Diclofop-methyl dissipation in clay soil under different tillage systems in central Italy

In order to evaluate the effect of simplified tillage systems on herbicide dissipation, diclofop-methyl residues were monitored in different soil layers (0-5 cm, 5-10 cm and 10-30 cm) under three different tillage systems: ploughing 25-30 cm deep (PT), disk harrowing 7-12 cm deep (RT) and no-tillage (NT) in a long-term experiment started in 1990 and carried out on clay soil. Diclofop-methyl residue concentrations in the soil were 0.25 ppm at peak time in topsoil and at lower quantities in the deeper layers. Diclofop-methyl residues in the topsoil were often higher with PT as compared to RT and NT. The presence of diclofop-methyl increased suddenly in untilled plots after a heavy rainfall period. This occurred in the 5-10 cm soil layer 60 days after application, and in the 10-30 cm soil layer 90 days after application. These data suggest a more rapid diclofopmethyl displacement to ground water through macropores under NT conditions. (C) 1998 Elsevier Science B.V. All rights reserved.