Current and residual effects of nitrogen fertilizer applied to grass pasture on production of beef cattle in central Saskatchewan

Abstract

Four rates of nitrogen fertilizer (0, 50, 100 and 200 kg N ha-1) were applied for 4 yr to two replications of a 32-yr-old crested wheatgrass (Agropyron cristatum) pasture at Lanigan, Saskatchewan, after which no fertilizer was applied for a further 4 yr. The pastures were grazed by pregnant yearling Hereford heifers using a “put-and-take” stocking system. Soil cores (0–60 cm) were taken to monitor soil NO3-N concentrations either in early spring, before grass growth commenced, or in late fall, after grass growth had ceased. Pasture measurements included available forage at the start of the grazing season, total forage production and the concentrations of crude protein, acid detergent fiber (ADF), ash, Ca, P, Mg, K, Cu, Zn, Fe and Mn. Heifers, fistulated at the esophagus, were used in 1984 and 1985 to obtain samples of the grazed herbage, which were analyzed for organic matter digestibility (OMD), protein and minerals, except P and K. Heifer intakes of digestible organic matter (DOMI), protein and minerals, except P and K, were estimated from their concentrations in fistula extrusa and estimates of intake obtained from extrusa digestibility and fecal output using Cr2O3 as a fecal marker. Phosphorus intake was estimated from fecal P concentration. Plasma samples were also collected and analyzed for concentrations of minerals.