UC Riverside

Many pesticide-leaching studies rely on the use of numerical models that account for various physicochemical and biological processes at a range of temporal and spatial scales. In leaching assessments for the registration of pesticides in the European Union and the United States, one-dimensional models are used that describe the vertical transport of soil water and pesticides to groundwater. One-dimensional models are most representative for spray and broadcast applications of pesticides, but they may not be adequate for spatially nonuniform applications such as microdrip irrigation. We tested whether an advanced numerical model capable of one-, two-, and three-dimensional flow and pesticide transport simulation [HYDRUS (2D/3D)] provides results consistent with one-dimensional numerical models commonly used for pesticide registration (PEARL, PELMO). Model comparison was used to assess conceptual uncertainty in soil physical representation of pesticide transport among numerical models across a range of applications. Simulations of soil water flow and pesticide and heat transport were conducted for four different hypothetical pesticides and nine European regulatory standard pedoclimatic scenarios (FOCUS). The results show that the predicted annual amount of pesticide mass leached below the depth of 1 m, for all substances, locations, and simulation years, was on the same order of magnitude among the three models. Additionally, the simulated 80th percentile of annual pesticide concentrations at the 1-m depth was not statistically different among models. HYDRUS (2D/3D) can, therefore, be used as an alternative model for pesticide assessment studies and provides a conceptual framework consistent with PEARL and PELMO but capable of two- and three-dimensional applications as well.