A FIELD-TEST OF ROOT-ZONE WATER-QUALITY MODEL - PESTICIDE AND BROMIDEBEHAVIOR

The Root Zone Water Quality Model (RZWQM) is a process-based model dev eloped recently by USDA-ARS scientists. The model integrates physical, chemical and biological processes to simulate the fate and movement o f water and agrochemicals over and through the root zone at a represen tative point in a field with various management practices. The model w as evaluated using field data for the movement of water and bromide, a nd the transformation and transport of cyanazine and metribuzin in the soil profile. The model reasonably simulated soil water and bromide m ovement. Pesticide persistence was predicted reasonably well using a t wo-site sorption model that assumes a rate-limited (i.e. long-term) ad sorption-desorption process with the additional assumption of negligib le degradation of inter-aggregate adsorbed pesticides.