|YOST, MATT - University Of Minnesota|
|MORRIS, THOMAS - University Of Connecticut|
|COULTER, JEFFREY - University Of Minnesota|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2013
Publication Date: 3/6/2014
Citation: Yost, M.A., Morris, T.F., Russelle, M.P., Coulter, J.A. 2014. Second-year corn after alfalfa often requires no fertilizer nitrogen. Agronomy Journal. 106(2):659-669.
Interpretive Summary: There are wide differences in the recommended fertilizer nitrogen rate farmers should apply to crops that follow legumes, like alfalfa. This is particularly true for the second crop, where relatively few field trials have been conducted. In field research conducted in Iowa and Minnesota, we found that the second year of corn grown after alfalfa needed no fertilizer nitrogen in more than 40% of the cases. In those fields where extra nitrogen was needed, the optimum rate varied widely. A commonly used index to predict corn response to nitrogen was a poor indicator of fertilizer need in second-year corn. This research showed that current recommendations by midwestern states are inadequate for second-year corn after alfalfa, which should stimulate research to provide the needed data and to develop methods to predict nitrogen supply to crops grown after legumes.
Technical Abstract: Terminated alfalfa (Medicago sativa L.) often provides N to at least 2 years of subsequent corn (Zea mays L.) crops, but the variability and inconsistency in fertilizer N guidelines for second-year corn in the midwestern United States need to be addressed. In several states, fertilizer N guidelines are the same for second-year corn after alfalfa as for continuous corn, whereas other states recommend reducing fertilizer N rates to second-year corn by 25 to 145 kg N/ha. Experiments were conducted at 28 farms in Iowa and Minnesota to determine fertilizer N requirements of second-year corn after alfalfa. Second-year corn in one-half of the trials showed no response to fertilizer N and the economically optimum N rate (EONR) for corn grain yield in the responsive trials ranged from less than about 67 to 196 kg N/ha. Furthermore, in about one-half of the trials there was no response of grain yield to fertilizer N in both first- and second-year corn. These results indicate that current university fertilizer N guidelines for second-year corn after alfalfa often are unreliable. At the widely adopted critical concentration of 21 mg/kg, the presidedress soil nitrate test (PSNT) correctly identified only 63% of the trials as responsive or nonresponsive to fertilizer N. When results of our experiments were combined with data from the literature, second-year corn grain yield responded to fertilizer N 55% of the time and the PSNT remained accurate only 65% of the time, indicating that more accurate forecasting of second-year corn N requirements is needed.