Rice is usually grown under flooded condition and as the plant demand for water is high, the cultivation areas are often located close to rivers for ease of irrigation. Consequently, the potential for contamination of water bodies is high and pesticides used during the rice season are frequently detected in the surface and groundwater systems adjacent to rice fields. The fate and transport of pesticide applied to rice paddy fields has been investigated using models such as RICEWQ, PCPF-1, PADDY, and SWAGW. However, these models can only be applied to watersheds where rice is exclusively cultivated. To address this problem, the PCPF-1@SWAT model was developed by coupling the field scale rice pesticide fate and transport model, PCPF-1, and the watershed multi-purpose agricultural model, SWAT. The PCPF-1@SWAT model was previously validated with the herbicide mefenacet in Japan. In this study the model was used to develop a framework of rice pesticide modeling in the Colusa Drain basin, California using monitoring data of molinate and thiobencarb. The simulation of hydrology in the Colusa Drain basin watershed presented a great challenge due to anthropogenic water transfer within and between sub-watersheds. Consequently the water flows predicted by the model were poor even when using monthly predictions. However, the simulated molinate and thiobencarb concentrations in paddy fields were similar to the concentrations reported in literature. The pesticide concentrations in the main drain were also accurately simulated despite sensitivity to factors affecting the paddy fields water balance . Therefore the water management and paddy fields conditions are critical inputs for realistic predictions of rice pesticide fate and transport at watershed scale.

Framework development of rice pesticide modeling in the Colusa Drain basin, California

248th National Meeting (2014)

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