Utilizing alfalfa in a crop rotation provides several benefits to the following corn crop. These rotational assets include reduced soil compaction, a reduction in soil-borne pathogens and insect pests, and greater corn yields. One other substantial benefit from alfalfa is the nitrogen (N) it provides for the following corn crop.
Alfalfa fixes N by taking it in from the atmosphere and/or soil and converts it to a usable form. During its life cycle, alfalfa sheds and regenerates fine roots which, along with the decomposition of leaves and stems, adds N to the soil. Additional N is available during termination of the crop with further decomposition of its shoots, crown, and roots. This contribution of N from alfalfa is available to the subsequent corn crop and is known as the alfalfa N credit.
The Alfalfa N Credit
The amount of N that is supplied by the previous alfalfa crop is called a N credit. According to various university studies, farmers planting corn after alfalfa can take N credits from 40 to 190 lb/acre, depending on such factors as the quality of the previous alfalfa stand, soil types, and other growing conditions.1-7 As a recommendation, Midwestern universities suggest that applied N fertilizer for corn following a good alfalfa stand can be reduced by up to 100% for first-year corn and by up to 50% or more for second-year corn.2
First-year corn yields rarely increase by adding supplemental N after alfalfa. By adhering to local alfalfa N credit guidelines and overall recommendations, the appropriate amount of N fertilizer can be applied which can help save money while maintaining expected yields.
Potassium, Phosphorous, and Sulfur Recommendations
Alfalfa production can remove high amounts of available phosphorus (P), potassium (K) and sulfur (S). Therefore, a fertility soil test should be conducted after an alfalfa crop to determine the potential availability of P, K, and S for first-year corn. Application rates for these nutrients should be applied according to the soil test results and expected corn yield.
Potassium: 0 to 255 lb K20/acre may be needed according to university guidelines and soil test results.1,4,7
Phosphorus: 0 to 160 lb P2O5/acre may be needed according to university guidelines and soil test results. Always make sure to credit N that may be applied with the P fertilizers when determining your N rates for corn.1,4,7
Sulfur soil concentration levels have steadily decreased because of decreased S emissions from coal burning power stations. If a S deficiency is confirmed by soil tests or has been noted in a previous crop, an application of SO4-S at a rate of about 15 lb/acre is recommended for fine-textured soils and about 25 lb/acre is recommended for coarse-textured soils.8,9,10
First-year corn rarely responds to additionally applied N. Assigning the proper N credit when calculating N fertilizer requirements for corn grown after alfalfa may result in a substantial decrease in the amount of fertilizer N rates needed without diminishing yield. Be sure to follow your local guidelines in establishing the proper alfalfa N Credit and calculating the appropriate N rates for corn following alfalfa.
1Clark, J., Gerwing, J., and Gelderman, R. 2019. Fertilizer recommendations guide. South Dakota State University Extension. https://extension.sdstate.edu/sites/default/files/2019-03/P-00039_0.pdf.
2Coulter, J., Yost, M., and Russelle, M. 2012. Nitrogen and tillage management for corn following alfalfa. Proceedings of the Integrated Crop Management Conference, Iowa State University. https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1107&context=icm.
3Fernandez, A.L., Sheaffer, C.C., Tautges, N.E., Putnam, D.H., and Hunter, M.C. 2019. Alfalfa, wildlife & the environment. 2nd Edition. National Alfalfa and Forage Alliance, St. Paul, MN. http://www.alfalfa.org/pdf/alfalfaenvironment2.pdf.
4Franzen, D.W. 2018. North Dakota fertilizer recommendation tables and equations. North Dakota State University Extension. SF882. (Revised) https://www.ag.ndsu.edu/publications/crops/north-dakota-fertilizer-recommendation-tables-and-equations/sf882.pdf.
5Nitrogen credits for alfalfa and soybean in Wisconsin. A3591. 2012. Nutrient and Pest Management (NPM) Program. University of Wisconsin. https://ipcm.wisc.edu/download/pubsNM/Legume_Credits_1008.pdf.
6Wortmann, C., Milander, J., Jansen, J., Anderson, B., and Wilson, B. 2019. Adding alfalfa to corn-soybean rotation can increase profit, reduce nitrate leaching. CROPWATCH. University of Nebraska-Lincoln Extension https://cropwatch.unl.edu/2019/adding-alfalfa-reduces-nitrate-leaching.
7Yost, M.A., Coulter, J.A., Russelle, M.P. 2021. Managing the rotation from alfalfa to corn. University of Minnesota Extension. http://corn.agronomy.wisc.edu/Management/pdfs/L001.pdf.
8Sawyer, J.E., Lang, B., and Barker, D.W. 2012. Sulfur fertilization response in Iowa corn and soybean production. Agronomy Conference Proceedings and Presentations. 43. Iowa State University.
9Camberato, J., Maloney, S., and Casteel, S. 2012. Sulfur deficiency in corn. Soil Fertility Update. Purdue University. https://ag.purdue.edu/agry/extension/Documents/Sulfur_Deficiency_Indiana.pdf.
10Peters, J. and Laboski, C. 2013. Is sulfur needed in alfalfa in Wisconsin? Focus on Forage. Wisconsin Team Forage. University of Wisconsin-Madison. https://fyi.extension.wisc.edu/forage/is-sulfur-needed-for-alfalfa-in-wisconsin/.
Web sites verified 5/20/21.