The structure of the soil is formed by coherent soil particles bound into a stable unit with organic matter. They are also referred to as aggregates. The development of aggregates depends on glues from soil organisms, such as bacteria that secrete a variety of substances. These bind soil particles into clumps. Earthworms mix and feed on soil and organic matter, which, in turn, they secrete with glues. Fungi, especially after the addition of organic matter, can form long filaments (hyphae), which run through the soil as bundles, cementing the soil particles together.
Root residues which have not yet decomposed can temporarily strengthen the soil structure. Clay and humus also stabilise the structure by means of “clay-humus complexes”. Iron oxides and other minerals such as calcium, magnesium and aluminium play an important part in this process as they strengthen the bond between clay and humus particles.
Oxygen in soil is needed to sustain life processes in roots. The carbon dioxide released in the process has to be disposed of again. Both the oxygen content of the soil and the rate at which it is supplied are important factors. This is only possible if the pores in the soil are connected to the atmosphere. A crumbly structure and sufficiently high organic matter content are important for getting enough oxygen into the soil. Soils that are prone to surface compaction should be hoed regularly to keep them open. Soil with less water and more air warms up faster in spring, which stimulates mineralisation.
Koopmans, C.J., J. Bokhorst, C. ter Berg en N. van Eekeren (2012). Bodemsignalen. Praktijkgids voor een vruchtbare bodem. Roodbont Uitgeverij, Zutphen. 96 p.