ARS | Publication request: Validating Topdressed K Fertilizer Recommendations in an Alfalfa-Corn Rotation

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 12, 2010
Publication Date: February 18, 2010
Citation: Yost, M., Russelle, M.P., Coulter, J., Sheaffer, C., Kaiser, D. 2010. Validating Top-Dressed K Fertilizer Recommendations in an Alfalfa-Corn Rotation [abstract]. Nutrients in Our Environment: Past, Present, and Beyond Conference, February 18, 2010, Mankato, Minnesota. Available: http://www.ctic.org/media/pdf/Poster_Booth_Abstracts.pdf.

Technical Abstract: Potassium (K) fertilizer prices are higher than average and may reduce bottom line returns for alfalfa growers. Potassium supports plant stress tolerance and plays a critical role in alfalfa yield by moving sugars from shoots to roots. Current University of Minnesota recommendations are to apply between 100 and 140 lb K20/acre for a 6 ton/acre yield goal in fields with medium testing soils (between 81 and 120 ppm K). These recommendations do not change with the age of the alfalfa stand. In 2008 and 2009, K fertilizer recommendations for last-year alfalfa in its third or fourth full year of production were tested on 10 farms with medium soil-test K levels. Alfalfa yield was not improved by topdressed potash in the early spring or after the first harvest, and no differences were found in overall forage quality. Relative feed quality averaged 200 across all potash rates, farms, and harvests in 2008. Neutral detergent fiber digestibility increased from an average of 44.7% to 47.7% as potash application increased from 0 to 200 lb/acre in 2008. End of season plant density was not affected by soil test K level before or after potash application. Based on these results, there is no apparent benefit from applying potash in the last year of alfalfa production when exchangeable K is greater than 80 ppm at the beginning of that growing season.