# Soil Moisture Influence on the FTIR Spectrum of Salt-Affected Soils
## 3 Results  
### Salinity and Moisture Characteristics  
The initial spectral profiles of a field sample of a clay loam topsoil (Fluvisol) and a sand topsoil (Arenosol) are shown in Figure 2.  
The salinity characteristics of the two soils contaminated with NaCl, Na\({}_{2}\)SO\({}_{4}\), Na\({}_{2}\)CO\({}_{3}\), as mono-salt in mixture, clearly demonstrate the effect of NaCl on the electrical conductivity of each of the 56 soil samples (Figure 3). The four levels of salt amounts added to the soil corresponded to a different electrical conductivity (EC\({}_{1:5}\)). EC\({}_{1:5}\) ranged from 0.35-1.41 dS/m for salinity level 1, 2.90-6.34 dS/m for salinity level 2, 8.04-12.90 dS/m for salinity level 3, and 13.30-22.40 dS/m for salinity level 4 (Figure 3). The EC\({}_{1:5}\) of the sand soil sample (KT2-a), to which more than 3.5 g NaCl was added, was higher. Figure 3: Electrical conductivity (EC\({}_{1:5}\) in dS/m) measured in a 1:5 (\(w/v\)) soil to water extract of two soil samples (TL2, KT2), four salinity levels and seven different salt types, where a: NaCl; b: Na\({}_{2}\)SO\({}_{4}\); c: Na\({}_{2}\)CO\({}_{3}\); d: NaCl:Na\({}_{2}\)SO\({}_{4}\) = 1:1; e: NaCl:Na\({}_{2}\)SO\({}_{4}\) = 1:5; f: NaCl:Na\({}_{2}\)SO\({}_{4}\) = 1:10; g: NaCl:Na\({}_{2}\)SO\({}_{4}\):Na\({}_{2}\)CO\({}_{3}\) = 1:1:1). Figure 2: Spectral profile of a field sample of a clay loam topsoil (Fluvisol, TL2) and a sand topsoil (Arenosol, KT2). Clear differences were observed between the moisture levels at different salt concentration levels for each of the two soils (Figure 4). Two soil types were included (sand, clay loam), the salinity included four levels and the sampling time consisted of five sampling days (Figure 4). All effects were statistically significant at the \(<\).001 level. The main effect yielded an F ratio of F(1, 240) = 1064, \(p<\) 0.001 for soil, F(3, 240) = 84, \(p<\) 0.001 for salinity level, and F(4, 240) = 4189, \(p<\) 0.001 for sampling time, indicating a significant difference between soils, salinity levels and sampling times. All of the interaction effects were significant, ranging from the interaction between the soil, salinity level and sampling time on soil moisture with an F ratio of F(12, 240) = 7.1, \(p<\) 0.001 to the interaction of the soil and sampling time on soil moisture with an F ratio of F(4, 240) = 79, \(p<\) 0.001. A model incorporating the salt type together with the soil type, salinity level and sampling time, but without considering interaction effects, did not have a significant influence on soil moisture, where F(6, 265) = 0.639, \(p=\) 0.699. Though differences were observed between salt types with respect to soil moisture, these were not significant. Overall, the higher the salinity level, irrespective of the salt type, the higher the soil moisture. This effect was more pronounced at lower moisture levels: for sand, the effect occurred from the second sampling day onwards and for clay loam, from the third sampling day onwards. Spectral Characteristics of Soil Samples Contaminated with NaCl, Na\({}_{2}\)SO\({}_{4}\), Na\({}_{2}\)CO\({}_{3}\)  
The spectral signatures of the Fluvisol and Arenosol soil samples showed that these were strongly affected by soil moisture. The results are discussed in terms of transmittance and absorbance patterns. We expressed spectral measurements in % transmittance projected on an infrared range from 4000 to 650 cm\({}^{-1}\) wavenumber equivalent to wavelengths from 2.5 \(\upmu\)m (near infrared) to 15.4 \(\upmu\)m (thermal infrared). Figure 5 represents the soil spectrum for the dry soil samples containing NaCl, Na\({}_{2}\)CO\({}_{3}\) or Na\({}_{2}\)SO\({}_{4}\). When the soil was dry, the spectral images showed some fluctuation in the  
Figure 4: Soil moisture changes for seven salt types, four salinity levels, five sampling days and two reference soil groups. wavenumber, ranging from 650 cm\({}^{-1}\) to 1200 cm\({}^{-1}\) (8.33-15.4 \(\upmu\)m), with a major spectral absorbance around 1000 cm\({}^{-1}\) (10 \(\upmu\)m) (Figure 5).