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Alfalfa Response to Potassium, Irrigation, and Harvest Management¹

The purpose of this research was to evaluate the combined effect of irrigation, K fertilizer, and harvest management variables on the production of multi-disease-resistant, winterhardy alfalfa (Medicago sativa L.) cultivars. A field experiment was conducted on a sandy, mixed Udic Haploboroll to determine the effects of three irrigation regimes, three harvest managements, and four annual K rates (0, 167, 334, and 501 kg ha–¹) on forage yield, forage quality, and persistence of‘Ramsey’ and ‘520’ alfalfa. No, full, and medium irrigation treatments were applied. Both full and medium irrigation regimes applied 3.5 cm of water when 50% of the extractable soil water had been depleted, but the medium irrigation was less frequent. Harvest managements consisted of: two harvests at full flower and one in late fall (HI), three harvests at one-tenth flower and one in late fall (H2), and three harvests at one-tenth flower (H3). Forage dry matter yield response to K increased with increasing irrigation, from 0.0033 Mg ha–1 kg–¹ K in nonirrigated to 0.0058 Mg ha–¹ kg–¹ K in fully irrigated alfalfa. Yield response to K was similar for harvest managements within no and medium irrigation regimes, but for the full irrigation regime, yield increased 0.0071 Mg ha–¹ kg–¹ K with harvest at one-tenth flower, and only 0.0031 Mg ha–¹ kg–¹ K with harvest at full flower. Following a severe winter after 2 yr of harvesting, the greatest stand and yield losses occurred with full irrigation and the most intensive (four-cut) harvest management. Mean final stands in the four-cut management were 19, 39, and 74% for full, medium, and nonirrigated alfalfas, respectively. Stand persistence and residual yield were increased by K fertilization under more frequent (one-tenth flower) harvest of irrigated alfalfa. Cultivars did not consistently differ in yield in two production years, but the less winterhardy 520 had greater final stands than Ramsey. Potassium fertilization is beneficial to yield and stand of alfalfa, although the response varies with irrigation and harvest management.

Key Words: Medigo sativa L. • Forage quality • Yield • Persistence • Cultivars

² Associate professor; soil scientist, USDA-ARS/U.S. Dairy Forage Research Center; former research assistant; and professor, respectively, Dep. of Agron. and Plant Genetics and Dep. of Soil Science, Univ. of Minnesota, St. Paul, MN 55108.

Received for publication April 16, 1985.

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