Nitrogen balances and leaching in four agricultural catchments in southeastern Norway

The aim of this paper is to evaluate the relations between nitrogen surface balances and nitrogen leaching in four small agricultural catchments in the southeastern part of Norway. The catchments were dominated by cereal production, and data were collected during the period from 1992 to 1996. There was a low linear correlation (R2 = 0.15) between nitrogen surface balances and nitrogen leaching for all catchments and years. The linear correlation between nitrogen leaching in autumn and nitrogen surface balances was good (R2 = 0.95), when only catchments with similar soil properties and years with similar weather conditions were included. When leaching losses were subtracted from nitrogen surface balances, the data showed large variations, from a surplus of 36 kg nitrogen ha−1 to a deficit of 5 kg nitrogen ha−1 as averages for the five year period. The deficit indicates a decreasing soil nitrogen content. A surplus occurs when the sum of changes in soil nitrogen content and gaseous losses is positive.