EFFECT OF WETTING DRYING CYCLES ON DISSIPATION PATTERNS OF BIOAVAILABLE IMAZAQUIN/

Greenhouse experiments determined differences in imazaquin bioavailabi lity over time under various soil moisture regimes, All soils were ini tially fortified with 63 ppb (w/w) Of commercially formulated imazaqui n, Treatments consisted of maintaining at field capacity for 15 wk (FC ), maintaining air-dry for 15 wk (AD), soil that was maintained air-dr y for 2 wk and then wet to field capacity at 2 wk intervals (2WAD), an d soil that was wet to field capacity at the initiation of the experim ent and at 2 wk intervals (2WFC), Little dissipation of imazaquin occu rred in the AD soil over the 100 d of this study, Rapid dissipation ov er the first 35 d occurred for the other three treatments, Imazaquin h alf-life ranged from 17 to 18 d for the FC, 2WAD, and 2WFC soils. Imaz aquin concentration increased or only slightly decreased in samples ta ken after the second watering in both the 2WAD and the 2WFC soils, Due to differences in adsorption/desorption of imazaquin with changing so il moisture levels, bioassays may not determine the dissipation of the actual concentration of imazaquin contained in soil.