## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Treatment** & **Physical Parameter of the Substrate** & **Dry Matter** & **TSS** & \(\beta\)**-Carotene** & **Lutein** & **Nitrates** \\ \hline \multirow{2}{*}{MW/control EC} & BD & 0.3399 & \(-\)0.3275 & \(-\)0.3837 & 0.1806 & 0.2598 \\ \cline{2-7}  & WHC & 0.0137 & \(-\)0.0542 & 0.1200 & 0.5242 & \(-\)0.1685 \\ \hline \multirow{2}{*}{L/control EC} & BD & 0.2636 & 0.4665 & \(-\)0.1945 & \(-\)0.0304 & \(-\)0.3964 \\ \cline{2-7}  & WHC & \(-\)0.2079 & 0.1375 & 0.2934 & 0.7782 * & 0.1842 \\ \hline \multirow{2}{*}{MW/high EC} & BD & \(-\)0.0352 & \(-\)0.3728 & 0.2074 & 0.2589 & 0.1367 \\ \cline{2-7}  & WHC & 0.5488 & \(-\)0.5961 & 0.1863 & 0.5225 & \(-\)0.1066 \\ \hline \multirow{2}{*}{L/high EC} & BD & 0.5151 & \(-\)0.0803 & 0.6098 & 0.5481 & \(-\)0.1091 \\ \cline{2-7}  & WHC & 0.7108 & \(-\)0.3257 & 0.2978 & 0.7962 * & \(-\)0.3576 \\ \hline \hline \end{tabular}  
* significant at \(p\leq\) 0.05.  
\end{table} 
Table 13: Multiple correlation coefficient (R) and coefficient of determination (D) for the content of dry matter, TSS, selected bioactive compounds and nitrates in cucumber fruit depending on the type of substrate and medium EC. of high EC concentration in the substrate as for cucumber (Figure 2a-f). The EC and pH values of the substrate and the physico-chemical characteristics of the plant root system environment are mainly influenced by the material of the growing medium [51; 52]. In our study, a negative correlation was found between the water holding capacity of the lignite substrate supplied with the standard EC of the growing medium and the average length and surface area of the leaf. In the study, the average length of a fully developed cucumber leaf was about 22.7 cm, and the calculated leaf area was about 629.8 cm\({}^{2}\) (Table S2 Supplementary Materials).Other researchers also reported a negative effect of low water content on leaf area of tomato grown on sheep wool or hemp fiber substrate [6]. A negative linear correlation (R = \(-\)0.8082) for water holding capacity of lignite substrate in L/control EC treatment was also reported for shoot diameter of cucumber plants. In the present study, the diameter of the cucumber shoot was on average 7.0 mm (Table S2 Supplementary Materials). Other researchers report that for tomato shoot diameter, varying substrate had no effect on this parameter [53; 54]. Different results were obtained by studying the effect of date palm waste substrate on shoot diameter and length of cucumber plants, where this substrate significantly affected the morphological parameters in question compared to, for example, rice husk substrate. According to [PERSON] et al. [55], the date palm substrate had the highest porosity, bulk density and water holding capacity compared to other tested substrates, which translated into good growth conditions for cucumber plants. The availability of nutrients and appropriate physical properties of the substrate affect vegetative growth, and this in turn affects the diameter of the stem. The larger the stem is, the more the vegetative plant growth is. Stems with the thickest stem diameter are less susceptible to damage and other abiotic stresses. Additionally, a thicker stem transports water and nutrients more efficiently [56]. Studies on the effect of lignite substrate on cucumber growth and yield in combination with eustness in the form of high EC showed higher plant stem diameter in the treatment with lignite substrate [20]. It is likely that the lignite substrate, due to its properties, humic acids and nutrient content [57], has a beneficial effect on stem thickness and consequently on plant growth. In the present study, a significant correlation was found between the WHC of the medium in both MW/control EC and L/control EC combinations to K content in cucumber leaves. The potassium content of cucumber leaves grown in these combinations was 35,252.0 mg\(\cdot\)kg\({}^{-1}\) DM for MW/control EC and 31,741.7 mg\(\cdot\)kg\({}^{-1}\) DM for L/control EC.