Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2000
Publication Date: N/A
Citation: Interpretive Summary: Corn and soybean production, two major agricultural crops, is heavily dependant on herbicides to control weed competition. Atrazine and alachlor are the two most widely used herbicides in this cropping system; but atrazine specifically has been detected in surficial aquifers across the Midwest, particularly those aquifers under shallow sandy soils. The objective of this research was to assess the performance of the highly efficient ridge tillage, corn and soybean farming system across four states (MN, ND, SD, and WI) for protecting ground water quality, yet sustain a viable agriculture. For four years, the fate and movement of atrazine and alachlor in this farming system were studied at four sites in four states. Even though the same farming system was used at the four sites, soils and climate varied widely. Analyses of our extensive data set clearly show that movement of atrazine, and to a lesser extent alachlor, through the soils and into ground water is not consistent from soil to soil, even though three of the soils are classified as sandy and depth to aquifer only varied from 3.3 to 4.9 m. These results graphically demonstrate that site- specific characteristics must be built into any farming system that successfully protect ground water quality - one size does NOT fit all, even for sandy soils. The results of this study will alert regulators, producers, consultants, technology transfer agents (ES and NRCS), researchers, and system modelers that protective and sustainable farming systems must be designed with flexibility to accommodate the site-specific nature of soils and climates as they vary across landscapes and regions.
Technical Abstract: This study was conducted to evaluate atrazine (2-chloro-4-ethylamino-6- isopropyl-1,3,5-triazine) and alachlor (2-chloro-N- (methoxymethyl)acetamide) dissipation and movement to shallow aquifers across the Northern Sand Plains region of the United States. Sites were located at Minnesota on a Zimmerman fine sand, North Dakota on Hecla sandy loam, South Dakota on a Brandt silty clay loam, and Wisconsin on a Sparta sand. Herbicide concentrations were determined in soil samples taken to 90 cm four times during the growing season and water samples taken from the top one m of aquifer at least once every three months. Herbicides were detected to a depth of 30 cm in Sparta sand and 90 cm in all other soils. Some aquifer samples from each site contained atrazine with the highest concentration in the aquifer beneath the Sparta sand (1.28 ug L**-1). Alachlor was detected only one in the aquifer at the SD site. The time to 50 percent atrazine dissipation (DT50) in the top 15 cm of soil averaged about 21 d in Sparta and Zimmerman sands and more than 45 d for Brandt and Hecla soils. Atrazine DT50 was correlated positively with percent clay and organic carbon (OC), and negatively with percent fine sand. Alachlor DT50 ranged from 12 to 32 d for Zimmerman and Brandt soils, respectively, and was correlated negatively with percent clay and OC and positively with percent sand.