Contributions of soil erosion and decomposition to SOC loss during a short-term paddy land abandonment in Northeast Thailand

Abstract

The dynamics of soil organic carbon (SOC) during agricultural abandonment mainly depend on the balance between input from new vegetation type and loss caused by microbial decomposition and soil erosion at an eroded site. However, there is still a challenge to quantify the amount of SOC loss caused by erosion and decomposition. In the Mun River basin of Northeast Thailand, the agricultural lands converted from C3 wood forest before 60 years ago were studied, in which four soil profiles from paddy land and abandoned paddy lands for 1, 3, and 5 years were selected to analyze SOC contents and their stable carbon isotope composition (δ13C). The SOC in the agricultural soils was mainly derived from past C3 wood (δ13C: –28.4‰) and modern rice (δ13C: –20.2‰). In the paddy land, the average content of C3 wood-derived SOC was 2.38 g kg–1 while that of rice-derived SOC was 4.80 g kg–1. The C3 wood-derived SOC decreased by 1.3–1.6 times, while the rice-derived SOC decreased by 7.1–12.6 times with the continuous consumption through decomposition and erosion during the short-term (1–5 years) paddy land abandonment. Total SOC contents decreased by about 70% after paddy land abandonment, in which 25.2–36.3% of SOC loss was associated with soil erosion, while 33.2–44.8% of SOC was lost through microbial decomposition. These results suggest that both microbial decomposition and soil erosion play key roles in SOC loss during short-term paddy land abandonment in tropical sandy soils.