Earthworm casts deposited on the surface of the soil are usually more water stable than aggregates in the bulk soil. Research has demonstrated that aggregate stability varies among species of earthworms, soil texture, age of casts, and food source. We examined the effects of freezing and thawing on the water stability of intact (undisturbed) earthworm casts in different soils, under different moisture contents and various freezing regimes. We compared casts produced by Lumbricus terrestris and Diplocardia spps. Treatments consisted of (1) moist casts placed immediately in petri dishes and sealed with parafilm, (2) air dried casts that were then frozen for 48 hours, (3) freshly collected casts that were immediately placed in the freezer for 48 hours followed by air drying, and (4) bulk soil. All samples were wet seived for 5 minutes through 4, 2, 1, .5, and .25 mm seives. Generally casts produced by both species of earthworms were more stable than the bulk soil. However, stability was reduced when wet casts were frozen and then air dried. Under these conditions casts were less stable than the bulk soil. Casts produced when the worms were fed plant residues were more stable than those produced when the worms fed on mineral soil. L. terrestris casts appear to be more water stable than those produced by Diplocaridia spp. Additional studies on the effects of freezing and thawing on the stability of earthworm casts will be discussed.

Dr. Edwin C. Berry
USDA, ARS
National Soil Tilth Laboratory
2150 Pammel Drive
Ames, Iowa  50011
Phone: (515) 294-9604
Fax: (515) 294-8125
E-mail: berry@nstl.gov