SMALL-SCALE AND LARGE-SCALE EFFECTS OF ENDOGENIC EARTHWORMS ON SOIL ORGANIC-MATTER DYNAMICS IN SOILS OF THE HUMID TROPICS

The effects of endogeic earthworms on the soil organic matter (SOM) dynamics of moist tropical soils are: (i) a sharp increase of mineralization during digestion; (ii) the presence in fresh casts of large amounts of mineral nutrients which are reorganized in microbial biomass at the scale of days to weeks depending on soil properties; (iii) a subsequent blocking of mineralization at the scale of months to years in the compact structure of ageing casts (i.e. older than 1-2 weeks). It is hypothesized that, at the larger scale of soil profile and years, activities of earthworms will result in an acceleration of SOM turnover and the accumulation of labile rather than passive organic matter.