2.2. Determination of soil properties
The air-dried soil samples were sieved through a 2-mm mesh to remove any plant matter or debris prior to analysis. Prior to spectroscopic measurements, the soil properties of pH value, SOM contents, the concentration of Mg2+, Ca2+, K+ + Na+ were determined using conventional chemical methods (Sparks, 1996) and are listed in Table 1.
In this study, six different salt contents with various SOM contents were selected from the above soil samples. The low salt contents were 1.08 and 1.09 g/kg, the medium salt contents were 9.49 and 9.55 g/kg, and the high salt contents were 13.31 and 16.10 g/kg. The corresponding SOM contents were 3.53, 11.38, 8.60, 15.24, 5.78, and 7.52 g/kg, respectively.