The Potential of Interseeding Cover Crops into Corn to Address Issues in the Corn-Soybean Rotation.

Corn-soybean sequences dominate the US Mid-west, and are trending in eastern states and the province of Ontario, Canada.  However, the two-crop rotation has been associated with soil degradation, increased reliance on synthetic inputs, higher economic risk, and lower resilience compared to more complex cropping systems. The objective of this study is to assess whether cover crops can mitigate these issues in shorter growing seasons typical of the Northern Corn Belt and Eastern Canada. 

     This study examines the biomass potential of cover crops interseeded into corn (planted between rows at approximately V5 stage of development), and the impact on corn and subsequent soybean yield. A three-site study was initiated in Ridgetown, Elora, and Peterborough, ON, Canada. Treatments include corn harvested for silage (mid-September) and for grain (late October) and five cover crop treatments: red clover (RC) (Trifolium pratense), annual ryegrass (ARG) (Lolium multiflorum), a mixture of the two (RC+ARG) interseeded, and the same mixture broadcast by hand, all compared to a no cover crop control. Treatments were arranged in a split-plot design, with whole- and split-factors assigned as corn harvest or cover crop treatment, depending on experimental location. In the first season, the cover crops did not affect grain corn yield or silage dry matter (P=0.05).   Cover crop biomass in the following spring (before soybean planting) varied across locations and treatments, ranging from 0-1270 kg ha^-1.  Corn plots harvested for silage produced greater mean cover crop biomass compared to plots harvested for grain, the proportional difference ranging widely by site (49%, 169% and 8313% more biomass in silage vs grain corn at Peterborough, Elora and Ridgetown, respectively).  No difference was detected based on planting method (drilling and broadcasting).  The effect of the cover crop treatments varied by location, indicating that choosing a cover cropping approach should involve considerations of the individual context of the field. Our preliminary results indicate that the competitive nature of grain corn is a limitation to the biomass accumulation of interseeded cover crops and therefore their utility, though benefits are more likely in corn harvested for silage.