Evaluation of the Root Zone Water Quality Model (RZWQM) Using Field-Measured Data from the Tropical Zone, Thailand

Evaluation of a field scale agricultural non-point source simulation model against field experiment data is an important step that must be considered before a model can be used as a management tool. Field soil water content and metribuzin residue adsorbed in soil profile were intensively monitored and measured by the gravimetric method and the LC-MS/MS method, respectively, for a soybean field plot located at the Asian Institute of Technology, Thailand. The Root Zone Water Quality Model (RZWQM) was evaluated based on laboratory-measured soil hydraulic properties and pesticide residue in Bangkok clay soil. Reasonable agreement exists between the soil water content measured and predicted by RZWQM for 10-20 and 30-40 cm soil depths. The model slightly overestimated the pesticide residue at 0-10 cm soil depth 1 day after application at surface, whereas pesticide residue at 10-20 and 30-40 cm soil depths was in agreement with model acceptance. These results indicate that RZWQM can be used when properly calibrated to predict the movement of water and metribuzin through the soil profile in the tropical zone.