Imazaquin mobility in tropical soils in relation to soil moisture and rainfall timing

Summary This research studied the influence of soil type, soil moisture and incubation time before rain on the mobility of imazaquin in two highly weathered tropical soils, named clay and sandy clay. The soils were packed in glass columns and treated at three different moisture contents. Then, the applied imazaquin (150 g a.i. ha⁻¹) was incubated for 0, 1 and 30 d before rainfall simulation began. Leaching was significantly higher in the sandy clay soil, when imazaquin was applied to moist samples and rainfall occurred soon after application (in this case, 73.4% of applied imazaquin was leached). Leaching was always low in the clay soil (in all cases, <1.8% of applied imazaquin was leached). In addition, imazaquin leaching potential was overestimated by the low K _d value (1.24 L kg⁻¹) measured for the clay soil using batch equilibration data. For this soil, the vacuum displacement method also failed to predict leaching (in this case, 28.9% of applied imazaquin was leached). Consequently, batch equilibration and vacuum displacement methods cannot be used to predict leaching of anionic organic molecules, such as imazaquin, in fine-textured tropical soils. Moreover, soil type and weather patterns or irrigation timing must be considered before imazaquin application to avoid environmental or carry-over problems and to achieve maximum effectiveness of the herbicide.