Imazaquin movement in a field site that had Karnak silty clay soil was evaluated during a 2-yr study to determine if leaching was a significant dissipation mode for imazaquin. Imazaquin in water samples collected from subsurface tile drainage was measured by immunoassay. Total imazaquin losses due to leaching in 1993 were 0.8% of the total applied and in 1994, practically zero. Imazaquin concentrations as high as 80 μg L−1 were observed in drain water when rainfall occurred shortly after herbicide application. Imazaquin concentrations were lower with each successive drain flow event. Higher concentrations of imazaquin were associated with higher drainage flow, shortly after application. However, 40 d after application, the levels of imazaquin were low (<7 μg L−1) even when high tile flow occurred. The time between application and the first rainfall is an important factor in imazaquin leaching. In the dry growing season of 1994, imazaquin concentration in drain water did not exceed 5 μg L−1.

Little is known about the effectiveness of sensor-based variable rate nitrogen (VRN) fertilizer application at reducing nitrate-N losses. A variable rate in-season nitrogen (VRN) treatment was compared to a conventional pre-plant uniform rate nitrogen treatment in eight Minnesota, USA sub-fields. Water samples collected weekly during 2016 were analyzed for nitrate-N. The Drainmod model was able to accurately represent measured tile discharge and nitrate-N concentration data. Modeled nitrate-N losses in tile discharge were 16% lower in VRN than uniform treatments. These results show that in-season VRN fertilizer N management can significantly reduce nitrate-N loads from tile drained maize fields.