TILLAGE AND COVER CROP MANAGEMENT EFFECTS ON SOIL-WATER AND CORN YIELD

Subsoiling to alleviate compacted soil zones and planting cover crops to conserve soil water are accepted practices, but information regarding potential interactions between the two is limited. This study was designed to assess the effects of subsoiling and cover-crop management on soil water availability and corn (Zea mays L.) grain yield on Coastal Plain soils known to be responsive to in-row sub-soiling. The experiment was conducted on a Norfolk loamy sand in 1985 and a Norfolk sand in 1986, both in the family of fine-loamy, siliceous, thermic Typic Kandiudults. Factors evaluated were sub-soiling, cover crop (fallow or crimson clover [Trifolium incarnatum L.]), primary tillage (chisel plow or no-tillage) within fallow, and top-growth removal of crimson clover. Compared with fallow treatments, crimson clover depleted soil water in the surface 15 cm before corn planting by 28% in 1985 and 55% in 1986. Corn grain yield was reduced in the presence of crimson clover by 0.5 Mg ha-1 in 1985 and 0.9 Mg ha-1 in 1986. In 1985 only, grain yield reduction in the presence of crimson clover was entirely overcome by subsoiling. Averaged across cover crop and primary tillage factors, subsoiling increased grain yields by 25% (1.3 Mg ha-1) in 1985 and 86% (1.9 Mg ha-1) in 1986. Increased yields due to subsoiling were attributed to greater use of subsoil water by the corn crop. These results suggest that cover-crop desiccation should occur 7 to 10 d prior to corn planting to minimize the effects of soil water depletion under dry, early-spring conditions. Additionally, in-row subsoiling should be used on similar Coastal Plain soils responsive to deep tillage, irrespective of cover-crop use.