Combination citric acid and phytic acid co-esterified starch derivative with cellulose acetate as a coating for formulating a full biomass-based slow-release urea fertilizer

The development of coated slow-release fertilizers (SRF) utilizing low-cost and abundantly available biomass materials is still a significant challenge in sustainable agricultural production. Herein, based on the citric acid and phytic acid co-esterified natural starch (NS) derivatives (CAPAS) and cellulose acetate (CAc), a novel full biomass-based coated urea (CAPAS-CAc@urea) SRF was developed by utilizing multiple impregnation coating technology. The experimental results demonstrate that the synthesized CAPAS possesses higher hydrophobicity, film-forming ability, and a well-developed cross-linked network structure, ultimately leading to enhanced mechanical properties, hydrophobicity, and biodegradability of the CAPAS-CAc film. Importantly, the resulting CAPAS-CAc@urea SRF shows superior nutrient slow-release properties, endowing a cumulative N slow-release rate ∼ 77.5% (48 h) in water and ∼ 58.9% (29 d) in soil, which is approximately five times slower than that of uncoated urea. Kinetic fitting indicates that the N release of the prepared CAPAS-CAc@urea complies with the First-order kinetics model, which is governed by a Fickian diffusion mechanism. The results of the sugar sorghum pot experiment verify that CAPAS-CAc@urea exhibits the prominent function for promoting plant growth, primarily through improving root development. Consequently, this study provides a novel route for advancement of environmentally-friendly coated SRF with degradable biomass materials in the sustainable agriculture.