Pesticide transport to subsurface tile drains in humid regions of North America

This report reviews and summarizes findings from more than 30 North America n studies of pesticide transport into subsurface agricultural drains. Backg round information about subsurface drainage use and its importance for crop production and environmental protection is also presented. The presence of a subsurface drainage system generally increases the volume of infiltratio n and consequently decreases the volume of surface runoff water and sedimen t compared with similar soils where subsurface drainage systems are not ins talled. Therefore, in general, the presence of subsurface drainage decrease s surface runoff losses of sorbed compounds such as pesticides, both becaus e of lower runoff volumes and often also because of lower concentrations in the runoff resulting from the delayed initiation of runoff. Pesticide conc entrations and mass losses are usually much lower in subsurface drainage th an in surface runoff, often by an order of magnitude. In the medium- and fi ne-textured soils where subsurface drainage is common, the dominant mechani sm for pesticide transport to the drain tiles is most likely preferential f low during rainfall/drainage events occurring soon after pesticide applicat ion. Concentrations and mass losses in subsurface drains are highly variabl e from year to year, depending on weather patterns.