Efficient utilisation of nutrient in agricultural systems is essential in order to meet a sustainable production of food and reduce environmental harmful losses. Grass-clover mixtures are a key crop at e.g. dairy farms supplying high quality fodder and at the same time building up soil fertility. The main input of nitrogen in such system is derived from the nitrogen fixation of clover, which mean that understanding the below ground dynamics is essential to reduce nitrogen loss and set up soil-plant models to simulate effects of different management strategies. The present knowledge does however not support this.

Leaching of nitrogen have for many year only focussed on nitrate, but in resent year dissolved organic nitrogen (DON) have received increasing interest as DON have been found to constitute up to 50 percent of the total nitrogen lost. In order to assess the environmental fate of DON it is necessary to know the chemical and physical nature of DON being lost, as different forms of organic nitrogen will behave differently in soil matrix.

The aim of this project is to investigate leaching, origin and characteristics of DON from grass-clover mixtures as influenced by management and climatic conditions, and make this operational within existing soil-plant models in order to improve the utilization of nitrogen and reduce adverse environmental effects. This will be accomplished by conducting similar experiments in Iceland, Germany, Sweden, and Denmark having greater yet relevant climatic variability and incorporate new understanding regarding source and amount of nitrogen leaching, modes of nitrogen exchange between grass and clover, and nitrogen soil pool build-up into existing soil-plant models of grass-clover mixtures.

Contact:

Post doc Jim Rasmussen

Department of Agriculture and Environment

Faculty of Agricultural Sciences

University of Aarhus

PO Box 50, 8830 Tjele

Email: Jim.Rasmussen@agrsci.dk