Preparation and characterization of slow-release fertilizer through coating acrylate epoxidized soybean oil

A unique eco-friendly slow-release fertilizer (SRF) was developed using a clean process of spreading biodegradable acrylate epoxidized soybean oil (AESO) on the urea surface and simultaneously cross-linking by UV. The morphologies and properties of the coating layer were characterized using Fourier transform infrared, scanning electronic microscope, and mechanical property testing. The release rates were evaluated by standardized leaching in water, and a pot experiment assessed the SRF effects on corn growth. The results show that AESO has been uniformly coated on the urea granules and successfully cross-linked by UV light. The hardness and toughness of the coated urea particles increased significantly after the coating, which corresponded with the decrease in release rate. The optimized coating SRF (urea 92: AESO 8) achieved a 78% nitrogen cumulative release over 28 days, aligning with most international standards (75%). The nutrient release kinetics followed a characteristic “S” shaped curve, indicative of a typical diffusion mechanism, closely reflecting the law of nutrient demand during plant growth. Importantly, no initial burst phenomena were observed, and the release kinetics were effectively described by the Peppas model, validating the reliability and stability of this SRF. The effect of SRF on the corn growth showed that root length and plan length were increased by about 114% and 52%, respectively, during the first 20 days compared with the application of pure urea fertilizer. The release mechanism was further discussed based on coating thickness, diffusion confession, and fertilizer solubility. The AESO coating could be fully biodegradable in soil after 90 days.