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agriculture and environment

Soil at the interface between Agriculture and Environment

Luca MONTANARELLA (CCR-Ispra)

Soil, by which may be characterised the thin upper part of the Earth's crust where rock (lithosphere), air (atmosphere), water (hydrosphere) and living organisms (biosphere) interpenetrate (pedosphere), is a more complex medium than air and water. Soils are natural entities that exist in a wide range of different types. They may indeed be the most complex systems known to science. Composed of inorganic and organic matter, and with solid, liquid and gaseous components, they contain large numbers of living organisms and are the medium that supports life in its broadest sense. Agriculture has for a long time been based on the notion of the soil as an inexhaustible resource for continually increasing production. On the contrary, because of its very slow formation rate (100-400 years/cm of topsoil), soil must be considered as a non-renewable resource and must be preserved.

Agriculture and Soil Conservation 

Unlike air, water, and biota, which are mobile systems, soil is site-specific, and although more stable than the other three systems, it shows great variability in space and time (map 1).

Soils have at least six main functions relevant to human life: 

  • The production of biomass by agriculture and forestry.
  • Filtering, buffering and transformation activity, between the atmosphere, ground water, and the plant cover, protecting the environment and especially humans through the protection of the food chain and drinking water reserves. 
  • Soils are biological habitats and gene reserves, much larger in quantity and in quality than all the above ground biomass. 
  • Soils serve as a spatial base for technical, industrial and socio-economic structures and their development, e.g. for the construction of industrial premises, houses, transport systems, sports and recreation areas, dumping of refuse, and others. 
  • Soils are used as a source of raw materials, e.g. clay, sand and gravel for construction, and also as a reserve of water and energy. 
  • Finally, soils are a geogenic and cultural heritage, forming an essential part of the landscape in which we live and containing palaeontological and archaeological treasures of high value for the understanding of the history of earth and mankind. 

The problems of soil degradation and soil destruction are caused by the competition between these different forms of land use. Therefore, new perceptions and concepts for sustainable land use should be developed, which are in conformity with the constaints of nature. In this context, sustainable land use and protection of soil can be defined as the spatial (local or regional) and temporal harmonisation of all main uses of soil and land, minimising irreversible effects. This is a political rather than a scientific issue.

Soil is affected by physical, chemical and biological degradation (Table 1 and Box 1). Some agricultural activities contribute to these negative effects. However, it must borne in mind that industry, urbanization, road construction, fire, other human activities and, more generally, demographic pressure and climate changes are also major factors.

On the other hand, good agricultural practices, geared towards the conservation of the major soil functions, are well documented. Traditional farming practices ensured in many parts of Europe, especially in the Mediterranean region, the long-term conservation of soil fertility. Erosion control measures, integration of organic matter, crop rotation, etc. were all traditional farming practices well known to the European farmers. The European Union, through its Common Agricultural Policy, has well recognized the importance of such beneficial agricultural practices. An agri-environmental incentive plan, based on regulation 2078/92, plays an important role in preserving these agricultural practices, which tend otherwise to be abandoned in favor of more remunerative, but less sustainable, technologies.

The most significant forms of physical degradation of the soil due to agriculture are:

  • erosion;
  • desertification;
  • water-logging;
  • compaction.

Land use practices such as deforestation, overgrazing, some agricultural cultivation practices, removal of vegetative cover or hedgerows can exacerbate these occurrences. The increasing demand for water, the sometimes excessive mechanization and ploughing are further causes of such degradation.

The following processes characterize chemical degradation:

  • acidification;
  • salinization;
  • contamination by micro-pollutants, such as pesticides and their metabolites, heavy metals and nutrients i.e. nitrogen and phosphorous. (However, some pesticides may stay in the soil for some time without any consequences for the environment).

The major consequences of the above contamination are toxification and eutrophication.

Related agricultural practices are:

  • over-use of manure and mineral fertilizers; 
  • emissions of pollutants by intensive livestock production; 
  • spreading of sewage sludge on agricultural soils; 
  • the use of pesticides with unintended side-effects (slow degradation). 
As regards biological degradation, it should be remembered that the quality of the soil is mainly defined by its biological activity, which is affected by:
  • important humus mineralisation; and
  • changes in biodiversity.

Lowering the humus content makes soil more susceptible to compaction, erosion and other forms of physical degradation. Inappropriate land use practices, especially in agricultural fields, are most often the reason for this problem. The unintended side effects of pesticide use on soil life can explain many changes in biodiversity. However, this occurrence must be considered in conjonction with the degradations described above.

Environmental issues and trends regarding soil use in the EU

Sealing and Urbanisation

The current rate of soil loss by sealing through urban expansion and infrastructure in the Netherlands amounts to ca. 36 ha per day. In other countries of Europe, like Germany (120 ha per day), Austria (35 ha per day) and Switzerland (10 ha per day), similar soil losses by sealing through infrastructure and buildings have been observed. This urban sprawl increases the costs of urban infrastructure, traffic in urban areas, and energy consumption, and has negative effects on the quality of the countryside and the environment. This development is in direct competition with agricultural land uses and is threatening valuable agricultural soils all over Europe.

Soil Erosion

According to the Dobris+3 report, about 115 million hectares of European soils are suffering from water erosion and 42 million hectares from wind erosion (Table 2).

Soil erosion is a major socio-economic and environmental problem through Europe. It reduces the productivity of the land and degrades the performance and the effectiveness of the ecosystems. More than half of the land in Europe has suffered various degrees of soil erosion by water and about a fifth has been eroded by wind. The phenomenon is more acute in the southern countries, where it often reaches catastrophic dimensions, than in the northern territories. 

Soil erosion and salinisation have increased the risk of desertification in the most vulnerable areas, particularly in the Mediterranean region. Information on the extent and severity of desertification is limited; further work is needed on prevention strategies, possibly within the framework of the United Nations Convention to Combat Desertification (UNCCD). In particular the Regional Implementation annex (Annex IV) of the UNCCD deals with the extensive desertification phenomena of the northern Mediterranean countries.

Water Erosion

Table 2 indicates the importance of water erosion in Europe, in terms of area. The dominant effect is the loss of topsoil. That is often not conspicuous, but nevertheless potentially very damaging. Physical factors like climate, topography and soil characteristics are important in the process of soil erosion. In part, this explains the difference between the severe water erosion problem in Iceland but the virtual absence of erosion in Scandinavia where the climate is less harsh and the soils are less erodible. Comparison can be made between the erosion occurring on the coasts of the northern Mediterranean, from Spain to the Adriatic, and erosion occurring in North West Europe (Netherlands, N. Germany, Denmark). The Mediterranean region is subject to long dry periods followed by heavy bursts of erosive rainfall, falling on steep slopes with fragile soils, resulting in considerable amounts of erosion. This contrasts with NW Europe where soil erosion is slight because rain falls on mainly gentle slopes and is more evenly distributed throughout the year. Consequently, the area affected by erosion is much more restricted in its extent. In parts of the Mediterranean region, erosion is now irreversible and in some places has practically ceased because there is no more soil left! The natural formation rate for new soil is between 0.1 to 10 tonne/hectare/year. With such a very slow rate of soil formation, any regular soil loss of more than 1 t/ha/yr can be considered as irreversible within a time span of 50-100 years. Losses of 20 to 40 t/ha in individual storms, that may happen once every two or three years, are measured regularly in Europe with losses of more than 100 t/ha in extreme events. It may take some time before the effects of such erosion become noticeable, especially in areas with the deepest and most fertile soils or on heavily fertilised soils. However, this is all the more dangerous because, once the effects have become obvious, it is usually be too late to do anything about it. The major causes of soil erosion are still inappropriate agricultural practices, deforestation, overgrazing and construction activities. The problem is greatest in the Mediterranean region because of its fragile environmental conditions, but problems exist in most European countries. Land abandonment and forest fires, particularly in marginal areas, intensify soil erosion. Strategies, such as afforestation, for combating accelerated soil erosion are lacking in many areas. 

Wind erosion

The dominant result of wind erosion in Europe is loss of topsoil. It occurs mostly in south-eastern Europe. The removal of soil material is selective, even more so than for water erosion, as only fine particles (clay, organic matter with their adsorbed nutrients) are removed, leaving impoverished, coarse textured soil particles. The off-site effects are increased air pollution because of the presence of dust particles, the covering of fertile soil layers and, in the most extreme cases, complete burial and dune formation. Terrain deformation in the form of windblown depressions may also occur as well. Damage through wind erosion is practically irreversible.

Compared with water erosion, wind erosion shows a more distinct regional distribution in Europe. This suggests that physical factors, in particular climate, are relatively more critical than human influences. The fairly moist conditions prevailing in Western Europe and the nature of storm events, often associated with rain from oceanic depressions, diminish the chances of wind erosion. This is not a universal rule, however, demonstrated by the incidence of severe wind erosion in Iceland and the less severe, but still significant, events in certain parts of North West Europe (N. Germany, the Netherlands, E. England).

Extensive conservation measures such as windbreaks have considerably reduced the hazard. The widespread and serious wind erosion in the south eastern Europe (including the S. Russian plain) can be partly explained by the dry continental climate and sensitive soils in combination with inappropriate farming practices. Excessive drainage is a major cause of conditions that favour wind erosion. However, human activities again play their part in causing wind erosion. Overgrazing appears to be a major cause, in part because the areas most sensitive to wind erosion (semi-arid regions with sandy soils) are less suitable for other types of land use.

The Nordic Countries

The information available on soil erosion in the Nordic countries (i.e. Norway, Sweden, Finland and Denmark) was recently compiled in a report, edited by Rekolainen and Leek (1996). The report tries to assess the erosion risk over the whole territory of these countries. In Norway, Sweden, Finland and Denmark, water erosion is considered to be the main problem, not only because of the negative impact it may have on soils and agriculture but also because of its significant contribution to the phosphorus loading of freshwater bodies. The water erosion risk was assessed using a model based technology (a core model, USLE and a supporting model CREAMS for some, more detailed analyses). The necessary input data were derived from existing data sets on climate, soils, crop type and topography and the results presented in the form of maps.

When compiling the maps, it appeared necessary to adjust the modelling strategy to the available data in each country. This is probably the reason why the final results are presented in a relative form, with 5 classes of the relative erosion risk, although all calculations are based on a quantitative model. The maps covers the whole territory of Finland, Sweden and Denmark. In Norway, the necessary topographic data were only available for ca. 25% of the total territory. 

The following areas have a high risk of erosion: southern Finland; eastern Jutland, Seeland and Fünen in Denmark; the area around Oslo in Norway; the southern coast and the area between Göteborg and Arvika in the west and Västervik and Gävle in the east in Sweden. The qualitative nature of the documents makes it impossible to assess the severity of the problem in absolute terms.

The Central-Western Countries

Soil erosion by water in Central Europe is not as aggressive as in Southern Europe, because bioclimatic, topographic and human pressures have not been as acute as in the south (Yassoglou, 1987). 

The bioclimatic conditions in Western Europe also help avoid high rates of soil erosion. Favourable evapotranspiration rates and the even distribution of rainfall throughout the year facilitate the speedy regeneration of the protective vegetative cover of the land. Low relief and gentle slopes over large parts of the region contribute to the low rates of erosion, which average 0.24 t/ha/yr. In the mountainous regions of France, the losses range from 1.8 to 2.5 t/ha/yr whereas in small valleys in the Alps and the Apennines losses reach 25 t/ha/yr. However, the potential erosion risk, arising from removing the protective vegetative cover by cultivation, is significant even on the gently sloping land and considerably exceeds the tolerance level. In Belgium the area susceptible to water erosion is estimated at about 10 per cent of the agricultural land area, while improvements in artificial drainage have reduced the problem of waterlogging. Rates of soil loss in Belgium have been reported as high as 82 t/ha/yr., from bare fallow land on 5-7% slopes. The dominant form of soil erosion in France is water erosion, estimated to affect about 5 million hectares of agricultural land, or about 17 per cent of the total, compared with 0.5 million hectares at risk from wind erosion, mainly in the south of the country. Soil erosion now effects most of the main cereal growing areas in France and other major agricultural production regions. This compares with the 1950s when it is estimated that 2.7 million hectares were affected by erosion, or 8 per cent of total agricultural area. About 37% of the arable land in England and Wales show erosion rates above the tolerance value. In Germany, potentially erodible surfaces are those on hilly sites with slopes as low as 2-6%. 

Many data exist in the countries of Western-Central European, but the regional assessments of erosion risk are qualitative and based on a variety of methodologies. As a pilot exercise, a semi-quantitative assessment for France has been made by INRA in collaboration with the European Soil Bureau, the results being shown in map 2 (Kirkby et al. 1998). This approach could be applied to the whole continent and with local validation could provide a Pan-European soil erosion risk assessment map. In Spain, soil erosion in certain olive orchards on steep slopes has been measured at up to 50 tonnes per hectare. In total, erosion and desertification in this country are estimated to severely affect (soil losses of over 100 tonnes/ha/year) as much as 9 million hectares or 18 per cent of the total land area, with 13 million hectares (26 per cent) moderately affected (12-50 tonnes/ha/year). The factors that most influence vulnerability to erosion are steep slopes, drought followed by intense rainfall, lack of topsoil and sparse vegetation cover. A major part of the land affected by erosion in Spain is non-irrigated grassland, the so-called maquis or garrigue, and to a lesser extent areas of permanent crops such as vines, almond and olive groves. The cost of the direct impact of erosion - including the loss of agricultural production, impairment of reservoirs and damage due to flooding - is estimated by the EEA at 280 million ECU per year, with the cost of soil rehabilitation estimated at about 3,000 million ECU over a period of 15 to 20 years. 

Mediterranean Europe: The CORINE assessment 

In the Mediterranean, the climate, the strong relief (characterised by steep slopes and extensive dissection), and the long history of human intervention (in the natural ecosystems) have resulted in rates of soil erosion, that are more catastrophic than in other regions of the Continent.

According to CORINE (1992), about 66% of the rural area has a moderate to high potential risk of soil erosion (by water). The distribution of the risk in the region, and within the individual countries, is complex. A large proportion of land in Portugal, Greece and Spain (68%, 43% and 41% respectively) is at high risk from soil erosion, whereas the corresponding proportions in Italy and in Mediterranean France are less (27% and 9% respectively) (map 3).

High-risk areas tend to occur in the mountains of Cantabria, the Sierra Nevada, the Pyrenees, the Alps, the Apennines and the Pindos range. This reflects the control exerted by topography on slope and climate. High risk areas associated rugged terrain with subject to high climatic erosivity and soil erodibility also occur throughout Portugal, in Extremadura and Andalucia in Spain, in Corsica, in Sardinia, Calabria and Sicily in Italy, and in Crete and the Aegean Islands in Greece.

Extensive areas of bare rock cover approximately 10% of the land in Greece, Albania, and the Mediterranean sections of the former Yugoslavia. These areas can be considered to be mostly desert now and soil erosion has ceased to take place because there is practically no soil left. However, these areas still produce rapid surface runoff when it rains and this threatens lower lying land.

The area of actual erosion risk given the present vegetative cover, is considerably smaller than the area of potential risk and is estimated to cover 30% of Portugal, 29% of Spain 1% of Mediterranean France, 10% of Italy and 19% of Greece.

Salinisation

Soil salinisation affects nearly 4 million hectares, mainly in Mediterranean and Eastern European countries. The main causes are over-exploitation of water resources as a result of irrigation for agriculture, population increase, industrial and urban development and the expansion of tourism in coastal areas. The main effects in cultivated areas are lower crop yields and even total crop failure. Strategies to combat soil salinisation are lacking in many countries.

Activities on soil protection policies on EU level 

A lot has been said already on the issues at stake and on the activities in various European States, both within and outside the EU. Although a comprehensive policy on soil protection does not (yet) exist on European Community level, numerous initiatives, programmes and legislative measures exist which more or less directly affect soil protection (Box 2). 

Extensive research and data collection on the status of European soils has been undertaken within the EU in the framework of the 4th Framework Programme for research and Development. Georeferenced soil information within the EU is collected through the European Soil Bureau (ESB) of the Joint Research Centre, Ispra (Box 3).

Further important activities which support the Commission's own initiatives are undertaken by the European Environment Agency.


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