Persistence and leaching of the herbicides acetochlor and terbuthylazine in an allophanic soil: comparisons of field results with PRZM-3 predictions

Abstract

Rates of degradation and adsorption of acetochlor [2-chloro-N-ethoxymethyl-6′-ethylaceto-o- toluidide] and terbuthylazine [N 2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine] in a Horotiu sandy loam soil (Typic Orthic Allophanic) were determined under controlled temperature and soil moisture regimes. These were then combined with site-specific soil properties and climatic conditions in the Pesticide Root Zone Model (PRZM-3) to predict dissipation and leaching of the herbicides in the field. PRZM-3 significantly under-estimated dissipation of both herbicides in the field using parameters derived from the laboratory incubation studies. When these parameters were derived from the field trials, PRZM-3 adequately predicted dissipation of both herbicides using a two-rate dissipation sub-model but under-predicted the dissipation when a simpler single-rate sub-model was used. Earlier-than-expected appearance of both herbicides in sub-soil layers were postulated to result from the non-equilibrium adsorption/transport of the herbicides and preferential flow, which cannot be simulated by PRZM-3. © 2000 Society of Chemical Industry