Characterization of Nitrogen Release in Modified Controlled-Release-Fertilizer using Rice Husk Biochar

Rice husk biochar was added to modify ureic fertilizer in order to control nitrogen release in two methods: (1) mixed-granule and (2) as a coating. The mixed-granule fertilizer was made of varied compositions of rice husk biochar, ureic fertilizer, and clay as a binder, whereas the coating model was formulated from ureic fertilizer, biogas sludge, and clay as a core and coated with various compositions of biochar and clay. All of the samples were leached by 100 mL of water once every three days, and the leachate was analyzed for its nitrogen content. Of all samples, coated fertilizer with a composition of 20% biochar and 80% clay showed the slowest nutrient diffusion with an effective diffusivity (De) number of 2.85×10-8 cm/s2. The results show that both models increase fertilizer’s ability to hold nitrogen longer than pure fertilizer. Both methods, mixed-granule and coated, showed slow release rate patterns, particularly at the beginning of the leaching process, and held the nitrogen content longer. Both models’ release rates enable the modification of nitrogen release to meet the need for nitrogen in certain plantations.