Humus

Humus

Diagram of soil horizons, including humus.

Humus is a dark, organic material that forms in soil when plant and animal matter decays. It is an essential component of soil and plays a crucial role in maintaining soil health and fertility.

Formation

Humus is formed through the process of decomposition, where microorganisms such as bacteria and fungi break down dead organic matter. This process results in the release of nutrients back into the soil, which are then available for uptake by plants.

Composition

Humus is composed of complex organic molecules, including lignin, cellulose, and various proteins. These molecules are resistant to further decomposition, which allows humus to persist in the soil for long periods.

Functions

Humus serves several important functions in the soil:

• Nutrient Supply: Humus is a reservoir of nutrients such as nitrogen, phosphorus, and sulfur, which are essential for plant growth.
• Water Retention: It improves the soil's ability to retain water, making it available to plants during dry periods.
• Soil Structure: Humus helps to bind soil particles together, improving soil structure and aeration.
• pH Buffering: It acts as a buffer, helping to maintain a stable pH in the soil.

Soil Horizons

Humus is typically found in the uppermost layer of soil, known as the O horizon. This layer is rich in organic material and is crucial for the initial stages of plant growth.

Importance in Agriculture

In agriculture, maintaining a healthy level of humus in the soil is vital for sustainable crop production. Practices such as crop rotation, cover cropping, and the application of compost can help to increase humus levels in agricultural soils.

Related pages

• Soil fertility
• Compost
• Organic matter
• Soil microbiology