Optimum Nitrogen and Sulfur Required for Growth and Seed Productivity in Oilseed Brassicas.

Oilseed brassicas have high nitrogen (N) and sulfur (S) requirements to fulfill demands of oil and protein production. A greenhouse study was conducted at the North Florida Research and Education Center during the 2015/2016 season to quantify the effects of N and S nutrition on Brassica carinata cv. AAC A110 and B. napus cv. Canterra 1918 growth, yield and yield components. Four nutrient treatments (100N, 100S; 100N, 0S; 0N, 100S; and 0N, 0S of N and S in full strength Hoagland solution) were imposed 38 days after planting. Generally, S did not have an effect on plant growth when N was limited. Sulphur limitation changed the physiology (photosynthesis, conductance and transpiration) of carinata only when N was optimum in both species. Plant height, stem elongation rate, node numbers, node addition rate, primary and secondary branches and total leaf area response to suboptimum nutrient conditions differed between species. The number of primary and reproductive branches were greater when N was optimum regardless of S availability. Similarly, root, stem, leaves and reproductive structures were greatest when N was not limiting, however, S availability enhanced biomass production in both species. The root:shoot ratio was greatest under the most stressed conditions. In both species, seed yield was responsive to S availability only under optimum N conditions. Carinata and napus seed yield decreased by 16 and 31% when S was limiting. Oilseed brassicas require both N and S to maximize plant growth and seed productivity.