A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 2001

A monitoring and modeling study on pesticide fate and transport was conducted on clay loam soil planted to corn in northeastern province of Thailand. The objective was to measure and analyze pesticide dissipation in the surface/subsurface soil environment and to adopt and validate a pesticide transport model called PESTFADE (PESTicide Fate and Dynamic in Environment). Herbicide atrazine was applied at a rate of 2.98 kg/ha a.i. four days after the planting and two more applications at the same rate were made a few weeks before harvest. Field experiment was conducted for one cropping season. Soil and water samples were collected and analyzed for pesticide residues in runoff, sediment, soil profile and groundwater. The herbicide was found to dissipate quickly from the soil. PESTFADE was modified to account for multiple application of pesticide and was tested with the field data with two extra applications. The model showed close agreement with the measured value of the herbicide residue in soil surface, with a relative error of +0.0419 and a standard error of 1.9039. The sub-surface component was comparable with small values of RE and SE. Simulations were made with higher herbicide dose and high rainfall shortly after application. In both cases, herbicide lost in runoff were high, indicating high potential of contamination to the surface water systems. Although PESTFADE performed reasonably well, further study is however recommended for other soil, climate and crop conditions in Thailand to further establish the applicability and flexibility of the model.