On-farm soil organic carbon dynamics under conservation agriculture in different cropping systems of eastern Gangetic alluvial soils

and no-till practices sequester soil carbon (C) and improve soil texture. Little detailed information is available quantifying the effects of these practices in rice-based cropping systems on the alluvial soils which are widely found across key rice-cultivating regions of South and Southeast Asia and elsewhere. Here we quantify the effects on topsoil texture and organic C sequestration of two tillage options, zero tillage (ZT) and conventional tillage (CT) in farmers’ fields in an old and a recent alluvial soil in West Bengal, eastern India. We considered these effects under two rice-based cropping systems; the widespread rice-wheat (RW) system and the emerging rice-maize (RM) system. Our results demonstrate that conservation agriculture (CA)-based practices increased total organic carbon (TOC) by up to 13.5% relative to CT practices. On the old alluvial soil TOC was 20% higher than on the recent alluvial soil, because of higher background TOC content on the older soil. Soil C was higher under ZT than under CT in both alluvial soils and increased more under RM than under RW. This paper provides new data and insights into the accumulation of different C fractions and demonstrates that these fractions are strongly influenced by clay and sand content in soils, indicating the different potential for old and recent alluvial soils to stabilize and sequester organic C under CA management. Our findings are applicable to other comparable agroecologies globally where CA practices are implemented on alluvial soils. • Soil organic carbon (C) improves in the topmost soil surface through the adoption of conservation agriculture. • Addition of biomass residue enhances the soil organic C status as well as its fractions. • In the rice-maize (RM) system, the rate of C sequestration is notably higher than rice-wheat (RW) under CA. • Stabilization of C and its fractions was more apparent in heavier soils under low rainfall compared to lighter textured soils with higher rainfall • Soil organic C fractions are more stratified in clayey soils than in sandy soils.