Engineered biochar from sugarcane leaves with slow phosphorus release kinetics

The in-field burning of sugarcane leaf residues presents a major environmental and health burden in Thailand. In this study, sugarcane leaves were converted into a biochar-based slow release phosphorus (P) fertilizer via pyrolysis at 600 degrees C, and the influence of pre- and post-pyrolysis treatment on the P loading and release was investigated. The sugarcane leaves were pre-treated with an alkaline (diammonium phosphate, DAP) or an acidic P source (phosphoric acid, PA), with or without addition of MgO. Additionally, the biochar was post-treated with DAP to increase the P loading. Extraction of P in DI water and 2% formic acid were used as indicators for potential slow release. The microporous biochars had a specific surface area of 69-333 m2 g-1 and pre-treatment resulted in a P content of 34-82 g kg- 1. When MgO was included in the pre-treatment, XRD analysis confirmed formation of crystalline Mg2P2O7, irrespective of the P source. This Mg2P2O7 was responsible for slow P release in DI water over 240 h via a dissolution-controlled process. Post-treatment with DAP increased the P loading to 156 g kg- 1 in the form of water-soluble monoammonium phosphate (MAP), which did not contribute to slow release. The tunable P release via combinations of pre- and post-pyrolysis treatment makes these engineered biochars attractive as P sources for crops and presents an attractive solution to mitigate in-field sugarcane residue burning.

Automated summary

The conversion of sugarcane leaves into biochar-based slow release phosphorus fertilizer via pyrolysis can effectively mitigate the environmental burden of in-field burning. Pre- and post-pyrolysis treatments, including the addition of MgO and DAP, were found to enhance the slow release of phosphorus, making the engineered biochars attractive as P sources for crops.