# Effects of Manure Waste Biochars in Mining Soils
## Results
### Characterization of Amended Mining Soils: Trace Metal Mobility  
Tables 4-6 show pH, EC, and mobile metal content of the control soils and soils amended with the four biochars of the three areas at the end of the experiment. The addition of biochars significantly increased the pH of the soils of the Zarandas-Andalusia area (Table 4), shifting the pH from acidic to \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline  & **Z1** & **Z2** & **Z3** & **P1** & **P2** & **P3** & **P4** & **M1** & **M2** & **M3** \\ \hline pH & 4.68e1  & 4.34b & 3.63a & 8.16i & 8.09h & 7.90g & 7.89g & 5.67d & 5.84e & 7.30f \\
**EC (dS-m\({}^{-1}\))** & 0.06a & 0.09a & 0.22 hce & 0.19b & 0.35d & 1.49f & 2.24g & 0.49e & 0.23c & 0.25c \\
**C-oai (\%)** & 1.34c & 0.22a & 0.10a & 0.78b & 0.92b & 0.39a & 0.25a & 1.73d & 5.38e & 1.83d \\
**CEC** & 11.7e & 3.64a & 2.88a & 23.9f & 12.2e & 9.90c & 10.6 cd & 10.2c & 7.10b & 11.3 de \\
**(mmol-kg\({}^{-1}\))** & 130/7 bc & 1949c & 988 ab & 10001e & 6632d & 424a & 722 ab & 1915c & 706 ab & 961 ab \\
**K (g-kg\({}^{-1}\))** & 0.12a & 0.10a & 0.09a & 5.05c & 4.97c & 6.13d & 8.33g & 4.34b & 7.21f & 6.93e \\
**Texture** & Loamy & Loamy & Sandy & Sandy & Sandy clay & Sandy clay & Sandy & Sandy & Loamy & Sandy \\  & & loam & loam & loam & loam & loam & loam & loam & sand & loam \\ \hline \end{tabular}
\end{table} 
Table 2: Main properties of soils. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline  & **Z1** & **Z2** & **Z3** & **P1** & **P2** & **P3** & **P4** & **Ref.** & **Values\({}^{1}\)** & **M1** & **M2** & **M3** & **Ref.** & **Critical** \\  & & & & & & & & & & & & & \\ \hline  & & & & & & **(dry mg\(\cdot\)kg\({}^{-1}\), except Fe in dry g\(\cdot\)kg\({}^{-1}\))** & & & & & & & \\ \hline Cd & 0.5 & 0.5 & 0.5 & 5.84 & 20.1 & 8.62 & 16.4 & 750 & 12.7 & 0.99 & 1.81 & 1.0 & 3–8 \\ Cr & 97.3 & 2.56 & 2.42 & 61.5 & 39.2 & 50.9 & 43.2 & 1000  & 72.0 & 43.8 & 44.4 & 118.0 & 75–100 \\ Cu & 183 & 374 & 248 & 34.3 & 207 & 35.1 & 47.0 & 10,000  & 13.6 & 11.2 & 9.12 & 34.0 & 60–125 \\ Fe & 58.9 & 91.6 & 98.0 & 113 & 175 & 153 & 185 & - & 201 & 26.6 & 43.1 & - & - \\ Ni & 27.5 & 2.47 & 2.13 & 44.8 & 39.9 & 29.5 & 31.4 & 10,000 & 43.1 & 8.80 & 27.2 & 52.0 & 100 \\ Pb & 104 & 296 & 422 & 5072 & 2848 & 2321 & 2770 & 2750 & 3295 & 82.2 & 174 & 58.0 & 100–400 \\ Zn & 130 & 219 & 81.4 & 2575 & 8573 & 3580 & 6373 & 10,000 & 11,035 & 180 & 758 & 272.0 & 70–400 \\ As & 65.5 & 236 & 528 & 144 & 1183 & 234 & 530 & 40 & 110 & 19.3 & 44.4 & 38.0 & 20–50 \\ \hline \end{tabular} \({}^{1}\) Standard limits for industrial use of soils in Andalusia were used as reference values for Zarandas-Andalusia and Portman-Murcia areas [ENDFOOTNOTE] & 2: Risk-Based Soil Screening Levels for Cantabria soils were used as reference values for Mijarojos-Cantabria area [ENDFOOTNOTE] & 3: Standard limit value for Cr(M1).[ENDFOOTNOTE] & 4: Standard limit value for Cr(M1).[ENDFOOTNOTE] & 5: Critical soil \\ Ni & 27.5 & 2.47 & 2.13 & 44.8 & 39.9 & 29.5 & 31.4 & 10,000 & 43.1 & 8.80 & 27.2 & 52.0 & 100 \\ Pb & 104 & 296 & 422 & 5072 & 2848 & 2321 & 2770 & 2750 & 3295 & 82.2 & 174 & 58.0 & 100–400 \\ Zn & 130 & 219 & 81.4 & 2575 & 8573 & 3580 & 6373 & 10,000 & 11,035 & 180 & 758 & 272.0 & 70–400 \\ As & 65.5 & 236 & 528 & 144 & 1183 & 234 & 530 & 40 & 110 & 19.3 & 44.4 & 38.0 & 20–50 \\ \hline \end{tabular} \({}^{1}\) Values in different columns followed by the same letter are not significantly different (\(p=0.05\)) using the Duncan test.  
\end{table} 
Table 3: Pseudo-total metal content in soils. alkaline. The pH of the Z1 soil (pH: 5.81) increased by more than 2.2 pH units, while the pH of Z2 soil (pH: 5.10) increased by more than 2.8 pH units; for the Z3 soil (pH: 3.43), biochar addition increased the pH by more than 2.2 units. The addition of biochars significantly increased the pH of the soils of the Portman-Murcia Area (Table 5) although only the pH of the P2 soil (pH: 5.06) changed from acidic to alkaline values. The other three soils had an alkaline pH, with the pH increment after biochar addition being around 1 unit.