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Disappearance of 2,4-dichlorophenoxyacetic Acid and 2,4,5-trichlorophenoxyacetic Acid from Soil¹

ABSTRACT

2,4-D was incubated in the laboratory with different depths of Duffield silty clay loam, and its disappearance therefrom was determined by a cucumber root elongation test. The lag period before onset of decomposition and the time required for complete decomposition of 2,4-D increased with depth. The lag period varied from 14 days in the 0- to 6-inch sample to 42 days in the 18- to 21-inch sample. On retreatment with 2,4-D the differences among the depths were much smaller than with the original treatment.

Disappearance of 2,4-D and of 2,4,5-T under field conditions was studied in plots treated with these compounds at rates of 0.0, 0.2, 1.0, and 2.5 grams per square yard in 1949, and retreated with one gram per square yard in 1950. 2,4,5-T persisted more than 19 weeks; its persistence was not influenced by previous treatment. The effective concentration of 2,4-D was reduced more rapidly in soils in which it had decomposed previously. This compound persisted 5 and 6 weeks, respectively, in plots which had and had not been treated previously. A substance which stimulated root elongation of cucumber was produced during the decomposition of 2,4-D.

¹ Contribution from the Biological Laboratories, Chemical Corps, Camp Detrick, Frederick, Md.

² Soil Scientist; Graduate Research Assistant, Washington State College (formerly Agronomist, Camp Detrick); and Corporal, U. S. Army Reserve, respectively.