The residues of organic matter in the soil are transformed biologically over a shorter or longer time period. In the humification process. a part of the organic decomposition products formed the dark-coloured humus. The other part of the organic matter is also decomposed by the activities of heterotrophic organisms. https://www.roneverhart.com/AMS-Neve-1073SPX-Single-Preamp-and-EQ-p33827/