COMPARISON OF WATER-MOVEMENT AND QUALITY IN EARTHWORM BURROWS AND PAN LYSIMETERS

Although a number of investigators have suggested that earthworm burrows can affect water movement and quality, Little attempt has been made to directly measure their effect in the field. Using individual samplers, we monitored flow in Lumbricus terrestris L. burrows for 11 mo in adjacent no-till and conventionally tilled watersheds used for the continuous production of corn (Zea mays L.). Tension-free pan lysimeters were used to assess the composition and amount of bulk subsurface how in each watershed and SrBr2.6H(2)O tracer was broadcast on a 25-m(2) area surrounding the samplers. In both watersheds the earthworm burrows functioned as preferential flow paths collecting more water, NO3-N, Br, NH4-N, and Sr than an equivalent area of soil overlying the pan lysimeters. Transport through the bulk soil was less in the tilled than in the no-till watershed, and the burrows in the tilled watershed were less effective flow paths than those in the no-till watershed, apparently due to disruption by tillage. Based on an estimated 1.6 million burrows (greater than or equal to 5-mm diam.) per hectare, the amount of water, NO3-N, Br, and Sr transported in these macropores was small, representing < 5% of the totals measured using pan lysimeters. Data from burrow samplers and pan lysimeters installed in five farmer-owned, no-till fields under different soils and production practices supported the results obtained in the no-till experimental watershed.