Catch Crops in Practice in Danish Agriculture

Keywords: nitrogen legislation, nitrate leaching, soil mineral nitrogen, undersowing, early sowing.

Catch crops have been an important tool for the reduction of nitrogen leaching in the Danish legislation since 1998. A great deal of experience with catch crops and alternatives to catch crops both from research, trials and practice has been gained. Catch crops are a cost effective tool to reduce nitrogen leaching if the alternative is bare soil without a crop in the autumn. If a farmer is forced to change the crop rotation from winter cereals to spring sown cereal in order to give space for catch crops, he will have a significant decrease of income, especially on pig production farms on soils with more than 10% clay.

To reduce nitrogen leaching in crop rotations with a high proportion of winter cereals the effect of catch crops of yellow mustard or fodder radish spread 2-4 weeks before expected harvest of cereals and ploughed into the soil after the 20^th of September before sowing winter cereals has been tested. The effect of this system was found to be one half of that of a catch crop followed by a spring sown crop. Another possibility is to establish the winter cereal 2-4 weeks earlier than normal. Trials have shown a significant effect on the risk for nitrogen leaching, without yield loss.

Leif Knudsen, Knowledge Centre for Agriculture, Agro Food Park, 8200 Aarhus N, Denmark.

15 pages, 1 figure, 7 tables, 10 references.