Earthworm burrowing and feeding activity and the potential for atrazine transport by preferential flow

Soil columns with established earthworm burrow structures were subjected to 14 and 47 mm h−1 rainstorms to study the effects of Lumbricus terrestris L. burrowing and feeding activity on preferential atrazine transport in soil. Earthworm treatments for the soil columns were as follows: earthworms introduced 1 d prior to herbicide application, earthworms introduced 9 d after herbicide application and no earthworms added following herbicide application. Rainfall was applied at 9, 18, 29, 40 and 51 d following [U-ring-14C]atrazine applications onto crop residues at the soil surface. The concentration of radioactivity in leachate was greatest during the first rainfall simulation and decreased in the subsequent four simulated rainfall simulations. Preferential herbicide transport through earthworm burrows was observed during all rainfall simulations, but total atrazine and metabolites in leachate at the end of the five rainfall simulations were approximately 2-fold greater in the absence than in the presence of earthworms. Earthworm feeding activity reduced the potential for herbicide leaching by ingesting and transporting herbicide residues away from the soil surface and increasing the amount of non-extractable (non-leachable) herbicide residues in the soil.