POTASSIUM FERTILIZER AND POTATO LEAFHOPPER EFFECTS ON ALFALFA GROWTH

Potassium nutrition can alter plant resistance to environmental stresses. In two glasshouse experiments, the objectives were to assess the effects of K fertility and potato leafhopper (PLH) [Empoasca fabae (Harris)] feeding on mature and young (seven and four regrowth periods prior to PLH infestation, respectively) alfalfa plant (Medicago sativa L.) growth, regrowth, and carbohydrate reserves. Mature plants were grown on Claiborne (fine-loamy, siliceous, mesic, Typic Paleudult) and young plants on Doniphan (clayey, mixed, mesic, Typic Paleudult) top soil treated with 0,50, 100, and 200 mg K kg-1 soil. Three harvests were allowed to give K nutrition differences. Female PLHs were released into half of the caged plants for 3 wk for two subsequent harvests. Alfalfa herbage yield, shoot height, root weight, and root total nonstructural carbohydrates (TNC) increased with increasing K fertilizer. With mature plants, herbage yield, root weight, and TNC were reduced by PLH over K rates by 0.3 g plant-1, 0.36 g plant-1, and 22 g kg-1, respectively. Reduction by PLH to young-plant root TNC was an average of 44 g kg-1. At the same time, reduction in herbage yield and root weight increased with K fertility. Alfalfa maturity was delayed by the PLH. Susceptibility to PLH injury was greatest with young alfalfa plants. Increased K fertility did not reduce PLH injury in alfalfa; however, alfalfa growth and persistence improved, with or without PLH, with increasing K fertility.