Glucose-derived carbon coating on biochar from empty fruit bunches as slow-release P fertilizer

The surface properties of biochar play a vital role in controlling nutrient diffusion and release behavior. In this study, glucose was used as a carbon coating additive during biochar production to investigate its effects on physicochemical properties and performance as a component of slow-release phosphorus fertilizers. Biochar was produced by pyrolysis at 600 °C for 2 h in a muffle furnace, using varying ratios of glucose. Increasing glucose content led to a reduction in specific surface area, pore diameter, yield, pH, moisture, volatile matter, and ash content. Conversely, fixed carbon content and the I_D/I_G ratio from Raman spectroscopy increased, indicating a greater incorporation of carbon into the biochar matrix as a physical barrier. In addition, FTIR and XPS data further confirmed the more pronounced absorption peak of oxygen-containing functional groups, acting as a chemical barrier that reduced phosphorus release by up to 72.68% compared to biochar without glucose treatment over 30 d in water. Incubation studies in acidic sandy soil showed that biochar application improved soil pH and available phosphorus content, although these effects were diminished when glucose-treated biochar was used. Furthermore, seed germination experiments demonstrated that the inclusion of glucose led to increased plant dry weight and enhanced phosphorus availability. Overall, the findings suggest that glucose-derived carbon coatings can effectively modify the structure and functionality of biochar, enhancing its role in nutrient retention and controlled-release fertilizer systems. This study provides valuable insights into the potential application of glucose-coated biochar for sustainable soil management and improved phosphorus use efficiency.