DIAGNOSING SULFUR DEFICIENCY IN SPRING RED WHEAT: PLANT ANALYSIS

Sulfur (S) availability indicators are necessary for rational fertilizer use. The goals were to assess the predictive capacity of: i) malate:sulfate ratio in leaf; ii) total nitrogen (N):S ratio in aerial biomass; and iii) total N:S ratio in grain. Six experiments were carried out in Argentina for two years. Between 90 and 100% of samples were correctly diagnosed by total N:S ratio during tillering, and critical N:S ratios varied from 14.8:1 to 16:1. At the same time, malate:sulfate ratio diagnosed correctly between the 35 and 65% of the samples. Grains with S deficiency were determined as those with a total S concentration lower than 0.15% and a total N:S ratio higher than 13.3:1. Validation of these new thresholds allowed determining that 77% of the samples were correctly diagnosed. A linear association between grain N:S ratio and N:S in aerial biomass during stem elongation was found (r2 = 0.76-0.78, respectively).