Vol. 10, Special Issue 12 (2021)

The plots under ZT had nearly 11% and12% higher total SOC and particulate organic matter-C (POM-C) concentrations, respectively, compared with CT (~12 and 4 g kg^-1 soil, in that order) plots in the 0- to 5-cm soil layer. Plots under F₄ and F₅ had significantly higher total SOC and POM-C contents than F₂ and F₃ treated plots in both soil layers. Although the labile pools of SOC were positively affected by ZT and fertilization, the recalcitrant pool was not. Plots under ZT had higher macro-aggregates, mean weight diameter (MWD), and macro-aggregate-associated SOC compared with CT in the surface soil layer only. Similarly, F₄ or F₅ treated plots had higher macro-aggregates, MWD, and macro-aggregate-associated SOC compared with F₁, F₂, or F₃ treated plots in that layer.

Labile organic carbon (LOC) fractions and related microbial community in soils are considered to be early and sensitive indicators of soil quality changes. The tillage treatments significantly influenced soil aggregate stability and OC distribution. Higher MWD and GMD were observed in plowing every 2 years (2TS), plowing every 4 years (4TS) and no plowing (NTS) as compared to plowing every year without residue (T). With increasing soil depth, the amount of macro-aggregates and MWD and GMD values were increased, while the proportions of micro-aggregates and the silt+ clay fraction were declined. The OC concentrations in different aggregate fractions at all soil depths followed the order of macro-aggregates>micro-aggregates>silt+ clay fraction. In the 0-5 cm soil layer, concentrations of macro-aggregate-associated OC in 2TS, 4TS and NTS were 14, 56 and 83% higher than for T, whereas T had the greatest concentration of OC associated with the silt+ clay fraction in the 10-20 cm layer. Total organic C increased significantly with the integrated use of fertilisers and organic sources (from 13 to 16.03 g kg^–1) compared with unfertilized control (11.5 g kg^–1) or sole fertiliser (NPKZn; 12.17 g kg^–1) treatment at 0–7.5 cm soil depth. Averaged across soil depths, labile fractions like microbial biomass C (MBC) and permanganate-oxidisable C (PmOC) were generally higher in treatments that received farmyard manure (FYM), sulfitation pressmud (SPM) or green gram residue (GR) along with NPK fertiliser, ranging from 192 to 276 mg kg^–1 and from 0.60 to 0.75 g kg^–1 respectively compared with NPKZn and NPK + cereal residue (CR) treatments, in which MBC and PmOC ranged from 118 to 170 mg kg^–1 and from 0.43 to 0.57 g kg^–1 respectively. Oxidisable organic C fractions revealed that very labile C and labile C fractions were much larger in the NPK+FYM or NPK+GR+FYM treatments, whereas the less-labile C and non-labile C fractions were larger under control and NPK+ CR treatments.