Regional Groundwater Protection by Optimised Organic Farming Systems

In Denmark the public gives high priority to being able to use untreated ground water for drinking. There is a growing understanding that clean ground water can only be maintained through active means. A way of regulating land use in vulnerable areas could be to use organic farming. Pesticide use will then stop. However, this does not necessarily mean a stop to nitrate leaching. Probably the loss of nitrate will differ with the type of organic cropping system used and that is the focus of this study.

Our hypothesis is that some of the management steps that characterise organic farming systems can change both the quantity and the quality of the ground water compared with conventional farming. The idea is to focus on the aspects of organic farming systems that presumably will affect the ground water. The total effect of the different management steps on ground water can only be evaluated by the use of a model that integrates the effects from the farming system. This requires that the effects of the organic farm system on the model parameters that are of importance for nitrate leaching are determined.

We especially need knowledge about how the hydraulic parameters are affected by the farming system, and if there are aspects of organic farming systems that generally result in an increased leaching of dissolved organic carbon (DOC) from the plough layer, which can promote a DOC-driven denitrification in the subsoil of leached nitrate. We have identified five management tools that we think would be of particular importance to investigate. These are: (1) the level of application of farmyard manure, (2) the effect of crop rotation and catch crops on the hydraulic properties and denitrification, (3) the effect of N-fixing plants on denitrification, and the effect of tillage systems such as (4) reduced tillage and (5) on-land ploughing on hydraulic properties.

On the basis of these investigations we will be able to recommend systems of organic farming that are better able to reduce nitrate leaching and which will be tested in model scenarios to calculate the leaching from the vadose zone. Further, some of the scenarios will be modelled for a catchment area to see whether the effects will persist in ground water at the regional level.

Publications

Project title
I.16 Regional Groundwater Protection by Optimised Organic Farming Systems (ØKOVAND)

Project leader
Ole Hørbye Jacobsen
Danish Institute of Agricultural Sciences (DIAS)
Department of Crop Physiology and Soil Science
P.O. Box 50, DK-8830 Tjele
Tel: 8999 1761, Fax: 8999 1619
E-mail: Ole.H.Jacobsen@AgrSci.dk

Project participants
Per Schjønning, Soil Physics and Chemistry Group
Finn P. Vinther, Organic Matter and Microbial Ecology Group
Jørgen E. Olesen, Crop Production Group
Danish Institute of Agricultural Sciences (DIAS)
Department of Crop Physiology and Soil Science
P.O. Box 50, DK-8830 Tjele

Søren Hansen, Laboratory for Agrohydrology and Bioclimatology

Lars Stoumann Jensen, Plant Nutrition and Soil Fertility Laboratory