Radish and annual ryegrass alter corn yield response to nitrogen rate

Authors: Johnson, Jane; Scott, Drew; Weyers, Sharon

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2021
Publication Date: 7/22/2021
Citation: Johnson, J.M., Scott, D.A., Weyers, S.L. 2021. Radish and annual ryegrass alter corn yield response to nitrogen rate. Soil Science Society of America Journal. 85(6):2054-2066. https://doi.org/10.1002/saj2.20311.
DOI: https://doi.org/10.1002/saj2.20311

Interpretive Summary: Nitrogen is an essential nutrient for crops and typically is applied as fertilizer. It is an expensive input for producers and if it escapes into the ground or surface waters, it degrades the water quality. One of the management tools that might help is to plant cover crops as they help keep the nitrogen from escaping. Cover crops are crops that are planted after a cash crop like corn, soybean or wheat harvest. Their use is fairly common in areas that have long growing seasons, but in the northern Corn Belt including Minnesota the short-growing season makes it hard get the cover crops established following corn or soybean. However, planting a cover crop after wheat which is harvested in August instead of late September or October, allows time for cover crops to grow and take up extra nitrogen. This study tested to see if planting cover crops (annual ryegrass, or a daikon type radish) following wheat harvest reduced the amount of nitrogen fertilizer needed to the next year’s corn crop to get the same yield. The study was repeated for three growing seasons planting each of the cover crops after harvesting wheat. The mass of the cover crop and the nitrogen each captured was measured. The following year corn was planted and fertilized at one of four nitrogen rates to see if one or both of cover crops resulted in the same or greater corn yields but with less fertilizer. Radish increased corn yield at recommended nitrogen application rate. It was concluded that radish could improve corn yield and may help keep nitrogen fertilizer from escaping. This research is useful for land managers seeking to help protect the environment, get the best use of expensive fertilizer and realize high crop yield.

Technical Abstract: Fall-planted cover crops are a strategy for scavenging reactive forms of nitrogen (Nr) for the subsequent crop. In the northern U.S. Corn Belt, cover crop adoption is low because of the limited establishment time. Planting cover crops following wheat (Triticum aestivum L.) in three-crop rotation (Wheat/cover crop - corn [Zea mays L] - soybean [Glycine max L. (Merr.)]) maximizes 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 following a cover crop, corn yield could be maintained with less N-fertilizer compared to without a cover crop. The study had three cover crop treatments (annual ryegrass, radish, and the no-cover crop/control). Each cover crop treatment included four relative N application rates (0X, 0.25X, 0.5X, and 1X), the recommended rate). Radish resulted in the highest corn yield at the recommended (1X) N rates, but no-cover control resulted in the highest corn yields at less than recommended rates. Annual ryegrass resulted in similar corn yields as no-cover control treatments. Using data from all years combined, corn yields were predicted to be maximized with radish as a cover crop and an N application rate of 1.1X rate. Increased yields might be explained by higher plant-available N (PAN) in radish plots than annual ryegrass or no-cover control plots. No PAN was detected at corn harvest, suggesting minimal risk of N leaching. The results suggest that radish cover crop following wheat can improve corn yields.