## 3 Results and Discussion
### Chemical Properties of the Biochars  
The results obtained from the proximate and elemental analyses of the biochars are shown in Table 4. Higher fixed carbon values in the pine wood biochars contrast with the greater ash contents of bamboo biochars. The ash content in the wood biochars may have been affected by the presence of concrete that could have remained on the feedstock, because the pine wood was collected from construction wastes. The lowest value may be more representative. Note that the ash contents in the bamboo biochars were nevertheless notably higher than that in the wood biochars. As shown in Table 1, lignin contents of conifer woods may be higher than those of bamboo. According to [PERSON] et al. [53] decomposition of cellulose occurs rapidly at low temperatures (between 230 and 400 \({}^{\circ}\)C), while lignins decompose in a wider range of temperatures (160-900 \({}^{\circ}\)C). The differences in the patterns of stove temperatures between bamboo and wood, observed in Figure 1, may obey to differences in the biomass composition [4], due to the temperatures at which decomposition reactions take place, such as oxidation and dehydration. As previously discussed, higher contents of metallic cations have been related to lower pyrolysis temperatures [36; 37; 38]. The O:C ratios are significantly higher in the bamboo group, and within the latter group, they are directly related to higher and longer stove temperatures. The lower yield observed in BB3, and its significantly higher ash content and O:C ratio, may be a consequence of cellulose decomposition during the first minutes and oxidation during the intense peak of heat, sensed in minute 40 by thermocouple I. The latter seems to explain the inverted relation of SSA and hydrophobicity found in the bamboo biochars. In turn, the low O:C molar ratio presented in wood biochars agrees with low O:C ratios reported by [PERSON] et al. [18] on wood biochar surfaces (O:C = 0-0.19). The greater hydrophobicity observed in the pinewood biochars in Figure 3 was consequent with its lower O:C ratios. This relation of hydrophobicity to low O:C ratios has been observed and discussed in other works as well [51; 54]. In both groups of biochars, higher C:N ratios corresponded with higher stove temperatures, which could be explained by greater N volatilization. The H:C molar ratios were significantly similar between and within the groups. The elemental ratios H:C and O:C are indicators of the degree of dehydration and oxidation of the biochars respectively [55]. Low O:C ratios point to polycondensed aromatic structures, which are assumed to be resistant to microbial degradation due to chemical inertness [56], and consequently best suited for long-term soil carbon sequestration [1]. Table 5 presents the results obtained from the analysis of electrical conductivity (EC), relative liming effect (RLE), potential liming capacity (PLC) and pH. Significant differences (\(p<0.05\)) between the two groups of biochars for EC, RLE and PLC were evidenced. Pinewood biochars (WB) were much more limy than bamboo biochars (BB), but their EC was less than half as large, in accordance with lower ash contents. Biochars generally have a substantial liming capacity, to an extent due to mineral content present in the feedstock [4]. Significant differences (\(p<0.05\)) in pH were found between replicates showing higher values of pH in biochars with a higher degree of thermal alteration, in agreement with previous works (e.g., [15; 21]). For example, the higher ash contents and stove temperatures (Figure 1) registered for BB3 suggest it was thermally altered to a higher extent, and BB3 showed higher pH values in all three solutions. Cation and anion exchange capacities (CEC and AEC) show significant differences (\(p<0.05\)) between the two groups of biochars (Figure 4). Overall, pinewood biochars exhibited lower CEC values, around 6 cmolc kg\({}^{-1}\), a low value considering previous studies. According to [PERSON] et al.