Deterministic and stochastic modelling of water, heat and nitrogen dynamics on different scales with WHNSIM

With respect to groundwater quality objectives, it is difficult to understand the nitrogen balance and nitrogen dynamics of agricultural ecosystems without the support of deterministic and stochastic simulation tools. This paper focuses on the deterministic and stochastic modelling of water, heat and nitrogen dynamics in the soil compartments of agricultural ecosystems. The deterministic nitrogen simulation model for agricultural soils presented in this paper, WHNSIM, was originally designed for site conditions typical of southern Germany but can easily be applied to other regions due to its physically based design. Model results are compared with data originating from different experimental sites in Germany. Special consideration is given to the effects of spatial variability. Two different techniques of Monte Carlo simulation are used to study the impact of parameter variability on target variables of nitrogen dynamics on the field scale. Moreover, a procedure is presented that allows modelling nitrogen dynamics on the scale of small catchment areas, combining the geographical information system Arc Info with agricultural management data and model calculations.