Effects of Nitrogen and Sulfur on Canola Yield and Nutrient Uptake

Spring canola ( Brassica napus L. var. napus ) is becoming a significant oilseed crop adapted to the western USA. Often N and S limit crop growth. Field experiments were established to study the effects of N and S fertilization on seed yield, oil content, and N, P, K, and S uptake of spring canola. Four N rates in combination with three S rates were evaluated on two irrigated and three rainfed locations in the western triangle area of Montana near Conrad. Seed yields ranged from 0.1 to 3.8 Mg ha −1 . Seed yield and oil content N responses were closely related to available N (fertilizer N plus soil NO 3 –N in 90 cm of soil). Seed oil content varied from 370 to 510 g kg −1 and was depressed by increasing N. Optimum seed and oil yield occurred at about 200 kg N ha −1 . Two of the experimental sites responded to S. About 20 kg S ha −1 was adequate for optimum seed and oil yields. At the optimal N and S levels, total plant N, P, K, and S uptake averaged 140, 25, 170, and 60 kg ha −1 , respectively. Of the total N, P, K, and S accumulation, about 40% of the N, 30% of the P, and 85% of the K and S remained in the postharvest residue.