Improved PADDY model including photoisomerization and metabolic pathways for predicting pesticide behavior in paddy fields: Application to the herbicide pyriminobac-methyl

Abstract

An improved simulation model for predicting pesticide behavior in paddy fields based on PADDY was developed to include photoisomerization and metabolic pathways and applied to the herbicide pyriminobac-methyl. Isomerization of pyriminobac-methyl in paddy water by sunlight was modeled as a reversible first-order reaction between the (E)- and (Z)-isomers in response to UV-B irradiation. The formation and degradation of its main metabolites in flooded soil were expressed as consecutive first-order reactions. The model was validated by comparing calculated values with measured values from paddy lysimeter and field experiments. The improved PADDY model successfully simulated changes in the concentrations of pyriminobac-methyl and its metabolites over time under paddy conditions.