Question: how is soil processed into chemicals?

Lea Carlesso answered on 9 Nov 2017:

Technically soil is not processed into chemicals. However the plant residues and all others detritus, so called the Organic Matter, are processed by the biological compartment living in soils.
All these organisms (bacteria, fungi, invertebrates) are modifying the chemical structure of the organic matter until it turn into mineral nutrients.
These nutrients are the molecules required by the plants to grow. It closes the circle (from plant to soil to plant again).