ARS | Publication request: Herbicide volatilization trumps runoff losses, a multi-year investigation

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 6, 2011
Publication Date: September 27, 2011
Citation: Gish, T.J., Prueger, J.H., Daughtry, C.S., Kustas, W.P., Mckee, L.G., Russ, A.L., Hatfield, J.L. 2011. Herbicide volatilization trumps runoff losses, a multi-year investigation [abstract]. Eposure Model Public Meeting. 2011 CDROM.

Technical Abstract: Surface runoff and volatilization are two processes critical to herbicide off-site transport. To determine the relevance of these off-site transport mechanisms, runoff and turbulent vapor fluxes were simultaneously monitored on the same site for eight years. Site location, herbicide formulations, and agricultural management remained unchanged throughout the duration of the study. Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] and atrazine [6-chloro-N-ethyl-N’-(1-methylethyl)-1,3,5-triazine-2,4-diamine] were co-applied as a surface broadcast spray. Herbicide runoff was monitored from a month before application through harvest using H-flumes. A flux gradient technique was used to compute volatilization fluxes for the first 5 days after application using herbicide concentration profiles and turbulent fluxes of heat and water vapor as determined from eddy covariance measurements. Results demonstrate that volatilization losses for these two herbicides were significantly greater than runoff losses (P< 0.007) even though both have relatively low vapor pressures. The largest annual runoff loss for metolachlor never exceeded 2.5% while atrazine runoff never exceeded 3% of that applied. On the other hand, herbicide cumulative volatilization losses after only 5 days ranged from 5 to 63% of that applied for metolachlor and 2 to 12% of that applied for atrazine. Additionally, herbicide volatilization losses were strongly influenced by temperature when soils were moist. However, when soils were dry, soil temperatures had little impact on herbicide volatilization. Averaged over all years and both herbicides, off-site transport was about 25 times larger for volatilization than surface runoff. This research confirms that vapor losses for some commonly used herbicides frequently exceeds runoff losses and that herbicide vapor losses on the same site and with the same management practice can vary significantly year to year depending upon local environmental conditions.