EFFECT OF NITROGEN-FERTILIZER ON BEEF-PRODUCTION AND FORAGE QUALITY OF RUSSIAN WILDRYE

A grazing study was conducted for 12 yr on a Brown loam in a semi-arid climate at Swift Current, Saskatchewan to determine the effect of nitrogen (N) fertilizer on beef production, forage quality, and economic returns of Russian wildrye (Psathyrostachys juncea (Fisch) Nevski) (RWR). Treatments were: annual broadcast of N fertilizer such that available soil N (0-60 cm depth) plus applied N totalled 55 kg ha-1; an application in which available plus applied N totalled 110 kg ha-1; a one-time application of 390 kg N ha-1 (April 1977); and a control treatment with no fertilizer. Treatments were compared by regression analysis using soil available plus fertilizer N and age of stand as the independent variables. Pastures were grazed each year with yearling steers from early May until 5 cm grass height remained or when steers did not gain weight in a 2-wk period (resulting in an average grazing period of 120 d). Total grazing days averaged 166, 179, 165 and 132 days ha-1, respectively, for the four treatments. For the 55 N treatment, in which 32 kg N ha-1 was applied annually, an average of 1 kg of beef gain was obtained for each kilogram of N applied. Daily gain of steers averaged 0.84 kg d-1 for all years and treatments. Stocking rate (grazing days/ha) was positively correlated to spring soil moisture plus grazing season precipitation (r = 0.67) and negatively related to pan evaporation (r = 0.87). Fertilizer treatments marginally increased forage N and OMD early in the season. Forage N, phosphorus, and organic matter digestibility (OMD) declined in a linear relationship with time from 1 May. The rate of decline was not affected by the treatments. On the basis of liveweight gain, all fertilizer treatments were profitable. Profitability varied with the ratio of the cost of fertilizer N to steer price; annual fertilizer applications were more profitable than the one-time application.