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TECHNICAL REPORTS

Organic Compounds in the Environment

Behavior of Atrazine in Limited Irrigation Cropping Systems in Colorado: Prior Use Is Important

^a USDA-ARS, Water Management Research Unit, 2150 Centre Ave., Bldg. D, Suite 320, Fort Collins, CO 80526
^b Soil and Crop Sciences Dep., C-13 Plant Science Bldg., Colorado State Univ., Fort Collins, CO 80523-1170. Mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture

^* Corresponding author (Dale.Shaner{at}ars.usda.gov).

Received for publication October 28, 2008. Glyphosate-resistant (GR) corn may be a major component of new cropping systems to optimize the use of limited irrigation water supply while sustaining production. Because atrazine is an important tool for residual weed control in GR corn, we examined atrazine binding to soil, dissipation, movement, and early season weed control in limited and full irrigation cropping systems. These systems included continuous corn under conventional tillage and full irrigation (CCC-FI) and under no-tillage and deficit irrigation (CCC-DI), a sunflower-wheat-corn rotation under no-tillage and deficit irrigation (SWC-DI), and a wheat-fallow-wheat-corn rotation under no tillage and natural precipitation (WFWC-NP). Crop rotation and herbicide use history influenced atrazine behavior more than amount or type of irrigation. Atrazine dissipated more rapidly in the top 30 cm of soil in the CCC-FI and CCC-DI plots (half-life [T_1/2] = 3–12 d), which had received previous applications of the herbicide, compared with the SWC-DI and WFWC-NP plots, which had no history of atrazine use (T_1/2 = 15–22 d). Laboratory assays indicated that the different rates of degradation were at least partly due to differences in microbial degradation in the soil. Atrazine moved the most in the top 30 cm in the SWC-DI and WFWC-NP plots. This greater movement is probably due to the slower rate of atrazine degradation. Studies of the behavior of pre-emergence herbicides in new limited irrigation cropping systems must consider all characteristics of the systems, not just amount and timing of irrigation.

Abbreviations: CCC-DI, corn-corn-corn, deficit irrigation • CCCC-DI, corn-corn-corn-corn, deficit irrigation • CCC-FI, corn-corn-corn, full irrigation • CCCC-FI, corn-corn-corn-corn, full irrigation • CWSC-DI, corn-wheat-sunflower-corn, deficit irrigation • DAT, days after treatment • GC/MS-gas chromatography/mass spectrometry • GR, glyphosate-resistant • HPLC, high-pressure liquid chromatography • IWOP, irrigation water optimization project • SOM, soil organic matter • SWC-DI, sunflower-wheat-corn, deficit irrigation • T_1/2, half-life • WFWC-NP, wheat-fallow-wheat-corn, natural precipitation