Pesticides report .34. Pesticide runoff: Methods and interpretation of field studies

The objectives, design and interpretation of experimental measurements of pesticide losses in rainfall induced runoff from the surfaces of agricultural fields are reviewed. Microplot- and Mesoplot-scale experiments, which use artificial rainfall, and field- and watershed-scale experiments, which use natural rainfall, provide different but complementary information. The smaller-scale experiments are more controlled, replicable and easier to undertake but cannot represent those processes which vary over larger scales; thus they may not be representative of many real situations. Larger-scale field and watershed monitoring experiments provide realistic runoff concentrations, but they are more difficult and expensive. Because rainfall is uncontrolled, they are likely to provide unrepresentative data which are difficult to interpret and to extrapolate to other field and weather scenarios. A risk-of-runoff assessment of a pesticide may require information from a combination of these tests, together with the use of computer simulation modeling to integrate the results.