Residual Effects of Phosphorus and High Rates of Nitrogen on Shortgrass Rangeland

Abstract

Plots on shortgrass rangeland in southeastern Wyoming that received high rates of nitrogen applied once in 1970 or four times (1970 through 1973) were split, and phosphorus (P2O5) at 56 kg/ha was applied to half of each plot in the spring of 1975. Over a 3-year period (1975-77), average total herbage yields and yields of individual species were generally less for all treatments during the residual period (1975-77) than during the years of fertilization (1970 through 1973). Blue grama density decreased during the nitrogen fertilization period but increased during the 3 residual years, so that in 1977 density was almost the same as that in 1970. Western wheatgrass increased in all nitrogen treatments and generally remained high during the 1975-1977 period. During this residual period, previous nitrogen fertilization tended to increase the yield of western wheatgrass, forbs, and total herbage and decrease that of blue grama and dryland sedges. The application of phosphorus did not influence herbage yields or crude protein content of western wheatgrass or blue grama. Phosphorus also did not influence concentrations of calcium, magnesium and potassium in blue grama.