Abstract: An investigation was conducted to determine soil profile（0-3 m）changes in SOC，particulate organic carbon（POC），light fraction organic carbon（LFOC），and aggregate-associated carbon in a long-term field experiment site in an oasis farmland of the National Field Research Station of Desert Ecosystem in Fukang，Chinese Academy of Sciences. The following treatments were compared with the desert soil from which the oasis was created：inorganic fertilizer alone（NPK and N2P2K），inorganic fertilizer combined with wheat straw（NPKR and N2P2R2），and no fertilization（CK）. The result showed as follows：the SOC contents increased by 14%-56% in the topsoil（0-0.2 m），but decreased by 15%-33% in the subsoil（0.2-0.6 m）under all fertilizer applications of >20 years. In the deep layer（0.6-3 m）there were significant differences between the treatments with and without straw：SOC decreased by 5%-9% in treatments without straw，but increased by 4%-9% in treatments with straw. POC and LFOC also had the similar trends. All treatments increased the proportion of macro-aggregates（>0.25 mm）and its associated carbon throughout the soil profile. However， 44%-87% of total SOC was stored in silt+clay fraction， especially in the deep layer. This indicated the importance of SOC stabilization in silt+clay fraction for carbon sequestration. Application of inorganic fertilizer alone led to a significant decrease of SOC content in silt+clay fraction in the deep layer； this should be the main mechanism for SOC loss. Combined application of inorganic fertilizer and straw had the greatest effects on increasing SOC content and enhancing the formation of macro-aggregates， especially for the deep layer.

Key words: soil profile, soil organic carbon（SOC）, aggregates, long-term experiment, oasis