## 3 Results and Discussion
### Effect of the Addition of Biochar Materials on Se Uptake from Soil and Its Phytoextraction
The addition of 10 g of biochar significantly decreased the Se plant uptake from 8.28 to 5.72 mg/kg (\(p\) = 0.0274) for 1 mg/kg treatments, from 18.9 to 11.09 mg/kg (\(p\) = 0.0248) for 2 mg/kg treatments and from 43.17 to 21.3 mg/kg for 3 mg/kg treatments. Additionally, the activated biochar was more efficient in significantly decreasing Se uptake and its levels in plants compared to pristine biochar. Se levels significantly decreased from \begin{table}
\begin{tabular}{c c} \hline \hline
**Soil Parameters** & **Correlation Coefficient with Se in Plant** \\ \hline pH & 0.713 ** \\ \hline Oxygen redox potential & 0.691 ** \\ \hline Organic matter & 0.606 * \\ \hline Calcium & 0.719 ** \\ \hline Potassium & 0.675 ** \\ \hline Magnesium & 0.72 ** \\ \hline Sodium & 0.711 ** \\ \hline Selenium & 0.759 ** \\ \hline Aluminum & 0.688 ** \\ \hline Chromium & 0.669 ** \\ \hline Iron & 0.736 ** \\ \hline Manganese & 0.691 ** \\ \hline Cobalt & 0.698 ** \\ \hline Lead & 0.634 * \\ \hline Chloride & 0.538 * \\ \hline Sulfate & 0.77 ** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Correlation coefficients (r) of Se in plant with soil parameters. Figure 3: Bioaccumulation factors of Se calculated in the soil at different Se concentrations (1, 2, and 3 mg/kg) using different quantities of materials: 10 and 50 g of activated biochar and 10 g of pristine biochar collected at the end of the greenhouse experimental device. 8.28 mg/kg in soils with no biochar materials to 6.57 mg/kg (\(p\) = 0.00353) and 4.324 mg/kg after adding 10 g and 50 g of activated biochar, respectively, in the presence of 1 mg/kg of Se. Similarly, for the second dose (2 mg/kg), Se levels in plants significantly decreased by almost 5 fold from 18.9 mg/kg to 3.835 mg/kg (\(p\) = 0.0373) and 4.009 mg/kg after adding 10 g and 50 g of activated biochar, respectively. Finally, Se levels in plants showed a 6.5 fold decrease from 43.17 mg/kg to 6.62 mg/kg (\(p\) = 0.0296) and 6.61 mg/kg after adding 10 g and 50 g of activated biochar, respectively, in the presence of 3 mg/kg of Se. Hence, the activated biochar demonstrated higher efficiency than the biochar for diminishing Se uptake. The latter further decreased when adding a higher amount of activated biochar (50 g). This was further confirmed by the decrease in the Se bioaccumulation factor from 10.73 to 6.57 after biochar addition and to 4.75 after activated biochar addition (50 g) in the presence of a 1 mg/kg dose. For a 2 mg/kg dose, BAF decreased from 16.65 to 9.56 after the addition of biochar (10 g) and to 3.7 and 3.49 after the addition of activated biochar (10 and 50 g respectively). For the 3 mg/kg dose, BAF decreased from 21.74 to 13.08 and then to 4.25 after the addition of biochar and activated biochar (50 g), respectively. Thus, biochar, and especially activated biochar reduced the translocation of Se from soil to plant and then its bioaccumulation decreased with the increase to a higher amount of activated biochar. In total, activated biochar showed more efficiency in significantly decreasing Se uptake and accumulation in plants compared to pristine biochar. Thus, the activated biochar addition played an important role in supporting Se levels reduction in contaminated soil and consequently reducing soil phytoextraction performance. This finding was previously confirmed by [PERSON] et al. [46] and [PERSON] et al. [47] who reported that biochar rapidly immobilized heavy metals and reduced their bioavailability in soils and their uptake by non-hyperaccumulator plants. Hence, biochar materials reduced metal bioavailability and bioaccumulation in plants. Additionally, biochar amendment can hinder the phytoextraction of metals by precipitation, complexation, metal electron reduction, and root adsorption while it improves pH, fertility and water-holding capacity, and encourages revegetation [8]. For instance, phytoremediation of mine sludge soil with biochar at 0, 1, 5, and 10% rates promoted the plant species revegetation in metal- and metalloid-contaminated soils [48]. Furthermore, [PERSON] et al.