Variation in atrazine mineralization rates in relation to agricultural management practice

Atrazine (6-chloro-N-etllyl-N ''-(1-methylethyl)-1,3,5-triazine-2,4-diamine) mineralization rates were measured in surface soils with different agricultural management practices at the Ohio Management Systems Evaluation Area (Ohio MSEA) site in Piketon, OH, Two management practices were studied at this site: (i) a continuous-corn (Zea maps L.) plot (CC) receiving annual application of atrazine, and (ii) a crop-rotation plot (CR) with corn-soybean [Glycine max (L.) Merr.]-wheat (Triticum aestivum L.) and hairy vetch [Vicia villosa (L.) Roth] with reduced use of atrazine during corn years. Soil collected from a riparian zone (RZ) near the site served as an herbicide-free reference soil, The agricultural site (both CC and CR) had received atrazine applications for about 25 yr before this study, Uniformly ring-labeled C-14-atrazine was added to the soil samples in biometer flasks and (CO2)-C-14 evolution was measured by scintillation counting of alkaline trapping solution. Sterile controls showed no evolution of (CO2)-C-14. Within 30 d of incubation at 22 +/- 2 degrees C, about 80% of the initial radioactivity was evolved as (CO2)-C-14 in CC soils collected during different seasons of the year. Parallel samples fi om CR showed 15 to 30% atrazine mineralization while samples from RZ showed 3 to 7% (CO2)-C-14 evolution within 80 d of incubation, Prior amendment of soil samples from the three sites with 1 mg kg(-1) atrazine accelerated subsequent mineralization measured after 90 d of incubation, indicating enhanced activity of indigenous microorganisms. The CC mineralization data suggest that a single annual atrazine application sustains an active microbial community throughout the year.