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11 January 2010 14:29:37 |News

New report reviews available knowledge on threats to agricultural soils

The EU is preparing a Soil Framework Directive to protect European soils. Researchers from the Faculty of Agricultural Sciences, Aarhus University, have evaluated the current threats to Danish agricultural soils.
With an ever-increasing population on Earth, the demand for buildings and roads is also rising and this reduces the area available for agriculture and food production. At the same time, a decrease in the quality of the agricultural soil has been observed in many areas. In the southern part of Europe climate change causes desertification and salinisation of the soil. In other areas the soil is threatened by current land use.
From 2001 to 2004 the EU set up a thematic strategy for the protection of European soils. This included an extensive scientific report prepared by scientists, stakeholders and NGO’s. To protect European soils against further deterioration the EU Commission is continuing this work in their preparation of a Soil Framework Directive.
Report on Danish conditions

Scientists at the Faculty of Agricultural Sciences at Aarhus University have now prepared a report on the threats to soil quality and the functions that are particularly important under Danish conditions.
Senior scientist Per Schjønning from the Department of Agroecology and Environment, Aarhus University, coordinated the work. He identifies three major threats to Danish agricultural soils: soil compaction, reduction in organic matter content, and erosion caused by water runoff and soil tillage.
The scientists writing the report have assessed the extent of the different threats and how each threat can impair soil quality and functions. The threats are assessed on the basis of soil resilience, i.e. whether the damage is permanent or not.
From that perspective, a major threat is subsoil compaction caused by heavy agricultural machinery, says Per Schjønning:
- Compaction below approx. 40 cm appears to be effectively permanent. In addition, many soils in the eastern part of Denmark also have a critically low organic matter content and will take a very long time to recover.

Per Schjønning, therefore, advises that there should be an adjustment to management practices to increase soil organic matter content and to reduce the wheel load of the agricultural machinery used in the field.
Soil tillage erosion and – to a lesser extent – water erosion is also believed to contribute to a permanent deterioration of soil quality to an extent that calls for action.
Risk assessment
The procedure for identifying risk areas, risk reduction targets, and measures to implement these are discussed in the report for each threat separately.
A chapter is dedicated to the general strategy for identifying risk areas. The existing documents compiled by the EU authorities in connection with and as a follow-up to the report on the Soil Thematic Strategy are here deemed to be incomplete and ambiguous. The authors emphasize that it is crucial that this work is based on a more distinct differentiation of the elements involved in the risk assessment exercise.
There is thus a need for a very explicit definition of the mechanisms that affect the soil (climate and soil management) in relation to its vulnerability to these impacts.


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