Humus is the decaying organic matter found in the soil. It comes from plant and animal remains.

The chemical composition of humus varies because it depends on the action of living organisms in the soil, such as bacteria, protozoa, fungi and certain types of beetles, but it almost always contains varying amounts of proteins and certain uronic acids combined with lignins and their derivatives. Humus is a homogeneous, amorphous, dark and odorless material.

At the beginning of the decomposition, part of the carbon, hydrogen, oxygen and nitrogen dissipates rapidly in the form of water, carbon dioxide, methane and ammonia, but the other components decompose slowly and remain in the form of humus. The final products of the decomposition of humus are mineral salts, carbon dioxide and ammonia.

When decomposing into humus, plant residues become stable forms that are stored in the soil and can be used as food by plants. The amount of humus also affects the physical properties of the soil as important as its structure, color, texture and moisture retention capacity.

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