Decomposition involves the following processes :

1. Fragmentation - is the breaking down of the detritus into smaller particles . It increases the surface area of detritus for the action of microbes. 
2. Leaching is the downward movement of water soluble inorganic nutrients into the soil horizon and their precipitation as unavailable salts. 
3.Catabolism involves break down of detritus in the presence of extracellular enzymes released by the decomposers.
Usually the processes fragmentation , leaching and catabolism are carried out simultaneously on the detritus.
4.Humification  involves transformation of simplified detritus into fully decomposed, dark coloured and amorphous humus. Humus acts as a reservoir of nutrients.
5. Mineralisation is the further breakdown of the humus by microbes to relase inorganic nutrients.