Decomposition refers to the breakdown of complex organic matters into simpler substances. Decomposers are the microbial heterotrophs that carry out decomposition and use the decomposition products as a source of energy. The process starts with the fragmentation of detritus into smaller pieces by detritivores. Leaching refers to the process by which dissolved materials are carried with water down to the soil layers. Soil inhabiting microbes carry out decomposition of organic matter and the resultant partly decayed organic portion of the soil is referred to as humus;  the process of humus formation is called as humification. Nutrient present in the soil in biologically unavailable forms (for ex-nitrogen) are converted into biologically useful forms by the process of mineralization.