UPTAKE OF N, P AND S IN FERTILIZED PASTURE HERBAGE AND HERBAGE YIELD RESPONSE TO FERTILIZER AS AFFECTED BY SOIL NUTRIENTS

Uptake of N, P and S nutrients in the herbage of different pasture spe cies were determined at eight sites within pastures located on Luvisol ic soils in northeastern Saskatchewan, Canada. Also, the nutrient stat us of the soil was related to herbage yield response to N, P and S fer tilizers. Soil tests would be used to establish the initial response t o fertilizer and thereafter, nutrients removed from the soil could be replaced by fertilizer. Experiments in the study included one site wit h bromegrass (Bromus inermis Leyss.) and alfalfa (Medicago media Pers. ), six sites on a pasture mixture ( Bromus inermis Leyss., Festuca rub ra L., Poa pratensis L. and Medicago media Pers.) and one site with Ru ssian wildrye (Psathyrostachys juncea (Fisch.) Nevski) at both Pathlow and Pleasantdale pastures. Nitrogen and P fertilizers were applied at 0, 45 and 90 kg N ha(-1) in combination with P at 0 and 20 kg ha(-1). Sulphur treatments included 90N-20P-20S (sulphate source, kg S ha(-1) ) on pasture mixture sites and two treatments of 90N-20P-23S and 90N-2 0P-45S (elemental source, kg S ha(-1)) on bromegrass and alfalfa. Maxi mum uptake of nutrients were 103.6 kg N, 11.5 kg P and 5.2 kg S ha(-1) with the application of 90N-20P-45S (kg ha(-1)) on the bromegrass-alf alfa pasture. The controls resulted in the lowest uptake of 20.2 kg N, 1.9 kg P (pasture mixture) and 1.5 kg S ha(-1) (bromegrass and alfalf a). Yield response to N and P fertilizers (percentage yield over contr ol) was related to soil tests for N, P and S (r(2) = 0.42). Herbage yi eld increase (log(10) mean of years) from S fertilizer over the contro l was negatively related to the soil test for S on six sites (r(2) = 0 .77). Uptake of N, P and S in herbage gave an adequate estimate of nut rient removal and the amount of fertilizer to apply to maintain soil n utrient levels.