Interactive Effects of Cover Crop and Corn Residue Removal on Rainfed and Irrigated Corn Yield.

Many studies have evaluated the impacts of cover crops or crop residue removal on crop yield. However, few studies have evaluated the effects of cover crops after residue removal under both rainfed and irrigated systems. Cover crops may maintain or improve soil productivity after residue removal. We studied the effect of cover crop termination dates, corn residue removal, and their interactions on corn yield in both rainfed silty clay loam and irrigated silt loam sites in Nebraska. The treatments were five corn residue removal rates of 0, 25, 50, 75, and 100% after corn harvest and three winter cereal rye (Secale cereale L.) cover crop treatments [no cover crop, early termination (30 d before planting) and late termination (within 7 d of planting)] arranged in a randomized complete block design with four replications. The study was established in fall 2013 and data were collected in 2014 and 2015 on corn grain yield and cover crop biomass yield. At both sites, treatments had no effect on corn yield in 2014. In 2015, at the rainfed site, late termination cover crops reduced grain yield compared with control (16.1 versus 15.4 Mg ha^-1). In 2015, at the irrigated site, both cover crop and residue removal affected grain yield. The no cover crop plots had greater grain yield compared with late termination. The 0% residue removal had lower yield (14.8 Mg ha^-1) compared with 75% removal (16.9 Mg ha^-1). Cover crop biomass was greater with late termination of cover crops compared with early termination. Our study suggests that residue removal may reduce corn yields in rainfed sites but may increase yields in irrigated sites. It also suggests that late termination of cover crops may reduce corn yield in both rainfed and irrigated sites.