Soil organic matter: beyond a simple picture of humus
Soil organic matter includes living organisms, recent plant and animal residues, decomposing materials and compounds remaining for longer periods. These components undergo continual transformation.
From residues to microbial life
Leaves, roots and other materials feed soil organisms. Exudates also supply microbial activity while plants grow. The soil food web connects inputs with decomposition, nutrient cycling and plant growth, as described in the Soil Biology Primer co-authored by Dr Elaine Ingham.
What “humus” describes
Agronomic usage often describes humus as the more transformed and relatively stable part of organic matter. Modern research examines continually changing compounds. In their 2015 review, Johannes Lehmann and Markus Kleber proposed a continuum of materials at different decomposition stages rather than one chemically distinct substance.
Why some material persists
Persistence also depends on the environment. Compounds may bind to minerals or become protected inside aggregates, restricting decomposer access. Moisture, aeration and management affect transformation and retention.
Supporting many functions
Organic matter feeds organisms, retains and cycles nutrients, and contributes to structure. Its functions connect with the biology transforming it. Laboratory organic-matter measurements and observations of soil life provide complementary information about quantity and function.
Our field work
We connect organic-matter records with microscopy. Through cover, compost and liquid derivatives, we aim to restore microbiology supporting nutrition and structure, following our Soil Food Web School training.