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

Ecological importance of soil bacterivores for ecosystem functions

BackgroundBacterivores, mostly represented by protists and nematodes, are a key component of soil biodiversity involved in soil fertility and plant productivity. In the current context of global change and soil biodiversity erosion, it becomes urgent to suitably recognize and quantify their ecological importance in ecosystem functioning.ScopeUsing meta-analysis tools, we aimed at providing a quantitative synthesis of the ecological importance of soil bacterivores on ecosystem functions. We also intended to produce an overview of the ecological factors that are expected to drive the magnitude of bacterivore effects on ecosystem functions.ConclusionsBacterivores in soil contributed significantly to numerous key ecosystem functions. We propose a new theoretical framework based on ecological stoichiometry stressing the role of C:N:P ratios in soil, microbial and plant biomass as important parameters driving bacterivore-effects on soil N and P availability for plants, immobilization of N and P in the bacterial biomass, and plant responses in nutrition and growth

Effect of a legume cover crop (Mucuna pruriens var. utilis) on soil carbon in an ultisol under maize cultivation in southern Benin

Long term fallow is no longer possible in densely populated tropical areas, but legume cover crops can help maintain soil fertility. Our work aimed to study changes in soil carbon in a sandy loam Ultisol in Benin, which involved a 12-year experiment on three maize cropping systems under manual tillage: traditional no-input cultivation (T), mineral fertilized cultivation (NPK), and association with Mucuna pruriens (M). The origin of soil carbon was also determined through the natural abundance of soil and biomass C-13. In T, NPK and M changes in soil carbon at 0-40 cm were -0.2, +0.2 and +1.3 t C ha(-1) yr(-1), with residue carbon amounting to 3.5, 6.4 and 10.0 t C ha(-1) yr(-1), respectively. After 12 years of experimentation, carbon originating from maize in litter-plus-soil (0-40 cm) represented less than 4% of both total carbon and overall maize residue carbon. In contrast, carbon originating from mucuna in litter-plus-soil represented more than 50% of both total carbon and overall mucuna residue carbon in M, possibly due to accelerated mineralization of native soil carbon (priming effect) and slow mulch decomposition. Carbon originating from weeds in litter-plus-soil represented c. 10% of both total carbon and overall weed residue carbon in T and NPK. Thus mucuna mulch was very effective in promoting carbon sequestration in the soil studied

Earthworm management in tropical agroecosystems

In agrosystem field experiments, earthworm inoculation did not impede depletion of soil organic stocks in most cases, in spite of increased carbon inputs through enhanced primary production. Slight evidence of soil organic matter (SOM) protection was found in poorly structured soil, such as a yam plot in Ivory Coast (soil sieved before experimentation), and a pasture plot on Martinique. Aggregation inherited from past earthworm activities probably maintains SOM protection after earthworms have disappeared ; longer term experiments are necessary to observe C dynamics after the disappearance of inherited earthworm structures. In two experiments with maize in Ivory Coast and Peru, the activity of earthworms led to a small increase in the incorporation of organic matter from surface mulch in the SOM. Most of the C incorporated into the SOM originated from root material, and earthworm activities only slightly modified this pattern. Earthworm activity had significant effects on the distribution of C among particle size fractions. The general trend was a depletion of large (greater than 50 micrometers) particles and an accumulation of small (less than 2 micrometers) particles. Nutrient depletion in low-input cropping systems was not impeded by earthworm activities ; at Yurimaguas, some signs of a better conservation of K were noted after 3 years in the traditional rotation. (Résumé d'auteur

Effects of earthworms on soil organic matter and nutrient dynamics at a landscape scale over decades

International audienceThis chapter synthesizes information on the effects of earthworms on soil systems at scales longer than 1 year, and earthworm behavior that may affect these processes is detaile