The soil has an extraordinarily complex ecology. At first sight it appears to be a mineral, since it is to this realm that most of the matter that composes it belongs: it is the debris of the disintegration of the underlying mother rock and of the sediments that tell its geological history, floods, sands carried by the wind, volcanic depositions. But the mineral matrix is just the framework of the soil.
In fact soils are, each and in a different way, the evolutionary result of profound chemical and physical interactions between the minerals that compose them, the conditions of the environment and the living forms that harbour them. They are permeated with interstitial, aqueous and gaseous fluids, different in acidity, salt content, composition. In addition to this, soils are part of living organisms and tissues, along with molecules and organic structures that derive from their decomposition, which constitute the organic substance, with various degrees of transformation (humus). The organic substance is the component that gives the soil its essential characteristics: it is at the base of soil biodiversity and of the food chains that originate from decomposing microorganisms, it is able to retain the essential mineral nutrients for plant development, to modulate the ability to retain water, to absorb or transform toxic substances, preventing them from reaching the aquifers or plant roots, as well as preventing soil erosion. The soil is the fundamental chemical-biological laboratory of land above sea level, which regulates the biogeochemical cycles of the elements that constitute the fundamental building blocks of life: carbon, nitrogen, phosphorus, sulphur. The organic substance of the soil is also the most important terrestrial carbon reservoir: healthy soils keep it safe, preventing it from evaporating in the atmosphere as CO2, the gas responsible for the greenhouse effect. The soils of the planet contain a stock of carbon greater than twice that currently contained in the atmosphere as CO2 and the degradation of the organic substance of the soils results in climate-changing emissions, while good practices of agronomic and forest management allow to actively remove carbon dioxide from the atmosphere.