Yield Response of Canola to Nitrogen, Phosphorus, Precipitation, and Temperature

Canola (Brassica nupus L.) is a major crop in western Canada, and been used extensively as an alternative crop to wheat (Triticum aestivum L.). Yet, little information is available on the response of this crop to N and P fertilizers in relation to soil tests for these elements under varying environmental conditions. Accordingly, this study was conducted for a 16-yr period to determine the yield response of canola to N and P fertilizers in relation to soil tests for these elements in northeastern Saskatchewan on black Melfort silty clay (Typic Cryoboroll) previously cropped to spring wheat. Nitrogen fertilizer was applied at 45 and 134 kg N ha⁻¹ in factorial combination with 0, 10, 20, 30, and 40 kg P ha⁻¹. Extra treatments consisted of 10N–20P kg ha⁻¹ and a control with no fertilizer applied. Canola grain and straw response to N and P fertilizer was significant, but the N by P interaction was not significant. The interaction effects of Year by P and Year by N were significant, indicating a wide range of response to applied elements among years because of temperature, precipitation and soil nutrient effects. Grain yield was positively correlated to total precipitation and negatively correlated to mean maximum daily temperature for the months of July and August (R² = 0.32). The highest grain yield (2.46 t ha⁻¹) was obtained in 1987 with P fertilizer applied at 40 kg P ha⁻¹ (averaged across N rates), 162 mm of rainfall and an average maximum temperature of 21.2 °C. The lowest yield (0.37 t ha⁻¹) was obtained in 1989 with P fertilizer applied at 20 kg P ha⁻¹, 95 mm of rainfall and an average maximum temperature of 25.1 °C. In conclusion, soil tests for N and P accounted for much of the variation in yield response to these elements (r² = 0.58 and R² = 0.46, respectively) despite large yield differences among years because of temperature and precipitation.