Long-term impacts of farming systems and preceding crops on soil organic carbon and physiochemical properties in Vertisols of subtropical India

Soils contain the largest pool of terrestrial carbon that is vital for soil fertility. Integration of organic management can have positive effects on soil carbon storage. However, there is still contrasting evidence on the effects of organic management on soil organic carbon (SOC) and nutrients. Most of previous studies focus on temperate regions, on topsoil, are short-term and rarely consider the role that crops play in mediating these effects. Our analysis focuses on cotton systems in a sub-tropical region of central India. Our objective was to assess the long-term effects (12 years) of locally adapted organic and conventional farming systems on SOC and other soil properties, at two different soil depths (topsoil and subsoil) and, with different preceding crop rotation sequences. Our results show that organic systems build up significantly higher SOC stocks (13%) and N concentrations than conventional systems, but this effect was observed after 8 years. For N, we recorded this effect only in the topsoil. We further found that the preceding rotation sequence (PRS) affected soil K, P, and SOC, irrespective of farming systems. Higher K and SOC were recorded when PRS included cotton than when it included soybean. However, the effect of cotton on SOC was recorded in the subsoil, whereas the K effect was recorded in the topsoil. Our work highlights the importance of exploring factors such as soil depth and crop types to get a more comprehensive understanding of management effects on soil properties. We recommend that practices like composting and deep-rooted crop rotations are key to sustain SOC gains in smallholder Vertisols and improve soil health. • Organic systems recorded significantly higher SOC and N%, but only after 8 years • The significant effect on N% was recorded in the topsoil and not in the subsoil • Conventional systems with GMO cotton variety recorded lowest SOC stocks • Crop type in preceding rotation significantly influenced SOC and soil P and K • Crop type effects on SOC and soil K varied across the two soil depths