## 2 Materials and Methods
### Physical and Physico-Chemical Properties of the Substrate  
During the experiment, the pH and EC of the substrate were tested in triplicate from each treatment by taking the solution from the cultivation mats, the so-called mat extract, with a syringe at several places on the mat, at a height of 2, 4 and 6 cm, counting from the top surface of the mat--further defined as the top, middle and bottom of the mat, respectively. For the study, medium samples were taken from the substrate (mat extract) with a volume of approximately 100 cm\({}^{3}\) (single sample). Measurements were carried out 2 times a week 3 times a day at 9:00 a.m., 12:00 p.m. and 3:00 p.m. The method of preparing the substrate samples for evaluating the physical properties of the growing mats depended on the type of substrate. The physical properties of the lignite substrate were determined in accordance with the current standard PN-EN 10041 [40]. An important element of this method is the method of sample preparation, which is based on the natural settling of a loose substrate (10 cm layer), brought to a water potential of \(-57\) cm H\({}_{2}\)O. The determination of physical properties of lignite mats was carried out in cylinders of 10 cm diameter and 5 cm height (Figure S1a Supplementary Material) in a sand block (Eijkelkamp) (Figure S1b Supplementary Material). The determination of air-water properties in the vacuum range of 0-100 cm H\({}_{2}\)O was conducted using a 24 h time to establish water equilibrium at each of the 5 vacuum levels (\(-4.5\), \(-10\), \(-32\), \(-50\) and \(-100\) cm H\({}_{2}\)O). The samples were dried at 105 \({}^{\circ}\)C, and the shrinkage of the media was determined by measuring volume loss. The organic matter content after incineration was determined in accordance with PN-EN 13039 [41] (results are given in % DM), while porosity, bulk density of the substrate, referred to in the paper as BD, and water content were calculated according to the current standard PN-EN 13041 [40]. Physical properties of mineral wool mats, both new and after the experiment, were determined by the method developed at the experimental station Naaldwik in the Netherlands [40; 41; 42; 43; 44]. With a sharp knife, 15 cm \(\times\) 15 cm substrate samples were cut from the mats, placed in a grid box (Figure S1c Supplementary Material) 3 cm from the bottom and filled with distilled water to a level above 1 cm above the samples. The samples were kept in the water for 24 h and then, after removing the water, allowed to stand for 3 h before being flooded again with distilled water. After 30 min, the water was drained, and the samples were transferred to a sand block (Eijkelkamp), establishing a vacuum of \(-100\) cm H\({}_{2}\)O for 30 min. The samples were then once again flooded with distilled water 3 cm above the surface of the wool for 24 h, and then we proceeded to determine air-water properties in the vacuum range of 0-100 cm H\({}_{2}\)O, using the 24 h time to establish water equilibrium at each of the 5 vacuum levels (\(-4.5\), \(-10\), \(-32\), \(-50\) and \(-100\) cm H\({}_{2}\)O). After the sand block determinations were completed, the samples were dried at 103 \({}^{\circ}\)C in a laboratory fan dryer, and the shrinkage of the substrate was determined by measuring volume loss. Organic matter and ash content were also determined (PN-EN 13039) [41] in order to calculate the total porosity (PN-EN 13041) [40].  
The basic physical parameters of the substrate that have a significant effect on plant growth and yield are bulk density, porosity and air-water properties. These characteristics are closely correlated with each other (density-porosity; water capacity-air capacity), so volumetric density and water capacity were selected for comparison. The volumetric density (BD) results are presented in (kg m\({}^{-3}\)), while the results for the other substrate parameters including water content pressure at \(-10\) cm H\({}_{2}\)O, referred to in the paper by the abbreviation WHC, are presented in % vol.