# Soil Moisture Influence on the FTIR Spectrum of Salt-Affected Soils
## 2 Materials and Methods
### Laboratory Experimental Design
#### 2.2.2 Soil Salinity Experiment  
The electrical conductivity in a 1:5 (\(w/v\)) soil to water extract of the 11 soil samples was evaluated from slightly to strongly saline (Table 1). Two samples were taken for further experiments: Tien Lang 2 (TL2) and Kien Thuy 2 (KT2). The selected soil samples had an electrical conductivity (EC\({}_{1.5}\)) of 0.51 and 0.12 dS/m, which corresponds to a calculated ECe of 7.5 and 2.2 dS/m (Table 2), and were therefore classified as moderately saline and slightly saline soils, according to [16; 17].  
We subsequently conducted a salinity experiment on these two selected soils, whereby water and salt were added in controlled laboratory circumstances to obtain 56 different mixtures of soil (2), salt type (7) and salt amount (4). Seven salt types were prepared in the laboratory to obtain mixtures of: 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; and g: NaCl: Na\({}_{2}\)SO\({}_{4}\): Na\({}_{2}\)CO\({}_{3}\)= 1:1:1. From each of these salt mixtures 0.35 g, 1.75 g, 3.5 g and 7 g were weighed, mixed into 100 gr of air-dried and sieved soil, and subsequently brought to saturation level.  
The following mixtures were prepared:  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**ID** & **Location** & **Clay** & **Silt** & **Sand** & **EC\({}_{1.5}\)** & **Moisture** & **Textural** & \\  & & **(\%)** & **(\%)** & **(\%)** & **(dS/m)** & **(\%)** & **Class** & **RSG** \\ \hline gt1 & Gao Thuy & 10.40 & 10.26 & 79.34 & 0.30 & 20.1 & Sandy Loam & Fluvisol \\ gt2 & Gao Thuy & 9.52 & 1.24 & 89.24 & 0.24 & 21.8 & Loamy Sand & Fluvisol \\ gt3 & Gao Thuy & 8.76 & 2.52 & 88.72 & 0.28 & 21.9 & Loamy Sand & Fluvisol \\ vb1 & Vinh Bao & 25.44 & 40.32 & 34.24 & 0.54 & 31.4 & Loam & Fluvisol \\ tl1 & Tien Lang & 28.82 & 28.10 & 43.08 & 0.32 & 33.9 & Clay Loam & Arenosol \\ tl2 & Tien Lang & 37.08 & 38.82 & 24.10 & 0.51 & 34.5 & Clay Loam & Fluvisol \\ th1 & Tien Hai & 8.02 & 1.52 & 90.46 & 0.65 & 20.4 & Sand & Arenosol \\ th2 & Tien Hai & 9.38 & 2.46 & 88.16 & 0.44 & 28.2 & Loamy Sand & Fluvisol \\ kt1 & Kien Thuy & 19.8 & 19.82 & 60.38 & 0.60 & 24.2 & Sandy Loam & Arenosol \\ kt2 & Kien Thuy & 9.14 & 0.24 & 90.62 & 0.12 & 21.1 & Sand & Arenosol \\ tt1 & Thai Thuy & 18.58 & 18.02 & 63.40 & 0.29 & 25.1 & Sandy Loam & Fluvisol \\ \hline \end{tabular}
\end{table}
Table 1: Soil texture, USDA soil textural class and electrical conductivity (EC\({}_{1.5}\)) of topsoil samples at the coast of Hai Phong-Thai Binh. Reference soil groups are classified according to [14]. The locations are shown in Figure 1.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**ID** & **EC\({}_{1.5}\) (dS/m)** & **EC\({}_{e}\) (dS/m)** & **Temperature (\({}^{\circ}\)C)** & **Salinity Class** \\ \hline TL2 & 0.51 & 7.5 & 23.6 & Moderately saline \\ KT2 & 0.12 & 2.2 & 23.6 & Slightly saline \\ \hline \end{tabular}
\end{table}
Table 2: Electrical conductivity (EC\({}_{1.5}\)) in soils at Tien Lang (TL2) and Kien Thuy (KT2).  
* Salinity level 1 (slevel 1): 100 g of air-dried and sieved soil, to which 0.35 g salt was added (NaCl or Na\({}_{2}\)SO\({}_{4}\) or Na\({}_{2}\)CO\({}_{3}\) or a mixture of salts). Water was added until saturated soil moisture content;
* Salinity level 1 (slevel 2): 100 g air-dried and sieved soil, to which 1.75 g salt was added (NaCl or Na\({}_{2}\)SO\({}_{4}\) or Na\({}_{2}\)CO\({}_{3}\) or a mixture of salts). Water was added until saturated soil moisture content;
* Salinity level 1 (slevel 3): 100 gr air-dried and sieved soil, to which 3.5 g salt was added (NaCl or Na\({}_{2}\)SO\({}_{4}\) or Na\({}_{2}\)CO\({}_{3}\) or a mixture of salts). Water was added until saturated soil moisture content;
* Salinity level 1 (slevel 4): 100 g of air-dried and sieved soil, to which 7 g salt was added (NaCl or Na\({}_{2}\)SO\({}_{4}\) or Na\({}_{2}\)CO\({}_{3}\) or a mixture of salts). Water was added until saturated soil moisture content.