## 3 Results and Discussion
### Leachability of manure Blends through the Soil
#### 3.3.2. Leaching of Nitrogen, Phosphorous Anions and Phenols  
The leaching behavior of nitrogen and phosphorous anions and phenols with time from the soil/manure/biochar mixtures, together with the variation of pH and electrical conductivity in the leachates, is illustrated in Table 5. Addition of a higher amount of manure to the soil (100 g/kg instead of 50 g/kg) reduced the pH of the first water extract from 8.1 to 6.2. In both cases, the pH became neutral after a three-month period (7.1 in the case of MAS/soil 50 g/kg and 7.2 in the case of MAS/soil 100 g/kg). However, the more biochar was added (100 g/kg of COS-BIS, instead of 50 g/kg), the higher was the pH of the leachates (up to 8.5), due to the dissolution of some alkaline substances from biochar, such as carbonates of Ca, Mg and K (calcite, dolomite and fairchildite seen in Figure 1). Moreover, Table 5 shows that some readily soluble salts were released from the soil/manure blend in the first leachate, increasing the electrical conductivity values (2.8 mS/cm in the case of MAS/soil 50 g/kg and 4.9 mS/cm in the case of MAS/soil \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Before Incubation**} & \multicolumn{4}{c}{**After Incubation**} \\ \cline{2-9}
**Sample** & **d** & **pH** & **EC** & **WHC** & **d** & **pH** & **EC** & **WHC** \\  & **(g/cm3)** & **pH** & **(mS/cm)** & **(g/g)** & **(g/cm3)** & **pH** & **(mS/cm)** & **(g/g)** \\ \hline Soil & 1.06 & 7.80 & 1.05 & 0.92 & & & & \\ MAS/soil 50 g/kg & 1.02 & 7.70 & 1.10 & 0.94 & 1.0 & 6.35 & 0.20 & 1.0 \\ MAS/soil 100 g/kg & 1.01 & 7.60 & 1.10 & 0.94 & 0.63 & 6.30 & 0.40 & 1.0 \\ COS-BIS/MAS/soil & 1.01 & 7.68 & 1.06 & 0.94 & 0.64 & 6.38 & 0.45 & 1.18 \\
50 g/100 g/kg & & & & & & & & \\ COS-BIS/MAS/soil & 1.0 & 7.79 & 1.05 & 0.94 & 0.61 & 6.41 & 0.20 & 1.20 \\
100 g/50 g/kg & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Physicochemical properties of solid blends. Figure 4: FTIR spectra of pig manure biochar activated by steam at 800 \({}^{\circ}\)C.  
100 g/kg). In the presence of COS-BIS biochar, these values dropped significantly and were very low after 22 days leaching time (0.4-1 mS/cm). As previously mentioned, a higher pH and a lower electrical conductivity favor availability of nutrients for plants. Regarding the concentration of NO3\({}^{-}\) in effluents, from Table 5 it can be seen that this was higher in the case of soil/ manure mixtures (21-45 mg/L) and decreased with leaching time. However, upon addition of COS-BIS biochar to the mixture some retention of nitrate ions occurred (concentration in leachates 7-27 mg/L), revealing either their adsorption on biochar surface, or nitrogen binding in heterocyclic compounds that were not easily solubilized [18]. According to previous research [44], this retention can improve the uptake of manure nitrogen by plants. Furthermore, Table 5 clearly indicates that no phosphates were released in the presence of biochar in the solid blends, in accordance with the insoluble whitlockite magnesium in biochar (Figure 1). Phosphate ions measured in the soil/ manure leachates (6-89 mg/L) were most probably associated with the hydroxyapatite mineral identified in the manure sample (Figure 1). Therefore, the extractability of phosphate ions was mainly correlated with the mineral phases, in which phosphorous was incorporated. Field experiments, however, may provide more relevant information. Finally, the quantity of extracted phenols in all cases was low (1.7-2.9 mg/L). The decrease in COD with leaching time for all solid mixtures is represented in Figure 5. As can be observed, COD values of soil/ manure mixtures were higher than soil/ manure/biochar mixtures, but also exceeded literature data reported for other manure samples [45]. Once biochar was admixed to the above mixture, COD was reduced up to 10 times at the end of the three-month period.