In the field, surface applied cyanazine 2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] did not move below 5 cm in a Monona silty clay loam (Typic Hapludoll) which received 20 cm of water over a 54-day period. In hand-packed soil columns in the laboratory, surface-applied diuron and cyanazine penetrated to depths of 10 and 20 cm, respectively, when leached over a comparable time period and with amounts of water similar to that used in the field. Soil thin layer chromatography and adsorption isotherm studies showed that diuron was adsorbed more strongly than was cyanazine. In general, both compounds were degraded more rapidly at the higher temperatures when incubated at 5, 20, 35, and 50 C over a 20-week period. Degradation was slowest at 5 C in a Valentine loamy fine sand (Typic Ustipsamment). Diuron appeared to break down most readily at 35 C. Cyanazine was usually decomposed by the 10th week at 5 C and the 5th week at higher temperatures.

Concentrations of 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 2,4,5‐trichlorophenoxyacetic acid (2,4,5‐T) in soils and leachates from field mini‐lysimeters were monitored for up to 28 months to characterize the patterns of herbicide mobility in soils under climatic conditions of the Palouse region of the Pacific Northwest. The lysimeters contained soils from Washington, Wyoming, or Mississippi, and were treated with 1,120 or 5,600 kg/ha of a 1:1 mixture of 2,4‐D and 2,4,5‐T n‐butyl esters in 1976, 1977, or 1978. The winter of 1976–1977 was mild and relatively dry, and little leachate could be collected. However, subsequent winters were wet and the soil columns were saturated by the following springs. Less than 1 ppm of 2,4‐D was found in leachates from Washington and Wyoming soils receiving the herbicide application in 1976 or 1977, though over 30 ppm was found in leachates from Washington soil treated in 1978. Over 10 ppm of 2,4‐D could be found in leachates from the acidic Mississippi soil receiving the high rate of herbicide application in 1977 or 1978. Concentrations of 2,4,5‐T in the same leachates were higher for the Washington and Wyoming soils, but lower (than corresponding concentrations of 2,4‐D) for the Mississippi soil. In all cases, 96–99% of the undegraded herbicides in the lysimeters remained in the 0‐ to 10‐cm soil layer after two to three winters, and only 0.14–1.65% of the 2,4‐D and 0.33–3.7% of the 2,4,5‐T remaining in the lysimeters were present in the 10‐ to 30‐cm depths. Mobility characterization by soil thin‐layer chromatography showed that the ester form of both herbicides was relatively immobile, the acid form was less mobile in the Mississippi soil than in the Washington and Wyoming soils, and 2,4‐D was slightly more mobile than 2,4,5‐T under corresponding conditions.

The patterns of dissipation of 2,4‐D (2,4‐dichlorophenoxyacetic acid) and 2,4,5‐T (2,4,5‐trichlorophenoxyacetic acid) n‐butyl esters, applied in 1:1 mixtures at 560 or 2,800 kg/ha of each herbicide to soils in field mini‐lysimeters, were monitored periodically from December 1976 to April 1979. The lysimeters were located in Pullman, Wash., and packed with soils from Washington, Wyoming, and Mississippi. Both 2,4‐D and 2,4,5‐T were dissipated to < 1% of the initial concentration at the lower application rate in the Washington and Wyoming soils; however, at the higher application rate, dissipation of 2,4‐D was greatly impeded and dissipation of 2,4,5‐T was negligible in these soils. Dissipation of both herbicides in the acidic Mississippi soil was extremely slow even at the lower application rate. Surface soil pH was lowered following herbicide application. Some downward movement of both herbicides from the 0‐ to 5‐cm to the 5‐ to 10‐cm soil layer was evident. By the end of the experimental period, revegetation had begun only on the Washington and Wyoming soils treated at the lower application rate.