Enhancing slow-release performance of biochar-based fertilizers with kaolinite-infused polyvinyl alcohol/starch coating: From fertilizer development to field application

Conventional biochar-based fertilizers, which typically consist of a mixture of biochar, chemical fertilizers, and additives, offer benefits but often exhibit rapid nutrient release, limiting their long-term effectiveness. Herein, we explored the enhancement of slow-release performance in biochar-based compound fertilizers by incorporating a kaolinite-infused polyvinyl alcohol/starch (K-PVA/ST) coating, resulting in a new formulation denoted as K-PVA/ST-BCF. The results demonstrated that, compared to traditional NPK fertilizers, nitrogen leaching from K-PVA/ST-BCF in soil column leaching tests was reduced to 19.1 % over 29 days, while phosphorus and potassium leaching were reduced to 48.5 % and 72.3 %, respectively. Mechanistic investigations revealed that the inclusion of kaolinite in the PVA/ST matrix reduces swelling, improves water retention, and enhances mechanical properties, leading to a more gradual and sustained release of nutrients. Field trials on reclaimed land showed that K-PVA/ST-BCF increased wheat yield by up to 100 % compared to conventional NPK treatment. It also enhanced soil nitrogen content and organic matter, with organic matter reaching 22.7 g/kg at grain maturity. The economic assessment indicated that despite higher initial production costs compared to conventional NPK fertilizers, K-PVA/ST-BCF offers higher nutrient use efficiency, reduced management costs, and a net profit increase of $1525.86 per hectare.