Humuksen

Humuksen is a term used in Finnish soil science to refer to the stable, organic component of soil known in English as humus. Humus is the portion of soil organic matter that remains after relatively rapid decomposition, formed by the long-term microbial transformation and polymerization of plant and animal residues. It is dark in color, often fine-textured, and is intimately mixed with mineral soil; it tends to accumulate in the surface horizons.

Formation and composition: Humus forms through humification, a process in which litter and microbial residues are broken down and reassembled into complex, resistant molecules. The resulting material includes humic substances—humic acids, fulvic acids, and, in many soils, humin—and non-humic organic matter that is still decomposed to some extent. Humus binds to clay minerals and metal oxides, which stabilizes it and slows decomposition.

Functional role: Humus improves soil structure by promoting aggregation, increasing porosity, and reducing bulk density. It enhances water retention and cation exchange capacity, aiding nutrient availability. Humus also buffers pH and contributes to soil fertility and biodiversity by acting as a habitat and energy source for microorganisms.

Environmental and agricultural significance: Because it is relatively long-lived, humus is a major sink for carbon in soils and reflects soil health. Practices that conserve or build humus—such as organic amendments, cover crops, reduced tillage, and residue retention—help maintain soil fertility and resilience.