Impact of Moisture and Surface Meteorology On Pesticide Volatilization, a 10 Year Investigation.

Volatilization of pesticides can detrimentally affect the environment by contaminating soil and surface waters far away from where the pesticides were applied.  A 10-year study was conducted to focus on the impact of soil and climatic factors governing herbicide volatilization from an agricultural field.  For the first 5-years, atrazine and metolachlor vapor losses were continuously monitored for the first 120 hours after application and used to identify critical field-scale factors influencing herbicide vapor losses.  For the second 5-year period, herbicide vapor losses were continuously monitored along with those critical factors indentified during the first phase of the experiment.  A flux gradient technique was used to measure pesticide vapor profiles and used with turbulent fluxes of momentum, heat and water vapor (eddy covariance) to estimate a pesticide flux diffusivity, which allowed continuous measurements of metolachlor flux losses to be monitored.  Differences in meteorological and surface soil water contents were the critical factors governing pesticide volatilization losses among years. For example, when soil surface conditions approached saturation 62.2% of the applied metolachlor was lost to volatilization while under dry conditions losses were closer to 5%.  Although both atrazine and metolachlor are considered non-volatile, pesticide volatilization appears to be a major loss pathway. Additionally, analysis of infrared soil surface temperatures shows a correlation between surface soil temperatures and metolachlor volatilization when soils are wet but not when the soils were dry.  This research demonstrates that to eventually predict pesticide volatilization both surface soil water content and surface meteorological conditions must be understood and quantified.