Mathematical modelling for assessing pesticide leaching in agricultural soils at the field scale

From the seventies onwards, mathematical modelling has been introduced in pesticide science. At the onset, models, were mainly developed to unravel the complex soil system and to understand the particular role of specific processes int the overall fate of xenobiotics in soils. Yet, the potential to analyse with a "push on a button" effort effects of variable soil conditions, different pesticide management practices and variable climate and hydrogeological conditions on likely pesticide losses has definitely been the rational behind the continuous development of more pragmatic modelling codes. Nowadays a range of well documented leaching code are available. Unfortunately, guidelines for using and selecting the appropriate code are still in development. In addition, the current validations status of pesticide leaching models situates far beyond the model development front. This chapter reviews the modelling methodology applied for pesticide leaching modelling, aftera general description of the different modelling terms, a conceptual framework is given for developing and evaluating pesticide leaching models. Basic hypothesis and model parameter identification strategies are reported for thirteen simulation codes which have been tested within the COST 66 modellers intercomparison exercice