## 3 Results and Discussion
### Ability to Release Selected Mineral Components into the Aqueous Phase  
#### 3.2.1 Electrical Conductivity (EC) and pH of the Substrates  
The two types of coconut fibre used to produce the analysed substrate variants differed significantly in terms of pH. In the control treatments based on coconut fibres A and B, the average pH values were 5.85 and 6.40, respectively, indicating an acidic and slightly acidic reaction (Figure 1). Modification of coconut fibre A with the analysed additives significantly increased the pH, with the highest value recorded in variant AW_3. It should be noted that, in the case of fibre A, the applied coating additives led to a notable shift in the substrate's pH classification--from acidic in AW_0 to slightly acidic in AW_1 and AW_2, and to neutral in AW_3. These changes can be considered beneficial, as such pH levels are optimal for the growth and development of most plants, primarily due to improved nutrient availability, which directly supports plant growth and development [20]. In the case of coconut fibre B, the changes were somewhat less pronounced. Nevertheless, all the additives used to modify the base substrate also resulted in an increase in pH, similar to the effects observed in fibre A (Figure 1). The coating process and additives used to modify the substrates also had a significant effect on changes in the electrical conductivity (EC) of the analysed aqueous solutions (Figure 2). According to the presented data, the average EC values for both types of coconut fibre were lowest in the control treatments and increased following the application of both pelletised biochar and the combination of biochar and isolate. Comparing the two types of coconut fibre, substantially higher EC values were recorded in coconut fibre B. For this variant, average EC values ranged from 0.14 to 0.48 mS cm\({}^{-1}\), with the highest value observed in substrate BW_3. In contrast, substrates produced from coconut fibre A exhibited much lower average EC values, ranging from 0.08 mS cm\({}^{-1}\) (AW_0) to 0.17 mS cm\({}^{-1}\) (AW_1). In all cases, however, the EC values for the substrates in their initial state were relatively low. The observed changes are attributable to both the applied additives and the type of coconut fibre used. The issue of EC in horticultural cultivation is related to the excessive retention of nutrients supplied with irrigation water, which can \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Base Variant** & **Porosity** & **Bulk Density** & **Humidity** & **Susceptibility** \\  & \(\rho\) [\%] & **BD [kg m\({}^{-2}\)]** & **[\%]** & **to Compaction** \\ \hline AW\_0 & 47.2 \({}^{\text{dB}}\) & 256.3 \({}^{\text{AA}}\) & 35 \({}^{\text{AA}}\) & 65 \({}^{\text{AA}}\) \\ \hline AW\_1 & 37.3 \({}^{\text{BB}}\) & 315.6 \({}^{\text{BB}}\) & 35 \({}^{\text{AA}}\) & 64 \({}^{\text{AA}}\) \\ \hline AW\_2 & 41.2 \({}^{\text{CB}}\) & 319.3 \({}^{\text{BA}}\) & 35 \({}^{\text{AA}}\) & 64 \({}^{\text{AA}}\) \\ \hline AW\_3 & 34.8 \({}^{\text{AB}}\) & 393.5 \({}^{\text{CA}}\) & 35 \({}^{\text{aA}}\) & 64 \({}^{\text{AA}}\) \\ \hline BW\_0 & 35.3 \({}^{\text{BA}}\) & 290.5 \({}^{\text{AB}}\) & 33 \({}^{\text{AA}}\) & 72 \({}^{\text{AB}}\) \\ \hline BW\_1 & 31.3 \({}^{\text{BA}}\) & 290.5 \({}^{\text{AA}}\) & 33 \({}^{\text{aA}}\) & 71 \({}^{\text{AB}}\) \\ \hline BW\_2 & 26.8 \({}^{\text{AA}}\) & 353.1 \({}^{\text{BB}}\) & 33 \({}^{\text{AA}}\) & 73 \({}^{\text{AB}}\) \\ \hline BW\_3 & 24.7 \({}^{\text{AA}}\) & 438.3 \({}^{\text{CB}}\) & 33 \({}^{\text{AA}}\) & 72 \({}^{\text{AB}}\) \\ \hline \hline \end{tabular} NOTE: Different lowercase letters indicate significant differences between modifications of the same type of fibre, whereas uppercase letters denote significant differences between the same modifications applied to different fibres, with a significance level of \(\alpha=0.05\).  
\end{table} 
Table 1: Physical parameters of the investigated horticultural substrates. lead to a high concentration of salts in the upper layers of the substrate.