Agricultural sustainability: Biochar and bio-based polyurethane coupling coating to prepare novel controlled-release fertilizers

The application of bio-based controlled-release fertilizers is one of the sustainable methods for improving fertilizer effectiveness and reducing agricultural non-point source pollution. In this study, liquefied tobacco ( Nicotiana tabacum L.) stem (LTS) and castor oil were used as raw materials to prepare bio-based polyurethane coating (BPC). The BPC and biochar obtained through pyrolysis were coated on nitramine phosphorus to prepare bio-based double-coated controlled-release fertilizers (BDCRFs). The variables are the 3 %, 5 %, and 7 % BPC coating amounts and biochar from different sources (tobacco stem, fir wood and coconut shell were pyrolyzed at 500 ℃ under oxygen restriction) as components of BDCRFs. The results demonstrated that the excellent hydrophobicity (water contact angle = 138°) and lipophilicity (polyols contact angle = 30°) of tobacco stem biochar (TSB) was conducive to coupling with BPC to improve the controlled-release performance of BDCRFs. Column leaching test indicated the tobacco stem fertilizer (TSF) can achieve long-term controlled-release: with the coating rate of 3 %, 5 % and 7 %, TSF released 71 % ± 2 %, 66 % ± 2 % and 71 % ± 2 % of nutrients on 70, 84 and 124 days, respectively. Meanwhile, the kinetic analysis revealed that the nutrient release mechanism of BDCRFs followed the Ritger-Peppas model. Additionally, TSF with the excellent nutrient release performance were compared with conventional fertilizer (CF), nitramine phosphorus (NP), and no fertilizer (CK) in tobacco field experiments. The results indicated that the biomass, growth indexes and nutritional status of tobacco reached the highest under TSF-5 % treatment. Therefore, the nutrient release of BDCRFs matched the nutrient demand for tobacco growth, reducing the time and labor costs of topdressing and improving the nutrient utilization rate. Therefore, BDCRFs are considered as potential candidates for sustainable development of agriculture and the widespread development and application of controlled-release fertilizers. • Tobacco stem biochar coupling polyurethane to prolong fertilizers release time. • The cost of prepared fertilizers is much lower than commercial fertilizers. • Column leaching test showed tobacco stem fertilizer achieved long-term release. • Field experiment showed tobacco stem fertilizer improved tobacco growth. • Bio-based fertilizers promoted the circular and sustainable agriculture development.