Foraging by deep-burrowing earthworms degrades surface soil structure of afluventic Hapludoll in Ohio

The presence of deep-burrowing earthworms can affect soil structure and inf iltration, therefore influencing agricultural productivity. We investigated the effects of deep-burrowing earthworm species on soil structure at the s urface of chisel-plowed or ridge-tilled cropping systems in Pike County, OH , planted to corn (Zea mays L.). Earthworm populations were experimentally manipulated in field enclosures by adding predominantly deep-burrowing Lumb ricus terrestris L., or leaving enclosures unmodified in each tillage syste m. In 1995, after 2 years of hi-annual additions, we measured surface resid ue cover, dry sieved aggregates (DSA)- and water-stable aggregates (WSA), a nd carbon and nitrogen concentration of aggregates by size class, in each t reatment combination. Also, in 1998, we used tension infiltrometry to exami ne crusting effects at the soil surface among earthworm treatments in the c hisel-plow treatment. Earthworm additions yielded increased density and bio mass of L. terrestris than ambient controls, and to a greater extent in the ridged corn-soybean (Glycine max L. Mess.)wheat (Triticum aestivum L.) (CS W) than corn-soybean (CS) rotation. Percentage residue cover in CS cropping decreased with earthworm additions. Earthworm additions decreased the geom etric mean weight diameter (GMWD) of DSA and WSA in chisel-plow treatment c ompared to no additions. Earthworm additions influenced carbon-to-nitrogen (C/N) ratios for smaller DSA and WSA. Water-stable aggregate C/N decreased with size class. The overall effect of earthworm additions was an increase in deep-burrowing earthworms, a decrease in surface residue cover, and more pronounced crusting, which decreased mesopore conductivity. (C) 2000 Elsev ier Science B.V. All rights reserved.