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Trifluralin Volatilization Losses from a Soybean Field¹

ABSTRACT

We measured trifluralin (,,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) concentrations in air and calculated volatilization losses from a 1.26-ha field during application at soybean [Glycine max (L.) Merr.] planting and for 120 days after. Air samples, collected at three heights above the soil on 9 days during the season, showed that distinct trifluralin air concentration gradients existed throughout the study with concentrations highest closest to the ground. The highest concentration was measured during the application period (prior to soil herbicide incorporation) when a trifluralin level of 16,500 ng/m³ was recorded 20 cm above the ground. Generally, air concentrations were highest early in the season and decreased rapidly the first month. After herbicide incorporation, trifluralin air concentrations at 20 cm reached a maximum of 3,400 ng/m³ on day 2, and never exceeded 100 ng/m³ after day 35. Soil trifluralin levels at the 0.5-cm depth decreased from 1.65 to about 0.3 µg/g on day 35 and to about 0.1 µg/g after 120 days.

Seasonal trifluralin volatilization loss, excluding the application period, was estimated to be 22.4% of that applied with vapor losses during application amounting to 3.5% of the applied herbicide. Thus, total seasonal aerial losses were 25.9% of the originally applied herbicide. Of the total aerial losses, 13 and 15% were lost during application and through day 1, respectively. About half was lost during the first 9 days, and 90% in 35 days. Combined seasonal losses by other pathways (excluding volatilization) were almost 2.5 times greater than aerial losses.

Key Words: pesticides • pesticide flux • aerial losses • air concentrations • vaporization • vaporization • micrometeorology • degradation • soil persistence

¹ Contribution from South. Piedmont Conserv. Res. Center, Watkinsville, GA 30677, Athens, Georgia Area, South. Reg., Agric. Res. Serv., USDA, in cooperation with the Univ. of Georgia Exp. Stn.

² Soil Scientists and Chemist, respectively. Present address of senior author: USDA, ARS, Byron, GA 31008.

Received for publication June 2, 1976.