Phosphorus transformations in a ferralsol through ingestion by Pontoscolexcorethrurus, a geophagous earthworm

This paper analyses the transformations that result in increased inorganic phosphorus (Pi) content in a ferralsol after transit through the gut of the earthworm Pontoscolex corethrurus. Total, inorganic and organic P contents were measured in bulk samples of dry soil, incubated and non-ingested soil and surface casts, and in chemical extracts on samples previously separate d into three particle-size fractions (> 20, 2-20 and < 2 mu m). The total P content was the same in control, non-ingested soil and casts but remoisten ing and transit through the earthworm gut decreased organic P and increased inorganic P contents. Clay content in surface casts (19.7 %) was significa ntly higher than in the control soil (9.1 %). Phosphate content significant ly increased in the NaHCO3 extract from 3.17 in non-ingested soil to 5.04 m u g Pi.g(-1) soil in casts; the same trend was observed in NaOH extract wit h 27.4 in non-ingested soil and 45.8 mu g Pi.g(-1) soil in casts. Phosphate in casts was mostly concentrated in the finest fractions (0-2 mu m) with 8 3 % of extracted phosphate, opposed to 61 % in non-ingested soil. These cha nges resulted from a combination of selective ingestion of small particles and partial mineralisation of organic P (C) Elsevier, Paris.