A new class of biochar-based slow-release phosphorus fertilizers with high water retention based on integrated co-pyrolysis and co-polymerization

The development of slow-release phosphorus fertilizers (SRFs) with high water retention is of significance for modern agriculture. Herein, a new class of biochar-based SRFs are developed by an integrated co-pyrolysis and co-polymerization process (PSRFs). The water-retention performance and P slow-release behavior of PSRFs are evaluated, which are compared with other types of biochar-based SRFs derived from biochar-based phosphorus adsorption (MSRFs), co-pyrolysis of biomass-bentonite-nutrients (BSRFs), and the application of coating on BSRFs (CSRFs). The results show that the obtained PSRFs exhibits high water retention with the maximum swelling capacity of 94.2 g/g, far outstripping other tested SRFs. The water-retention performance of PSRFs is found to be positively correlated with their crosslinking agent contents. In addition, PSRFs has excellent P slow-release performance which is comparable with CSRFs (~51.5% of P release after 30 days), but much better than MSRFs and BSRFs with a complete P release after 30 days. Furthermore, pot experiments reveal that PSRFs has the highest P utilization efficiency (75.83% after 60 days), which can promote the growth of pepper seedlings better than other SRFs. Moreover, the soil burial tests indicate that PSRFs has a good biodegradability with the degradation ratio of 33.46% in 75 days. Finally, biological abundance analysis further reveals that Actinobacteria in soil is mainly responsible for the metabolism of starch and sodium alginate in PSRFs.