| This research employed a hierarchical approach which integrated organismal, population, and community measurements to assess ecosystem-level fluxes of nitrogen through earthworm communities dominated by Lumbricus terrestris L. and Aporrectodea tuberculata (Eisen) in corn agroecosystems. After five years of fertilizer treatments, total earthworm biomass was greater in plots receiving animal manure amendments, than in inorganically-fertilized plots, although earthworm biomass declined by one-half between the first and second year of the study probably due to unfavorable climatic conditions. Although the growth of A. tuberculata was not affected by the fertilizer treatments, L. terrestris grew significantly faster in manure-amended plots than inorganically-fertilized plots when soil temperatures were greater than 10{dollar}spcirc{dollar}C. Earthworm secondary production was calculated using both the instantaneous growth rate and size frequency methods which integrate field biomass estimates and field growth rates. Nitrogen flux through the earthworm community was estimated by combining earthworm secondary production estimates with species-specific excretion rates as determined by {dollar}sp{lcub}15{rcub}{dollar}N analysis. The annual nitrogen flux through earthworms, which was greatest in the manure amended plots, ranged from 23.3-86.6 kg N {dollar}rm hasp{lcub}-1{rcub} ysp{lcub}-1{rcub}{dollar} during the study. The flux of nitrogen through earthworm biomass was equivalent to 34-47% and 15-27% of plant requirements during 1994-95 and 1995-96, respectively. The annual consumption of organic matter by earthworms, based on species-specific efficiencies of nitrogen assimilation, was estimated to range from 8.5-14.3 Mg organic matter {dollar}rm hasp{lcub}-1{rcub} ysp{lcub}-1{rcub}{dollar} (which was equivalent to about 10% annually of the total organic matter). The forms and transformations of nitrogen released from dead earthworm tissues into the soil, microbial biomass and plant nitrogen pools was determined using {dollar}sp{lcub}15{rcub}{dollar}N tracers. Nitrogen from dead earthworm tissue cycled rapidly through microbial biomass, and about 70% of the nitrogen that was released from dead earthworm biomass was incorporated into plant shoot biomass within 16 days. A computer model was developed to simulate the flux of nitrogen through earthworms. It was concluded that the influence of earthworms on nitrogen cycling and organic matter processing in corn agroecosystems was substantial, and that nitrogen flux through earthworm communities was influenced significantly by agricultural management practices. |
