DISCRETE MODELING OF WATER AND PESTICIDE MOVEMENT IN SOIL

Simulations of water and pesticide movement are presented for the unsa turated zone. Water movement is studied with a two-dimensional Monte C arlo technique, where particles hop between the sites of a square latt ice according to probabilistic rules. We developed this lattice gas me thod for two-dimensional simulations of water flow in inhomogeneous me dia. Generalization to three dimensions is straightforward. The dynami cs of the pesticide is simulated by particle tracking. After presentin g the underlying discrete algorithms we emphasize calibration of the s ystem. A soil is divided into homogeneous horizons, and our model is c ompared with the conventional one-dimensional model PESTLA. We observe good agreement for both water content profile and pesticide distribut ion. The random elements in our algorithms cause moderate fluctuations in the results. As an example of two-dimensional simulation, spatiote mporal pesticide patterns under a ridge are compared with the distribu tion under a flat soil surface.