Integrating and Managing Oilseed Cash Cover Crops in a Corn and Soybean Rotation System.

Winter camelina (Camelina sativa L. Crantz) and pennycress (Thlaspi arvense L.) have the potential to provide ecosystem services and economic incentives when adopted as cover crops in a corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation. However, establishment efficiency of these oilseed crops in the northern Corn Belt and their impact on row crops is not well known. The objective of this study was to determine establishment success, yield, and impact of these cover crops when broadcast interseeded into standing corn (R4, R5 and R6) and soybean (R6, R7 and R8) stands ranging from mid-August to late September. A study was conducted in Ames, IA, in 2016 to determine the effect of these covers across three planting dates on soybean relayed in to it. Soybean yield averaged 4.1 Mg ha^-1 and was not affected by either cover crop. However, corn yield was 7% less with pennycress (13.1 Mg ha^-1) than camelina (14.1 Mg ha^-1). Fall establishment of oilseed plants resulted in greater success rate with later seeding dates. Fall pennycress biomass accumulation was 11% greater in soybean than corn, whereas camelina accumulated 26% more biomass in corn compared to soybean. Overall, the total spring cover crop biomass across three seeding dates in corn and soybean plots averaged 901 and 222 kg ha^-1 for pennycress and camelina, respectively, with an average spring green cover of 30% and 13% for pennycress and camelina, respectively. Pennycress and camelina yields were similar when interseeded into either corn (434 and 140 kg ha^-1, respectively) or soybean (426 and 126 kg ha^-1, respectively). However, oilseeds yield was affected by planting date and was maximized with later plantings. These preliminary results suggest that adopting oilseeds as a cover crop in a corn and soybean rotation is feasible in Iowa.