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What is humus in soil?

wormHumus is an integral part of almost all good growing soil. So, just what is humus? Soils are influenced, modified, and supplemented by living organisms. Plants and animals aid in the development of a soil through the addition of organic matter. Fungi and bacteria decompose this organic matter into a semi-soluble chemical substance known as humus. Larger soil organisms, like earthworms, beetles, and termites, vertically redistribute this humus within the mineral matter found beneath the surface of a soil.

Humus is the biochemical substance that makes the upper layers of soil become dark. It is colored dark brown to black. Humus is difficult to see in isolation because it binds with larger mineral and organic particles. Humus provides soil with a number of very important benefits:

  • It enhances a soil’s ability to hold and store moisture.
  • It reduces the eluviation of soluble nutrients from the soil profile.
  • It is the primary source of carbon and nitrogen required by plants for their nutrition.
  • It improves soil structure which is necessary for plant growth.

Organic activity is usually profuse in the near surface layers of a soil. For instance, one cubic centimeter of soil can be the home to more than 1,000,000 bacteria. A hectare of pasture land in a humid mid-latitude climate can contain more than a million earthworms and several million insects. Earthworms and insects are extremely important because of their ability mix and aerate soil. Higher porosity, because of mixing and aeration, increases the movement of air and water from the soil surface to deeper layers where roots reside. Increasing air and water availability to roots has a significant positive effect on plant productivity. Earthworms and insects also produce most of the humus found in soil through the incomplete digestion of organic matter.

To get the most out of your garden start with a garden soil test. Phoslab Environmental Service can help you get more out of your labor.