Study on slow release mechanism of carbon-based fertilizer coated with cellulose membrane modified by EAME

Objective To investigate the impact of modified cellulose membrane on the nutrient release properties of biochar-based fertilizers, and provide a theoretical foundation for constructing rational coated slow-release fertilizers.MethodECBIUF (Trans-9, 10-epoxyoctadecanoic acid methyl ester cellulose membrane coated biochar-based infiltrated urea fertilizer) was prepared using microcrystalline cellulose as a precursor and trans-9, 10-epoxyoctadecanoic acid methyl ester (EAME) under varying concentrations and temperatures to fabricate modified cellulose membrane. Leaching experiments were conducted to obtain urea release profile curves. The coating layers before and after release were characterized via contact angle measurements, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscope, to establish the release kinetic model.ResultCompared to unmodified biochar-based infiltrated urea fertilizer (BIUF), the EAME-modified cellulose membrane effectively delayed urea release. The cumulative nutrient leaching rate after the first two leaching cycles decreased from 53.29% (BIUF) to 22.62%, marking a 58% reduction. The total leaching cycles required for full nutrient release increased from 12 to 24, achieving a 100% extension. Enhanced slow-release performance was observed with higher EAME modification concentrations, reducing the initial two-cycle leaching rate from 42.42% to 22.62%. Conversely, elevated modification temperatures slightly weakened this effect, increasing the leaching rate from 22.62% to 24.31%. Kinetic analysis identified three distinct nutrient release phases: Rapid release of surface-crystallized urea, decelerated release of urea physically adsorbed in biochar pores, and prolonged slow-release of urea chemically bound to biochar. ConclusionEAME-modified cellulose membranes enhance the slow-release performance of biochar-based fertilizers through molecular interactions (e.g., hydrogen bonding via hydroxyl groups) and hydrophobic effects from long hydrocarbon chains. This dual mechanism improves fertilizer utilization efficiency and offers a novel approach for developing coated slow-release fertilizers.