Liebig actually discovered that plants take up solutes, these are dissolved substances. Well dissolved substances is a very broad statement, it does not mean in water only. Many things can be dissolved in substances other than water yet are not water soluble. The word dissolved means broken up into molecules, or ions in salts. The molecules only have to be disassociated to be solutes.
Good soil is a world of working microbes.
One gram of soil can contain over ten million bacteria. Around the roots of a healthy growing plant a dense coating of microbes may contain a population of from 100 to 200 billion microbes. The life span of a single microbe in this environment is approximately one half hour. Microbes live in colonies and are very mobile. In their rapid life cycle from creation to death they develop tremendous metabolic activity and steadily improve the structure of the soil.