Integrating Cover Crops into Corn-Soybean Rotations in the Upper Midwest.

Cover crops can provide economic and ecological benefits in annual cropping systems, but they are challenging to establish in corn-soybean rotations in the upper Midwest due to the limited growing season. Three planting methods were compared to establish cover crops (winter rye, red clover, hairy vetch, field pennycress, and a mixture of oat, pea, and tillage radish) via interseeding into corn at the seven leaf collar stage at two sites in southern Minnesota in 2014 and 2015. Planting methods included directed broadcast into the inter-row, directed broadcast with light incorporation, and a high-clearance drill. The high-clearance drill resulted in greater fall cover crop biomass than directed broadcast for all species except pennycress, and the drill and broadcast with incorporation methods increased red clover and hairy vetch spring biomass compared to directed broadcast without incorporation. Cover crops did not affect corn grain or silage yield; however, the subsequent soybean yield was reduced 10% at one location when hairy vetch was not completely terminated prior to planting. Soil nitrate-N in the spring was reduced by winter rye at both locations and by red clover, hairy vetch, and pennycress at one location. In all cases of soil nitrate-N reduction, cover crops produced greater than 390 kg DM ha^-1 of biomass in the spring prior to termination. This work supports that cover crops can be interseeded into corn at the seven leaf collar stage in the upper Midwest to reduce soil nitrate-N while maintaining main crop production, but effective termination is important to avoid risk of reducing soybean yield.