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

The presence of deep-burrowing earthworms can affect soil structure and in®ltration, therefore in ̄uencing agricultural productivity. We investigated the effects of deep-burrowing earthworm species on soil structure at the surface of chisel-plowed or ridge-tilled cropping systems in Pike County, OH, planted to corn (Zea mays L.). Earthworm populations were experimentally manipulated in ®eld enclosures by adding predominantly deep-burrowing Lumbricus terrestris L., or leaving enclosures unmodi®ed in each tillage system. In 1995, after 2 years of bi-annual additions, we measured surface residue cover, dry sieved aggregates (DSA)and water-stable aggregates (WSA), and carbon and nitrogen concentration of aggregates by size class, in each treatment combination. Also, in 1998, we used tension in®ltrometry to examine crusting effects at the soil surface among earthworm treatments in the chisel-plow treatment. Earthworm additions yielded increased density and biomass of L. terrestris than ambient controls, and to a greater extent in the ridged corn±soybean (Glycine max L. Mess.)± wheat (Triticum aestivum L.) (CSW) than corn±soybean (CS) rotation. Percentage residue cover in CS cropping decreased with earthworm additions. Earthworm additions decreased the geometric mean weight diameter (GMWD) of DSA and WSA in chisel-plow treatment compared to no additions. Earthworm additions in ̄uenced 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. # 2000 Elsevier Science B.V. All rights reserved.