## 3 Results and Discussion
### Functional Composition of SOM  
Several findings are worth mentioning with respect to results of FTIR spectroscopy. SOM and SOC contents were significantly correlated with the peak areas integrated between 3020 and 2800 cm\({}^{-1}\) (Table 3). The r values were equal to 0.87 and 0.84, respectively, which correspond with a <0.001 significance level. This suggests that a substantial part of SOM in samples is probably built by aliphatic structures. At the same time, the correlation is the partial consequence of minimal overlapping of functional groups in this frequency region. Peak areas reflect the relative amount of methyl, methylene, and methine groups only. A significant correlation (r = 0.8, \(p\) < 0.001) was observed between the 1505-1560 cm\({}^{-1}\) peak area and content of soil N. This is due to various types of amide vibrations occurring in the mentioned frequency region. Soil reaction showed a significant negative correlation with the 1740-1710 cm\({}^{-1}\) peak area (r = \(-\)0.71, \(p\) < 0.001). Apart from esters, the degree of infrared absorption in the 1740-1710 cm\({}^{-1}\) band is caused by C=O stretching of carboxylic groups, which contribute to the acidic character of the studied soils. Absorbance in this frequency region partially reflects the amount of dissociating carboxylic acids. A negative correlation between infrared absorption in the 1740-1710 cm\({}^{-1}\) range and soil pH has been reported previously by [PERSON] et al. [41] and [PERSON] et al. [33]. The results of correlation and regression analysis suggest that some frequency bands and associated peak areas had a greater effect on SWR data than the others. For example, \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & **3020–2800** & **1740–1710** & **1640–1620** & **1560–1505** & **1475–1460** & **1455–1400** & **1395–1365** & **1190–1135** \\ \hline Log WDPT\({}_{\rm A}\) & 0.29 * & \(-\)0.02 & \(-\)0.04 & 0.06 & 0.31 * & \(-\)0.40 ** & 0.37 * & \(-\)0.51 *** \\ Log WDPT\({}_{\rm P}\) & 0.26 & 0.00 & \(-\)0.13 & 0.14 & 0.21 & \(-\)0.26 & 0.35 * & \(-\)0.51 *** \\ MED & 0.34 * & 0.08 & \(-\)0.08 & 0.16 & 0.28 & \(-\)0.29 * & 0.44 ** & \(-\)0.48 *** \\ VF & 0.23 & 0.36 * & 0.25 & 0.24 & 0.07 & 0.37 * & 0.04 & 0.49 *** \\ SOM & 0.87 *** & 0.72 *** & 0.66 *** & 0.68 *** & 0.77 *** & 0.31 * & 0.81 *** & 0.12 \\ SOC & 0.81 *** & 0.65 *** & 0.50 *** & 0.75 *** & 0.67 *** & 0.41 ** & 0.68 *** & 0.18 \\ pH & \(-\)0.71 *** & \(-\)0.75 *** & \(-\)0.51 *** & \(-\)0.46 ** & \(-\)0.63 *** & \(-\)0.01 & \(-\)0.55 *** & \(-\)0.14 \\ Sand & \(-\)0.14 & \(-\)0.22 * & \(-\)0.25 * & \(-\)0.07 & \(-\)0.17 & \(-\)0.03 & \(-\)0.10 & \(-\)0.1 \\ Silt & 0.14 & 0.21 * & 0.28 & 0.08 & 0.15 & 0.05 & 0.08 & 0.17 \\ Clay & 0.11 & 0.15 & 0.07 & 0 & 0.14 & \(-\)0.03 & 0.11 & \(-\)0.12 \\ \hline \end{tabular}
\end{table} 
Table 3: Correlations (r values and corresponding \(p\) < 0.05 *, 0.01 **, and 0.001 *** significance levels) between FTIR peak areas integrated in eight frequency intervals (cm\({}^{-1}\)), SWR data (WDPT, MED), and basic soil properties. the simple correlations between WDPT or MED results and IR absorption in 1740-1710, 1640-1620, and 1560-1505 cm\({}^{-1}\) frequency regions were insignificant. At the same time, none of these three bands was successfully tested as a partial predictor in multiple regression analysis. For these bands, a higher degree of overlapping of individual functional groups is characteristic. Vibrations of aromatic rings overlap with vibrations of C=O, C=N, and C-N groups in the case of the 1640-1620 cm\({}^{-1}\) and particularly 1560-1505 cm\({}^{-1}\) band. Apart from that, an additional factor should be considered when interpreting the FTIR data. The absorbance within individual bands at 1560-1505 and 1740-1710 cm\({}^{-1}\) is proportional to the relative amount of carbonyl, carboxyl, and amide groups. Even though these groups themselves are hydrophilic, they are bound amphiphilic compounds, which may contribute to SWR depending on their spatial arrangement.