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 a gricultural fields are reviewed. Microplot- and Mesoplot-scale experim ents, which use artificial rainfall, and field- and watershed-scale ex periments, which use natural rainfall, provide different but complemen tary information. The smaller-scale experiments are more controlled, r eplicable 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 exp eriments provide realistic runoff concentrations, but they are more di fficult and expensive. Because rainfall is uncontrolled, they are like ly to provide unrepresentative data which are difficult to interpret a nd to extrapolate to other field and weather scenarios. A risk-of-runo ff assessment of a pesticide may require information from a combinatio n of these tests, together with the use of computer simulation modelin g to integrate the results.