Impacts of Land Use Changes on Soil Carbon and Nitrogen Stocks (Case Study: Shahmirzad Lands, Semnan Province, Iran)

Soil carbon and nitrogen contents play an important role in sustaining soil physical and chemical quality and lead to healthy environments. Conversion of rangelands to arable lands might change carbon and nitrogen sequestration. In order to evaluate the effects of land use changes on soil Organic Carbon (OC) and Nitrogen stock (N), forty soil samples were collected from four depths in two sites of rangelands (Astragalus parrowianus and Acantholimon erinaceum) and one site of walnut garden in north west of Shahmirzad, Semnan province, Iran. The soil properties were measured as gravel percent, particle size distribution, bulk density, OC and N. Results of analysis of variance showed no significant difference of soil OC among garden and rangelands but there was a significant difference for N and higher values were obtained in the garden site. The C/N ratios were similar in both rangelands and they were significantly higher than that for garden. Moreover, the values of OC, N stock and C/N ratio were lower in subsurface layer of soils. The correlation between traits indicated that the values of OC, N and C/N ratio had a significant correlation with soil particle size distribution. Both N and OC stock were positively correlated with clay, soil N content, soil OC and negatively correlated with sand%, silt%, gravel and bulk density. It was concluded that by land use changes from rangeland to garden, the OC values were constant; the C/N ratio were decreased whereas the soil N values were dramatically increased.