Sulphur Nutrition and Oilseed Quality

Abstract

Oilseed rape has a high requirement for sulphur and is particularly sensitive to any shortfall in sulphur supply. Yield responses of oilseed rape to sulphur supply have been reported in many countries. Soil sulphur content has been found to influence the level of yield response from a site and results indicate that correct sulphur nutrition is critical for double low varieties. An interaction between nitrogen and sulphur has been noted, indicating that there is a requirement to balance application of these nutrients for optimum response. The response of oil content to sulphur application is less consistent than that of yield, but increases in oil content appears more likely where a low sulphur status occurs. Small changes in fatty acid composition may occur. Differences in protein content according to sulphur application are usually small and associated with sulphur deficiency. Content of sulphur bearing amino acids may be reduced at low sulphur conditions.

Sulphur availability has a larger effect on the content of glucosinolates, sulphur containing secondary metabolites, in both the vegetation and the seed of oilseed rape plant. Site and variety type have a large effect on glucosinolate response to sulphur application, with low sulphur or deficient sites and high glucosinolate varieties being associated with the largest increases in glucosinolate content following sulphur application. Glucosinolates have been shown to be associated with biocidal effects, with glucosinolate levels raised by sulphur application being effective in reducing and delaying disease levels. However, glucosinolate levels raised within the plant foliage by sulphur supplementation could not fully substitute for fungicide application in terms of disease control and subsequent effects on yield. External application of glucosinolates allowed greater accuracy in timing and targeting of glucosinolates. Effectiveness against a range of organisms has been demonstrated, although development for use in the commercial situation may be difficult due to health and safetly implications of handling glucosinolate products in this form. Biofumigation, where soil borne pathogens and pests are suppressed by biocidal compounds released during the hydrolysis of glucosinolates during the breakdown of Brassica tissues offers an alternative means of delivery of glucosinolates to the target.