ARS | Publication request: Behavior of Atrazine In Limited Irrigation Cropping Systems in Colorado: Prior Use Is Important

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 6, 2009
Publication Date: September 1, 2009
Citation: Shaner, D.L., Wiles, L., Hansen, N. 2009. Behavior of Atrazine In Limited Irrigation Cropping Systems in Colorado: Prior Use Is Important. Journal of Environmental Quality. 38:1861-1869.

Interpretive Summary: Due to the pressure on water for irrigated agriculture in the Great Plains, different cropping systems are being evaluated to optimize use of limited irrigation water supply while sustaining production. Corn is a major component of many of these cropping systems and atrazine is used to provide residual weed control. In this research we examined the dissipation and movement of atrazine under different cropping patterns including continuous corn with full irrigation, continuous corn with deficit irrigation, sunflower-wheat-corn rotation with deficit irrigation and wheat-fallow-wheat-corn rotation with extremely deficit irrigation. We found that atrazine dissipated more rapidly in the continuous corn rotations which had received multiple applications of the herbicide. In plots that had not received any prior applications of atrazine, the herbicide degraded more slowly and moved deeper into the top 30 cm of the soil profile. There was a decrease in the residual activity of atrazine where it dissipated the most rapidly leading to greater emergence of weed seedling. These results show that cropping patterns have an effect on the dissipation, movement and efficacy of atrazine and these factors need to be taken into consideration when planning a weed management program.

Technical Abstract: The Irrigation Water Optimization Project was begun in 2005 at Colorado State University to develop cropping systems to optimize use of limited irrigation water supply while sustaining production. Corn is a major component of many of these cropping systems and atrazine is used to provide residual weed control. We examined the behavior of atrazine under different cropping patterns in 2007 and 2008, including continuous corn under conventional tillage and full irrigation (CCC-FI), continuous corn 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 extremely deficit irrigation (WFWC-DI). Atrazine bound more tightly to soil from the CCC-FI and CCC-DI plots compared to soil from the SWC-DI and WFWC-DI plots. The differences were not due to variation in soil organic matter but to the type of crop residue in the soil, since atrazine bound more tightly to corn residue compared to wheat residue. Atrazine dissipated more rapidly in the top 30 cm of soil in the CCC-FI and CCC-DI plots (Half life (T1/2= 3-12 d), which had received previous applications of the herbicide compared to the SWC-DI and WFWC-DI plots that had no history of atrazine use (T1/2=15-22 d). Laboratory assays confirmed that the differences in the rates of atrazine degradation in the field were at least partly due to differences in the soils’ ability to metabolize the herbicide. Atrazine leached the most in the top 30 cm in the SWC-DI and WFWC-DI plots probably due to the herbicide’s longer half life and less soil binding. These results show that cropping patterns can have a major effect on atrazine behavior.