Summary
Mineral N concentrations ranged from 133.1 to 167.8 μg g-1 dry soil in fresh casts of the endogeic earthworm Pontoscolex corethrurus fed on an Amazonian Ultisol; this was approximately five times the concentration in non-ingested soil. Most of this N was in the form of NH sup+inf4 . N also accumulated in microbial biomass, which increased from a control value of 10.5–11.3 to 67.5–74.1 μg g-1 in fresh casts. During a 16-day incubation, part of the NH sup+inf4 -N was nitrified and/or transferred to the microbial biomass. Total labile N (i.e., mineral+biomas N) decreased sharply at first (ca. 50% in the first 12 h), and then more slowly. The exact fate of this N (microbial metabolites, denitrification, or volatilization) is not known. After 16 days, the overall N content of the casts was still 28% higher than that of the control soil. Incubation of the soil before ingestion by the earthworms significantly increased the production of NH sup+inf4 in casts. We calculate that in a humid tropical pasture, 50–100 kg mineral N may be produced annually in earthworm casts. Part of this N may be conserved in the compact structure of the cast where the cast is not in close contact with plant roots.
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Lavelle, P., Melendez, G., Pashanasi, B. et al. Nitrogen mineralization and reorganization in casts of the geophagous tropical earthworm Pontoscolex corethrurus (Glossoscolecidae). Biol Fertil Soils 14, 49–53 (1992). https://doi.org/10.1007/BF00336302
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DOI: https://doi.org/10.1007/BF00336302