Soil health responses, nutrient turnover, and carbon footprint dynamics during early adoption of conservation agriculture in secondary laterites

Globally 13% area is under Lateritic soils characterized by compact, vesicular honey-comb structure with low silica-to-sesquioxide ratios resulting in low water and nutrient retention capacity, making them challenging for sustainable crop production. Degraded general health of these soils makes them unusually vulnerable to shifts in management practices. Soil health can be closely tagged with tillage regimes and residue handling in cropping systems since these practices drive microbial turnover and stabilise organic matter. When aligned with conservation agricultural (CA) practices, the improvement is often surprisingly rapid in lateritic profiles, especially the secondary laterites where disrupted aggregates and depleted carbon stocks react quickly to reduced disturbance and a consistent surface mulch. Given this background, a field experiment was initiated in 2022 in secondary laterites to evaluate the effect of varying tillage treatments and residue management practices on soil carbon pools and biochemical properties in rice-wheat cropping system during the transitional phase of CA adoption. The results from the study showed that zero-tillage (ZT) coupled with retained-residues (RR) significantly enhanced Walkley black carbon (WBC) at top soil (15 cm) by 0.33% within three years, whereas, for conventional tillage (CT), WBC content was reduced by 1.55% from initial values. The CA practices also resulted in higher soil respiration rate and favourable bulk density, suggesting an increased microbial turnover and organic matter decomposition. Furthermore, ZT and RR exhibited significant increments in labile pools of organic carbon viz. permanganate oxidizable organic carbon (23-25%), microbial biomass carbon (36-40%) and in soil enzymatic properties viz. dehydrogenase (6-10%), urease (38-42%), acid (58-64%) and alkaline phosphatase (40-44%) respectively, over those under CT. In contrast, traditional CT was recorded with higher soil compaction, reducing microbial activity and overall biochemical quality indices. System yield was also found to be highest under ZT with RR. ZT coupled with RR reduced the carbon footprint over CT due to higher carbon sequestration. The findings indicate that CA with proper residue management can strengthen soil biochemical health, system productivity, and overall sustainability in lateritic soils of tropical and subtropical regions. Their limited buffering capacity, coupled with a tendency for rapid degradation, means that these soils often exhibit a relatively swift positive response when disturbance is reduced and surface residues are maintained.