There is a big literature on this topic and the data seem to be quite variable between studies. Fundamental considerations relate to reflectance and scattering properties as a function of wavelength and particle size. What is the purpose of the IR measurements?
In my opinion big literature on NIR spectra measurement is a problem, because there are many different results from various authors.
Our urpose of the NIR measurements is, first of all, assessment soil quolity with some parameners - SOM, C organic, nutrients and, second, detect the difference between indicators of surface soils and soils that are buried under the earth ramparts