Sustainable development of tannin-based slow-release nitrogen fertilizers from chestnut burrs: Synthesis, characterization and their effects on pakchoi growth

To address the growing demand for sustainable agricultural chemicals, this study innovatively utilizes discarded chestnut burrs as a renewable resource to develop tannin-based amine compounds through amine functionalization via Mannich reaction. Subsequently, facile physical blending with urea yielded tannin-based slow-release nitrogen fertilizers (TSRNFs), and their nitrogen-release behaviors were investigated. The results indicated that the synthesized tannin-based amine compounds achieved a high nitrogen content of 14.28 wt% and a reduced C/N ratio, validated by XPS and elemental analyses. Most notably, these compounds synergistically retard nitrogen release through dual mechanisms including self-degradation and strong binding with urea via electrostatic/van der Waals interactions confirmed by molecular dynamics simulations. Soil column leaching experiments demonstrated that ethylenediamine-modified TSRNFs reduced cumulative nitrogen release by 57.83 % compared to urea over 49 days, with release kinetics optimally fitting the Ritger-Peppas model (R 2 = 0.988) and governed by Fickian diffusion. Pot experiments with pakchoi demonstrated that TSRNFs could increase the plant height, fresh weight, and dry weight of pakchoi compared with the control check (CK) and urea treatment groups. Additionally, the vitamin C and nitrate contents in the TSRNFs group were 58.8 % higher and 24.4 % lower than those in the CK group, respectively. In summary, the TSRNF developed in this study was readily prepared, cost-effective, and exhibited excellent performance, holding promise for application in sustainable and low-carbon agriculture as a novel biomass-based slow-release fertilizer. • Tannin-based slow-release nitrogen fertilizers were prepared. • Ethylenediamine-modified tannin showed good slow-release performance. • The nitrogen release mechanism approached Fickian diffusion. • Electrostatic and van der Waals interactions promoted nitrogen capture. • The slow-release fertilizer improved the growth and quality of pakchoi.