Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: November 5, 2000
Publication Date: N/A
Technical Abstract: Conservation tillage is frequently used for corn and soybean production to reduce soil losses. The herbicides normally used in this production practice, however, are often detected in surface runoff at high levels. This problem might be reduced by growing transgenic, glufosinate-tolerant corn (Liberty-Linked) and glyphosate-tolerant soybean (Roundup Ready) and replacing pre-emergence, residual herbicides with post-emergence, contact herbicides. Annual herbicide losses in runoff from 2 chisel-plowed, 2 no-till, and 3 reduced-input, disked watersheds were monitored on an individual event basis. In crop year 1998 annual losses of glufosinate (0.007 to 0.25% of applied) were similar to losses of atrazine (0.003 to 0.64% of applied). The maximum concentration of glufosinate in a single runoff event was 97 ppb and maximum atrazine concentration was 394 ppb. Similarly, losses of glyphosate ranged from 0.12 to 1.17% of applied (max conc. 182 ppb) whereas metribuzin losses were 0.14 to 0.64% of applied (ma conc. 44 ppb). In this crop year, when runoff frequently occurred in June shortly after application of the post-emergence herbicides to the standing crops, annual losses of glufosinate and glyphosate were of similar magnitude to those of the pre-emergence products. Nevertheless, the post-emergence herbicides are of lower toxicity than the pre-emergence products and should have less environmental impact.