Soil separates rocks from the atmosphere and constitutes the epidermis of the land. Soil is as crucial to life on Earth as water.
Soils are made up of solid, liquid and gaseous materials that organise porosity. They are assembled in horizons (successive layers) and form a continuous cover of highly variable thickness. The nature of soils varies in space depending mainly on geology, topography, climate, time and living organisms. Our knowledge of soils through morphological observations on the field and analyses helps us understand their qualities, fragility, and the pressures they are subject to. Soils are classified and named. Despite their importance, we know little about them.
However, soils should be the subject of more attention because they are decisive in water dynamics (regulation, reservoir, distribution), in pollution processes through a protective effect (filtration, buffer effect, decomposition, degradation or immobilisation of pollutants) or a source effect (when they have been contaminated), and for ecosystems (plant rooting, animal life in and on soils). They support economic activities (primarily agriculture, followed by human infrastructures), play a role in carbon sequestration (as a climate change moderator) and can be a receptacle for materials (sludge, sewage, treated waste water). Soils contribute to several Sustainable Development Goals1.
However, soils are subject to many types of pressure: sealing due to urban sprawl and infrastructure; erosion by rain, wind and certain agricultural practices; diffuse or point source pollution by contaminants; overexploitation with a drop in fertility and biodiversity of soil organisms; drying out due to drainage; waterlogging due to floods; compaction by agricultural or forestry machinery; salinisation due to irrigation and rising sea levels; acidification; desertification; etc. Soil degradation can be very rapid and is irreversible on a human scale. Indeed, it takes thousands of years to reconstitute soil (1,000 years for 1 cm in temperate zones). Soil is therefore a non-renewable resource that must be preserved.
A first step is to preserve soils with high agronomic quality for agriculture.
Due to their role in regulating the quantity and quality of surface water and groundwater, we should also consider soils in water management.
1-Source of production and income if well managed (MDG 1), support for agricultural production and fight against hunger (MDG 2), retention of dangerous elements to preserve health (MDG 3), protective role with regard to water quality, purifying power and receptacle of sanitation by-products (MDG 6), regulation of rainwater and sources of amenity in urban areas (MDG 11), fertility and agricultural production (MDG 12), climate action through carbon dioxide sequestration (MDG 13), support and habitat for terrestrial life (MDG 15)