Change in soil organic carbon after slope cropland changed into terrace in southwest China

Abstract

As an important soil and water conservation engineering measure in mountainous and hilly areas, the carbon pool management strategy of terraces is of great significance for maintaining food security and mitigating global warming. However, little is known about its carbon sequestration potential and mechanism. Employing space–for–time substitution, this study investigated the change characteristics of soil organic carbon pool accumulation and distribution after the transition from slope cropland to terrace, as well as the potential for soil carbon sequestration in terraces with different land use patterns (rainfed cropland (CL) and orchard (OR)) across various ages (3–, 6–, 9–, 13–, and 20–year–old) in the Sichuan Basin. During the past 20 years, the SOC, density (SOCD), labile organic carbon (LOC), inert carbon (IOC) and carbon pool management index (CPMI) of the terrace all exhibited an initial decline followed by an increase, generally peaking at 13–year–old before gradually decreasing. Notably, the ages of terrace and its interaction with land use patterns were the main factors affecting the change of organic carbon components (P < 0.05). BD was a significant negative correlation with SOC accumulation (P < 0.05), while TP and C/N were a significant positive correlation with SOC (P < 0.05). Compared with slope cropland, terrace increased soil carbon sequestration mainly by promoting the accumulation of free particulate organic carbon (fPOC), occluded particulate organic carbon (oPOC) and mineral bonded organic carbon (mSOC) (increased by 46.48 %, 96.87 % and 3.93 %, respectively). Compared with OR, CL had higher carbon pool management potential. In conclusion, terraces, especially rainfed cropland terraces, have advantages in carbon increase and sequestration, and will become a potential carbon “sink” under scientific management.