## 3 Results and Discussion  
Figure 1 presents the average pH of the soil from the three-year field experiment. Overall, all applications of BAs resulted in a significant increase (\(p<0.000\)) in soil pH (Table 2) compared to the control, which received no K fertilizer. This effect was further modified by the crop plant species (\(p<0.000\)) (Figure 1, Table 2). Figure 1: Effect of ashes from biomass combustion on soil pH in KCl (**A**) and H\({}_{2}\)O (**B**) under the cultivation of various crop species (mean \(\pm\) SE). Mean \(\pm\) standard error; identical superscripts (a, b, c..h) denote non-significant differences between means according to the post hoc [PERSON]’s HSD test. The original soil selected for the experiment was acidic (Table 1). After three years of research, the pH ranges of the soil in KCl and H\({}_{2}\)O in the analyzed experimental variants were found to range from 4.22 to 5.90 and from 5.36 to 6.87, respectively (Figure 1). The most significant increase in pH over the three years was observed with the highest doses of ash--BAs_2.0 and BAs_2.5--in the soils where winter rapeseed and potatoes were cultivated. A slight effect of BAs was observed in the soil under spring barley. Compared to the original soil selected for the experiment, the control soil where spring barley and potatoes were grown exhibited lower pH values, indicating progressive acidification. After three years of research, it was also found that fertilization with traditional NPK mineral fertilizers led to a gradual decrease in pH (Table 1, Figure 1). Generally, the application of BAs also resulted in a decrease in the HAC of the soil (Figure 2). Overall, all the applications of BAs resulted in a significant decrease (\(p<0.000\)) in soil HAC (Table 2) compared to the control. The results were modified further by the interaction between the experimental factors (\(p<0.001\)) (Figure 2, Table 2). After three years of research, the soil was generally characterized by lower average HAC values compared to the soil before the experiment. The best results were achieved with the highest dose of BAs_2.5 in the soil under winter rapeseed cultivation, where the average HAC value was 0.53 cmol(+) kg\({}^{-1}\), representing a reduction of over 43% compared to the original soil. Given the high pH of the BAs used in the experiment (pH = 12.8), the results obtained were expected. The literature extensively documents the reduction in soil acidification resulting from the application of BAs [9; 15; 34; 35; 36; 37]. Long-term studies conducted by [PERSON] et al. (2004) confirmed a sustained improvement in pH observed even 5-6 years after the application of ashes [38]. In general, the use of BAs reduces soil HAC and increases the saturation of the soil sorption complex with alkaline cations (Ca\({}^{2+}\), Mg\({}^{2+}\), K\({}^{+}\), and Na\({}^{+}\)) [20]. Research conducted by [PERSON] et al. (2012) demonstrated a significant increase in the pH value of light soil when at least 2 Mg of BAs per hectare was applied. According to other studies, a significant increase in pH was achieved with a minimum dose of 8 Mg ha\({}^{-1}\)[15]. In our research, the maximum dose of BAs was 2.5 Mg ha\({}^{-1}\). Particularly with lower doses, this may not result in noticeable effects regarding reduced hydrolytic acidity (HAC) and increased pH. It is important to note that, due to their significant content of alkaline substances, the application of excessively high doses of ashes may produce undesirable  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Variable** & & **BAs\_D** & **CPS** & **BAs\_D \(\times\) CPS** \\ \hline pH KCl & F & 25.63 & 36.46 & 14.83 \\  & \(p\) & **0.000** & **0.000** & **0.000** \\ \hline pH H\({}_{2}\)O & F & 21.56 & 7.52 & 7.  
outcomes, such as increased leaching of nutrients and pollutants, as observed by previous studies [39]. It has been indicated that BAs are most effective in altering pH in strongly acidic soils with low organic matter content.