Operational use of agro-meteorological data and GIS to derive site specific nitrogen fertilizer recommendations based on the simulation of soil and crop growth processes

The spatial and temporal coincidence of nutrient supply and the demand of the crops is especially important for nitrogen to prevent ground water contamination. High spatial and temporal variability of soil mineral nitrogen and high costs impede a frequent and dense soil sampling under practical conditions. Temporal dynamics of relevant state variables, such as soil-crop nitrogen dynamics, are derived in agricultural system models from temporally stable soil attributes being estimated once for a field, and agro-meteorological data. The model HERMES was used in combination with a GIS to derive site specific fertilizer recommendations by subsequent model runs at different development stages combining actualized real weather data and a typical weather scenario of the specific site for a predictive calculation of the nitrogen deficiency. For two fields, site specific nitrogen recommendations were calculated based on the simulation of crop growth and nitrogen dynamics using the spatial distribution of relevant soil and terrain characteristics. On one field a retrospective calculation of yield response on fertilization showed differences of yield response between single locations. Model-derived recommendations and real management performance were compared. For the other field real time model recommendations were derived for two years. Compared with a Nmin/Hydro-N-sensor based fertilizer estimation method the model-based strategy yielded savings of 40 kg ha−1 for both years without grain yield reduction.