Modeling soil organic carbon stocks and changes in a Nepalese watershed

Land use, land use change and forestry activities play an important role in determining whether soil is a sink or source of atmospheric carbon dioxide (CO₂). The effects of land use change on greenhouse gases and climate change are receiving greater attention in many developing countries. We simulated changes in soil organic carbon (SOC) pool over 100 years (1950–2050) under managed dense Shorea forest (DS), rainfed upland (Bari) and irrigated low land (Khet) of Pokhare Khola, a mid-hill watershed of Nepal, using the Century model. The model was calibrated and parameterized on the basis of biophysical and weather data of the watershed and field measurements made in September/October 2004. Historic C pool data were calculated using the IPCC inventory guidelines for the year 1976 and 1989. The Century model performed well in representing the effects of various land management systems on SOC in the Pokhare Khola watershed. There was a dramatic loss of SOC following the removal of tree biomass and conversion to agriculture. However, it was shown that partial recovery of lost SOC is possible through better forest management, especially if erosion is abated. In the cultivated land we found better recovery by addition of farm yard manure and fertilizer. In all the land use systems, the SOC recovery was lower under the climate change scenario than under prevailing climate.