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Title: Spatial Distribution of Enhanced Atrazine Degradation across Northeastern Colorado Cropping Systems

Author
item Shaner, Dale
item STROMBERGER, MARY - Colorado State University
item KHOSLA, RAJ - Colorado State University
item HANSEN, NEIL - Colorado State University
item HELM, ALAN - Colorado State University
item BOSELEY, BRUCE - Colorad0 State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2010
Publication Date: 1/1/2011
Citation: Shaner, D.L., Stromberger, M., Khosla, R., Hansen, N., Helm, A., Boseley, B. 2011. Spatial Distribution of Enhanced Atrazine Degradation across Northeastern Colorado Cropping Systems. Journal of Environmental Quality. JEQ 40:46-56.

Interpretive Summary: Enhanced atrazine degradation has been reported throughout the world. This phenomenon reduces the length of residual activity of atrazine and requires more careful management by farmers to ensure good weed control. We conducted a survey of 45 fields in northeastern Colorado to determine the extent of enhanced atrazine degradation and to determine if we could develop a model to predict where enhanced degradation might occur. Approximately 44% of the fields tested showed enhanced atrazine degradation. Modeling showed that the most important factors that were related to enhanced atrazine degradation were recent atrazine use history, soil pH and organic matter content. Fields that had a pH greater than 6.1 and had received atrazine the previous year were the ones that showed enhanced atrazine degradation. These results show that enhanced atrazine degradation is relatively widespread in northeastern Colorado and should be considered when a farmer applies the herbicide, particularly if atrazine had been used in the previous year.

Technical Abstract: Reports of enhanced atrazine degradation and reduced residual weed control have increased in recent years, sparking interest in identifying factors contributing to enhanced atrazine degradation. The objectives of this study were to 1) assess the spatial distribution of enhanced atrazine degradation in 45 commercial farm fields in northeastern Colorado (Kit Carson, Larimer, Logan, Morgon, Phillips, and Yuma counties) where selected cultural management practices and soil bio-chemo-physical properties were quantified; 2) utilize Classification and Regression Tree analysis (CART) to identify cultural management practices and (or) soil bio-chemo-physical attributes that are associated with enhanced atrazine degradation; and 3) translate our CART analysis into a model that predicts relative atrazine degradation rate (rapid, intermediate, or slow) as a function of known management practices and (or) soil properties. Enhanced atrazine degradation was widespread within a 300-km radius across northeastern Colorado, with approximately 44% of the fields demonstrating rapid atrazine degradation activity (laboratory-based DT50 < 3 d). The most rapid degradation rates occurred in fields that received the most frequent atrazine applications. There was agreement between atrazine DT50 and the presence of atzC gene for most but not all soils. CART analysis resulted in a prediction model that correctly classified soils with rapid atrazine DT50 80% of the time, and soils with slow degradation (DT50 > 8 d) 62.5% of the time. Significant factors were recent atrazine use history, soil pH, and organic matter content. The presence/absence of atzC gene was not a significant predictor variable for atrazine DT50. In conclusion, enhanced atrazine degradation is widespread in northeastern Colorado but if producers know their atrazine use history, soil pH and OM content, they should be able to identify fields exhibiting enhanced atrazine degradation using our CART model.