Establishing Cover Crops in Standing Corn in the Upper Midwest.

Cover crops can provide several ecological services in annual crop rotations, including reductions in agricultural runoff and N loss, but have not been widely implemented in the upper Midwest due to challenges in establishment with the short growing season. A study was initiated in 2014 to investigate the suitability of five cover crop options (cereal rye (Secale cereale), red clover (Trifolium pratense), hairy vetch (Vicia villosa), field pennycress (Thlaspi arvense), and a mixture of oat (Avena sativa), pea (Pisum sativum), and tillage radish (Raphanus sativus)) planted into V7 corn via three interseeding methods (a multi-purpose cover crop InterSeeder^TM, directed broadcast, and directed broadcast with light incorporation) at the University of Minnesota Southern (Waseca, MN) and Southwestern (Lamberton, MN) Research and Outreach Centers. Cover crop treatments did not affect corn grain yield in either year at Waseca, or in 2015 at Lamberton (P > 0.05). At Lamberton in 2014, winter rye treatments resulted in (0.5 Mg ha^-1) less corn grain than other cover crop treatments and the no-cover control (average 9.6 Mg ha^-1). Spring cover crop biomass and tissue N were affected by cover crop species (P < 0.05), but not by planting method in both years at Lamberton, and in 2015 at Waseca. In these site-years, winter rye resulted in the greatest biomass, ranging from 540 to 2158 kg DM ha^-1 and tissue N (15 to 45 kg N ha^-1). At Waseca in 2014, the broadcast with incorporation planting method achieved dry matter and tissue N values equivalent to corresponding InterSeeder^TM treatments, and significantly greater than broadcast without incorporation in hairy vetch and red clover. In all site years, all successfully established cover crop treatments (except red clover) reduced spring soil NO₃-N at 0 to 15 cm compared to the no-cover control. Cover crops can be established via interseeding into V7 corn in the upper Midwest, and can serve to reduce N loss while maintaining corn yield, although specific agronomic management requires further assessment to develop reliable practices.