RESPONSES OF 2 WHEAT-VARIETIES TO SULFUR ADDITION AND DIAGNOSIS OF SULFUR DEFICIENCY

Sulphur deficiency has become increasingly widespread in wheat in the U.K. Growth, nutrient content and biochemical responses to S and N sup ply of a breadmaking wheat variety (Hereward) and a non-breadmaking va riety (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 suscept ible to the imbalance of N to S than the Hereward variety. At GS 37, t he concentrations of total S and sulphate-S of shoots, chlorophyll met er readings and the concentrations of glutathione of the uppermost ful ly 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 grea ter 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 cu rves 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 relations hip between DM yield and the glutathione concentration, with a critica l value of 240 nmol g(-1) FW. There were no advantages of using % of t otal 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 pu rposes, a much higher S status at GS 37 was required to ensure no loss es of DM yield due to S deficiency at maturity.