Soil Constituents and Structure May 05 2015

Soil is a largely unrecognised wonder of the natural world. When dried it normally comprises about 70% minerals and 30% plant litter, humus, fungi and a variety of other animal life forms. To determine the mineral content of oven dried soil the organics are burnt off to form ash and the remaining mineral content is weighed.

Over billions of years the bare rocks of the earth were transformed to create an intricate microscopic landscape. Soil provides plants with accessible nutrients necessary for life by enabling the conversion of constantly replenished plant material.

The top horizon of a soil profile comprises coarse decomposing plant litter which becomes progressively finer with depth until invisible to the eye. This decomposition is started by various fungi which can release nutrients to the soil. Fungi release enzymes capable of breaking down even coarse organic material, like wood, to exude nutrient in the form of humus for the nourishment of both plant and animal life forms. 70-90% of land plants will form a partnership with fungi for nutrient exchange. Water and minerals are exchanged for photosynthesised sugars. Oyster mushrooms which are deficient in nitrogen are now being used effectively to remedy soils contaminated with petrochemicals in the USA.

Microorganisms such as:




Tardigrades (water bears/moss piglets)


Rotifers create the fertility of the soil.

The animal with the greatest impact is the earthworm – the eco-system engineer, which burrows into the earth to create a ventilation system. They forage above ground by night and eat and digest the dead vegetation underground supporting the work of the fungi. The material, which is digested by bacterial action in the earthworm’s gut, produces soil which is rich in nutrient.

So to keep nutrients flowing from dead plants to live plants we need to interpose the action of fungi, bacteria, animals and microorganisms to create a cycle of life.

The minerals need to eventually be arranged to create an open scaffold to enable the process to continue efficiently with the availability of air and water to supply the processes and to provide accessible routes and drainage for the various roots mycelium and microorganisms.