ABSTRACT
Sulfur (S) is one of the most abundant elements in the earth’s crust and is essential for all biological systems (Tisdale, Nelson, and Beaton 1985). It may occur in several forms, such as native elements, sulfates, sulfides, and organic combinations with carbon and nitrogen. Sulfur is designated as one of the secondary nutrients in a system that classifies nitrogen, phosphorus, and potassium as primary fertilizer nutrients. It is as important as nitrogen, phosphorus, and potassium, but its deficiency and the quantity required are relatively low. In addition, fertilizers such as ammonium sulfate contain about 24% S, simple superphosphate contains about 12% S, magnesium sulfate contains 13% S, potassium sulfate contains 17% S, and gypsum contains 19% S. Sulfur is added to soils along with N and P fertilizers and also through rainfall (especially in industrialized regions), from the atmosphere, and through fungicides. However, modern technology has developed higher grade N and P fertilizers that do not contain S. Furthermore, industries release less and less S into the atmosphere in order to comply with environmental regulations. Under these conditions, S deficiency is expected in modern high-yielding crop cultivars, including rice.
