Optimizing fabrication of coated fertilizers integrated with biochar for enhanced slow-release properties: Mechanisms and cost-effectiveness analysis

The growing need for environmentally friendly fertilizers that sustain agricultural productivity has spurred research into biochar-based fertilizers. This study optimized biochar-based fertilizers by incorporating biochar into PVA/starch-coated fertilizers at different locations: within the coating (BCmid/PVA/ST-SRF), on the outer surface (BCout/PVA/ST-SRF), and within the capsule (BCin/PVA/ST-SRF). BCin/PVA/ST-SRF showed the best slow-release performance, significantly reducing N and P leaching (N: 71.54%, P: 44.19%) compared to BCmid/ PVA/ST-SRF (N: 77.70%, P: 51.66%) and BCout/PVA/ST-SRF (N: 78.59%, P: 54.51 %), and outperforming commercial fertilizers. Mechanistic studies indicated Fickian diffusion governed nutrient release from BCin/ PVA/ST-SRF, where biochar acted as an initial barrier within the PVA/ST film. Additionally, the superior swelling and mechanical properties of the PVA/ST film contribute to the excellent slow-release performance of BCin/PVA/ST-SRF. Pot trials with bok choy demonstrated enhanced growth and nutrient utilization (N: 84.91 %, P: 13.40%) with BCin/PVA/ST-SRF, and improved nutritional indices. Economic analysis highlighted the scalability and commercial viability of BCin/PVA/ST-SRF production.