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Atrazine Dissipation in s-Triazine–Adapted and Nonadapted Soil from Colorado and Mississippi: Implications of Enhanced Degradation on Atrazine Fate and Transport Parameters

^a USDA-ARS, Southern Weed Science Research Unit, P.O. Box 350, Stoneville, MS 38776
^b USDA-ARS, Water Management Research Unit, 2150 Centre Ave., Fort Collins, CO 80526
^c Dep. of Agro-Environmental Science and Technology, Univ. of Bologna, V. le Fanin 44, Bologna, Italy 40127
^d USDA-ARS, Corn Plant Host Resistance Unit, Dorman 117 Box 9555, Mississippi State, MS 39762

View larger version (12K): [in this window] [in a new window]   Fig. 1. Proposed metabolic pathway(s) responsible for the rapid dissipation of atrazine in Colorado (CO) and Mississippi (MS) atrazine-adapted soil. Abbreviations denote genes coding for the following enzymes: atzA, atrazine chlorohydrolase; trzN, s-triazine hydrolase; atzB, hydroxyatrazine ethylaminohydrolase; atzC, N-isopropylammelide isopropylaminohydrolase; TrzD, cyanuric acid amidohydrolase; atzD, cyanuric acid hydrolase; atzE, biuret hydrolase; atzF, allophanate hydrolase; and trzF, allophanate hydrolase (Boundy-Mills et al., 1997; Cheng et al., 2005; de Souza et al., 1998; Fruchey et al., 2003; Martinez et al., 2001; Mulbry et al., 2002; Sadowsky et al., 1998; Seffernick et al., 2002; Shapir et al., 2002; Shapir et al., 2005; Shapir et al., 2006; Smith et al., 2005; Topp, 2001; Wackett et al., 2002).

View larger version (30K): [in this window] [in a new window]   Fig. 2. Atrazine dissipation in Colorado (CO) and Mississippi (MS) s-triazine–adapted and non-s-triazine–adapted soil as a function of incubation temperature (10 or 40°C) and soil moisture content (40 and 70% field capacity). Symbols represent the mean of three replications for each of the following treatments: 10°C at 40% field capacity (closed circles), 10°C at 70% field capacity (open circles), 20°C at 40% field capacity (closed inverted triangles), and 20°C at 70% field capacity (triangles). Lines represent the best fit of the first-order kinetics model: Ct = Coe–kt. Error bars indicate 1 SD and do not appear when smaller than the symbol for the mean.

View larger version (29K): [in this window] [in a new window]   Fig. 3. Deisopropylatrazine (DIA) concentrations in Colorado (CO) and Mississippi (MS) s-triazine–adapted and non-s-triazine–adapted soil as a function of incubation temperature (10 or 40°C) and soil moisture content (40 and 70% field capacity). Symbols represent the mean of three replications for each of the following treatments: 10°C at 40% field capacity (closed circles), 10°C at 70% field capacity (open circles), 20°C at 40% field capacity (closed inverted triangles), and 20°C at 70% field capacity (triangles). Error bars indicate 1 SD and do not appear when smaller than the symbol for the mean. LSD0.05 (Temp x Moisture x Soil x Time) = 0.006.

View larger version (25K): [in this window] [in a new window]   Fig. 4. Desethylatrazine (DEA) concentrations in Colorado (CO) and Mississippi (MS) s-triazine–adapted and non-s-triazine–adapted soil as a function of incubation temperature (10 or 40°C) and soil moisture content (40 and 70% field capacity). Symbols represent the mean of three replications for each of the following treatments: 10°C at 40% field capacity (closed circles), 10°C at 70% field capacity (open circles), 20°C at 40% field capacity (closed inverted triangles), and 20°C at 70% field capacity (triangles). Error bars indicate 1 SD and do not appear when smaller than the symbol for the mean. LSD0.05 (Temp x Moisture x Soil x Time) = 0.003.

View larger version (25K): [in this window] [in a new window]   Fig. 5. Hydroxyatrazine (HA) concentrations in Colorado (CO) and Mississippi (MS) s-triazine–adapted and non-s-triazine–adapted soil as a function of incubation temperature (10 or 40°C) and soil moisture content (40 and 70% field capacity). Symbols for all graphs represent the following treatments: 10°C at 40% field capacity (closed circles), 10°C at 70% field capacity (open circles), 20°C at 40% field capacity (closed inverted triangles), and 20°C at 70% field capacity (open triangles). Error bars indicate 1 SD and do not appear when smaller than the symbol for the mean. LSD0.05 (Temp x Moisture x Soil x Time) = 0.021.

View larger version (26K): [in this window] [in a new window]   Fig. 6. Cumulative 14CO2 evolved reported as percent of total 14C-ring–labled atrazine added in Colorado (CO) and Mississippi (MS) s-triazine–adapted and non-s-triazine–adapted soil as a function of incubation temperature (10 or 40°C) and soil moisture content (40 and 70% field capacity). Symbols represent the mean of three replications for each of the following treatments: 10°C at 40% field capacity (closed circles), 10°C at 70% field capacity (open circles), 20°C at 40% field capacity (closed iverted triangles), and 20°C at 70% field capacity (triangles). Error bars indicate 1 SD and do not appear when smaller than the symbol for the mean. LSD0.05 (Temp x Moisture x Soil x Time) = 2.714.