Copyrolysis of Biomass, Bentonite, and Nutrients as a New Strategy for the Synthesis of Improved Biochar-Based Slow-Release Fertilizers

Biochar is gaining increasing attention in the field of agriculture, since it can not only be used as a soil amendment for improving soil quality but also as a promising carrier for slow-release fertilizers. Currently, developing cost-effective, environmentally friendly, and high-performance biochar-based slow-release fertilizers (BSRFs) is still challenging. In this study, we propose a new strategy for the synthesis of improved BSRFs by copyrolysis of biomass (cotton straw), nutrients (K3PO4), and bentonite under microwave irradiation. The results show that the presence of bentonite during the copyrolysis process is beneficial for improving the slow-release performance of BSRFs. The mechanistic study based on SEM, TEM, XRD, and XPS characterizations integrated with the release kinetic study reveal that the presence of bentonite in the pyrolysis process facilitates the formation of a desirable structure within BSRFs to improve the slow-release performance, and the formation of P-related chemical bonds during the bentonite participated pyrolysis process also contributes to the improved slow-release performance for P. Moreover, the slow-release performance of BSRFs agrees very well with their positive effects on the growth of pepper seedlings in pot experiments. The economic assessment suggests that the as-synthesized BSRFs should have the advantage of low production costs. We hope this proposed strategy can bring some inspirations for the development of more promising BSRFs in the future.