Reduced nitrogen fertilization to corn following alfalfa in an irrigated semiarid environment

Nitrogen fertilization of corn (Zea mays L.) following alfalfa (Medicago sativa L.) can be reduced due to the considerable amounts of N released by this legume, but most research on this subject has been conducted in rainfed areas. The objective of this study was to determine the response of corn to N fertilization following high-yielding alfalfa in irrigated semiarid conditions. Seven field experiments were conducted between 2006 and 2008 in the Ebro Valley, Northeast Spain. Fields were sprinkler, furrow, or flood irrigated. Treatments comprised six N rates (0, 50, 100, 150, 200, and 300 kg N ha^-1) applied to corn as two sidedressings. The N contained in the alfalfa roots and crowns ranged from 54 to 212 kg N ha^-1, depending on the field. Alfalfa provided enough N to the subsequent corn to achieve from 10.3 to 16.7 Mg ha^-1 of grain yield without N fertilization. Nitrogen fertilization was not required to maximize corn yields in three of seven fields. In the other four sites, the optimum nitrogen rates (ONR) that maximized corn yields ranged from 115 to 196 kg N ha^-1. The highest ONR generally were observed in flood-irrigated fields than in sprinkler-irrigated fields. Net economic return from N fertilization was maximized at N rates between 0 and 150 kg N ha^-1, suggesting that N applications for corn succeeding alfalfa can be greatly reduced compared to rates normally applied in irrigated semiarid areas (300 kg N ha^-1).