In order to study the imazaquin persistence in a Rhodic Eutrudox Soil cultivated with soybean cv IAC-8, a field experiment was carried out at Ribeirão Preto Experimental Station, in 1988/89. A complete split-plot randomized block design with four replication was used. In the main plots were studied the rates of 0, 75, 150 and 300g ai/ha of imazaquin in a pre-emergence application. The plot rows were sorted and soil samp les we re taken in the it rows sorted subparcelas. The imazaquin residual activity was evaluated by bioassay using cucumber (Cucumis sativus L. cv Sprent) as test-plant. The duration in days of the residual effect of each dose in the soil was estimated using polinomial regression analysis established by the dosage. For 75 and 150g ai/h a of imazaqui n, after 10 days the test - plant did not show any effect in the growth. With 300g ai/ha, the residual effect ceased only after 22 days. Furthermore, in the 60, 48 and 43 days after imazaquin application for the 75, 150 and 300g ai/ha, respectively, again growth reduction of the test-plant was observed. Only after the 89 days for the 75g/ha dose and 104 for the 105 and 300g ai/ha of imazaquin, the residual activity of the herbicide were not observed any more in the soil. There was no effect of the imazaquin dosage in the yield of the soybeans.
Herbicide; bioassay; residual activity