Effects of biochar additions on the soil chemical properties, bacterial community structure and rape growth in an acid purple soil

Biochar is considered as a universal conditioner to improve soil quality, but its effects of different addition rates on soil properties, bacterial community structure and plant growth are still unclear, particularly in the typical acid purple soil in the southwest of China. In this study, 110 days of rape growth pot experiment under the application rate of 0.0% rice husk biochar (CK), 0.8% (CT1), 2.0% (CT2) and 4.0% (CT3) to the acid purple soil. Results showed that all biochar additions improved soil pH, soil organic carbon (SOC), total phosphorus, available phosphorus, available potassium concentrations in the acid purple soil. The activity of both invertase and catalase, not urease, was significantly increased with the increasing of biochar addition rates. The 16s-gene sequencing results showed that the Chao1 index was increased only under CT3, and the Shannon index was increased after all biochar applications. Furthermore, biochar increased the relative abundance of bacteria that play important roles in soil carbon and nitrogen cycles, SOC decomposition, plant diseases control and growth. The plant height and biomass production of rapes were increased under the low biochar level (CT1), but not under the higher rates of CT2 and CT3. These results demonstrated that biochar, as a soil conditioner to the acid purple soil, could increase soil pH value, SOC, available phosphorus and potassium and affect carbon and nitrogen cycles related to bacterial communities for promoting plant performance under low application rate.