Doctoral Dissertations

Date of Award

12-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Thomas C. Mueller

Committee Members

William A. Krueger, Donald D. Tyler, Fred D. Tompkins

Abstract

Studies were conducted in 1992 and 1993 to evaluate the adsorption, dissipation, and movement of fluometuron and norflurazon in three soils representative of the cotton growing regions of the southeastern United States. Field experiments were established in Jackson, Tennessee; Stoneville, Mississippi; and Griffin, Georgia on areas which had no fluometuron or norflurazon exposure for three years prior to plot establishment. The studies utilized a randomized complete block design and treatments were replicated four times in tilled areas.

Fluometuron and norflurazon were applied preemergence (PRE) at 1.7 kg ai ha-1 broadcast. Soil samples were obtained in one of two ways: surface (0 to 8 cm) soil samples were collected from each plot prior to and immediately following herbicide application, and at approximately 14, 28, 56, and 112 days after treatment (DAT) using hand-held soil probes. These samples were utilized to examine surface fluometuron and norflurazon dissipation. Two full-length depth cores from the 0- to 120-cm soil zone were collected at approximately 28, 56, and 112 DAT. Samples obtained from the 0 to 120 cm depth were divided into 0- to 8-, 8- to 15-, 15- to 30-, 30- to 45-, 45- to 60-, 60- to 90-, and 90- to 120-cm soil zones to examine fluometuron and norflurazon distribution within the soil profile.

Additional studies were conducted in 1993 to examine fluometuron adsorption and dissipation under laboratory conditions. Untreated soil from the 0- to 8-, 30- to 45- and 60- to 90-cm zones was collected in 1993 from plots utilized in the field study. Adsorption of fluometuron and norflurazon on soil was determined using a slurry technique, and a distribution coefficient (Kd) was calculated for each location and depth combination. Dissipation of fluometuron and norflurazon under controlled conditions was determined for each location by depth combination by fortifying untreated soil with either fluometuron or norflurazon and incubating at 30 C. Fluometuron and norflurazon were quantified with High Pressure Liquid Chromatography (HPLC).

The ability of the Pesticide Root Zone Model (PRZM) and Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) model to simulate fluometuron and norflurazon movement was evaluated with site-specific environmental data. Tests of model performance were demonstrated using both site-specific and database sorption and dissipation parameters. Fluometuron or norflurazon concentration in total mass within each profile was chosen as a measure of model accuracy.

Fluometuron and norflurazon adsorption was correlated with organic matter but not with other soil characteristics. First-order kinetics described fluometuron dissipation under field and laboratory conditions (r2≥0.82). Fluometuron dissipation was more rapid under field conditions than under laboratory conditions in soil from two of three locations, and field dissipation was slower under dry conditions. Fluometuron half-life in soils from the 0 to 8 cm depth ranged from 9 to 28 days under field conditions and from 11 to 43 days in the laboratory. Fluometuron half-life was positively correlated with soil depth and inversely correlated with soil organic matter.

Norflurazon dissipation under controlled conditions in soil from the 0 to 8 cm zone was not different among locations, with half-life ranging from 63 to 167 days. Norflurazon dissipation was more rapid under field conditions than under laboratory conditions with half-life ranging from 7 to 79 days in the 0 to 8 cm soil horizon.

Neither norflurazon nor fluometuron was detected below 15 cm in the soil profile in any soil, based on data obtained from soil cores. Concentrations in the 8 to 15 cm soil zone were <36 ppbw 112 days after treatment. Site-specific parameters increased PRZM accuracy in predicting total norflurazon concentration in the soil profile, and PRZM more accurately predicted norflurazon than fluometuron concentration when site-specific parameters were utilized. The use of database variables increased the accuracy of PRZM to predict fluometuron but decreased the accuracy of norflurazon predictions. PRZM provided more correct predictions of norflurazon concentration in the soil profile than did GLEAMS; however, both models performed similarly with regards to fluometuron. The use of site-specific data increased the accuracy of GLEAMS to predict fluometuron but not norflurazon. Simulations better predicted norflurazon concentration than fluometuron concentration when averaged over all model by parameter input combinations.

Soil organic matter and environmental conditions affected fluometuron and norflurazon dissipation. Migration of fluometuron or norflurazon into subsurface soil zones was minimal, and PRZM and GLEAMS demonstrated their utility to accurately predict herbicide behavior in these soils when correct input parameters were employed.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS