Question: What is the electromagnetic spectrum?

James Taylor answered on 24 Jun 2014:

The electromagnetic spectrum is just all available (energy) waves (also called radiation waves). It goes from energy waves that are very long – like radio waves that are 100s of metres in length to gamma waves that are very short (length of atoms). It includes micro waves, infra-red waves, visible light and x-rays. The shorter the wavelength the more energy (and the more harm they can do to us). SO Radio waves are no harm at all, but x-ray and gamma rays can harm us (cause cell mutations because they act at this level). It is a spectrum, because it is a continuous from radio to gamma rays.

We use it in soil because infra-red, visible, x-ray and gamma-radiation all interactt in different ways with plants and soil (and animals but not my specialty), So they way they are emitted tells us different things. This is how most senors in agriculture work, with a particular part of the EMS.