Distribution and transport of atrazine as influenced by surface cultivation, earthworm population and rainfall pattern

Several laboratory studies were conducted to evaluate the effects of soil surface cultivation, earthworm ( L) population, and rainfall pattern on 14C-atrazine (2-chloro-4-ethylamino-6-isopropylanunos-triazine) leaching through intact soil cores. Soil cores (16 cm dia x 20 cm deep) were collected from a seven year no-till (NT) corn field. Earthworms (0, 4, or 8 core−1) were introduced into the cores. Half of the cores were cultivated (2.5 cm depth) and the rest of the cores were left uncultivated prior to 14C-atrazine treatment (2.74 mg core−1). Cores were subjected to a rainfall pattern in which a low intensity rain (16 mm of rain in 2.5 h) was followed 48 h later by a high intensity rain (27 mm of rain in 1.5 h). The saturated hydraulic conductivities (Ksat) of cores with 0, 4, and 8 worms core−1 were 0.8, 3.4, and 5.3 cm h−1, respectively. Increasing the number of earthworms in each core from 0 to 8 worms, increases the amount of atrazine (% of applied) leached through untitled cores from 8.5 to 13.5% and for tilled cores from 1.0 to 5.0%. Much more atrazine was leached through untitled soil cores than tilled cores at both low and high rainfall intensities. The results of thus study suggest that herbicide transport is dependent on a combination of rainfall parameters, soil macroporosity, and disruptive surface cultivation.