Organophosphate Fertilizers Based on Biochars and Phosphorus Availability in the Soil

To address the low phosphorus (P) use efficiency of soluble phosphate fertilizers, there is a need to develop P sources that better align with crop cycles in highly weathered tropical soils. This work’s hypothesis was that mixing or coating soluble fertilizers with biochar would reduce fertilizer solubility, allowing for a slow and steady release of P, thereby enhancing soil availability. The research aimed to evaluate the solubility and availability of P in soils treated with organophosphate fertilizers composed of biochar and triple superphosphate (TSP) under laboratory conditions. Thus, fertilizers were prepared by either mixing or coating TSP with coffee straw biochar, poultry litter biochar, or eucalyptus bark biochar in ratios of 20 and 40% biochar to 80 and 60% TSP, respectively. After these fertilizers were incubated in a red-yellow latosol for 30 days, it was found that biochar-based fertilizers had lower water solubility and a more gradual P release. PLB-based fertilizers demonstrated up to 50% lower water solubility than TSP, providing a slower and more consistent P release. The coating method resulted in a lower initial P release but a higher final release compared with the mixture. Increasing the biochar content decreased fertilizer water solubility. The results suggest that biochar addition can enhance the efficiency of soluble phosphate fertilizers by moderating P release.