Persistence and leaching of atrazine, alachlor, and cyanazine under no-tillage practices

Soil residues of atrazine, alachlor, and cyanazine were measured in no-till corn plots that had received annual herbicide applications from 1981–1985. Treatments were as paired combinations of herbicides at recommended rates. Three cores were collected from 3–4 replicated plots per treatment; sampling occurred late in 1983, then periodically during the growing season in 1984 and 1985. Persistence up to 6 weeks after herbicide application was in the order: atrazine > cyanazine > alachlor. Sampling after ca. 6 weeks gave the order atrazine > alachlor > cyanazine. Atrazine and alachlor were found to the lowest sampled depths in 1983 (1–1.5 m) and 1984 (0.4–0.5 m). Cyanazine was not detected below 0.3 m. In 1985, atrazine leached to ≥0.3–0.5 m by 40 days, but no subsoil residue was detected at 139 days. Alachlor and cyanazine had virtually disappeared by 40 days.