Clortoluron dissipation in clay soil under different tillage systems.

In order to evaluate the effect of simplified tillage systems on herbicide dissipation, chlortoluron (CHLO) residues were monitored in the soil, in a long-term experiment. The field trial was located at a flat site of central Italy (Pisa), on a day soil, where three tillage systems -ploughing 25-30 cm deep (CT), disk harrowing 7-12 cm deep (RT) and no-tillage (NT)- have been applied since 1986. Three soil layers (0-5 cm, 5-10 cm and 10-30 cm) were monitored during a period of 90 days: 1; 7; 15; 30 and 90 days after herbicide application. The highest molecule concentration (444 ppb) was recorded in the topsoil, 15 days after application due to the appreciable rainfall events that washefd off CHLO from the canopy to the topsoil. CHLO residues were often lower under RT and NT as compared to CT. The molecules dissipation from the peak time to the end of the observation period was more rapid under NT conditions.