Loss of Fall‐Applied 2,4‐D in Spring Runoff from a Small Agricultural Watershed

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Abstract
The loss of 2,4‐D (2,4‐dichlorophenoxyacetic acid) applied in fall to wheat (Triticum aestivum L.) stubble on fields of Wood Mountain loam soil in semiarid southwestern Saskatchewan was measured in surface runoff from snow. The range of runoff volumes over the 6‐y period was representative of runoff observed over a 30‐y period at the same location.The loss of 2,4‐D was greater from the treated stubble compared with fallow, which served as the control. The average loss from the control of 1.3 g/ha gives an indication of background limits that can be expected if 2,4‐D is applied a year earlier.The 2,4‐D loss in snowmelt runoff is similar to losses in rainfall runoff from a severe storm soon after application.The 6‐y average loss was 4.1% of the amount applied (0.42 kg/ha). Correlation analysis showed the amount of loss to be a function of runoff.The average flow‐weighted mean concentration of 31 µg/L was well below the USEPA maximum permissible level of 100 µg/L, and slightly above the U.S. National Academy of Sciences and National Academy of Engineering objective of 20 µg/L for drinking‐water standards.

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