Identifying N-Responsive Fields of First-Year Corn After Alfalfa.

More than 400 site-yr of field research have been published in the U.S. and Canada on the response to fertilizer N of first-year corn (Zea mays L.) after alfalfa (Medicago sativa L.), yet we are still unable to accurately predict when fertilizer N will increase yield in corn following alfalfa. This body of research covers a wider range of weather, soil, and crop management conditions than any single study, and may contain clues for predicting fertilizer N requirements that have been missed by others. After developing this database, we ‘mined’ the data using statistical ‘meta-analysis’ techniques to determine factors (soil type, precipitation, crop management, etc.) that relate to fertilizer N response of first-year corn after alfalfa. From the subset of these studies where the economically optimum N rate could be calculated, we determined which variables contribute to estimating the N rate required in responsive site-yr. We then validated these predictors using our independent set of data from 37 recent site-yr (2009-2011) of on-farm research in Minnesota, Wisconsin, and Iowa.