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

The presence of deep-burrowing earthworms can affect soil structure and infiltration, therefore influencing 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 field enclosures by adding predominantly deep-burrowing Lumbricus terrestris L., or leaving enclosures unmodified 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 infiltrometry 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 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.