Assessment and measurement of soil health indicators using spectroscopic techniques

Soil health is a comprehensive reflection of many ecosystem functions and services of soils, which covers a range of indicators including physical, chemical and biological properties. The assessment of soil health and measurement of its indicators should follow the criteria of simplicity, inexpensiveness, rapidity and reliability, but previous measurement methods seldom meet all of these requirements at the same time. Spectroscopy is a method that utilizes a light source to irradiate the measured materials and cause the movement of atoms, molecules and electron within the substance to form a spectral image. It has many advantages such as non-destructive, non-polluting, cheap, fast, reliable, and multi-indicator measurements, making it an ideal way to measure soil health indicators. This study summarizes the principles and current research situations of common spectroscopic methods (including near-infrared (NIR), visible to near-infrared (Vis-NIR), mid-infrared (MIR), Fourier transform infrared spectroscopy (FTIR), Raman (scattering) spectroscopy and X-ray fluorescence (XRF)) in the determination of various properties in soil studies. We also give our recommendations of corresponding spectroscopic methods for different assessment scenarios and purposes. Finally, we point out current research gaps and future study directions. The feasibility and advantages are confirmed for using spectroscopic techniques on soil health studies, which is conducive to the practical application and uniform assessment of soil health indicator determination in the future.