Fragmentation is one of the steps during decomposition, in which detritus is converted into small fragments. Humification leads to dark coloured amorphous substance called humus that is highly resistent to microbial action and undergoes decomposition at an extremely slow rate. Catabolism is the set of metabolic pathways that breaks down molecules into smaller units to release energy. Leaching refers to the loss of water soluble plant nutrients from the soil due to rain and irrigation.