Modeling Pesticide Fate and Nonideal Transport From A Slow Release, Pesticide Treated Seed

Authors: SABBAGH, G. - BAYER CROPSCIENCE; FOX, G. - OKLAHOMA STATE UNIVERSITY; Ma, Liwang; Malone, Robert - Rob; ARTHUR, E. - BAYER CROPSCIENCE; DYER, D. - BAYER CROPSCIENCE

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2007
Publication Date: 3/1/2007
Citation: Sabbagh, G.J., Fox, G.A., Ma, L., Malone, R.W., Arthur, E.L., Dyer, D.G. 2007. Modeling Pesticide Fate and Nonideal Transport From A Slow Release, Pesticide Treated Seed. Transactions of the ASABE 50(2):523-532, 2007.

Interpretive Summary: Pesticide treated seeds are commonly used in agricultural production, but the fates of pesticide in the soil environmental are largely unknown. This research was designed to investigate the fates of an insecticide from treated corn seeds in laboratory columns. Ten 60-cm soil columns were packed with a silt loam soil and each column was planted with one corn seed treated with active ingredient of an experimental pesticide. The results were modeled using the Root Zone Water Quality Model (RZWQM), which is capable of simulating slow release, instantaneous equilibrium (IE) and equilibrium kinetic (EK) sorption, and irreversible binding. The model was calibrated for hydrology (i.e., leachate from the bottom of the soil columns), crop growth, and total pesticide in the soil profile. Measured insecticide concentrations were compared to model predictions for IE and EK sorption scenarios across a range of sorption parameters derived from batch and time-dependent sorption studies. The model over-predicted the leachability of the insecticide regardless of adsorption mechanisms (IE or EK). Model deviations from observations were hypothesized to be due to the model representing a theoretical two-dimensional process in one-dimension and also the potential for preferential flow paths formed by root formation. Long-term (i.e., 20-year) simulations suggested that significant differences (i.e., average of 8% compared to less than 1% cumulative leaching) arise between IE and EK sorption after several plantings of the pesticide treated seed.

Technical Abstract: This research evaluated the predictive ability of a pesticide fate and transport model to simulate the potential for pesticide leaching from slow release, insecticide treated corn seeds. Column studies consisted of ten 60-cm soil columns of silt loam soil each planted with one corn seed treated with active ingredient of an experimental pesticide. The results were modeled using the Root Zone Water Quality Model (RZWQM), which is capable of simulating slow release, instantaneous equilibrium (IE) and equilibrium kinetic (EK) sorption, and irreversible binding. The model was calibrated for hydrology (i.e., leachate from the bottom of the soil columns), crop growth, and total pesticide in the soil profile. Measured concentrations were compared to model predictions for IE and EK sorption scenarios across a range of sorption parameters derived from batch and time-dependent sorption studies. Modeling scenarios failed to predict the observed pesticide confinement (70% of applied pesticide) to primarily the upper 15 cm of the soil profile, with 1 to 20% of applied in the upper 15 cm for IE sorption and 3 to 18% of applied for EK sorption at the end of the simulation period. Both IE and EK sorption scenarios failed to predict pesticide in leachate (observed cumulative of 0.12% of applied) unless using minimum IE and EK sorption parameters. Model deviations from observations were hypothesized to be due to the model representing a theoretical two-dimensional process in one-dimension and also the potential for preferential flow paths formed by root formation. Long-term (i.e., 20-year) simulations suggested that significant differences (i.e., average of 8% compared to less than 1% cumulative leaching) arise between IE and EK sorption after several plantings of the pesticide treated seed.