Soil Moisture Effect On the Diurnal Pattern of Pesticide Emission: Measurement and Simulation.

Pesticides are a critical component in modern agriculture. However, volatilization is one of the principal processes leading to their widespread dispersion in the environment. Accurate estimation of pesticide volatilization rates is essential for assessing the effects of such emissions upon environmental ecosystems including human welfare.

This study focuses on the impact of surface soil water content on the diurnal pattern of pesticide emission. The measured data were collected during the period of June-July 2000 at a UC-Davis field site. In these experiments, diazinon was surface applied on Yolo silty clay soil with different initial water contents. Over the course of the experiments, diurnal change of volatilization rates, soil-water contents, and soil temperatures were measured at two depths several times per day, and total amount of pesticide remaining in the soil was measured at the end of the experimental period. The volatilization rates were measured using a dynamic flux chamber. For simulation, we used a comprehensive non-isothermal volatilization model and different approaches to simulate heat and water transport in soil that were recently verified in water evaporation studies. Results show that the volatilization diurnal pattern is strongly affected by the water transport modeling approach.