Effects of tillage on norflurazon sorption, degradation and mobility in a Mississippi delta soil

Document Type

Article

Publication Date

7-1-2007

Abstract

The fate of pesticides in agricultural systems and impact on water quality remain important environmental issues. Recent studies have found the herbicide norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3-(2H)- pyridiazone] in groundwater and surface water. Although there are data on the sorption, degradation, and mobility of this compound in different soils, none address effects of tillage on its fate. Also, the accuracy of independent sorption and degradation data for predicting norflurazon mobility has not been assessed. This study compared sorption, degradation, and mobility of norflurazon in Dundee (fine-silty, mixed, thermic, Aeric Ochraqualfs) soil from conventional-tillage (CT) and no-tillage (NT) plots of a long-term tillage experiment. Sorption was determined for the 0- to 10-, 10- to 20-, and 20- to 30-cm depths of these soils in a 24-h batch equilibration study. Sorption was well-described by the Freundlich model and related to soil organic C, being greater in surface NT than CT soil and generally decreasing with depth. Degradation was tracked in dosed (0.256 μmol/25 g; C-labeled) soil samples for 14, 28, 56, and 112 days, followed by methanol extraction and high-performance liquid chromatography analysis. Norflurazon degraded with formation of desmethyl-norflurazon, nonextractable C residue, and loss of CO2. Degradation rate was adequately described by first-order models and decreased with depth but was not affected by tillage. Rate constants ranged from 0.012 to 0.005 day. Mobility in intact cores (~30 cm long) of CT and NT soil showed less mass eluted from and greater retention in NT cores, consistent with greater sorption. Transport showed preferential flow (Br tracer) that was described by a mobile/immobile water model. Norflurazon mobility could be reasonably well described using the batch sorption and degradation data. © 2007 Lippincott Williams & Wilkins, Inc.

Publication Source (Journal or Book title)

Soil Science

First Page

534

Last Page

545

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