Advancing nutrient management in agriculture: Rice straw to nitrogen, phosphorus and potassium-containing hydrogel as slow-release fertilizer

Rice ( Oryza sativa ) straw management is challenging due to its large volume and environmental and health risks associated with traditional disposal methods. Sustainable practices like composting, bioenergy production, biochar, and other industrial applications can address these issues while providing economic advantages. This study introduces a method for converting Rice straw into a slow-release hydrogel containing nitrogen, phosphorus, and potassium (NPK) fertilizers. The process involves a series of acid-base pretreatment to enhance Rice straw reactivity, followed by graft copolymerization with acrylamide (AM) and N,N′-methylenebisacrylamide (MBA) to form a three-dimensional network that retains water and plant nutrients. The application of ammonium persulfate-ferrous sulfate (APS-FS) redox initiator system reduces the gelation time (<2 min) and ensures stable hydrogel structures of whole Rice straw and Rice straw derived cellulose, hemicellulose and lignin-based hydrogels. The hydrogel's structure ensures a slow release of NPK fertilizers, enhancing nutrient use efficiency and providing water to plants. Additionally, achieving over 98 % atom economy indicates that the overall hydrogel production process is a zero-effluent system. Despite challenges in scalability and performance variability under different environmental conditions, the Rice straw-based hydrogel offer promising economic and environmental benefits, positioning them as a valuable tool in sustainable agriculture. • Rice straw is converted into a slow-release hydrogel containing NPK nutrients. • The hydrogel slows NPK fertilizer dissolution and has excellent water retention. • The agriculture industry could benefit from NPK rice straw hydrogel. • 98 % atom economy shows rice straw conversion and hydrogelation are sustainable.