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Title: The importance of potassium in resistance to crown rot disease in alfalfa

item Samac, Deborah - Debby
item SHEAFFER, CRAIG - University Of Minnesota
item WELLS, M. SCOTT - University Of Minnesota

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: 4/26/2017
Publication Date: 5/1/2017
Citation: Samac, D.A., Sheaffer, C.C., Wells, M. 2017. The importance of potassium in resistance to crown rot disease in alfalfa. Forage Focus. May 2017. p. 16.

Interpretive Summary:

Technical Abstract: Nitrogen, phosphate, and potassium (potash, K2O) are the three most important nutrients in alfalfa growth and development. Nitrogen fertilization is not required because alfalfa has a high rate of biological nitrogen fixation. Phosphorus and potassium are frequently applied as fertilizer, but potassium is the most common nutrient deficiency of alfalfa stands. Potassium is reported to reduce susceptibility to diseases, although there is little data to support this observation, and the interaction of potassium with disease resistance is not well understood. To better understand the relationship between potassium and stand persistence, researchers with the USDA-Agricultural Research Service in St. Paul, MN and University of Minnesota colleagues have carried out several experiments to measure the impact of potassium fertility on forage yield and crown rot disease. In the first experiment, five cultivars were evaluated at four locations in Minnesota with diverse soil types and environments. Potassium was applied as potash (K2O) at rates of 0, 125, or 350 pounds/acre each year. Plants were rated for the amount of crown rot at the end of the third production year. There was a clear benefit of potassium fertilization to crown rot resistance across all locations and all cultivars. It was also found that the cultivars responded differently to potassium fertilization. At the higher rate, two cultivars had higher percentages of healthy plants, suggesting that the potassium fertility revealed their genetic potential for greater disease resistance. In a second ongoing experiment, forage yields and crown rot of a single cultivar were evaluated at Waseca, MN on a clay loam soil. A significant reduction in crown rot with potassium fertilization was observed. These results suggest that one reason that potassium fertility increases winter survival and stand life is due to a reduction in crown rot disease.