## 3 Results and Discussion
### Short-Term Effects of Biochar and Biofertilizer on Soil Characteristics  
After the first cultivation cycle, the soil pH presented important variations among treatments relative to the initial value (Table 3). The low buffer capacity showed by the studied soil was in accordance with its sandy nature and low contents of clay and organic matter. The pH decrease in CT and BT20 could be due to urea oxidation. On the other hand, the biochar saturation with alkaline ions (Ca and K) added by the biofertilizer could explain the pH increase in BBfT. However, at the end of the second cultivation cycle, pH shows a tendency to return to the initial value in all treatments. This could be due to the gradual increase in OM observed with all treatments. Soil pH modification by biochar is an area  
Figure 4: Available phosphorus (P\({}_{\rm{av}}\)) in studied soil (S), with biochar (S + B), and with different treatments: CT: soil + 100% of chemical fertilization, BT20 and BT50: soil + biochar +, 20, or 50% of chemical fertilization, respectively, and BBfT: soil + biochar + biofertilization. Different letters indicate significant difference (\(p<0.05\), Duncan test and one-way ANOVA, respectively). requiring further investigation since the majority of studies only report the initial change, or follow up for a very short time, or do not consider the effect that the development of a crop in that soil, the addition of fertilizers or other products to the soil will have. In some times, the effect is the opposite of the expected one. For example, [PERSON] [6] studied 10 acidic and neutral soils to which they added alkaline biochar; in eight soils, pH increased as expected; however, in two acidic soils, pH decreased. EC varied significantly between cultivation cycles, as shown in Table 3. In the first cycle, it increased with all treatments because of salts addition with fertilization (chemical and biological). In contrast, in the second cycle, a significant diminution was observed due to adjustment fertilization doses. It is important to mention that EC always remained less than 2000 \(\upmu\)S\(\cdot\)m\({}^{-1}\). In general, the physical characteristics of the soil improved with treatments. On the one hand, BD remained significantly lower than that of the initial soil. Even at the end of the second cycle, all treatments except CT showed lower values than soil + biochar, and of course, lower than calculated bulk density (Table 3). These results showed that in addition to the dilution effect, biochar was acting as a soil conditioner [65]. A frequently asked question is how long-lasting are the changes produced by biochar in the soil. [PERSON] et al. [30] found that BD of three soils added with different biochars, after 3 years, diminished relative to the initial soil mixed with biochar, except in the cambsiol added with woodchip biochar, where BD increased slightly. However, in all cases, biochars avoided soil consolidation observed in control treatments. On the other hand, WHC increased significantly (\(p<0.05\)) with all treatments in each cultivation cycle relative to the initial soil and soil + biochar as follows: BBfT \(>\) BT50 \(>\) BT20 \(>\) CT (Figure 2a). In CT, the increase in WHC could be explained by the hydration of the added fertilizer salts. In the rest of the treatments, once biochar is combined with soil, it undergoes oxidation and tends to become more hydrophilic as a result of the formation of acidic functional groups on its surface, which explains the gradual WHC increases in each cycle (Figure 2a) [67; 68]. [PERSON] et al. [36] observed this same behavior; the hydrophilicity of biochar increases as it ages. They also found that WHC of biochar pyrolyzed at 300 \({}^{\circ}\)C was significantly higher than those pyrolyzed at 500 \({}^{\circ}\)C and 600 \({}^{\circ}\)C. This is important information for future research with this kind of soil. Regarding exchangeable bases, K increased with biochar and all treatments relative to initial concentration (Table 3).