COMPARISON OF THE PESTICIDE ROOT ZONE MODEL SIMULATED AND MEASURED PESTICIDE MOBILITY UNDER 2 TILLAGE SYSTEMS

The USEPA's Pesticide Root Zone Model (PRZM) was evaluated to determine its ability to predict pesticide movement in the unsaturated zone of a Plainfield sand (Typic Udipsamments) profile under no-till (NT) and moldboard plow (MB) tillage practices. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methyl-ethyl) acetamide] distribution in the root zone was measured by analysis of soil cores taken from nonirrigated field plots. The mobility of carbofuran (2,3-dihydro-2,-dimethyl-7-benzofuranyl methylcarbamate) and chlorpyrifos [O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] was measured using intact soil columns extracted from adjacent field plots and subjected to a typical irrigation schedule. Predicted depth of pesticide penetration, depth to peak concentration, and amount of pesticide leached from the root zone were compared with measured pesticide distributions and leaching patterns. Acceptable agreement between PRZM simulations and measured data was obtained early in the growing season whereas the model generally predicted greater-than measured pesticide penetration at later sampling dates.