Nitrogen Management for Corn After Alfalfa: Current Practices and Opportunities.

The majority of research studies support the conclusion that on medium-textured soils, alfalfa (Medicago sativa L.) typically provides all or most of the N needed to maximize grain yield of the following corn (Zea mays L.) crop. Thus, it is not surprising that the most frequent and extreme cases of over-application of N in corn often occur when fertilizer or manure N are applied to corn after alfalfa. Although it is more common for first-year corn to require additional fertilizer N on sandy and fine-textured soils, no reliable methods exist across soil types to predict which fields need to be fertilized. This uncertainty, in combination with the concern that alfalfa will not provide sufficient N to support the high corn yields common today, may contribute to low adoption of alfalfa N credits for corn in the Upper Midwest. In 2012, a mail and phone survey of Minnesota growers was conducted to: i) quantify the extent to which they have adopted alfalfa N credits; ii) learn the determinants of adoption and non-adoption; and iii) investigate sources of information growers use to determine fertilizer N rates in alfalfa-corn rotations. All Minnesota growers (approximately 2,180) with at least 40 ha of alfalfa and 20 ha of corn were asked to participate in this survey. The survey investigated farm characteristics, farm management practices, and grower beliefs (e.g., factors that affect adoption, reliable sources of information). Survey responses were aggregated by county and analyzed using continuous and categorical statistics. As the first comprehensive picture of N management in alfalfa-corn rotations in the Upper Midwest, this survey clarifies the extent of adoption of alfalfa N credits to corn and is expected to provide a firm foundation for educational efforts and future research.