THE PERFORMANCE OF THE DANISH SIMULATION-MODEL DAISY IN PREDICTION OFN-MIN AT SPRING

Denmark the Danish Agricultural Advisory Centre has for some years use d the soil content of mineral nitrogen in spring in fertilizer recomme ndations. Since 1986 these recommendations have been based on soil sam ples carried out at all intersections of a nationwide 7 km square grid in Denmark. It was hoped that it may be possible to replace soil meas urements with values of soil mineral-N calculated with a model. The Da nish simulation model DAISY, which among other things simulates change s in the inorganic N content of the soil, was evaluated with respect t o the N-min content in the early spring under bare soil and under wint er cereal. For both situations the precrop was cereals. The performanc e of the model was evaluated in farming systems receiving mineral fert ilizer and in some instances organic manures. The results were analyse d according to type of subsoil: sandy or loamy. Predictions were 11 kg N ha(-1) less than the measured values as a mean and the differences between simulated and measured values were high for fields receiving o rganic manures. Predictions were less than +/- 10 kg N ha(-1) of measu red values in 25-58% of cases for the different types of crop cover at the time of soil sampling, type of subsoils and fertilizer strategies , respectively. Predictions were less than +/- 20 kg N ha(-1) of measu red values in 48-89% of cases for the different situations. The best p redictions were obtained for sandy subsoils covered by winter cereal a nd supplied with mineral fertilizer only. It is concluded that the qua lity of the data used as input in the model has to be increased and th at further developments of parts of the DAISY model are needed before modelling can be a useful tool in N fertilizer recommendations.