Tests of the Pesticide Root Zone Model and the Aggregate Model for Transport and Transformation of Aldicarb, Metolachlor, and Bromide

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Abstract
Mathematical models are widely used to predict leaching of pesticides and nutrients in agricultural systems. This work was conducted to investigate the predictive capability of the Pesticide Root Zone Model (PRZM) and the Aggregate model (AGGR) for the pesticides aldicarb [2‐methyl‐2‐(methylthio)propionaldehyde O‐(methylcarbamoyl)oxime], metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide], and for a bromide tracer. Model predictions were compared with data collected during 1984 to 1987 in the Dougherty Plain area of southwestern Georgia. Field data were used to estimate mean concentrations of pesticide and bromide residues in the soil profile on various dates after application in each of four growing seasons. Both models tended to predict rates of movement of bromide tracer compounds in excess of that observed. For metolachlor, a pesticide with a sorption‐partition coefficient that is higher than for other compounds in the study, both models provided reasonably accurate predictions within the upper 30‐cm zone. For the pesticide aldicarb, results were more variable. The results suggest that the hydrologic components of both models are more accurate for the upper zones, but they are imprecise in deeper zones, underpredicting vertical dispersion and overpredicting transport velocity.

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