Integrated co-pyrolysis and coating for the synthesis of a new coated biochar-based fertilizer with enhanced slow-release performance

Although biochar-based fertilizers prepared by the co-pyrolysis of biomass and other nutrients containing feedstocks have been extensively demonstrated to be promising slow-release fertilizers, a further improvement of their slow-release performance is still highly required. Here, new coated biochar-based slow-release fertilizers (CSRFs) by the integrated co-pyrolysis and coating technology. The results indicate that the application of coating to the surface of biochar-based slow-release fertilizers (BSRFs) derived from the co-pyrolysis of cotton straw, Mg3(PO4)2 and bentonite can significantly improve the slow-release performance. The cumulative release concentration of P is found to be 1.98 g/L from BSRFs within 30 days, while the maximum cumulative release concentration of P from CSRFs is only 0.82 g/L. The P-release rate constants of CSRFs are only about half of those of BSRFs. In addition, the as-prepared CSRFs exhibit superior degradability compared to BSRFs, and 35.21% of CSRFs is degraded within 60 days, which is much higher than that of BSRFs. Finally, pot experiments reveal that pepper seedlings fertilized by CSRFs grow much better than those fertilized by BSRFs.