USE OF SUNFLOWER AND SOYBEAN AS BIOINDICATORS TO DETECT ATRAZINE RESIDUES IN SOILS

Atrazine is selective for maize, sugarcane and sorghum and may interfere with successor crops such as sunflower and soybean. Despite this problem, there are few studies about the residual effect of this herbicide in these crops. Thus, the objective of the research was to evaluate the residual effect of atrazine through bioavailability of the herbicide in sandy and clayey soils, using soybean and sunflower as bioindicators. The design was completely randomized with four replications and a 2 x 7 + 1 factorial scheme, that is, two doses (2,000 and 2,500 ha(-1)), seven application times (0, 15, 30, 45, 60, 75 and 90 days between application (DBA) of herbicide and bioindicator sowing) and one control without application. Dry mass and chlorophyll content of the bioindicators were evaluated at 20 days after sowing. The accumulation of dry mass of the bioindicators in the two types of soil was reduced at 90 DBA. The chlorophyll content at 0 DBA was zero for soybean and sunflower, due to the reduction of dry mass by approximately 100%. It was concluded that the residual effect of atrazine at a dose of 2,500 g ha(-1) was higher in clayey soils due to the low bioavailability of the product in the soil solution. Therefore, it is recommended to sow sunflower and soybean in both soils after 90 DBA, because atrazine interferes with the chlorophyll content and percentage of dry mass reduction.