Interaction of Fertility Level with Harvest Date and Frequency on Productiveness of Mixed Prairie

Abstract

Management practices are needed which will insure sustained production from fertilized mixed prairie. Prior to establishing grazing management practices, a better understanding of N and P fertilizer effects on the vegetation is needed. The interaction of harvest date and frequency with annual applications of N and P was studied over an 8-year period near Mandan, N. Dak. Yield increases were significant when 40 lb. N/acre (40-N) and 80-N were applied, but application of 160-N produced little or no increase over the yield from 80-N. Average yields were 548, 1,298, 1,875 and 1,908 lb./acre for the 0-, 40-, 80- and 160-N levels, respectively. Without N, response to P was small and generally not significant. When N was applied annually, response to P became significant in the fourth and subsequent years. Yields at all fertilizer levels decreased as frequency of harvest increased. Greatest yield reductions occurred when the sequence included harvest in June.