Humification

What is Humification?

Humification implies humus formation. Humus is a black amorphous material formed by microorganisms' decomposition of dead and decaying organic matter. This humification definition explains what is humification. 

Humification meaning varies with mineralisation. In mineralisation, inorganic nutrients are recycled, as the name suggests. In order to form inorganic compounds, organic matter can further decompose.

Organic matter is converted into organic polymers in the process of humification, which are stable and cannot be further decomposed by organisms and remain as humus.

Humus

In environmental studies, humus (stems from the Latin humus for 'earth') refers to the amorphous fraction of soil organic matter without the "cellular cake structure characteristic of plants, micro-organisms or animals". The bulk density of the soil is greatly influenced by humus and contributes to its retention of moisture and nutrients.

While the terms humus and compost are used interchangeably informally, they are separate components of soil with distinct origins; humus is formed by anaerobic fermentation, while compost is the product of aerobic decomposition. Humus is often used in agriculture to describe mature or natural compost collected from a forest or other random source for use as a soil conditioner. A topsoil horizon that includes organic matter is often used to describe it.

More specifically, humus is the dark organic matter that forms in the soil, particularly through the action of anaerobic organisms, when dead plant and animal matter (including aerobic compost) further breaks down. There are many nutrients in humus that enhance soil health, the most significant being nitrogen. The proportion of humus carbon to nitrogen (C:N) is 10:1.

Humification Process in Soil

The humification process in soil takes place by rock weathering, humification of plant remains and laterisation.

1. Weathering

• By chemical or mechanical means, weathering is the degradation of rocks into smaller parts. It is essential for soil formation and growth. The mineral content of the soil is given by weathering. 

• The features of the soil are influenced by such minerals. Chemical rock weathering changes the pH of the soil. 

• Carbonation releases calcium, making the soil more alkaline. The soil texture may also be affected by chemical weathering. Hydrolysis transforms granite feldspar into Kaolin clay that gives a clay-like texture to the soil. Chemical weathering can also influence the colour of the soil. The composition of the soil is determined by mechanical weathering.

2. Humification 

• In the humification process, the decomposition of plant twigs, wood, etc. creates humus. Humification determines the consistency of the soil, its colour and texture.

• The humus-rich soil is black or dark brown in colour. Also based on humification is the water content of the soil.

• Humus supports in binding of the soil particles. For the growth of microorganisms, humification preserves the optimal pH in the soil. It enhances soil fertility and the soil's organic content.

3. Laterisation 

• It is a type of chemical weathering which includes carbonation, oxidation, and leaching. This natural process can directly affect soil growth, affecting the water content, pH, and structure of the soil. 

• This process is observed to happen in the areas including hot areas such as equatorial settings (The Amazon in South America). The soil texture is influenced by laterisation.

• Mineral grains are dissolved, preventing the formation of crumbly nature of the soil and therefore leading to the  production of platy soils like latosols in turn. 

• The pH of soils is also affected by laterisation. 

• Extreme leaching is found to occur in areas including equatorial rainforests with heavy monsoon precipitation. By the leaching method, the minerals are removed, leaving more acidic soil water in place.

Advantages of Organic Matter and Humus in the Soil

Some agree that the significance of chemically stable humus is the fertility it gives to soils in both a physical and chemical context, while some agricultural experts focus more on other characteristics of it, such as its capacity to suppress disease. 

By increasing microporosity, it helps the soil in maintaining moisture and promotes the development of good soil structure.

The introduction of oxygen into complex organic molecular assemblages produces several active, negatively charged sites which bind positively charged ions (cations) of the plant nutrients, making them more accessible to the plant through ion exchange. Humus facilitates the feeding and reproduction of soil species, and is also defined as the "life-force" of the soil.

• The mechanism by which soil organic matter is transformed into humus feeds the population of soil microorganisms and other creatures and thus maintains high and stable levels of soil life.

• The rate at which soil organic matter is transformed into humus encourages or limits the coexistence in the soil of animals, plants, and microorganisms.

• Stable humus and Effective humus can be stated as the additional sources of nutrients for  the microbes such that the former provides an easily accessible supply and the latter serves as a reservoir of long-term storage.