# Soil Moisture Influence on the FTIR Spectrum of Salt-Affected Soils
## 5 Conclusions  
Soil moisture had a large impact on the soil spectrum. The impact of salt contamination was located in three main wavelength ranges: 3400-3200 cm\({}^{-1}\), 1700-1600 cm\({}^{-1}\) and 1100-900 cm\({}^{-1}\). The salt-contaminated soils did not have the same diagnostic absorbance as the spectral signatures of the salt minerals. The spectra of soil contaminated with NaCl and Na\({}_{2}\)SO\({}_{4}\) salts was similar to the spectra of soils that were not contaminated with salt. The spectra of soil contaminated with Na\({}_{2}\)CO\({}_{3}\) salt showed clear signs of spectral absorbance in the wavenumbers ranging from 1360 to 1464 cm\({}^{-1}\). At wavelength 6.99 \(\upmu\)m, there was no relationship between the absorbance and soil moisture, but the absorbance was proportional to the salt content (R\({}^{2}\) = 0.8529; RMSE = 0.68 g) and electrical conductivity (R\({}^{2}\) = 0.4972; RMSE = 3.8 dS/m). Therefore, these spectra could be used to estimate Na\({}_{2}\)CO\({}_{3}\) salt content in moist soil. Moreover, these wavelengths were not affected by soil moisture. The relationship between the soil moisture and spectral absorbance value was high at wavelengths below 6.7 \(\upmu\)m, resulting in a quadratic relation between soil moisture and absorbance at wavelength 6.13 \(\upmu\)m (R\({}^{2}\) = 0.7979; RMSE = 5.2%). Advances in thermal infrared sensor technologies may offer possibilities for soil salinity monitoring in difficult to access locations.  
Conceptualization, L.T.T.H. and A.G.; methodology, L.T.T.H. and A.G.; validation, L.T.T.H., A.G., D.T.L., D.T.Q., N.T.H., N.N.T., N.T.B., V.T.K.D. and P.H.L.; investigation, L.T.T.H., A.G., D.T.L., D.T.Q., N.T.H., N.N.T., N.T.B., V.T.K.D. and P.H.L.; resources, L.T.T.H., D.T.L., D.T.Q., N.T.H., N.N.T., N.T.B., V.T.K.D. and P.H.L.; data curation, L.T.T.H., A.G., D.T.L., D.T.Q., N.T.H., N.N.T., N.T.B., V.T.K.D. and P.H.L.; writing--original draft preparation, L.T.T.H. and A.G.; writing--review and editing, A.G.; visualization, L.T.T.H., A.G., N.N.T. and P.H.L.; supervision, L.T.T.H. and A.G.; project administration, L.T.T.H. and A.G. All authors have read and agreed to the published version of the manuscript.  
This work has been funded by the Vietnam Academy of Science and Technology (VAST) under the \"Determination of salinity level of surface soil for agricultural cultivation in some areas near coastal estuaries of Hai Phong-Thai Binh by hyperspectral remote sensing imagery\", with the project code: VAST01.02/17-18. This article was supported by the Vietnam-Belgium bilateral project: \"Monitoring Climate Impact and Disaster Resilience of Vietnamese Agro-ecosystems\" (MINERVA). Vietnam Ministry of Science and Technology (MOST): NDT.96.BE/20; and Belgian Federal Science Policy Office (BELSPO): BL/67/VT44.  
Spectral data are available on the website [[https://speclib.ga/labspectral.php](https://speclib.ga/labspectral.php)]([https://speclib.ga/labspectral.php](https://speclib.ga/labspectral.php)) (accessed on 6 April 2022).  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.