Does Conservation Agriculture Deliver Climate Change Mitigation Through Soil Carbon Sequestration in Tropical Agro-Ecosystems?

Conservation agriculture (CA), comprising minimum soil disturbance, retention of crop residues and crop diversification, is widely promoted for reducing soil degradation and improving agricultural sustainability. It is also claimed to mitigate climate change through soil carbon sequestration: we conducted a meta-analysis of soil organic carbon (SOC) stock changes under CA practices in two tropical regions, the Indo-Gangetic Plains (IGP) and Sub-Saharan Africa (SSA), to quantify this. In IGP annual increases in SOC stock compared to conventional practice were between 0.16 and 0.49 Mg C ha-1 yr-1. In SSA increases were between 0.28 and 0.96 Mg C ha-1 yr-1, but with much greater variation and a significant number of cases with no measurable increase. Most reported SOC stock increases under CA are overestimates because of errors introduced by inappropriate soil sampling methodology.