FACTORS AFFECTING PREFERENTIAL FLOW OF WATER AND ATRAZINE THROUGH EARTHWORM BURROWS UNDER CONTINUOUS NO-TILL CORN

Watershed studies have documented that summer storms produce less runoff from fields farmed with continuous no-tillage corn (Zea mays L.) than from the same soils when corn is produced with conventional tillage practices. The lack of tillage favors a continuous surface cover of crop residue and the persistence of earthworm burrows, which have been shown to be preferential flow paths for water and chemicals, especially during intense summer storms. We investigated factors affecting preferential water and chemical transport in burrows formed by the earthworm Lumbricus terrestris (L.) in the field using individual burrow samplers and in the laboratory using blocks of undisturbed soil subjected to simulated rainfall. Rainfall amount and intensity and antecedent soil moisture content affected the amount of water transmitted in earthworm burrows, with high intensity storms on relatively dry no-till soils producing the greatest amounts of preferential flow. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) transport was affected by the factors influencing the amount of preferential flow and by the time of storms relative to the time of herbicide application. Atrazine movement in earthworm burrows was greatest when high-intensity rainfall occurred shortly after application. Atrazine transport was reduced by a delay in rainfall and by low-intensity events prior to high intensity, percolate-producing events.