A 580/70R38 tractor drive tire with an aspect ratio of 0.756 and a 650/75R32 tire with an aspect ratio of 0.804 were operated at two dynamic loads and two inflation pressures on a sandy loam and a clay loam with loose soil above a hardpan. Soil bulk density and cone index were measured just above the hardpan beneath the centerline and edge of the tires. The bulk densities were essentially equal for the two tires and cone indices were also essentially equal for the two tires. Soil bulk density and cone index increased with increasing dynamic load at constant inflation pressure, and with increasing inflation pressure at constant dynamic load. In comparisons of the centerline and edge locations, soil bulk density and cone index were significantly less beneath the edge than beneath the centerline of the tires. Soil compaction is not likely to be affected by the aspect ratio of radial-ply tractor drive tires when aspect ratios are between 0.75 and 0.80.

Soil strain transducers were used to determine strain in an initially loose sandy loam soil in a soil bin beneath the centerline of an 18.4R38 radial-ply tractor drive tire operating at 10% travel reduction. The initial depth of the midpoints of the strain transducers beneath the undisturbed soil surface was 220 mm. Strain was determined in the vertical, longitudinal, and lateral directions. Initial lengths of strain transducers were approximately 118 mm for the longitudinal and lateral transducers and 136 mm for the vertical transducer. The tire dynamic load was 25 kN and the inflation pressure was 110 kPa, which was a recommended pressure corresponding to the load. In each of four replications, as the tire approached and passed over the strain transducers, the soil first compressed in the longitudinal direction, then elongated, and then compressed again. The soil was compressed in the vertical direction and elongated in the lateral direction. Mean natural strains of the soil following the tire pass were −0.200 in the vertical direction, +0.127 in the lateral direction, and −0.027 in the longitudinal direction. The mean final volumetric natural strain from the strain transducer data was −0.099, which was only 35% of the mean change in natural volumetric strain calculated from soil core samples, −0.286. This difference likely resulted from the greater length of the lateral strain transducer relative to the 69 mm lateral dimension of the soil cores. The strain transducer data indicated the occurrence of plastic flow in the soil during one of the four replications. These results indicate the complex nature of soil movement beneath a tire during traffic and emphasize a shortcoming of soil bulk density data because soil deformation can occur during plastic flow while soil bulk density remains constant.

A Trelleborg Twin 421 Mark II 600/55-26.5 steel-reinforced bias-ply forwarder drive tire at inflation pressures of 100 and 240 kPa and dynamic loads of 23.9 and 40 kN was used at 5% travel reduction on a firm clay soil. Effects of dynamic load and inflation pressure on soil–tire contact pressures were determined using six pressure transducers mounted on the tire tread. Three were mounted on the face of a lug and three at corresponding locations on the undertread. Contact angles increased with decreases in inflation pressure and increases in dynamic load. Contact pressures on a lug at the edge of the tire increased as dynamic load increased. Mean and peak pressures on the undertread generally were less than those on a lug. The peak pressures on a lug occurred forward of the axle in nearly all combinations of dynamic load, inflation pressure, and pressure sensor location, and peak pressures on the undertread occurred to the rear of the axle in most of the combinations. Ratios of the peak contact pressure to the inflation pressure ranged from 0 at the edge of the undertread for three combinations of dynamic load and inflation pressure to 8.39 for the pressure sensor on a lug, near the tire centerline, when the tire was underinflated. At constant dynamic load, net traction and tractive efficiency decreased as inflation pressure increased.

Conservation farming systems are rapidly increasing in popularity. As these changestake place, there is an obvious need to maximize the efficiency and effectiveness of the morecommon conservation farming tools. Chisel-sweep systems have an advantage over manyconservation tillage tools because they maximize the residue left on the surface for erosioncontrol while providing the tillage necessary for weed control and seedbed preparation. Theaccumulation of residue within the confines of the tillage tool is a common problem. The properclearance vertically between the soil surface and the supporting framework for the tillage deviceis necessary for the passage of residue. A coulter directly ahead of the wingtips of each leadingsweep, operating at the same depth as the sweep, reduced draft of the sweep-coulter systemup to 45% as compared to the draft of a sweep plus coulter system with the coulter operatingdirectly ahead of the sweep center. Coulters directly ahead of the wingtips of sweeps permitpassage of the sweeps through heavy residue without problems of residue clogging, althoughthere is a tendency for more residue buildup on the sweep shanks when wingtip coulters areused.

Extensive cone index measurements were used to evaluate the soil condition resulting from five years of a cotton ( Gossypium hirsutum L.) wheat ( Triticum aestivum L.) double cropping experiment. Four cotton tillage systems including a conservation tillage practice of in-row subsoiling and planting into wheat residue stubble and two traffic systems were analyzed. The USDA-ARS Wide-Frame Tractive Vehicle (WFTV) was used to control traffic in the experimental plots. Contour graphs of cone index were used to determine differences in tillage and traffic systems. Traffic was found to reconsolidate soil that was initially completely disrupted to a 0.51-m depth into a soil condition similar to one that had never received a subsoiling treatment. Traffic was also found to decrease the total soil volume estimated for root growth using a 2 MPa limiting cone index value, hut not the maximum rooting depth beneath the row, when an annual in-row subsoiling practice was used.

Cotton ( Gossypium hirsutum L.) has been grown continuously on many of the silt-loam and silty-clay loam soils of Alabama's Tennessee River Valley for over a hundred years. For many of the farms in the region, conservation tillage is the only practical option available to meet soil conservation compliance guidelines, however. yields with no-tillage have not been competitive to conventional tillage on these soils. In 1995 we began a study to develop a conservation tillage system for these soils that would improve soil quality while maintaining yield levels. The study is located at the Alabama Agricultural Experiment Station’s Tennessee Valley substation. Belle Mina, AL on a Decatur silt loam. The experimental design is a randomized complete block of four replications. Treatments ate: 1) fall ridging with subsoiling, 2) fall ridging without deep tillage, 3) flat planting with subsoiling, 4) flat planting without deep

A 580/70R38 radial-ply tractor drive tire was operated at two dynamic loads and two inflation pressures at 10% travel reduction on a sandy loam with loose soil above a hardpan. Soil-tire interface pressures on the face of a lug were measured as the lug passed through the soil-tire contact zone. Soil-tire interface pressures were concentrated more at the middle of the lug and at the edge of the,tread than near the centerline of the tire when the tire inflation pressure was 40 kPa and the corresponding correct load was used. When the inflation pressure was 120 kPa and the corresponding correct load was used, the interface pressures were distributed more uniformly among the three locations on the lug. Overinflation caused relatively high interface pressures at the middle of the lug and near the tire centerline, and caused the length of the footprint and the footprint area to be relatively small. When the tire was underinflated, greater interface pressures were concentrated at the edge of the tread and the length of the footprint and the footprint area were relatively large. Distributions of soil-tire interface pressures on lugs of a radial-ply tractor drive tire on loose soil are more uniform if the tire is operated at a combination of dynamic load and inflation pressure recommended by the manufacturer than if the tire is overinflated underflated.

Field traffic by heavy agricultural machinery can cause serve structural degradation of arable land. This may result in surface runoff, restricted availability of water, oxygen and nutrients to plant roots and therefore in reduced crop yields. In order to prevent these impacts and to develop appropriate counter-measures the complete compaction process must be understood. In this study the effect of increasing dynamic loads on the stress and strain relationship was examined using a stress state transducer (SST) attached to a displacement transducer system (DTS). Three different dynamic loads, ranging from 13.2 to 25.3kN, were applied each by two passes on a firm sandy loam (Typic Kandiudults) at 10% wheel slip. During the first pass the calculated major principal (σ1), mean normal (MNS) and octahedral shear stresses (OCTSS) increased significantly with increasing dynamic loads. For the second pass in contrast to these calculated stress values, except the major principal (σ1), were not affected by the applied dynamic loads. While the vertical displacement of the transducer during the first pass was more than doubled with each dynamic load step, the soil volume element above the transducer was vertically deformed at a constant rate of 25%, independent of the dynamic load. Since no further vertical deformation of this soil volume element was induced by the second pass and additional vertical soil movement was detected, soil compaction is expected to progress to deeper soil layers as the dynamic load and the wheeling frequency increases. Thus the reduction of wheel loads and the avoidance of repeated wheeling events in one tire track may contribute to a sustainable land management of firm soils.

Soil compaction due to traffic and natural reconsolidation limi ts the abilit y of crop roots to expand into deep zonesof moistureavailabilit y. This study was conducted to determine whether the total absence of traffi c substantially improved the resulting soil condition. Extensive cone index measurement swereused toevaluatethesoil strength resulting from 5 years of a cotton (Gossypi um hirsutum L.)-wheat (Triticum aestivum L.) double cropping experiment. Four cotton tillage systems, including a conservation tillage practice of in-row subsoiling and planting into wheat residue stubble, and two traffi c systems were analyzed. The USDAARS Wide-Frame Tracti ve Vehicle was used to control tra ff ic in the experimental plots. Contour graphs of cone index were used to determine differences in tillageand traff ic systems. Traffic was found to reconsolidate soil that was initially completely disrupted to a 0.51 m depth into a soil condition similar to one that had never received a subsoiling treatment. Traffic was also found to decrease the total soil volume estimated for root growth using a 2 MPa limitin g cone index value, but not the maximum rooting depth beneath the row, when an annual in-row subsoiling practicewasused. Soil compaction plaguesmany partsof theworld and affects many different crops. In the southeaster n part of the United States, cotton has been found to be particularl y susceptibl e to soil compaction (Cooper et al., 1969). Where soil compaction isaproblem, subsoilinghasbeenfound to help alleviate it (Campbel et al., 1974). Subsoiling severely compacted soil provides increased rooting depth that helps the plants withstand short-term drought conditions prevalent during the growing season in the southeastern United States. Soils in this region are subsoiled to a depth of between 0.3 and 0.5 m on an annual basis. Thisisnecessar y becauseof wheel trafficand natural forces that cause this soil to reconsolidate. Identifying the major cause of soil compaction is difficul t becaus e of the interaction of wheel traffic and natural forces. The use of the Wide Frame Tractive Vehicle (Fig. 1) (Monroe and Burt, 1989) at the National Soil Dynamics Laborator y allows experi ments to be conducted to determine the amount of soil compaction caused by wheel traffic versus the amount of soil compactioncausedby natural forces. USDA-ARS, National Soil Dynamics Lab., P.O. Box 3439, Auburn, AL 36831-3439. Received 28 Aug. 1997. *Corresponding author (rlraper@eng.auburn.edu). 131 RAPER ET AL.: USING IN-ROW SUBSOILING TO MINIMIZE SOIL COMPACTION Figure 1. Wide-Frame Tractive Vehicle used at the USDAARS National Soil Dynamics Laboratory to study the effects of traffic-free zones on soil compaction. This machine spans a 6-m growing zone that can then be kept completely free of wheel traffic unless a traffic treatment is specified. This vehicle operates on raised traffic paths and facilitates research to determine the effects of traffic and tillage on soil condition without confounding effects from nearby traffic. MATERIALS AND METHODS An experiment was conducted between 1987 and 1991 on coastal plains soils at the Alabama Agricultural Experiment Station, Auburn University, Agricultural Engineering Research Farm at Shorter, AL. The soil used was a CahabaWickham-Bassfield sandy loam complex (Typic Hapludults) that contained a well-developed 0.08 to 0.15 m thick hardpan at a 0.2 to 0.3 m depth. The Cahaba soil is a fine-loamy, siliceous, thermic Typic Hapludult. The Wickham soil is a fineloamy, mixed, thermic Typic Hapludult. The Bassfield soil is a coarse-loamy, siliceous, thermic Typic Hapludult. Prior to starting the experiment, wheel traffic was run in a moldboard plow furrow incrementally across the field at a 0.2 m depth to reduce the natural variation in the depth and thickness of the hardpan. A split-plot experiment using cotton and wheat as a double crop was designed with four replications. The main plots were (i) conventional traffic and (ii) no traffic. The subplots contained various common cotton tillage systems including: (i) complete surface tillage (disked and field cultivated) and annual in-row subsoiling to a 0.4 m depth and planting (disk, field cultivate, in-row subsoil and plant); (ii) initial complete disruption of hardpan in 1987 (but with no annual subsoiling thereafter), complete surface tillage, and planting (complete disruption in 1987, disk, field cultivate, and plant); (iii) complete surface tillage, and planting (disk, field cultivate, and plant); and (iv) in-row subsoiling to a 0.4 m depth (strip-tillage) with no surface tillage (in-row subsoil and plant). The initial complete disruption treatment (complete disruption in 1987, disk, field cultivate, and plant) was accomplished by using a V-frame subsoiler on 0.25 mcenters operating to a 0.51 mdepth. A KMC 1 in-row subsoiler planter was used to plant cotton into the wheat stubble/residue in the strip-tillage treatment (in-row subsoil and plant) and to plant the annual subsoiling treatment. The same planter with the subsoilers removed was used to plant the remaining tillage systems. The Wide Frame Tractive Vehicle was used for all tillage treatments, even in plots that received traffic. All traffic treatments were applied with a John Deere 4440 or a high clearance sprayer. These machines would have been used had the Wide Frame Tractive Vehicle not been available. All plots were eight rows in width and four-row equipment was assumed to apply the correct traffic treatments. Recommended weed and insect control practices were used throughout the growing season for all plots. Cotton (McNair 220) was planted in 0.76 m rows at 220 000 seeds/ha. At the end of the 5-year experiment, penetrometer readings were taken with an automatic recording penetrometer to determine changes in soil condition during this time. The penetrometer with base area of 130 mm 2 (ASAE, 1991), and mounted on the Wide Frame Tractive Vehicle was used to sample each subplot at five different locations. At each location, five penetrations were made, starting from the row middle on the untrafficked side of the row, and moving in 0.19 m increments across the row into the trafficked row middle (corresponds to traffic middle in treatments that received traffic). This sampling procedure allowed both tillage and traffic treatments to be analyzed. Four replications Use of a company name does not imply USDA approval or recommendation of the product or company to the exclusion of others which may be suitable. 132 JOURNAL OF COTTON SCIENCE, Volume 2, Issue 3, 1998

Trenches placed midway between rows were filled with a mixture of soil, cellulose material, and poultry litter. Soybeans and grain sorghum were grown in rows adjacent to the trenched areas for multiple years. Results showed that a trenching effect, with or without the presence of cellulose, significantly increased plant yields, particularly in dry years. Cone index measurements taken three years after the trenches were created showed no sign of hardpan consolidation from natural forces.

Soi l compactio n du e t o traffi c an d natural reconsolidatio n limit s th e abilit y o f cro p root s to expan d int o dee p zone s o f moistur e availability . This stud y wa s conducte d t o determin e whethe r th e total absenc e o f traffi c substantiall y improve d the resultin g soi l condition . Extensiv e con e index measurement swer euse dt oevaluat eth esoi lstrength resultin g fro m 5 year s o f a cotto n (Gossypium hirsutu m L.)-whea t (Triticu m aestivu m L. ) double croppin g experiment . Fou r cotto n tillag e systems, includin g a conservatio n tillag e practic e o f in-row subsoilin g an d plantin g int o whea t residu e stubble, an d tw o traffi c system s wer e analyzed . Th e USDA­ AR S Wide-Fram e Tractiv e Vehicl e wa s use d to contro l traffi c i n th e experimenta l plots . Contour graph s o f con e inde x wer e use d t o determine difference s i n tillag e an d traffi c systems . Traffi c was foun d t o reconsolidat e soi l tha t wa s initially completel y disrupte d t o a 0.5 1 m dept h int o a soil conditio n simila r t o on e tha t ha d neve r receive d a subsoilin g treatment.� Traffi c wa s als o foun d to decreas e th e tota l soi l volum e estimate d fo r root growt h usin g a 2 MP a limitin g con e inde x value , but no t th e maximu m rootin g dept h beneat h th e row, whe n a n annua l in-ro w subsoilin g practic e wa s used.

A 580/70R38 tractor drive tire with an aspect ratio of 0.756 and a 650/75R32 tire with an aspect ratio of 0.804 were operated at two dynamic loads and two inflation pressures on a sandy loam and a clay loam with loose soil above a hardpan. Soil stresses were determined just above the hardpan beneath the centerlines and edges of the tires. Rut depths were measured at the centerline and edge of each tire track. The octahedral shear stress and rut depth were nor significantly different for the tires. The peak octahedral normal stress was not significantly different for the two tires when the dynamic loan was 17.2 kN, but was significantly greater for the 650/75R32 tire when the dynamic load was 30.9 kN, Soil stresses and rut depths increased with increasing dynamic load at constant inflation pressure, and with increasing inflation pressure at constant dynamic lend. Net traction and tractive efficiency decreased with increasing inflation pressure at constant dynamic load. At constant inflation pressure, tractive efficiency increased with increasing dynamic load. In comparisons of the centerline and edge locations, soil stresses were significantly less beneath the edges than the centerlines of the tires. Ratios of the mean stress beneath the centerline To the mean beneath the edge for four combinations of dynamic load and inflation pressure ranged from, 2.18 to 3.77 for the peak octahedral normal stress and 1.76 to 3.18 for the corresponding octahedral shear stress. Ratios of the rut depth at the centerline to the edge ranged from 1.04 to 1.49. In summary, for these two tires with their slightly different aspect ratios, no fundamental differences were found that would clearly indicate that one tire was better than the other.

Stress state transducers (SSTs) were used to determine the orientation of the major principal stress, σ1, in soil beneath the centeline of an 18.4R38 radial-ply R-1 drive tire operated at 10% slip. Two soils, a sandy loam and a clay loam, were each prepared twice to obtain two density profiles. One profile of each soil had a hardpan and the soil above the hardpan was loose. The soil in the second profile was loosely tilled. The stress state was determined at a depth of 358 mm in the sandy loam and 241 mm in the clay loam soil. The tire was operated at two dynamic loads (13.2 and 25.3 kN), each at two levels of inflation pressure (41 and 124 kPa). When the orientation of σ1 was determined directly beneath the axle, the mean angles of tilt in the direction of travel ranged from 6 to 23 degrees from vertical. Inflation pressure did not significantly affect the angle when the dynamic load was 13.2 kN in the sandy loam soil, and neither inflation pressure nor dynamic load significantly affected the angle in the clay loam soil. When the dynamic load was 25.3 kN in the sandy loam soil, the orientation of the major principal stress determined directly beneath the axle was tilted significantly more in the direction of travel when the tire was at 41 kPa inflation pressure than when at 124 kPa. These changes in stress orientation demonstrate the importance of measuring the complete stress state in soil, rather than stresses along only one line of action. The changing orientation of σ1 as the tire passes over the soil indicates the soil undergoes kneading and supports future investigation of the contribution of changes in stress orientation to soil compaction.

Soil stresses were determined just above a hardpan beneath the centerlines of tires representative of front and rear tires of a mechanical front wheel drive (MFWD) tractor with dual rear tires. Rut depths were measured at the centerline of each tire track. A 14.9R30 R-1 front tire and an 18.4R42 R-1 rear tire were operated on a sandy loam and a clay loam soil with loose soil above hardpans in soil bins, using three combinations of dynamic load and inflation pressure representative of a tractor hitched to a row-crop planter. When a tractor of this type is used with either an integral planter with liquid chemical carried on the tractor, or a towed planter without liquid chemical carried on the tractor, the front tires cause greater soil stresses and rut depths than the rear, so the front tires are likely to compact the soil more than the rear tractor tires. A tractor configured for use with a towed planter without liquid chemical carried on the tractor generates lesser soil stresses and rut depths, and therefore is less likely to compact soil beneath the tractor tires than a tractor configured for an integral planter with liquid chemical carried on the tractor.

Soil stresses were measured under a 18.4R38 R-1 radial-ply tractor tire, operated at two levels each of dynamic load and inflation pressure. Stress state transducers were placed at two depths beneath the centerline of the path of the tractor tire in two different compaction profiles in each of two soils. Peak soil stresses and soil bulk density increased with increases in both dynamic load and inflation pressure.

This chapter reviews management-practices needed for developing disposal systems using organic wastes as resources using information from the literature and studies conducted by USDA-ARS and Auburn University. Application of noncomposted organic wastes into agricultural soils accomplishes the composting process in situ because microorganisms incorporate C and other elements into soil organic matter and valuable nutrients are returned to the soil where they originated. The infrastructure needed for the collection, storage, and transport steps in municipal solid waste management by municipalities. Effective weed control with soil-applied herbicides is dependent on a sufficient concentration of herbicide being available in the soil solution. Amending soil with newsprint and different N sources enhanced microbial populations and activity in comparison to nonamended soil. There was a rate response of fungal populations to the carbon/nitrogen (C/N) ratio, where populations increased with increasing C/N ratio. A newsprint medium was used to detect microorganisms that could use newsprint as a sole source of nutrients.

A finite element modelling technique is being developed as a management tool that can be used to predict and avoid excessive soil compaction. Values of normal stress between a rigid wheel and the soil were obtained using an instrumented bar across the width of the wheel. These values were used to apply loads to the finite element model. A non-linear stress-strain relationship was used that shows that soil compaction is a function of both normal and shearing stress. The linear-elastic parameters, Young's Modulus and Poisson's ratio, are updated at small increments of load to follow the non-linear stress-strain relationship closely. Values of octahedraI normal (mean normal) and major principal stress are predicted accurately in some situations but not at the high load condition in an initially uniformly loose soil profile.