Soil organic carbon and soil erodibility response to various land-use changes in northern Thailand

Conversion from forestland to agricultural land can influence soil organic carbon (SOC) stocks and soil erodibility. Therefore, the objectives of this study were to assess the SOC stocks and soil erodibility changes relative to land-use changes in the Mae Chaem Basin, Chiang Mai Province, Thailand. Seven adjacent fields were selected and studied during two periods of land-use change: 1) conversion of natural forest to maize fields and 2) replacement of maize with other crops (pumpkin, upland rice, integrated farming, and mango) and grassland. These adjacent fields were located on hillslopes with elevations and slopes ranging from 600 to 800 m a.s.l. and 9 to 25 %, respectively. Soil samples were collected at depths of 0-100 cm from five pits in each field. SOC stocks were estimated using depth-and mass-based approaches. Soil erodibility was calculated based on the Environ-mental Policy Integrated Climate (EPIC) model equation. The results showed that the natural forest contained 174.4 Mg C ha(-1) of SOC stock at 0-100 cm soil depths. After conversion to maize fields, the SOC stock (0-100 cm) was reduced to 96.1 (44.9 % lost) and 82.7 (52.5 % lost) Mg C ha(-1) according to the depth-based and mass -based approaches, respectively. Replacement of maize fields by grassland and pumpkin tended to increase the SOC stocks, whereas they decreased in mango, integrated farming, and upland rice due to the loss of organic matter. This study detected that silt concentration has a highly positive correlation, whereas SOC has a strongly negative correlation with soil erodibility. Grassland had the lowest soil erodibility compared to the other croplands due to lower silt concentration and higher organic carbon. This study indicated that land-use types and conversion time influenced SOC stocks, with variations between soil depths.