Multifunctional Yeast Cell Wall-Based Polyurethane Coatings for Self-Healing Controlled-Release Fertilizers with Enhanced Nitrogen Use Efficiency and Rhizosphere Microbial Regulation

The low nitrogen use efficiency of conventional fertilizers causes substantial nutrient loss and environmental pollution. Developing high-performance and sustainable coatings for controlled-release fertilizers (CRFs) is crucial for improving nutrient use and reducing environmental impacts. In this study, we designed and prepared a biobased polyurethane coating derived from yeast cell wall (YCW) through liquefaction, polyesterification, and multiple modifications. The optimized coating showed a smoother and denser structure, higher tensile strength (12.5 MPa), and effective self-healing performance, with a self-healing efficiency of 83.9%. The optimized CRF extended the nitrogen release period from 7 to 35 days at the same coating content. In addition, it effectively repaired microcracks that may occur during handling, transportation, or soil application. In pot experiments with Brassica rapa, the optimized CRF increased nitrogen use efficiency by up to 16.6% and enhanced plant growth. Rhizosphere microbial analysis further showed that CRF treatments maintained higher bacterial diversity than conventional urea and selectively shaped microbial community composition, with several keystone amplicon sequence variants positively associated with nitrogen use efficiency. This work presents a renewable and self-healing coating strategy that combines material design with CRF performance, offering a promising pathway toward more efficient and environmentally sustainable agricultural practices.