Reducing pesticide transport in surface and subsurface irrigation return flow in specialty crop production

This study investigated the transport of 9 pesticides in surface and subsurface irrigation return flow from a container-plant production system over 3 16-day monitoring periods. Pesticides were applied 3 times during the year and the pesticides were selected to provide a range of physiochemical properties. Pesticides are most commonly transported in water and irrigation return flow is a driving factor, therefore, irrigation methods were investigated to determine effects on irrigation return flow volume and transport of pesticides. A control overhead irrigation and two treatments irrigating based on substrate volumetric moisture content (θ) were used. Pesticide transport in irrigation return flow was related to days after application, physiochemical properties and irrigation method. Additionally, pesticide transport was disproportionately reduced, in respect to physiochemical properties, in subsurface irrigation return flow in response to irrigation methods. θ-based irrigation treatments reduced irrigation volume applied by 49% and 77% compared to the control leading to a reduction in the volume of surface irrigation return flow by 71% and 92%. The θ-based treatments reduced the total surface and subsurface volume of irrigation return flow by 52% and 78% versus the control. In most cases, pesticides movement in surface irrigation return flow exhibited a linear or quadratic decrease for the control, while pesticide movement via subsurface irrigation return flow was related more to physiochemical properties limiting mobility rather than irrigation return flow volume or irrigation practice. This study demonstrates pesticide movement in irrigation return flow can be substantially reduced by selecting pesticides with low solubility/high adsorption coefficients whenever possible, and reducing the volume/application of irrigation to non-target areas. Pesticide movement in surface and subsurface irrigation return flow (IRF) reflect the physiochemical properties of each compound. Surface IRF is capable of transporting both soluble and insoluble pesticides; whereas, insoluble pesticides (which typically possess greater sorption coefficients) are unlikely to infiltrate through subsurface profiles. Irrigating container plants based on substrate moisture content and/or using micro-irrigation systems like spray stakes reduces water use, IRF, and pesticide movement compared to common overhead practices. [Display omitted] •Substrate moisture based irrigation reduces water