Pesticide Mobility in Surface and Subsurface Irrigation Return Flow in a Container Plant Production System

The objectives of this study were to determine the effects of irrigation method on the movement of 10 commonly used pesticides in container nursery production. Pesticide transport under three irrigation methods at a nursery engineered to collect irrigation return flow (IRF) from the production surface and subsurface was determined. Pesticide applications occurred three times throughout the study, followed by a 16-day monitoring period. The irrigation applied and surface and subsurface IRF volumes generated from single irrigation events were measured and subsamples of the IRF water were analyzed to assess pesticide presence. Overhead irrigation served as the control with two microirrigation treatments, one applying a fixed amount of water each day and the other scheduled using substrate moisture sensors. Microirrigation reduced irrigation volume by >75% and surface IRF by up to 100%. Subsurface IRF was similarly reduced by microirrigation, yielding 23–47% lower volumes. Pesticides with greater solubilities and lower adsorption coefficients were more mobile than the inversely characterized compounds, particularly in subsurface IRF. The least soluble pesticides had a reduced presence in surface and, to a larger extent, subsurface IRF. Reductions or elimination of surface IRF by using microirrigation reduced the transport of all pesticides by >90%. Pesticides that had a higher solubility were found in subsurface IRF regardless of irrigation method. This study demonstrates the importance of both the irrigation delivery method and pesticide physiochemical properties on the environmental fate of pesticides in nursery settings. Microirrigation can reduce and often eliminate surface IRF, limiting the movement of pesticides regardless of physiochemical properties; whereas, the selection of pesticides that are less soluble can be an effective way to limit the subsurface movement of pesticides, regardless of irrigation method.