Intensifying Production in the Northern Corn Belt By Incorporating Cash Cover Crops.

Relay cropping soybean with the winter oilseeds, camelina (Camelina sativa L. Crantz) and pennycress (Thlaspi arvense L.) in corn and soybean rotations in the northern Corn Belt, USA may be economically viable. However, questions remain regarding the optimum time to interseed these covers into standing corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Therefore, a multi-location field study with sites in Iowa, Minnesota, and North Dakota was initiated in 2016 to evaluate cover crop establishment, yield, and impact on relayed soybean across three planting dates ranging from late August to late September. Preliminary results indicated that broadcast interseeding did not affect corn and soybean yields which averaged 14.78 and 4.02 Mg ha^-1, respectively. Although cover crop stand establishment in the fall was best with earlier planting dates, cover crop biomass and green cover averaged 50% lower when broadcasted in standing corn compared with soybean. Although fall establishment in corn was less than in soybean, spring biomass and green cover were not significantly different when broadcasted into corn (1071 kg ha^-1 and 21.6%, respectively) or soybean (697 kg ha^-1 and 22.2%, respectively). Overall, oilseed yields were low but later planting dates increased yields by nearly 200 kg ha^-1. There was not a difference in yield when planting pennycress and camelina into corn (466 and 184 kg ha^-1, respectively) compared with soybean (386 and 143 kg ha^-1, respectively). Although yields were less, camelina seed oil content (335 g kg^-1) was greater than pennycress (309 g kg^-1), and was maximized with later planting dates and when broadcasted into corn. Results indicate that establishing winter oilseeds as cover crops is feasible in corn and soybean rotations in the northern Corn Belt. However, more work is needed to determine whether winter oilseed yields can be improved for harvest as cash cover crops.