Radish and annual ryegrass alter corn yield response to nitrogen rate

Fall-planted cover crops are a strategy for scavenging residual reactive N. In the northern U.S. Corn Belt, the short growing season continues to limit adoption of cover crops. Planting cover crops following wheat (Triticum aestivum L.) in a three-crop rotation (wheat [cover crop]-corn [Zea mays L]-soybean [Glycine max L. (Merr.)]) increases establishment time. Two cover crops noted for N scavenging, annual ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot) and radish (Raphanus sativus L. 'Tillage'), were selected. We hypothesized that corn yield could be maintained with less N fertilizer when following a cover crop compared with no cover crop as determined by direct comparison and regression analyses. The study was repeated 3 yr and had three cover crop treatments: annual ryegrass, radish, and the no-cover-crop control. A second treatment, factorially applied in corn years, was N application rates relative the recommended rate of 0x (0 kg N ha(-1)), 0.25x (39-48 kg N ha(-1)), 0.5x (78-95 kg N ha(-1)), and 1x (157-190 kg N ha(-1)). When cover crops were planted after wheat, about 60 kg N ha(-1) yr(-1) was measured in the roots and shoots of radish and annual ryegrass, representing 35 or >60% of the inorganic N in the soil. Corn yield averaged 5% higher following radish and 13% lower following annual ryegrass compared with the no-cover control. Both cover crops scavenged residual N, but neither cover crop treatment supported the hypothesis that corn yield could be maintained with less N fertilizer compared with no cover crop.