How do soil microbes recycle nutrients?

As plant and animal residues enter the soil they are colonized by a whole range of micro-organisms. As the residues are broken down nutrients are released and recycled through the soil. Initially, the easiest compounds to break down are attacked first, leaving the more resistant compounds to accumulate in the soil. Eventually, microbial waste products and resistant plant residues combine to form soil humus in a process called humification. All the residues entering the soil must be broken up and recycled by micro-organisms before they can be used again by plants.