Trifluralin Volatilization Losses from a Soybean Field

Abstract

We measured trifluralin (α,α,α‐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.

Simulating the Transport and Fate of Trifluralin in Soil

“…The maximum volatilization rate of trifluralin was 0.18 mg d-1 at Day 1 and near zero in about two weeks. A similar finding was reported by White et al (1977). The volatilization rate of trifluralin decreased primarily because the surface applied trifluralin was incorporated into the soil.…”

“…In this study, the model was calibrated using the experimental data reported by White et al (1977). These authors studied trifluralin (α,α,α-reifluoro-2,6-dinitro-N,N-dipropyl-ρtoluidine) volatilization losses from a soybean field at Watkinsville, GA, USA.…”

“…Table 1 lists the values of the input parameters for the simulation conditions used in this study. It should be noted that all of the input values were directly quantified from the field data reported by White et al (1977) or indirectly from other authors who have estimated the input values based on the same dataset reported by White et al (1977). One exception was the uptake rate of trifluralin by soybean, which was estimated based on Boersma et al (1991).…”

“…This occurred because large amounts of trifluralin were available for surface runoff and erosion loss at the first rainfall event, which was within the first week of trifluralin application to the soil. As the time elapsed after the trifluralin application, most trifluralin was strongly adsorbed by the soil and was subject to degradation by micro-organisms as well as to volatilization into the atmosphere (Parr and Smith, 1973;White et al, Journa39l of Sustainable Watershed Science & Management -ISSN 1949-1425 58 1977). As a result, little to no trifluralin runoff and erosion losses were found during the third rainfall event at Day 48.…”

Transport of trifluralin on wind-eroded sediment

“…During the 38 d prior to the first erosion event on 1991 Oct. 16, only 9 mm of rainfall occurred and the soil surface was relatively dry during this period. Throughout the 140-d period between herbicide application and the first wind erosion event, mean air temperatures were above normal (Table 2) so soil moisture and temperature would have been conducive to both to microbial degradation (Kearney et al 1976;Golab et al 1979;Graper and Rainey 1989a, b) and vapour loss (White et al 1977;Glotfelty 1981;Glotfelty et al 1984;Grover et al 1988;Majewski et al 1993) of trifluralin for much of this period. Vapour loss is one of the main routes of trifluralin dissipation following incorporation into soil and Grover et al (1988) reported a 23.7% vapour loss of trifluralin following soil incorporation at the same study site over a 67-d period in 1983.…”