Spectroscopy is a non-destructive technique used for the analysis of soil properties. It
involves the use of electromagnetic radiation to measure the absorption, transmission, or
reflection of light at various wavelengths. Spectroscopy has been widely used for soil
analysis due to its ability to provide rapid and accurate results for - multiple parameters.
There are various types of spectroscopy that can be used for soil analysis, including visible
and near-infrared (Vis-NIR) spectroscopy, mid-infrared (MIR) spectroscopy, and Raman
spectroscopy. However, in this report, we will focus on the use of near-infrared spectroscopy
(NIRS) for soil analysis.
- NIRS measures the interaction of near-infrared light with matter, which is influenced by the
chemical and physical properties of the sample. It has been demonstrated that NIRS can
provide rapid and accurate results for a range of soil properties.
- NIRS analysis is non-destructive, which means that the same soil sample can be
re-analyzed or used for other analyses
- it can provide multiple results from a single scan, reducing the need for multiple expensive
laboratory analyses. NIRS can be used to analyze the mineralogy
- common soil properties that can be analyzed using NIRS include organic carbon, total
nitrogen, pH, cation exchange capacity, texture, and available nutrients (e.g., phosphorus,
potassium).
- scanning soil samples with near-infrared light and collecting the reflected or transmitted
light. The collected spectra are then pre-processed and analyzed using multivariate analysis
methods to develop calibration models. These models are then used to predict the
concentration of soil properties in new soil samples.
- It can also be a valuable tool for soil management and precision agriculture.
- The radiation from the source triggers vibrations of the molecular bonds of the soil
constituents, allowing them to absorb light differently. The result is an absorption curve with
highly characteristic shape that is used for soil analysis and property predictions.
- This spectral region, however, can provide crucial information on numerous organic and
inorganic soil constituents. All absorptions that are observed in the NIR region between 780
and 2500 nm are a product of the OH, NH, CH, SO and CO vibrations showing a large
dipole moment.
- Essentially what we measure is the interaction between the IR radiation and the particular
molecular combinations of the original fundamental vibrations originating in the Mid Infrared
(MIR) region. Within the near infrared region (NIR), soil spectra is characterized by relatively
few broad absorption features in comparison to the mid-infrared (MIR) part of the spectrum.
The reason is that the bands are mostly broad and often overlapping.
- NIRS involves passing near-infrared light through a soil sample and measuring the intensity
of the transmitted or reflected light. This data is then compared to a calibration model to
determine the chemical composition and physical properties of the soil. Calibration models
are developed by analysing a large number of soil samples with traditional laboratory
methods and correlating the data to the near-infrared spectra.