Release pattern of sulphur from sulphitation pressmud amended Sub-tropical recent floodplain soils

Sulphur (S) mineralization is an important process in S cycling that governs its availability to the plants. The effect of two moisture regimes on S mineralization from sulphitation pressmud (SPM) (C = 42.7%; S = 0.28%; C: S = 153:1; N = 2.44%; C: N = 18:1) in the two floodplain soils with contrasting CaCO₃ content was evaluated under controlled laboratory conditions. Study was carried out by incubating calcareous (Typic Ustifluents) and non-calcareous (Typic Ustipsaments) soils for 12 weeks with SPM @ 0.5 and 1.0% and inorganic-P (Pi) @ 25 mg P kg⁻¹ soil under aerobic [60% water-filled pore space (WFPS)] and nearly-saturated (90% WFPS) moisture regimes at 32±2°C to investigate S mineralization. Mineralization of S started quickly in both the soils but declined steadily under nearly-saturated soil condition over the entire observational period. Under aerobic conditions, the application of SPM @ 0.5% resulted in increase of SO₄^2- - S from 15.4 to 18.4(19.5%) mg S kg⁻¹ soil and 15.7 to 19.2(22.3%) mg S kg⁻¹ soil with an apparent S recovery of 42.4 and 30.8% in calcareous and non-calcareous soils, respectively. The S mineralization of SPM was significantly higher in the non-calcareous soil as compared to the calcareous soil. The addition of Pi resulted in 12.7 and 16.2% increase in SO₄^2--S concentration over no-Pi application under aerobic and nearly-saturated moisture regime, respectively.