Atrazine Adsorption in Sandy Soils of Wisconsin
Seybold, C. A. | McSweeney, K. | Lowery, B.
Previous studies have shown the mobility of atrazine [2-chloro-(4-ethylamine)-6-(isopropylamino)-s-triazine] to be greatly different between characteristically similar sandy soils in Wisconsin. This study was conducted to determine if there are differences in atrazine adsorption capacity between sandy soils from Wisconsin, and if differences exist, what soil properties might be contributing to these differences. Atrazine distribution coefficients (Kd) were determined, and amounts of selected soil constituents (i.e., organic matter, clay, Fe oxides) were characterized by horizon in five sandy soils from different geographic regions of Wisconsin. The Kd values were strongly and significantly correlated to the OC content (r² = 0.84). Also, clay contents in the lower subsoil horizons were significantly correlated to the Kd (r² = 0.51). The organic fraction is the most important constituent for adsorption of atrazine in these sandy soils that contain small amounts of organic matter and clay. The Kₒc (Kd × 100/%OC) values varied considerably among soils and within soils with depth, and is attributed to differences in the ability of organic matter to adsorb atrazine and in contributions from clay minerals in the lower subsoil horizons. The pattern of Kₒc variation with depth is consistent across all soils. Surface soils that developed under forest have much larger Kₒc values than those that developed under prairie vegetation. We suggest that the larger atrazine adsorption capacity of organic matter in soils originally formed under forest vegetation contributes to the lower mobility of atrazine observed in these soils.
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