# Optimization of Blended Biochar Pellet by the Use of Nutrient Releasing Model
## 4 Discussion  
Patterns of Accumulated NH\({}_{4}\)-N Releasing Amount with Different Pellets and Application of a Modified Hyperbola Model  
Nitrogen fertilizers generally occur in chemical transformations such as ammonification, nitrification, denitrification, nitrogen fixation, and immobilization in soil [29; 30]. Urea is widely applied as nitrogen fertilizer due to the rapid release of N to soil, from which plants use only 40%, and 60% is lost in different ways [31]. The maximum evaporative loss was estimated to be from 26.5% to 29.4%, which contributes to greenhouse gases. Therefore, a slow N releasing fertilizer is the best way to minimize N\({}_{2}\)O emission from soil [32]. In the NH\({}_{4}\)-N accumulation amount during leaching periods, it was observed that the greater biochar, the less releasing amount there is. This reason for this might be attributed to the NH\({}_{4}\)-N sorption in the biochar. This finding might be attributed to the previous experimental result, showing that the higher the amount of biochar contained in the pellet, the greater the sorption of NH\({}_{4}\)-N [26]. It might be assumed that Mg, NH\({}_{4}\)-N, and PO\({}_{4}\)-P in the biochar and pig manure compost could be synthesized to struvite [Mg (NH\({}_{4}\))\({}_{2}\)PO\({}_{4}\)\(\cdot\)6H\({}_{2}\)O] as slow-release fertilizer during processing time of biochar pellet. [PERSON] et al. (2015) reported that the soluble compounds of total Mg and total P contained 1% to 21% and 1% to 33%, respectively, in biochar [33]. For applying the releasing model of a modified Hyperbola model, it was observed that there was a basic law that greatly reduced the NH\({}_{4}\)-N release from the BCP treatments compared to the PMC because of changes of its physical properties with pelletization. In addition to the biochar pellets with various combination rates of pig manure compost, the accumulated NH\({}_{4}\)-N and PO\({}_{4}\)-P releasing amounts in the BCP treatments decreased from 49% to 91% and from 61% to 91.3% more than those of the PMC, respectively. Therefore, these biochar pellets had more potential ability on greenhouse gas emission reduction, as well as eutrophication than that of PMC when applied to cropland for agricultural sustainability. Pattern of Accumulated PO\({}_{4}\)-P, K and SiO\({}_{2}\) Releasing Amounts with Different Pellets and Application of a Modified Hyperbola Model  
A large amount of nitrogen and phosphate fertilizer is applied to soil every year to increase soil fertility. Yearly, the present consumption of rock phosphorous as fertilizer is over one million tons [34]. Excessive phosphorous in lakes and ponds is a major cause of eutrophication, which occurs on a global scale and destroys aquatic ecosystems [35]. Accelerated eutrophication not only affects aquatic ecosystems, but also indirectly inhibits economic progress [36]. Muriate of potassium chloride (KCI) is applied as a dominant chemical fertilizer to supply available K to crops [37]. Si is usually taken up by plant as an uncharged monosilic acid (H\({}_{4}\)SiO\({}_{4}\)), and polymerized silica gel (SiO\({}_{2}\)-nH\({}_{2}\)O) is known to be as high as 90% of soluble phytolith formed in plants [38]. Biochar application increased soil and plant available Si content in the shoot of crops [39; 40]. Biochar pellet is important in improving the sustainable agricultural ecosystem by providing plant nutrients as well as carbon sequestration. For total water-soluble accumulated amounts of major plant nutrients, there was high level of significant difference (\(p<0.0001\)) among all treatments (Table 6). It was observed that the total water-soluble accumulated amounts in the BCP (2:8) were significantly highest for NH\({}_{4}\)-N, PO\({}_{4}\)-P, K, and SiO\({}_{2}\) except for the BCP (8:2) compared to the PMC. For applying a modified Hyperbola model, the slightly reduced releasing PO\({}_{4}\)-P fitted with this modified equation from the PMCP treatment compared to the PMC according to pelletization of pig manure compost.