Fate of a symmetric and an asymmetric triazine herbicide in silt loam soils
Koskinen, W.C. | Conn, J.S. | Sorenson, B.A.
The formation of 14C-atrazine and 14C-metribuzin degradation products and their distribution in the top 90 cm of silt loam soils under field conditions was determined over a 16-month period. The metribuzin experiment was conducted on Tanana (3.8% organic carbon (OC), pH 6.5, 14% clay) and Beales (6.4% OC, pH 4.7, 8% clay) silt loam soils while the atrazine experiment was conducted on a Port Byron silt loam soil (2.4% OC, pH 5.4 and 23% clay). Metribuzin degraded rapidly in both soils: 12% remaining at 1 MAT; 2% remaining by 16 MAT. The maximum amount of metabolites desamino, or desaminodiketo-metribuzin found was 4%; most of the 14C remaining was in the form of unextractable bound residues. The majority of the metribuzin residue remained in the surface soil. Some metribuzin residues leached to 45 cm: 0.1 and 0.3% of the applied 14C remained in the 6.4 and 3.8% OC soils, respectively. In the atrazine experiment, 68% of the applied 14C was present 16 months after treatment (MAT). Radioactivity moved to 30-40 cm by 1 MAT. Atrazine accounted for 20% of the 14C applied 16 MAT, and was the predominant 14C-compound in soil below 10 cm through 16 MAT. Hydroxyatrazine (HA) (13% of the 14C present 1 MAT) was the major degradation product in the top 10 cm of soil. Predominant degradation products at depths greater than 10 cm were HA and deethylatrazine. Deisopropylatrazine and deethyldeisopropylatrazine were also detected 1 MAT.
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