Comparing field data from north Germany with simulations of the nitrogen model N-SIM.

The nitrogen model N-SIM was developed to simulate the nitrogen regime in cropped soils. Transport processes of water, nitrogen species and heat are considered for a one-dimensional layered soil structure including plant uptake, mineralisation, immobilisation and denitrification. To establish the prediction capabilities of the model for N-fertilizer recommendations, the model needs to be tested by data sets obtained from diverse agroecosystems and field sites. Therefore it was an opportunity to compare simulation results with field data from two research catchments in north Germany, Krummbach and Eisenach. To account for the most common case, where input data are missing and have to be estimated, only a minimum data set was used to apply the model. No model calibration and no fitting of parameters was done. Under these restrictions the model predicted soil nitrate contents for the 0-90 cm deep soil profile to within ± 15 kg ha-1 for 68% of all times and to within ±20 kg N ha-1 for 91% of all times. Also, simulation results for plant N-uptake provided reasonalbe predictions, though an underestimation of N-uptake was found in the grain filling period