Soil moisture and metolachlor volatilization observations over three years

Authors: Gish, Timothy; Prueger, John; Kustas, William - Bill; Daughtry, Craig; McKee, Lynn; Russ, Andrew - Andy; Hatfield, Jerry

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2008
Publication Date: 7/14/2009
Citation: Gish, T.J., Prueger, J.H., Kustas, W.P., Daughtry, C.S.T., McKee, L.G., Russ, A.L., Hatfield, J.L. 2009. Soil moisture and metolachlor volatization observations over three years. Journal of Environmental Quality. 38:1785-1795.

Interpretive Summary: Pesticides are a critical component of modern agriculture and are used worldwide to maintain food and fiber production. However, pesticides appear in the environment where not intended and are considered toxic, and as such considerable research has been conducted to quantify the occurrence and impact on the environment. A three year study was conducted to focus on evaluating the impact of surface soil water on the metolachlor volatilization process. Metolachlor volatilization losses to the atmosphere were monitored at two locations within a field where local meteorological conditions, soil, management, and landscape feature were nearly identical. However, the two within field locations differed with regard to soil moisture as one location was generally wetter due to the existence of subsurface flow pathways. Results show that the field location without subsurface flow pathways had soil water contents and pesticide volatilization losses that were about half that of the wetter location. However, when rainfall was limited and subsurface flow pathways were not activated, both the soil moisture and pesticide vapor losses were nearly identical. Furthermore, analysis of the infrared temperatures suggests a correlation between surface soil temperatures and metolachlor volatilization when soils are wet, but not when the soils were dry. This study demonstrates the importance of soil moisture on pesticide volatilization and the need for quantifying surface soil moisture and meteorological conditions when conducting field pesticide volatilization studies.

Technical Abstract: Volatilization of pesticides from agricultural land is of a concern because of potentially detrimental environmental and ecological impacts. A 3-year study was conducted to focus on the impact of surface soil water on metolachlor volatilization from a single field with different surface soil water regimes created by subsurface water flow paths. Metolachlor vapor fluxes were monitored at two locations within the field where local meteorological conditions, soil, management, and landscape feature were constant. The two monitoring locations differed with surface soil water content at V2 were generally greater due to the existence of subsurface flow pathways, relative to V1. Results show that for the first two years (2004 & 2005) surface soil water content at the V1 location were nearly half that of at V2. During 2004 and 2005, cumulative metolachlor vapor fluxes at the dry location, V1, were also about half that of the wetter location, V2. However, in the third year (2006) drought conditions rendered the soil water content at the two locations (V1 and V2) to be nearly identical, resulting in similar metolachlor volatilization losses. Furthermore, analysis of the infrared temperatures (IRT) suggests a correlation between surface soil temperatures and metolachlor volatilization when soils are wet, but not when the soils were dry. Last, field averaged metolachlor volatilization losses were highly correlated with increasing surface soil water contents with r2 = 0.995. This study demonstrates two issues: 1) the need for quantifying surface soil moisture and meteorological conditions when conducting field pesticide volatilization studies: and 2) the need for developing soil water content observations for footprints on the order of 100’s of meters.