Modeling soil organic carbon dynamics under shifting cultivation and forests using Rothc model

Shifting cultivation (jhum) and forest land are the main land uses in North Eastern region of Indian Himalaya, but in the long term this form of agriculture is not acceptable due to the soil degradation following the cutting of forest vegetation, and the consequent biodiversity loss, high erosion rates and nutrient loss through runoff. No information on soil organic carbon (SOC) dynamics and simulation studies are available, so an attempt was done using RothC model. The model was parameterized on measured SOC contents of forest and jhum sites, and average SOC stocks and changes were simulated for a period of 5 years in forest and jhum sites under the baseline and the projected climate change conditions available for Nagaland state (2021-2050). Forest sites under the baseline climate showed a steady-state condition, and simulated SOC decreased by 0.04 t C ha(-1) yr(-1) during 5 years. In addition simulations indicated that forest land use could not benefit from climate change in a 10 years period (SOC changes showed a decreasing trend from 0.36 to 0.06 t C ha(-1) yr(-1)). Jhum sites showed negative changes in SOC stocks both under the baseline (0.40 t C ha(-1) yr(-1)) and the projected climate change conditions (0.50 t C ha(-1) yr(-1)). Indeed, SOC decreases under climate change were inversely related to the duration of the jhum cropping cycle, almost linear in the first five years (from 0.65 to 0.41 t C ha(-1) yr(-1)), and thereafter only slightly decreasing (from 0.39 to 0.32 t C ha(-1) yr(-1)). We can conclude that under climate change conditions the jhum cropping cycle can be extended for a longer period without substantial effects on SOC decreases.