Dynamics of Sulphur in a Calcareous Loam Soil Amended with Sulphur-35 Labelled Sesbania aculeata Green Manure

Kinetics of release of S contained in ³⁵S labelled Sesbanla aculeata green manure was studied at 2 and 5 per cent (fresh weight basis) levels of green manure, at 20 and 35°C temperature and at submergence and field capacity moisture regimes in a calcareous loam soil. Total amount of S extracted by 0.5 M NaHCO₃, ranged from 13.5 to 124.7 and 77.5 to 218.7 μg g⁻¹ soil at submergence and field capacity moisture regimes, respectively. On an average, amount of S in the soil extracted with 0.01 M CaCl₂, was 1.7 to 2.5 times less than that extracted with 0.5 M NaHCO₃. Between 6th and 11th weeks, relatively large amounts of 0.5 M NaHCO₃ extractable organic-S were observed. Peaks of inorganic-S soluble in 0.5 M NaHCO₃ were found at 3 to 6 and then at 12 to 16 weeks of incubation. Differences among different levels of green manure and temperature on mineralization of green manure-S became prominent only after 10 weeks of incubation. The amount of green manure-S extracted by 0.5 M NaHCO₃ or 0.01 M CaCl₂ was almost equal and varied from 5 to 9 μg g⁻¹ at 2% and from 5 to 24 μg g⁻¹ at 5 per cent level of green manure applied at field capacity moisture regime.