Humus in Soil and Its Role in Soil Fertility

Humus is a black, organic substance that occurs in soil as plant and animal matter decomposes. Humus is the dark brown or black material that remains after the majority of the organic litter has decomposed. Earthworms also assist in the mixing of humus and minerals in the soil. Humus provides a variety of nutrients that are beneficial to soil health.

Humus soil component is one of the important features in the fertility of the soil.

In agriculture, "humus" may also refer to mature or natural compost that has been harvested from a forest or other naturally occurring source for use as a soil conditioner. It's also a term for a topsoil horizon that's rich in organic matter (humus type, humus form, humus profile).

Component of Soil

Minerals, liquids, gases, organic matter, and microorganisms make up soil, which is a porous medium. Soil is a complex natural body with properties resulting from the combined effects of climate and biotic activities, as changed by topography, acting on parent materials over time, according to the conventional description.

There are Five Components of Soil that are Present in the Ecosystem: 

Minerals: 

Sand and silt are examples of primary minerals, which are soil materials that are identical to the parent material from which they formed. They usually have a round or irregular shape. Secondary minerals, on the other hand, are formed when primary minerals are weathered, releasing essential ions and forming more stable mineral types like silicate clay.

Water: 

The ability of a soil to retain water is primarily determined by the texture of the soil. The more small particles there are in the soil, the more water it can hold. As a result, clay soils have the highest water-holding ability, while sands have the lowest. Because of organic matter's high affinity for water, it also affects the water-holding capability of soils. The higher the amount of organic material in the soil, the greater the ability of the soil to retain water.

Organic Matter: 

Organic matter is made up of dead plants and animals, and as a result, it has a high capacity for retaining and/or providing essential elements and water for plant growth. Soils with a high organic matter content often have a high CEC, making them some of the most beneficial for plant growth. Organic matter also has a high “plant available” water-holding capacity, which can help soils with low water-holding capacity, such as sand, develop more.

Gases: 

The next most basic part of the soil is gases or air. Since air can fill the same spaces as water, it can make up anything from 2% to 50% of the volume of soil. Root and microbe respiration are both dependent on oxygen, which aids plant development. Belowground plant functions, such as nitrogen-fixing bacteria, depend on carbon dioxide and nitrogen.

Microorganisms: 

Microorganisms are the final basic element of soils, and although they are abundant in the soil, they account for less than 1% of the total amount. The main decomposers of raw organic matter are microorganisms. Decomposers convert raw organic matter into humus, which is rich in readily available plant nutrients, by consuming organic matter, water, and air.

Humification: 

Microorganisms decompose a substantial portion of the organic matter in the soil, converting it to inorganic minerals that plants' roots can consume as nutrients. Mineralization is the term for this method. Nitrogen (nitrogen cycle) and other nutrients (nutrient cycle) in decomposed organic matter are recycled in this process. Depending on the conditions of decomposition, a portion of the organic matter does not mineralize and is instead converted into concatenations of organic polymers through a mechanism known as "humification." These organic polymers are stable and makeup humus because they are immune to the action of microorganisms. This consistency means that humus becomes part of the soil's permanent structure, strengthening it.

Benefits of Soil Organic and Humus

• The conversion of soil organic matter to humus feeds the population of microorganisms and other creatures in the soil, ensuring high and stable soil life levels.

• The rate at which soil organic matter is converted to humus promotes (when fast) or inhibits (when slow) plant, animal, and microorganism coexistence in the soil.

• Effective humus and stable humus are both additional sources of nutrients for microbes, with the former acting as a short-term storage reservoir and the latter as a long-term supply.

• Humus is a colloidal material that boosts soil's cation exchange potential, allowing it to store nutrients by chelation. Although these nutrient cations are available to plants, they are retained in the soil and are not washed away by rain or irrigation.

• Humus can retain the moisture equivalent of 80–90% of its weight in water, increasing the soil's ability to survive drought.

• Humus' biochemical composition allows it to buffer, or moderate, excessively acidic or alkaline soil conditions.

• Humus' dark colour, which is normally brown or black, aids in the warming of cold soils in the spring.

• Humus can help to mitigate climate change because of its ability to sequester carbon.