The role of application timing and vegetative filters on reducing atrazine runoff

This research would suggest that changing the herbicide application timing could reduce surface water quality impairments. In order of improvement, early preplant application reduced losses of atrazine in surface runoff compared to applying at planting time by 61%. Fall and postplant application reduced atrazine losses compared to application at planting time by 84% and 97%, respectively. Fall and early preplant application was effective because atrazine does not degrade at the low soil temperatures. These applications are made during periods that have the least potential for runoff. The post application is made during the period of the year with the greatest potential for runoff but is applied at 20 percent of the labeled rate. These alternative application times do have increased costs and can show reduced weed control depending on the climate or ensuing weather. If farmers are given extension education and incentives to use these practices, there is an increased chance to assure that meeting the current water quality standards is feasible.; To examine completely the efficiency of the grass filter strip in improving water quality, this sampling scheme examined both the filter inflow and outflow. The inflow portion consists of two components: (1) runoff from the field plot up-slope from the filter, and (2) rainfall that fell directly on the filter. If the two components of the inflow are added and then the outflow volume subtracted from the inflow, this value is a reasonable estimation of the infiltration. Nearly all of the literature on vegetative filters describes infiltration of runoff water as the primary mechanism for reduction of pesticides. Limited results have been presented to support this hypothesis. This study shows that application dates, other than at planting time, have significantly reduced loss of atrazine in runoff.; This study suggests that using a grass filter strip along with alternative atrazine application dates in the fall or early spring result in the most benefit from a grass filter. The grass filter system has the greatest atrazine loss if it is applied at planting time in May. These results suggest that additional practices beyond grass filter strips may be needed to clean up runoff.; Simulation results using the water quality model, GLEAMS, would suggest that changing the timing of herbicide application could reduce surface water quality impairments. Simulation results compared favorably with results from a three-year field study that showed similar trends that are seen in the simulation. In order of improvement, early pre-plant application reduced losses of atrazine in surface runoff compared to applying at planting time by 42 percent. Fall application and post planting application reduced atrazine losses compared to application at planting time by 68 and 85 percent, respectively.