Estimation of Runoff Ratios of Pesticide Residue from Paddy Fields Using the RICEWQ Model

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Abstract
Runoff ratios, of losses by runoff to applied amounts, of pesticides butachlor, oxadiazone, chlorpyrifos‐me, diazinon, 2,4‐D and carbaryl were estimated using the RICEWQ model in certain paddy fields. To reflect the actual water management by farmers, the water balance of a paddy field in Korea was monitored. A hydrology submodel was calibrated with observed field data. Laboratory incubation tests were conducted and the decaying pesticide concentrations monitored. Parameters for the pesticide submodel were determined by using incubation test results after calibration. The RICEWQ model simulated runoff and concentrations of the pesticide using the calibrated hydrologic and pesticide submodels under a conventional pesticide application scenario. The runoff ratio of each pesticide was estimated based on simulation results. When the application date of the pesticide was varied up to 7 days, the runoff ratios of butachlor, oxadiazone, chlorpyrifos‐me, diazinon, 2,4‐D and carbaryl varied between 13.1 ~ 17.5, 1.2 ~ 1.4, 0.57 ~ 0.66, 12.0 ~ 20.5, 21.9 ~ 28.9 and 12.7 ~ 14.3%, respectively. In general, pesticides with a longer half‐life and a lower soil‐water partitioning coefficient for organic compounds (Koc) resulted in a higher runoff ratio. The simulation results showed that proper application practice and drainage management are to be recommended to reduce the runoff ratio of pesticides. Copyright © 2016 John Wiley & Sons, Ltd.

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