The effectiveness of a grassed waterway in decreasing 2,4‐D [(2,4‐dichlorophenoxy) acetic acid] content in surface runoff was investigated. Corn (Zea mays L.) plots were treated with 2,4‐D (0.56 kg/ha) and runoff produced by applying simulated rain was directed through a 24.4‐m‐long grassed waterway. The 2,4‐D concentrations were measured under wet and dry antecedent waterway and plot conditions. Reduction in 2,4‐D load in waterways results from water loss by infiltration, sediment loss, and by attachment‐absorption on vegetative and organic matter. Of the simulated rainfall applied 1 day after application of 2,4‐D, 50% of the water ran off the plots under dry antecedent soil conditions, and 78% ran off under wet conditions. Infiltration reduced runoff flowing down the waterway an additional 25% under dry conditions and 2% under wet conditions. Suspended sediment reduction in the waterway was 98 and 94% of the total amount moving from the plot for the dry and wet waterway conditions, respectively. The total loss (on sediment and in solution) of the applied 2,4‐D from the plot in the dry and wet states was 2.5 and 10.3%, respectively. Of the 2,4‐D lost from the plots and entering the 24.4‐m waterway, approximately 30% reached the end of the waterway, regardless of antecedent soil moisture.
A large fraction of many applied pesticides are lost to the air and dissipated. Microclimatological methods were used to determine the diurnal loss rates by volatilization of trifluralin applied and incorporated into the soil of a 1.26‐ha upper Piedmont plateau watershed. Trifluralin flux decreased to very low levels during daytime when surface soil water content was low even though turbulence, soil temperature, and evaporative demand were high. During nighttime, when evaporative demand subsided and the surface soil water content increased, the trifluralin flux increased as the surface soil water content increased. Trifluralin and lindane flux on a limited plot‐size study were compared and both pesticides reacted similarly to environmental conditions, except lindane volatilized more rapidly.When the soil surface was not wet, trifluralin and lindane fluxes appeared to be controlled by surface soil water content and the water content's effect on pesticide adsorption to the soil particle. Apparently, adsorption to the soil particle upon soil drying is a reversible process since efflux of the pesticides was rapid when soil was rewetted by dew or rainfall to above the equivalent of three molecular layers of adsorbed soil water. Under controlled soil‐water conditions, where the soil surface remained wetter than three molecular layers of adsorbed water, the pesticide fluxes responded to increased soil temperature and turbulence, and atmospheric stability conditions.
Movement of 2,4‐D [(2,4‐dichlorophenoxy) acetic acid] was not significant in either surface or subsurface runoff from a small agricultural watershed on a sandy Coastal Plain soil. Surface runoff levels were highest for the first runoff event after herbicide application (0.56 kg/ha) each year, and initial concentrations were related to the time lapse between herbicide application and the date of the first runoff event. Maximum concentrations were 8.1, 6.2, and 2.5 µg/liter in 1970, 1971, and 1972, respectively. The corresponding time lapse for the same years was 20, 27, and 34 days. Persistence studies showed that the 2,4‐D concentration in the surface 0.5 cm of soil decreased 95%, from 4.7 to 0.23 ppm in only 7 days, and after 34 days the soil concentration was only 0.01 ppm. Although subsurface flow was three times greater than surface runoff during the 3‐year period, 2,4‐D movement in subsurface water was negligible. Concentrations were usually zero or < 1 µg/liter. Soil sampled to a 90‐cm depth showed no 2,4‐D accumulation or build‐up in the soil profile. Simulated rains (8.25 cm in 30 min) applied to subplots on the watershed showed that there is a potential for greater 2,4‐D losses in surface runoff when it rains soon after herbicide application. When rains were applied 1, 8, and 35 days after herbicide application, the average 2,4‐D concentrations in runoff were 25.2, 5.8, and 0.7 µg/liter, respectively.
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.
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