Soil structure changes induced by the tropical earthworm Pontoscolex corethrurus and organic inputs in a Peruvian ultisol

Inoculation of Pontoscolex corethrurus (Glossoscolecidne, Oligochaeta) in a Peruvian ultisol under several treatments (without or with organic input) has been previously shown to increase macroaggregation and bulk density and to decrease water infiltration and soil moisture. In the present study, we used image analysis of thin sections of soil to understand the impact of e arthworm on the structure of the upper layer of the soil. Morphological ana lysis allowed to quantify the abundance of casts, soil compactness, pore mo rphology and connections between different pore classes. This approach was applied to experiments carried out at Yurimaguas (Peru), in four plots. Two of them had been inoculated with Pontoscolex corethrurus. In each case, on e control plot was conducted without organic input, the other with crop res idues and legume green manure. Morphological parameters were measured in fo urteen horizontal sections within the first 3 cm. They showed compaction of soil surface due to cast coalescence in plots with earthworms but without organic input and illustrated the typical crumb structure induced by earthw orms in plots with organic input. (C) 2000 Editions scientifiques et medica les Elsevier SAS.