Comparing the Nitrogen and Potassium Requirements of Canola and Wheat for Yield and Grain Quality

Grain yield increases (responses) of canola (oilseed rape, Brassica napus L.) and spring wheat (Triticum aestivum L.) to application of nitrogen (N) and potassium (K) fertilizers were compared in the same experiment at eight field sites over three years (2000-2002) in southwestern Australia. Four rates of N (0-138 kg N/ha as urea) and four rates of K (0-60 kg K ha-1 as potassium chloride) were applied. Significant grain yield responses to applied N and K occurred for both crop species at all sites of the experiment, and the NxK interaction was significant. Canola required an average of 26% more applied N and 32% more applied K than wheat to produce 90% of the maximum grain yield. Applying increasing rates of K increased the rate of N required for 90% of maximum grain yield. Likewise, applying increasing rates of N increased the rate of K required for 90% of the maximum grain yield. Fertilizer K had no significant affect on the concentration of oil in canola grain or concentration of protein in both canola and wheat grain. Application of increasing rates of N decreased the concentration of oil while increasing the concentration of protein in canola grain, and increased concentration of protein in wheat grain. The NxK interaction was not significant for concentration of oil or protein in grain.