Assessment of a Biochar-Based Controlled Release Nitrogen Fertilizer Coated with Polylactic Acid

Conventional nitrogen (N) fertilizers used in crop production typically have use efficiencies of only 30 to 40%. While reduced efficiency can be a result of multiple factors (rate, placement, source), mismatched timing between N availability and N crop demand is a significant cause of reduced efficiency. This study aims to develop a biochar-based controlled release nitrogenous fertilizer (BCRNF) from relatively low-cost renewable materials to improve N availability when needed by the corn crop thus reducing N losses and improving nitrogen use efficiency. Ammonium sulfate was impregnated in biochar and then pelletized into particles. Three concentrations (3%, 6%, and 10%) of polylactic acid (PLA) solutions were used to coat the particles to produce BCRNF. The effects of different PLA concentrations on N release and physical properties of BCNRFs were investigated in both water and soil conditions. Water absorption and retention, thermal stability, and microstructures of BCRNFs were also analyzed to determine the N release mechanism of BCRNFs. The BCRNF coated by 10% and 6% of PLA both released 70% of N over 12 days in water and 25 days in soil. The biochar held 14% N that was not released into the water. However, coating with PLA, increased N holding to 16% inside BCRNF particles. The thermal properties of BCRNFs were stable under 230 degrees C. The PLA concentration of the coating layer significantly affected not only the N releasing time and rate but also the morphology and thermal properties of BCRNFs. Higher PLA concentrations resulted in a longer releasing time at lower N release rates. This study demonstrates that a biochar-based controlled-release nitrogen fertilizer (BCRNF) can enhance N release time and rate in both water and soil environments through the integration of biochar absorption and a PLA coating. Further development could yield a BCRNF that can optimally synchronize timing and amount of available N with crop N demand to increase N use efficiency.

Automated summary

This study aims to develop a biochar-based controlled-release nitrogen fertilizer (BCRNF) to improve nitrogen supply time and rate, thereby increasing nitrogen use efficiency. Through impregnating ammonium sulfate in biochar and coating with polylactic acid, 70% of nitrogen was released in 12 days in water and 25 days in soil. The thermal stability was good, and the PLA concentration significantly affected the nitrogen release time and rate.