The objectives of this study were to determine if burrows produced by two species of earthworms (Aporrectodea tuberculata and Lumbricus rubellus) found in continuous corn (Zea mays L.) in Minnesota altered the infiltration rate and depth distribution of surface applied water. Each species was introduced (212 m−2) to in situ cylinders in plots initially void of worms that had been subjected to tillage with and without residue or no‐till with and without residue for 5 yr. Burrows produced by both species of worms during a 46‐d period increased average infiltration rates of 30 mm of water relative to controls after 46 d. Surface residues more than doubled the number of burrows open to the surface relative to incorporated residues (48 vs. 15 for L. rubellus, 37 vs. 15 for A. tuberculata). Cocoon production, an indicator of potential survivability, was present for both species in the no‐till‐surface residue treatment and for A. tuberculata also in the till‐incorporated residue treatment. Bromide (Br‐) tracer and mass balance for Br‐ in all treatments showed infiltration and Br‐ movement in the upper 5 cm of the profile was fastest in tillage treatments with worms and residues and that Br‐ movement beyond 19 cm was greatest for the no‐till treatments with worms and residues. Pore continuity and survival potential for worms in the no‐till‐residue treatment suggest that this treatment might increase populations of worms in cropland while altering the hydraulic status and erosion susceptibility of soils in the north central USA.

Viable bacteria were found to coexist with developing embryos in egg capsules (cocoons) of the earthworm Eiseniafetida. Earthworms were reared under standardized conditions, and bacterial densities were measured in distinct batches of cocoons collected weekly for 10 weeks. Cocoons weighing 12 mg contained a mean viable bacterial population of approximately 108 CFU/g of cocoons. No difference was found in viable counts obtained from cocoons incubated at 15°C and cocoons incubated at 24°C. Viable bacterial numbers increased with cocoon age, while acridine orange direct counts of microbial cells were stable at approximately 109 cells per g of cocoons. Bacteria isolated from cocoons were used to develop antisera in rabbits for the production of strain-specific fluorescent antibodies. Fluorescent antibody and selective plating techniques were used to monitor populations of these bacteria in earthworm bedding and to determine whether cocoons acquire bacteria from the environment in which they are formed. Cocoon isolates were readily recovered from cocoons formed in inoculated bedding at densities of 108 CFU/g of cocoons. Bradyrhizobiumjaponicum USDA 110 and UMR 161 added to bedding were also recovered from cocoons, but at lower densities than cocoon isolates. Escherichia coli K-12(pJP4) inoculum was recovered from bedding but not from cocoons. The bacterial complement ofEiseniafetida cocoons is affected by inoculation of selected bacterial isolates in the worm growth environment.

Earthworm (Lumbricus rubellus Hoffmeister) activity in the field has been implicated in increased rates of residue turnover, surface soil stabilization, and increased infiltration rates due to macroporous flow. A growth‐chamber study was conducted to evaluate some of the field variables associated with L. rubellus activity and tillage systems. Polyethylene buckets packed with sieved soil had either surface‐applied, incorporated, or no corn (Zea mays L.) residue, each with or without worms. Treatments were subjected to diurnal temperature and light sequences, and periodic additions of water were made over 60 d to maintain near‐optimum moisture conditions. Corn was grown in the cultures for an additional 30 d and was harvested before a small amount of concentrated Br solution was sprayed on the soil surface. Cultures were then subjected to simulated rainfall. Corn residue in the surface‐residue treatment with worms degraded 30% faster than in the no‐worm control. Plant growth and N content were not affected by the presence of worms. Burrows and casts formed under surface residue were greater in number and stability than in other worm/residue combinations. The surface‐residue treatment with worms reduced runoff and caused incoming water to bypass the surface soil matrix, moving small quantities of Br to significantly greater depths than in other treatments. Depth of peak Br concentration was greater in no‐residue treatments than in surface‐residue/worm or incorporated‐residue/worm or no‐worm treatments, indicating a substantial difference in the displacement of surface‐applied Br during rainfall. L. rubellus may alter the water balance of field soils while simultaneously hastening decomposition of the residue mat.

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