Stand age affects fertilizer nitrogen response in first-year corn following alfalfa

Knowledge about how stand age affects N response in first-year corn (Zea mays L.) following alfalfa (Medicago sativa L.) is needed to improve N credit predictions. In a 3-yr study, we evaluated response to N in first-year corn following fall-terminated 1- to 3-yr-old alfalfa stands with stand densities of 33 to 579 plants m^-2 at Lamberton and Waseca, MN, each year. At both locations, alfalfa stand age had minor impacts on soil inorganic N content and aboveground corn dry matter (DM) yield, N concentration, and N uptake during first-year corn. On medium-textured soil at Lamberton, first-year corn following 3-yr-old alfalfa stands required no fertilizer N to economically optimize grain yield, but required 64 and 97 kg N ha^-1 following 2- and 1-yr-old stands, respectively, at the fertilizer cost (US$ kg^-1 N)/corn grain price ($ kg^-1 grain) ratio of 5.6. At the same price ratio on fine textured soil at Waseca, first-year corn required 94 kg N ha^-1 following both 2- and 3-yr-old stands and 118 kg N ha^-1 following 1-yr-old stands. Therefore, current alfalfa N credit guidelines from land-grant universities that are based on alfalfa stand density at termination were not accurate for alfalfa stands ≤3 yr old that frequently had high densities. These results also confirm that alfalfa stand age affects the frequency and level of fertilizer N response in first-year corn, and support the role of soil texture in altering the effect of stand age.