2,4-D degradation and 2,4-D degrading microorganisms in soils

In laboratory studies on Cecil loamy sand and Webster sandy clay loam, the authors examined the influence of soil-water tension and soil temperature on super(14)C-2,4-D degradation and the formation of nonextractable super(14)C-residues, correlated the degradation rate with the growth rate of 2,4-D degrading microorganisms. super(14)C-2,4-D rapidly mineralized in the two soils maintained at 0.1 and 0.33 bar of soil-water tension. Because the total amounts of metabolites in the solvent extracts never exceeded 5% of the total super(14)C activity, the disappearance rate of extractable super(14)C essentially represented the disappearance rate of extractable super(14)C-2,4-D. Extractable super(14)C in the super(14)C-2,4-D treated soils maintained at 1 bar and below disappeared rapidly, and at the same time nonextractable super(14)C rapidly formed, whereas extractable super(14)C in soils maintained at 15 bars disappeared at much slower rates, and the formation of nonextractable super(14)C was also slower. After 14 d of slow disappearance, however, extractable super(14)C in the Cecil soil held at 15 bars started disappearing at a constant rate of 3.6% of applied super(14)C per day. The disappearance rates in soils incubated at 35 degree C were generally smaller than those incubated at 25 degree C.