Effects of Animal Traffic on Soil Compaction in Wheat Pastures

Grazing of hard red winter wheat ( triticum aestivum L.) in the U.S. southern Great Plains during the fall and winter, followed in the summer by the harvesting of grain, has been of great economic importance. With the increase in conservation tillage, however, there is growing concern that the compaction effects grazing has on the soil may not be eliminated by subsequent tillage. This study was conducted to quantify the extent to which soil compaction occurs as a result of animal traffic on wheat pasture. Of the three locations that were evaluated in the 1986–1987 growing season, two were on a silt loam soil and the third a sandy loam. Cattle ( Bos taurus ) grazed wheat until the early joint stage of growth, and measurements of soil strength, soil moisture, and bulk density were taken before initiation of grazing and immediately after grazing termination. Bulk density measurements and gravimetric soil moisture evaluations were made at 1.2 in. increments through the soil profile to a depth of 16.5 in. Data for soil strength evaluation, using a mechanical cone penetrometer, were collected at 0.8 in. increments also to a depth of 16.5 in. Increases in both the bulk density and the soil strength of the grazed areas were found in all three sites, although the depth to which the differences were measured varied from site to site. Animal traffic increased bulk density by as much as 16% and soil strength by 270% in surface zones. In the sandy loam soil, the bulk density was increased to a depth of 8 in. and the soil strength to 12 in.; while in the silt loam soils, the bulk density was increased only 5 in. These data indicate that compaction does result from grazing wheat pasture and may extend to a depth where some tillage practices may not eliminate it. The possible effects that this compaction may have on wheat growth and its yield, and the tillage practices necessary to alleviate this compaction require further study.