Prognosis and diagnosis of sulfur status in maize by plant analysis

The analysis of sulfur concentration (S-C) and nitrogen to S ratio (N/S) in plant tissue are some of the suggested tools to evaluate S deficiency in maize (Zea mays L.). However, the convenience of one over the other and the tissue that should be analyzed (upper leaf or shoot) is still questioned. Therefore, the objectives of our study were to: i) evaluate the stability of shoot and upper leaf N/S ratio with increasing shoot biomass (BM), ii) compare S-C vs N/S in shoot or upper leaf as S prognosis tools, and iii) evaluate the use of S-C simultaneously with grain N/S as a S diagnostic method in maize. Different S fertilization rates (0-32 kg S ha(-1)) were evaluated in nine field experiments where S and N concentration were determined in maize shoot, uppermost fully developed leaf, and grain samples. The main results of our study were: i) the N/S ratio in shoot and upper leaf was not stable with increasing BM; ii) the S prognosis capacity was similar when measuring S-C or N/S on the shoot or upper leaf in vegetative growth stages, and iii) S-C in grain allowed an adequate S diagnosis, which was not improved by including N/S in the prediction. In conclusion, based on its simplicity and reliability, we suggested the use of S-C in the upper leaf at approximate to V-6 stage as a S prognosis tool (2.1 g kg(-1) threshold). In addition, a 1.12 g S kg(-1) threshold in grain was adequate for S diagnosis.