# Soil Moisture Influence on the FTIR Spectrum of Salt-Affected Soils
## 3 Results
### Salinity and Moisture Characteristics
Figure 5B shows an additional absorbance from 1200 to 1500 cm\({}^{-1}\) (6.67-8.33 \(\upmu\)m), with a peak spectral absorbance around 1300 cm\({}^{-1}\) (7.69 \(\upmu\)m) that represented dry soil contaminated with Na\({}_{2}\)CO\({}_{3}\). The transmittance was fluctuating in the wavenumber ranges from 3600 to 2900 cm\({}^{-1}\) (2.78-3.45 \(\upmu\)m) and strongly fluctuating from 1700 to 1500 cm\({}^{-1}\) (5.88-6.67 \(\upmu\)m), due to the  
Figure 5: Spectral profile of dry soil samples contaminated with **(A)**: NaCl; **(B)**: Na\({}_{2}\)CO\({}_{3}\); and **(C)**: Na\({}_{2}\)SO\({}_{4}\) at four different salinity levels. influence of moisture in the soil (Figures 6-8). The higher the moisture, the deeper the absorbance. These fluctuations did not appear when the soil was dry for a wavelength range from 1200 to 650 cm\({}^{-1}\) (8.33-15.38 \(\mu\)m). Figure 6 represents the soil spectral signature at different moisture levels and contaminated with Na\({}_{2}\)CO\({}_{3}\). Three absorbance bands were similar to the spectrum of soil contaminated with NaCl (Figure 5) or Na\({}_{2}\)SO\({}_{4}\) (Figure 8), ranging from 3600 to 2900 cm\({}^{-1}\); from 1700 to 1500 cm\({}^{-1}\); and from 1200 to 650 cm\({}^{-1}\). An additional absorbance peak appeared in the wavelength range from 1500 to 1200 cm\({}^{-1}\) (Figure 7). This wavenumber range displayed a deep absorbance depending on the salt concentration, that also appeared when the soil was dry and not affected by soil moisture. Spectral characteristics of the soils contaminated with NaCl are depicted in Figure 6. The spectra of the NaCl saline soils were the same as when the soil was dry for different salinity levels, not showing a difference in the spectral absorbance at 775 cm\({}^{-1}\) and 911 cm\({}^{-1}\). When the soil had different moisture levels and the same salinity level (Figure 6), the higher the moisture content, the higher the spectral absorbance around 775 cm\({}^{-1}\) and 911 cm\({}^{-1}\). When the moisture was at saturation, the spectral shape from 680 cm\({}^{-1}\) to about 1200 cm\({}^{-1}\) changed. The characteristics of the soil spectrum contaminated with Na\({}_{2}\)CO\({}_{3}\) are depicted in Figure 7. In the highly and severely Na\({}_{2}\)CO\({}_{3}\) contaminated soils, a spectral absorbance appeared in the wavenumber range 1240-1480 cm\({}^{-1}\), and more specifically around 1380 cm\({}^{-1}\), whereby the depth differed with soil moisture. In the soils contaminated with NaCl (Figure 6), this absorbance does not appear, but in the soils contaminated with Na\({}_{2}\)CO\({}_{3}\) the higher the salinity level, the higher the absorbance or lower the transmittance (Figure 7). This spectral interval proved important for detecting the Na\({}_{2}\)CO\({}_{3}\) content in the soil. Figure 6: _Cont._  
Figure 6: Spectral profile of a NaCl contaminated Fluvisol (clay loam) at different moisture levels, and an increasingly higher salinity level from (**A–D**). Figure 7: _Cont_. The spectral characteristics of the soil contaminated with Na\({}_{2}\)SO\({}_{4}\) (Figure 8) depended on the soil moisture. In comparison to the general spectral characteristics described for the Na\({}_{2}\)CO\({}_{3}\) contaminated soil (Figure 7), the Na\({}_{2}\)SO\({}_{4}\) contaminated soil (Figure 8) did not show any additional absorbance peak. However, there was no clear difference between the samples of the dry soil spectrum with different salinity levels (Figure 5). Absorbance occurred when the soil was moist. The higher the soil moisture, the lower the transmittance or the higher the absorbance (Figure 8). Figure 3:0 Spectral profile of a Na\({}_{2}\)CO\({}_{3}\) contaminated Fluvisol (clay loam) at different moisture levels and an increasingly higher salinity level from (**A**–**D**). Figure 3:1 Spectral profile of a Na\({}_{2}\)SO\({}_{4}\) contaminated Fluvisol (clay loam) at different moisture levels and an increasingly higher salinity level from (**A–D**).