Influence of sulphur and nitrogen on seed yield and quality of low glucosinolate oilseed rape (<i>Brassica napus</i> 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.