ARS | Publication request: Topdressed K for Last-Year Alfalfa May Not Pay

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: March 4, 2010
Publication Date: March 15, 2010
Citation: Russelle, M.P., Sheaffer, C., Kaiser, D., Coulter, J. 2010. Topdressed K for Last-Year Alfalfa May Not Pay. Forage Focus. March issue. p. 11 and 14.

Technical Abstract: Land Grant universities generally publish fertilizer recommendations for various crops, but these recommendations require periodic validation and improvement. The cost for potassium fertilizer tripled a couple of years ago, escalating the economic risk to farmers who apply fertilizer in excess of plant requirements. We initiated on-farm research in Minnesota to determine what the economically optimum potassium rate is for alfalfa, an important forage crop for livestock. We focused on the last year of production of this perennial crop, suspecting that less potassium was needed. We conducted research on 10 farm fields that had levels of soil potassium low enough to expect a crop response to fertilizer potassium. We found that alfalfa did not grow better with added potassium and that forage quality was not improved enough to cover the cost of the fertilizer. Our preliminary conclusion is that farmers can avoid the extra cost of adding potassium fertilizer to alfalfa during its last year of production. This should improve farm profits and reduce unproductive use of this natural resource.