Burrowing activity of the geophagous earthworm Pontoscolex corethrurus (Oligochaeta : Glossoscolecidae) in the presence of charcoal

In: Applied Soil Ecology, 2003, 23 (3), pp.267-271. The geophagous earthworm Pontoscolex corethrurus is frequently found in burnt tropical soils where charcoal plays an important role in soil fertility. We studied the burrowing activity of this species in two-dimensional (2D) microcosms with one half-filled with soil and the other with a 3:2 (w/w) mixture of charcoal and soil (CHAR + soil). We measured the volume of empty burrows and those filled with black or brown casts in both substrates, as well as the initial and final fresh weights of the worms. The correlation between brown cast production and both initial and final fresh weights of the worms, reinforced by the presence of feeding cavities in soil but not in CHAR + soil, suggests that P. corethrurus would ingest soil to obtain its nutrient requirements, in contrast to charcoal which was ingested for other purposes. We observed that at equal burrow volume created in the two substrates, P corethrurus produced smaller black casts than brown, suggesting that burrows were created in CHAR + soil mainly by pushing aside the particles of this lighter substrate. The observed transport of charcoal to soil points to the importance of P. corethrurus in the incorporation of charcoal particles into organic-poor soil.