Vol. 11, Special Issue 4 (2022)

RT significantly increased (by 24%–90%) the OC content in mineral-SOC within small macro-aggregates in the 0–60 cm layer, while there was a 23%–80% increase in the 0–40 cm layer with NT. The plots with CT had the largest proportion of micro-aggregates (27%). In the 5–10 cm layer, plots with residue retention in both CT and ZT or with monoculture of wheat in plots under ZT without residues (1.4 mm) had the greatest MWD. The 0–10 cm soil layer had a greater proportion of small macro-aggregates compared to large macro-aggregates and micro-aggregates. The contribution of macro-aggregates to SOC stock was larger (36–66%) under CA in the 0–7.5-cm soil layer. Adoption of CA improved the macro-aggregate content, MWD and GMD of aggregates, and aggregation ratio. The reports show that deep rooted, crop-based systems, have higher total soil C stocks and more C in the smallest (< 53 μm) soil fractions indicating the recalcitrant (longer-term storage) nature of C and implying consequent ecosystem benefit of reduced chances for soil C release back to the atmosphere. Moreover, the mean stratification ratio (SR) (i.e. a ratio of the concentrations of SOC in the soil surface to those in a deeper layer) of SOC for 0–5:5–10, 10–15, 15–20, 20–25 and 25–30 cm were found higher (> 2) under CA practices compared to intensive tillage-based conventional agricultural practice.

Furthermore, because conventional cultivation destroyed aggregates, the dominant aggregate size fractions were < 0.5 mm for farmland and > 0.5 mm for other land uses. Compared to the corresponding values in farmland, the mean weight diameter (MWD) in forestland and grassland increased by 808%–417%, and the stability ratio of water-stable aggregate (WSAR) increased by 920%–553%. Aggregate formation and its dominant size fraction were associated closely with its carbon fractions.