Although soil degradation processes in Europe vary considerably from Member State to Member State, with different threats having different degrees of severity, soil degradation is an issue all over the Union:
- An estimated 115 million hectares or 12% of Europe’s total land area are subject to water erosion, and 42 million hectares are affected by wind erosion.
- An estimated 45% of European soils have low organic matter content, principally in southern Europe but also in areas of France, the UK and Germany.
- The number of potentially contaminated sites in EU-25 is estimated at approximately 3.5 million. [source: COM(2006)231, 22.9.2006]
The accumulation of organic matter in soil has taken several hundreds or thousands years. Soil in the world contain approximately 1,500 Gt of carbon (650 Gt in vegetation), and it is the most important compartment of carbon in the terrestrial biosphere (Robert, 2000). Agricultural activities reduce the stock of organic matter of the soil, where the losses in organic matter are often not sufficiently compensated by the additions, leading to an overall decline in the pool of soil organic matter (Lickacz et al., 2001). Tillage usually influences the structure of the soil in a positive way, causing improved aeration and better drainage. However, inappropriate tillage or tillage undertaken when the soil is in and adverse condition – both very common – may provoke the inverse effect: the soil may then be compacted, and the aeration decreased (Lickacz et al., 2001). This process has significant negative consequences on the biologic activity of the soil.
Below a certain level of soil organic matter, the levels of production fall, either directly, because of a deficiency in nutrients of organic origin, or indirectly, because of a degradation of the structure of the soil. According to Loveland et al. (2003), a threshold of 3,4% of soil organic matter (2 % soil organic carbon) is the level below which potentially serious decline in soil quality may occur. Le Villio et al. (2001) consider a threshold value between 2 or 3 % of soil organic matter in a silty soil. From an environmental and economic point of view, several regions in southern Europe have a critical level of soil organic matter below which the agricultural production could be sharply decreased. In Mediterranean regions, the low levels of soil organic matter of certain densely populated regions are already producing alarming consequences on the levels of production.
Soil depletion and impoverishment cause three main environment-related problems and human level: (1) soil erosion of farming areas, (2) marginalization and abandonment of agricultural land, and (3) soil sealing.
(1) Soil erosion by water is a widespread problem throughout Europe. Physical factors like climate, topography and soil characteristics are important in the process of soil erosion. The Mediterranean region is particularly prone to erosion because it is subject to long dry periods, followed by heavy bursts of erosive rain, falling on steep slopes with fragile soils. With a very slow rate of soil formation, any soil loss of more than 1 t/ha/year can be considered as irreversible within a time span of 50-100 years. The level of soil erosion in the involved regions is between 1 and 10 t/ha/ye (data from IRENA – PESERA project).
(2) The marginalisation of farming areas is driven by a combination of social, economic, political and environmental factors. Marginalisation makes farming less viable over time, leading to the eventual abandonment of agricultural land (within farms or as a whole farm). The environmental effects of marginalisation are linked to the abandonment of agricultural land, which may lead to a loss of landscape diversity and related loss in biodiversity, and to an increasing vulnerability to fires, and in some cases, soil erosion. This arises from a regrowth of different shrubs and eventually woodland vegetation on abandoned agricultural land, which suppresses biodiversity-rich grasslands and leads to an increased fire risk in Mediterranean areas.
(3) The conversion of agricultural land to artificial surfaces, which is also known as soil sealing, can impact on soil, water and biodiversity resources. Sealing increases the risks of soil erosion and water pollution, disturbs agricultural habitats, impacts on animal migration patterns and affects the hydrological cycle (increased water runoff and decreased water retention) leading to an increased risk of floods. In addition, it affects the esthetical value of agricultural landscapes, and increases their fragmentation, which can result in more noise and emissions because of increased traffic levels.
From the point of view of policy makers and land managers, whose mission is to try and stop the degradation of soils, the assessment of soil conditions is crucial. Current methods, though, can only provide “static” physicalchemical reports about the status of soil in a given moment, upon which only short-term actions can be based. The BIOREM monitoring technology is based on the fact that one of the effects of the decrease of soil organic matter is a net decline of the biological activity of the soil (see the Soil Biodiversity Report of the Technical Working Group Established under the Thematic Strategy for Soil Protection). Starting from a quantitative and qualitative molecular characterization of the biochemical profile of the soil, the BIOREM method can detect the presence and status of enzymatic processes, demonstrating its ability to provide a more thorough, dynamic picture, extremely useful for the development of precisely targeted, far-sighted restoration and development strategies.
As a side note, it important to underline that there is a positive correlation between soil organic carbon and crop yield, so practices that increase soil fertility and crop productivity also mitigate GHG emissions, particularly in areas where soil degradation is a major challenge (Lal 2004). Also, based on Silver et al. (2000), it can be estimated that the restored soil will sequester C at a rate of 130 g/cm2/year for the first 20 yr, and then at an average rate of 41 g/cm2/year for the following 80 years.
All the above issues are strongly connected to European environmental policy and legislation, since soil depletion and its consequences do not only have a biophysical dimension, but at the same time also a socio-economic dimension. Policy makers are expected to make extra efforts at an EU level to bring these two dimensions closer to each other. This is reflected – for instance – in the way that the Common Agricultural Policy has progressively included more environmental requirements. Another example: an appropriate soil management is essential for many Natura 2000 sites, and the limiting impacts of marginalisation will also be relevant in meeting the requirements of the Birds and Habitats Directives, let alone obviously the fulfilment of the Thematic Soil Strategy and the endless connection to other fields of policy relevance.