Optimization of Blended Biochar Pellet by the Use of Nutrient Releasing Model

For the recycling of biomass conversion materials, this experiment was conducted to investigate plant nutrient releasing characteristics, and to determine an optimum blended ratio of biochar for producing a biochar pellet based on a column leaching study. The treatments consisted of only pig manure compost (PMC) as a control, pig manure compost pellets (PMCP), and biochar pellets (BCP) blended with biochar and pig manure compost with the following ratios: 9:1, 8:2, 4:6, and 2:8. Results showed that the accumulated amount of ammonium nitrogen (NH4-N) was in order of PMC > PMCP > BCP (2:8) > BCP (4:6) > BCP (8:2) > BCP (9:1) ratios. The highest accumulated amounts of phosphate phosphorus (PO4-P) and potassium (K) were 1953 and 1917 mg L−1 in the PMC and PMCP, but the lowest in the BCP (9:1) were 223 and 1078 mg L−1, respectively. It was shown that the highest accumulated amount of silicon dioxide (SiO2) was 2329 mg L−1 in the BCP (8:2), but the lowest in the PMC was 985 mg L−1. The estimations for accumulated NH4-N, PO4-P, K, and SiO2 releasing amounts in all the treatments were significantly fitted with a modified Hyperbola model. The optimum mixing rate was estimated to be BCP (2:8). Therefore, biochar pellets might be useful in obtaining basic information on slow-release fertilizer for sustainable agriculture.