Measuring Soil Salinity

Measuring soil salinity is important for efficient soil and water management in arid and semi-arid environments. Excess salinity can be caused by nature or man: lack of rainfall, erosion, and rising water tables can cause salts to accumulate in the upper soil layers; so too can improper irrigation practices. Degradation of soil has a negative impact on agriculture as well as the environment.

Soil salinity has a direct effect on the variety and quality of vegetation that can grow in an area. Excess salinity can diminish water uptake in plants while the presence of high salinity in clay can destroy good soil structure.

The PSR+ field spectroradiometer offers an accurate, non-destructive instrument for measuring salinity in soils in situ that is faster and less expensive than traditional lab-based electrical conductivity tests. Used alone or in conjunction with multi-spectral and hyperspectral imaging from flyovers and satellites, the PSR+ can offer a more complete picture of soil salinity across a large area.

Scans taken in the VNIR bands (visible, near infrared) from 350-1000nm contain data on soil color, presence of iron, moisture, and organic matter. Scans in the near infrared (NIR) bands from 1000-2500nm can provide data on silicates, hydroxides, some sulphates, amphiboles, carbonates, water, and organic matter. The PSR+ covers the full range from 350-2500nm with three photodiode array detectors.

Spectra collected in the field or the lab with a PSR+ portable agricultural spectroradiometer are saved as ASCII files for analysis using third party software, for example the R software analysis program or a chemometrics package.

In plants suffering from salinity stress, there is increased visible reflectance and decreased NIR reflectance. For researchers who want to use vegetation indices such as the Normalized Difference Vegetation Index (NDVI) or Soil Adjusted Vegetation Index (SAVI), there is access to these and 17 other vegetation indices from the PSR+ DARWin SP Data Acquisition software included with every system.

In addition, for those working with an existing soil spectral library or who want to build their own library, the optional EZ-ID sample identification software with Custom Library Builder module is available. EZ-ID provides fast sample identification by matching a scan from an unknown target sample to a known sample spectra from a library. Making your own library is as easy as scanning and adding metadata to your file.