Preparation and characterization of slow-release fertilizer encapsulated by biochar-based waterborne copolymers

To enhance the effectiveness of polyvinyl alcohol (PVA) coated fertilizers, a novel slow-release fertilizer was developed using biochar and waterborne copolymer of PVA and polyvinylpyrrolidone (PVP) as coating materials. The effects of botanical origins and doses of biochar as well as copolymer concentrations on biochar-copolymer structures and properties were investigated. Our results indicated that the water absorbency of blend films differing in biochar origins showed different responses to these three factors. Generally, biochar decreased water absorbency of copolymer with an increased degradability, and contributed to improving the slow-release property of coated urea. In particular, rice biochar-based copolymer (S5 film) had less hydrophilic OH bonds and encapsulated urea granules more compactly and densely. The urea particles coated with rice biochar-based copolymer (S5 film) exhibited an excellent release behavior of 65.28% nutrient leaching on the 22th day. Therefore, this work has demonstrated the potential of biochar-based copolymer from different botanical biochar for improving the effectiveness of fertilizers.