First-year corn after alfalfa showed no response to fertilizer nitrogen under no-tillage

Although fertilizer N response of first-year corn (Zea mays L.) following alfalfa (Medicago sativa L.) has been reported for more than 350 site-years of research, N responses under no-tillage have been reported for only 17 site-years. To determine the rate of N fertilizer required for first-year corn after alfalfa in no-tillage systems, on-farm experiments were conducted at seven locations in southern Minnesota and southwestern Wisconsin. The accuracy of the presidedress soil nitrate test (PSNT) and basal stalk nitrate test (BSNT) to identify the need for supplemental N in first-year, no-tillage corn also was evaluated. Across seven site-years, no yield response to fertilizer N was observed for corn grain, cob, stover, or silage yield, confirming that alfalfa N credits can supply the entire N requirement of no-tillage corn following alfalfa. Critical levels of PSNT used in other U.S. Corn Belt states, incorrectly predicted responses to supplemental N at all six locations where PSNT was measured (soil NO₃-N concentrations were ≤18 mg kg^-1), suggesting that critical levels may need to be reduced in no-tillage corn following alfalfa. In this first report under no-tillage conditions, the BSNT concentrations in nonfertilized corn after alfalfa were in the marginal range at two locations (between 250 and 700 mg NO₃-N kg^-1) and optimum or above at the other five locations, indicating that the BSNT incorrectly characterized N supply in two of seven cases.