Variation in Atrazine Mineralization Rates in Relation to Agricultural Management Practice
Ostrofsky, Ellen B. | Traina, Samuel J. | Tuovinen, O. H.
Atrazine (6-chioro-N-ethyl-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 mays 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 ¹⁴C-atrazine was added to the soil samples in biometer flasks and ¹⁴CO₂ evolution was measured by scintillation counting of alkaline trapping solution. Sterile controls showed no evolution of ¹⁴CO₂. Within 30 d of incubation at 22 ± 2°C, about 80% of the initial radioactivity was evolved as ¹⁴CO₂ in CC soils collected during different seasons of the year. Parallel samples from CR showed 15 to 30% atrazine mineralization while samples from RZ showed 3 to 7% ¹⁴CO₂ 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.
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