|CHAPTER 07: SOIL - INTRODUCTION|
Soil is often seen as an inert medium, merely a support for human activities. However, soil is more than that: it is a dynamic, living system which comprises a matrix of organic and mineral constituents enclosing a network of voids and pores which contain liquids and gases. The structural arrangements of these components determine the main soil types in Europe; 320 different major soil types can be identified in the EU (CEC, 1985). In addition, soils contain populations of biota ranging from bacteria and fungi to worms and rodents (Figure 7.1); the chemical, physical and biological properties of soils vary both vertically and horizontally at a variety of scales. Soil is formed from the combined effects of climate, vegetation, soil organisms and time on rocks and parent materials (Jenny, 1941). So, any alteration in one of these components may result in changes in the soils. Soil genesis is a long process the formation of a layer of 30 cm of soil takes from 1000 to 10 000 years (HÃ€berli et al, 1991). It is formed so slowly that soil can be considered as a non-renewable resource.
Soil is a complex system where crucial biogeochemical processes occur. In the top 30 cm of one hectare of soil, there are on average 25 tonnes of soil organisms, that is: 10 tonnes of bacteria and actinomycetes, 10 tonnes of fungi, 4 tonnes of earthworms and 1 tonne of other soil organisms such as springtails, mites, isopods, spiders, coleoptera, snails, mice, etc. (Blum, 1988). Earthworms, alone, can represent from 50 to 75 per cent of the total weight of animals in arable soils; in one hectare, 18 to 40 tonnes (that is a layer 1 to 5 mm deep) of soil is ingested each year by the earthworms and passed onto the surface. The number of worms varies with the soil and its management. The soil fauna and flora recycle organic matter to form humus and mix it with the mineral material; they also create and maintain the airways within the soil that are essential to plant roots; some species found in soil control others that are pests to crops.
The carbon stored in soils is nearly three times that in the above-ground biomass and approximately double that in the atmosphere (Eswaran et al, 1993). Replenishing carbon is a slow process not easily achieved; soil protection should therefore, apart from its other benefits, assist in maintaining this reservoir of soil carbon (see also Chapter 27).
In contrast with the earlier concern for the atmosphere and hydrosphere, the need to protect the soil has been appreciated only more recently. Soil is static and thus acts as an enormous receptacle for any type of pollutant which can be mobilised under different triggers (such as acidification) and finally released to the environment. Since the residence time of these substances is far longer in the soil than in air or water, effects are often hidden for a long time. Soil-related problems are also site-specific, which makes any attempt at generalisation very difficult. The unique capability of the soil for recycling biodegradable waste, and the delay until effects are usually detected, has led to complacency, and concern for the well-being of soils has been slight. But soil is necessary for the growth of crops of food, fibre and timber, and it is an essential component of all terrestrial ecosystems. Consequently, the role of the soil is of vital importance to humankind and the maintenance of a healthy natural environment. The 1972 European Soil Charter (Council of Europe, 1972) recognised for the first time that any biological, physical or chemical degradation of soil should therefore be of primary concern and that appropriate measures to protect soils should be implemented without delay. Unlike air and water, soil can be owned as personal property, which renders soil conservation or protection policies difficult to enforce and requires acceptance by landowners and managers. The data and information sources used in this chapter are described in Box 7A.
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