Interactive effects of N and S fertilizers on canola yield and seed quality on S-deficient Gray Luvisol soils in northeastern Saskatchewan

On marginally S-deficient soils in the Parkland region, application of high rates of N and other fertilizers in combination with more frequent production of canola (Brassica napus L. or B. rapa L.) causes rapid depletion of S and nutrient imbalance in soil, and S deficiency and yield reduction for canola. Field experiments on Gray Luvisol (Boralfs) soils deficient in available N and S were conducted in northeastern Saskatchewan. Interactive effects of N (0, 50 100 and 150 kg N ha-1) and S (0, 10, 20 and 30 kg S ha-1) rates on yield, seed quality, and uptake of S and N in canola were determined. In the absence of S application, increasing N rate made the S deficiency symptoms more severe, and reduced yield, S concentration, oil concentration, S uptake and N uptake of seed, but there was a general response of no effect or some increase in protein concentration, S and N uptake in straw up to 50 or 100 kg N ha-1. When S was applied, canola yield, S concentration, S uptake and N uptake of seed as well as the yield and S uptake of straw increased with increasing N rate. Irrespective of S rate, fertilizer N reduced oil concentration and increased protein concentration in canola seed. With S fertilization, yield, S uptake and N uptake of seed and straw, and total S concentration and oil concentration in seed were substantially increased, whereas there was no consistent change in protein concentration of seed. The response of these parameters to S application was generally greater at higher N rates. Sulphur and N uptake measured data indicated that significant N x S interaction effects were more frequent and pronounced for seed yield than for straw yield, indicating that the response to N rate was relatively more dependent on the S level for seed than for straw. In summary, the results suggest that an increased amount of S is needed on these S-deficient Gray Luvisol soils in northeastern Saskatchewan to adequately meet the S requirements at high N rates for optimum yield and quality of canola.