Determination of the origin of the different growing abilities of two populations of Millsonia anomala (Omodeo and Vaillaud), a tropical geophageous earthworm

Des individus de l'espèce de ver endogé géophage #Millsonia anomala$ provenant d'une métapopulation de savane ne peuvent pas grossir lorsqu'ils sont introduits dans un sol de forêt alors que les individus de forêt peuvent croître dans les deux milieux. Des élevages de vers en laboratoire dans les deux types de sol ont été menés pour expliquer les différences observées. La qualité de la matière organique ainsi que les microorganismes présents dans le sol peuvent être responsables du taux de croissance des vers. L'hypothèse la plus probable est que la capacité de digérer la matière organique du sol serait acquise dans les premiers moments de la vie quand pour la première fois des populations de microorganiqmes du sol envahissent le tube digestif du ver et que ces microorganismes demeurent dans l'intestin du ver tout le reste de sa vie. (Résumé d'auteur

Effects of a tropical geophagous earthworm, Millsonia anomala, on some soil characteristics, on maize-residue decomposition and on maize production in Ivory Coast

Maize was grown under field conditions in the presence and absence of the tropical endogenic earthworm #Millsonia anomala (Omodeo and Vaillaud, 1967) in soil of a secondary forest of central Ivory Coast. Experimental units were isolated by PVC sheets to limit earthworm movements. Decomposition and redistribution of nitrogen from maize crop residues incorporated in the soil were monitored using 15N-labelled residues. The density of #M. anomala decreased from 50 to 15.9/m2 during the cultivation period (90 days). Activity of #M. anomala$significantly modified the structure of the soil by increasing the proportion of large aggregates (over 2 mm in diameter). Maize production was increased by 12$. Nonetheless, total nitrogen exportation was not significantly different between the two treatments. Furthermore, N from the organic residues left after the cultivation period was less easily assimilated by plants in treatments with earthworms. (Résumé d'auteur

Earthworm management in tropical agroecosystems

The effects of earthworms on soil structure and the resulting physical properties in natural or cultivated systems were studied in different sites of the Macrofauna project. Four main results were obtained from these experiments : (1) In kaolinitic soils (Lamto, Manaus, Yurimaguas), irrespective of clay content, andogeic earthworms play a major role in soil structure formation and maintenance, while in smectitic soils (Martinique), the effects of earthworms on soil structure formation and maintenance are not as clear. In the Vertisols of Martinique, the effect of roots and organic materials seem predominant in soil structure development and earthworms play a secondary role. (2) Endogeic earthworm species have different effects on soil properties. Large earthworms such as #Pontoscolex corethrurus or #Millsonia anomala egest large and compact casts. They increase the proportion of large aggregates in soil and the bulk density ; they are called "compacting species". Conversely, small earthworm species such as eudrilid worms feed at least partly on large compact casts and egest smaller and fragile aggregates. They decrease the proportion of large aggregates in soil and the bulk density ; they are called "decompacting species". The effects of "compacting species" on soil structure formation seem to be linked to the presence of organic residues at the soil surface. In agroecosystems of Yurimaguas (Peru), the intense activity of #P. corethrurus$ and the coalescence of surface casts lead to the formation of a compact surfacecrust with impedes water infiltration in the absence of organic residues, but a favourable macroaggregate structure develops in the presence of organic residues and leguminous mulch. (3) The introduction of earthworms in agroecosystems changes soil physical properties and especially water retention and infiltration... (D'après résumé d'auteur

The Life Cycle of Toxoplasma gondii in the Natural Environment

Chapitre 1International audienc

Effects of a tropical geophageous earthworm, M. anomala (Megascolecidae), on soil characteristics and production of a yam crop in Ivory Coast

This study was an attempt to validate under field conditions some results of the effects of earthworms on soil organic matter dynamics, obtained under confined circumstances, and on enhanced plant production. Yams were grown in the presence or absence of the tropical endogeic earthworm #Millsonia anomala (Omodeo and Vaillaud, 1967) for 3 years. Field experiments were conducted in the middle of Ivory Coast using experimental plots isolated by PVC sheets. At the beginning of the cropping sequence, earthworm biomass was adjusted to 25 g/m2. The presence of worms affected soil structure by increasing the proportion of large aggregates that were mainly ageing casts. In the presence of #M. anomala, soil C mineralisation decreased by 5% after 3 y, but distribution of C among granulometric fractions of soil organic matter was the same in the two treatments. Yam tuber production was increased by 20%, 0% and 53% at the first, second and third crop, respectively, in presence of #M. anomalia$. The earthworms affected both soil and plants but the origin of these effects were unclear. (Résumé d'auteur

Determination of the origin of the different growing abilities of two populations of Millsonia anomala (Omodeo and Vaillaud), a tropical geophageous earthworm

Des individus de l'espèce de ver endogé géophage #Millsonia anomala$ provenant d'une métapopulation de savane ne peuvent pas grossir lorsqu'ils sont introduits dans un sol de forêt alors que les individus de forêt peuvent croître dans les deux milieux. Des élevages de vers en laboratoire dans les deux types de sol ont été menés pour expliquer les différences observées. La qualité de la matière organique ainsi que les microorganismes présents dans le sol peuvent être responsables du taux de croissance des vers. L'hypothèse la plus probable est que la capacité de digérer la matière organique du sol serait acquise dans les premiers moments de la vie quand pour la première fois des populations de microorganiqmes du sol envahissent le tube digestif du ver et que ces microorganismes demeurent dans l'intestin du ver tout le reste de sa vie. (Résumé d'auteur