Sulfur Mineralization: A Key Process for Diagnosing Its Deficiency in Wheat

Consideration of S mineralization could aid the development of S diagnostic methods in wheat (Triticum aestivum L.) but this process has not been investigated under field conditions. The objectives of this study were to evaluate: (i) the use of a simplified S balance to quantify apparent S mineralization (Smin-app) during the wheat growing cycle, (ii) the relationship between Smin-app and S mineralization indicators [N mineralized in anaerobic incubation (Nan) and total and particulate organic C (TOC and POC)], and (iii) the reliability of the proposed S mineralization indicators (Nan, TOC, and POC) for diagnosing S availability alone or combined with SO42--S content at sowing (S-ini). Fourteen field experiments were conducted to evaluate grain yield in response to S fertilization. Soil samples were taken before sowing and S-ini, Nan, TOC, and POC were determined. Additionally, Smin-app was calculated in 7 out of 14 experiments through a simplified S balance. The main outcomes were: (i) Smin-app allowed us to compare S mineralization capacity among soils and was closely related to relative wheat grain yield (R-2 = 0.92), (ii) Smin-app was related to S-ini, Nan, TOC, and POC, (iii) POC was the S mineralization indicator that had the best performance for diagnosing S deficiency and its use in combination with S(ini )allowed for satisfactory diagnosis of S status in wheat via the equation: relative grain yield = 81.5 + (0.19 x S-ini) + (1.56 x POC) (R-a(2) = 0.66). Sulfur mineralization proved to be an important process for wheat S nutrition.