Effects of Cover Crop and Nitrogen Rate on Corn Grain and Silage Yield, Nitrogen Loss in Tile Drainage and Soil Health

Nitrogen is an essential input for profitable corn production. Previous research has shown subsurface tile drainage systems deliver nitrate-N to surface waters and thereby degrade water quality (Randall and Mulla, 2001, Dinnes et al., 2002). Row crop agriculture in the Midwest is under scrutiny to reduce nitrate concentrations and loads in tile drainage. The use of cover crops and applying appropriate rates of N for corn are potential management strategies to reduce nitrate loads in tile drainage water. However, research in Minnesota has shown cover crop establishment can be difficult (Strock et al., 2004), often producing minimal cover crop growth (biomass) which results in less or inconsistent nitrate reduction in tile drainage water compared to other areas in the Midwest with longer growing seasons and milder winters (Kaspar et al., 2007).

There are cropping systems where cover crops could be more effective as nitrate scavengers and soil protectors. These cropping systems include following canning crops, like sweet corn and peas, small grains and when corn is harvested for silage in early September. In these systems there is considerably more time for cover crop establishment and growth in the fall before soils freeze in Minnesota. Furthermore, after silage corn a cover crop could protect the soil from erosion and potentially replenish carbon lost during the silage (biomass) harvest which would improve sustainability.

The species of cover crop, establishment date and termination date can affect its potential to sequester N and carbon (C). Cereal rye is effective at scavenging N when it’s established early and not terminated until spring. However, Vetsch et al. (unpublished) found cereal rye can negatively affect corn production and economics by decreasing yield or increasing input costs due to greater fertilizer N requirement, cover crop seed costs and herbicide costs for cover crop termination. A cover crop blend like oat, forage pea and radish are less expensive alternatives than cereal rye due to seed costs and no herbicide needed for termination. The potential of winter terminated cover crops to scavenge N and sequester C in a corn silage cropping system in Minnesota is not known. Furthermore, it’s not clear if nitrate loss in tile drainage is different between corn silage and corn grain systems.

Farmers are interested in the soil health benefits of cover crops, but also their potential to sequester carbon, especially in continuous corn systems with minimal or reduced tillage. The proposed study, which was initiated in 2021 on the tile drainage research facility in Waseca, provides an opportunity to simultaneously measure the effects of cover crops on corn production, nitrate loss in tile drainage and soil health metrics.

The objectives of this study are to quantify the effects and interactions of cover crops and N rates on corn production, nitrate-N concentration and loss in tile drainage, N uptake, NUE, economic return and soil health parameters.