Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 11, 2000
Publication Date: N/A
Interpretive Summary: The corn and soybean rotation is one of the most widely used farming systems in the cornbelt. As currently practiced, this farming system is herbicide dependent, some of which has leached to ground water. The focus of this research was to determine the fate and movement of the herbicide, atrazine, one of the most widely used corn herbicides, in a corn and soybean farming system that applies herbicide only in a band over the row, reducing by two thirds the total amount of product applied. Mechanical cultivation (ridge building) was used to control weeds in interrow areas. During the first 60 days after application, atrazine concentrations in the zone of application had decreased by 90 percent, associated with some movement into the 0.075 and 0.15 m soil layer. Ninety-eight percent of applied atrazine was dissipated by the end of the growing season and by the end of the second year (soybean with no atrazine applied) detections were few and near the detection limits of instrumentation. Significant horizontal movement of atrazine was never observed, nor movement below 0.6 m was never detected. Farmers now have a farming system available that will allow continued use of a corn and soybean rotation while protecting ground water quality at the same time.
Technical Abstract: The fate and movement of herbicides, particularly atrazine is of great interest as farming systems are designed to protect ground water quality in concert with crop production. The effects of time and water (rain + irrigation) inputs on the distribution and dissipation of atrazine banded over the corn row were measured for two years in a ridge tillage, corn and soybean rotation. The soil was a fine sand (mixed, frigid, Argic Udipsammet). 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 in 0.075 m intervals. Within the first 22 DAT (days after treatment), atrazine concentrations decreased by 65 percent in the application zone and had not leached below 0.075 m, in spite of a 50 mm rain post application. A 60 mm rain between 22 and 29 DAT moved atrazine quantitatively into the next depth increment (0.075 to 0.15 m). By 60 DAT and 240 mm of accumulated rain, atrazine concentrations had decreased by 90 percent in the zone of application, but continued to move into the 0.075 to 0.15 m layer. At this time, atrazine movement appeared to be greater on the windward side of the row, a possible result of crop canopy causing an asymmetrical delivery of incoming rainfall onto the soil surface. Ninety-eight percent of applied atrazine was dissipated by the end of the first growing season (143 DAT) and by the end of the second year (729 DAT), detections of residual atrazine were very limited, near the detection limit (5 ug kg**-1), and confined to the zone directly below the treated area. Significant horizontal movement of atrazine was never observed; even when detections occurred, mean concentrations did not exceed 10 ug kg**-1. Atrazine was never detected below 0.6 m.