Abstract: Diuron, simazine, and terbacil were applied in field plots annually from 1981 to 1995. Soil was sampled at selected times after herbicide application in 1993, 1994, and 1995 to determine herbicide residue changes with time and soil depth. Diuron residues were found mainly in the upper 20 cm of soil; residue concentration decreased exponentially with time. Less than 1% of the initial concentration after application in summer was present the following spring. Terbacil residues were found in soil below the upper 20 cm. Terbacil degraded more slowly than diuron, and residues in spring were less than 30% the level of the previous summer. Simazine plus hydroxysimazine soil residues were present in all depths to 100 cm and were higher than diuron or terbacil at these depths. Simazine plus hydroxysimazine residues in spring were nearly 40% the level of the previous summer. With all three herbicides, soil residues were greatest in the upper 20 cm of soil during 2 to 3 wk following application. Data confirmed that diuron did not leach, whereas simazine can migrate through the soil. Terbacil migrated intermediately in depth relative to diuron and simazine. After 15 annual applications, herbicide residues were present but were not accumulating.
Nomenclature: Diuron, N′-(3,4-dichlorophenyl)-N,N-dimethylurea; simazine, 6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine; desethylsimazine, 2-chloro-4-(ethylamino)-6-amino-s-triazine; di-desethylsimazine, 2-chloro-4,6-diamino-s-triazine; hydroxysimazine, 2-hydroxy-4,6-bis(ethyl-amino)-s-triazine; terbacil, 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione.
Additional index words: Herbicide movement.
Abbreviations: DAT, days after herbicide treatment; GC-MS, gas chromatography–mass spectrometry; HPLC-PDA, high-performance liquid chromatography with photodiode array detector; MS, mass spectrometry; ODS, octadecyl silane; SFE, supercritical fluid extraction.