Impact of hairy vetch cover crop on herbicide transport under field and laboratory conditions

This study was conducted to evaluate the effect of hairy vetch cover crop r esidue on runoff losses of atrazine and metolachlor under both no-till corn field plots and from a laboratory runoff system. A 2-year field study was conducted in which losses of atrazine and metolachlor from vetch and non-ve tch field plots were determined from the first runoff event after applicati on (5 and 25 days after application in 1997 and 1998, respectively). A labo ratory study was conducted using soil chambers, designed to simulate field soil, water, vegetation, and herbicide treatment conditions, subjected to s imulated rain events of 5, 6, 20 and 21 days after application, similar to the rainfall pattern observed in the field study. Atrazine losses ranged fr om 1.2 to 7.2% and 0.01 to 0.08% and metolachlor losses ranged from 0.7 to 3.1% and 0.01 to 0.1% of the amount applied for the 1997 and 1998 runoff ev ents, respectively. In the laboratory study, atrazine runoff losses ranged from 6.7 to 22.7% and 4.2 to 8.5% and metolachlor losses ranged from 3.6 to 9.8% and 1.1 to 4.7% of the amount applied for the 5-6 and 20-21 day event s, 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 c ould occur. Runoff losses of both herbicides were slightly higher from non- vetch than vetch field plots. Losses from the laboratory study were related to runoff volume rather than vegetation type. (C) 2001 Elsevier Science Lt d. All rights reserved.