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

L'importance agricole des termitières épigées dans le nord du Cameroun (l'exemple des nids de Macrotermes subhyalinus et d'Odontotermes magdalenae)

Cette étude vise à décrire les caractéristiques agropédologiques des nids de M. subhyalinus et d'O. magdalenae et à déterminer leur importance dans deux agrosystèmes du nord du Cameroun. Elle montre que les propriétés pédologiques des nids font de ces stations un élément indépendant du découpage du parcellaire et de la conduite des itinéraires techniques. Dans les sols ferrugineux de piémont, les nids de Macrotermes génèrent de véritables îlots de fertilité desquels sont dégagées des productions substantielles en céréale. En redistribuant des argiles 2/1 en surface du sol, ils augmentent la CEC et les teneurs en cations échangeables, tout en favorisant la structuration des horizons superficiels. Dans les vertisols, les nids d'Odontotermes détruits se singularisent par une forte macroporosité qui leurs confère un comportement hydrique et mécanique spécifique. L'hétérogénéité ainsi créée est valorisée pour réduire la durée des pépinières de muskuwaari et étaler les chantiers de repiquage.This work aims to describe the agropedologic characteristics of the mounds built by M. subhyalinus and O. magdalenae and to specify their role in two farming systems of the north of Cameroon. It shows that the singular pedological properties of the nests put these stations as an area independent of the field pattern and the crop managment. On an arenitic alfisol, the mounds of Macrotermes create true islands of fertility from which substantial productions of cereals are obtained. By redistribuiting 2/1 clays on the soil surface, they increase the CEC and the contents of exchangeable cations, while promoting structuring processes. On a vertisol, the mounds of Odontotermes, after their pulling-down, are made conspicuous by a strong macroporosity which confer theni specific water retention and particular mechanical behavior. Heterogeneity thus created s used to reduce the time required for seedbeds of muskuwaari and to lenghten the operations of the transplanting of sorghum.PARIS12-CRETEIL BU Multidisc. (940282102) / SudocSudocFranceF

De la caractérisation du milieu naturel à l'étude des pratiques paysannes : les éléments d'une synthèse délicate

International audienceDurant les deux dernières décennies, la région de Mouda, dans le nord du Cameroun, a fait l'objet de nombreuses études concernant la dynamique du milieu naturel. Dans un terroir de cette région, la présente étude se propose de caractériser les usages locaux concernant l'exploitation des ressources ligneuses et des terres. S'appuyant sur les conclusions des travaux scientifiques antérieurs, cette caractérisation permet de s'interroger sur les risques environnementaux générés par les principales activités anthropiques. L'absence de connexion entre les réflexions portant, d'une part, sur la dégradation des ressources naturelles et, d'autre part, sur la caractérisation des pratiques et des activités anthropiques a jusqu'ici empêché d'appréhender précisément l'étendue et la gravité des processus de dégradation à l'échelle du terroir. (Résumé d'auteur

Prediction of the contact area of agricultural traction tyres on firm soil

International audienceEquations were developed to enable reliable calculations to be made of the contact area for a wide range of traction tyres from independent easily accessible variables taken on firm ground. Given that when tyre size TS (section width [m] × outer diameter of tyre [m]), increases the specific contact area, As (ratio of the contact area to the tyre volume), decreases and tyre stiffness increases, it is worth taking into account tyre intrinsic properties by studying the impact of external constraints such as load and inflation pressure on the contact area. Based on a wide range of measurements (64, from a total of 28 tyres used on 12 grassland and open ground sites), three classes will be proposed for estimation of the contact area on firm agricultural soil: i) small tyres with TS < 0.6, ii) medium tyres with 0.6 ≤ TS < 1.2, and iii) large tyres with TS ≥ 1.2. When considering not only TS but also load and inflation pressure as explainable variables, an increase in R2 by 5% was observed. In addition, after taking into account intrinsic properties of the tyre, a new tyre classification has been proposed leading to an additional increase of R2 by about 2%. Compatibilities with algorithms developed by other authors are discussed

TROPHY : Un outil d’évaluation des risques de contamination des eaux souterraines et superficielles par les produits phytosanitaires en milieu volcanique antillais

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Thermal degradation of pesticide active substances: Prioritisation list

This study aims at estimating which pesticide active substances (ASs) are the best candidates to study potential further degradation of the AS above 120°C. To achieve this, a prioritisation list was built following five consecutive criteria. This first includes substances that are anthropogenic, have a carbon backbone structure, are authorized in the European Union, and have a defined maximum residue limit (MRL). Then, substances were selected according to their physicochemical and structural properties, MRL in main food commodities, standard price and degradation in hydrolysis studies below 120°C. The results showed that out of the initial 1 478 substances reported in the European pesticide database, 24 ASs were selected as the best candidates to test the assumption of degradation above 120°C. This prioritisation list could be useful for future research studies to build their own list and save time in selecting suitable candidates according to their criteria

TROPHY : Un outil d’évaluation des risques de contamination des eaux souterraines et superficielles par les produits phytosanitaires en milieu volcanique antillais

International audienc