Fate of 2,4-D in a Naff Silt Loam Soil
1978
Wilson, R. G. | Cheng, H. H.
Laboratory studies were conducted to determine the adsorption, desorption, hydrolysis, and breakdown of commercially formulated isooctyl ester and dimethylamine salt of 2,4-D [(2,4-dichlorophenoxy) acetic acid] in a Naff silt loam soil. More 2,4-D was adsorbed to the surface soil than to soil at lower depths, and the percentage of 2,4-D adsorbed decreased as the total amount of 2,4-D present increased. Adsorbed 2,4-D was gradually desorbed from soil by successively exchanging the solution in equilibrium with soil with distilled water. Formulated 2,4-D isooctyl ester applied to moist soil underwent hydrolysis to the anionic form at a rapid rate, with >80% of the ester hydrolyzed in 72 hours. High amounts of 2,4-D in runoff (sediment and water) retarded the active degradation of carboxyl-¹⁴C 2,4-D when 2,4-D was incubated in runoff from a wheat field treated with various formulations and rates of 2,4-D. The presence of the ester formulation at the high rate of application increased the lag period before degradation of carboxyl-¹⁴C and ring-¹⁴C 2,4-D occurred in soil. However, once the active breakdown of carboxyl-¹⁴C and ring-¹⁴C 2,4-D was initiated, little difference could be detected in the degradation patterns. At the end of the 10 weeks of incubation in runoff or in soil, only 1% of the ¹⁴C-2,4-D originally applied to the soil could be identified as 2,4-D.
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