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.
Little trifluralin (α,α,α‐trifluoro‐2,6.dinitro‐N,N‐dipropyl‐p‐toluidine) moved in the surface flow from a small agricultural watershed located in the Southeastern Coastal Plain. Movement of trifluralin in 1974 and 1975 in surface water was 0.17 and 0.03%, respectively, of the total amount applied (1.12 kg/ha). Trifluralin movement in the shallow subsurface flow (above the 214 cm depth) was recorded only in 1974 and was negligible. Trifluralin was detectable in the soil from the 1974 application before the 1975 application. Soil concentration of trifluralin in 1974 was 320 ng/g (immediately after application) in the 0‐ to 10‐cm depth and after 114 days the concentration decreased to 73 ng/g. However, no trifluralin was detected in the 30‐ to 60‐cm depth 60 days after application. Simulated surface runoff from subplots on the watershed produced measurable concentrations of trifluralin 38 days after application, but it could not be detected after 71 days. Trifluralin movement was greater in runoff caused by simulated rainfall than that from natural rainfall due to the high application rate of water (19.1 cm/hour) and the lack of a vegetational buffer. Trifluralin loss in the simulated rainfall runoff water from a small plot directed through a 24.4‐m waterway was reduced 96% under dry and 86% under wet conditions. Hence, trifluralin movement can be significantly reduced and possibly managed by buffer strips or vegetated waterways adjoining cropped areas. Appropriate use of these buffer areas should reduce to acceptable levels the chemical concentration in the runoff before the runoff reaches the surrounding streams.
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