## 3 Results and Discussion
### Chemical Properties of the Biochars
[57], CEC of biochars reported in literature is highly variable, normally ranging from 5 to 50 cmolc kg\({}^{-1}\), and rarely up to around 200 cmolc kg\({}^{-1}\). Meanwhile, CEC values of soil organic matter range between 200 and 400 cmolc kg\({}^{-1}\)[56]. In our case, BB1 presented the overall highest CEC, with 19.97 cmolc kg\({}^{-1}\), followed by BB3 with 15.40 cmolc kg\({}^{-1}\). General agreement exists that CEC in biochars is attributable to the presence of functional groups, such as carboxyl, rich in oxygen and negative charges, e.g., [PERSON] et al. [58]. [PERSON] et al. [15] pointed out that lower temperature biochars tend to show higher CEC, while higher temperature biochars show higher pH; in other words, CEC varies inversely with charring temperature while pH varies directly. Most biochar studies focus on wood biochars. Our results show higher CEC values in the bamboo biochars (BB1 and BB3) coinciding well with higher O:C ratios, but seemingly also with higher pH. However, this \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **BB1** & **BB2** & **BB3** & **WB1** & **WB2** & **WB3** \\ \hline Proximate analysis & & & & & & \\ Fixed carbon \% & 58.6 & 58.1 & 42.1 & 73.4 & 80.7 & 64.8 \\ Ash content \% & 20.0 & 17.4 & 36.1 & 9.4 & 1.7 & 15.4 \\ Elemental analysis & & & & & & \\ C \% & 66.7 bc & 61.5 b & 38.3 a & 74.5 cd & 75.1 cd & 75.8 d \\ N \% & 0.45 a & 0.51 a & 0.61 a & 0.20 a & 0.22 a & 0.20 a \\ H \% & 2.1 b & 2.2 bc & 1.6 a & 2.2 cd & 2.3 d & 2.6 e \\ S \% & 0.15 a & 0.23 a & 0.25 a & 0.09 a & 0.11 a & 0.17 a \\ O \% \% & 10.6 ab & 18.1 b & 23.2 d & 13.6 abc & 20.6 cd & 5.8 a \\ C:N molar & 177 a & 148 a & 97 a & 434 b & 402 b & 454 b \\ H:C molar & 0.37 a & 0.42 a & 0.39 a & 0.35 a & 0.36 a & 0.40 a \\ O:C molar & 0.12 ab & 0.22 b & 0.45 c & 0.14 ab & 0.21 b & 0.06 a \\ \hline \end{tabular} Distinct letters in a variable for the different treatments means that they are significantly different (\(p<0.05\)).  
\end{table} 
Table 4: Proximate and elemental analysis of bamboo biochar (BB), pinewood biochar (WB) and replicates (1, 2 and 3). \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **BB1** & **BB2** & **BB3** & **WB1** & **WB2** & **WB3** \\ \hline
**EC (mS cm\({}^{-1}\))** & 2.5 ab & 2.5 a & 2.4 b & 0.9 c & 1.0 d & 1.2 e \\
**RLE** & 5.0 a & 0.6 a & 1.9 a & 11.5 b & 9.6 b & 10.9 b \\
**PLC** & 1.0 a & 0.1 a & 0.4 a & 2.4 b & 2.0 b & 2.3 b \\
**pH H\({}_{2}\)O** & 7.6 a & 10.0 b & 10.3 bc & 9.8 b & 7.3 a & 10.6 c \\
**pH KCl** & 10.1 ab & 9.8 a & 10.1 ab & 10.4 b & 10.4 b & 11.3 c \\
**pH CaCl\({}_{2}\)** & 8.0 a & 9.8 b & 10.2 d & 8.8 c & 8.7 c & 10.5 d \\ \hline \end{tabular} Distinct letters in a variable for the different treatments means that they are significantly different (\(p<0.05\)).  
\end{table} 
Table 5: Electrical conductivity (EC), relative liming effect (RLE), potential liming capacity (PLC) and pH analysis of bamboo biochar (BB) and pinewood biochar (WB) replicates. trend is not observed among our pinewood biochars. Apparently, differences in feedstock can have an important influence on the CEC results. No significant differences were found in AEC values between the two groups of biochars.