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Silent but deadly! Organic farming combats flood dangers

24.08.2005 - (idw) Bundesforschungsanstalt für Landwirtschaft (FAL)

On the one hand water is a vital element, on the other it is an extreme danger for mankind.

Although the number of floodings over the last centuries has been more or less constant, their magnitude has steadily increased during the last decades. Very few countries have been free of flood disasters. In Germany the 2002 once a century flood of the Elbe river destroyed whole cities, and at present Austria and Switzerland are suffering from extreme floods.

Soil compaction and slaking result in a reduction of a soil's infiltration capacity for water. Trigger factors for this "stealth or silent sealing" (picture 1) of our soils are due to decreasing organic matter contents, decreasing biological activity and increasing compaction caused by high mechanic stress of soil structures. But, conversely, high infiltration rates of healthy soils can reduce the intensity of flood incidents.

Scientists of the Institute of Plant Nutrition and Soil Science and the Institute of Organic Farming at the Federal Agricultural Research Centre (FAL) in Germany have examined the connections between physical, chemical and biological soil parameters and the infiltration capacity of soils on different sites. It is known from numerous investigations that soil cultivation techniques that do not use the plough, ("conservation tillage") on conventional farms contribute to better infiltration. But on organic farms a much larger number of positive factors for the development of "bio-pores" in the soil exist. Such bio-pores are the key to improved infiltration and are mainly created by earthworms.

Organically managed soils show approximately seven times more earthworms and twice as high infiltration rates as soils on conventional farms. Employing crop rotations with forage crops (for example clover or grass) and catch crops, as well as an optimal supply of organic materials results in a higher humus content in organically managed soils. Research results from FAL show a positive effect of such organic farming techniques on soil structure and infiltration rates after only three years (picture 2).

Bearing in mind the recent disastrous flood incidents, the scientists at the institutes propose the maintenance of site specific high infiltration rates as a powerful means for flood prevention. In this context, they say, substantial support of organic farms is justified to pay for a service provided by the farms to the community which does not itself pay for the higher costs of organic farming. They also conclude that support for organic farming could be an efficient measure to counteract anthropogenic soil consumption which contributes to flooding dangers.

Contact: Prof. Dr. Dr. Ewald Schnug, PD Dr. Gerold Rahmann, Federal Agricultural Research Centre (FAL), Institute of Plant Nutrition and Soil Science and Institute of Organic Farming, Bundesallee 50, 38116 Braunschweig, Germany, fone +49 531 596 2101, fax +49 531 596 2199, E-mail:
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