ABSTRACT:
Twenty-three field sites in North Dakota, where highly erodibte soil is placed under permanent vegetation in the U.S. Conservation Reserve Program (CRP) from five to eight years, were surveyed for the presence or absence of earthworms. Soils were sampled to determine chemical and physical properties, and soil cores were collected to estimate earthworm populations. Earthworm species identified at 12 CRP sites were Aporrectodea tuberculata (Eisen), Aporrectodea trapezoids (Duges), Aporrectodea caliginosa (Savigny), Dendrobaena octaedra (Savigny), and Lumbricus rubellus (Hoffmeister). Sites with earthworms were associated with organic matter levels of greater than 2.5%. Sand content of the 11 sites without earthworms averaged 67% (±13), and the soil usually contained what appeared to be sharp shiny crystals or grains that might not be ideal for earthworm survival. Dendrobaena octaedra and Lumbricus rubellus were found at sites with the highest soil organic matter and nitrate-N levels plus low sand percent. Soil P, K, pH and EC levels were not related to the presence or absence of earthworms in these CRP sites. Total earthworm population estimates from five CRP sites averaged 6.3 million ha−1 (±4.7), with adults, juveniles, and cocoons at 0.6 (±0.4), 4.5 (±3.1), and 1.2 (±2.0) million ha−1, respectively. Earthworm populations along a 90-meter transect from the edge of the CRP field were similar when averaged over the five sites. An estimate of population at the other seven earthworm sites was not possible because environmental stress as earthworms tended to migrate only to areas in the field where taproot plant species were located. The presence of wetlands or tree habitat in these CRP fields could not be used as criteria for determining the presence of earthworms.
Footnotes
Edward J. Deibert is a professor and Rodney A. Utter is a research specialist with the Soil Science Department at North Dakota State University in Fargo, North Dakota.
- Copyright 2003 by the Soil and Water Conservation Society
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