# Optimization of Blended Biochar Pellet by the Use of Nutrient Releasing Model
## 1 Introduction  
Technology of carbon sequestration (C seq.) and mitigation of carbon dioxide equivalency (CO2-_equivv._) emissions need to be developed by using by-products of agricultural biomass through carbon-recycle systems in cropland. By-products from agricultural biomass consist of carbonaceous materials such as rice hulls, crop residues, trimming branches, animal waste, and bio-waste from fruit and vegetable markets. In Korea's agricultural sector, the total potential biomass production is estimated at 58,010 Gg yr\({}^{-1}\)[1], which can be converted into a less non-degradable form through biomass conversion technology. Biochar, a porous and carbonaceous material obtained from biomass conversion with thermal treatment under limited oxygen, is one practical option for soil carbon sequestration. It contains a non-degradable structural carbon with double bonds and an aromatic ring that cannot be broken down by microbial organism activities [2]. The produced biochar could be utilized for several purposes [3] However, in its application, 30% is lost due to wind, while 25% is lost during spreading in cropland [4]. On the other hand, one disadvantage of biochar application in the fieldis the presence of fine dust caused by wind during the spreading of biochar, which could affect farmer's respiratory organs. The application of 5% biochar produced at 700 \({}^{\circ}\)C had the most significant C seq. during rice and leaf beet cultivation [5]. For cropland C seq., [PERSON] et al. [6] reported that C seq. is highest at 2.3 tons ha\({}^{-1}\) in corn fields incorporated with biochar and cow manure compost. The mitigation of CO\({}_{2}\)-_equiv_. emission is estimated at 7.3 to 8.4 T ha\({}^{-1}\) and profits ranged from $57 to $163 when incorporated with 2600 kg ha\({}^{-1}\) of biochar in corn fields. Biochar's effects in agro-ecology have been suggested to come from the plant's sorption and retention abilities of available nutrients [7]. Biochar from holm oak tree (_Quercus ilex_) increased ammonium nitrogen (NH\({}_{4}\)-N) adsorption in sandy acrisol associated with humid and tropical climates, but had no effect on nitrate nitrogen (NO\({}_{3}\)-N) sorption in the column experiment [8]. However, the largest amount of sorption of NH\({}_{4}\)-N and binding strength, constant for biochar derived from rice husks, have been calculated as 0.5 mg L\({}^{-1}\) and 0.03 mg L\({}^{-1}\), respectively [9]. [PERSON] [10] reported that rates of nitrogen (N) mineralization and nitrification are low in corn fields incorporated with biochar, compared to plots with different organic composs alone. These could be attributed to the sorption capacity of NH\({}_{4}\)-N to biochar. Phosphorous (P) and potassium (K) are essential elements for both crop growth and the maintenance of crop productivity [11; 12]. The maximum sorption amount and binding strength constant of PO\({}_{4}\)-P are estimated at 0.1 mg L\({}^{-1}\) and 0.06 mg L\({}^{-1}\), respectively, for biochar derived from oak tree [13]. K deficiency in soil is mainly due to presence of 90% to 98% of insoluble K forms or due to the high soluble form of the available K [14; 15; 16; 17]. Crop residues of rice and sugarcane contain applicable amounts of silicon (Si) [18; 19]. Si plays an important role in plant cell wall strength and insect defense, as well as nutrient uptake improvement [20; 21; 22]. Plant silicon is thought to be a recycling Si pool that can be accumulated in surface soil after litter fall and recovered from plant decomposition [23]. A biochar pellet is one option to reduce fine dust and biochar loss by strong wind and intensive rainfall, thus decreasing handling and storage costs [24]. For soil incorporation, poultry litter was mixed, pelletized, and slowly pyrolyzed to produce biochar pellets [25]. [PERSON] et al. [26] indicated that biochar pellets mixed with organic compost could be a promising option for soil C seq. and control of major plant nutrients during crop cultivation.