page_title: Humus
hierarchical_section_title: Humus
caption_attribution_description: English: The soil profile with 5 horizons, edited and improved.
context_page_description: In soil science, humus denominates the fraction of soil organic matter that is amorphous and without the "cellular cake structure characteristic of plants, micro-organisms or animals". Humus significantly affects the bulk density of soil and contributes to its retention of moisture and nutrients. Although the terms humus and compost are informally used interchangeably, they are distinct soil components with different origins; humus is created through anaerobic fermentation, while compost is the result of aerobic decomposition.
  In agriculture, "humus" sometimes also is used to describe mature or natural compost extracted from a woodland or other spontaneous source for use as a soil conditioner. It is also used to describe a topsoil horizon that contains organic matter.
  More precisely, humus is the dark organic matter that forms in soil when dead plant and animal matter breaks down further, specifically through the action of anaerobic organisms. Humus has many nutrients that improve the health of soil, nitrogen being the most important. The ratio of carbon to nitrogen of humus is 10:1.
context_section_description: In soil science, humus (derived in 1790–1800 from the Latin humus for 'earth, ground') denominates the fraction of soil organic matter that is amorphous and without the "cellular cake structure characteristic of plants, micro-organisms or animals". Humus significantly affects the bulk density of soil and contributes to its retention of moisture and nutrients. Although the terms humus and compost are informally used interchangeably, they are distinct soil components with different origins; humus is created through anaerobic fermentation, while compost is the result of aerobic decomposition.
  In agriculture, "humus" sometimes also is used to describe mature or natural compost extracted from a woodland or other spontaneous source for use as a soil conditioner. It is also used to describe a topsoil horizon that contains organic matter (humus type, humus form, humus profile).
  More precisely, humus is the dark organic matter that forms in soil when dead plant and animal matter (including aerobic compost) breaks down further, specifically through the action of anaerobic organisms. Humus has many nutrients that improve the health of soil, nitrogen being the most important. The ratio of carbon to nitrogen (C:N) of humus is 10:1.
caption: Humus has a characteristic black or dark brown color and is an accumulation of organic carbon. Besides the three major soil horizons of (A) surface/topsoil, (B) subsoil, and (C) substratum, some soils have an organic horizon (O) on the very surface. Hard bedrock (R) is not in a strict sense soil.