Effect of fertiliser phosphorus and nitrogen on the concentrations of oil and protein in grain and the grain yield of canola (Brassica napus L.) grown in south-western Australia

The effect of fertiliser phosphorus (P) and nitrogen (N) on seed (grain) yield and concentration of oil and protein in grain of canola (oil-seed rape; Brassica napus L.) was measured in two field experiments undertaken at eight sites from 1993-2005 in south-western Australia, on soils deficient in P and N. Six rates of P (0-40 kg P/ha as single superphosphate) and four rates of N (0-138 kg N/ha as urea) were applied. Significant grain yield increases (responses) to applied P occurred in both experiments and these responses increased as rates of applied N increased. For grain production, the P x N interaction was significant in all eight years and locations of the two experiments. Application of P had no effect on concentration of oil and protein in grain. Application of N always decreased the concentration of oil and increased the concentration of protein in grain. For canola grain production in the region, responses to applied N always occur whereas responses to applied P are rare, but if soil P testing indicates likely P deficiency, both P and N fertiliser need to be applied.