Soil organic carbon response to no-till is conditioned by edaphoclimatic moderators in tropical agriculture: Evidence from Brazil

Fixed-depth soil sampling can bias soil organic carbon (SOC) stock comparisons between no-tillage (NT) and conventional tillage (CT) when bulk density differs between systems, yet many tropical syntheses have not corrected for this effect. A systematic review compiled 46 studies from 58 sites across five Brazilian biomes, Cerrado, Mata Atlântica, Amazônia, Caatinga, and Pampa, and applied a CT-anchored equivalent soil mass (ESM) framework to harmonize SOC stocks across cumulative depth strata of 0–20, 0–40, 0–60, and 0–100 cm. The dataset was dominated by Ferralsols (Latossolos, Oxisols), Cambisols (Cambissolos, Inceptisols) and Acrisols (Argissolos, Ultisols). In the paired meta-analytic subset, NT increased SOC stocks by 18% relative to CT (NT/CT = 1.18, 95% CI: 1.11–1.26), although the prediction interval (0.84–1.74) indicated substantial context dependence. ESM-standardized profiles showed that gains extended to 0–60 cm in the Cerrado and Mata Atlântica, whereas responses were near zero in the Caatinga and largely surface-confined in Amazônia. Time since NT adoption was not a significant moderator, despite NT showing higher SOC stocks throughout the entire evaluated period. In moderator analyses of SOC stocks under NT, clay content showed a positive association, whereas mean annual rainfall showed a negative association. These findings demonstrate that mass-corrected, profile-integrated accounting substantially alters estimates of NT mitigation potential in tropical agroecosystems and underscore the need for carbon accounting frameworks to incorporate ESM approaches and stratification by texture and moisture regime to avoid systematic bias in cross-climate comparisons. Such integration is relevant for Measurement, Reporting, and Verification systems supporting national climate commitments, including Brazil’s Nationally Determined Contribution and Low Carbon Agriculture Plan, but is equally applicable to global assessments of conservation agriculture. • NT increased SOC stocks by 18% relative to CT, but strongly context dependent. • SOC stocks in tropical biomes increase with clay but decline with rainfall. • ESM-corrected SOC gains extended to 0–60 cm in the Cerrado and Mata Atlântica. • NT/CT SOC stocks gains were greatest by 8-year, time not moderating. • Mass-corrected accounting is essential for unbiased SOC stocks assessments.