Long term soil carbon sequestration potential of smallholder croplands in southern Ethiopia with DAYCENT model

Considering the importance of soil organic carbon (SOC) and the scarcity of data on how soil management influences its storage in the region, this study assessed the long-term impact of different soil management systems on SOC in southern Ethiopia using the DAYCENT model. The conservation management systems considered were minimum tillage, crop residue (CR) retention, fertilization and their combinations. We parameterized the model with data from studies in the literature. We then modeled conventional cropping system for smallholding farms over a 30-year period (1991-2020) as the business as usual scenario (BAU). Then we assessed the impact of alternative conservation management scenarios compared with the BAU scenario. Our results indicated that the conservation management scenarios increased SOC at 0-20 cm depth in the range 0.34-9.71 Mg C ha^-1 over 30 years when compared to BAU practices. The individual effect of fertilization, CR retention or minimum tillage management practices on SOC stock were lower than the response of the combined conservation management practices. The combined 50%-75% CR retention, no-tillage (NT), and 32 kg N ha^-1 fertilization provided the highest SOC sequestration. These combinations, increased SOC in the range 8.10-9.71 Mg C ha^-1 over 30 years equivalent to rates of 0.27-0.32 Mg C ha^-1 yr^-1. While long-term empirical data from field experiments are lacking, model results suggest that the combined 50-75% CR retention, NT, and increased N fertilization have a potential to increase SOC sequestration in resource-limited smallholding croplands. The results may be useful for researchers, policy maker and other stakeholders.