A slow-release fertilizer of urea prepared via biochar-coating with nano-SiO2-starch-polyvinyl alcohol: Formulation and release simulation

Chemical fertilizer is widely used to increase crop yield in conventional agricultural system. However, low use efficiency of chemical fertilizer could lead to its excessive application, and thus decreasing soil quality, causing environmental pollution. This study was designed to evaluate the physicochemical characteristics and slow-release properties of the biochar-coated nitrogen fertilizer with different formulations. The slow-release fertilizers were prepared with the biochar-fertilizer ratio of 1:9, 2:8 and 3:7, using urea as the fertilizer core, biochar as the coating material, and nano-SiO 2-starch-polyvinyl alcohol as binder. The results showed that the compression resistance, wear resistance and moisture resistance of biochar-coated urea increased with the increase of the biochar-fertilizer ratio, which indicated that the biochar coating could decrease the ingredient loss when packaging, transportation and storage. The cumulative nitrogen release, the cumulative leaching of ammonium nitrogen and nitrate nitrogen of the biochar-coated nitrogen fertilizer were lower than those of non-coated one, especially the cumulative leaching of nitrate nitrogen decreased from 34.19% to 15.42% when the biochar coating increased from 10% to 30%. The dynamic characteristics of the cumulative release of nitrogen, the cumulative leaching of ammonium nitrogen and nitrate nitrogen with time in soil could be quantitatively simulated by Elovich equation. Therefore, biochar coating could effectively improve the use efficiency of fertilizer, and had a good slow-release performance.