Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: November 5, 2000
Publication Date: N/A
Technical Abstract: The pre-emergence herbicides normally used for corn and soybean production (atrazine, alachlor, metribuzin, linuron) are sometimes detected in runoff and groundwater at high levels. This problem may be reduced by growing transgenic, glufosinate-tolerant corn (Liberty-Linked) and glyphosate-tolerant soybean (Roundup Ready). Therefore, atrazine, alachlor, ,linuron, and glufosinate were surface applied to 3 large monolith lysimeters, and alachlor, metribuzin, and glyphosate were surface applied to 4 other large (2.4 m deep) monolith lysimeters. Herbicide losses in percolate were monitored throughout the growing season after a worst-case scenario: 10 cm of simulated rainfall in 2 hr shortly after herbicide application. Eight grab samples were collected from each lysimeter within 24 hours of rainfall initiation and composite samples were collected throughout the growing season. The highest concentrations of atrazine (79-95 ppb), alachlor (4-13 ppb), linuron (4-14 ppb), and metribuzin (8-15 ppb) were generally detected within two hours of rainfall initiation on all eight lysimeters. Only a few glyphosate and glufosinate samples were above detection limits (5 ppb). The post-emergence herbicides are of lower toxicity compared to the pre-emergence herbicides and we generally observed less transport to shallow groundwater, therefore, they should have less adverse environmental impact.