Cover crop and nitrogen rate management practices influence corn NDVI and nitrogen content

Cover crops are rarely adopted in the northern Corn Belt because of short growing periods but could provide benefits when grown between wheat (Triticum aestivum L.) and corn (Zea mays L.). We evaluated corn normalized difference vegetation index (NDVI) and leaf N (at six leaf, ear leaf, 75% silk, and physiological maturity), over three growing seasons in response to factorial treatments of cover crop of annual ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot], radish [Raphanus sativus L.], and no‐cover control, and N rate (0×, 0.25×, 0.5×, and 1×) relative to the recommended rate based on pre‐plant soil tests (157–190 kg N ha−1). Grain N was also measured in the last study year (2016) to evaluate if leaf N indicated grain N. Radish cover crop increased corn NDVI relative to the no‐cover control, but annual ryegrass decreased NDVI relative to no‐cover control. This response to cover crop treatment suggests that radish cover crop may improve corn nutritional status. Corn receiving 1× N rate had the slowest decrease in leaf N over the growing season, but 2016 data revealed that grain from all treatments receiving some level of N had similar N content. Root biomass was also highest in the 0.5× N rate treatment and could explain the previously reported result that 0.5× N rate results in highest corn yield. Taken together, these results suggest that half the recommended N fertilizer can be used with little effect on nutritional status of corn following spring wheat in the northern Corn Belt. Core Ideas Compared with no cover, corn NDVI was higher following radish cover crop. Compared with no cover, corn NDVI was lower following annual ryegrass cover crop. Corn leaf N decreased slowest in the full (1×) N rate treatment. Corn root biomass was highest at half (0.5×) of recommended N fertilizer rate.