Influences of Agricultural Practice and Summer Grazing on Soil Compaction in Wheat Paddocks

Abstract

Agriculture in the Southern Great Plains (SGP) relies on production systems that combine yearling cattle and grazing of winter wheat. Incorporating summer legumes into the fallow period of wheat would allow longer grazing seasons and potential improvements in livestock gain, but may adversely affect soil conditions. This study examined the impacts of additional grazing during summer on soil compaction within paddocks of grazed wheat. Four 1.6 ha paddocks were used to study two systems of producing forage by conservation tillage during 1999 and 2000. Both systems combined winter and spring grazing of wheat with either grazing of an annual legume during summer (SL) or chemical fallow during summer (SCF). Enclosures (n = 2) were established in each paddock to serve as ungrazed controls. Soil compaction was measured by resistance to a cone penetrometer to 300 mm soil depth on three dates (May and December 1999, June 2000), and measures of bulk density and soil moisture were collected. Regression analyses showed a significant relationship between resistance and bulk density across agricultural practices, and separate relationships for grazing treatments. The SL agricultural practice produced greater compaction of soil than SCF below 75 mm depth, with gradual increases over the last two sampling dates. In contrast, grazing generated increases in compaction at all depths on all dates, with the largest increases noted between 50 and 100 mm. Results suggest that combining grazing of wheat with grazing legumes during the summer, under conservation tillage, may not represent sustainable management in the short term.