THE EFFECT OF N, P, S FERTILIZER, TEMPERATURE AND PRECIPITATION ON THE YIELD OF BROMEGRASS AND ALFALFA PASTURE ESTABLISHED ON A LUVISOLIC SOIL

This study was conducted over a 12-yr period to determine the effect of N, P, and S (elemental) fertilizers on yield of bromegrass (Bromus inermis Leyss.) and alfalfa (Medicago media Pers.) pasture established on a Gray Wooded, Luvisolic soil (Waitville loam) in northeastern Saskatchewan. Nitrogen fertilizer was applied at 0, 45, and 90 kg N ha-1 in combination with phosphate fertilizer applied at 0 and 20 kg P ha-1. Two additional treatments combined 90 N + 20 P (kg ha-1) with 23 S and 45 S (kg ha-1). In the first 3 yr of the study, only the application of N increased yields, from 2.54 to 3.45 t ha-1. The combination of time (years 1978-1980) and N fertilizer applied up to the rate of 90 kg N ha-1 resulted in a reduction in percentage alfalfa in the sward from 30.9 to 3.8% (Yr X N interaction). Over the 12-yr period, N increased average herbage yield from 1.99 to 2.95 t ha-1; P, from 2.23 to 3.05 t ha-1 and S from 3.48 to 4.19 t ha-1, respectively. The interaction effects of N X Yr, P X Yr and S X Yr all were significant indicating a wide range of response to the fertilizer elements among years. Herbage yield was positively related to total precipitation and negatively to mean maximum temperature for the months of May, June and July. The highest yield (7.49 t ha-1) was obtained with fertilizer (90N-20P-23S kg ha-1), 220 mm of rainfall (May, June and July) with an average maximum temperature of 19.7-degrees-C. The lowest yield (0.84 t ha-1) was obtained with a control (no fertilizer), 160 mm of rainfall and average maximum temperature of 25.2-degrees-C (fertilizer X temperature-precipitation interaction). Results of this study suggest that a rise in average temperature without a corresponding increase in precipitation, would produce a significant drop in bromegrass herbage yield.