Dairy farms have large on-farm resources of N, including animal manure and forage legumes grown in rotation with corn. I conducted two experiments evaluating agronomic need and environmental impact of N applications to different phases of alfalfa-corn rotations.; The first experiment compared N response of first- and second-year corn following alfalfa with that of continuous corn. A two-year experiment was initiated at Waseca and Rosemount, MN, in both 1990 and 1991. First-year corn following alfalfa had lower fertilizer and manure N use efficiency than continuous corn, in agreement with previous research on similar soils. Soil NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar}-N 13 months after N application was typically greater in first-year corn following alfalfa compared to continuous corn. In contrast to previous research, fertilizer N use efficiency and fertilizer effects on residual soil NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar}-N were similar in second-year corn following alfalfa and continuous corn. Efforts to reduce losses of excess soil NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar}-N from the corn portion of alfalfa-corn rotations should focus on reducing N application to first-year corn following alfalfa.; A second experiment investigated the effect of surface applied dairy manure slurry on herbage yield, N content, and soil NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar}-N of 'Agate' and 'Ineffective Agate' alfalfa. Alfalfa was established in Aug. 1990 at Rosemount and Waseca, MN, and manure was applied after the first cutting in June 1991. At both locations over 70% of manure NH{dollar}sbsp{lcub}4{rcub}{lcub}+{rcub}{dollar}-N was apparently lost via volatilization in the first 7 to 10 days after application. At Rosemount, manure increased Ineffective Agate yield and N uptake in each of the three herbage harvests after application. Manure increased soil NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar}-N primarily in the top 7.5 cm, but effects disappeared 53 d after application. At Waseca, manure reduced Agate yield and had no effect on Ineffective Agate N uptake. Soil NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar}-N increased in the top 7.5 cm until rain apparently leached NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar}-N downward in the soil profile. Broadcast surface applications of manure to established alfalfa can be recommended only when NH{dollar}sb3{dollar} volatilization losses are acceptable and proper manure management limits damage to the alfalfa stand.
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