A 200-l/ha aqueous emulsion containing 2 kg/ha of formulated trifluralin (Treflan EC) was sprayed on three .01-ha Congaree sl plots. The trifluralin was incorporated by hand raking. The trifluralin content of the top meter of soil and underlying groundwater was monitored for 1024 days. Rainfall during this period was 420 cm.
After placement, trifluralin seemed to remain within the top 20-cm soil layer, while its concentration decreased nonlinearly with time. The herbicide disappeared from soil in two episodes, clearly delineated by a semilog plot: a relatively rapid (Kinitial = .0365), relatively brief (∼1 mo) episode; and a relatively slow (Ksteady state≤.0015), long (99 percent loss ≃ 72 mo) episode. Half-lives of these episodes were 19 days (initial) and about 450 days (steady state).
Complementary sorption and movement in soil column studies supplied additional data for an attempt to characterize trifluralin dissipation in the field.
Soil may be a greater repository of trace amounts of pesticides than hitherto suspected.
Two-stage, or multistage, first-order kinetics may provide a more suitable model for predicting residue dissipation than the simple first-order kinetics model.