Engineered biochar-attapulgite clay composite: A novel slow-release phosphorus fertilizer

Sustainable agricultural practices are in high demand, and the development of innovative materials for slow nutrient release holds utmost importance. Phosphorus (P) stratification limits plant P availability in no-till farming systems. To address this, a nano composite-based P fertilizer to release nutrients in the root zone following surface soil application is constructed. The nanocomposite fertilizers (BAP-SRFs) were formed by a combination of different amounts of biochar (BC), attapulgite clay (ATP) and KH 2 PO 4 , followed by a high-temperature treatment (500 °C). XANES analysis revealed the enrichment of the surface with carbon (C), oxygen (O) and P-containing functional groups, and the bond formation of P with calcium (Ca) and magnesium (Mg) and organic C. Batch desorption and dynamic release experiments provided conclusive evidence that an interplay between ATP and P contents is crucial for the optimum delivery of P in both aqueous and soil media. The slowest release of P in water was achieved in BAP-SRF, which had a BC to ATP ratio of 2 and was loaded with 200 mg of KH 2 PO 4 . Pseudo-second-order kinetics presented the best fit for P release, demonstrating that the release mechanism of P is primarily based on diffusion. The visual diffusion of P in soil provides critical evidence of the slow-release nature of the BAP-SRFs as compared to commercial single super phosphate. The experimental findings were further corroborated by the first principles density functional theory calculations, which highlighted that BC and ATP make an excellent combination to interact with the KH 2 PO 4 and slow down its release. The engineered nanocomposite P fertilizers developed here may provide a solution for the intractable issue of P stratification in no-till farming systems. The presented research article highlights the synthesis of novel nanocomposite from waste-derived biochar and attapulgite clay loaded with phosphorus. The optimized structure of the nanocomposite allows for slow and controlled delivery of P in water and soil which is demonstrated via batch desorption and dynamic release experiments. • Low-cost biochar and attapulgite clay-based phosphorus nano fertilizer. • Phosphorus bonded to calcium, magnesium and organic carbon. • Higher clay content is the main control factor for the slow release of phosphorus. • Pseudo-second order kinetic fits P release that occurs mainly via diffusion. • Visual diffusion proves that P release is much slower than single superphosphate.