## 2 Materials and Methods  
### Experiment Design  
Two years pot experiment was established with second-generation energy crop _Mxg_ (rhizomes from three-year-old plants), produced by the Institute of Sugar Beets and Bioenergy crops, Ukraine. Two rhizomes were planted in each pot and grown from May 2016 to November 2017 under greenhouse conditions. A total of 1 kg of ceramzite as drainage and 1 kg of sand were put in every pot together with 10 kg of soil. The size of the pot was 35 cm upper diameter and 19.5 cm lower diameter (approximately 17 L volume). Three soil variants were prepared in duplicates: post-military soil (MIL) from former military airport Hradcany, agricultural soil (AGR) from nearby farms and petroleum-contaminated soil (OIL). Characterization of all soils is provided in Table 1. Soils were sieved through 1 cm mash and homogenized before the experiment establishment. AGR soil was preliminary intended to serve as a control (i.e., rich soil from locality near the MIL soil which should presumably not limit the plants growth), nevertheless, the laboratory analyses revealed slight contamination by cadmium (Table 1) in levels that were not detectable during in situ screening with handheld XRF. Except for increased Cd (likely originating from the use of inorganic phosphate fertilizers, see Section 3.2), other soil parameters were appropriate for the presumed profitable growth of Mxg. Therefore, it was decided to keep this soil mainly for comparison, not to call it to control. MIL soil was collected directly from the Hradcany airport near one of the plane hangars from the depth 0-30 cm. OIL soil was prepared with the intention to simulate the historical pollution of Hradcany airport with petroleum compounds. The central portion of contamination in the airport site was already removed during remediation, and residual contamination is located in deeper layers (approximately 2-4 meters, although with high variability) [34; 35]. Thus, it was decided to prepare OIL soil as a mixture of MIL soil and petroleum industry sludge soil (ratio 3:1; m/m) to achieve real but defined petroleum contamination. The sludge soil was previously characterized by [PERSON] et al. [36] and used in previous studies [36; 37]. \begin{table}
\begin{tabular}{c c c c c} \hline
**Parameter** & **AGR** & **MIL** & **OIL** & **Preventive Value*** \\ \hline pH (KCl) a & 6.27 & 6.61 & 7.30 & - \\ Available P [mg/kg dw] a & 249 & 40 & 28 & - \\ Available K [mg/kg dw] a & 83 & 59 & 764 & - \\ Available Ca [mg/kg dw] a & 833 & 671 & 4409 & - \\ Available Mg [mg/kg dw] a & 79 & 86 & 205 & - \\ TOC [\% dw] b & 1.14 \(\pm\) 0.05 a & 1.24 \(\pm\) 0.10 a & 4.46 \(\pm\) 0.32 b & - \\ N\({}_{\text{tot}}\) [\% dw] a & 0.66 & 0.57 & 0.68 & - \\ S [\% dw] a & 0.09 & 0.14 & 0.22 & - \\ \hline
**Contamination** [mg/kg dw] & & & & \\ \hline C10-C40 b & \textless{}100 a & \textless{}100 a & 8642 \(\pm\) 351 b & 100 \\ Cd (aqu regia) a & 1.73 & 0.91 & 2.07 & 0.5 \\ Pb (aqu regia) a & 15.23 & 73.22 & 86.13 & 60 \\ Zn (aqu regia) a & 38.83 & 308.48 & 312.01 & 120 \\ Cd (CaCl\({}_{2}\)) a & 0.05 & \textless{}0.01 & 0.01 & - \\ Pb (CaCl\({}_{2}\)) a & 0.01 & \textless{}0.01 & \textless{}0.01 & - \\ Zn (CaCl\({}_{2}\)) a & 4.21 & 5.13 & 4.35 & - \\ \hline \end{tabular}  
* preventive value declared in the Czech legislation; if the value is exceeded, precautions should be taken into consideration, and further inputs of the element/compound to the soil reduced [33]. TOC = total organic carbon; C10-C40 = aliphatic hydrocarbons with the carbon number range between 10–40.  
\end{table} 
Table 1: Characterization of soils used in the experiment (sample of homogenized soil prepared before planting; a n = 1, \({}^{\text{b}}\) mean \(\pm\) SD, n = 4), the same letters behind values mark comparable results (\(p\) \(<\) 0.05). During vegetation season pots were watered 2-3 times per week with rain water to prevent the substrate from drying out completely to avoid drought stress.