Quantitative Estimate of the Heterogeneity of Solute Fluxes Using the Dispersivity Length for Mathematical Models of Pesticide Migration in Soils

Mathematical models of solute movement in soils are used as management means for assessing the migration of agrochemicals and calculating environmental risks. In these models, the soil block includes the soil values of dispersivity length or solute diffusivity as one of the main parameters. Under laboratory conditions, this parameter was determined experimentally in soil columns by recording the dynamics of the effluent concentration and solving inverse problems. A direct experimental method of field determination based on the movement of marker solution was tested. For the prediction, risk calculation, and management of pesticide application using physically based mathematical models, the following stepwise procedure is recommended: (1) model parameterization based on experimental soil properties; (2) use of the field dispersivity length, which was 3–11 cm for the 0- to 40-cm layer, exceeded 12 cm for deeper fissured BEL and BT (40- to 60-cm) horizons with prismatic structure, and had a median value of 21 cm in layers below 60 cm in experiments on an agrosoddy-podzolic soil (Eutric Albic Glossic Retisol (Abruptic, Loamic, Aric) (WRB, 2014) from Moscow oblast.