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Humus

Updated on March 22, 2014

Preface

Humus is the most important substance in the earths soil. In soil science , humus refers to any organic matter that has reached a point of stability, where it will not break down no further and might if conditions do not change, remain as it is for centuries, if not for millenia. As stated by a dictionary of English language “Humus: the dark organic material in soils, produced by the decomposition of vegetable or animal matter and essential to the fertility of the earth. It is what makes plant life possible. It a important part of the cycle of life. Dead beings decay in order to help living plants grow tall and strong, then in turn animals eat the plant... thus the food chain is complete. Humus is the beginning of all life on earth – plant or animal!

Its conservation and understanding will allow humans to keep up the diversity of life on earth!

Benefits of soil, organic matter & Humus.

The process that converts raw organic matter into humus feeds the soil population of microorganisms and other creatures, thus maintains high and healthy levels of soil life. The rate at which raw organic matter is converted into humus promotes the limits the coexistence of plants, animals and microbes in the soil. Effective and stable humus are further sources of nutrients to microbes, the former provides a readily available supply and the latter acts as a longer-term storage reservoir. Humus also can hold the equivalent of up to 95% of its weight in moisture, and therefor increases the soil's capacity to withstand drought conditions. Also something very important is that humus' dark colour helps to warm up cold soils in the spring.

Humus

Humus nonliving, finely divided organic matter in soil, derived from microbial decomposition of plant and animal substances. Humus, which ranges in colour from brown to black, consists of about 60 percent carbon, 6 percent nitrogen, and smaller amounts of phosphorus and sulfur. As humus decomposes, its components are changed into forms usable by plants.

Soil, with a rich Humus content

Chemical content of Humus

As explained above Humus consists of 50-60 % carbon, 5-6% Nitrogen and smaller amounts of other elements. The components that make the soil dark brown or black in colour are called Humic acids. They are not soluble in water under acidic conditions (pH<2) but are soluble at higher pH values. Humic acids are the major extractable component of soil humic substances.

Another important part of Humus are the Fulvic acids. They are acids that are soluble in all pH conditions and are yellow to yellow-brown in colour. The last main part of Humus is Humin. These are Humic substances that are not soluble in water and in alkali. They are only black in colour.


Functions of organic matter in soil

Organic matter is very important to the existence of life on the earth and is closely connected to the Nitrogen cycle. It has many function including:

1.Nutritional function – Organic matter has both direct and indirect effects on the availability of nutrients for plant growth. It serves as a source N, P & S though the process of mineralization/humification by soil microorganisms.

2.Biological function – It affects the activities of flora and fauna greatly. It serves as their energy source. Numbers if bacteria and fungi are closely interconnected to humus content and may help plants resist attacks by pathogens.

3.Physical and physico-chemical function – Organic matter promotes good soil structure thus improving aeration and the keeping of moisture in soil. Also it buffers the exchange capacity of soils.

A Great TED presentation

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