The behavior of oxyfluorfen herbicide and chlorpyrifos insecticide applied at different concentrations in a
soil submitted to a severe and continued 120-day drought and their influence on soil enzymatic activities
(dehydrogenase, urease, b-glucosidase and phosphatase activities) and soil biodiversity (analyzed by
phospholipid fatty acids) were studied under controlled laboratory conditions. Two levels of irrigation
were employed: (1) watered soils, where the soils were maintained at 60% of their water holding
capacity, and (2) non-watered soils, without irrigation. In watered soils,the oxyfluorfen herbicide and the
chlorpyrifos insecticide both caused a toxic effect on both soil enzymatic activity and soil diversity. This
decrease was greatest when the highest dose of herbicide was applied to the soil. The application of
pesticides to the non-watered soil caused a greater inhibition of soil enzymatic activities and microbial
population possibly due to the combined effect of both pesticide toxicity and soil drought conditions. For
this reason, the degradation of pesticides in non-watered soil was lower than in the case of watered soils,
which probably made the persistence in soil of both pesticides longer. This suggests that, in drought
conditions, soil pollution by these pesticides increases over time