Valorization of palm oil fronds waste for biochar-slow-release fertilizer

The palm oil industry can cause adverse impacts on the environment due to liquid waste from the processing industry and solid waste from plantations. Solid waste from oil palm plantations, such as palm fronds, can be reused into biochar as a slow-release fertilizer coating material. This study aims to study the effect of variations in the composition of coating materials and binder materials on the release of nitrogen in biochar-slow-release fertilizer and the kinetics of its release. The variations used were the biochar/zeolite ratio of 20%:80%-80%:20%, castor oil as a binder, and the amount of urea fertilizer of 30% of the total mass. The results showed that the optimum result for castor oil binder was biochar/zeolite ratios of 50%:50%. The leaching test found that this formula could retard total nitrogen release for up to 30 days, compared to 13 days for the unmodified formulation. Kinetic release analysis using the zero-order model showed that the release mechanism of all samples follows Fick’s law of diffusion, which is related to controlling the release rate from the barrier membrane.