## 3 Results and Discussion  
### Biochar and Biofetilizer Characteristics  
Except for pH, usually alkaline, biochar characteristics vary broadly because they depend upon the origin of feedstock and the pyrolysis conditions. Bamboo biochar used in this study showed a moderately alkaline pH (8.2); different from that strongly alkaline (9.3) produced by [PERSON] et al. [23] (9.3), and significantly different from that which was  
Figure 1: Experimental design for the greenhouse study. BT20 and BT50: soil + biochar + 20% or 50% of chemical fertilization, BBFT: soil + biochar + biofetilization, CT: soil + 100% chemical fertilization. strongly acidic (5.2) of [PERSON] et al. [60], all of them produced from bamboo at 450 \({}^{\circ}\)C. According to several researchers, pyrolysis temperature is a determining factor for biochar pH: at a higher temperature, higher biochar pH [16; 30; 31; 32; 36; 44]. [PERSON] et al. [44] reported several studies where different feedstocks were pyrolyzed at 500 \({}^{\circ}\)C, and the pH of biochars varied from 8.82 to 10.5. According to the above, the differences in pH of [PERSON]'s and ours biochar could be due to biochar's time and storage conditions. In the case of [PERSON] et al. [60], it would be interesting to confirm if the great exposed surface of the fine particles of biochar they used (smaller than 0.45 mm) increased the oxidation to such an extent that the resulting pH was acid. Mostly vegetable materials produce biochars richer in C, and with lower contents of N, P, and other nutrients than animal origin materials. Table 1 shows that the biochar used in this study presented C and N\({}_{\text{T}}\) contents within the reported ranges for those of plant origin: 34-82% for C, 1700-17,000 mg\(\cdot\)kg\({}^{-1}\) for N\({}_{\text{T}}\), but a higher P\({}_{\text{av}}\) content than those reported (0.02-0.68 mg\(\cdot\)kg\({}^{-1}\)) [28; 44; 61]. The previous data confirm that the value of biochar as a soil conditioner is based mainly on its porous structure, surface charge, and recalcitrant nature rather than on its ability to provide nutrients directly. In addition, the biochar showed a low BD (0.2 g\(\cdot\)cm\({}^{-3}\)), which is beneficial to diminish soil compaction; low EC (1021 \(\mu\)S\(\cdot\)m\({}^{-1}\)), which is adequate to preserve the non-saline current condition of the soil, and high values both for CEC (37 cmol+kg\({}^{-1}\)) and WHC (61%) to improve the efficiency of fertilizer use, and to increase water availability for plants, respectively. Our biochar presented lower BD than [PERSON] et al. (0.29 g\(\cdot\)cm\({}^{-3}\)), which we attributed to the particle size, since ours contained 66.5% of medium and large particles (1-9.5 mm) while [PERSON]'s only had fine particles (<0.45 mm). The CEC value coincides with those reported by [PERSON] (30 and 41 cmol+kg\({}^{-1}\)) reported for biochars obtained at 300 \({}^{\circ}\)C and 450 \({}^{\circ}\)C, respectively. Finally, the low HC\({}_{\text{org}}\) molar ratio of biochar indicated high stability (Table 1). According to [PERSON] et al. [25], a low value of HC\({}_{\text{org}}\) ratio indicates high biochar aromaticity and, therefore, high stability of carbon in the biochar. The characteristics observed in the bamboo biochar used in this study, such as low bulk density and high porosity, surface area, and charge, are typical of biochars obtained at 400-600 \({}^{\circ}\)C, as [PERSON] et al. [62] reported. Our biofertilizer, prepared from \(O\). _ficus indica_, presented a moderately acid pH (Table 2) as well as that obtained by [PERSON] et al. [48] from \(O\). _helibravoana_. Acidic pH helps to keep nutrients available in biofertilizers. The P\({}_{\text{T}}\) content was similar in both biofertilizers, ours and [PERSON]'s et al. [48], but ours had higher N\({}_{\text{T}}\), K, and Mg concentrations, and lower Cu and Fe contents (Table 2).