Labile carbon dynamics under initial transition to regenerative agriculture

Understanding the dynamics of labile organic carbon (LOC) is critical for evaluating the short-term impacts of regenerative agricultural practices on soil health. We assessed changes in key LOC fractions such as permanganate oxidizable carbon (POXC) measured by 0.01M, 0.02M, 0.033M potassium permanganate, microbial biomass carbon (MBC), and very labile carbon (C VL ) across four long-term conservation agriculture (CA) experiment sites located in contrasting agro-ecological zones of South Asia namely Karnal, Patna, Aduthurai, and Gazipur. At each site, four cropping system scenarios (S) were evaluated: S1, current farmers practice; S2, current farmers cropping system with partial CA; S3, current farmers cropping system with full CA; and S4, diversified crop rotation with full CA. Soil samples were collected from 0-15 and 15-30 cm depth after two cropping cycles. Results showed that POXC, MBC, C VL , oxidizable organic carbon (SOC) and total organic carbon (TOC) increased following CA adoption during the initial years. Across locations, POXC, C VL , and TOC consistently followed the order S4 > S3 > S2 > S1. Compared with S1, POXC values under S3 and S4 were higher by 6-27% (POXC 0.01M), 9-49% (POXC 0.02M), and 16-50% (POXC 0.033M), indicating enhanced carbon recycling in surface soils. Among all LOC fractions, POXC measured at 0.02 M showed the greatest sensitivity to management practices, supporting its suitability as a rapid, cost-effective proxy for soil health assessment. Overall, these findings highlight the potential of integrating regenerative agriculture practices as nature-based solutions and best-management approaches to accelerate carbon farming in tropical and subtropical cereal-based systems.