Evaluation of a nitrogen transport and transformation model in a bare soil

Simulation models are useful tools to understand the interaction between th e transformation and the transport of nitrogen in the field. This study was done to calibrate, test and analyse a mechanistic, one-dimensional model t hat describes the transport and transformations of nitrogen in the soil. Th e physical module describes transport of water, heat and solute, and the bi ological module simulates transformations of C and N with a restricted numb er of measurable organic pools. The calibration was based mainly on laborat ory experiments independent of those used to evaluate the model. The evalua tion procedure used field data collected on a bare loamy soil. The profiles of water content, water potential, temperature, chloride and nitrate (N-15 -labelled and unlabelled) concentrations were measured from 0 to 150 cm con tinuously for 1 year. Simulated results were in goad agreement with experim ental data. However, some discrepancies were noticeable for chloride and ni trate concentrations in the deep layers. These differences were probably du e to an underestimation of mass transport in the deep layers. A sensitivity analysis was carried out to determine the response to changes in some para meters in terms of mineralization, leaching and model efficiency. Mineraliz ation is more sensitive to biological factors whereas nitrate leaching is m ore sensitive to initial and boundary conditions and hydraulic parameters. The experiment ran for only 1 year, which was too short a time to test biol ogical factors.