Herbicide dissipation and dynamics modelling in three different tillage systems

The half-lives (t50) of the herbicides metolachlor, terbuthylazine and isoproturon and the occurrence of desethyl-terbuthylazine and monomethyl-isoproturon were measured in soils managed with three different tillage systems (conventional tillage, ridge tillage and no tillage). The first-order dissipation model was well adapted to the field data. Under the trial conditions, characterised by silty soil, scarce permeability, and reduced rainfall, the tillage system did not substantially influence the dynamics of the herbicides; the t50 was reduced in no tillage only with metolachlor, the more volatile herbicide. The measured concentrations were then compared with those calculated with SoilFug, a fugacity-based mathematical model; the calculated values approximate the kinetics of both herbicides and metabolites with good precision.