Organic Matter in Soils' Organic Matter in Soils is a term used to describe the organic material found in soil, such as HUMUS. HUMUS is a dark, organic material that is formed when plant and animal matter decomposes. It is an important component of soil, providing nutrients for plants and helping to retain moisture. HUMUS also helps to improve soil structure, making it more porous and allowing air and water to move through it more easily.