|YOST, MATT - University Of Minnesota|
|COULTER, JEFFREY - University Of Minnesota|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2013
Publication Date: 3/6/2014
Citation: Yost, M.A., Russelle, M.P., Coulter, J.A. 2014. Field-specific fertilizer nitrogen requirements for first-year corn following alfalfa. Agronomy Journal. 106(2):645-658.
Interpretive Summary: Current fertilizer nitrogen recommendations are made by states based on limited, usually local databases built on field research or on a general summary of findings from the region. In the case of crop rotations, where corn follows alfalfa, for example, the resulting recommendations have been problematic due to the variable amount of nitrogen supplied by alfalfa to the corn crop. Collaborative research between an ARS scientist in St. Paul, MN, and colleagues at the University of Minnesota took a more comprehensive approach by analyzing all published results of this crop rotation in North America. Their findings indicate that, in most cases, simple predictors like weather and the age of the alfalfa stand can tell whether the corn will need nitrogen fertilizer in a particular field and, if so, how much the farmer should apply. This breakthrough in fertilizer nitrogen recommendations should help farmers apply the right amount of nitrogen, increasing profitability and reducing environmental damage caused by excess nitrogen.
Technical Abstract: Current fertilizer N guidelines may not adequately account for variable N supply to corn (Zea mays L.) grown after alfalfa (Medicago sativa L.). Nitrogen supplied by alfalfa often is adequate for optimum grain yield of the subsequent corn crop, but fertilizer N sometimes is needed. Using 259 site-years of data from the literature and multiple logistic regression, we were able to successfully identify responsiveness to fertilizer N in first-year corn following alfalfa in 89 to 97% of the cases on fine-textured soils and on medium-textured soils with spring-terminated alfalfa, and in 73 to 90% of the cases on medium-textured soils with fall-terminated alfalfa. Only 1 of 11 site-years on coarse-textured soils did not require fertilizer N, preventing identification of conditions that result in high N supply after alfalfa on these soils. Using multiple linear regression, =68% of the variation in actual EONR across a range of PRs was explained on fine-, medium-, and coarse-textured soils by simple predictors such as alfalfa termination time, alfalfa stand age, and weather conditions from October through spring. Although more data are needed to validate the models, this approach to field-specific fertilizer N guidelines for first-year corn following alfalfa appears, in many cases, to adequately identify when no N is needed and provide improved rate estimates when N response is expected. This novel approach to fertilizer N recommendation may prove effective for other rotations.