Enrichment of soil organic carbon (SOC) stocks through sequestration of atmospheric CO 2 in agricultural soils is important because of its impacts on improving soil quality and agronomic production, and also for adaptation to and mitigation of climate change. Thus, a 15-yr soil fertility management experiment was conducted in the semi-arid tropical region of central India to evaluate the impact of crop residue C input on soybean ( Glycine max L.)-safflower ( Carthamus tinctorius L.) cropping sequence and SOC sequestration in soils of Vertisolic order (Vertisols). Retention of crop residues of soybean/safflower, and application of farmyard manure (FYM) at 6 Mg (t) ha -1 alone or in combination with 20 kg N and 13 kg P ha -1 supplied through chemical fertilizers or comparatively higher dose of chemical fertilizer (60 kg N and 35 kg P ha -1) either maintained or increased the SOC stock. However, the combination of FYM and chemical fertilizer increased the profile SOC stock (69.9 Mg ha -1), overall SOC build up (37.1%) and also sequestered high amount of SOC (11.9 Mg C ha -1 or 0.79 Mg C ha -1 yr -1) compared with control and chemical fertilizer alone. Higher grain yield (2.10 and 1.49 Mg ha -1 of soybean and safflower, respectively) was obtained through the application of FYM at 6 Mg ha -1+N 20P 13. For every Mg C ha -1 increase in the root zone, there was 0.145 and 0.059 Mg ha -1 increase in grain yield of soybean and safflower, respectively. Stabilization of the SOC stock requires a minimum input of 3.47 Mg C ha -1 yr -1. Application of 40 kg N+26 kg P ha -1 through chemical fertilizer also maintained the SOC stock at the antecedent level based on the SOC stocks in 1992. Therefore, the combined use of organic manure (crop residues and FYM) along with chemical fertilizer is essential to enhancing the SOC sequestration in a soybean-safflower sequence under rainfed conditions on Vertisols in central India.
