Diagnosis of Sulfur Deficiency in Soybean using Seeds

The objectives of this study were to obtain a reliable index for the evaluation of the S nutrition status in soybean [ Glycine Max (L.) Merr.] and to identify the critical S level in relation to seed yield and quality. Two Oxisols were used: A‐horizon soil from Serra dos Gerais, and A‐ and B‐horizon soils from Sambaiba in Maranhão State, Brazil. Soybean plants in pots were grown in a greenhouse with the supply of 0 to 80 mg S kg −1 soil. The seed S concentration was a more reliable index of seed yield because of the higher correlation between S concentration and yield. In the plants with visible symptoms of S deficiency, the seeds contained 1.5 g S kg −1 , and the seed yield was 60% of the control. Electrophoresis analysis indicated that the critical seed S concentration for deficiency of protein components was 2.0 g kg −1 when the yield was 80% of the control. The S concentration was 2.3 g kg −1 or higher for >90% yield when the composition of the protein components was identical with that in the original seeds obtained under sufficient S fertilization. We classified the S concentration in the seeds as: deficient (S < 1.5 g kg −1 ), very low (1.5 ≤ S < 2.0 g kg −1 ), low (2.0 ≤ S < 2.3 g kg −1 ), and normal (2.3 g kg −1 ≤ S). Because of stable S concentration, easy sampling, and sufficient time for planning of fertilizer application for the subsequent cropping, seed analysis is preferable to leaf analysis.