The net and combined effects of minimum tillage and straw mulching on carbon accumulation in global croplands

Abstract

Despite remaining controversial, minimum tillage (MT) carries hope for more soil organic carbon (SOC) accumulation across global croplands to mitigate climate change. The combined use of MT with/without straw mulching (SM) in current studies, however, limits us from understanding the relative contributions of certain conservation principles, and thus their potential for carbon accumulation. In this study, a synthesis was conducted based on a global database to explore the SOC accumulation potential by separating the relative importance of MT and SM. The results show that SM had a better performance in enhancing soil properties than MT, including decreasing soil bulk density (BD) as well as increasing SOC concentration down to deeper soil layers. Adopting SM, MT and the combination of SM and MT (SMMT) significantly promoted SOC sequestration in the 0–30 cm soil, but had no significant impact on SOC sequestration when deeper soil layers were considered. Nevertheless, the overall SOC sequestration rate under SM was over two times higher than MT, and especially, adopting SM could maintain SOC stock in the subsoil. Furthermore, we found that adoption of SMMT had positive impacts on SOC stock accumulations with increasing experimental duration, mean annual precipitation (MAP), and mean annual temperature (MAT) in the surface 0–5 cm soil. The results highlight that it is equally important to increase SOC sequestration in the surface soil and maintain SOC stock in the subsoil, which has been overlooked in current assessments. Further increase of carbon sequestration could be expected by applying proper MT practices over long-term in certain climatic conditions, but a reform of current MT framework through involving SM more deeply is critical in global sustainable agriculture.