PHOTODEGRADATION OF MECOPROP AND DICHLORPROP ON DRY, MOIST AND AMENDED SOIL SURFACES EXPOSED TO SUNLIGHT

The effects of environmental conditions on the photodecomposition of t wo phenoxy-alkanoic acid herbicides were investigated on different soi l surfaces conditions under sunlight exposition. A technique has been developed to study this process on moist nonsterile soil surfaces. A s low rate of disappeareance occurs in the three soils exposed to sunlig ht in absence of water. Photolysis of these herbicides is controlled b y soil texture and its adsorption capacity. The organic matter does no t have a sensitizing effect on the photodecomposition of these herbici des on dry soil surfaces. On nonsterile moist soil surfaces exposed to sunlight, the photolytic process prevails in the two first days of ex posure and the transformation kinetics fits the Hoerl function better than the first-order exponential equation. (C) 1998 Elsevier Science L td. All rights reserved.