PREDICTION OF NITRATE LEACHING LOSSES FROM ARABLE LAND UNDER DIFFERENT FERTILIZATION INTENSITIES USING THE SOIL-SOILN MODELS

The ability of the SOIL-SOILN models to predict nitrate leaching rates from arable land under different fertilizer inputs is tested. The SOIL model predicts water and temperature conditions in a layered soil profile and provides driving variables for the SOILN model which describes nitrogen inputs, transformations and losses. SOILN model predictions were compared with measurements of nitrate leaching at application rates of zero, 100 and 200 kg N per hectare (N0, N100 and N200) in a long-term field experiment in south-west Sweden. Large discrepancies between model predictions and measurements of nitrate leaching were found in some years (up to 100%) and were attributed to important soil processes which are either not included in the model (macropore flow) or are difficult to model satisfactorily (partitioning between surface runoff and infiltration during snowmelt periods, crop nitrogen uptake). Nevertheless, long-term mean yearly leaching losses at the different nitrogen application rates (3, 6 and 46 kg per hectare at N0, N100 and N200, respectively) were reasonably well estimated by the model.