Agriculture is an essential industry, with 38% of land under agricultural production, worldwide. In Germany the fraction of agricultural land is 55%. Thus agriculture represents an important aspect of human activity. Since industrialization its productivity has been greatly increased especially in the industrial countries by modern technology like fertilization, irrigation, pesticide application and genetic modifications of plants and animals. These changes have in turn influenced the global environment through the alteration of nutrient cycles, water quality, atmospheric chemistry or soil degradation. It is known that agricultural crop production causes huge environmental nitrogen losses. For example, high nitrogen fertilisation rates result in an average nitrogen surplus of 80-110 kg N ha^-1 a^-1 in German agricultural systems. Among other consequences such as inorganic and organic nitrogen exposure of surface waters and groundwater, nitrogen surplus increase N₂O- and NO trace gas emissions from arable soils. From a viewpoint of climate change a reduction of N trace gas emissions improve environmental sustainability. Based on environmental indicators different instruments have been developed to assess farming systems in view of their sustainability. One of these instruments is the REPRO (Reproduction of the soil organic matter) model. REPRO needs several information from the farmstead, its ecological boundary conditions and of the specific agricultural management. Based on this data set, matter and energy fluxes as well as nutrient balances are calculated. In particular, REPRO carries out an ecological (erosion, soil structure, nitrate leaching, crop protection, biodiversity) and economic (breakeven analysis and full costing) analysis. In dependence on this analysis it further evaluates the environmental effects caused by the farm management and suggests alternative farming practices. Even though REPRO already calculates a broad range of farm matter and energy fluxes, the model needs further extension to also cover climate sustainability indicators such as N trace gas emissions. This is achieved by linking REPRO with the Denitrification-Decomposition (DNDC) model. DNDC is a process-oriented simulation model of soil carbon and nitrogen biogeochemistry. It consist of two components: (1) Sub-models for soil climate, crop growth and decomposition predict soil environmental variables such as temperature, soil moisture, pH, Eh, and substrate concentration profiles. (2) Nitrification, denitrification, and fermentation sub-models estimate N- and C- trace gas fluxes based on the aforementioned soil environmental variables. Trace gas fluxes from agricultural soils are highly variable in space and time. Hence, the simulation and prediction of trace gas emissions from agricultural soil is still very challenging and remains uncertain. Due to this, it is necessary to estimate N trace gas emissions for every specific field site of a farm. By linking the DNDC model to the REPRO model, it will be possible to predict N₂O and NO emissions depending on site conditions and management practices for all relevant agricultural cropping systems in Germany. The overall method of the integrated model will be presented. First results of the farmstead specific DNDC applications for Germany are shown. Finally, a Monte Carlo based uncertainty analysis is conducted to provide information on the uncertainty of model parameters and input data of the DNDC model.