the extent of brought about by subsoiling and recompaction caused wheel traffic. were by preplant Sampling was restricted to plots planted to sugarbeets in the corn-dry bean-sugarbeet rotation and plots planted to small grains in the soybean-wheat and oat-soybean rotation. was further restricted to plots in which the DTMP-CST, DTMP-NST, NDTMP- CST, and NDTMP-NST treatments appeared. the With one exception, sampling Physical conditions of soil in plow layer were measured during the first and second crop year after subsoiling. Subsoil physical conditions were measured during the second, and third crop year after subsoiling. mm diam and Undisturbed soil cores 76- 76-mm length were obtained with a double-cylinder, hammer- driven sampler (Blake, 1965) and weighed in the field balance (Ainsworth, Denver, CO, Model determine volumetric water content. each rep of first, using a portable SC-2000 Electronic Balance) to Five soil cores were obtained from each treatment and at each of two depths (0.03 to 0.10 and 0.13 to 0.20 m) within the plow layer and one depth (0.27 to 0.34 m) below the normal depth of plowing. All soil cores obtained from the plow layer were taken during 1985 in plots planted to sugarbeets. first crop year One half of these after subsoiling (site 1). plots represented The other half represented the second crop year after subsoiling as these plots were established 1984 when they were planted to dry beans (site 2). each depth and site were completed in one day to sampling conditions in terms of soil water content. 23 June for the 2.5 the in Sampling efforts at circumvent variable Sampling dates were: to 10.1 cm depth at site 2; 24 June for the same 54 depth at site 1; 25 June for the 12.7 to 20.3 cm depth at site I; and 21 August for the same depth at site 2. The number of soil cores obtained from the last measurement depth were doubled, wherever possible, by sampling during successive field Soil seasons. cores obtained from this depth, in plots representing the first crop year after subsoiling, were obtained during 1983 and 1984 where primary tillage variables respectively. were Soil applied cores during taken in the 1983 fall were of 1982 and 1983, from plots planted to sugarbeets and those taken in 1984 were from plots planted to oats. Soil had to be excavated to a depth of about 0.24 m soil cores could be before undisturbed obtained at the 0.27 to 0.34 m depth. This process was destructive and diminished the area available for yield measurement. All remaining samples at this depth were obtained from plots planted to small grains so that cores could be taken after harvest of oats or wheat. cores taken in plots representing the second crop year after were taken obtained during 1984 and 1985. Soil cores Soil subsoiling in plots representing the third crop year were obtained only during 1985. Each undisturbed soil core was used to determine porosity, water retention in the -1 to -100 kPa matric pore size distribution, and saturated bulk potential water retention range, hydraulic conductivity (Ksat). Soil cores were saturated by wetting from the bottom for at least Soil density, 48 h. at matric potentials of -1, -2, -3, -4 and -6 kPa was determined using a tension table apparatus (Learner and Shaw, 1941). Drainage steps corresponding to matric potentials of -10, -33.3, and -100 kPa were achieved using a pressure plate apparatus (Richards, 1965). Cores obtained during the 1985 field season were final drainage step. not subjected to the 55 Water loss between total soil porosity. potential range saturation and oven drying was taken to represent Sample shrinkage over the -1 was negligible. potential could be determined water content from distribution by subtracting the total porosity. was -100 kPa matric Therefore, air porosity at each matric matric potential of -6 kPa was taken to size to the measured volumetric Air porosity at the soil water represent macroporosity. Pore determined using capillary concepts as effective pore sizes corresponding to various matric potentials were estimated using the capillary rise formula (Vomicil, 1965). Soil cores obtained during In 1985 were resaturated after removal from the last drainage step. Saturated hydraulic conductivity of these samples was determined using the constant head method (Klute, 1965). Tillage analysis effects of undisturbed Treatments appropriate on soil variance. soil were for cores compared a physical Analyses were (Steel and Torrie, 1960). Our were were combined evaluated using over years where obtained during successive field seasons. using split-plot properties least significant arranged in sampling scheme differences (LSD) randomized complete blocks precluded statistical tests of depth and rotation effects on soil physical properties. RESULTS AND DISCUSSION Subsoil Physical Conditions Soil bulk density (Db) and porosity (P), below the normal depth of plowing, and during the first crop year after Table 1. subsoiling are shown in Deep tillage followed by moldboard plowing (DTMP) reduced bulk density and increased porosity from levels under moldboard plowing (NDTMP). Though significant, these differences alone were not large as Db -3 under DTMP averaged 0.05 Mg m Differences (4 percent) less than Db under reported in Table 1 compare favorably with those reported by researchers on lake plain soils in neighboring areas of Canada. et al. (1980) showed that average Db of the 0 to 0.30 m before application of subsoiling depth 5 Db measurements percent compaction treatments. below values compaction measured The magnitude of changes experiment by obtained closest to the soil surface where tillage effects were likely greatest. alleviate Douglas St. Rosalie clay decreased the brought about by subsoiling may have been biased in their the NDTMP. on Plowing below conventional depths did not Brookston clay based on Db and P measurements traffic associated with conventional spring (Bolton et al., 1981). The influence of wheel tillage on Db and P is also demonstrated in Table 1. Normal preplant wheel traffic associated with conventional spring tillage (CST) increased -3 Db about traffic subsoiled 0.06 was and Mg m restricted and to nonsubsoiled decreased interrows P accordingly from levels where bordering plots (NST). Both areas appeared to be equally susceptible to compaction at the 0.27 to 0.34 m depth. The magnitude of the Db increase caused by wheel traffic was about the same as the Db decrease produced by deep tillage. The combined effects 56 of deep tillage and controlled 57 Table 1. Influence of primary and secondary tillage on bulk density and porosity of Charity clay at the 0.27 to 0.34 m depth during the first crop year. Secondary Tillage _____________Primary Tillage________ CST_________________ NST bulk density (Db) , Mg DTMP NDTMP --------- 1.33 B a 1.38 B b 1.26 Aa 1.32 Ab !?LSDp(.05)-0.05 LSDs(.05)“0.06 porosity (P) 3 DTMP NDTMP _3 0.50 Ab 0.48 Aa 0.54 B b 0.51 B a LSDp(.05)-0.02 LSDs(.05)-0.03 T7 Means in each row followed by the same upper-case letter are not different at the indicated probability level using LSD as the criterion for significance. Means in the same column followed by the same lower-case letter are not different. 2/ LSD for comparison of two primary tillage means at the same or different levels of secondary tillage. 3/ LSD for comparison of two secondary tillage means at the same level of primary tillage. 58 traffic were evident as the Db under DTMP-NST was 0.12 Mg m -3 less than the Db under the NDTMP-CST treatment. Bulk, density is not the most sensitive indicator of soil compaction because it reflects only changes in total soil porosity (Voorhees, 1983). Since soil aeration can be impeded at certain times on Charity clay, soil environment for root growth water retention properties. air porosities over is better characterized by its soil Figure 1 compare soil at values. the Water water retention and the -0.1 to -100 kPa matric potential range (i.e., matric suction ranging from 0.1 to 100 porosity) the matric contents kPa). Water content (and air potential of -0.1 kPa correspond to saturated at saturation reflect differences in soil porosity (Table 1) but water retention fox matric potentials ranging from -1.0 to -100 kPa was not influenced significantly by the four treatments shown in Figure lb. By contrast, air porosities under DTMP-NST were consistently greater than values under NDTMP-CST for (Figure la). Results the illustrated same in range of matric potentials Figure la are important because water drains freely under gravity only from pores larger than 30 to 60 Jim in diameter to a water potential no less than about -5 to -10 kPa in most soils (Cannell and Jackson, 1981). In addition, the air porosity of 0.10 3 -3 m m is frequently cited as the level inadequate for Flocker, 1961). traffic, plant growth below air soil aeration is (Wesseling and van Wyk, 1957; Vomocil and Only subsoiling followed by produced which porosities greater controlled than 0.10 m preplant 3 m -3 wheel at matric potentials greater than -10 kPa (Figure la). The primary and secondary tillage variables affected pore distribution (PSD) which in turn produced the differences illustrated Figure la. Figure size in 2 compare the PSD under the various combinations of 59 0.20 ro £ 0.10E o o. 0.00 C^TNDTMP ■ nst CST 0 .5 0 - - nstdtmp E r' g 0 .4 0 - LSD(.05) I 0.50 0.1 1.0 10.0 100.0 Matric S uction (kPa) Figure 1. Air porosities (a) and soil water retention (b) at the 0.27 to 0.34 m depth during the first crop year as affected by primary and secondary tillage. 60 Pore Volume (m^ m ”~3) 0*44-i | ^ § £ z Q 0.41 -_| otn ztn fcj o zw O.38-,D0 Si 0.10^f 0.05H 0.00 - >150 1 5 0 -2 5 2 5 - 4 .4 < 4 .4 Pore Radius Intervals (/4m) Figure 2. Pore size distribution of Charity clay at the 0.27 to 0.34 m depth during the first crop year as affected by primary and secondary tillage. 61 primary and secondary tillage. correspond to Fore radii of 150, 25, and 4.4 fim matric potentials of -1, -6, and -33.3 kPa, respectively. Based on the capillary model, pores with radii less than 4.4 retain fim water at the -33.3 kPa matric potential and pores with radii greater than 150 are fim air filled at the -10 kPa matric potential. that the volume of pores with radii greater than 150 fim controlling wheel traffic after Figure 2 shows was doubled by subsoiling (DTMP-NST) compared to the normal tillage and traffic patterns (NDTMP-CST). The volume of pores in the remaining size classes were unaffected but it is the large pores that facilitate soil aeration by draining readily under gravity. Data reported in Table 1 and in Figures 1 and 2 represent the combined result of measurements obtained during successive field seasons (1983 and 1984) from plots representing the first crop year after 1984 subsoiling. In only, subsoil physical conditions were measured in plots that where subsoiled and chiseled (DTCH) in addition to plots subjected to the treatments discussed up to this point. four Results shown in Table 2 indicate that subsoiling followed by shallow chiseling produced the most desirable physical conditions as Db was lowest, P and macroporosity (air porosity at the -6 kPa matric potential) were highest soil at the 0.27 to 0.34 DTCH. Furthermore, m depth appeared to be less susceptible to recompaction under DTCH compared to DTMP. seemed under Conventional spring tillage to increase Db, reduce P and M only in plots which were moldboard plowed after subsoiling (DTMP). Changes brought about by subsoiling were not evident during the second and third crop year despite the fact controlled on one half of the plots. that post-subsoiling traffic was Soil physical properties during a second and third crop year are reported in Table 3. Soil bulk density, 62 Table 2. Influence of primary and secondary tillage on bulk density, porosity, and macroporosity of Charity clay at the 0.27 to 0.34 m depth during the first crop year . Secondary Tillage _____________Primary Tillage________ CST_________________ NST bulk density (Db) DTMP DTCH NDTMP 1.37 B a b 2 1.32 Aa 1.42 Ab 1.29 Aa 1.31 Aab 1.38 Ab ?LSDp(.05)“0.07 LSDs( .05)-0.08 porosity (P) _________ m 3 DTMP DTCH NDTMP -3__________ 0.48 Aab 0.50 Ab 0.47 Aa 0.52 Bb 0.51 Ab 0.48 Aa LSDp(.05)-0.03 LSDs(.05)«0.03 macroporosity (M) DTMP DTCH NDTMP ---------- m 0.06 Aa 0.11 Ab 0.06 Aa 3 m -3 --------0.11 Bab 0.12 Ab 0.08 Aa LSDp(.05)»0.04 LSDs(.05)-0.05 1/ Measured only during the 1984 field season. 2/ Means In each row followed by the same upper-case letter are not different at the Indicated probability level using LSD as the criterion for significance. Means In the same column followed by the same lower-case letter are not different. 3/ LSD for comparison of two primary tillage means at the same or different levels of secondary tillage. 4/ LSD for comparison of two secondary tillage means at the same level of primary tillage. 63 Table 3. Influence of primary and secondary tillage on bulk density, porosity, and saturated hydraulic conductivity (Ksat) of Charity clay at the 0.27 to 0.34 m depth during the second and third crop year. Primary _______________ Tillage Crop Year 2 Crop Year 3 CST_________ NST_________ CST_________ NST bulk density (Db) DTMP NDTMP _3 1.38 Aa* 1.39 Aa 1.33 Aa 8 1.35 Aa «LSDp(.05)«0.06 LSDs(.05)-0.06 1.35 B a 1.36 B a LSDp(.05)-0.05 LSDs(.05)-0.05 porosity (P) 3 DTMP NDTMP 1.29 Aa 1.31 Aa -------------------- m 0.49 Aa 0.51 B a 0.49 Aa 0.50 Aa LSDp(.05)-0.02 LSDs(.05)-0.02 _3 m -----------------0.49 Aa 0.51 B a 0.50 Aa 0.50 Aa LSDp(.05)-0.02 LSDs(.05)-0.02 Ksat * , , 10 m s * 1 ------------4 A V DTMP NDTMP 4.7 Aa 4.2 Aa LSDp(.05)-21 LSDs(.05)-19 18 Aa 17 Aa 2.9 Aa 6.2 Aa 6.7 Ba 8.4 B a LSDp(.05)-6.4 LSDs(.01)-1.3 1 / M e a n s i n each row followed by the same upper-case letter are not different at the indicated probability level using LSD as the criterion for significance. Means in the same column followed by the same lower-case letter are not different. 2/ LSD for comparison of two primary tillage means at the same or different levels of secondary tillage. 3/ LSD for comparison of two secondary tillage means at the same level of primary tillage. 64 porosity, and saturated hydraulic conductivity (Ksat) were similar under DTMP and NDTMP. Burnett and Hauser (1968) suggest that physical changes created by deep tillage are long lasting where the soil is fine textured throughout the profile, as is Charity d a y , The authors add that and where the tillage operation is changes may be implement used is a subsoiler or chisel. to substantiate this claim transient drastic. if the deep tillage Data reported in Table 3 and are important for two reasons. changes produced by subsoiling should ideally persist through seem First, more than one crop year because farm managers are unable to subsoil each hectare of their farms each fall. For example, soil water content can be too high during the fall of some years to deep tillage operations impractical to apply on that a soil achieve are optimum more shattering. drastic resembling than Charity Second, subsoiling are clay. Since the texture of this soil is uniform throughout the profile, profile mixing is not beneficial except accompany mixing. for the additional In additon, larger and soil more loosening powerful equipment required as the desired amount of soil manipulation increases. below the normal depth which may is Chiseling of plowing seems to be the most practical deep tillage operation on Charity clay even though changes produced may be transient. The effects of preplant wheel traffic were evident during each crop year unlike the effects of subsoiling which were the first crop year. preplant detected through Data reported in Table 3 demonstrate the effects of wheel traffic on Db, P, and Ksat. Physical properties for crop year 2 were Influenced by only one application of preplant wheel as they were only measured in traffic wheat plots that were planted after soybean harvest, during the fall of the first crop year, but without applying the 65 secondary tillage treatments. significant, data in Table Though 3 differences suggest that were generally not Db was lowest under NST. Saturated hydraulic conductivities seemed much higher under NST averaging 17.5x10 ^ m s * (6.3 cm h *) compared to 4.4x10 ^ under CST. Statistical comparison of Db, m s * (1.6 cm h *) P, and Ksat means for the second crop year was hampered by the fact that these soil parameters were measured in only three of four reps. Soil physical properties measured in the third crop year represent the cumulative effects of preplant wheel traffic applied during each of three consecutive field seasons. Normal amounts of preplant wheel traffic -3 decreased bulk density by about 0.05 Mg m controlled (Table 3). These from levels where traffic was differences are about the differences reported in Table 1 where preplant wheel traffic was only once. Thus, recompaction caused by same as applied three consecutive years of normal preplant wheel traffic was no greater than recompaction caused by only one application of wheel traffic. Comparisons shown in Figures 3 and 4 illustrate further the physical changes caused by preplant wheel traffic during the second and third crop year. Water retention of soil at the 0.27 to 0.34 m depth was unaffected by primary or secondary tillage. The corresponding averaged because they were not Influenced by the primary over tillage potentials DTMP and NDTMP variables ranging significantly during from the (Figure -1 to second 3). Air air porosities porosities for were matric -33.3 kPa were influenced positively and and third crop year by controlling .preplant wheel traffic (NST). Since large pores are affected most by tillage and compaction, the volume of pores with radii greater than 150 fim are compared in Figure 4. In aggreement with data in Table 3, deep tillage effects were not evident 66 0.15 0 .10 LSD(.05) I 0 .0 5 ro NST CST 0.00 ro 0.15 a 0. 0 .1 0 - 0 .0 5 - 0.00 0.1 1.0 10.0 100.0 Matric S uction (kPa) Figure 3. Air porosities of Charity clay at the 0.27 to 0.34 m depth during the second (a) and third (b) crop year as affected by secondary tillage. 67 CST NDTMP CZZ1 NST E X ) CST DTMP NST' 0 .0 9 - Pore Volume (m^ m 0 .12 - 0 .0 6 - L SD (.05) 0 .0 3 - 0.00- YR1 YR2 YR3 Figure 4. Influence of primary and^secondary tillage on the volume of large pores (i.e., > 150 x 10 o in diameter) at the 0.27 to 0.3A m depth during the first (YR1), second (YR2), and third (YR3) crop year. 68 after the first crop year (YR1). Wheel induced compaction decreased the volume of pores in this size class most extensively during the first crop year but differences can also be seen in YR2 and YR3. The effects of Wheel traffic on subsoil physical conditions shown in Tables 1 and 3 and in Figures 3 and 4 are not surprising as Wheel traffic associated with normal farming operations can compact soil to a depth 0.45 m (Voorhees et al., 1978). of However, normal farming operations may include the use of combines or transport vehicles that are considerably larger than the 4.2 M g tractor used to apply wheel traffic in this study. In Sweden, Ericksson et al. (1974) were unable to detect measurable changes in porosity and permeability in the upper part of the subsoil axle loads less than 6.0 Mg. at Charity clay appears to be sensitive to Wheel induced compaction below the normal depth of plowing even when soil at this depth was not previously loosened by deep tillage. Topsoil Physical Conditions Soil physical properties layer) are reported in applied at two depths within Ap horizon (i.e., plow Tables 4 and 5. Primary tillage variables, prior to plot establishment, had no effect on Db, Ksat, or water content at either depth. Soil porosity at the 0.03 to 0.10 m depth was enhanced by deep tillage based one treatment comparison shown in Table 4. Data in Tables 4 and 5 demonstrate that preplant wheel traffic caused significant compaction at compaction was assessed. increased depths and during each year that Wheel traffic associated with the CST treatment Db of the 0.03 to 0.10 m depth by 15 and 18 percent during the first and second decreased both P year, respectively accordingly. Saturated (Table 4). hydraulic order of magnitude lower under CST than under NST. The same treatment conductivities were an As an example, normal preplant Wheel traffic decreased Ksat to 1.5x10 ^ m s ^ (5.4 cm h""^) from 69 Table 4. Influence of primary and secondary tillage on bulk density, porosity, saturated hydraulic conductivity (Ksat), and volumetric water content of Charity clay at the 0.3 to 0.10 m depth during the first and second crop year. Primary Tillage Crop Year 1 CST NST Crop Year 2 CST NST bulk density (Db) DTMP NDTMP 1.29 B a 1 1.31 B a 1.11 Aa 1.15 Aa M b m"3 1.32 Ba 1.37 B a *LSDp(.05)-0.06 LSDs(.01)-0.07 LSDp(.05)«0.05 LSDs(.01)«0.05 porosity (P) 3 DTMP NDTMP 0.53 Aa 0.52 Aa 0.58 B b 0.56 B a 105 _ 19 B a 15 B a LSDp(.05)-8.9 LSDs(.01)«ll LSDp(.05)“0 .02 LSDs(.01)-0.03 ... 2.1 Aa 1.8 Aa 1 0.37 B a 0.38 B a -1 20 B a 24 B a LSDp(.05)=6.7 LSDs(.01)-12 water content DTMP NDTMP 0.57 B a 0.57 Ba LSDp(.05)-0.02 LSDs(.01)=0.02 Ksat 2.2 Aa 0.8 Aa -3 0.50 Aa 0.49 Aa LSDp(.05)-0.02 LSDs(.01)-0.02 DTMP NDTMP 1.14 Aa 1.14 Aa 0.32 Aa 0.34 Aa _•! 0.38 Ba 0.37 Ba 0.33 Aa 0.31 Aa LSDp(.05)-0.02 LSDs(.01)-0.03 T 7 M e a n s I n each row followed by the same upper-case letter are not different at the indicated probability level using LSD as the criterion for significance. Means in the same column followed by the same lower-case letter are not different. 2/ LSD for comparison of two primary tillage means at the same or different levels of secondary tillage. 3/ LSD for comparison of two secondary tillage means at the same level of primary tillage. 70 Table 5. Influence of primary and density, porosity, saturated hydraulic volumetric water content of Charity depth during the first and second crop Primary _______________ Tillage secondary tillage on bulk conductivity (Ksat), and clay at the 0.13 to 0.20 m year. Crop Year 1 Crop Year 2 CST_________ NST_________ CST_________ NST bulk density (Db) DTMP NDTMP 1.27 Ba* 1.28 B a 1.11 Aa 8 1.42 B a 1.14 Aa 1.45 B a i?LSDp(.05)-0.05 LSDs(.01)«0.07 LSDp(.05)«0.09 LSDs(.01)-0.12 porosity (P) - , m DTMP NDTMP 0.53 Aa 0.53 Aa 0.58 B a 0.57 B a 105 m s 2.1 Aa 3.6 Aa 22 B a 20 B a LSDp(.05)«9.7 LSDs(.01)-12 DTMP NDTMP 0.43 B a 0.43 Ba LSDp(.05)-0.04 LSDs(.05)-0.05 ---------0.51 Aa 0.56 Ba 0.50 Aa 0.57 B a LSDp(.05)«0.04 LSDs(.01)-0.04 LSDp(.05)-0.02 LSDs(.01)-0.02 DTMP NDTMP 1.26 Aa 1.25 Aa -1 --------1.5 Aa 5.8 Aa 2.1 Aa 6.4 Aa LSDp(.05)“5.3 LSDs(.05)-4.7 0.38 Aa 0.38 Aa i in-3 —— ——— 0.31 Ba 0.30 Ba — 0.29 Aa 0.27 Aa LSDp(.05)=0.03 LSDs(.05)=0.02 T] Means In each row followed by the same upper-case letter are not different at the Indicated probability level using LSD as the criterion for significance. Means In the same column followed by the same lower-case letter are not different. 2/ LSD for comparison of two primary tillage means at the same or different levels of secondary tillage. 3 / LSD for comparison of two secondary tillage means at the same level of primary tillage. 71 17x10 ^ m s ^ Differences (61 cm h *) where wheel traffic was controlled. reported in Table 4 were significant at the 0.01 probability level and were approximately the same each year. All indicators of soil compaction at the 0.13 to 0.20 m depth were also significantly influenced by the secondary tillage variables (Table 5). B u l k density was 13 and 14 percent higher, F was 8 and 11 under CST than NST, repsectively. the first crop year, Ksat averaged 21x10 NST compared hydraulic to 2.8x10 ^ conductivities influenced by secondary m s* (10 cm measured in tillage based reported in lower Preplant wheel traffic reduced Ksat, but less dramatically at this depth than at the 0.03 During percent h *) the to Table 5. m depth. m s * (76 cm h ^) with with second on 0.10 CST crop the least . Saturated year were not significant differences (LSDs) However, the average Ksat of 6.1x10 ^ m s * under NST was greater than the average of 1.8x10 ^ m s ^ for CST at the 0.05 level of significance. Field water contents of soil samples obtained for physical measurements are included in Tables 4 and 5 to illustrate the influence that wheel induced compaction can have on profile soil water content under NST. Raghaven was These and compacted results that plots. are (1978) higher Differences in agreement where with machinery moisture Volumetric by those in occurred reflect true effects variables on soil physical conditions. by differential of in heavily Tables 4 and 5 were not in wheel tracked and non-wheeled plots. measured at sampling reported traffic altered the soil contents illustrated created by the sampling procedure used or extraction content. consistently and significantly higher under CST than McKyes environment such water the plant water Thus, water contents ,secondary tillage 72 Water content differences in Tables 4 and 5 can be attributed in part to varying rates of evaporation under CST and NST. extensive in the surface 0.15 the second crop year, were obtained immediately following a 13 day period in which rainfall totaled 47 mm. diminished be Except for undisturbed soil cores obtained from the 0.13 to 0.20 m depth in cores can m of soil but is reduced where soil is compacted by wheel traffic (Voorhees, 1985). soil Evaporation as a Differential evaporation under CST and result NST was and differences caused by wheel traffic can be attributed primarily to altered drainage and soil water retention under CST. Air porosities and soil water retention at the 0.03 to 0.10 m depth, during the first and second crop year, are shown respectively. tillage variables, porosities were averaged for DTMP and NDTMP. 5 and 6, water contents and air Conventional spring tillage water retention for the -1 to -33.3 kPa matric potential range in both years. (Figures Figures Since the relationships shown in Figures 5 and 6 were not influenced by the primary increased in 5a At each matric and 6a) but to potential, a CST decreased air porosity greater extent than the water content increase due to total porosity differences between CST and NST (Table 4). Bullock et al. (1985) showed that wheel induced compaction can decrease macroporosity study were by over comparable. half. One Changes caused by wheel traffic in this application of wheel traffic reduced 3 macroporosity, m -3 0.20 air porosity at the -6 kPa matric potential, from 0.18 m under NST to a level of 0.08 m m 3 - 3 m 3 m -3 under NST but only 0.07 m crop year (Figure 6a). Macroporosity (Figure 5a). 3 - 3 m is Macroporosity was under CST during the second an indicator of the soil aeration status following a heavy rain because it approximates the volume of air-filled pore space near field capacity. Controlling preplant wheel 73 0 .3 0 ro 'E PO £ 0.20- 0.10-J a a. 0.00 0 .6 0 CST NST ro I 0 .5 0 - E ro £ §, 0 .4 0 - 0 .3 0 — 0.1 1.0 10.0 100.0 Matric Suction (kPa) Figure 6. Influence of secondary tillage on air porosity (a) and soil water retention (b) of Charity clay at the 0.03 to 0.10 m depth during the second crop year. 75 traffic improved soil aeration as critically low air porosities are less likely to occur under NST than under CST. Pore size distributions 5 and 6 corresponding to relationships shown inFigures are illustrated in Figure 7. Wheel traffic associated with CST increased water retention and decreased air porosity because the volume of small pores was increased at the expense of the volume of large pores. The volume of pores in the intermediate size classes was relatively unaffected by one or two years of preplant wheel traffic. The and water retention at the 0.13 to 0.20 m depth, during the first and second year, are influence of demonstrated secondary in Figures tillage 8 an on 9, air porosities respectively. Though significant, differences shown were smaller than those reported shallower measurement depth. Air porosities The for the for the -1 to -33.3 kPa matric potential range were reduced by a factor of year. highly 2 during each crop corresponding pore size distributions in Figure 10 show that CST created small pores at the expense of pores with radii greater than 150 fim . CONCLUSIONS Normal fall and spring tillage operations on charity clay create unfavorable physical conditions for crop growth as internal poor and soil aeration may be impeded at certain drainage critical times. Physical conditions of Charity clay were improved below the normal of plowing by may depth subsoiling in the fall when the soil was relatively dry. Results of this Investigation indicate subsoiling is persist through subsoiling traffic is controlled. only that one Results changes crop also brought year indicate about by even when post­ that shallow chiseling after subsoiling may be more beneficial than moldboard plowing. 76 0.41 £ 0*37 J lsd (. o i ) £ £ 0 .0 5 0.00 YR1 YR2 >150 YR1 YR2 1 5 0 -2 5 YR1 YR2 2 5 - 4 .4 YR1 YR2 < 4 .4 Pore Radius Intervals (ju.m) Figure 7. Pore size distribution of Charity clay at the 0.03 to 0.10 n depth as affected by secondary tillage during the first (YR1) and second (YR2) crop year. 77 0 .3 0 'g E 0.200 .1 0 - o CL 0.00 0.60 o - o CST NST a- a 0 .5 0 - E >§, 0 .4 0 - L S D (.0 1 )I 0 .3 0 0.1 1.0 10.0 100.0 Matric S uction (kPa) Figure 8. Influence of secondary tillage on air porosity (a) and soil water retention (b) of Charity clay at the 0.13 to 0.20 m depth during the first crop year. 78 m 0.20- Pa (m^ 0 .3 0 0 .1 0 - 0.00 0 (m** m 3) 0 .6 0 o - o CST a—a NST 0 .5 0 - 0 .3 0 1.0 10.0 100.0 Matric Suction (kPa) Figure 9. Influence of secondary tillage on air porosity (a) and soil water retention (b) of Charity clay at the 0.13 to 0.20 m depth during the second crop year. 79 0 .4 5 0 .4 1 ro cn to I 0 .3 7 - ro Q) 0 .1 5 -t E _3 O > 0 .1 0 - LSD(.01) 150 YR1 YR2 1 5 0 -2 5 YR1 YR2 2 5 - 4 .4 < 4 .4 Pore Radius intervals Qzm) Figure 10. Pore size distribution of Charity clay at the 0.13 to 0.20 m depth as affected by secondary tillage during the first (YRl) and second (YR2) crop year. Wheel traffic associated with conventional spring tillage recompacted soil loosened by deep tillage and increased the density of subsoil normal fall tillage was applied. Effects of wheel traffic on physical properties below the normal depth of plowing were evident each were not cumulative when applied three years in succession. surface of Charity clay induced compaction. distribution horizon. were proved Saturated where year but The unstable to be extremely susceptible to wheel- hydraulic conductivity and pore size the most sensitive indicators of compaction in the Ap Subsoiling followed by controlled preplant wheel traffic produced the most favorable environment for root growth based on improved internal drainage and soil aeration. LIST OF REFERENCES Blake, G.R. 1965. Bulk density. In C.A. Black et al. (ed.) soil analysis. Agronomy 9:374-390. Methods of Bolton, E.F., V.A. Dirks, and M.M. McDonnell. 1981. Effect of fall and spring plowing at 3 depths on soil bulk density porosity and moisture in Brookston clay. Can. Agric. Eng. 23:71-76. Bullock, P., A.C.D. Newman, and A.J. Thomasson. 1985. Porosity aspects of the regeneration of soil structure after compaction. Soil Tillage Res. 5:325-342. Burnett, E., and V.L. Hauser. 1968. Deep tillage and soil-plant-water relations, p. 47-52. In Tillage for greater crop production. Am. Soc. Agric. Eng., St. Joseph, MI. Buxton, D .R., and J.C. Zalewski. 1983. Tillage and cultural management of irrigated potatoes. Agron. J. 75:219-225. Cannell, R.Q., and M . B . Jackson. 1981. Alleviating aeration stresses, p. 141-192. In G.F. Arkin and H.M. Taylor (ed.) Modifying the root environment to reduce crop stress. Am. Soc. Agric. Eng., St. Joseph, MI. Carter, L.M. 1985. Wheel traffic is costly. Trans. ASAE 28:430-434. Cassel, D.K., and L.A. Nelson. 1985. Spatial and temporal variability of soil physical properties of norfolk loamy sand as affected by tillage. Soil Tillage Res. 5:5-17. Douglas, E., McKyes, F. Taylor, S. Negi, and G.S.V. Raghavan. 1980. Unsaturated hydraulic conductivity of a tilled clay soil. Can. Agric. Eng. 22:153-162. Erickson, A.E. 1982. Soil Aeration, p. 91-104. In P.W. Unger and D.M. Van Doren (ed.) Predicting tillage effects on soil physical properties and processes. Spec. Pub. 44. Am. Soc. Agron., Madison, WI. Eriksson, J., I. Hakansson, and B. Danfors. 1974. The effect of soil compaction on soil structure and crop yields. Swedish Inst. Agr. Eng. Bull. 354. Uppsala, Sweden. Klute, A. 1965. Laboratory measurement of hydraulic conductivity of saturated soil. In C.A. Black et al. (ed.) Methods of soil analysis. Agronomy 9:210-221. Larson, W.E., and R.R. Allmaras. 1971. Management factors and natural forces as related to compaction p. 367-427. In K.K. Barnes et al. Compaction of agricultural soils. Am. Soc. Agr. Eng., St. Joseph, MI. 81 82 Learner, R.W., and B. noncapillary porosity 33:1001-1008. Lucas, State Shaw. 1941. A simple apparatus for measuring on an extensive scale. J. Am. Soc. Agron. R.E.,and M.L. Vitosh. 1978. Soil organic matter dynamics. Univ. Agric. Exp. Stn. Res. Rep. 358, E. Lansing, MI. Mich. Raghaven, G.S.V., and E. McKyes. 1978. Effect of vehicular traffic on soil moisture content in corn (maize) plots. J. Agric. Eng. Res. 23:429-439. Richards, L.A. 1965. Physical condition of water in soil. In C.A. Black et al. (ed.) Methods of soil analysis. Agronomy 9:128-152. Robertson, L.S., and A.E. Erickson. 1980. Compact soil-visual symptoms. Mich. State Univ. Ext. Bull. E-1460. Ross, C.W. 1986. The effects of subsoiling and Irrigation on potato production. Soil Tillage Res. 7:315-325. Steel, R.G.D., and J.H. Torrie. 1960. Statistics. McGraw-Hill, New York. Principles and Procedures of Trouse, A.C., Jr. 1983* Observations on under-the-row subsoiling conventional tillage. Soil Tillage Res. 3:67-81. after Unger, P . W . , and B.A. Stewart. 1983. Soil Management for efficient water use: an overview, p. 419-460. In Taylor et al. (ed.) Limitations to efficient water use in crop production. Am. Soc. Agron., Crop Scl. Soc. Am., and Soil Sci. Soc. Am., Madison, WI. Vepraskas, M.J., and G.S. Miner. 1986. Effects mechanical impedance on tobacco root growth. Soil 50:423-427. of subsoiling and Sci. Soc. Am. J. Vomocil, J .A., and W.J. Flocker. 1961. Effect of soil compaction on storage and movement of soil air and water. Trans. ASAE 4(2):242-246. Vomocil, J.A. 1965. Porosity. In C.A. Black et al. (ed.) analysis. Agronomy 9:299-314. Methods of soil Voorhees, W . B ., C.G. Senst, and W.W. Nelson. 1978. Compaction and soil structure modification by wheel traffic in the northern corn belt. Soil Sci. Soc. Am. J. 42:344-349. Voorhees, W.B. 1983. Relative effectiveness of tillage and natural forces in alleviating wheel-induced soil compaction. Soil Sci. Soc. Am. J. 47:129-133. Voorhees, W . B ., S.D. Evans, and D.D. Warnes. 1985. Effect of preplant wheel traffic on soil compaction, water use and growth of spring wheat. Soil Sci. Soc. Am. J. 49:215-220. 83 Wesseling, J., and W.R. van Wyk. 1957. Soil physical conditions In relation to drain depth. In J.N. Luthin (ed.) Drainage of agricultural soils. Agronomy 7:461-504. Williford, J.R. 1980. A controlled-traffic system for cotton production. Trans. ASAE 23:65-70. Woodruff, C.M., and D.D. Smith. 1946. Subsoil shattering and subsoil liming for crop production on claypan soils. Soil Sci. Soc. Am. Proc. 11:539-542. Chapter 3 Influence of Deep Tillage and Controlled Traffic on Profile Water Content of Two Lake-Plain Soils INTRODUCTION Normal tillage operations associated with row crop production In the Saginaw Valley create unfavorable soil conditions for root growth. reported In the previous chapter demonstrate that fall moldboard plowing and normal amounts of preplant wheel highest bulk densities During the first year of produced at Data traffic (NDTMP-CST) produced the (Db) in three depth increments of Charity clay. plot establishment, the NDTMP-CST treatment Db of 1.31 (Table 4), 1.28 (Table 5), and 1.38 Mg m ^ (Table 1) depths of respectively. 0.03 to 0.10, Deep tillage 0.13 to 0.20, and 0.27 to 0.34 m, and controlled traffic (DTMP-NST) produced _3 the most favorable soil conditions as Db was 1.14, 1.11, and 1.26 Mg m for the same depths. Daddow and Warrington (1983) and Jones (1983) developed relationships between soil texture and Db that limit root growth. limiting bulk densities clay operations. (e.g., these with values reported in Chapter 2 suggest that root growth may be mechanically percent Comparison of Charity impeded clay), on a soil especially consisting under However, the growth limiting Db is higher of 70 normal tillage on a soil with high shrink-swell potential because roots can proliferate along planes of weakness upon that develop upon drying. drying, mechanical Since Charity clay cracks moderately impedance may limitation to root growth on this soil. 84 not be the most important 85 Soil aeration is probably the single most important physical limitation of Charity clay. The effects of tillage and wheel traffic on pore size distribution (PSD), demonstrated in a sensitive Chapter 2. indicator of soil compaction, Deep tillage and controlled traffic altered PSD such that internal drainage was improved (i.e., Ksat was water were increased), retention was decreased, and air porosity was increased over the - 1.0 to -100 KPa matric potential range. critically low air Soil aeration was improved as porosities are less likely to occur and may persist for a shorter period of time under DTMP-NST than NDTMP-CST. Susceptibility of a soil to the development determined by its physical conditions but the of poor aeration is occurrence stress is dictated by the prevailing weather conditions. impedance is depend on cumulative contents and influencing root rainfall strength growth, which (Vepraskas root in et When mechanical influences 1986). because the soil water Seasonal rainfall influences the occurrence and duration of aeration stress manner aeration growth has been shown to turn al., of in a similar abundance of air-filled pores depends on soil water content. The objectives of this portion of the study prevailing weather conditions, evaluate further the and wheel were: (1) given the effects of tillage traffic on the environment of Charity clay for root growth by monitoring soil water content during the 1983 to 1985 growing seasons; and (2) evaluate the effects of the same treatments on water content of a second lake plane soil during 1983. MATERIALS AND METHODS A second field experiment, in addition to the experiment on Charity clay (fine, illitic (calcareous), mesic Aerie Haplaquept), was during the mesic Mollic Experiments fall of 1982 on Parkhill loam (fine-loamy, mixed, nonacidic, Haplaquept), were located conducted at five two miles sites in east of Ithaca, MI. 1983 to compare the effectiveness of the ameliorative procedures on a problem clay) with loam). the soil (Charity a soil characterized by fewer physical limitations (Parkhill The experiment at the through initiated fall of 1983. second The site (site 2) was carried out experimental design, treatments, and methods used to apply the treatments were identical to those described in Chapter 2 for the experiment on Charity clay near Swan 1). Thus, treatments existing tillage (site (DTMP-CST); deep tillage-moldboard plow and no spring tillage (DTMP-NST); (3) no deep tillage-moldboard plow and conventional spring tillage and MI during 1983 on Parkhill loam were: (1) deep tillage-moldboard plow and conventional spring (2) Creek, (4) the same as (NDTMP-CST); treatment 3 except no spring tillage was applied (NDTMP-NST). Daily rainfall was Research Farm using precipitation amounts monitored standard at U.S. the Saginaw Weather Bureau Valley Bean and Beet equipment. Daily for the second study site, on Parkhill loam, were obtained from a recording station at Alma, MI. A neutron probe (Campbell Pacific Nuclear Corporation; Pacheco, CA; Model 503 Hydroprobe), calibrated in situ, was used to monitor soil water content during 1983 on Parkhill loam and during the 1983 to 1985 seasons on Charity clay. 0.30, 0.46, growing Measurements were obtained from depths of 0.15, 0.61, and 0.76 m in plots planted to corn on Parkhill loam. 86 87 One access tube was installed In each plot, in one of the two center-rows of the four row plots, and equidistant from adjacent plants which were spaced at 0.30 m within the row. Neutron probe measurements were obtained from only the 0.15, 0.30, and 0.46 m depths on Charity clay tfiere the depth of rooting is limited by naturally dense subsoil. Soil water content was measured in plots where corn and sugarbeets appeared except for 1985 when it was in plots planted to corn. restricted to plots monitored only Access tubes were installed only in plots representing the first crop year also a after subsoiling. Access tubes were where the DTMP-CST, DTMP-NST, NDTMP-CST, and NDTMP-NST treatments appeared even though the number of treatments was increased from four to eight after 1983. Neutron probe calibration was conducted during the 1982 and 1984 field seasons on Charity clay. The relationship between soil water content and neutron probe readings at the 0.15 m depth is shown in Figure datum represents the mean of to maximize the relationship was determined. Each eight volumetric water contents plotted against the mean of four ratios. included 11. Values obtained in 1982 and range of water contents 1984 over were which Undisturbed soil cores 76-mm diam and 76-mm in length were used to determine the volumetric water consisted counts divided by a standard count. used content of one-minute neutron equation shown in Figure 11 Charity clay and Parkhill the was loam to at calculate the contents. water 0.15 m depth. Ratios The of Neutron probe readings were probably influenced by nearness to the soil surface only at this depth (Grant, 1975). The relationship between volumetric water content and neutron probe ratio at the 0.30 m depth is shown in Figure 12. Only values obtained 88 0.50 OBSERVED-1982 OBSERVED-1984 REGRESSION 9 5 3 C.l. E 0 .3 0 - E ^ 0.20- e m .0 6 8 3 + .2372*RAT!0 R2 = 0 .9 3 0 .1 0 -0 .5 0 0 .7 0 0 .9 0 1.30 1.50 1.70 Ratio Figure 11. Linear regression of soli water content on neutrori-probe ratio at the 0.15 m depth. 0 .5 0 e = .0 2 3 5 + .2 1 46*RATI0 0 .4 0 - E R2 = 0 .9 6 0 .3 0 - E ^ 0.20- — — o 0 .1 0 1.30 1.50 1.70 9 5 3 C.J. r e g r essio n : OBSERVED * 1.90 Ratio Figure 12. Linear regression of soil water content on neutron-probe ratio at the 0.30 m depth. 89 during 1984 were used to determine the equation given in Figure 12. This calibration equation was used to calculate water content of both soils at all depths greater than 0.15 m. Treatment each depth, Treatments effects on each were (Steel measurement compared appropriate for a blocks on soil water content were evaluated separately for split-plot least design and Torrie, 1960). reported where significance level. using date, was using analysis significant arranged in of variance. differences randomized (LSD) complete The least significant differences are established at the 0.05 probability RESULTS AND DISCUSSION Site 1 Rainfall patterns during 1983 to 1985 at the Saginaw Valley Research Farm are illustrated in Figures 13 and 14. the April in rainfall during to September period in 1983 and 1985 were approximately equal averaging 600 mm (Figure period Cumulative 1984 was 13a). 514 mm. Cumulative rainfall Precipitation during the same for the six month period exceeded the long term average (1940-1985) of 456 mm each year. The distribution of from 1983 to 1985. demonstrate that growing season precipitation differed each year Monthly precipitation departures shown in Figure rainfall was approximately average during each month in 1984. by an equal By contrast, 1983 13b to the long term was characterized excessively wet period early in the growing season. Rainfall was 125 mm above normal for April and May combined, accounting for 84 percent of the 149-mm departure for the April to September period. was much different during the 1985 growing season as The situation precipitation was below normal from April to July but exceeded the long term average by 174 mm during the August to September period. in Figures 13 and 14 suggest that Rainfall patterns illustrated conditions for crop growth varied greatly during the three year study. Hater content of Charity clay at the 0.15, 0.30, and 0.45 m depths during 1983 to 1985 are shown in Figures 15 to 19. water content reflect daily rainfall occurrences each Figure Temporal variation of that are included and seasonal rainfall reported in Figures 13 and 14. contents under both corn and sugarbeets were excessive during part of the measurement period in 1983 first measurement date were lower 90 Hater the early (Figures 15 and 16). Since precipitation was above normal during April and May, the in water than expected. contents on These initial Precipitation (m m ) 91 800- a - 1983 1984 1985 600400- r 200- --- i— i— |— i— i— |— I— i— ]— r 1 16 MAY APR 31 15 3 0 JUN T t —r 15 3 0 14 29 JUL AUG T 13 28 SEP 120- E £ v i_ u 4J o Q. Q> O 8040- b ■ ro oo 05 jo 00 tJ- 05 00 — P ® " -4 0 - APR MAY JUN JUL AUG SEP Figure 13. Cumulative growing season precipitation (a) and monthly precipitation departures (b) during 1983 to 1985 at the Saginaw Valley Bean and Beet Research Farm. 92 1983 40- Precipitation (m m ) 20 - 40- 20 - 60 1985 * Initiation of water content m easurem ents 40- 20 - APR MAY JUN JUL AUG SEP Figure 14. Dally growing season precipitation during 1983 (a), 1984 (b), and 1985 (c) at the Saginaw Valley Bean and Beet Research Farm. 93 0.50 a - o CST a— a NST 0.40 0.30 I LSD(.05) 0.15 m 0.20 0.50 3 - o CST NST X— \ a— a £ 0.40 H 0.30 H 0.30 m 0.20 0.50 3 - o NDTMP—CST a—a DTMP-NST 0.40 0.30 0.45 m (m m ) 0.20 60.0 Precipitation 40.0 H 20.0H 0.0 JUN JUL AUG SEP Figure 15. Water content of Charity clay at three depths in plots planted to corn (a-c) and daily precipitation (d) during 1983. 94 0.50 ,LSD(.05) o - o CST ir-t NST 0.40 0.30 0.15 m 0.20 0.50 N tn E E 0.40 0.30 0.20 0.50 o - e n d tm p - c s t : a—a DTMP-NST : 0.40 0.30 0.45 m 0.20 6O.O-1 ( g E Precipitation 4 0 .0 20 .0 - 0.0 JUN JUL AUG SEP Figure 16. Water content of Charity clay at three depths in plots planted to sugarbeets (a-c) and daily precipitation (d) during 1983. 95 measurements suggest that subtantial loss of water from the surface m of soil must 0.45 have occurred during the 5 June to 24 June period when rainfall was only 4 mm (Figure 14a). constant depth during the last 45days of measurement at each Soil water content was relatively In 1983 (3 August to 17 September). A much different situation existed In 1984 as water content of Charity clay at the 0.15 m depth was consistently low during the August period (Figures 17 and 18). 24 to the measurements were lower than Initiated only four days after the occurrence of a 64 mm rainfall (Figure 14b). The water content at each depth Increased gradually under corn and sugarbeets during the August 8 Water contents first measurement date In 1984 were expected because neutron probe to Water contents decreased gradually at the 0.30 and 0.45 m depths during the same 45 day period. corresponding June 8 to 22 September period (Figures 17 and 18) as the dally amount of plant water extraction decreased. The 19. water content of Charity clay during 1985 Is Illustrated In Figure Above produced normal August excessive water and September contents on precipitation (Figure the last two measurement dates. Soil water excesses were also evident during the first few days (Figure 19) as was the case diverse seasonal rainfall patterns similarities between water In 1983 (Figures 15 and 16). In contents 1983 and 1985, far greater measurements were negligible than average Initiated rainfall. that during year of July Given the these apparent In 1983 and 1985 were produced In part by the timing of water content measurements. was 13b) April after For example, and a 20 May day in rainfall 1983 period but with Rainfall was 48 mm for the 20 day period preceding the Initial water content measurements in 1985 (Figure 14c) rainfall for the April to July period was below normal. even though 96 0.50 0.40 I LSD(.05) 0.30 a—a NST a - o CST 0.15 m 0.20 0 (m^ m - ^) 0.50 0.40 x 0.30 a—a NST CST 0.30 m 3-o 0.20 0.50 0.40 0.30 a—a DTMP-NST ; 3 - o NDTMP—CST • 0.45 m (mm) 0.20 Precipitation 4 0 .0 - 20.0 0.0 24 JUN JUL 24 AUG 23 SEP 22 Figure 17. Water content of Charity clay at three depths in plots planted to corn (a-c) and daily precipitation (d) during 1984. 97 0.50 I LSD(.05) 0 .4 0 0 .3 0 - a- a NST o—o CST 0.15 m 0.20 0.50 E 0 .4 0 0 .3 0 0.30 m 0.20 0.50 0 .4 0 0 .3 0 - 0.20 E a—a DTMP-NST • 0 - 0 NDTMP—CST * 0.45 m 60.0 E '_/ c o a Q. 4 0 .0 - 20.0 - a fi a. 0.0 24 JUN JUL 24 AUG 23 SEP 22 Figure 18. Water content of Charity clay at three depths in plots planted to sugarbeets (a-c) and daily precipitation (d) during 1984. 98 0.50 0 .40 0 .3 0 a— a NST 0.15 m 0-0 CST 0.30 m A—a NST 0 - 0 CST 0.45 m a—a DTMP-NST 0 - 0 NDTMP—CST - 0.20 0.50 E E 0 .4 0 H 0.30-4 0.20 0 .50 0.40 0 .30 0.20 E E c o 60.0 4 0 .0 - •*-> a -M CL 20.0H a fi a. 0.0 24 JUN JUL 24 AUG 23 SEP 22 Figure 19. Water content of Charity clay at three depths In plots planted to corn (a-c) and dally precipitation (d) during 1985. 99 Seasonal variation of soli water content could have been assessed more effectively by obtaining measurements more content was monitored primarily frequently. However, water to evaluate treatment effects on this soil parameter at discrete points in time. Cassel and Nelson (1981) suggest that measurement of volumetric water content may be inappropriate for comparison of tillage effects on soil conditions due to variation of water content within any one experimental treatment. Our results fail to substantiate the authors claim as water contents for the 0.15 and 0.30 depths were measurably m different under the secondary tillage variables that were applied in this study. Hater content data for the 0.15 and 0.30 m depths (Figures 15a,b to 19a,b) were averaged for DTMP and NDTMP because water content depths was unaffected by the primary tillage variables. at the 0.15 of primary prior and corn Charity clay at measurement these T h u s , each datum and 0.30 m depths represent the mean of eight observations (i.e., 2 levels to at tillage x sugarbeet the 0.15 m period in 4 reps). planting (Figures applied increased the water content of depth, during 1983 Hheel traffic the 15 occasionally detected on later measurement earliest portion and 16). dates in of the Differences were plots planted to corn. Water content of the 0.15 and 0.30 m depths were consistently and significantly greater under CST than NST in 1984 Differences were planted to corn CST and NST as large at 3 m causing an even larger air because the (Chapter 2, Tables 4 and 5). smaller as 0.07 m -3 (Figures at the 0.15 porosity 17 and 18). m depth in plots difference between total soil porosity was diminished under CST Though significant, differences both depths in plots where sugarbeets appeared. appeared Significant 100 differences between water content under CST and NST were occasionally detected at the 0.15 m depth In 1985 (Figure 19). The effects of preplant wheel traffic on soil moisture levels, suggested by periodic water content measurement, produced results similar to those reported In Chapter 2. The water content of undisturbed soil cores obtained for physical measurements was higher In plots compacted by preplant wheel traffic than In nontrafficked plots (Tables 4 and 5). The undisturbed soil cores from the plow layer were obtained during 1985 when CST Increased water content of the 0.15 m depth on only three measurement dates (Figure 19). were detected more Differences frequently reported In Figures 17 and 18. may have between CST and NST seemed larger and during 1984 based on water contents This suggests that preplant wheel traffic altered the physical conditions of the plow layer to a greater extent In 1984 than In 1985. Varying soil water content under CST and NST can primarily to the direct Influence of the secondary tillage soil conditions. been shown logical Since tillage can affect root density, differences caused by under CST and NST. seemed most prevelant after periods of frequent or Such conditions tend differential agreement with results primarily It to assume that differences in Figures 15 to 19 may be due In excessive rainfall. any, on to be proportional to root density (Garay and Wilhelm, 1983; part to differential extraction of water by plants However, variables Plant water extraction from a particular soil layer has Lascano and van Bavel, 1984). Is be attributed of water Chapter to diminish extraction 2, differences, if under CST and NST. In differences can be attributed to physical changes (e.g., water retention, internal drainage) associated with wheel induced compaction. 101 Water content of Charity clay at the 0.45 m depth was unaffected by the primary and secondary tillage variables on virtually every measurement date based on statistical comparison of this depth is treatments. Water content at reported for the DTMP-NST and NDTMP-CST treatments which produced the most dissimilar soil conditions at the 0.27 (Chapter 2). 19c verify that water contents at the 0.45 m depth Figures 15c to to 0.34 m depth were the same under these diverse treatments during the three year study. Site 2 Figure 20 illustrates cumulative rainfall and the distribution of growing season precipitation in 1983 near the second study site. April and May rainfall was above normal (Figure 20b) as was rainfall during the same period at site 1 (Figure 13b). However, the rainfall departure for the June to August period was -92 mm at the second site compared mm at site 1. to -19 Precipitation for the April to September period at site 1 (on Charity clay) exceeded the precipitation at site 2 (on Parkhill loam) by 100 mm. Thus, growing season precipitation differed substantially at the two sites during 1983. The water content of Parkhill loam at the 0.15 and 0.30 m depths are illustrated in Figure 21. Soil moisture levels appeared to be unaffected by two relatively large rainfalls near period (Figure after mid July. 20c) as the induced compaction of the measurement measurement intervals masked soil parameter. increased the water content of Parkhill loam at the 0.15 m depth (Figure 21a). loam middle water content at these depths were stable Again, the length of the temporal fluctuation of this Wheel the The physical properties of Parkhill were not characterized to the same extent as those for Charity clay (Chapter 2). However, it seems reasonable to assume that physical Precipitation (m m ) 102 800 600 400- 200- APR JUN MAY JUL AUG SEP Departure (mm) 120- b - 8040- 0 -4 0 JZL APR MAY JUN JUL AUG SEP Figure 20. Cumulative growing season precipitation (a) and monthly precipitation departures (b) during 1983 at Alma, MI. 103 0.45 0.35 I LSD(.05) Q (m 3 m 3 ) 0 .2 5 0.15 m 0.15 0.45 o - o NDTMP A1 a DTMP 0.35 0.25 0.30 m (mm) 0.15 60.0 Precipitation 4 0 .0 20.0 - 0.0 JUN JUL AUG SEP Figure 21. Water content of Parkhill loam at two depths in plots planted to corn (a-b) and daily precipitation (c) during 1983. 104 changes caused by preplant wheel traffic were similar on the two soils, at least for the 0.15 m depth. The secondary tillage effect on water content of the 0.30 m depth. variables had no Values averaged for CST and NST levels of secondary tillage in Figure 21b show that water content was slightly higher in nonsubsoiled plots (NDTMP) than in subsoiled plots (DTMP). The primary and secondary tillage variables had no effect on water content of Parkhill loam at the 0.46, 0.61, and contents for only the was wheeling. probably m depths. Hater diverse treatments, NDTMP-CST and DTMP-NST, are reported for these depths in Figure 22. depths 0.76 Soil at the 0.61 and 0.76 m unaffected by tillage or by pressure from preplant If treatment differences were evident at these depths, they r could have been attributed to altered depth of root penetration or root densities under the various treatments. Figures 22b and 22c demonstrate that plant water extraction was extensive at each depth but similar under the two treatments which should have produced diverse physical conditions at shallower depths. Data in Figure 22 suggest that corn rooting was not altered substantially by the treatments applied on Parkhill loam based on periodic water content measurements in 1983. CONCLUSIONS The distribution of growing season precipitation varied greatly during the three year study at the Saginaw patterns and May during April Valley the Farm. Rainfall were similar at the two study sites in 1983, the only year in which experiments were During Research conducted at two sites. critical June to August period of 1983, precipitation was 92 mm below normal at site 2 (on Parkhill loam) compared to only 19 mm below normal at site 1 (on Charity clay). 105 0.45 0.35 0 .2 5 0.46 m 0.15 0.45 ndtmp- cst; DTMP-NST ■ E E 0 .3 5 0.25 0.61 m 0.15 0.45 &-o a-a n d tm p -c st; DTMP-NST - 0 .3 5 0 .2 5 0.76 m 0.15 9 /2 9 /1 7 Date Figure 22. Water content of Parkhill loam at the 0.46 (a), 0.61 (b), and 0.76 m (c) depths during 1983 in plots planted to corn. Water content of Charity clay and Parkhill loam, determined by neutron scattering, were related to the prevailing rainfall patterns for the most part. The seasonal variation of assessed more frequently. effectively each soil water content yearby obtaining could measurements such under NST. decreased that water more Preplant wheel traffic air porosity tillage of the plow content was consistently greater under CST than associated with accordingly (NST) Improved soil aeration when primary been However, water content measured at weekly intervals verified that preplant wheel traffic altered thephyslcal conditions layer have soil the CST treatment indicating that controlled traffic water excesses occurred. The variables had no effect on the water content of Charity clay at the 0.15 to 0.30 m depths or water content of the 0.46 to 0.76 m depths. Parkhill loam at LIST OF REFERENCES Cassel, D.K., and L*A. Nelson. 1981. Selection of variables to be used in statistical analysis of field-measured soil water content. Soil Sci. Soc. Am. J. 45:1007-1-12. Daddow, R.L., and G.E. Warrington. 1983. Growth limiting soil bulk densities as influenced by soil texture. Watershed Systems Development Group (WSDG) USDA, Govt. Service Report WSDG-TN-00005. 17 pp. Garay, A.F., and W.W. Wilhelm. 1983. Root system characteristics of two soybean Isolines undergoing water stress conditions. Agron. J. 75:973977. Grant, D.R. 1975. Measurement of soil moisture near the surface using a neutron moisture meter. J. Soil Sci. 26:124-129. Jones, C.A. 1983. Effect of soil texture on critical bulk densities for root growth. Soil Sci. Soc. Am. J. 47:1208-1211. Lascano, R.J., and C.H.M. van Bavel. 1984. Root water uptake and soil water distribution: test of an availability concept. Soil Sci. Soc. Am. J. 48:233-237. Steel, R.G.D., and J.H. Torrie. 1960. Statistics. McGraw-Hill, New York. Principles and Procedures of Vepraskas, M.J., G.S. Miner, and G.F. Peedin. 1986. Relationships of dense tillage pans, soil properties, and subsoiling to tobacco root growth. Soil Sci. Soc. Am. J. 50:1541-1546. 107 Chapter 4 Seedling Emergence, Rooting, and Crop Yields as Affected by Deep Tillage and Controlled Traffic INTRODUCTION Soil loosening produced traffic affect plant conditions• by subsoiling and compaction caused by wheel growth Rosenberg through (1964) their suggested effects that on the conditions must be considered before the physically soil physical prevailing weather measured properties can he correlated with plant growth. Numerous Investigators have since demonstrated that plant response to actions that alter the soil physical environment vary climate. Where water stress is the primary production, root impeding layers can be stress depth by increasing explored volume. the rooting Subsoiling has been disrupted shown or dramatically limitation to with to alleviate crop water proliferation within the to increase crop yields during dry years in this way (Campbell et al., 1974; Parker et al., 1975; Kamprath et al., 1979). When water stress is not limiting, as in wet years or when adequately irrigated, crop yields may not subsoiling be improved by (Weatherly and Dane, 1979; Buxton and Zalewski, 1983; Box and Langdale, 1984; Ross, 1986; Miller, 1987). The deleterious effects of wheel induced compaction on corn (Phillips and Kirkham, 1962; Raghaven et al., 1978; Negi et al., 1980), sugarbeet (Blake et al., 1960; Hebblethwaite et al., 1980), soybean (Nelson et al., 1975), and oat yields (Blackwell et al., 1985) have been demonstrated. 108 109 However, plant response to (Rosenberg, 1964) compaction varies with weather conditions just as subsoiling to alleviate water stress produces results that depend on weather. During wet years, Gaultney et al. (1982) and Lindeman et al. (1982) showed that compaction tends to reduce of corn and soybeans, actually favored by (Raghaven et respectively. moderate wheel By contrast, induced yields crop yields were compaction in dry years al., 1979; Anazodo et al., 1983; Voorhees et al., 1985) as compaction presumably increased soil water availability. Poor physical conditions of Charity clay limit yields at the Saginaw Valley Bean-Beet Research Farm during unstable surface and some years. This soil has poor internal drainage due to its naturally dense subsoil that impedes water movement. Charity clay, and other imperfectly drained soils in the area, may lack adequate aeration for root growth certain times during an the season as a result. at Plants with root growth impeded by these physical limitations may experience water stress when rainfall is deficient. Tillage of a soil with poor aeration temporarily the aeration problem (Burnett 1982). Field studies were conducted characteristics can correct and to Hauser, evaluate 1968; the Erickson, potential for reducing the physical limitations of Charity clay and a second lake plain soil. Both soils were subsoiled and subsequent traffic was controlled to avoid recompaction of the loosened soil. various 2. Physical changes by primary and secondary tillage variables were reported in Chapter Environmental conditions were characterized each daily produced rainfall amounts weekly basis (Chapter 3). and year by measuring monitoring profile soil water content on a 110 The objectives of this portion of the study were: (1) to evaluate the influence of physical changes brought about by tillage and (2) on crop growth; determine whether or not plant responses each year were related to seasonal rainfall and therefore environmental stresses. MATERIALS AND METHODS Field experiments were conducted in 1983 on Parkhill loam (fine-loamy, mixed, nonacldic, mesic Mollic Haplaquept) Charity clay and from 1983 to 1985 (fine, illltic (calcareous), mesic Aerie Haplaquept). The experimental design at each location was a split-split-plot, arranged randomized complete blocks, and replicated four times. consisted of the following primary tillage variables in tillage-moldboard (NDTMP). were: were (DTMP); Secondary tillage (1) (NST). plow conventional and in in Main plots 1983: (1) deep (2) no deep tillage-moldboard plow variables, applied as subplot treatments spring tillage (CST); and (2) no spring tillage Equipment and procedures used to described on Chapter 2. established at each location so apply the tillage treatments A sufficient number of main plots that tillage effects on were growth and production of several crops could be tested. Subplots were split to Include two cultivars of each crop. were planted using a four-row (0.51 m spacing) except those planted to small grains. minimum All plots tillage planter Plot dimensions were 2.1 m wide x 20.1 m in length for the experiment on Charity clay and 2.1 m x 15.2 m at the second location on Parkhill loam. 1983 Crops and cultivars used experiments are shown in Appendix Table 1. for Planting dates, seeding rates, and fertilizer application rates are also given in Appendix 1. the Table Herbicide programs used for each crop are shown in Appendix Table 2. The same experimental design was used during 1984 and 1985 on Charity clay but the number of main plot treatments applied during 1983 and 1984 was increased moldboard plowing one half of shallow chiseling from two to four. This was the of accomplished by the subsoiled and nonsubsoiled the other half. fall areas and Primary tillage variables applied to the main plots were: (1) deep tillage-moldboard 111 plow (DTMP); (2) deep 112 tillage chisel plow (DTCH); and (3) no deep tillage-moldboard plow (NDTMP); and (4) no deep tillage-chisel plow (NDTCH). were reduced from 20.1 to 10.0 m In length Individual where plots four main plot treatments were applied. As Indicated In Chapter 2, plots established for 1983 and 1984 on Charity clay were maintained through 1985. Crops were rotated to sequences described In Chapter the crop were applied to main plots only effects deep on of tillage once crop 2. so that growth according Primary tillage variables the possible could be residual determined. established during the first, second, or third year after application the primary tillage variables are referred to as 'first year', year', or 'third year' plots, respectively. year plots Crops grown of 'second the first- represent the 'first crop year' and so forth for crops grown on second and third-year plots. The cumulative effects of preplant wheel traffic on crop growth was evaluated by applying variables in Plots prior to planting Management practices used for the secondary tillage each spring but without re-randomization. crops grown during 1984 and 1985 are illustrated in Appendix Tables 3 to 6. The influence of the DTMP-CST, DTMP-NST, NDTMP-CST, and NDTMP-NST treatment combinations on emergence of row crop seedlings was by measuring plant density periodically after planting each Seedling emergence was evaluated only in the first-year plots plots in 1983). determined (ie., year. all Plant density at harvest was measured in each plot, at both locations, planted to row crops in 1983. The density of corn and sugarbeet plants at harvest was measured in 1984 and 1985. Root length density (RLD) of the Pioneer 3901 corn, C20 dry bean, and Hodgson 78 soybean cultivars on Charity clay except for RLD was determined of corn which was determined only in 1983. each year Root length 113 density was measured during the latter part of August each year where the DTMP and NDTMP treatments appeared but only where these variables were applied the previous fall. using the tillage Root samples, two per plot In 1983 and one In each plot In 1984 and 1985, were depth primary taken to the 0.46 method described by Srivastava et al. (1982). were taken between the center two rows of the four row plots m Samples with the sampling device positioned next to one of the center crop rows. Samples were fractionated into 18 76x76x76 m m subsamples, three at each of six depths. Roots were separated from the soil In each subsample using the method developed by Smucker et al. (1982) after soaking for hours in sodium hexametaphosphate. equation developed intersect method by Tennant 16 Root length was determined using the (1975) for application (Newman, 1966) on a regular grid. of the line Root dry weight was determined but only for the last three 76-mm measurement depths as it was difficult to remove plant residue from subsamples corresponding to depths within the plow layer. Yields of all four-row plots. area in 1983 row crops were taken from the center two rows of the Sugarbeet roots were harvested manually and 1984. Second and from a 6.2-m third-year plots were harvested mechanically in 1985 using a two-row sugarbeet lifter after removing tops by flailing. Harvest areas were 9.8 and 20.4 m third-year plots, respectively. 2 plots Excessive rainfall during were harvested manually from 6.2-m 2 the for the second and the fall 1985 prevented completion of sugarbeet harvest using this procedure. first-year 2 of The areas as a result. Excess soil was removed from the roots before yield samples were weighed. Ten roots from each yield sample were obtained for quality analysis. Raw juice was extracted from lengthwise. The juice the brei produced by sawing the roots obtained was frozen immediately and analyzed at 114 the Michigan Sugar company analytical laboratory. Sucrose content, clear juice purity (CJP), recoverable sucrose content, and alph-amino-N content was determined using procedures described by Dexter et al. (1967). Corn was harvested manually from 7.7-m 2 areas. A shelling percentage of 82 percent was used to adjust ear-sample weights to equivalent weights of corn grain. Yields are reported on a 155 g kg * moisture content basis. Dry bean plants were pulled manually from harvest areas of 6.2 m threshed after drying for manually from harvest increased to 7.7 m plot combine. 2 a few areas of hours. 6.2 Soybean m 2 plants in 1983. were 2 and pulled Harvest areas were in 1984 and 1985 when soybeans were harvested using a Yields of dry bean and soybean seed were corrected to seed moisture contents of 180 and 130 g kg *, respectively. Oat plants were taken manually from a 2.4-m section of 2 the center six rows of each plot in 1983. Plants from these 2.6-m using A plot combine was used to harvest the center a plot thresher. eight rows of the oat and wheat plots in 1984 and were dictated by plot dimensions, and were 10.0 m In length to 27.3 m Yields of oat where areas were 1985. Harvest ranged from 13.0 m plots were threshed 20.1 2 m areas where plots in length. and wheat grain for 1985 are reported on a 140 and 120 g kg * moisture content basis, respectively. Yields for 1983 and 1984 were uncorrected for grain moisture as only testweights of oat and wheat grain were available. Tillage variance. (Little effects on plant parameters Treatments were compared using and Hills, 1978). Analysis were evaluated by analysis of least significant of variance of crop combined over locations for 1983, the only year in which the were conducted at two sites. differences yields were experiments Analyses were combined over years for the 115 experiment on Charity clay. All combined analyses were applied to single crop cultivars and procedures described by McIntosh (1983) were test the various effects. used to RESULTS AND DISCUSSION Corn Response Emergence of corn seedlings at the two study sites in 1983 and one site in 1984 and 1985 is shown in Figure 23. Plant densities were averaged over the two primary tillage variables (DTMP and NDTMP) because they no effect on the measured values. Emergence was also unaffected by secondary tillage except for 1983 when plant densities were had on Charity clay favored by controlled traffic on the first measurement date (Figure 23b). Grain moisture at harvest in 1983 was higher under CST than under NST (Appendix Table 7) indicating that the crop matured the latter. that rapidly under Raghaven et al. (1978) and Gaultney (1980) also demonstrated compaction retards maturation and therefore increases the moisture content of the grain at harvest. emergence more and The effects of compaction on seedling crop maturity during the wet year of 1983 was due in part to impeded soil aeration under CST. Root distribution of the Pioneer 3901 corn cultivar was measured during only 1983 on Charity clay. Mean squares from analysis of variance of root length density (RLD) at six depths and root weight density (RWD) three depths are shown in Appendix Table 9. at Corn root density was influenced significantly by soil depth but was unaffected by the tillage variables. Root length densities at six depths, averaged for the DTMP and NDTMP primary tillage variables, are illustrated in Figure 24. 2.1x10 4 m m decreased -3 (2.1 cm cm monotonically -3 ) at the 0.11 m to 1.0x10 4 m m depth. -3 Root Maximum RLD was length density at the 0.42 m depth. weight density for the three depths below the Ap horizon are reported Appendix Table 10. 116 Root in 117 Days After Planting (DAP)—14 TLSD(.05) 3901 GL 3901 GL JLSD(.01) Plants I 3901 GL 3901 GL DAP* 18 ILSD(.05) 2 - 3901 DAP* 21 JLSD(.05) cn cn 3901 3744 3901 3744 Cultivar Figure 23. Emergence of corn seedlings on Parkhill loam in 1983 (a) and on Charity clay during 1983 to 1985 (b-d) as affected by secondary tillage. Cultivars used were Great Lakes-422 (GL), Pioneer-3901 (3901), and Pioneer-3744 (3744). 118 0.00 o - o CST a—A NST 0.15H Q. 0.30H LSD 0.45 0.4 1.0 1.6 2.2 RLD ( 1 0 “ 4 m m - 3 ) Figure 24. Corn root length density on Charity clay in 1983 as affected by secondary tillage. 119 Grain moisture, population, and grain yield were unaffected by primary or secondary tillage on Parkhill loam in 1983 similar (Table 6). Yields were for both cultivars despite lower populations in plots planted to the Great Lakes 422 cultivar than the Pioneer 3901 cultivar. All plant populations reported in Table 6 were lower than the desired population of 64 500 plants ha Table 7 compares corn grain yield on Charity clay under the various combinations of primary and secondary tillage. were Yields of both cultivars increased by controlling wheel traffic (NST) in 1983, the same year when seedling emergence was slowed and grain moisture wheel track compaction (CST). was increased by These results are in agreement with those of Van Doren (1959) where damage to corn from soil compaction occurred at planting time and was attributed to poor seedling emergence. Erbach et al. (1986) suggested that tillage systems with the best early growth tend to have the greatest grain yields. and yields are expected to be traffic Thus, seedling emergence, maturity, diminished by excessive preplant wheel on Charity clay when early season rainfall is above normal as in 1983. Yields of the Pioneer 3744 cultivar, grown in the second-year plots (CY2) in 1984, were affected by secondary tillage but the effects different where deep tillage and normal fall tillage were applied. yields in Grain 1984 exceeded yields reported for 1983 and 1985 regardless of the cropping history (CY1 and CY2). only were This discrepancy can be explained by the observation that plant populations were similarly greater in 1984 than in the preceding and following year (Appendix Table 8). Sugarbeet Response The effects of secondary tillage on seedbed conditions for emergence and early growth of sugarbeets are illustrated in Figure 25. Final 120 Table 6. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on corn grain moisture, plant population, and grain yield during 1983 on Parkhill loam. Cultivar Pioneer -3901 P/S Moisture CST NST Population CST NST - percent - --3 -1 10 plants ha CST Yield NST - Mg ha -1 - DTMP NDTMP 32.6 32.6 32.2 33.3 58.8 52.3 57.8 56.5 8.44 8.18 7.80 7.50 Great Lakes DTMP -422 NDTMP 26.5 27.5 25.3 27.3 44.2 39.4 46.5 46.8 8.16 7.19 7.34 7.71 Moisture NS NS NS ** P S P x S C P x C NS NS S x C P x S x C NS LSDp(.05) 4.8 LSDs(.05) 4.1 1 * >** - significant at the nonsignificant; LSDp(.05) * same or different levels of S two S means at the same level Statistics^* Population NS NS NS ** Yield NS NS NS NS NS NS NS NS NS NS 11.9 1.88 10.7 1.21 0.05 and 0.01 levels, respectively; NS ■ LSD for comparison of two P means at the and C; LSDs(.05) ■ LSD for comparison of of P and C. Table 7. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on corn grain yield from 1983 to 1985 on Charity clay. 1983. CYl o C P-3901 P-3744 P/S DTMP DTCH NDTMP NDTCH DTMP DTCH NDTMP NDTCH NST — — 9.24Aa 8.52Aa — — — 10.2Aa 9.88Ba 8.35Aa 9.45Ba 8.19Aa 8.59Aa CST NST 12.0 12.4 12.6 12.0 11.7 12.2 11.2 11.5 12.2 12.5 12.4 12.0 12.5 12.2 11.3 11.9 — «• CST 1985 CY2 CYl NST CY3 CST NST ------------- Mg ha 1 11.3Aa 11.9Aa 8.55 8.14 ll.OAa 11.7Aa 8.17 7.08 9.13 8.59 8.75 8.30 missing 9.02 8.84 8.83 7.91 •• 12.5Ab 11.8Aa 11.3Aa 12.8Bb 8.63 8.60 8.46 8.63 CST NST CST w a NST m « « m» 8.30 9.06 8.35 7.82 8.72 7.83 7.42 7.36 II N M N M II 1984 1985 CY2 CY3 CYl CY2 CYl P NS NS NS NS ** S NS NS NS ** P x S NS NS NS NS ** ** NS NS NS C P x C NS NS NS NS NS S x C NS NS NS NS NS * P x S x C NS NS NS NS 1.41 1.1 1.57 LSDp(.05) 1.0 1.31 LSDs(.05) 1.05 1.2 0.7 1.34 1.30 1 CY1 = crop year 1; CY2 * crop year 2; CY3 = crop year 3. 2 P-3901 = Pioneer hybrid 3901; P-3744 = Pioneer 3744 except for 1983 when C No. 2 was Great Lakes 422. 3 Pairs of CST and NST means In each row followed by the same upper-case letter are not different using LSD as the criterion for significance. Means in each column and within the same cultivar followed by the same lower-case letter are not different. 4 *,** = significant at the 0.05 and 0.01 levels, respectively; NS = nonsignificant; LSDp(.05) = LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) 3 LSD for comparison of two S means at the same level of P and C. Statistics: 1983 CY1 NS ** CY2 121 4 CST 1984 CY1 122 Days After Planting (DAP)* 14 H23 H20 H23 H20 DAP=*18 H23 H20 Plants H23 H20 DAP=18 H20 H20 Cultivar Figure 25. Emergence of US-H23 (H23) and US-H20 (H20) sugarbeet seedlings during 1983 on Parkhill loam (a) and during 1983 to 1984 on Charity clay (b-c) as affected by secondary tillage. 123 stands were somewhat lower than the plant densities reported In Figure 25 because plants were thinned approximately 5 plants m each June to the desired spacing Emergence of sugarbeet seedlings on of Charity clay was Influenced by secondary tillage In 1983 (Figure 25B) and In 1984 (Figure 25c) but the effects were opposite each year. Trends seed shown in Figure 25b were probably produced by varying depth of placement environments rather under than the and NST. CST direct The freezing-thawing and wetting-drying, planting clay. mm each year, have effects of natural between differing weathering fall tillage soil forces of and spring a mellowing effect on the surface of Charity Though depth bands on the seed opening disks were adjusted to 25 for each planting, sugarbeet seed was forced to a greater depth under NST where the soil was not effect was most altered prominent by preplant wheel traffic. This during the spring of 1983 when rainfall was above normal and the most favorable conditions for seedling growth and development should have existed under NST. Sugarbeet 8. productivity on Parkhill loam during 1983 is given in Table The density of sugarbeet plants in each harvest area differed under the various combinations of primary and secondary tillage as indicated by the significant P x S interaction. Though significance of the primary tillage main effect was not established at the deep tillage (DTMP) seemed that the two probability level, to produce consistently higher root yields than normal fall tillage (NDTMP). suggests 0.05 The cultivars significant were P affected x C interaction differently by deep tillage. Sugarbeet yield is commonly recoverable sucrose is the Recoverable sucrose yield reported marketable seemed in terms product consistently of (Adams higher root yield but et al., 1983). where the DTMP 124 Table 8. Influence of primary tillage (P)f secondary tillage (S), and cultivar (C) on sugarbeet plant density, root yield, and recoverable sugar yield (RSY) during 1983 on Parkhill loam. Cultivar P/S Population CST NST - 1 - plants m US-H20 US-H23 RSY Root Yield CST NST CST NST - 1 - DTMP NDTMP 4.62Aa* 4.23Aa 4.23Aa 4.53Aa 75.5 64.4 72.8 62.4 9.67 DTMP NDTMP 4.49Aa 4.25Aa 4.35Aa 4.43Aa 68.3 64.5 70.4 63.8 1 0 . 6 1 1 . 0 9.68 9.67 1 1 . 6 11.4 9.58 2 Statistics Root Yield NS NS NS NS * RSY Population P NS NS NS NS S * NS P x S NS NS C P x C NS NS NS NS S x C NS NS NS P x S x C NS 13.2 L SDp(.05) 0.48 1.96 0.42 4.79 0.95 LSDs(.05) 1 Means In each row followed by the same upper-case letter are not different using LSD as the criterion for significance. Means in each column and within the same cultivar followed by the same lower-case letter are not different. 2 *,** - significant at the 0.05 and 0.01 levels, respectively; NS ■ nonsignificant; LSDp(.05) * LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) =» LSD for comparison of two S means at the same level of P and C. 125 treatment was applied compared to NDTMP (Table terms of sugar 8 ). Sugarbeet quality In content, clear juice purity, recoverable sugar content, and alpha-amino-N content, were unaffected by the tillage methods used on Parkhill loam (Appendix Table 11). Root yields on Charity clay (Table 9) were favored by controlled traffic In 1983 even though plant stands at harvest (Appendix were diminished by the same practice. Table 12) Yields averaged across cultivars and primary tillage treatments were greater under NST (71.3 Mg ha- 1 ) than under CST (62.9 Mg ha *). the secondary tillage During 1985, NST Increased root variables were applied once yields where (CYl) and where they were applied for three consecutive years (CY3). The primary tillage variables affected root yields In 1984 and 1985 but only where they were applied the previous fall (Table 9). The two deep tillage treatments (DTMP and DTCH) Increased root yields 7.8 Mg ha * from the combined average for NDTMP and NDTCH In 1984. Treatments that Included moldboard plowing produced the highest yields In 1985. Responses illustrated in Table 9 are consistent literature which demonstrate that compaction reduces with evidence in the root yields (Blake et al., 1960; Hebblethwaite and McGowan, 1980) and that soil air porosity is an important factor in sugarbeet production (Farnsworth and Baver, 1940; Smith and Cook, 1946). content is levels. Compaction prevelant excessive under was and Soil aeration can air most NDTMP-CST porosity severe (Chapter and 2). is be impeded when water reduced to critically low impeded This aeration treatment was combination reduced internal drainage and increased soil water retention compared the other tillage combinations. lowest root yields in 1983 when most to The NDTMP-CST treatment produced the above normal April and May rainfall Table 9. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on sugarbeet root yields from 1983 to 1985 on Charity clay. c US-H20 US-H23 P/S DTMP DTCH NDTMP NDTCH DTMP DTCH NDTMP NDTCH CY2 CYl CST NST 69.2Aa 74.8Aa 58.4Aa 70.5Aa 61.4Aa 72.6Aa 62.7Aa 67.2Aa CST NST 80.7Ab 69.2 75.6Aab 75.9Aab 77.6 69.5Aa 81.0Ab 83.1Ab 75.2Aab 70.9Aa 78.4Aab 65.8 80.6Ab 73.4Aab 67.5 70.8Aa 1983 CYl NS * CYl NST CST 83.2Ab 82.0Ab 74.4Aab 72.3Aa 3 Statistics: 1985 CY2 1984 1983 CYl CST NST ----- Mg ha ” 1 ----------76.4 79.7Aab 87.0Aa 79.1Aab 80.8Aa 71.6 88.4Ab 8 6 .8 Aa 77.4Aa 79.1Aa 73.5 72.6 86.1Ab 73.7Aa 84.2Ab 73.2Aa 88.2Aab 8 6 .8 Bab 93.3Bb 80.8Aa 1984 CYl ** CY2 NS NS NS * CYl * ** CY3 CST NST 57.6 71.5 65.7 74.3 71.2 72.9 72.9 72.5 63.7Aa 74.2Aa 62.3Aa 77.3Ba 70.1 72.0 72.7 68.9 76.4 69.7 72.7 74.6 61.8Aa 77.lBa 56.6Aa 73.3Ba 1985 CY2 NS NS NS NS NS NS NS CST NST CY3 P NS ** S NS P x S NS NS NS NS NS NS C NS NS P x C NS NS NS NS NS S x C NS NS NS NS NS P x S x C NS NS NS NS NS LSDp(.05) 13.8 9.4 10.5 1 1 . 0 9.8 14.8 LSDs(.05) 13.7 10.3 8 . 8 8.4 1 1 . 2 13.3 1 CYl = crop year 1; CY2 = crop year 2; CY3 = crop year 3. 2 Pairs of CST and NST means in eachrow followed by the same upper-case letter are not different using LSD as the criterion for significance. Means in each column and within the same cultivar followed by the same lower-case letter are not different. 3 * f** = significant at the 0.05 and 0.01 levels, respectively; NS = nonsignificant; LSDp(.05) » LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) 9 LSD for comparison of two S means at the same level of P and C. 127 (Chapter 3) produced frequent occurrances of soil water excess during the early part of the growing season. Negative associations between demonstrated in recent studies. increased curvilinearly decreased linearly but beet As N fertilization increased, root yield sucrose (Halvorson quality and root yield have been and content Hartman, (1986) found a negative relationship between yield and clear 1980). juice purity Campbell and Cole sucrose content and root for data collected from 17 environments (years x locations) in the Red River Valley. Sucrose, content Similar relationships were not evident in this (Appendix Table 13), clear juice purity (Appendix Table 14), and therefore recoverable sugar content unaffected by study. (Appendix Table 13) were secondary tillage where root yields were increased by NST (CYl in 1983; CYl and CY3 in 1985). Primary tillage influenced root yields in 1984 and 1985 (CYl only) but had no effect on sugarbeet quality for the same combinations of Year x Crop-Year. Recoverable sucrose yields (Table 10) and root yields were Influenced similarly by tillage because quality was maintained and/or controlled traffic Increased root where yields. deep Controlled traffic increased recoverable sucrose yields in 1983 averaging 11.3 ha * under treatments recoverable tillage NST and CST, respectively. increased root yields sucrose yields were effects probability level on economic in 1985 by 7.8 Mg the ha * were significant and 9.9 Mg two deep tillage in 1984 increased 1.1 Mg ha yield (CYl Where tillage (CYl), The secondary at the 0 . 0 1 and CY3) as NST increased recoverable sucrose yields, especially for the US-H23 cultivar. The NST treatment used in this study was designed to avoid recompaction of soil loosened by deep tillage and to conditions produced by natural weathering forces exploit the ideal seedbed each winter. Tillage Table 10. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on recoverable sucrose yield of sugarbeets from 1983 to 1985 on Charity clay. 1984 1983. CYl 1 C P/S CST CY2 CYl NST CST CST NST 2 US-H20 US-H23 DTMP DTCH NDTMP NDTCH ll.lAa 12.0Aa 9.2Aa 11.2Aa DTMP DTCH NDTMP NDTCH 9.7Aa ll.SAa 9.7Aa 10.5Aa Statistics: 3 1983 CYl NS * 12.9Aa 12.8Aa 11.8Aa 11.2Aa 12.5Aa 11.8Aa 11.8Aa ll.OAa 11.9Aab 12.8Ab 11.5Aab ll.OAa 11.8Aa 12.4Aa ll.lAa ll.lAa 1985 CY2 CYl NST CST NST ----- Mg h a 1 ----------12.0Aa 13.1Aa 12.3 11.9Aa 12.3Aa 11.7 11.4 13.0Aa 12.9Aa 11.6Aa 11.9Aa 1 1 . 1 1 0 . 1 11.5 1 0 . 6 11.5 12.8Ab ll.OAa 12.4Aab 11.2Aa 1984 NST 8.2Aa 10.5Ab 9.8Aab 10.9Ab lO.SBa ll.OAa ll.2Aa 10.7Aa lO.OAa 10.4Aa 10.6Aa lO.OAa 11.2Aa 10.6Aa 10.9Aa ll.lAa 1985 CY2 NS * CST NST 9.3Aa 9.4Aa 8.9Aa 8.7Aa 9.4Aa 12. IBa 8.7Aa 11.4Ba CY3 P NS S NS P x S NS NS NS NS NS NS NS C NS NS NS P x C NS NS NS NS NS NS S x C NS NS NS NS NS NS P x S x C NS NS NS NS NS NS LSDp(.05) 2.3 1 . 8 1 . 8 1.5 1.7 2 . 1 LSDs(.05) 2.3 1.7 1.3 1 . 8 1 . 6 1 . 8 1 CYl = crop year 1; CY2 = crop year 2; CY3 = crop year 3. 2 Pairs of CST and NST means in each row followed by the same upper-case letter are not different using LSD as the criterion for significance. Means in each column and within the same cultivar followed by the same lower-case letter are not different. 3 * t** = significant at the 0.05 and 0.01 levels, respectively; NS = nonsignificant; LSDp(.05) = LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) = LSD for comparison of two S means at the same level of P and C. CYl ‘ * CY2 NS NS NS * 13.3Aab 13.0Bab 13.5Ab 11.9Aa CY3 CST CYl * ** 129 methods similar to the NST treatment have been developed In western parts of the United States to control erosion. In North Dakota, root yield and recoverable were equal under a conventional sucrose content of beets tillage system that included secondary tillage and that did not and in and to (Halvorson be a and Hartman, because comparable Root and levels under production yields 1984). Reduced tillage is successful management practice in these areas when yields can be maintained while the therefore at systems conventional tillage in Colorado (Glenn and Dotzenko, 1978) Montana considered other include secondary tillage (Sojka et al., 1980). recoverable sucrose yields were maintained reduced three costs were number of are minimized. actually increased tillage operations, and Our results are significant as the number of tillage operations was reduced. Sugarbeet quality in terms differed only between cultivars. amino-N (Appendix Table 16) of sucrose B y contrast, content (Appendix Table 13) levels of the impurity were affected by primary and/or secondary tillage for several combinations of Year x Crop-Year. Tillage variables that increase yields seemed to increase the amino-N content of beets. In 1984 (CYl), the amino-N content was greatest under deep tillage (DTMP and DTCH) averaging 98 mmol kg * for DTMP and DTCH compared to 80 mmol kg * for the treatments that did not include deep tillage (NDTMP and NDT C H ) . Controlled traffic increased yields and the amino-N content of the US-H23 cultivar in 1985 but only for the first crop year. Our results suggest that N fertility x tillage interactions should be considered when tillage methods for sugarbeet production on the prevailing soils are altered. Soybean and Dry B ean Plant Responses Emergence both soils of in soybean 1983 seedlings was enhanced by controlled traffic on (Figure 26). Differences between NST and CST 130 Days After Planting*DAP 24 20 DAP=14 29 16 ]lSD(.01) 1 ** = significant at the 0.05 and 0.01 levels, respectively; NS = nonsignificant; LSDp(.05) = LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) = LSD for comparison of two S means at the same level of P and C. 143 CST and NST, respectively. attributed to Response to controlled traffic In 1983 can be Impeded seedling emergence (Figure 27) and reduced stands (Table 11) under the CST treatment. Differences between CST and NST were greatest In 1985 when controlled traffic Increased yields of the C20 and Swan Valley the second-year plots (CY2) cultivars grown by 16 and 39 percent, respectively (Table 15). Yields of dry beans grown In the third-year plots during 1985 also favored by controlled traffic compared to 2.71 Mg ha * for CST. maturity In averaging Soil 2.89 compaction Mg were ha~^ for NST retarded dry bean In addition to reducing yields as grain moisture at harvest was usually higher for the CST than the NST treatment (Appendix Table 18). Oat and Wheat Response Wheat and oats are Important crops in the Saginaw Valley, a prominent dry bean and sugarbeet production area in Michigan of Agriculture, 1986). Tillage effects (Michigan Department on the growth of these small grains were not of primary concern in this study. and wheat grain were determined whenever they However, yields of oat appeared in one of the rotations described in Chapter 2. Controlled traffic Increased oat yields during the wet year of 1983, especially for the Mariner cultlvar (Table 16). were Yields of Marinar oats 0.58 Mg ha * (20 percent) greater under NST than under CST in 1983. Yields of both cultivars were favored by conventional spring tillage on 1984 when the seasonal distribution of rainfall was near normal. Primary plots in tillage 1985 influenced (Table 16). the yield of oats grown in the first-year Yields were consisted of only shallow chiseling (NDTCH). yields because lowest where fall tillage The NDTCH treatment reduced stands were poor and weeds were controlled ineffectively where this treatment was applied. Table 16. Influence of primary tillage (P), secondary tillage (S), and cultlvar (C) on oat yields from 1983 to 1985 on Charity clay. 1984 CYl 1983. CYl Cultlvar P/S CST NST CST , a- Heritage Mariner Statistics •• DTMP DTCH NDTMP NDTCH 3.96Aa 3.83Aa 3.60Aa 4.04Ba DTMP DTCH NDTMP NDTCH 2.82Aa 3.56Ba 3.10Aa 3.52Ba 3 1983 CYl NS ** 1985 CYl NST CST 6.19Aa 5.98Aa 5.44Aa 5.74Aa - - Mg ha - 1 ------3.55Ab 5.90Aa 5.28Aa 3.03Aab 3.33Aab 5.34Aa 2.42Aa 5.47Aa 5.33Aa 5.13Ba 4.91Aa 4.87Aa 4.67Aa 4.22Aa 4.54Aa 4.72Aa -n m it 1984 CYl NS * CY3 NST 3.30Ab 2.81Aab 2.56Aab 2 .06Aa CST NST , — — — — 4.12Ab 3.24Aab 3.36Aab 2.49Aa 3.91 3.80 3.81 3.95 3.33Ab 2.56Aab 2.69Aab 1.83Aa 3.47 3.74 3.33 3.68 1985 CYl * CY3 NS NS NS NS NS NS NS P S NS NS P x S NS NS ** ** * C P x C NS NS NS * S x C NS NS * P x S x C NS NS LSDp(.05) 0.38 0.93 1.07 0 . 8 8 LSDs(.05) 0.38 0.91 0.72 0.96 1 CYl = crop year 1; CY3 = crop year 3. 2 Pairs of CST and NST means In each row followed by the same upper-case letter are not different using LSD as the criterion for significance. Means in each column and within the same cultlvar followed by the same lower-case letter are not different. 3 * t** s significant at the 0.05 and 0.01 levels, respectively; NS ■ nonsignificant; LSDp(.05) = LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) = LSD for comparison of two S means at the same level of P and C. 145 Wheat yields were favored by controlled traffic In 1985 averaging 0.15 Mg ha * higher under NST than under CST secondary (Table 17). Response to the tillage variables is surprising because they were applied only once, prior to establishment of the preceding crop (soybeans). planted to wheat were chiseled uniformly to a depth of after soybean harvest. differences produced Charity clay. 0.15 All plots to 0.20 m Shallow chiseling should have diminished physical by the CST and NST treatments in the surface of The small but significant response to secondary tillage in 1985 can be attributed to the influence of preplant wheel traffic on soil physical conditions below the depth of shallow chiseling (Chapter 2). Location effects on yield responses in 1983 Identical tillage experiments were conducted at two locations in 1983. The soil at one location was Parkhill loam and Charity clay at the other. Analysis of variance of yields that year were combined over locations to compare tillage effects on crop growth for the two soils. Yields of both corn cultivars and one dry bean cultivar varied between locations (Table 18) as yields were Parkhill loam. that yields greater on Charity clay than on The significant primary tillage (P) main effect indicates of the US-H20 sugarbeet cultivar were increased by deep tillage on the average. Significant location x tillage Interactions (L x P or L x S) suggest that the tillage variables affected crop Charity clay differently. The L x growth P and significant for the Corsoy-79 soybean cultivar. in L Parkhill loam and x S interactions were Both deep tillage and conventional spring tillage tended to increase yields of this cultivar on Parkhill loam (Table 12) but not on Charity clay (Table 14). The collective response of each dry bean cultivar to secondary tillage was pronounced as indicated by the significant secondary tillage (S) main 146 Table 17. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on wheat yields from 1984 to 1985 on Charity clay. 1984, CY2 Cultivar P/S CST 1985 CY2 NST CST NST - 1 Frankenmuth Arther DTMP DTCH NDTMP NDTCH ------- Mg ha 5.34 5.42 5.66 5.45 -------5.19Aa 5.23Aa 4.96Aa 4.93Aa DTMP DTCH NDTMP NDTCH 5.47Ab 5.41Ab 5.16Aat 4.95Aa 4.27Aa 4.01Aa 4.07Aa 3.92Aa 4.34Aa 4. lOAa 4.17Aa 4.15Aa 3 Statisitics P S P x S LSDp(.05) LSDs(.05) 1984 CY2 NS NS NS 0.35 0.33 P S P x S C P x C S x C P x S x C LSDp(.05) LSD s ( .05) 1985 CY2 NS * NS ** NS NS NS 0.37 0.30 1 CY2 ■ crop year 2. 2 Pairs of CST and NST means in each row followed by the same upper­ case letter are not different using LSD as the criterion for sig­ nificance. Means in each column and within the same cultivar followed by the same lower-case letter are not different. 3 ** ■ significant at the 0.05 and 0.01 levels, respectively; NS ■ nonsignificant; LSDp(.05) - LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) * LSD for comparison of two S means at the same level of P and C. Table 18. Mean squares from combined analysis of variance oyer locations for sugarbeet root yield (SRY), sugarbeet recoverable sugar yield (RSY), corn grain yield (CGY), soybean and dry bean seed yields In 1983. df US-H20 RY US-H23 US-H20 RSY US-H23 P3901 CGY 2 GL422 H-78 Soybean C-79 Dry bean C20 SV L3 2.41 4.52 0.078 17.404** 8.748* 588 314 255 1 0.647 3 603 069* 720 720 6 69.83 32.35 1.318 0.853 1.061 B/L 0.684 180 835 174 021 307 940 192 545 P 1 673.81* 106.18 20.979* 5.281 840 942 1.268 1.308 873 644 3 894 279 098 0.117 1 20.29 19.36 0.641 0.775 0.087 78 755 992 288* 222 795 77 520 L x P Error a 65.38 1.635 1.060 184 278 60 799 50 711 6 48.05 0.919 0.619 149 884 84.44 3.400 1 144.88 0.497 0.719 141 419 85 037 434 615** 1 223 830** S 4.485 1 L x S 250.99* 101.35 5.273 2.785 6.642* 1.609 431 497** 465 420* 136 673 166 869* P x S 1 25.99 44.35 0.959 0.068 40 449 3 399 0.928 0.218 5 716 28 096 16.70 L x P x S 1 7.97 0.586 0.252 0.096 2.091 10 357 31 063 18 755 64 1 0 0 Error b 1 2 36.95 53.43 1.214 0.579 67 493 1.129 0.799 31 286 28 789 21 991 1 Location 1 = The experiment on Charity clay, Swan Creek, MI; location 2 * the experiment on Parkhill loam, Ithaca, MI. 2 P3901 = Pioneer hybrid 3901; GL422 = Great Lakes 422; H-78 » Hodgson 78; C-79 ■ Corsoy 79; SV * Swan Valley. 3 L = location; B * blocks; P ■ primary tillage; S * secondary tillage; *,** significant at the 0.05 and 0 . 0 1 levels, respectively. 148 effect (Table 18). soils Controlled traffic Increased dry bean yields on both but responses were much greater on Charity clay (Table 15) than on Parkhill loam (Table secondary tillage 13). on Varying the two response soils of dry bean yields produced the significant to LxS Interactions Illustrated in Table 18. Yearly Variation of Yield Response on Charity clay The significant Year (Y) effects suggest that yields of crops grown in the first-year plots differed from one year to the next (Table 19). variation Is an expected consequence of distributions that the diverse seasonal occurred during 1983 to 1985 (Chapter 3). to primary tillage were not evident in analyses combined for This rainfall Responses the three- year study period. Significant year x tillage interactions (Y x P or Y x S) are evident in Table 19. These interactions occur in tillage studies because: (1) soil physical changes created by tillage vary from year to year soil conditions that exist when depending tillage is applied, especially water content; and (2 ) crop response to varying soil conditions depend prevailing weather each year. traffic tended to increase corn yields in in 1984 (Table 7) on the Yields of one corn, soybean, and dry bean cultivar exhibited significant Y x S interactions (Table 19). yields on when 1983 rainfall and 1985 Controlled but was near normal. interaction was significant for the Hodgson-78 soybean cultivar decrease The L x S because conventional spring tillage enhanced yields during only 1985 (Table 14). Controlled the wet year nonsignificant traffic of for increased 1983 the (Table Swan yields of both drybean cultivars during 15). The L x S interaction was Valley cultivar (Table 19) because yields were improved by controlled traffic during each year. Yields of the C20 Table 19. Mean squares from combined analysis of variance over years for sugarbeet root yield (SRY), sugarbeet recoverable sugar yield (RSY), corn grain yield (CGY), soybean and dry bean seed yields on Charity clay at the Saginaw Valley Research Farm, Swan Creek, MI. RY df US-H20 RSY US-H23 US-H20 US-H23 CGY P3901 Soybean H-78 Dry bean C-79 C20 SV Y3 2 1208.21** 1925.57** 15.655** 28.390** 45.285** 1 166 285** 501 383* 1 380 386** 678 093 72.35 0.919 1.043 0.497 49 381 76 331 280 049 B/Y 9 66.18 142 796 46.32 4.302 1.829 1.013 53 273 54 197 690 151 875 P 1 135.51 2 2 264 113 Y x P 2 49.17 3.213 0.267 0.321 91 423 151 275 145 2 0 1 175.62 9 27.39 1.279 1.407 0.445 Error a 53.41 51 570 136 397 85 649 83 150 484** 1 4.113 4.644 19 148 219* 272 918** 1 838 S 167.37 168.86 1.114 509 2 183 817* 42 423 300 474** 174 361 Y x S 89.42 110.60 2.791 2.702 4.174** 1 P x S 0.30 0 . 0 2 1 80 910 0.81 0.226 0.180 33 904 649 316 160 2 Y x P x S 2 68.84 47.12 1.576 0.611 50 417 54 751 0.631 25 116 104 660 Error b 18 80.77 2 . 0 2 2 68.29 1.846 45 626 27 0 0 0 73 639 0.579 26 955 1 Year 1 = 1983; year 2 = 1984; year 3 = 1985; the analyses included only yields from plots where the DTMP and NDTMP primary tillage variables appeared and where these tillage variables were applied the previous fall. 2 P3901 = Pioneer hybrid 3901; H-78 = Hodgson 78; C-79 = Corsoy 79; SV ■ Swan Valley. 3 Y = Year; B = blocks; P = primary tillage; S =» secondary tillage; *,** significant at the 0.05 and 0 . 0 1 levels, respectively. 150 dry bean cultivar were Increased by controlled traffic during only 1983 resulting in the significant Y x S interaction. CONCLUSIONS Plant responses to tillage substantiate the results of Chapter 2 where deep tillage and controlled traffic improved soil On soybeans Parkhill loam, yields of sugarbeets, physical consistently greater where deep tillage was applied fall tillage. conditions. and dry bean were compared to normal Deep tillage may have alleviated water stress on Parkhill loam where rainfall was well below normal for the June to August period. Deep tillage tended years on Charity clay. deep tillage to increase sugarbeet yields during two of three Yields of one soybean cultivar were during 1983. improved by Physical changes brought about by subsoiling were shown to persist through only one crop year in Chapter 2. In agreement with results of Chapter 2, yield responses to deep tillage were evident only where subsoiling was applied the previous fall. Soil compaction created by preplant wheel traffic dependent crop responses in 1983, a year characterized by and dry June to August period. produced soila wet spring Wheel-induced compaction reduced stands on Parkhill loam but produced the highest soybean yields. The secondary tillage variables had little effect in yields of three other crops. The effects of preplant wheel traffic were more evident on Charity clay than on Parkhill loam in 1983 as controlled traffic improved seedling emergence, increased dry bean rooting, and Increased the yields of five crops. Crops were more of four responsive to controlled traffic on Charity clay because this soil has a greater tendency to develop aeration stress. Dry beans and sugarbeets proved to be most sensitive induced compaction to wheel- as preplant wheel traffic diminished yields of these crops in 1985 as well as in 1983. LIST OF REFERENCES Adams, R.M., P.J. Farris, and A.D. Halvorson. 1983. Sugar beet N fertilization and economic optima: Recoverable sucrose vs. root yields. Agron. J. 75:173-176. Anazodo, U.G.N., 6 .S.V. Raghaven, E. McKyes, and E.R. Norris. 1983. Physico mechanical properties and yield of silage corn as affected by soil compaction and tillage methods. Soil Tillage Res. 3:331-346. Beaver, J.S., and R.R. Johnson. 1981. Response of determinate and indeterminate soybeans to varying cultural practices. Agron. J. 73:833838. Blackwell, P.S., M.A. Ward, R.N. Lefeure, and D.J. Cowan. 1985. Compaction of a swelling clay soil by agricultural traffic: effects upon conditions for growth of winter cereals and evidence for some recovery of structure. J. Soil Sci. 36:633-650. Blake, 6 .R., D.B. Ogden, E.P. Adams, and D.H. Boelter. 1960. Effect of soil compaction on development and yield of sugar beets. J. Am. Soc. Sugar Beet Technol. 11:236-242. Box, J.E., Jr., and G.W* Langdale. 1984. The effects of in-row subsoil tillage and soil water on corn yields in the southeastern Coastal Plain of the United States. Soil Tillage Res. 4:67-78. Burnett, E., and V.L. Hauser. 1968. Deep tillage and soil-plant-water relations, p. 47-52. In Tillage for greater crop production. Am. Soc. Agric. Eng., St. Joseph, MI. Buxton, D.R., and J.C. Zalewski. 1983. Tillage and cultural management of irrigated potatoes. Agron. J. 75:219-225. Campbell, R.B., D.C. Reicosky, and C.W. Doty. 1974. Physical properties and tillage of Paleudults in the southeastern Coastal Plains. J. Soil Water Conserv. 29:220-224. Campbell, L.G., and D.F. Cole. 1986. Relationships between taproot and crown characteristics and yield and quality traits in sugarbeets. Agron. J. 78:971-973. Dexter, S.T., M.G. Frakes, and F.W. Snyder. 1967. A rapid and practical method of determining extractable white sugar as may be applied to the evaluation of agronomic practices and grower deliveries in the sugar beet industry. J. Am. Soc. Sugar Beet Technol. 14:433-454. Erbach, D.C., R.M. Cruse, T.M. Crosbie, D.R. Timmons, T.C. Kaspar, and K.N. Potter. 1986. Maize response to tillage-induced soil conditions. Trans. ASAE 29:690-695. 151 152 Erickson, A.E. 1982. Soil Aeration, p. 91-104. In P.W. Unger and D.M. Van Doren (ed.) Predicting tillage effects on soil physical properties and processes. Spec. Pub. 44. Am. Soc. Agron., Madison, WI. Farnsworth, R.B., and L.D. Baver. 1940. The effect of soil structure on sugar beet growth. Sugar Beet J. 5:172-175. Gaultney, Thesis, L.D. 1980. The effect of subsoil compaction on corn yield. M.S. Dep.Agric. Eng., Purdue, Univ., W. Lafayette, IN. 93 pp. Gaultney, L . , G.W. Kurtz, G.C. Steinhardt, and J.B. Liljedahl. 1982. Effects of subsoil compaction on corn yields. Trans. ASAE 25:563-575. Gerlk, T.J., J.E. Morrison, Jr., and F.W. Chichester. 1987. Effects of controlled-traffic on soil physical properties and crop rooting. Agron. J. 79:434-438. Glenn, D.M., and A.D. Dotzenko. 1978. Minimum vs conventional tillage in commercial sugar beet production. Agron. J. 70:341-344. Gray, L.E., and R.A. Pope. 1986. Influence of soil compaction on soybean stand, yield, and Phytophthora root rot incidence. Agron. J. 78:189191. Halvorson, A.D., and G.P. Hartman. 1980. Response of several sugarbeet cultivars to N fertilization: Yield and crown tissue production. Agron. J. 72:665-669. Halvorson, A.D., and G.P. Hartman. 1984. Reduced seedbed tillage effects on Irrigated sugarbeet yield and quality. Agron. J. 76:603-606. Hebblethwaite, P.D., and M. McGowan. 1980. The effects of soil compaction on the emergence, growth and yield of sugar beet and peas. J. Sci. Food Agric. 31:1131-1142. Kamprath, E.J., D.K. Cassel, H.D. Gross, and D.W. Dibb. 1979. Tillage effects on biomass production and moisture utilization by soybeans on Coastal Plain soils. Agron. J. 71: 1001-1005. Lindemann, W.C., G.E. Ham, and G.W. Randall. 1982. Soil compaction effects on soybean nodulation, N_(C9H,) fixation and seed yield. Agron. J. 74:307-311. L 1 4 Little, T.M., and F.J. Hills. 1978. Agricultural Experimentation. John Wiley & Sons, New York. Lueschen, W.E., and D.R. Hicks. 1977. Influence of plant population on field performance of three soybean cultivars. Agron. J. 69:390-391. Mayfield, W . , R.A. Hoyum, W.T. Dumas, and A.C. Trouse. 1978. Tillage to correct soil compaction. Alabama Coop. Extension Serv. Circ. ANR-41. 8 pp. McIntosh, 155. M.S. 1983. Analysis of combined experiments. Agron. J. 75:153- 153 Michigan Department of Agriculture. 1986. Michigan Agricultural Statistics 1986. Michigan Agricultural Statistics Service, Lansing, MI. Miller, D.E. 1987. Effect of subsoiling and irrigation regime on dry bean production in the Pacific Northwest. Soil Sci. Soc. Am. J. 51:784-787. Negi, S.C., E. McKyes, F. Taylor, E. Douglas, and 6.S.V. Raghaven. 1980. Crop performance as affected by traffic and tillage in clay soil. Trans. ASAE 23:1364-1368. Nelson, W.E., G.S. Rahi, and L.Z. Reeves. 1975. Yield potential of soybean as related to soil compaction induced by farm traffic. Agron. J. 67:769-772. Newman, E.I. 1966. A method of estimating the total length of root in a sample. J. Appl. Ecol. 3:139-145. Parker, M.B., N.A. Minton, O.L. Brooks, and C.E. Perry. 1975. Soybean yields and Lance nematiode populations as affected by subsoiling, fertility, and nematiclde treatments. Agron. J. 67:663-666. Phillips, R.E., and D. Kirkham. 1962. Soil compaction in the field and corn growth. Agron. J. 54:29-34. Raghaven, 6.S.V., E. McKyes, G. Gendron, B. Borglum, and H.H. Le. 1978. Effects of soil compaction on development and yield of corn maize. Can. J. Plant Sci. 58:435-444. Raghaven, G.S.V., E. McKyes, F. Taylor, P. Richard, and A. Watson. 1979. The relationship between machinery traffic and corn yield reductions in successive years. Trans. ASAE 22:1256-1259. Rosenberg, N.J. 1964. Response of plants to the physical effects of soil compaction. Advan. Agron. 16:181-196. Ross, C.W. 1986. The effects of subsoiling and irrigation on potato production. Soil Tillage Res. 7:315-325. Smith, F.W., and R.L. Cook. 1946. The effect of soil aeration, moisture, and compaction on nitrification and oxidation and the growth of sugar beets following corn and legumes in pot cultures. Soil Sci. Soc. Am. P r o c . 11:402-406. Smucker, A.J.M., S.L. McBurney, and A.K. Srivastava. 1982. Quantitative separation of roots from compacted soil profiles by the hydropneumatic elutriation system. Agron. J. 74:500-503. Sojka, R.E., E.J. Delbert, F.B. Arnold, and J. Enz. 1980. Sugarbeet production under reduced tillage - prospects and problems. N.D. Farm Res. 38(12):14-18. Srivastava, A.K., A.J.M. Smucker, and S.L. McBurney. 1982. An improved mechanical soil-root sampler. Trans. ASAE 25:868-871. 154 Tennant, D. 1975. A test of amodified line estimating root length. J. Ecol. 63:955-1001. intersect method of Van Doren, D.M. Jr., 1959. Soil compaction studied to determine effect on plant growth. Ohio Farm Home Res. 44:317. Voorhees, W.B., S.D. Evans, and D.D. Harnes. 1985. Effect of preplant wheel traffic on soil compaction, water use, and growth of spring wheat. Soil S d . Soc. Am. J. 49:215-220. Weatherly, A.B., and J.H. Dane. 1979. Effect of tillage on soil-water movement during corn growth. Soil Sci. Soc. Am. J. 43:1222-1225. Wilcox, J.R. 1974. Response of spacings. Agron. J. 66:409-412. three soybean strains to equidistant Chapter 5 Evaluation of Tillage Effects on Soil Aeration Using a Simulation Model and the Stress Day Index Approach INTRODUCTION The Impact of two ameliorative procedures, deep tillage and controlled traffic, were evaluated using conventional approaches up to Taylor this point. and Arkln (1981) described the disadvantages, associated with the approaches utilized In Chapters 2 to 4. costly, time First, consuming, and destructive. root observations are Second, crop response to soil physical changes created by tillage can be masked by other environmental and management factors. Simulation models, a collection of quantitative relationships designed to describe a system, can be used to evaluate the modifications. Computer simulations derived impact from of root these models allow researchers to distinguish crop response to root zone changes from comfounding responses. time using recorded zone other More importantly, simulations for long periods of or generated weather data can be used to determine probabilities of crop response and benefit (Arkln and Taylor, 1981). Feddes (1981) reviewed numerous models based on relationships between water use and crop production. The author suggested that few attempts have been made to evaluate the effects of soil manipulation on production through water use. This may be explained in part by our inability to predict physical changes brought about by tillage. Models based on production system. water use describe only one part of the more complex Soil aeration may 155 be an important part of some 156 production drained systems, or prone especially to In humid regions where soils are poorly compaction. Until recently, few models were available that described the dependence of crop growth on soil aeration. Whlsler et al. (1982) described a cotton growth simulation model (GOSSYM) that was modified to account for the effects of cultivation wheel and traffic on (1) hydraulic properties, (2) mechanical impedance, and (3) changes in root growth due to Oj evaluated by calculating Oj concentrations diffusion into the soil profile. growth in GOSSYM stress. Oxygen through The soil due to deficiency reduced root status one dimensional influences elongation is rates cotton during anaerobiosis. A quantitative evaluation of aeration stress should combination of deficiency duration, intensity (e.g., crop species and its growth stage (Erickson, 1982). O2 include some concentration), The stress day index (SDI) concept proposed by Hiler and Clark (1971) meet these requirements. The authors suggested that the SDI concept is applicable to characterization of both water and aeration stresses. The stress day index for a given period is the product of a stress day factor and a crop susceptibility factor. The stress day factor (SD) is a measure of the degree of water or 0 ^ deficit. factor (CS) day crop susceptibility quantifies the plant susceptibility to a given stress. magnitude depends on the crop species stress The index and stage of development. Its The for growth period i can be expressed by the following equation: n SDI - £ ( S D . x CS ) i-1 where n represents the number of growth periods. (I) 157 Stress day Index models were Incorporated Into the water management model, DRAINMOD, to quantify the effect of excessive and water conditions (Hardjoamldjojo and Skaggs, 1982). deficient The SDI models of Shaw (1974, 1976) were used to account for yield response soil water deficit. This to cumulative The stress day factor originally defined by Sleben (Wessellng, 1974) was used to conditions. soil stress day calculate the SDI for excessively wet factor is the sum of excess water in the surface 30 cm of the soil profile and Is expressed as: 24 SEW301 - 1/24 £ where SEW^ q ^ « SEW^ q for day 1 and surface at the end of the jth f(X j ) (2) - the water table depth below the hour. The function In equation 2 is evaluated as follows: f(Xj) “ 30 - Xj for Xj < 30 cm (3) Xj > 30 cm (4) and f(Xj) ■ 0 for The depth of water table has no direct influence on crop growth but it is an indicator of the prevailing soil water conditions (Hardjoamldjojo et al., 1982) and therefore aeration stress. Air porosity (Fa) of the soil is Its physical characteristic that has the greatest influence on gas exchange (Russell, 1977). Thus, a stress day factor based on Pa may account for the degree of soil aeration stress more effectively depth can than water table depth. becalculated if simulated water the contents are soil The air porosity at any soil porosity available, and relatively constant as water content changes. CERES-Maize (Jones and isknown, ifthe measured soil or volume is The crop simulation model Kiniry, 1986) may lend itself to application of 158 the SDI approach In this calculated on a daily basis. study because the soil water balance is Furthermore, soil inputs can be manipulated to account for tillage effects on soil properties. The objectives of this section were: (1) Evaluate the impact of tillage on soil aeration by simulating profile soil water content under corn and applying the SDI method; and (2) assuming aeration on Charity clay, determine yields the are limited by poor probability of benefit from subsoiling and controlled traffic using generated weather data. MATERIALS AND METHODS Soil physical conditions produced by various combinations of primary and secondary tillage were demonstrated In Chapter 2. and spring growth. the Conventional fall tillage (NDTMP-CST) produced unfavorable conditions for crop Deep tillage combined with controlled traffic (DTMP-NST) reduced physical decreased limitations bulk large pores. of Charity clay. The DTMP-NST treatment density and Increased porosity, especially the volume of These changes Improved Internal drainage of the surface and Increased air porosity version of at CERES-Malze high soil (Jones and water potenials. The standard Kinlry, 1986) was used to simulate dally water contents under the diverse treatments NDTMP-CST and DTMP-NST. The model was modified to account for the unique conditions that existed at the experiment site. Model Modifications Runoff Is negligible at the Saginaw Valley Bean and Beet Research Farm because the site is level. The CERES-Malze model uses the "curve number" method to estimate runoff (USDA, Soil Conservation Service, user can force zero runoff In the 1972). The original version of the model by entering the appropriate runoff curve number (CN2). All precipitation and/or irrigation occurlng on a given day enters the soil profile when runoff is zero. for Charity clay as ponding levels are high and can rainfall This produces an unrealistic situation occur is when antecedent excessive. soil moisture A fraction of received on a particular day may not Infiltrate until the the rain following day under these conditions. The water balance subroutine of CERES-Malze (Jones et al., 1986) was altered to permit ponding during excessively variable quantify the amount of ponding that may (STOR) was added to 159 wet periods. A storage 160 occur. The curve number method was retained runoff (RUNOFF) water content. so for calculation of dally that dally Infiltration depends on the profile soil This method also provides the user with the opportunity to manipulate CN2 and therefore “adjust" the potential dally infiltration for varying soil conditions. The STOR value for day 1 is calculated as follows: ST0R1 - RAIN1 + ST0R±_ 1 where S0R^_^ is the (5) value of STOR on the previous day (usually zero). Daily infiltration (WINF) becomes: WINFi - ST0R1 - RUNOFF± (6) where RUNOFF^ represents water in the form of rain on day 1, plus ponding from the previous day that failed to infiltrate. The new value of STOR becomes: ST0Ri - RUNOFF^ The soil STOR > 0 . evaporation routine (7) was altered for those situations where Soil evaporation (ES) normally decreases the water content of the first soil depth. SW(1) - SW(1) - ES(.1)/DLAYR(1) Soil water content and DLAYR(l), respectively. to cm units. depth (8) of layer 1 are represented by SW(1) and The factor, 0.1, facilitates conversion from mm When STOR > 0 and STOR < ES, the water content of the first soil depth decreases by the amount: SW(1) - SW(1)-(ES-ST0R)(.1)/DLAYR(1) afterwhich STOR is reset to zero. (9) When STOR > ES, the water content of the first soil depth is unchanged by ES. The new STOR value becomes: ST0R1 * ST0Ri - ES (10) Water balance output produced by the original version of CERES-Maize is illustrated in Appendix Table 19. This version of the model and CERES 161 models In general, evaluate soil water balance using the equation described by Ritchie (1985): S - PRECIP + I - EP - ES - RUNOFF - DRAIN (11) where the quantity of soil water (S) changes with precipitation (PRECIP), Irrigation (I), evaporation from plants (EP) and soil (ES), RUNOFF, and drainage from the profile (DRAIN). Equation 11 Is used to evaluate the soil water balance In the modified version of CERES-Malze when STOR > 0 . The value of STOR > 0 when ponding occurs and the following relationships hold: S1 - WINF± - E P ± - DRAINt (12) and STOR. - STOR. . + PRECIP. - WINF. - ES., 1 1-1 1 1 1 The WINF^ term (13) ' 7 appears In both equations because water that enters the profile diminishes ST0R^_^ by the same amount. Finally, ponding ceases on day 1 (i.e., STOR^ becomes zero) when: ST0Ri_ 1 < WINF± + ES1 (14) The soil water balance equation can be written: S - WINF1 - DRAINt - EPj^ - [ESi - ( S T O R ^ - W I N F ^ ] which reduces (15) to: S “ ST0R1_ 1 - DRAIN± - ES^ Water balance output was modified (16) to illustrate the relationships in equations 11 to 16 (Appendix Table 20). Model Inputs The soil and weather data required by CERES-Malze have been documented (Ritchie et simulations al., are 1986). shown in Soil inputs Appendix used Tables for 21 to the 23, Variable names are included as column headers but were not actual input data. 1983 to 1985 respectively. part of the Seven layers of varying depths, in descending order 162 from the surface, were used to describe the profile under each treatment. Since the texture of Charity clay depths of is uniform throughout the profile, of the first four soil layers were chosen to correspond to depths physical properties and were soil water evaluated content measurements. Soil physical for the first three soil layers (Chapter 2). The neutron probe method was used to monitor soil water content of the second through fourth soil layer (Chapter 3). The lower limit (LL) of plant extractable water and the drained upper limit (DUL) were determined lowest LL. water content from measured soil water contents. measured at each depth was assumed to approximate The DUL for each depth was chosen so that simulated matched the The measured values during wet periods. water contents A new water content at saturation (SAT) was calculated (Ritchie et al., 1986) whenever the DUL was altered during this fitting process. Measured and simulated water contents under the NDTMP-CST treatment compared favorably each year from 1983 to 1985 (Appendix Figures 1 to 3). Simulated water contents were within the 95 percent confidence about each intervals measured value except for those produced during the last 30- day period in 1985 (Appendix Figure 3). This descrepancy had no bearing on calculation of the stress day index for 1985. Soil water content differences measured under the (Appendix Figures 4 to 6) were duplicated by altering data as needed. year for Different the root two treatments the soil profile The LL and DUL, of soil layers 1 and 2, were lower each DTMP-NST treatment distribution than weighting values used for NDTMP-CST. factors (WR) and runoff curve numbers were used for NDTMP-CST and DTMP-NST to account for varying conditions created by each treatment. soil Profile plant-extractable soil water (PGSW) was assumed to be the same under the two treatments. 163 Dally rainfall, experiment site* maximum and minimum temperatures were recorded at the Daily solar radiation was measured at the site but complete records were available for only the 1985 field season. Solar radiation for 1983 sunshine as a starting point. relationship between Lansing, MI. Different period. and 1984 were produced using daily percent Baker and Haines percent sunshine and relationships daily were determined the insolation for East obtained for each 7-day These relationships were used to estimate daily solar radiation data for 1985 at East Lansing, MI. East (1969) Lansing and measured Estimated daily solar radiation at solar radiation at the experiment site were compared and proved to be highly correlated (r 2 - 0.935). The following predictive equation was obtained: S0LRADsc - -25.4 + ( .93)SOLRADel (17) where S0LRADsc is solar radiation at the experiment site (Swan Creek, MI) and SOLRAD^ represents solar radiation at East Lansing, MI. equation 17 are arbitrary as long as they are the same for Units for S0LRADgc and SOLRAD , . el A long term study of tillage effects on soil aeration was conducted using 100 years of generated weather data. (Richardson, 1984) produces data records from surrounding stations. records each for include only profile (DUL) soil given simulation. day of in 31 are weather generator set This data set was October used based on historic weather The original data theyear. the 16 April to water that The period for each consisted of fragmented to year. The content was initialized at the drained upper limits Appendix Table 21 for each year of the 100-year 164 Calculation of Stress Day Index Cumulative stress day Index (SDI) was calculated using the equation Introduced by Hiler and Clark (1971): n SDI - £ ( S D * csi> (18) i-1 where 1 ■ days after planting, SD^ Is the stress day factor for day 1, and CS^ is the crop susceptibility factor for day 1. Skaggs (1982) reported the following Hardjoamidjojo empirically derived and crop susceptibility factors for corn: csi csi csi Crop - 0.51 for 0 < i < 43 (19) - 0.33 for 42 < i < 81 (20) - 0.02 for 80 < i (21) susceptibility factors used here were those given in equations 19 to 21 but equation 21 was modified so that: CS1 - 0.02 for 80 < i < 121 (22) Thus, the SDI was calculated for the 120-day period after planting (i.e., n ■ 120 in equation 18). Daily stress day 0.10 m soil layer. factors were based on air porosity (Pa) of the 0 to The exchange of gases between the soil and atmosphere becomes impeded as Pa of this (1961) proposed the layer decreases. following model to Millington and describe theeffect Quirk of Pa on gaseous diffusion: Ds/Do - Pa3 *33/P2 where Ds is (23) the gas diffusion coefficient in soil, Do is the diffusion coefficient in air, and P is the soil porosity. At low air porosities, Sallam et al. (1984) found best agreement between calculated and measured 165 relative diffusion coefficients when the Pa exponent was modified as follows: Their Ds/Do - Pa3,1/P2 (24) model was used to calucalte SD^ in this investigation. Equation 24 was transformed using - L O G ^ q so that SD^ increased as Pa decreased. _3 Stress day factors were calculated only for Pa < 0.15 m m aeration was assumed to occur unimpeded at Pa > 0.15 mm -3 . The as soil final equation obtained was: SD± - -L0G10(Pa3,1/P2 ) - [-L0G10(0.153,1/P2 )] The constant on the right hand side of equation 25 was included so that SD^ * 0 at Pa ■ 0.15 m 3 m -3 . Equation 25 reduces to: - L0G1q (.152 ) - L0G10(Pa3,1) Thus, SD^ (25) calculated in this way depends only on air porosity. produced by equation 26 are demonstrated in Appendix Figure 7. (26) Values RESULTS AND DISCUSSION Evaluation of Model Modifications Two versions of CERES-Malze, using identical model inputs, were used to produce the simulated water contents Illustrated in Figure 30. contents produced by the modified version of the model Water exceeded those produced by the original version but only during excessively wet periods. During dry periods, profile soil water contents are low and the tendency for runoff to occur is diminished. Both versions of the model produce similar water balance output under dry conditions. The modified version of the model Increases the amount of water that enters the profile during the season because runoff is suppressed. soil water deficit factors dictate growth rate CERES-Maize, the water balance 24 and 25). eventual yields in modifications increased simulated corn yields for 1983 by decreasing the soil water Tables and Since deficit factors (appendix Results reported in the remainder of this section were produced exclusively by the modified version of CERES-Maize. Tillage Effects on Soil Aeration During 1983 to 1985 Simulated water contents under the NDTMP-CST and DTMP-NST treatments for the three years in which field studies were conducted are illustrated in Figures 31 to 33. primarily Differences between treatments also existed in the 0.20 to During one 0.35 differences are evident, simulated water contents under NDTMP-CST than under year, 1984, m soil layer. Where were the DTMP-NST treatment. suggested by the simulated data in Figures 31 to 33 are those demonstrated in the 0 to 0.10 and 0.10 to 0.20 m soil layers where physical changes created by tillage were most prominent. differences are slightly higher Treatment effects consistent with produced by periodic water content measurement during 1983 to 1985 (Appendix Figures 4 to 6). 166 167 0.50 0.40/-s n ro 0.300.20 0 — .10 m £ 0.500.40 0.20 5/1 NO RUNOFF WITH RUNOF 10— .20 m 8/29 Date Figure 30. Comparison of simulated water contents at two depths under the NDTMP-CST treatment during 1983 using a version of the model that allows runoff and a modified version that suppresses runoff. 168 0 .5 0 0 .4 0 0 .3 0 0 — .10 m 0 .5 0 t— A'O-.iQ'rri ' ' ‘ i— i— i— r t— r T l— i— |— i— i— i— i— i— p 0 .4 0 ? 0 .3 0 E 0.20 T v_✓ E 0 .5 0 ® 0 .4 0 T t— i— i— |— i— i— i— i— i— |— i— i— r i— r— i— T 1 0 .3 0 0.20 " I“ I I I" I 0 .5 0 0.20 5 /1 ,35—.50 m DTMP-NST NDTMP-CST “ i— i— i— 6 /3 0 i— i— 1“ 7 /3 0 8 /2 9 Date Figure 31. Comparison of simulated water contents at four depths under the NDTMP-CST and DTMP-NST treatments for 1983. 28 169 0.500.40 0.30 0.20 J 0 —.10 m i r i ii— I— i— i— i— i— i— |— i— i— i— i— i— |— r 0.50 .10— .20 m 1 T T T T 1 6 (m 3 m 3 ) 0.40 0.30 x, 0.20 J T t— m — r t— r T t— i— r T T T T T i— r T i i i 0.50 0.40 0.30 0.20 J 1— i— i— t— i— r T 0.50 .3 5 -.5 0 m t— i— i— r T T T T T T T T 0.40 0.30 0.20 5/1 DTMP-NST NDTMP-CST 5/31 Date Figure 32. Comparison of simulated water contents at four depths under the NDTMP-CST and DTMP-NST treatments for 1984. c 170 1• : • 1• 1• i ' r 1 • i " '1 i i •t • 1 —1—i—i—i—i—i—p fa : 0.20 ^ j o-^ .10—.20 m 1 1 I 0.20 rO j - i i i i | .20—.35 m • i 1 1 1 1 1 1 " ^ J 1 1 1 1 ' 1 I 1 I -------------------------, 0.20 j '.3f>-.50 m1 ................ 1 ....................‘ ' ' ’ ‘ i — DTMP-NST : i—| |NDTMP-CST , | | | r 0.20 5/1 5/31 6/30 7/30 8/^29 9/28 9/*: Date Figure 33. Comparison, of simulated water contents at four depths under the NDTMP-CST and DTMP-NST treatments for 1985. 171 The CERES-Malze model was used primarily to simulate water contents so that soil aeration under each treatment could be assessed. Nevertheless, It Is Interesting to compare measured and predicted yields for simulations illustrated in the six Figures 31 to 33 (one for each curve). The measured and predicted yields differed by only 55 kg ha * for the NDTMP- CST treatment in 1983 (Appendix Table 26). Measured remaining yields exceeded simulations predicted (Appendix values Tables 27 for each to 31). of the The five model underestimated the measured yields by an average of 8.6 percent (standard deviation ■ 1.5%) for these five simulations. suggests that CERES-Maize accounted for the This systematic deviation year-to-year variation of corn yields. Simulated air porosity (Pa) at each depth was obtained by subtracting the water content from measured values of soil porosity (Chapter 2). The seasonal variation of simulated Pa during 1983 to 1985 is demonstrated in Figures 34 to 36. only subtle The treatments produced large Pa differences water content differences (Figures 31 to 33). despite The DTMP-NST treatment increased Pa by an amount that that reflects the soil porosity increase. Note that identical soil porosities (P) were used for the 1983 and 1985 simulations (Figure 34 and 36). The measured water contents in 1984 (Appendix Figure 5) were lower than values (Appendix Figures 4 and 6). measured in 1983 and 1985 This trend is not consistent with seasonal rainfall patterns observed at the experiment site (Chapter 3, Figure 13). Soil inputs (including P) were altered for the 1984 simulations so water contents under each treatment resembled the measured values. measured that Since water contents were suspect in 1984, the Pa curves in Figure 35 172 0.40 Soil Porosity (P) — 0.52 P - 0.58 0.20 ®i 0.40 tV- 0 — .10 m 0.00 ^— r T r it — v 1r P - 0.53 P - 0.58 £ 0.20 - £ Cl .10—.20 m 0.00 0.40 ^— i— r t— r P - 0.48 P = 0.52 0.20 20—.35 m 0.00 5/1 6/30 9/28 Date Figure 34. Comparison of simulated air porosities at three depths under the NDTMP-CST (solid line) and DTMP-NST (dashed line) treatments for 1983. 173 0.40 Soil Porosity (P) - 0.50 P - 0.56 „ / I „ 0.20 ! ' r " '» r i / V 1/ A!s\±i 0—.10 m 0.00 0.40 t— i— r t— £ 0 .20 - t— i— i— i— r t— i— i— r t— i— r i/ E cl i— r 0.51 0.56 .10—.20 m 0 .0 0 0.40 = 0.48 = 0.51 0 .20 .20—.35 m 0.00 5/1 29 Date Figure 35. Comparison of simulated air porosities at three depths under the NDTMP-CST (solid line) and DTMP-NST (dashed line) treatments for 1984. 174 0.40 P - 0.52 P - 0.58 s “\ 0.20 0—.10 m 0.00 0.40 m Soil Porosity (P) = 0.53 P = 0.58 £ 0.20 £ .10—.20 m S. o.oo 0.40 T T t— i— i— | — i— r T t— i— ]— i— i— i— i— i— |— i— r T r i" i P = 0.48 P = 0.52 0.20 .20—.35 m 0.00 5/1 30 7/30 Date Figure 36. Comparison of simulated air porosities at three depths under the NDTMP-CST (solid line) and DTMP-NST (dashed line) treatments for 1985. 175 and the cumulative stress day Index (SDI) values calculated for 1984 may be unrealistic. Tillage effects on soil aeration during 1983 to 1985 were assessed by calculating the number of wet days and the SDI for each treatment 20). Air porosity fell below where wheel traffic caused aeration suggests that soil the 0.15 m 3 m -3 compaction. (Table (wet days) most frequently This indicator of soil 1984 growing season was the most stressful during the three year study as 61 wet days occured under the NDTMP-CST treatment• The number of wet days is a poor indicator of soil aeration status. is not sensitive to the degree of aeration It stress or varying crop susceptibility to stress, both of which affect the SDI. Deep tillage and controlled traffic reduced the 20). growing SDI each year (Table The 1983 season was the most stressful in terms of soil water excesses as the SDI corresponding to each treatment exceeded the values obtained for 1984 and 1985. The SDI approach produced results that are consistent with the observed seasonal rainfall patterns (Chapter 3) and yield responses to the various tillage variables (Chapter 4). by The 1983 growing season was characterized an excessively wet period during the early part of the growing season when corn is most susceptible to soil water excesses (Hardjoamidjojo Skaggs, 1982). Deep and tillage improved yields of two crops during 1983. Controlled traffic increased yields of four out of five crops grown that year, including corn. Results of this study suggest that yields of crops grown on Charity clay were influenced by soil aeration to a greater extent in 1983 than in 1984 or 1985. Alleviation of soil compaction through deep tillage and 176 Table 20. Soil aeration stress on Charity clay during 1983 to 1985 as affected by tillage. Treatment Wet Days* SDI 1983 NDTMP-CST 56 28.5 DTMP-NST 29 5.9 NDTMP-CST 61 18.4 DTMP-NST 7 1.3 NDTMP-CST 59 15.0 DTMP-NST 16 1.0 NDTMP-CST 59 20.6 DTMP-NST 17 2.7 1984 1985 3-Year avg. 1 Wet Days ■ the number of days during-the^first 120 days after planting when Pa < 0.15 m m . 177 controlled traffic minimized the aeration problem each year based on the stress day indices reported in Table 20. Long-Term Study of Tillage Effects Soil Inputs given in weather data were used Appendix in the Table 21, and 100 years of generated long-term evaluations. The frequency distribution of predicted grain yield under the two treatments are given in Figure 37. As Indicated earlier, soil water deficit factors influence yields predicted by CERES-Maize. The distributions illustrated in Figure 37 suggest that the weather data produced widely varying conditions in terms of soil water deficits. The frequency distributions of predicted yields were similar for NDTMPCST and DTMP-NST because the profile plant-extractable soil water was the same for each treatment. for both treatments. Predicted yields averaged about 8.84 Mg ha * Measured yields, averaged for 1983 to 1985, were 10.3 Mg ha * for DTMP-*JST, and 9.76 Mg ha * for the NDTMP-CST treatment. The model predicted total crop number of wet days and SDI values omitted from subsequent failure calculated comparisons because one year (Figure 37). for the same year The were the simulated soil water contents are unrealistic in the absence of plant water extraction. The number of wet days averaged 67 under NDTMP-CST for the 100-year simulation (Figure 38a). depth is less than This value suggests that Pa of the 0 to 0.10 0.15 m 3 measurement period each year. m -3 m during about 50 percent of the 120-day Wet days may occur only 20 times, on the average, under the DTMP-NST treatment (Figure 38b). The frequency distribution of SDI under the two treatments are compared in Figure 39. The SDI averaged 23.7 with conventional fall and spring tillage but ranged from 8.8 to controlled traffic produced 50.8 an (Figure 39a). Deep tillage and average SDI of about 2.7 (Figure 39b). 178 20 NDTMP-CST a: 15- 1 0 -i Frequency 5g JS2S3 : ► w . >♦♦♦♦♦«>♦;♦♦♦< ►%%♦< DTMP-NST v>%* >♦%» > > v >♦%? >♦«? v v v 0-S22 4.0 8.0 12.0 16.0 Yield (Mg h a“ ^) Figure 37. Frequency distribution for 100 years of predicted yields under two tillage treatments. 179 Frequency NDTMP-CST DTMP-NST 60 80 120 140 Wet Days Figure 38. Frequency distribution for the number of wet days under NDTMP-CST and DTMP-NST produced by 100-year simulations for each treatment. 180 Frequency NDTMP-CST w vw w w vww w w w ► % ? i S 5 ►?♦?< M ► % ? ► % ? ►:♦?< P DTMP-NST P 20 30 40 S tress Day Index Figure 39. Frequency distribution for stress day index under NDTMPCST and DTMP-NST produced by 100-year simulations for each treatment. 181 The SDI averaged 2.7 for the same treatment during the three years of field study (Table 20). The probability of benefit from deep tillage and controlled traffic can be determined using the years of simulated data. NDTMP-CST in 1983 frequency He start by the SDI of yield reductions under Fifteen SDI values occur in the class 28.5 (Figure 39a), the value calculated for the NDTMP-CST treatment in 1983. Another 18 observed values occur in classes containing SDI values of > 30. This suggests that 33 of the 99 years (33 percent) were at least as stressful excesses. assuming were due In part to Impeded soli aeration at certain times during the growing season. containing distribution of SDI produced by 99 as 1983 in terms of soil water Using the same approach, SDI for NDTMP-CST exceeded the value for 1985 (15.0) 83 percent of the time. The SDI index values factors (CS) for corn. used here were based on crop susceptibility The CS factors varied from 0.51 for the first 42- day period after planting to 0.02 for day 81 to 120 after planting. SDI approach planted at would The likely produce different results for crops that are different times or exhibit different susceptibility to aeration stress. CONCLUSIONS The water balance output of the CERES-Maize model simulated measured soil water contents under corn reasonably well. The diverse treatments, NDTMP-CST and DTMP-NST, produced similar water contents at each depth but differing air porosities. The cumulative stress day index, based on seasonal variation of air / porosity in the aeration. Deep 0 to 0 . 1 0 tillage m depth, and was a sensitive measure of soil controlled traffic improved soil aeration each year (i.e., decreased SDI). Soil water excesses under conventional £all and spring tillage may cause yield reductions on Charity clay during at least one of three years. LIST OF REFERENCES Arkin, G.F., and H.M. Taylor. 1981. Root zone modification: systems considerations and constraints p. 393-402. In G.F. Arkin and H.M. Taylor (ed.) Modifying the root environment to reduce crop stress. Am. Soc. Agric. Eng., St. Joseph, MI. Baker, D.G., and D.A. Haines. 1969. Solar radiation and sunshine relationships in the North Central Region and Alaska. N.C. Reg. Pub. 195. Minn. Agr. Exp. Sta. Tech. Bull. 262. 372 p. Erickson, A.E. 1982. Soil Aeration, p. 91-104. In P.W. Unger and D.M. Van Doren (ed.) Predicting tillage effects on soil physical properties and processes. Spec. Pub. 44. Am. Soc. Agron., Madison, WI. Feddes, R.A. 1981. Water use models for assessing root zone modifications, p. 347-390. In G.F. Arkin and H.M. Taylor (ed.) Modifying the root environment to reduce crop stress. Am. Soc. Agric. Eng., St. Joseph, MI. Hardjoamidjojo, S., and R.W. Skaggs. 1982. Predicting the effects of drainage systems on corn yields. Agric. Water Mgmt. 5:127-144. Hardjoamidjojo, S., R.W. Skaggs, and G.O. Schwab. 1982. Corn yield response to excessive soil water conditions. Trans. ASAE 24:922927,934. Hiler, E.A., and R.N. Clark. 1971. Stress day index to characterize effects of water stress on crop yields. Trans. ASAE 14:757-761. Jones, C.A., and J.R. Kiniry. (ed.) model of Maize growth and development. College Station, TX. 1986. CERES-Maize, a simulation Texas A&M University Press, Jones, C.A., J.T. Ritchie, J.R. Kiniry, and D.C. Godwin. 1986. Subroutine structure, p. 49-112. In C.A. Jones and J.R. Kiniry (ed.) CERES-Maize, a model of Maize growth and development. Texas A&M University Press, College Station, TX. Millington, R.J., and J.M. Quirk. 1961. Permeability of porous solids. Trans. Faraday Soc. 57:1200-1207. Richardson, C.W. 1984. WGEN: a model for generating variables. U.S. Dept, of Agric. Res. Serv., ARS- 8 , 83 p. daily weather Ritchie, J.T. 1985. A user-oriented model of the soil water balance in wheat. In W. Day, and R.K. Atkin, (ed.) Wheat growth and modeling. Plenum Publishing Corporation. Ritchie, J.T., J.R. Kiniry, C.A. Jones, and P.T. Dyke. 1986. p. 37-48. In C.A. Jones and J.R. Kiniry (ed.) CERES-Maize, a simulation model of Maize growth and development. Texas A&M University Press, College Station, TX. 183 184 Russell, R.S. 1977* Plant root systems: their function and Interaction with the soil* McGraw-Hill, Berkshire, England. Sallam, A., W.A. Jury, and J. Letey. 1984. Measurement of gas diffusion coefficients under relatively low air-filled porosity. Soil Sci. Soc. A m . J . 48:3— 6. Shaw, R.H. 1974. A weighted moisture stress index for corn in Iowa. Iowa State J. Res. 49(2):101-114. Shaw, R.H. 1976. Moisture stress effects on corn in Iowa in 1974. Iowa State J. Res. 50(4):335-343. Taylor, H.M., and G.F. Arkin. 1981. Root zone modification: fundamentals and alternatives, p. 3-17. In G.F. Arkin and H.M. Taylor. Modifying the root environment to reduce crop stress. Am. Soc. Agric. Eng., St. Joseph, MI. USDA, Soil Conservation Service. 1972. National Engineering Handbook, Hydrology Section 4, Chapters 4-10. Vesseling, J. 1974. Crop growth and wet soils. In J. van Schilfgaarde (ed.) Drainage for agriculture. Agronomy 17:7-37. Whisler, F.D., J.R. Lambert, and J.A. Landivar. 1982. Predicting tillage effects on cotton growth and yield, p. 179-198. In P.W. Unger and D.M. Van Doren (ed.) Predicting tillage effects on soil physical properties and processes. Spec. Pub. 44. Am. Soc. Agron., Madison, WI. Chapter 6 SUMMARY AND CONCLUSIONS Normal fall and spring tillage operations on charity clay create unfavorable physical conditions for crop growth as internal poor and soil aeration may be impeded at certain drainage critical times. Physical conditions of Charity clay were improved below the normal of plowing by depth subsoiling in the fall when it was relatively dry. physical measurements revealed that changes brought about may Is by Soil subsoiling persist through only one crop year even when post-subsoiling traffic is controlled. Results subsoiling be more beneficial than the normal fall tillage practice may also indicate that shallow chiseling after moldboard plowing. Wheel traffic associated with conventional spring tillage recompacted soil loosened by subsoiling but also increased the density of the subsoil where normal fall tillage was physical properties applied. Effects of wheel traffic on below the normal depth of plowing were evident each year but were not cumulative when applied three years in succession. The unstable surface of Charity clay proved to be extremely susceptible to wheel-induced compaction. Saturated hydraulic conductivity and pore size distribution were the most sensitive indicators of compaction in the Ap horizon. produced Subsoiling followed by controlled preplant wheel traffic the most favorable soil environment for root growth in terms of aeration. Since aeration can be impeded at times on precipitation and weekly profile soil water contents 185 Charity were clay, daily monitored to 186 determine the occurrence of this environmental combinations of primary and secondary tillage. on water content stress under various The Influence of tillage of Parkhill loam was also evaluated in 1983, the only year In which the experiment was conducted at a second site. The distribution of growing season precipitation varied greatly during the three year study at the Saginaw Valley Bean and Beet Rainfall patterns sites in 1983. during April During the precipitation was 92 and critical mm below Research Farm. May were similar at the two study June normal to August at the period of 1983, second study site (on Parkhill loam) compared to only 19 mm below normal at the Bean and Beet Research Farm. Water content of Charity clay and Parkhill loam, determined by neutron scattering, were seasonal related variation effectively However, each water of year to the rainfall patterns each year. soil water content could have been assessed more by content obtaining measured measurements at weekly more intervals frequently. verified preplant wheel traffic altered the physical conditions of the plow such that water content spring tillage than in plots wheel traffic The decreased was consistently where air traffic porosity that layer greater under conventional was controlled. accordingly controlled traffic diminished the aeration problem. Preplant indicating The primary that tillage variables had negligible effects on the water content of of Parkhill loam in 1983 and on water content of Charity clay during 1983 to 1985. Plant responses to tillage substantiate measurements which demonstrated that subsoiling improved soil bean yields compared to conditions. were fall and results of controlled physical traffic On Parkhill loam, sugarbeet, soybean and dry consistently normal the greater tillage. where subsoiling was applied This deep tillage practice may have 187 alleviated water stress on Parkhill loam where rainfall was well below normal for the June to August period in 1983 Deep tillage tended years on Charity clay. subsoiling during to increase sugarbeet yields during two of three Yields of one soybean cultivar were 1983. Yield improved by responses to deep tillage were evident only where subsolllng was applied the previous fall just as physical changes were evident only during the first crop year after subsoiling. Soil compaction created by preplant wheel traffic dependent crop responses in 1983, a year characterized by and dry June to August period. produced soila wet spring Wheel-induced compaction reduced stands on Parkhill loam but produced the highest soybean yields. The secondary tillage variables had little effect in yields of three other crops. The effects of preplant wheel traffic were more evident on Charity clay than on Parkhill loam in 1983 as controlled traffic improved seedling emergence, increased dry bean rooting, and Increased the yields of five crops. Crops were more to practices. the damaging effects Dry beans and sugarbeets wheel-induced compaction four responsive to controlled traffic on Charity clay because this soil has an unstable surface and susceptible of is therefore of excessive or untimely tillage proved to be most sensitive to as preplant wheel traffic diminished yields of these crops in 1985 as well as in 1983. Tillage effects CERES-Maize model and output of on soil evaluated further using the method. The theCERES-Maize model simulated measured soil produced porosities. were the stress day index under corn reasonably well. NST, aeration similar water water contents The diverse treatments, NDTMP-CST and water contents balance DTMP- at each depth but differing air 188 The cumulative porosity in the aeration. 0 Deep stress to 0 . 1 0 day m tillage index, based on seasonal variation of air depth, and was a sensitive measure of soil controlled traffic improved soil aeration each year (i.e., decreased SDI). Soil water excesses under conventional fall and spring tillage may cause yield reductions on Charity clay during at least one of three years. Recommendations Results of this investigation indicate that deep beneficial operation during some years on fine-textured Results of the computer soil aeration. Michigan Charity clay conditions (i.e., the final on soils where a of soils. through forage crops applied recognized problem exists. water content) may be suitable for deep cutting a Deep tillage is not feasible after harvest of some crops commonly grown in the Saginaw Valley but it should be whenever possible is simulation study suggest that subsoiling may increase yields in at least one of three years on improved tillage and are almost tillage Soil after always suitable following small grain harvest. Where normal fall tillage (i.e., moldboard plowing) is necessary, secondary tillage can be reduced or eliminated for several crops yield loss. secondary crops years. as Minimization of preplant wheel traffic associated with tillage is important for the sensitive dry bean yields of these and sugarbeet crops can be increased dramatically in some Management of problem soils must include occasional procedures without ameliorative and compaction prevention by controlling or reducing preplant wheel traffic. APPENDIX TABLES Table 1. Crop cultivars, planting dates, row spaclngs, seeding rates, and fertilizer application rates used at two study sites in 1983. 3 2 Cultivar* Crop beets Seeding rate 4 Desired population Micro­ nutrients 0 Mn,Zn 44 0 Zn m 0.51 seeds m ^ 4/28 P3901.GL422 1 5/12 0.51 3.3 H78.C79 1 5/11 0.51 2 1 420 18 0 35 0 Mn,Zn C20,SV 1 6/09 0.51 15 292 27 0 52 0 Mn,Zn Her,Mar 1 4/28 0.18 90 13 0 26 0 Mn,Zn US -H20,US-H23 2 5/10 0.51 1 1 96.9 2 2 0 46 67 B P3901.P3744 2 5/10 0.51 64.5 16 31 116 Zn H78.C79 2 5/10 0.51 2 1 420 18 0 34 29 Mn,Zn C20,SV 2 6/08 0.51 15 292 27 0 52 soybeans dry beans oats corn soybeans dry beans 3.3 64.5 — K 1 1 1 plants 96.9 Fertilizer Rates'* N band post P US -H20,US-H23 corn beets Site Planting Row spacing Date 30 2 2 kg ha * --0 62 174 152 0 Mn,Zn 1 P3901 * Pioneer hybrid 3901; GL422 = Great Lakes 422; H78 = Hodgson 78; C79 “ Corsoy 79; SV ■ Swan Valley; Her = Heritage; Mar = Mariner. 2 Site 1 = Charity clay, Saginaw Valley Bean and Beet Research Farm, Swan Creek, MI; site 2 * Parkhill loam, Ithaca, MI. 3 Sugajbeets were planted at the indicated rate but ljter thinned to a spacing ofapproximately 5 seeds m ; the seeding rate for oats is given^in kg ha 4 Actual units for plant population are 10 plants ha 5 Fertilizers were applied in a band at planting; Postemergence N wasapplied asammonium nitrate. Table 2. Herbicide program used for 1983. Herbicide Crop sugarbeets corn Pyrazon 5-amino-4-chloro-2-phenyl-3(2H)-pyridazone Diethatylethyl N-chloroacetyl-N-(2,6 -diethyl phenyl) -glycine ethyl ester 1 , 2 1 , 2 Cyanazine Alachlor soybeans dry beans dry beans oats chemical name site*- common name 1 , 2 1 2 1 Linuron Alachlor 2- [[4-chloro-6-(ethylamino)-l,3,5-triazin-2 -yl]amino]- 2 -methylpropanenitrile 2-chloro-N-(2,6 -diethylphenyl)-N -(methoxymethyl)acetamide N '-(3,4-dichlorophenyl)-N-methoxy-N-methylurea 2-chloro-N-(2,6 -diethylphenyl)-N - (methoxymethyl)acetamide Chloramben Dinoseb 2 3-amino-2,5-dichlorobenzoic acid -(l-methylpropyl)-4,6 -dinltrophenol Chloramben Dinoseb 3-amino-2,5-dichlorobenzoic acid 2 -( 1 -methylpropyl)-4, 6 -dinit rophenol Application method rate kg ha a.i. 4.5 Pre-e^ 2 . 8 Pre-e 2 . 2 Pre-e 2 . 2 Pre-e 1 . 2 Pre-e 2 . 2 Pre-e 2 . 2 3.4 2 . 2 1.7 Pre-e Pre-e Pre-e Pre-e None 1 site 1 = Charity clay, Saginaw Valley Bean and Beet Research Farm, Swan Creek, MI; site 2 » Parkhill loam, Ithaca, MI. 2 Pre-e = preemergence nonincorporated. Table 3. Crop cultivars, planting dates, row spacings, seeding rates, and fertilizer application rates used in 1984. Crop Cultivar* „ 2 Crop Year Planting Row Date spacing Seeding^ Desired^ population rate Fertilizer Rates^ N P band post - 1 beets soybeans dry beans oats 2 5/03 5/03 0.51 0.51 3.3 3.3 H78,C79 1 , 2 5/18 0.51 C20,SV 1 , 2 6/07 US-H20,US-H23 corn wheat seeds m * 4/27 m 0.51 P3901,P3744 1 , 2 1 kg ha Micro­ nutrients _ _ plants 96.9 37 64.5 64.5 58 58 2 1 420 44 0 2 0 Mn,Zn 0.51 15 292 31 0 14 Mn,Zn 1 1 Fran 2 10/20/83 0.18 135 Her,Mar 1 4/12 0.18 90 0 37 0 157 2 0 2 57 0 17 Mn,Zn 26 26 Zn Zn 0 17 none Mn,Zn 1 P3901 and P3744 = Pioneer hybrids 3901 and 3744, respectively; H78 ** Hodgson 78; C79 = Corsoy 79; SV = Swan Valley; Fran = Frankenmuth; Her = Heritage; Mar = Mariner. 2 Crop year = 1 indicates that the crop appeared only in plots where the primary tillage variables were applied the previous fall; 2 indicates that the crop appeared only in plots established for the second crop year; 1 , 2 indicates that the crop appeared in plots representing both the first and second crop year. 3 Sugarbeets were planted at the indicated rate but later thinned to a spacing ofapproximately 5 seeds m ; seeding rates for wheat and oats^are given iy kg ha-*. 4 Actual units for plant population are 10 plants ha 5 Fertilizers were applied in a band at planting; Postemergence N was applied as ammonium nitrate. Table 4. Herbicide program used for the experiment on Charity clay in 1984. Herbicide Crop sugarbeets corn common name Pyrazon 5-amino-4-chloro-2-phenyl-3(2H)-pyridazone Diethatylethyl N-chloroacetyl-N-(2, 6 -diethyl phenyl) -glycine ethyl ester Cyanazine Alachlor soybeans dry beans chemical name Linuron Alachlor Chloramben Alachlor oats None wheat None 2-[[4-chloro-6-(ethylamino)-l,3,5-triazin-2 -yl]amino]- 2 -methylpropanenitrile 2-chloro-N-(2,6 -diethylphenyl)-N - (methoxymethyl)acetamide N '-(3,4-dichlorophenyl)-N-methoxy-N-methylurea 2-chloro-N-(2,6 -diethylphenyl)-N -(methoxymethyl)acetamide 3-amino-2,5-dichlorobenzoic acid 2-chloro-N-(2,6-diethylphenyl)-N - (methoxymethyl)acetamide 1 Pre-e = preemergence nonincorporated. Application rate method kg ha a.i. 4.5 Pre-e*- 2 . 8 Pre-e 2 . 2 Pre-e 2 . 2 Pre-e 2 . 2 Pre-e 2 . 2 Pre-e 2 . 8 Pre-e 2 . 2 Pre-e Table 5. Crop cultivars, planting dates, row spaclngs, seeding rates, and fertilizer application rates used In 1985. 2 Cultivar* Crop Crop Year 3 Planting Row Date spacing Seeding rate 4 Desired population Fertilizer Rates3 N band post P - 1 beets soybeans dry beans oats 4/23 4/23 P3901,P3744 1,3 5/03 0.51 H78.C79 1,2,3 5/14 0.51 C20,SV 1,2,3 5/21 US-H20,US-H23 corn wheat 2,3 m 0.51 0.51 Fran Her,Mar 1 2 1 3 seeds m * 3.3 1 1 1 1 plants 96.9 96.9 kg ha 0 3 0 6 77 0 _ _ 14 35 Mn,B Mn,B 33 Zn 64.5 73 2 1 420 49 0 2 2 Mn,Zn 0.51 15 292 62 0 28 Mn,Zn 10/15/84 0.18 135 4/12 4/12 0.18 0.18 8 6 8 6 0 37 44 188 Micro­ nutrients 48 0 0 17 0 2 0 none Mn,Zn Mn,Zn 1 P3901 and P3744 = Pioneer hybrids 3901 and 3744, respectively; H78 » Hodgson 78; C79 » Corsoy 79; SV = Swan Valley; Fran = Frankenmuth; Her = Heritage; Mar = Mariner. 2 Crop year = 1 indicates that the crop appeared only in plots where the primary tillage variables were applied the previous fall; 2 indicates that the crop appeared only in plots established for the second crop year; 1,3 the first and third; and 1,2,3 the first, second, and third crop year. 3 Sugjrbeets were planted at the indicated rate but later thinned to a spacing of approximately 5 seeds m ; seeding rates for wheat and oats are given in kg ha . 4 Actual units for plant population are 10~ plants ha-*. 5 Fertilizers were applied in a band at planting; postemergence N for wheat was applied as ammonium nitrate; postemergence N for corn was applied by spraying a liquid consisting of 28% N between the rows. 6 Due to an error, the indicated rates of N and P were doubled for the US-H20 sugarbeets planted in plots established for the third crop year. Table 6. Herbicide program used for the experiment on Charity clay in 1985. Herbicide Crop sugarbeets corn common name Application rate method kg ha * a.i. 5-amino-4-chloro-2-phenyl-3(2H)-pyridazone 3.4 Pyrazon .Ethofumesate (+)-2-ethoxy-2,3-dihydro-3,3-dimethyl -5-benzofuranyl methanesulfonate 2 . 2 Diethatylethyl N-chloroacetyl-N-(2,6 -diethyl phenyl) -glycine ethyl ester 2 . 2 (+)-2 -ethoxy- 2 ,3-dihydro-3,3-dimethyl Ethofumesate -5-benzofuranyl methanesulfonate 0 . 8 Desmediphamf ethyl[3-[[(phenylamino)carbonyl]oxy]phenyl]carbamate Phenmedipham 3-[(methoxycarbony1)amino]phenyl(3 1 . 1 -methylphenyl)carbamate Endothal 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid 0 . 6 Cyanazine Alachlor soybeans chemical name Metribuzin Metolachlor Acifluorfen 2-[[4-chloro-6-(ethylamino)-l,3,5-triazin-2 -yl]amino]-2 -methylpropanenitrile 2-chloro-N-(2, 6 -diethylphenyl)-N -(methoxymethyl)acetamide 4-amino-6-(l,l-dimethylethyl)-3-(methylthio) -1,2,4-triazin-5(4H)-one 2 -chloro-N-( 2 -ethyl- 6 -methylphenyl)-N -( 2 -methoxy-l-methylethyl)acetamide 5-[2-chloro-4-(tri fluoromethyl)phenoxyl] - 2 -nitrobenzoic acid i Pre-e Pre-e Pre-e Post Post Post 2.5 Pre-e 2 . 8 Pre-e 0.4 Pre-e 2 . 2 Pre-e 0.3 Post Table 6 (Cont'd). Herbicide Crop common name Glyphosate Chloramben Metolachlor dry beans oats None wheat None 1 Pre-p 3 chemical name Application rate method kg ha a.i. N-(phosphonomethyl)glyclne 1.7 3-amino-2,5-dichlorobenzoic acid 2.2 2-chloro-N-(2-ethyl-6-methylphenyl)-N -(2-methoxy-l-methylethyl)acetamide 2.2 preplant nonincorporated; Pre-e 3 preemergence nonincorporated; Post 3 Pre-p Pre-e Pre-e postemergence. Table 7. Influence of primary tillage (P), secondary tillage (S), and cultivar (C) on corn grain moisture at harvest from 1983 to 1985 on Charity clay. 1983 CY1 c2 P/S CST 1984 CY1 NST CY2 CST NST 23.3 23.5 23.1 23.3 23.8 22.9 23.8 23.6 22.9 24.1 24.3 23.1 24.0 23.7 CST 1985 CY2 CY1 NST CST NST CST CY3 NST CST NST 26.2 24.7 24.2 26.5 27.6 26.1 29.5 28.0 3 P-3901 P-3744 DTMP DTCH NDTMP NDTCH 34.0Aa DTMP DTCH NDTMP NDTCH 31.5Ba 4 Statistics: 34.5Aa 29.2Aa 1983 CY1 NS ** 31.6Aa 32.3Aa 27.6Aa 27.8Aa 2 2 . 8 2 2 . 6 22.5 2 2 . 2 22.4 23.0 2 2 . 0 22.9 1984 22.7 21.7 28.7Aa 28.5Aa 29.7Aa 30.4Aa 31.4Aa 30.6Aa 29.8Aa 31.8Aa missing 28.1Aa 29.7Aa 29.8Aa 28.1Aa 31.0Aa 31.2Aa 29.5Aa 30.1Aa M H n tt «« It «• 1985 CY2 CY2 CY3 CY1 P NS NS NS S NS NS P x S NS NS NS NS ** C NS NS NS P x C NS NS NS NS S x C NS NS NS NS P x S x C NS NS NS NS LSDp(.05) 2.9 3.0 1.5 5.2 LSDs(.05) 2.4 1 . 6 1.4 2.9 5.1 1 CY1 = crop year 1; CY2 ■ crop year 2; CY3 = crop year 3. 2 P-3901 * Pioneer hybrid 3901; P-3744 = Pioneer 3744 except for 1983 when H No. 2 was Great Lakes 422. 3 Pairs of CST and NST means in each row followed by the same upper-case letter are not different using LSD as the criterion for significance. Means in each column and within the same cultivar followed by the same lower-case letter are not different. 4 *,** = significant at the 0.05 and 0.01 levels, respectively; NS = nonsignificant; LSDp(.05) = LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) = LSD for comparison of two S means at the same level of P and C. CY1 NS NS NS NS NS NS NS 1.7 Table 8. Influence of primary tillage (F), secondary tillage (S), and cultivar (C) on corn plant population from 1983 to 1985 on Charity clay. 1984 1983. CY1 c2 P/S CST CY2 CY1 NST CST NST 1985 CY2 CY1 NST CST CST NST CST CY3 NST CST NST 47.8 52.6 48.1 47.5 46.8 43.6 45.2 40.0 - 1 P-3901 P-3744 DTMP DTCH NDTMP NDTCH DTMP DTCH NDTMP NDTCH Statistics: P S P x S C 4 56.5 56.5 57.8 53.6 45.2 42.6 44.9 43.6 1983 CY1 NS NS NS ** 70.U a 72.0Aa 69.4Aa 66.5Aa .2Aab 62.6 70.7Ab 58.5Aa 65.2 66.5Aab 70.1Aa 74.9Aa 67.8Aa 73.9Aa 73.3Ab 70.4 70.4Aab 63.0Aa 64.6 67.5Aab 6 plants h a ----- 65.5 49.7 53.6 45.5 52.9 6 8 . 8 45.5 50.9 47.5 50.0 1 0 6 64.9 65.5 52.9 51.7 49.1 54.9 53.3 57.1 51.3 47.5 1984 CY1 NS * NS NS NS NS NS 9.4 CY2 NS NS NS NS NS NS NS CY1 NS NS NS NS NS NS NS 14.6 14.2 missing M N M M M N M 1985 CY2 CY3 NS NS NS NS NS NS NS P x C NS S x C NS P x S x C NS LSDp(.05) 1 2 . 0 9.2 7.5 8 . 6 LSDs(.05) 5.9 7.2 1 1 . 6 1 CY1 = crop year 1; CY2 = crop year 2; CY3 = crop year 3. 2 P-3901 = Pioneer hybrid 3901; P-3744 = Pioneer 3744 except for 1983 when C No. 2 was Great Lakes 422. 3 Pairs of CST and NST means in each row followed by the same upper-case letter are not different using LSD as the criterion for significance. Means in each column and within the same cultivar followed by the same lower-case letter are not different. 4 *,** = significant at the 0.05 and 0.01 levels, respectively; NS = nonsignificant; LSDp(.05) = LSD for comparison of two P means at the same or different levels of S and C; LSDs(.05) = LSD for comparison of two S means at the same level of P and C. > Table 9. Mean squares from analysis of variance for two measures of root density of soybeans (SB), dry beans (IB), and corn grown on Charity clay from 1983 to 1985. df SB 1983 DB df Corn df 1984 SB DB df SB 1985 df DB 198 RLD11 0.17977 0.26761 1 0.2779 0.50069 1 P‘ 1 0.02059 0.32842 1 0.85474 0.41939 2 0.11539 Error a 3 0.24722 0.2535 3 0.33262 0.46489 3 3 1.32053 0.92158* 1 0.1089 0.23990 1 0 . 0 0 2 1 0 1 0.00194 0.10901 1 0.15029 S 1 PxS 1 0.20430 0.53467 1 0.30206 0.00327 1 0.17966 0.5791 1 1 0.10143 6 Error b 4 0.3250 0.36232 0.3119 0.26122 0.30912 0.12006 6 6 5(1) 0.10033 1.94008** 2.26657** 5 D 5 3.66945** 1.36465** 5 3.0119** 5 3.10461** 5 1.99942** 0.09967 PxD 5 5 0.13413* 0.07428 0.0473 5 0.01915 5 0.03853 5 0.05116 SxD 5 0.04382 0.29740* 5 0.2103 0.08446 5 0.02998 5 0.02821 5 0.10626 5 0.05282 5 0.14329* 0.07528 0.02619 PxSxD 0.07306 0.1816 5 5 5 0.09246 0.09412 40 0.04282 Error c 60 0.05995 0.2721 60 0.04989 60 0.05803 55(5) 0.06336 KWU 1 0.019601 0.00838 0.001410 P 1 1 2.1670 0.03242 1 0.23876 1 0.34291 Error a 3 0.008384 0.01622 2 0.004833 4.3117 3 0.39089 0.03076 3 3 0.20965 1 0.000941 S 0.05899 1 0.031746 1 0.0003 1 0.00603 1 0.20064* 0.03985 PxS 1 0.010067 0.00159 1 0.010623 1 2.3654 0.37206 1 0.00209 1 0.01435 Error b 6 4 1.6814 0.005676 0.01611 0.006023 0.19078 0.00342 6 6 5(1) 0.02274 D 2 0.083961* 0.9253** 2 0.120252** 2 1.5037 0.38706** 2 0.08741* 2 0.09775 PxD 2 2 0.023923** 0.00760 0.015522 2 1.1163 0.01570 0.00976 2 2 0.02558 SxD 2 0.003231 0.02227 2 0.002047 0.6485 0.01827 2 2 0.00859 2 0.01255 2 PxSxD 0.009782* 0.00158 2 0.000117 2.8495 2 0.03453 2 0.04046 2 0.00480 Error c 24 0.01132 16 0.002625 0.004865 24 0.9000 0.04677 24 0.01579 2 2 (2 ) 0.03629 1 RLD * Root length density; RWD = Root weight density (i.e., dry weight of roots per unit volume). 2 P = primary tillage; S = secondary tillage; D = depth; *,** significant at the 0.05 and 0.01 levels, respectively; degrees of freedom enclosed in ( ) indicate the number of df lost due to missing values. Table 10. Influence of primary tillage (P), secondary tillage (S), and depth on root weight density of soybean (SB), dry bean (DB), and corn roots during 1983 to 1985 on Charity clay. 1983 DB CST NST SB Depth P/S ---m - 0.23-0.31 0.31-0.38 0.38-0.46 CST NST - 6 — DTMP NDTMP DTMP NDTMP DTMP NDTMP — — 292 146 124 — 2 2 2 185 126 156 132 114 1 1 1 105 117 LSDp(.OS ) 1 LSDs(.05) — - 1 0 202 125 122 132 115 102 -3 g cm 289 259 147 150 128 123 1984 Corn CST NST 316 241 182 215 160 155 6 8 CST NST ..-5 -3 g cm 123 126 119 167 260 75 45 136 90 136 47 41 1 0 106 99 135 126 81 *— — 350 333 195 272 166 205 1985 DB SB CST NST • *507 753 270 605 224 328 235 171 DB SB CST _ — — — 672 428 372 281 313 276 NST -3 g cm 494 472 216 381 377 332 197 209 253 337 271 145 - CST NST 6 1 0 — . — 488 208 365 208 336 161 590 160 429 505 — — _ 653 418 482 342 338 310 481 272 averaged