## 3 Results and Discussion
Slow pyrolysis results in the release of volatile organic matter, hemicellulose, and lignin, and was associated with overall shrinkage, melting, and cracking, resulting in the highly heterogeneous and complex structure of biochar, with many pores of different diameters [78; 79; 80; 81]. These results highlight the importance of biomass type as one of the most important determinants of final biochar properties. The analysis shows that surface area is directly related to total pore volume, which gives biochar an elevated capacity to adsorb cations across its surface [62; 82; 83; 84]. A higher matrix surface area increases ion exchange with nutrients at the surface. Therefore, mixing biochar into the soil can increase the soil's cation exchange capacity [84; 85; 86]. Moreover, surface area and total pore volume both influence  
Figure 2: Scanning Electron Microscopy (SEM) images showing differences in morphology of biochar produced from different biomass feedstocks. biochar's ability to retain nutrients and water within the pore matrix, thus stabilizing their availability within the soil to support crop growth [58; 87]. The results indicated that biochar with high average pore diameter influenced the volume of water and nutrients retained in the pore matrix; biochar with larger pores is able to retain larger amounts of solution and nutrients and subsequently release them for root uptake. This study revealed that chemical composition of biochar (C, H, O and N), H/C ratio, O/C ratio, the chemical structure (aliphatic and aromatic structures) as well as the product's physical characteristics (surface area, total pore volume and pore size) are associated with biochar's higher cation ion exchange capacity [58; 89; 88]. Pyrolysis temperature is an important determinant of physical and chemical properties of biochar, since it governs the extent of cleavage of chemical bonds within key components of the biomass (lignin, cellulose, hemicellulose). At 200-300 \({}^{\circ}\)C volatile fractions are transformed into low molecular weight liquids and gases instead of biochar [90; 91]. Meanwhile, the dehydration of hydroxyl groups and thermal degradation of cellulose and lignin become increasingly significant at higher temperatures [91; 92]. During pyrolysis, hemicellulose decompose first at temperatures ranging from 200 to 260 \({}^{\circ}\)C; cellulose breakdown begins at 240-350 \({}^{\circ}\)C, and decomposition of lignin begins from 280-500 \({}^{\circ}\)C [93]. A dramatically increased surface area in the biomass char is observed to begin at 400-500 \({}^{\circ}\)C [94]. When the temperature is increased to 500-600 \({}^{\circ}\)C, aromatic organic compounds (mainly amorphous carbon, the main component of biochar) begin to break down [37; 74]. The amorphous carbons are structured as aromatic rings, giving biochar its characteristic stability [75; 76; 77]. Pyrolysis temperature is therefore a key determinant of biochar yield as well as pore size and volume [80; 81]. The bonds between aromatic compounds define the structure and properties of biochar. The main surface functional groups are hydroxyl, methyl, carboxylic and alkene groups [91]. However, [PERSON] et al. (2012) [74] found that carboxyl and carbonyl group originating from carbohydrates appeared with the highest intensity at 300 \({}^{\circ}\)C and then decreased at higher temperatures. In contrast, other functional groups were concentrated or formed during decomposition. Aromatic skeletal vibration and aromatic C-H deformation increased until the temperature reached 500 \({}^{\circ}\)C [94; 95; 96]. As temperature increased, the char became progressively more aromatic and carbonaceous. The hydroxy, aliphatic C-H, carbonyl and olefinic CC groups were lost at higher temperatures. The aromatization process begins at \(\sim\)350 \({}^{\circ}\)C and continues to higher temperatures [97]. Many chemical interactions between biochar and the environment are directly related to its surface chemistry.