Soil organic carbon (SOC) and soil inorganic carbon (SIC) are important C pools in the Loess Plateau of Northwest China,however,variations of SOC and SIC stocks under different cultivation practices and nitrogen (N) fertilization rates are not clear in this area.A long-term field experiment started in June 2003 was conducted to investigate the SOC and SIC stocks in a calcareous soil of the Chinese Loess Plateau under four cultivation practices,i.e.,fallow (FA),conventional cultivation (CC),straw mulch (SM),and plastic fdm-mulched ridge and straw-mulched furrow (RF),in combination with three N fertilization rates,i.e.,0 (N0),120 (N120),and 240 (N240) kg N/hm2.Results indicate that the crop straw addition treatments (SM and RF) increased the contents of soil microbial biomass C (SMBC) and SOC,and the SOC stock increased by 10.1％-13.3％ at the upper 20 cm soil depth in comparison to the 8-year fallow (FA) treatment.Meanwhile,SIC stock significantly increased by 19％ at the entire tested soil depth range (0-100 cm) under all crop cultivation practices in comparison to that of soil exposed to the long-term fallow treatment,particularly at the upper 60 cm soil depth.Furthermore,moderate N fertilizer application (120 kg N/hm2) increased SOC stock at the upper 40 cm soil depth,whereas SIC stock decreased as the N fertilization rate increased.We conclude that the combined application of crop organic residues and moderate N fertilization rate could facilitate the sequestrations of SOC and SIC in the calcareous soil.