To explore the effects of biochar and straw application on soil carbon constitution and transformation, an incubation experiment was conducted to study the characteristics of the release of carbon dioxide,as well as the changes in microbial biomass carbon and organic carbon in soil after applying biochar or straw only, or biochar plus straw. The results showed that the straw mineralization rate of organic carbon in soil was 21.50% at 2% application level, which was much higher than that of biochar (8.09%). With the same addition amount of biochar and straw at 4% level for 200 days incubation, the soil organic carbon content was 24.40 and 17.40 g·kg-1,respectively. It suggested that the positive impact of biochar application on improving soil organic carbon was greater than that of straw. The application of biochar had protective function on soil original organic carbon. Biochar promoted the straw mineralization and resulted in positive interaction effect between biochar and straw on mineralization of soil organic carbon. The application of straw increased soil microbial biomass carbon (MBC) greatly, while biochar had less impact on MBC. The application of straw and biochar also increased soil microbial biomass carbon, but the interaction effect could be positive or negative, which was dependent on the incubation time or application rate.
Keywords: biochar; dark loessial soil; organic carbon mineralization; soil organic carbon; straw.