Comparing and evaluating pesticide leaching models: results for the Tor Mancina data set (Italy)

This paper describes the results of an evaluation of pesticide leaching modelling, using data collected on four lysimeters in Italy. The experimental data were collected during a 3 year period at Tor Mancina (Rome, Italy), on a clay-loam calcareous soil. Monitored variables are the soil water drainage, the bromide leaching and the metolachlor leaching. Two different irrigation schedules were considered in the experimental design. The models inadequately described the monitored breakthrough of water, bromide and pesticide. Poor modelling performance was firstly attributed to an inappropriate model structure, poorly representing the specific conditions of Mediterranean soils. In particular, the models did not allow to represent correctly the preferential flow that was observed during some of the flow events. Secondly, deficiencies were identified in the calibration procedures, and the application of a well defined modelling practice. The lack of such a good modelling practice induced user subjectivity in the estimation of the model parameters, which had an impact on the modelling results.