Assessing sulfur status in lupins and wheat

Abstract

The effect of sulfur (S) supply on growth and S distribution within lupin and wheat plants was studied in a glasshouse experiment using pots containing 11 lupin or 15 wheat plants in 6 kg soil. Shoot growth and grain yield increased with increasing S supply, and both species produced maximum grain yield at 60 mg S/pot. Wheat yielded a lower percentage of maximum grain yield than lupin where no S was applied. Sulfur concentrations in all shoot parts increased with increasing S supply in both wheat and lupins. In wheat, S concentrations decreased with increasing plant age. At all rates of S, concentrations in old leaves were higher than in the youngest leaves. In lupins, S accumulated in stems when supply was adequate but decreased markedly with S deficiency and plant age. Concentrations in other parts of lupins generally did not change with plant age. Sulfur concentrations in the youngest open leaf blades were higher than those in old leaves at all rates of S. For lupins, critical S concentrations in the young leaves (0.28%), stems (0.07%), and whole shoots (0.15%), and the critical nitrogen (N) to S ratio in young leaves (22), are likely to be valid as diagnostic indices for S deficiency as they do not appear to be affected by plant maturity. In contrast, critical S concentrations (0.14-0.31% S) and N to S ratio (9-19) in young leaves of wheat plants changed sharply with plant age; neither is useful as a diagnostic aid unless the maturity of the plant in known. Field surveys were conducted in the agricultural regions of Geraldton and Dowerin in Western Australia to investigate the incidence of S deficiency in lupin and wheat crops. Sulfur concentrations in lupins and wheat from Dowerin were higher than those sampled at Geraldton. Lupin crops from both regions and wheat from Dowerin had an adequate S supply. Of the wheat sampled at Geraldton, 36% was deficient or marginal in S.