## 2 Materials and Methods
### Plant Material  
The test plants were yellow lupine (_Lupinus luteus_ L.), winter oilseed rape (_Brassica napus_ L.), spring triticale (_Triticoscale_ Wittm.), narrow-leaf lupine (_Lupinus angustifolius_ L.), black radish (_Raphanus sativus_), and phacelia (_Phacelia_ Juss.).  
Two factors were considered in the research. The first-order factor was soil contamination with fluorine, applied as potassium fluoride (commercial form), while the second  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multicolumn{6}{c}{**Element (g kg\({}^{-1}\) DM)**} \\ \cline{2-7}  & **F** & **P** & **K** & **Mg** & **Ca** & **Na** \\ \hline Lime (CaO) & 0.50 & 0.12 & 0.75 & 2.55 & 339.21 & 0.09 \\ Charcoal & 2.00 & 0.71 & 9.30 & 2.62 & 7.33 & 0.79 \\ Loam & 0.088 & 0.40 & 21.0 & 17.7 & 23.92 & 7.99 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition of substances added to soil in order to inactivate fluorine.  
factor consisted of the comparison of three substances (time, charcoal, and loam) added to soil to alleviate the fluorine pollution of soil.  
The soil pollution with fluorine, depending on the sensitivity of the test plants, was:  
* 0, 20, 40, and 60 mg F kg\({}^{-1}\) of soil for narrow-leaf lupine.
* 0, 100, 200, and 300 mg F kg\({}^{-1}\) of soil for yellow lupine, winter oilseed rape, spring tritticale, black radish, and phacelia.  
The choice of these doses was based on the average total fluorine content in Polish soils according to Kabata-Pendias [23]. With respect to narrow-leaf lupine, the soil contamination with fluorine was lower than in the other trials because papilionaceous plants are more sensitive to the presence of different xenobiotics in the soil. In addition, the sensitivity of plants to soil fluoride contamination was estimated from preliminary studies conducted prior to setting up this pot experiment. Another plant sensitive to fluorine soil pollution was yellow lupine. In this case, the residual effect of fluorine soil pollution was investigated.  
The materials neutralizing the fluorine soil contamination were lime (in an equivalent dose of 1 hydrolytic acidity-HAC of soil) and charcoal and loam in amounts of 3% relative to the mass of soil in a pot. Additionally, NPK mineral fertilization was added to the soil in identical doses for all pots to cover the demand for plant nutrients. Nitrogen was applied in a dose of 11 mg N (urea), phosphorus of 48 mg P (triple superphosphate 46%), and potassium of 111 mg K kg\({}^{-1}\) of soil (potassium salt 57%). Before setting up the experiment, the soil was dried and sieved (1 cm sieve diameter). A batch of soil weighing 9.0 kg was thoroughly mixed with the mineral fertilizers and with fluorine and neutralizing substances and transferred to adequately labelled pots. Each object was performed in triplicate. Next, the test crops were sown, finally leaving 13 plants per pot except for the trial with black radish, where 8 plants per pot were left to grow. During the plant growth and development, the soil moisture in the pots was constant (60% of capillary water capacity). Yellow lupine and narrow-leaf lupine were harvested at the flowering stage (BBCH 65), winter oilseed rape at the flowering stage (BBCH 65), spring tritticale at the stage of full grain maturity (BBCH 89), phacelia at the stage of full flowering (BBCH 65), and black radish at the final stage of root development (BBCH 49).