Effects of Nitrogen Source and Phosphorus on Crested Wheatgrass Growth and Water Use

Abstract

The effects of four nitrogen (N) sources upon crested wheatgrass growth were studied for five years at Mandan, North Dakota. The four sources-ammonium nitrate, ammonium sulfate, calcium nitrate, and urea-were applied annually at rates of up to 160 lb N/acre both with and without annual phosphorus (P) fertilization. Dry matter production of crested wheatgrass was increased by N and P fertilization in all years. Only in years of higher production did higher N rate, N source, or any interactions, influence yields. Average yields for the 5-year period were also increased by fertilization with P and with increasing rates of N-but were not influenced by N source. Responses to N fertilization increased by about 380 and 490 pounds for each acre-inch increase in water supply (above 5 inches) with and without P, respectively. In contrast, response to P fertilization was about 50 lb/acre-inch regardless of water supply. Dry matter production and response to N fertilization were both closely correlated with May precipitation (r is greater than or equal to 0.89).