HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Ma, Q. L. Articles by Ahuja, L. R. Search for Related Content PubMed Articles by Ma, Q. L. Articles by Ahuja, L. R. GeoRef GeoRef Citation Agricola Articles by Ma, Q. L. Articles by Ahuja, L. R. Related Collections Pesticides Coupled Flow/Transport Models Organic Compounds

DIVISION S-1—SOIL PHYSICS

Modeling the Fate of Acetochlor and Terbuthylazine in the Field Using the Root Zone Water Quality Model

^a Formerly with AgResearch, Hamilton, New Zealand
^b Currently with Environmental & Turf Services, Inc., 11141 Georgia Ave., #208, Wheaton, MD 20902
^c HortResearch, Ruakura Research Centre, P.B. 3123, Hamilton, New Zealand
^d USDA-ARS, Great Plains Systems Research, P.O. Box E, Fort Collins, CO 80522

^* Corresponding author (qinglima{at}aol.com)

Data collected from a 3-yr controlled field study in Hamilton, New Zealand were used to examine whether the Root Zone Water Quality Model is capable of predicting water movement and pesticide fate in the field based on key lab-measured parameters and environmental variables. Acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl) acetamide; 2.5 and 5.0 kg a.i. ha^–1] and terbuthylazine (C₉H₁₆ClN₅; 1.5 and 3.0 kg a.i. ha^–1) were applied onto nine field plots (3 by 9 m each). Soil core samples were taken to a depth of 1 m to determine soil water contents and pesticide concentrations. Dissipation of both pesticides in the field at both application rates followed first-order kinetics (adjusted r² > 0.91). The mean dissipation half-life was 16 d for acetochlor and 25 d for terbuthylazine. Relatively small amounts of the pesticides leached below 5 cm and none leached below 10 cm. Predicted soil water contents in the soil profile were not significantly different from those measured in the field (p > 0.84). Predicted acetochlor and terbuthylazine masses in the soil profile based on a linear instantaneous-equilibrium (I-E) partitioning model matched those measured in the field (adjusted r² > 0.93). However, predicted pesticide concentrations in the soil profile were less satisfactory, with 68 and 35% of the predicted concentrations being within a factor of 2 of the measured concentrations for 0- to 5- and 5- to 10-cm depths, respectively. Calibration of each pesticide sensitive parameter individually did not significantly improve the overall predictions of pesticide mass and concentrations in the soil profile when the I-E partitioning model was used. The predictions were improved when a two-site, equilibrium-kinetic (E-K) sorption model was used.

Abbreviations: E-K, equilibrium-kinetic • FIFRA, Federal Insecticide, Fungicide and Rodenticide Act • FOCUS, Forum for the coordination of pesticide fate models and their uses • HPLC, high-pressure liquid chromatography • I-E, instantaneous equilibrium • MWHC, maximum water holding capacity • NRMSE, normalized root mean square error • OECD, Organization for Economic Co-operation and Development