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Improving Predictability and Adoption of Alfalfa N Credits for Corn

Study author(s): Jeff Coulter, University of Minnesota, Department of Agronomy and Plant Genetics
Years of study: 2012
Location(s): Illinois, Iowa, Minnesota, Missouri, New York, Ohio, Ontario, Pennsylvania, Wisconsin

Important: for the complete report, including all tables and figures, please download using the link(s) to the right.


A total of 259 field trials from the northern and central U.S., including 31 on-farm trials conducted in Minnesota from 2009 to 2011, were analyzed to determine the underlying factors affecting the response to N fertilizer in first-year corn following alfalfa. Results indicate that response to N fertilizer is strongly influenced by soil texture, alfalfa stand age at termination, and termination time. On coarse-textured soils (loamy sands), N fertilizer was needed to optimize grain yield of first-year corn 96% of the time. On fine-textured soils (clay loams, silty clay loams, and sandy clay loams), N fertilizer was needed 53% of the time. On medium-textured soils (loams, silt loams, sandy loams, and fine sandy loams), the response to N was dependent on the time of alfalfa termination. On medium-textured soils, first-year corn following an alfalfa stand that was at least three years old (establishment year plus one production year) responded to N fertilizer only 5% of the time when alfalfa was terminated in the fall, compared to 17% of the time when alfalfa was terminated in the spring. More frequent response to N fertilizer on medium-textured soils occurred when corn followed younger alfalfa stands. These results were shared with Minnesota growers and their advisors through meetings and field days, articles in the farm press, and an extension bulletin (

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