INFLUENCE OF THE LABORATORY INCUBATION METHOD ON CHLOROTOLURON AND TERBUTRYN DEGRADATION IN SOIL

Degradation of the herbicides chlorotoluron and terbutryn was assayed using three different incubation systems: columns of undisturbed soil, columns packed with sieved soil, and flasks. Two different soils were employed, a sandy loam (A) and a loam soil (B), and different tempera ture (4-32 degrees C) and moisture content (7-13%) conditions were ass ayed. Dissipation of both herbicides in soil A for treatment T2 (25 de grees C and 10% of moisture content) was significantly different in th e three different incubation systems assayed. In the case of soil B, w ith lower organic matter content, the obtained half-lives for treatmen t T2 were statistically indistinguishable in all the incubation system s, with the exception of the flask incubation of terbutryn. Incubation in packed cores generally yielded longer half-lives than flask incuba tions in all the other treatments for both soils and both compounds. D ifferences among incubation systems were greater with terbutryn than w ith chlorotoluron, which has a lower sorption coefficient.