USE OF EMPIRICAL EQUATIONS TO DESCRIBE DISSIPATION OF METRIBUZIN AND PENDIMETHALIN

Four equations were evaluated as predictors of the rate of herbicide d issipation in soil. A biexponential equation was superior to the first -order equation for metribuzin and pendimethalin dissipation under fiv e moisture levels and three temperatures in laboratory and field studi es. The Hoerl function, adapted in the course of this work, is also a good descriptor. The first-order equation predicts slower initial and more rapid later dissipation than actually occurs and these deficienci es are not shared by the biexponential or Hoerl equations. The first-o rder equation ignores small residues remaining late in the dissipation process. These residues are important from an environmental point of view and the Hoerl and biexponential equations are more capable of dea ling with them.