Ecological Modelling, 16 (1982) 67-75 Elsevier Scientific Publishing Company, Amsterdam--Printed in The Netherlands 67 DEVELOPMENT AND VERIFICATION OF SIMULATION MODELS FOR DESCRIBING PESTICIDE DYNAMICS IN SOILS * P.S.C. RAO and R.E. JESSUP Soil Science Department, IFAS, University of Florida, Gainesville, FL 32611 (U.S.A.) (Accepted for publication 7 January 1982) ABSTRACT Rao, P.S.C. and Jessup, R.E., 1982. Development and verification of simulation models for describing pesticide dynamics in soils. Ecol. Modelling, 16: 67-75. Mathematical models currently available for describing pesticide dynamics in soils were reviewed. Processes included in this review were: retention (adsorption-desorption), transfor- mations (chemical and/or biological degradation), and convective-dispersive transport with soil-water. A large number of simulation models, with varying degrees of complexity and scope, are presently available. However, verification and extensive use of these models has generally been difficult owing to inadequate methods of measuring and/or estimating the necessary model input parameters. The ability to formulate and numerically solve complex simulation models apparently exceeds our ability to verify these models using the limited experimental data base presently available. Given the uncertainties of model parameters and the field-scale soil heterogeneity, deviations of a factor of two or more between measured and simulated results may be common. Therefore, for general use, simple models with a minimum number of inputs may provide a sufficiently accurate description of pesticide dynamics in agricultural ecosystems. Only limited amounts of field data are presently available to verify even the simple process-orientated models. INTRODUCTION Various processes and factors govern the fate of soil-applied pesticides. An understanding of these processes and factors can lead to better manage- ment practices and reduce the potential for contamination of surface and * Contribution from Soil Science Department, University of Florida, Gainesville, FL 32611. This research was supported in part by funds from U.S. Environmental Protection Agency Grants R-805529 and R-806744, as well as funds from the Center for Environmental Programs, Institute of Food and Agricultural Sciences, University of Florida. Approved for publication as Florida Agricultural Experiment Station Journal Series No. 3531. 0304-3800/82/0000-0000/$02.75 © 1982 Elsevier Scientific Publishing Company