Sulfentrazone behavior in surface soil : dissipation, degradation, adsorption and mobility

A rapid method for the determination of sulfentrazone in soils is described. The method consists of extraction of soil samples with methanol, filtration, liquid chromatographic separation of methanol-soluble components by using a C₁₈ column, and ultraviolet detection with absorbance at 220 nm. Recoveries from fortified soils were >85% for sulfentrazone from the surface soils. Average percent relative standard deviations over the soils examined was 7.7%. The limit of detection for sulfentrazone was 40 ng/g soil.

Sulfentrazone dissipation and degradation was examined in field and laboratory experiments. Field studies were conducted in 1995, 1996 and 1997 at Knoxville, TN on soils of the Sequatchie loam series. Sulfentrazone half-life varied with rainfall under field conditions. In 1995, the half-life of sulfentrazone was 113 d. In 1996, the half-life was 25 d. In 1997 (location one), the half-life of sulfentrazone was 24 d. In 1997 (location two), the half-life of sulfentrazone was 85 d. Injury to cotton from sulfentrazone was observed the year following application when half-lives were ≥ 85 d.

Sulfentrazone degradation, under controlled conditions, in autoclaved soil and nonautoclaved soil taken from 0 to 10 cm and 30 to 40 cm depths had half-lives of 198, 93, and 102 d, respectively. In general, sulfentrazone dissipation was influenced by both microbial and chemical degradation mechanisms.

Sulfentrazone adsorption and mobility was evaluated in seven soils with varying soil properties under laboratory conditions. Adsorption was evaluated using a modified slurry technique. Mobility was evaluated using packed soil columns under saturated flow conditions. The order of adsorption to soil was Drummer silt loam > Sequatchie loam > Dothan loamy sand > Bosket sandy loam > Maiden loamy sand > Commerce silty clay loam > Harkey clay loam. Greater adsorption of sulfentrazone occurred in soils with greater organic matter content and lower pH. The Maiden loamy sand was the only soil that did not follow this trend possibly due to high sand and low organic matter content. Sulfentrazone movement under saturated flow conditions in 27 cm soil-packed columns varied with each soil. In general, movement was greater in soils with low adsorption. Sulfentrazone movement was limited to the upper 9 cm in the Sequatchie loam and Drummer silt loam. Movement increased down the column with increasing pH. Sulfentrazone movement was greater in coarse textured soils regardless of pH.