RESPONSE OF REED CANARYGRASS TO NITROGEN AND POTASSIUM FERTILIZATION

Applications of N are mandatory if acceptable yields are to be obtained from pure stands of reed canarygrass (Phalaris arundinacea L.). Potassium requirements and the N x K interaction are not well defined, however. A 3 x 3 factorial field experiment was conducted from 1983 to 1988 to evaluate the response of reed canarygrass to N and K fertilization. Rates of K were 0, 200, and 400 lb/acre and were applied annually. Nitrogen was applied at 0, 200, and 400 lb/acre in 1983 and 1984 and 100, 200, and 300 lb/acre from 1985 to 1988. Yields were consistently increased by N application. Initially, the response to K was minimal but in 1986 N x K interactions developed. Yield response to K was inconsistent when made in conjunction with 100 lb N/acre. At higher rates of N, however, positive curvilinear responses to K were obtained. Concentrations of K in the herbage reflected applied K levels. At the lowest N level, the application of K resulted in tissue concentrations of K that varied from 1.2 to 3.7%. These variations, however, were not associated with increased yields. When N was applied at 200 to 300 lb/acre, optimum yields occurred when herbage had K concentrations of 2.5 to 2.7%. Without K fertilization, soil test K values remained low (22 to 43 ppm). As K was applied, changes in soil test K varied with N level. The greatest increase in soil K occurred when low N fertilization was combined with high K fertilization, a change reflecting a major difference between applied K and K uptake. Where 200 or 300 lb N/acre was applied, recovery of K was approximately 100% when K was applied at 200 lb/acre. Maintaining soil test K between 40 and 60 ppm supplied sufficient K to support high yields of reed canarygrass fertilized with 100 to 300 lb N/acre.