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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Hairy Vetch Cover Crop on Herbicide Transport under Field and Laboratory Conditions

Authors
item Isensee, Allan
item SADEGHI, ALI

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 22, 2000
Publication Date: N/A

Interpretive Summary: Hairy vetch is a legume cover crop that is increasingly being used in corn production because it supplies nitrogen and provides early season weed control. The vetch is killed prior to corn planting leaving a dense mat of vegetation that intercepts large amounts of any applied pesticides. Several studies were conducted to determine the effect of this vetch residue on the erunoff losses of two corn production herbicides. A 2-yr study was conducted in which losses of atrazine and metolachlor from vetch and no vetch field plots were determined from the first runoff event after application (5 and 25 days in 1997 and 1998, respectively). A laboratory study was conducted using soil chambers designed to simulate field soil, water, vegetation, and herbicide treatment conditions which were then subjected to simulated rain events 5 and 6 and 20 and 21 days after application. Runoff losses of both herbicides was slightly higher from no vetch than vetch field plots. Losses from the laboratory study were related to runoff volume rather than vegetation type. Runoff losses of both atrazine and metolachlor from the 5-6 day laboratory study were higher but not statistically different from the 1997 field results. However, runoff losses of both herbicides was much higher, 15 to 50 times, than from the 1998 field study. The lower losses from the field study were due to smaller rainfall amounts and a series of small rains prior to the runoff event that likely washed herbicides off crop residue and into soil where adsorption could occur. The laboratory system simulates field conditions well, especially if rain amounts are closely duplicated.

Technical Abstract: This study was conducted to determine the effect of hairy vetch cover crop residue on runoff losses of atrazine and metolachlor under both vetch and non-vetch corn field plots and from a laboratory runoff system. A 2-yr study was conducted in which losses of atrazine and metolachlor from vetch and no vetch field plots were determined from the first runoff event after application (5 and 25 days after application in 1997 and 1998, respectively). A laboratory study was conducted using soil chambers designed to simulate field soil, water, vegetation, and herbicide treatment conditions which were then subjected to simulated rain events 5 and 6 and 20 and 21 days after application. Atrazine losses ranged from 1.2 to 7.2% and 0.01 to 0.08% and metolachlor losses ranged form 0.7 to 3.1% and 0.01 to 0.1% of the amount applied for the 1997 and 1998 runoff events, respectively. In the laboratory study, atrazine runoff losses ranged 6.7 to 22.7% and 4.2 to 8.5% and metolachlor losses ranged from 3.6 to 9.8% an 1.1 to 4.7% of the amount applied for the 5-6 and 20-21 day events, respectively. The lower losses from the field study were due to smaller rainfall amounts and a series of small rains prior to the runoff event that likely washed herbicides off crop residue and into soil where adsorption could occur. Runoff losses of both herbicides was slightly higher from no vetch than vetch field plots. Losses from the laboratory study were related to runoff volume rather than vegetation type. The laboratory system simulates field conditions well, especially if rain amounts are closely duplicated.

Last Modified: 8/27/2014
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