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Sulfur Nutrition of Rapeseed: I. Influence of Fertilizer Nitrogen and Sulfur Rates¹

ABSTRACT

Both sulfur and nitrogen deficiencies have been observed in large acreages of western Canadian soils. These deficiencies prompted an investigation of the interactive effects of N and S on rapeseed (Brassica napus L.), a S-sensitive crop that is extensively grown on these soils. Four rates of N (0, 50, 100, 300 mg N kg^–1 soil) and four rates of S (0, 5, 15, 40 mg S kg^–1 soil) were applied in all combinations to rapeseed grown in a pot culture experiment. Maximum seed yield responses to N and S were observed only when the availability of N and S was in approximate balance. Excessive N applications relative to S availability severely suppressed seed production. This effect was attributed to the accumulation of toxic levels of N metabolites. Excessive S applications relative to N availability produced excessive accumulation of S in the plant tissue. The leaves, and, to some extent, the stems, were the predominant sites of excess nutrient accumulation. Seed nutrient concentrations remained relatively stable over all fertilizer treatments. In most plant parts, the applications of one element reduced the concentrations of the other element by a "dilution" effect. The optimum ratio of available N to available S in the soil was estimated to be 7 to 1. Ratios below 7 resulted in inefficient utilization of the assimilated S, while ratios exceeding 7 resulted in reduced seed yields.

¹ Contribution of the Saskatchewan Inst. of Pedology no. R332, Dep. of Soil Science, Univ. of Saskatchewan, Saskatoon, Sask., S7N 0W0 Canada.

² Graduate Student and Professor, respectively.

Received for publication August 31, 1982. Accepted for publication August 4, 1983.