Eddie C. Burt

Conservation Tillage and Traffic Effects on Soil Condition

The soil condition resulting from a five-year cotton-wheat double cropping experiment in a sandy loam Coastal Plain soil was investigated using intensive measurements of cone index and dry bulk density. Four tillage treatments including a strip-till (no surface tillage with in-row subsoiling) conservation tillage practice were analyzed. The traffic was controlled in the experimental plots with the USDA-ARS Wide-Frame Tractive Vehicle. Besides the environmental benefits of maintaining the surface residue, the strip-till treatment decreased cone index directly beneath the row, decreased surface bulk density, increased surface moisture content, decreased energy usage, and increased yields. Controlled traffic was beneficial only when in-row subsoiling was not used as an annual tillage treatment. Although differences in soil condition were seen beneath the row middles where traffic occurred, this did not affect the soil condition directly beneath the row.

SOIL STRESSES UNDER A TRACTOR TIRE AT VARIOUS LOADS AND INFLATION PRESSURES

Abstract 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.

The effects of reduced inflation pressure on soil-tire interface stresses and soil strength

Abstract Inflation pressures as low as 41 kPa have been recommended by agricultural tire manufacturers for minimizing an oscillatory vibration problem, commonly called “power hop”. Other benefits of these lower inflation pressures might include decreased soil-tire interface pressures, increased tire performance, and decreased soil compaction. Measurements of soil-tire interface stresses were made at four positions on the lugs and a three positions between lugs on an 18.4-R38 R-1 radial factor tire operated at four combinations of dynamic load and inflation pressure. These measurements showed that as inflation pressure increased, the soil-tire interface stresses near the center of the tire increased, while the stresses near the edge of the tire did not change. The increased stresses near the center of the tire were also transferred to the soil as a compaction increase sensed with the cone penetrometer. “Correctly” inflated tires (i.e. lower inflation pressures) also improved net traction and tractive efficiency.

Effect of total load on subsurface soil compaction.

ABSTRACT TWO different size tires carrying unequal total loads that resulted in approximately equal soil surface pressures were run over soil pressure transducers buried at 18-, 30-, and 50-cm depths. The larger tire consistent-ly produced higher soil pressures at these depths. Froehlichs equation approximately described the soil pressure distribution in both a sandy soil and a clay soil with uniform density profiles. However, when a com-pacted layer was inserted in the density profile, this equation was no longer suitable. The data indicated no simple relationship between soil pressures and bulk densities.

Inflation Pressure and Dynamic Load Effects on Soil Deformation and Soil-tire Interface Stresses

An 18.4 R38 R-1 radial tractor tire at inflation pressures of 41 and 124 kPa and at dynamic loads of 13.1 and 25.3 kN was evaluated to determine the effects of the new load-inflation pressure tables on soil deformation and contact stresses. Measurements of rut width and deformed rut area were conducted with a profile meter. Soil-tire interface stress measurements were also made to determine stresses occurring between the tire and the soil and to determine the tire footprint length. Inflation pressure and dynamic load effects were found on rut width, contact length, and contact area. Dynamic load effects were also found on deformed rut area. Increased levels of soil-tire interface stress was found near the center of the tire when inflation pressure or dynamic load was increased.

Some Comparisons of Average to Peak Soil-Tire Contact Pressures

Comparisons are made among several methods of determining the contact pressure between a tire and the soil. Results show that on compacted soils the peak pressures measured at the soil-tire interface are much greater than mean pressures determined from measure-ments and much greater than pressures calculated by dividing the dynamic load by contact area. On uncompacted soil, peak pressures are almost equal to the inflation pressure.

Total axle load effects on soil compaction

Abstract Theoretical and applied research has shown that the pressure at a point in the subsurface soil is a function of both the surface unit pressure and the extent of the area over which it is applied (total load). Thirty years ago, most of the soil compaction from vehicle traffic was in the plow layer and was removed by normal cultural practices. As equipment has increased in size and mass, machine designers have increased tire sizes to keep the soil surface unit pressure relatively constant. However, the increase in total axle loads is believed to have caused an increase in compaction at any given depth in the soil profile, resulting in significant compaction in the subsoil. Two tires of different sizes, a standard agricultural tire and a flotation tire were used to support equal loads. Soil pressures were measured at three depths in the soil profile directly beneath each of the tires. Two soils were used and each was prepared first in a uniform density profile, and then they were prepared with a simulated traffic pan (layer of higher density) at a depth of approximately 30 cm. Results showed that the presence of a traffic pan in the soil profile caused higher soil pressures above the pan and lower pressures below it than was the case for a uniform soil profile. The soil contact surface of the flotation tire was approximately 22% greater than the agricultural tire. The greater contact surface did reduce soil pressures at the soil surface, of course, but the total axle load was still the dominant factor in the 18–50 cm-depth range used in this study.

Tire lug height effect on soil stresses and bulk density

Soil stresses and increases in soil bulk density were measured beneath the centerline of one new 18.4R38 radial-ply R-1 tractor tire and two similar tires with lug heights of 55% and 31% of the new tire lug height. Each tire was operated with an inflation pressure of 110 kPa, a dynamic load of 25.0 kN and 10% slip. Soil stress state transducers (SSTs) measured the stresses at three depths in both a hardpan soil profile and a uniform soil profile, each in a sandy loam and a clay loam soil. The initial depths of the SSTs ranged from 164 to 288 mm. Analysis of the original soil stress data showed that lug height did not significantly affect the peak octahedral normal stress or its corresponding octahedral shear stress. When outliers were removed from the peak stress data, however, lug height significantly affected the octahedral normal stress in the sandy loam soil. In the uniform profile of the sandy loam and in the hardpan profile of the clay loam, the new tire generated the greatest bulk density increase, which was significantly greater than the bulk density increase caused by the 55% tire. In the sandy loam with the hardpan profile, the 55% lug height tire generated a significantly greater bulk density increase than either the new or 31% tire.

Soil stress state orientation beneath a tire at various loads and inflation pressures

Abstract Stress state transducers (SSTs) were used to determine the orientation of the major principal stress, σ 1 , 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 σ 1 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 σ 1 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.

Multiple pass effects of skidder tires on soil compaction

ABSTRACT THE effects of tire size, dynamic load, inflation pressure, and multiple passes on bulk density varied significantly with soil type. The biggest changes in bulk density occurred between the pre-test soil condition and the first pass. The results of this study also indicated that bulk density values are reduced by lowering inflation pressure and increasing tire size