WHOLE-SEASON GRASS RESPONSE TO AND RECOVERY OF NITROGEN APPLIED AT VARIOUS RATES AND DISTRIBUTIONS IN A HIGH RAINFALL ENVIRONMENT

High rates of nitrogen (N) fertilizer are often used on perennial gras s in the coastal region of British Columbia and the Pacific Northwest, but there is little information on optimum rates for abundant high-qu ality yields and on their environmental implications. A field trial wa s conducted in each of 3 yr to determine the effect of rates and distr ibutions of N on whole-season herbage yield and quality, and pre- and post-season extractable inorganic N in the soil. Yearly rates were 100 , 200 and 400 kg N ha(-1) applied to each of four cuts in the followin g distributions: 1.00/0/0/0, 0.50/0.25/0.25/0 and 0.25/0.25/0.25/0.25, Whole-season yield was increased by increasing rates of N in all thre e trials, but the increase varied from 17% (Trial 1) to 127% (Trial 3) . Distributing the N uniformly through the season resulted in only a 5 % increase in yield compared with applying all of the N at the beginni ng of the season. Rate of N had a substantial effect on average herbag e crude protein and nitrate concentrations, but the distribution effec t was greater on herbage N constituents than on yield. increasing rate s of N consistently increased average herbage nitrate concentrations, and crude protein in two of three trials. Applying all of the N at the beginning of the season increased average herbage crude protein and n itrate concentrations more than distributing it evenly through the sea son. Extractable inorganic N in the soil at the end of the season incr eased only at 400 kg N ha(-1) rate and was not affected by distributio n. Although distribution pattern influenced herbage yield and nitrogen concentrations, distribution did not influence total herbage N uptake or recovery in herbage plus soil. Rates and distributions of N on gra ss influenced herbage yield and quality, and soil extractable inorgani c N in different ways; therefore, compromises in N management are requ ired to optimize forage yield and quality, and soil nitrate concentrat ions. Autumn soil inorganic N testing may be useful as feedback inform ation for fertilizer recommendations in the subsequent season. Spring soil inorganic N testing was a poor predictor of crop response to fert ilizer in the high rainfall environment of the study.