Influence of sulphur and nitrogen on seed yield and quality of low glucosinolate oilseed rape (Brassica napus L)

Influence of S and N application on seed yield and quality of a double low (low erucic acid and glucosinolate content) variety of winter oilseed rape (Brassica napus L) was examined in field experiments at both S‐sufficient and S‐deficient sites. At the S‐sufficient site, application of S had no significant influences on seed yield, yield components, seed protein and oil contents, and resulted in only a marginal increase in seed glucosinolate content. Application of N increased seed yield and protein content, but decreased oil content concurrently. A significant increase in seed glucosinolate content in response to the increasing N rate was obtained at this site, which was more noticeable in those treatments with applied S than without. In contrast, at the S‐deficient site, there were significant interactions between S and N on seed yield, protein and glucosinolate contents. Increasing the N rate beyond 150 kg ha−1 did not increase seed yield in the absence of applied S. However, with an application of 300 kg N ha−1, seed yield increased by 10·7% with an application of 50 kg S ha−1. The effect of N on seed yield was achieved mainly through enhanced pod formation, and that of S through reduced pod abortion. Sulphur application also increased seed protein content at the high N rate, and increased methionine content at the expense of aspartic acid. On average, a two‐fold increase in seed glucosinolate content in response to an application of 100 kg S ha−1 was obtained at the S‐deficient site. Also, increasing the N rate decreased seed glucosinolate content in the absence of applied S, but increased it when S was applied. The interaction between S and N on seed glucosinolate content was explained in terms of the allocation of S towards primary and secondary metabolites within plants.