GUNNAR KAHL, PAMORNWAN NUTNIYOM, THILO STRECK
University of Hohenheim, The Uplands Program, Institute of Soil Science and Land Evaluation, Germany
During the last decades a change in land use has been accompanied by an increased input of agrochemicals in mountainous regions of Northern Thailand. Particularly in sloped areas agrochemicals may be lost to the streams by lateral flow and transported to the lowlands, thereby contaminating drink and use water. Our research aims at measuring and modelling water flow and agrochemical transport at hill slope scale in Northern Thailand. Special emphasis will be put on lateral surface and subsurface water flow and solute transport as well as on the fate of pesticides in soil. During two rainy seasons plot (2m x 3m) transport experiments will be carried out. Two pesticides will be applied and seepage water will be collected at a profile with wick samplers and surface runoff collectors. Also water content and suction will be measured. Soil samples will be collected at the end of the experiment and residual solute concentrations will be analysed. Twenty-five soil samples taken at the hill slope will be analysed for clay content, pH, and Corg. Further, sorption-desorption isotherms and degradation under different moisture and temperature conditions will be measured with a subset of 10 samples. Pedotransfer functions will be estimated, with which pesticide sorption can be assessed from basic soil variables. Pesticide loss at hill slope scale will be calculated with a simulation model. To receive independent data for testing the model two flumes have been installed upstream and downstream in the downhill river, which allow for detection of pesticide loss from the whole hill slope. Data from the second year will be used to validate the model. Surface runoff is expected to have the largest impact on pesticide loss. After the experiments the prediction of pesticide outwash via surface and subsurface water flow depending on slope, pesticide- and soil properties will be possible. Detailed knowledge of pesticide transport, sorption and degradation processes will make it possible to adjust application in order to minimise leaching and improve water quality. The pedotransfer functions will be helpful in the future to evaluate the potential of pesticides to contaminate ground- and surface water.
Keywords: Degradation, hill slope, lateral flow, pesticides, soil, sorption-desorption, water quality