Vol. 11, Special Issue 2 (2022)

The sensitivity of each soil labile organic C fraction to the different treatments varied in the 0–5 cm soil layer. Compared to conventional tillage, the percentages of >2 mm macro-aggregates and water-stable macro-aggregates in rice-wheat double conservation tillage (zero-tillage and straw incorporation) were increased 17.22% and 36.38% in the 0–15 cm soil layer and 28.93% and 66.34% in the 15–30 cm soil layer, respectively. Furthermore, the large macro-aggregates (> 2 mm) with the highest proportion of size distribution represented the major pool of SOC stock (47.3–51.2%) and mineralization amount (38.2–43.6%) in the 0–30 cm layer, followed by that in the small macro-aggregates (0.25–2 mm), regardless of tillage practices. Plots with fertilization of 50% NPK + 50% GM (1.8 t ha⁻¹) had significantly higher total soil organic C (TOC), LOC, macro-aggregate-associated C concentrations, and soil aggregation than other treatments. However, increasing the quantity of C input could enhance soil C sequestration or reduce the rate of soil C loss, depending largely on the local soil and climate conditions. SOC can be best preserved by crop rotations with conservation tillage practices such as no or reduced tillage, and with additions of residues, chemical fertilizers and manure SOC change was significantly influenced by the crop residue retention rate and the edaphic variable of initial SOC content. Soil disturbance by tillage leads to destruction of the protective soil aggregate. This in turn exposes the labile C occluded in these aggregates to microbial breakdown. A higher number of macro-aggregates along with greater accumulation of particulate organic C indicate the potential of conservation tillage for improving soil carbon over the long-term in rice-wheat rotation in North India.