## 3 Results and Discussion
### Biomass Yield of Sorghum on the TE-Contaminated Site  
For the cultivar Biomass 133, the germination rates ranged from 72% in the unpolluted condition to more than 76% in polluted conditions (80% in area 1, 76% in area 2, 84 % in area 3). Concerning the cultivar Trudan HL, the rates ranged from 94% in the unpolluted condition to 92% in area 1, 94% in area 2, and 84 % in area 3. These results indicated that high contamination levels did not seem to be a problem concerning sorghum germination.  
The dry weight of both cultivars was calculated after sampling plant individuals in the three areas (Table 2). The growth of the Trudan HL was similar on the three areas. Concerning cultivar Biomass 133, its growth in area 3 was the lowest, with a dry weight 15 times lower than in area 2 and 8 times lower than in area 1 (Table 2, \(p<0.05\)). The highest growth was thus on the area 2 (Table 2, \(p>0.05\)).  
Since area 2 presented the lowest metal contamination, a direct and negative correlation could be drawn between yield and contamination. However, the successful germination and plant growth confirmed the metal-tolerance of both cultivars, which is in agreement with other studies reporting that this characteristic is widespread in this species [13; 33; 34; 46]. Therefore, in addition to the pollution level of the different areas, other factors could explain the differences in dry weight observed between the areas, such as competition with plant colonizers. As observed in Figure 1, some plants naturally colonized areas 1 and 3, resulting in a competition between these indigenous species and the sorghum. From a practical point of view, this confirms that a mechanical weeding, at least at the beginning of the culture, is necessary to favor the sorghum' growth and ensure its sustainable implantation [47].  
The biomass yields per hectare of the two sorghums are reported in Table 3. They were calculated in area 2, from plots of 25 m\({}^{2}\), where all biomass was harvested and extrapolated per hectare. A strong correlation between dry matter (DM) and fresh matter (FM) (r = 0.99, \(p<0.05\)) was observed, which decreased the uncertainty of the DM extrapolation. The extrapolated yields for the two cultivars were comparable to those obtained on an agricultural site under optimal conditions [40; 41]. This result suggested that both cultivars were adapted to the climatic conditions found in the Hauts-de-France region and that the contamination did not negatively affect biomass production.  
Indeed, the extreme temperature of 41.5 \({}^{\circ}\)C and the water deficiency that occurred one month after field sowing (not shown) did not reduce the growth of both cultivars, which agrees with [48], who showed that reduced irrigation or the absence of irrigation has limited impact on the yield of sorghum. In the context of climate change, in which high temperatures and drought periods are expected to increase, these crop cultivars could represent an alternative to the current ones, such as maize, in this region.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Area** & **Average Dry Weight Per Plant (g)** \\ \hline \multirow{3}{*}{**Trudan Headless**} & 1 & 16 \(\pm\) 9 \({}^{\text{a}}\) \\ \cline{2-3}  & 2 & 43 \(\pm\) 16 \({}^{\text{a}}\) \\ \cline{2-3}  & 3 & 16 \(\pm\) 8 \({}^{\text{a}}\) \\ \hline \multirow{3}{*}{**Biomass 133**} & 1 & 125 \(\pm\) 88 \({}^{\text{b}}\) \\ \cline{2-3}  & 2 & 247 \(\pm\) 98 \({}^{\text{c}}\) \\ \cline{2-3}  & 3 & 16 \(\pm\) 15 \({}^{\text{a}}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Average dry weight by plant of the 2 sorghum cultivars sampled at harvest for the 3 areas (10 samples by area, mean + SD). Significant differences between conditions are indicated by different letters at the level of \(\alpha\) = 0.05.