The section above has shown that there is a close relation between relief and soils, another of the natural environment’s systems. The weathering of rocks provides soils with their minerals. These are supplemented with air, water and organic matter, which give them their characteristic features. Figure 2 shows the distribution of the various components in an ideal soil: it can be seen that whereas the mineral portion accounts for 45% of the total, the organic portion accounts for only 5%.
Feliu i Gueorguieva (2003) define soil as “a multifunctional medium of complex composition that is formed by the weathering of the mother rock that sustains it or by external contributions. It contains its very own biological community and, as an interface, has a wide range of physical and chemical interactions with water and air.”
Therefore, both the creation (pedogenesis) and the development of soils are closely connected to other natural systems, as can be seen by the factors that play a role in their formation: the mother rock, living organisms, the climate, relief and time.
Just as important as the mother rock on which the soil rests are the living organisms, especially vegetation, which provide the organic components that make it possible for the uppermost layer of the soil – known as humus – to form. Without soil it is very difficult for vegetation to develop, but without vegetation soil might disappear: the vegetation acts as protection against such external agents as the climate, which can erode the soil, a process that is speeded up if there is a considerable slope.
Soil has some basic functions in the environment (Feliu i Gueorguieva, 2003):
· It serves as a habitat and a genetic reserve (source of biodiversity)
· It provides a base from which food and biomass can be produced.
· It regulates the balance between surface and underground waters.
· It protects the quality of underground waters (natural filter).
· It acts as a drain for carbon dioxide (CO2).
· It is a source of raw materials.
· It has a social, economic and cultural function.
But soil is in a highly fragile equilibrium and this fragility is accentuated by the intervention of humans, who can wipe away all traces of it in some areas.
To combat the processes of erosion and desertification that were taking place the world over, in 1977 the United Nations Conference on Desertification was held in Nairobi (Kenya), where it became evident that desertification – with all its attendant problems – had made considerable advances and that anthropic action was responsible for 87% of soil losses.
Subsequently, in November 1982 the World Soil Charter was signed in Rome (Italy). It set out 13 principles, the second of which stated
Recognizing the paramount importance of land resources for the survival and welfare of people and economic independence of countries, and also the rapidly increasing need for more food production, it is imperative to give high priority to promoting optimum land use, to maintaining and improving soil productivity and to conserving soil resources.
As well as quantitative loss, soils can also degrade qualitatively in the form of decreases in fertility because of loss of organic matter (mineralization), salinization, compactation or contamination as a result of dumping (solids or liquids).