Responses of two wheat varieties to sulphur addition and diagnosis of sulphur deficiency

Sulphur deficiency has become increasingly widespread in wheat in the U.K. Growth, nutrient content and biochemical responses to S and N supply of a breadmaking wheat variety (Hereward) and a non-breadmaking variety (Riband) were investigated in a pot experiment. Shoot dry matter (DM) at stem extension (Zadok's GS 37) and at maturity was increased markedly by S. Grain production of the Riband variety was more susceptible to the imbalance of N to S than the Hereward variety. At GS 37, the concentrations of total S and sulphate-S of shoots, chlorophyll meter readings and the concentrations of glutathione of the uppermost fully expanded leaves were increased significantly by increasing S supply, whereas the concentrations of nitrate and amides were decreased by S. The greatest relative changes in response to S supply were those of the glutathione and asparagine concentrations. Riband also showed greater response to S than Hereward. Critical values of various diagnostic indices at GS 37 were derived from the relationships between DM yield and different indices. The two varieties showed similar diagnostic curves except that for the ratio of total N to total S (N:S) in shoots. Either total S or sulphate-S can be used alone as a good indicator of deficiency, and with values of 1500 and 190 mg kg(-1) DM in shoots for the two indices respectively. There was also a well defined relationship between DM yield and the glutathione concentration, with a critical value of 240 nmol g(-1) FW. There were no advantages of using % of total S as sulphate-S. Shoot N:S ratio was found to be less accurate in predicting S deficiency than total S or sulphate-S. For prognostic purposes, a much higher S status at GS 37 was required to ensure no losses of DM yield due to S deficiency at maturity.