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 temperature (4−32 °C) and moisture content (7−13%) conditions were assayed. Dissipation of both herbicides in soil A for treatment T2 (25 °C and 10% of moisture content) was significantly different in the three different incubation systems assayed. In the case of soil B, with lower organic matter content, the obtained half-lives for treatment T2 were statistically indistinguishable in all the incubation systems, with the exception of the flask incubation of terbutryn. Incubation in packed cores generally yielded longer half-lives than flask incubations in all the other treatments for both soils and both compounds. Differences among incubation systems were greater with terbutryn than with chlorotoluron, which has a lower sorption coefficient.