Asymmetrical distribution and dissipation of band-applied atrazine in soil

Movement of herbicides, particularly atrazine [2-chloro-N-ethyl-N'-(1-methy lethyl)-1,3,5-triazine-2,4-diamine], is of great interest, as farming syste ms are designed to protect water quality. The effects of time and precipita tion on the distribution of atrazine banded over corn (Zea mays L,) rows we re measured for 2 41 in a ridge-tillage corn-soybean [Glycine max (L.) Merr .] rotation. The soil was a Zimmerman fine sand (mixed, frigid Lamellic Udi psamment), During the growing season, soil atrazine was determined at 0.1-m horizontal intervals perpendicular to the row to a depth of 0.3 m. Within the first 22 days after treatment (DAT), atrazine concentrations decreased 65% in the application zone and had not leached below 0.075 m, A 60-mm rain between 22 and 29 DAT first moved atrazine into the 0.075- to 0.15-m depth increment. By 60 DAT and 240 mm of accumulated rain, atrazine concentratio ns had decreased by an estimated 90% in the zone of application. Atrazine m ovement appeared to be greater on the windward side of the row. An estimate d 98% of applied atrazine was dissipated by the end of the first growing se ason and by the end of the second year, detections of residual atrazine wer e very limited and confined to the zone directly below the treated area, Si gnificant horizontal movement of atrazine was never observed. Atrazine was not detected in soil samples below 0.6 m to a depth of 2.4 m.