Submitted to: Terramechanics Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2008
Publication Date: 4/6/2009
Citation: Way, T.R., Kishimoto, T., Torbert III, H.A., Burt, E.C., Bailey, A.C. 2009. Tractor tire aspect ratio effects on soil bulk density and cone index. Terramechanics Journal. 46(1):27-34. Interpretive Summary: Soil compaction limits crop roots from reaching more soil to access water and nutrients, and reduces rates of water infiltration into soil, resulting in increased soil erosion. Effects of tractor tire dimensions, air pressures and the amount of weight carried per tire, on soil compaction must be determined so soil compaction can be reduced. Soil compaction measured by changes in the soil density and indicated by the force needed to push a small steel cone down through the soil, was found to decrease as the tire air pressure decreased and as the weight carried by the tire decreased. The soil density and the cone penetration force beneath the centerline of the tire were considerably greater than values beneath the edge of the tire tread, indicating greater soil compaction beneath the centerline than the edge. Soil density and cone penetration force were not affected by the ratio of cross-sectional height to width, known as the aspect ratio, of two tires. The aspect ratio of one tire was typical of tractor drive tires that have been used for many years in the U.S. The second tire had a lower aspect ratio, typical of tires that have become increasingly popular in the U.S. Increases in crop productivity and decreases in soil erosion are expected to occur if the weight carried per tractor tire is minimized and the tire air pressure is set at the correct pressure to match the weight.
Technical Abstract: 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.