## 2 Materials and Methods
### Experimental Design  
Seedlings were grown in a greenhouse. The chemical properties of the substrate were determined with the use of standard methods before the experiment (Table 1). The content of N-NO\({}_{3}\) was determined using colorimetry with a phenoldisulfonic acid (UV-1201V spectrophotometer, Shimadzu Corporation Kyoto, Kyoto, Japan). Phosphorus was determined by the vanadium molybdate yellow colorimetric method (UV-1201V spectrophotometer, Shimadzu Corporation Kyoto, Japan). Calcium and potassium were determined using atomic emission spectrometry (AES) (BWB Technologies UK Ltd. Flame Photometers, Newbury, England). Magnesium was extracted with 0.01 M CaCl\({}_{2}\) and quantified using atomic absorption spectrophotometry (AAS1N, Carl Zeiss Jena, Germany). Salinity was measured using conductory (N5773 conductivity meter, Teleko Wroclaw, Wroclaw, Poland), and pH in H\({}_{2}\)O was determined by the potentiometric method. Seedling trays were filled with the tested substrates. Substrate parameters are presented in Table 1.  
Seeds were planted in the first ten days of September 2021 and January 2022 in plug trays with 54 cells each, with a cell volume of 0.11 dm\({}^{3}\). Three trays filled with the same substrate and planted with the seeds of the same _Brassica_ species constituted one treatment. A tray with 54 seedlings constituted one replicate (Figure 1). Greenhouse conditions were adapted to different stages of plant development. During seed germination, trays were covered with PP 18 polypropylene fabric to maintain temperature at 24-26 \({}^{\circ}\)C and a humidity of 80%. The greenhouse climate was controlled by a computer. After seedling emergence, temperature and humidity were decreased to 16 \({}^{\circ}\)C and 60%, respectively. Seedlings were watered by a mixing system, and supplemental light was provided by HPS 600W PL94 600 W/230 V sodium lamps. Supplemental light was provided around the clock in the first days after seedling emergence. On successive days, greenhouse temperature was maintained at 21 \({}^{\circ}\)C during the day and 19 \({}^{\circ}\)C at night \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Substrate** & **pH-H\({}_{2}\)O** & \begin{tabular}{c} **Conductivity** \\ **(m5 cm\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **Salinity** \\ **(g N\({}_{\text{C}}\)1 dm\({}^{-3}\))** \\ \end{tabular} & \begin{tabular}{c} **N-NO\({}_{3}\)** \\ **(mg dm\({}^{-3}\))** \\ \end{tabular} & \begin{tabular}{c} **P** \\ **(mg dm\({}^{-3}\))** \\ \end{tabular} & \begin{tabular}{c} **K** \\ **(mg dm\({}^{-3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Mg** \\ **(mg dm\({}^{-3}\))** \\ \end{tabular} &
\begin{tabular}{c} **N-NH\({}_{4}\)** \\ **(mg dm\({}^{-3}\))** \\ \end{tabular} \\ \hline Control & 6.55 & 0.94 & 1.43 & 121 & 105 & 235 & 1430 & 130 \\ PRO1 & 5.60 & 0.80 & 1.22 & 107 & 85 & 206 & 720 & 81 \\ PRO2 & 5.62 & 0.86 & 1.30 & 133 & 87 & 200 & 750 & 69 \\ PRO3 & 5.93 & 1.04 & 1.58 & 129 & 59 & 150 & 860 & 30 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical and chemical properties of the substrates analyzed in the experiment. Figure 1: _Brassica_ seedlings. (60% humidity), and supplemental light was provided for 16 h each day. In early stages of plant development, seedlings were irrigated and additionally sprayed with mist if required. Seedlings were irrigated on successive days of the experiment. Seedling trays were watered automatically for 10 min, and irrigation treatments were repeated according to need. Substrate moisture was controlled with an LB-797C soil moisture sensor. Plants were watered when substrate moisture decreased to 20%. Pests and diseases were not observed during the experiment, and chemical protection agents were not applied. Plants were regularly watered and twice supplied with the PGMix 14-16-18 (Yara, Szczecin, Poland) fertilizer at 0.5 kg m\({}^{-3}\) (EC = 3.2 mS\(\cdot\)cm\({}^{-1}\)).