## 3 Results and Discussion
The O/C molar ratio decreased during carbonization, leading to dehydration reactions which reduced the hydrophilicity of the surface of the biochar material [63; 64; 65]. These characteristics give biochar long-term stability, allowing it to endure in soil for hundreds of years [66; 67; 68]. Table 2 summarizes the analyses of the structure and morphology of biochar made using different feedstocks. The results revealed that surface area and total pore volume of cassava stem biochar were the highest at 200.46 m\({}^{2}\)/g and 0.1219 cm\({}^{3}\)/g, respectively, followed by corncob biochar (56.35 m\({}^{2}\)/g and 0.0405 cm\({}^{3}\)/g) and cassava rhizome biochar (18.38 m\({}^{2}\)/g and 0.0284 cm\({}^{3}\)/g). As for average pore diameter, cassava rhizome biochar had the widest pore diameter at 61.69 A, followed by corncob biochar (28.72 A) and cassava stem biochar (24.35 A), respectively. Using scanning electron microscopy (Figure 2), analysis of morphology of the three biochar products revealed that biomass type influenced morphology under identical pyrolysis conditions in the same retort. Moreover, biochar obtained from different parts of the same plants also demonstrated different morphological characteristics and structures. Biochar produced from cassava rhizomes and cassava stems have a higher pore density than corncob biochar, while corncob biochar has a high pore size distribution than biochar produced from cassava rhizomes and stems. These results are consistent with measurements of their respective surface areas and total pore volumes. \begin{table}
\begin{tabular}{c c c c} \hline  & **Corncob** & **Cassava Rhizome** & **Cassava Stem** \\ \hline C (wt\%) & 81.35 \({}^{\text{a}}\)\(\pm\) 1.42 & 64.25 \({}^{\text{b}}\)\(\pm\) 1.53 & 62.95 \({}^{\text{b}}\)\(\pm\) 3.71 \\ H (wt\%) & 2.42 \({}^{\text{a}}\)\(\pm\) 0.17 & 2.73 \({}^{\text{a}}\)\(\pm\) 0.17 & 2.24 \({}^{\text{a}}\)\(\pm\) 0.12 \\ N (wt\%) & 1.22 \({}^{\text{b}}\)\(\pm\) 0.14 & 1.65 \({}^{\text{a}}\)\(\pm\) 0.08 & 1.37 \({}^{\text{ab}}\)\(\pm\) 0.06 \\ O (wt\%) & 15.23 \({}^{\text{b}}\)\(\pm\) 1.27 & 31.80 \({}^{\text{a}}\)\(\pm\) 1.27 & 33.44 \({}^{\text{a}}\)\(\pm\) 3.81 \\ H/C ratio & 0.36 \({}^{\text{a}}\)\(\pm\) 0.02 & 0.43 \({}^{\text{a}}\)\(\pm\) 0.12 & 0.42 \({}^{\text{a}}\)\(\pm\) 0.01 \\ O/C ratio & 0.14 \({}^{\text{b}}\)\(\pm\) 0.015 & 0.37 \({}^{\text{a}}\)\(\pm\) 0.02 & 0.39 \({}^{\text{a}}\)\(\pm\) 0.08 \\ C/N ratio & 80.60 \({}^{\text{a}}\)\(\pm\) 8.41 & 45.72 \({}^{\text{b}}\)\(\pm\) 2.34 & 54.08 \({}^{\text{b}}\)\(\pm\) 4.51 \\ Molecular formula & CH\({}_{0.36}\)O\({}_{0.14}\) & CH\({}_{0.51}\)O\({}_{0.37}\) & CH\({}_{0.43}\)O\({}_{0.40}\) \\ Surface area (m\({}^{2}\)/g) & 56.35 \({}^{\text{b}}\)\(\pm\) 0.79 & 18.38 \({}^{\text{b}}\)\(\pm\) 2.21 & 200.46 \({}^{\text{a}}\)\(\pm\) 26.18 \\ Total pore volume (cm\({}^{3}\)/g) & 0.0405 \({}^{\text{b}}\)\(\pm\) 0.0041 & 0.0284 \({}^{\text{b}}\)\(\pm\) 0.0029 & 0.1219 \({}^{\text{a}}\)\(\pm\) 0.01 \\ Average pore diameter (Å) & 28.72 \({}^{\text{b}}\)\(\pm\) 2.29 & 61.69 \({}^{\text{a}}\)\(\pm\) 1.64 & 24.35 \({}^{\text{b}}\)\(\pm\) 1.82 \\ \hline \end{tabular} Note: Data are shown as the Mean \(\pm\) SE. \({}^{\text{a}}\), \({}^{\text{b}}\), Means followed by a different letter are significantly different at the 0.05 level (\(p<0.05\)).  
\end{table} 
Table 2: Properties of biochar product. The physical structure of biochar was dependent on the types of biomass feedstock as well as pyrolysis conditions [69; 70; 71]. After pyrolysis, the easily decomposed C in the original biomass can be stored \"permanently\" (\(>\)100 years) as biochar [72; 73]. The high pyrolysis temperatures lead to dissociation of organic aromatic C bonds, resulting in production of amorphous C [74; 58; 62; 63; 37]. The C in biochar appears mostly in the form of amorphous C in which C atoms are connected in aromatic rings [75; 76; 77].