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Water Resources of North Dakota |
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Field experiments were conducted in Princeton, Minnesota, and Oakes, North Dakota, to compare atrazine movement through different Upper Midwest sand plains. At each site, 3.3 kg/hectare of atrazine and 84 kg/hectare of bromide were applied to 10 m x 10 m bare-soil plots. One month after application, atrazine and bromide concentrations and other soil properties were measured in 4.2-m-long composite soil cores. The unsaturated zone at Princeton is composed of Zimmerman loamy fine sand that contains an average of (by weight) 73% quartz, 21% feldspar, 2% carbonate, 2% clay, and 2% organic carbon. The average grain-size distribution is 95% sand, 3% silt, and 2% clay. A total of 24.46 cm of rain and irrigation water fell on the plot during the experiment, and the average evaporation rate was 0.14 cm/day. The unsaturated zone at Oakes is composed of Embden fine sandy loam that contains an average of 42% quartz, 39% feldspar, 11% carbonate, 2% clay, and 6% organic carbon. The average grain-size distribution is 76% sand, 22% silt, and 2% clay. A total of 15.84 cm of water fell on the plot during the experiment, and the average evaporation rate was 0.35 cm/day. At Princeton, peak atrazine concentrations were 41 mg/kg at 30-cm depth and peak bromide concentrations were 2.6 mg/kg at 200-cm depth. At Oakes, peak atrazine concentrations were 191 mg/kg at 2.5-cm depth and peak bromide concentrations were 4.4 mg/kg at 15-cm depth. These data show that peak bromide concentrations were about five to six times deeper than peak atrazine concentrations at each site. Differences in the depths of atrazine and bromide penetration at Oakes compared to Princeton are related to differences in soil properties and climatic conditions.
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