The Impacts of Land Use Change in 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 help to have healthy environments. The continues conversion of rangelands to arable lands has the potential to change carbon and nitrogen sequestration. In this study to evaluate the effects of land use change on soil organic carbon and nitrogen stock, forty samples collected from northwest of Shahmirzad town in Semnan province of Iran. Samples collected from two types of rangelands (Astragalus parrowianus and Acantholimon erinaceum) and Walnut garden in four depth of soil. The values of soils gravel percentage, particle size distribution, bulk density, organic carbon and total nitrogen have been measured and analyzed. Results showed that there is no significant difference in soil organic carbon (SOC) stock values among garden and rangelands but nitrogen stock in garden showed the higher values and had significant difference with rangelands. The C/N ratio in rangelands was similar unlike garden that showed significant decrease. Moreover, the values of soil organic carbon and total nitrogen (TN) stock and C/N ratio have been decreased in subsurface layer of soils. The results of correlation matrix indicated that the values of SOC and TN stock and C/N ratio had the high correlated with soils particle size distribution. Clay percentage indicated high positive correlation while silt and sand demonstrated negative correlation. Overall, in opposite of SOC stock, land use change from rangeland to garden had significant effect on soil nitrogen stock and increased it dramatically while decreased C/N ratio, considerably.