Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2007
Publication Date: 7/1/2007
Citation: Gaston, L.A., Locke, M.A., McDonald, J.A., Dodla, S., Liao, L., Putnam, L., Udeigwe, T. 2007. Effects of Tillage on Norflurazon Sorption, Degradation and Mobility in a Mississippi Delta Soil. Soil Science 172:534-545.
Interpretive Summary: Studies have reported detection of norflurazon herbicide in ground and surface waters. Research was conducted to evaluate potential conservation management options that may mitigate off-site movement of norflurazon. This research compared sorption, degradation and mobility of norflurazon in soil from conventional-tillage and no-tillage soils. It was determined that norflurazon sorption in these soils was strongly related to organic matter, decreased with depth in both soils and was greater in no-tillage soil. Norflurazon degradation rates were slower with increased soil depth (approximately 60 day half-life in the surface versus more than 120 days at lower depths), likely due to lower microbial populations that would facilitate degradation. Mobility of norflurazon was less in no-tillage soils, and this increased retention was attributed to higher organic matter. Quantifying relationships between norflurazon and characteristics of no-tillage soils should be useful for predicting the contribution of conservation management in mitigating impacts of pesticides on the environment.
Technical 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 ground and surface waters. While there are data on the sorption, degradation and mobility of this compound in different soils, none address effects of tillage on its fate. Also, 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 – 10, 10 – 20 and 20 – 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 'mole / 25 g; 14C-labeled) soil samples for 14, 28, 56 and 112 d, followed by methanol extraction and HPLC analysis. Norflurazon degraded with formation of desmethyl-norflurazon, nonextractable 14C residue and loss of 14CO2. Degradation rate was adequately described by first-order models and decreased with depth but was not affected by tillage. Rate constants ranged from > 0.010 to 0.005 d-1. 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.