|Kustas, William - Bill|
Submitted to: Water, Air, and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2016
Publication Date: 2/2/2017
Citation: Prueger, J.H., Alfieri, J.G., Gish, T.J., Kustas, W.P., Hatfield, J.L., Daughtry, C.S., McKee, L.G. 2017. Multi-year measurements of field-scale metolachlor volatilization. Water, Air, and Soil Pollution. 228:84. doi: 10.1007/s11270-017-3258-z.
Interpretive Summary: The amount of pesticides applied annually in US farming operations is well over 100 million tons and yet the amount of pesticide volatilization to the atmosphere is not well known. Pesticide volatilization is a process where pesticides move from a liquid phase on soil or vegetation surfaces to a chemical gas phase that is then released to the atmosphere. In this study we measured concentrations of a commonly used pre-emergent herbicide (metolachlor) for a corn production system for 13 consecutive years. Using meteorological parameters that were measured at the same time as the pesticide measurements in the air were made, we computed the volatilization losses for the first five days after application each year. Our results showed that volatilization losses were significantly greater than previously believed. Our results also confirmed that volatilization losses for metolachlor were greater than the losses from leaching and runoff, which were long believed to be the dominant source of pesticide losses after application. Additionally the volatilization losses were closely correlated with soil water content, which varies across years as a function of local meteorological conditions. The information in this study is important for model validation of pesticide transport, producers of corn and soybeans and for development of improved pesticide application strategies (timing of application) to minimize volatilization losses.
Technical Abstract: Volatilization is a critical pathway for herbicide loss from agricultural fields, and subsequent deposition downwind from the edge of the field. To better understand the volatilization process, field-scale turbulent volatilization fluxes of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide) were quantified for 13 consecutive years using a combination of herbicide concentration profiles and eddy diffusivities derived from turbulent fluxes of heat and water vapor. Location, type of herbicides, and agricultural management practices remained unchanged during this study in order to evaluate the effect of soil moisture on metolachlor volatilization. Twenty gravimetric surface soil moisture samples (0-5 cm) were collected immediately after herbicide application and then at 0430 h each morning to determine the impact of surface moisture on herbicide volatilization. Five days after application, cumulative herbicide volatilization ranged from 5% to 63% of that applied. Metolachlor volatilization remained an important loss process more than 5 days after application when the soil surface was moist. Conversely, if the soil surface was dry, negligible volatilization occurred beyond 5 days. Furthermore, the total amount of metolachlor volatilized into the atmosphere increased exponentially with surface soil water content during application (r2 = 0.78). Metolachlor volatility was found to be governed largely by surface soil moisture.