Expert-N A tool for simulating nitrogen and carbon dynamics in the soil-plant-atmosphere system

Expert-N is a program package for the simulation of water, nitrogen and carbon dynamics in the soil-plant-atmosphere system. It is made up of a number of modules that describe different approaches to soil water flow, soil heat transfer, soil carbon and nitrogen turnover, crop processes and soil management. Each module is composed of different sub-modules which themselves contain different algorithms that can be selected to model each sub-process. The algorithms currently provided by Expert-N were taken from published models such as LEACHM, CERES, HYDRUS, SUCROS, NCSOIL, and DAISY or were developed by the Expert-N team. In their complexity they range from functional approaches, more frequently used for management models, to more mechanistic approaches, prevalent in research models. Simulations are done one-dimensional vertical and, depending on the spatial variation of main parameters, are considered representative for the plot or the field scale. The modular structure allows an exchange of sub-modules, which enables the user to analyse the impact of different modelling approaches on the simulation result component by component. Moreover, this flexibility allows the user to build a complete model that suits the availability of required input data and the specific purpose of the study. Expert-N comprises a user-friendly data input system to enter soil, weather, management and crop data. The input data needed for the simulation depends on the demands of the algorithms chosen. Or the other way around, input data availability may determine which of the algorithms can be run. Moreover, measured time series of soil water and inorganic nitrogen contents or crop data can be entered into the database and used to determine the goodness-of-fit of the simulation. These data are held in an Access database linked to Expert-N. Numerous screen graphics allow the dynamics of soil water, carbon, nitrogen and plant parameters to be followed while the simulation is still running, and detailed output files are written at the end of each simulation.