SHORT-TERM AND LONG-TERM EFFECTS OF THE ENDOGEIC EARTHWORM MILLSONIA-ANIMALA (OMODEO) (MEGASCOLECIDAE, OLIGOCHAETA) OF TROPICAL SAVANNAS, ON SOIL ORGANIC-MATTER

This study aimed to establish the effects of Millsonia anomala, a tropical geophagous earthworm common in the humid savannas of Lamto (Ivory Coast), on soil organic matter dynamics over different time scales under laboratory conditions. The texture of casts produced by the worms fed on a shrub savanna soil was not significantly different from that of the soil, which showed that M. anomala ingested soil particles without selection. Physical fractionation of soil organic matter showed that the coarse organic fraction (250-2000-mu-m) was depleted by 25-30% in fresh casts compared to the control noningested soil; this was mainly due to a fragmentation of coarse organic debris. Incubation of casts and a 2-mm sieved control soil under laboratory conditions for more than 1 year showed that the C mineralisation rate was almost four times lower in the casts (3% year-1) than in the control soil (11% year-1). We therefore concluded that on a long time scale M. anomala populations may significantly reduce the decomposition rate of soil organic matter in Lamto savannas.