Soil mineralizable sulphur: A sulphur availability index

Forms of sulphur (S) and S supplying capacity of Mollisols of low, medium and high category of available S, were investigated from tarai region. One hundred and twenty surface-soil samples were collected, and grouped into low (A), medium (B) and high (C) available S content. Among 120 samples, 10 representative soils were selected and analyzed for their physico-chemical properties. The soils were neutral in reaction; EC ranged from 0.43 to 1.26 dSm¹; and organic carbon content ranged between 7.2 and 36.1 g kg⁻¹. Available S in soil ranged from 6.25 to 36.25 mg g⁻¹; organic-S and inorganic-S ranged from 362 to 538 mg kg⁻¹ and 278 to 1178 mg kg⁻¹, respectively. Sulphur mineralization study indicated that mineralization increased up to the 10^th week and then declined. Highest amount of mineralizable –S content was obtained at the 8^th week in all the three groups of soils. Order of S-mineralization was found as group C > group B > group A. The maximum cumulative S-mineralization was noticed in group B soil. Group C soil did not show a consistent pattern.