Nitrogen Fertilizer Requirement for Inbred Corn Following Corn or Soybean

There is a need for information regarding the N benefit provided to inbred corn (Zea mays L.) grown in rotation with soybean (Glycine max L. Merr.). Our objective was to evaluate response of irrigated inbred corn to N fertilization in corn-following corn (C-C) and corn-following-soybean (C-S) cropping sequences. Fertilizer N was applied at rates from 0 to 144 lb/acre to three inbred corn lines grown following hybrid corn or soybean. Corn yields averaged 29% higher following soybean than following corn. In the C-C cropping sequence, seed yield increased with increasing N application rate in seven of nine cases, with the yield-based optimum N rate (NY) varying from 67 to 119 lb of N per acre. In the C-S cropping sequence, yield response to fertilizer N was observed in only four of nine cases, with one inbred line failing to respond in any of the three study years. Where responses occurred in the C-S sequence, NY ranged from 53 to 96 lb/acre. Growing seed corn in rotation with soybean decreased NY by an average of 42 lb/acre compared to the C-C sequence. Results provide no evidence that the soybean N credit used for inbred corn should be any different than that used for hybrid corn.