A biochar-based coated urea for enhanced nitrogen utilization in wheat farming: Field performance, soil microbial response and life cycle assessment

Nitrogen use efficiency (NUE) of conventional urea remains low, leading to significant economic and environmental challenges. While biodegradable polymer-coated slow-release fertilizers offer a promising alternative, their performance is often hampered by rapid nutrient release. This study developed a new biochar-amended coated urea (0.25BC-PVA/SA-SRU) using a polyvinyl alcohol/sodium alginate (PVA/SA) hydrogel matrix to enhance nitrogen utilization in wheat. A comprehensive field experiment demonstrated that 0.25BC-PVA/SA-SRU significantly increased grain yield by approximately 36.2% and 25.5% compared to conventional urea and unamended PVA/SA-coated urea, respectively. Mechanistic insights revealed that the biochar amendment served as a multifunctional modifier within the hydrogel: its microporous structure and adsorption capacity decelerated urea diffusion and minimized burst release, while its hydrophobic nature regulated water infiltration, collectively synchronizing nitrogen release with crop demand. This tailored release kinetics, validated by soil column leaching tests, underpinned a remarkable NUE of 51.0%—more than double that of conventional urea (24.7%). Furthermore, the coating decomposition and biochar incorporation created synergistic soil benefits: they enhanced cation exchange capacity and organic matter content, while the biochar's porous architecture served as a microbial hotspot, significantly increasing bacterial diversity and enriching key taxa involved in nitrogen cycling. Life cycle assessment confirmed the broad environmental advantages of 0.25BC-PVA/SA-SRU, showing consistent impact reductions across multiple categories. The integration of biochar into a biodegradable coating thus establishes a synergistic strategy for sustainable intensification of cereal production, simultaneously addressing agronomic productivity, soil ecological health, and environmental sustainability. • Biochar-amended PVA/SA coated urea boosts wheat yield by 36.2% vs. conventional urea. • Nitrogen use efficiency more than doubles, reaching 51.0% with the novel fertilizer. • Coating regulates N release, enriches soil microbiota, and improves soil health. • LCA confirms reduced environmental impacts across multiple categories.