SIMULATION OF NITROGEN DYNAMICS IN FARMLAND AREAS OF DENMARK (1989-1993)

Each year since 1986 information has been collected about the farming systems at intersections of a nationwide 7 km square grid in Denmark. These management data and corresponding soil analyses were used in the model DAISY to simulate water and nitrogen dynamics. The model was va lidated with respect to harvested dry matter yield and nitrogen conten t in the soil. Simulated nitrate leaching from farmland areas from 1 A pril 1989 to 31 March 1993 was related to precipitation zones, soil ty pe, fertilizer strategies and cropping systems. The mean simulated nit rate leaching for the whole of Denmark was 74 kg N/ha/yr, with a large yearly variation in the period considered. The simulated nitrate leac hed from soils with a sandy subsoil corresponded to 51% of the applied fertilizer, twice that leached from soils with a loamy subsoil. The a pplication of pig manure resulted in average leaching losses of 105 kg N/ha/yr. The simulated nitrate leaching losses at sites where only ar tificial fertilizer was applied were in the following order: cereal wi th undersown grass < crop followed by winter cereal or winter rape < c ereal or rape without a catch crop < root crops without a catch crop. Where only artificial fertilizers were applied, the simulated mean ann ual leaching was 59 kg N/ha from spring barley and 40 kg N/ha from win ter wheat. A map of simulated nitrate leaching in Denmark was produced using a Geographical Information System.