Preparation of a new biochar-based microbial fertilizer: Nutrient release patterns and synergistic mechanisms to improve soil fertility

The contradiction between population growth and soil degradation has been increasingly prominent, such that novel fertilizers (e.g., biochar and microbial fertilizers) should be urgently developed. Biochar is a promising fertilizer carrier for microbial fertilizers due to its porous structure. However, the preparation and mechanisms of the effects of biochar-based microbial fertilizers have been rarely investigated. In this study, biochar, Bacillus, and exogenous N-P-K fertil-izers served as the raw materials to prepare biochar-based microbial fertilizers (BCMFs) by optimizing the preparation methods and the process parameters. Moreover, the release patterns of N-P-K were analyzed. A pot experiment was performed on pakchoi to examine the effect of the BCMFs and explore its synergistic effect on soil fertility. The results of this study indicated that adsorption by biochar maintained bacterial activity, whereas the granulation process re-duced bacterial activity. The adsorption-granulation process increased the content of total nitrogen and organic matter in the soil while enhancing the slow-release effect of the BCMFs. The Elovich model was capable of describing the ni-trogen release of the BCMFs, including the diffusion and chemical processes. As indicated by the result of the column leaching experiment, the BCMFs stopped nutrient leaching more significantly than the conventional fertilizers (CF), especially in stopping N and P leaching. The use of the BCMFs improved the available soil nutrients and soil quality while enhancing the abundance of bacteria correlated with carbon and nitrogen metabolism in the soil. Moreover, a 20 % reduction in the use of the BCMFs did not significantly affect the soil available N and P and the growth status of pakchoi. The result of redundancy analysis indicated that the cation exchange capacity (CEC), NH4+-N, NO3--N, beta-glucosidase (BG), urease (URE), and alkaline phosphatase (AlkP) were the six critical environmental factors for the mi-crobial community structure and could explain 94.8 % of the variance. The BCMFs up-regulated the levels of the above six factors, especially CEC and BG, thus improving the soil quality and enhancing the soil fertility.

Automated summary

The contradiction between population growth and soil degradation requires the urgent development of novel fertilizers like biochar and microbial fertilizers. This study investigated the preparation and effects of biochar-based microbial fertilizers (BCMFs) by optimizing the preparation methods and the process parameters. The results showed that the adsorption-granulation process of biochar improved soil fertility by increasing total nitrogen and organic matter content, while also reducing nutrient leaching. The use of BCMFs enhanced soil quality and abundance of bacteria related to carbon and nitrogen metabolism.