Abstract:The applications of biochar and straws are effective methods to improve soil organic carbon and soil aggregate composition. However, their effectiveness in improving soil quality is unclear at the long-term scale. In this study, a 5-year field experiment was conducted to study the impact of organic manure and biochar with equal amount of carbon input on soil aggregate composition, stability and organic carbon contents in an upland red soil in middle subtropical region. The study included five treatments: blank treatment (CK), fertilizer (N), straw (NS), the mixed application of pig manure and straw (NSM) and the biochar (NB). Soil aggregate size fraction was examined by dry and wet sieving methods, respectively. The results showed that soil organic carbon contents increased significantly after 5-year application of different types of organic carbon sources, and the order was as follows: NB> NSM> NS. For dry sieving, the results revealed that macro-aggregate contents ( R0.25) and mean weight diameters (MWD) were significantly higher under NSM and NB treatments than the N treatment. In general, the contributing rates of macro-aggregates to SOC in 0.25-2 mm fraction increased under NS and NB treatments. For wet sieving, the results revealed that R0.25 and mean weight diameters MWD were significantly higher under NSM and NS treatments than the N treatment. The percentage of aggregate destruction (PAD) significantly reduced under NS and NSM treatments, but increased under NB treatment. The contributing rates of macro-aggregates to SOC in >2 mm fraction increased under NSM and NS treatments. In general, the mixed application of pig manure and straws had a stronger capacity to improve synergically soil aggregate stability and organic carbon content in comparison with the straw or biochar returning.