No-tillage soybean performance in cover crops for weed management in the western Corn Belt

Frequency of soil moisture depletion and subsequent crop yield reduction re sulting from water use by cover crops is unclear. Effect of cover crop resi dues and irrigation on soybean emergence, canopy volume, grain yield, and s oil moisture in eastern Nebraska were determined. Cover crop treatments inc luded five common species and a bare soil control. Precipitation treatments included rainfed conditions and weekly irrigation events of 18 mm (0.7 in) in June and July. Above-normal May rainfall in 1995 and 1996 resulted in s imilar percent volumetric soil water contents (%VSWC) in the surface 15.2-c m (6.0-in) soil layer. Soybean emergence was unaffected by residue dry matt er levels below 3,170 kg/ha (2,830 lb/ac). Early-season soybean growth was similar across all treatments; however cover crop biomass greater than 2,17 0 kg/ha (1,940 lb/ac) reduced soybean canopy volume 33 to 44% during mid-se ason droughts. Yields were highest when stand densities were maintained and weeds were suppressed. This research develops a greater understanding of h ow cover crop residues influence soybean performance, ultimately reducing r eliance on postemergent herbicide use for weed control in no-tillage system s.