Enhancement of soil structure

Good soil structure helps with physical fertility of soil. Both the large soil animals (e.g. earthworms) and the tiny microbes have roles in improving soil structure. Soil with good structure has many beneficial effects including enhanced water transmission into and through soil, lower bulk density and lower potential for soil erosion.

Large Soil Animals

Earthworm tunnels - horizontal and vertical.

Large soil animals make tunnels through the soil. These are often called macropores as they form the larger pores in the soil. Some earthworms, dung beetles, spiders, ants and cicadas (as they emerge from the soil to change into adults), make vertical tunnels that open to the soil surface and down which water can infiltrate. Other tunnelers form macropores that don’t open to the soil surface (earthworms, termites). The formation of holes (or macropores) in the soil, helps water transmission and soil hydrology. If water can easily enter the soil, less runs off to cause erosion.

Soil animals mix soil layers together and also mix organic matter that they eat with mineral soil layers. Ants, earthworms and termites bring organic matter into the soil from the surface and deposit it, thus increasing the organic matter content of soil. This helps water retention in soil.

Earthworm activity lowers soil bulk density and makes soil more friable - roots can penetrate this soil more easily.

Diagram of a soil aggregate.


Bacteria and fungi help in the formation of water-stable soil aggregates. Fungal hyphae grow around and between soil mineral and organic particles and physically bind them together. Both bacteria and fungi secrete polysaccharide mucilages which are sticky and glue the soil particles together into aggregates. These aggregates can be stable to the action of water for several months and help prevent slaking and dispersion of the soil.