In tropical areas, where crop production is limited by low soil quality, the development of techniques improving soil fertility without damage to the environment is a priority. In French Guiana, we used subsistance farmer plots on poor acidic soils to test the effect of different organic amendments, bitter manioc peel (M), sawdust (Sw) and charcoal (Ch), on soil nutrient content, earthworm abundance and yard-long bean (Vigna unguiculata sesquipedalis) production. The peregrine Pontoscolex corethrurus was the only earthworm species found. Pod production and plant growth were lowest in unamended soil. The application of a mixture of manioc peel and charcoal (M+Ch) improved legume production as compared with other organic mixtures. It combined favourable effects of manioc peel and charcoal. Manioc peel improved soil fertility through its low C:N ratio and its high P content, while charcoal decreased soil acidity and exchangeable Al and increased Ca and Mg availability, thus alleviating possible toxic effects of Al on plant growth. The M+Ch treatment was favourable to P. corethrurus, the juvenile population of which reaching a size comparable to that of the nearby uncultivated soil. The application of a mixture of manioc peel and charcoal, by improving crop production and soil fertility and enhancing earthworm activity, could be a potentially efficient organic manure for legume production in tropical areas where manioc is cultivated under slash-and-burn shifting agriculture.

The endogeic earthworm Pontoscolex corethrurus (Glossoscolecidae) is a peregrine species commonly found in tropical lands cleared by man for cultivation. We compared the charcoal consumption and casting activity of a population of P. corethrurus from a cultivated area under repeated slash-and-burn (fallow population) with that of a population living in a field cultivated after recent burning of a mature forest (forest population). Their cast production was measured in containers in the presence of pure charcoal, soil of fallow and forest origin, or a mixture of charcoal and soil. The forest population defecated less in pure charcoal than in forest soil, whereas the reverse was observed in the fallow population. When living in fallow soil, both populations defecated more at the surface of a mixture of charcoal and soil than at the surface of pure soil (x 2 and x 3 with fallow and forest population, respectively). In forest soil, both populations showed an increased charcoal consumption (x 12). In the light of these experiments, we hypothesized that an adaptation of P. corethrurus to charcoal and fallow soil exists, supporting the observed distribution of this earthworm species in tropical open lands.

The geophagous earthworm Pontoscolex corethrurus is frequently found in burnt tropical soils where charcoal plays an important role in soil fertility. We studied the burrowing activity of this species in two-dimensional microcosms with one half filled with soil and the other with a 3:2 (w:w) mixture of charcoal and soil (CHAR+soil). We measured the volume of empty burrows and those filled with black or brown casts in both substrates, as well as the initial and final fresh weights of the worms. The correlation between brown cast production and both initial and final fresh weights of the worms, reinforced by the presence of feeding cavities in soil but not in CHAR+soil, suggests that P. corethrurus would ingest soil to fulfill its nutrient requirements, in contrast to charcoal which was ingested for other purposes. We observed that at equal burrow volume created in the two substrates, P. corethrurus produced smaller black casts than brown casts, suggesting that burrows were created in CHAR+soil mainly by pushing aside the particles of this lighter substrate.

Abstract. Following a full mast production in autumn 1995 in the old‐growth beech forest of la Tillaie (France), cupules, live and dead 1‐yr old seedlings were counted in September 1996 in 40 plots, representing a wide range of ecological conditions. The influence of geomorphology and forest stage on mast production and on seedling establishment and survival was studied. Maximum seedling abundance did not occur in areas with the largest cupule abundance, but this result was not statistically significant. The presence of a shallow sandstone table under Fontainebleau sand, where beech is far from its ecological optimum, positively influenced the production of mast but negatively influenced seedling survival. Contrary to expectation, the early biostatic rather than the late biostatic phase seemed to be the best stage for beech regeneration. Gaps also provide good environmental conditions for seedling establishment. Humus and light conditions, water availability and competition between beech individuals may explain the results. Light was the main factor influencing mast production in mature stages, and drought was an important factor causing seedling mortality. This study points out the importance of seedling survival for regeneration patterns in beech forests.

It is now attested that a large part of the Amazonian rain forest has been cultivated during Pre-Colombian times, using charcoal as an amendment. The incorporation of charcoal to the soil is a starting point for the formation of fertile Amazonian Dark Earths, still selected by Indian people for shifting cultivation. We showed that finely separated charcoal was commonly incorporated in the topsoil by Pontoscolex corethrurus, a tropical earthworm which thrives after burning and clearing of the rain forest, and that this natural process could be used to improve tropical soil fertility. Our paper is a contribution to the present debate about (i) the origin of black carbon in fertile Dark Earths, (ii) the detrimental vs favourable role of Pontoscolex corethrurus in tropical agriculture, (iii) natural processes which might be used to increase tropical soil fertility

International audienceSlash-and-burn cultivation in the humid tropics can cause changes in the composition of topsoil, depending on the duration of the fallow. We studied differences between practices, using the small-volume micromorphological method, to quantify the distribution of solid components in the topsoil, concentrating on plant organs and biogenic structures created by soil animals. We compared samples of topsoil from five plots, two at Maripasoula, an Aluku village along the Maroni river (French Guiana), with short fallow (= 8 years), and the other three at Elahe, a Wayana village along the same river, with long fallow (= 25 years). At both sites structures created by arthropods other than ants gave way to ones formed by ants and annelids under the influence of fire and cultivation. This change was more abrupt under long fallow, because of the time needed to restore the arthropod community. Charcoal and charred plant material were incorporated by earthworms into the mineral soil, forming dark grey to black aggregates. Charcoal became mixed with the mineral soil faster at Elahe than at Maripasoula, where it accumulated in the topsoil. The reason seems to be an imbalance between charcoal inputs (from repeated fires) and the capacity of burrowing animals (earthworms, ants) to mix it with the mineral soil

A biofertilisation assay was conducted in Maripasoula (French Guiana), testing the effects of three different organic amendments (manioc peels, sawdust and wood charcoal) and the inoculation of the endogeic earthworm Pontoscolex corethrurus on pod production of Vigna unguiculata sesquipedalis and on soil chemical 2 properties (pH, C, N, total and exchangeable P and K). Pod production was highest with manioc peels as available P increased in the soil. Wood charcoal also had a beneficial effect on pod production as it decreased acidity and increased the C:N ratio in the soil. In sawdust-amended soil, pod production did not differ from that in unamended soil. Inoculation of earthworms at a density of 80 sub-adults m-2 did not significantly affect either pod production or soil nutrient content directly, although it increased the positive effect of manioc peels on pod production. Soil nutrient content, pod production and earthworm density at the end of the experiment were negatively correlated with soil moisture and positively with each other. Despite the strong effect of moisture, this assay demonstrated an interaction between the earthworm P. corethrurus and the legume V. unguiculata sesquipedalis mediated by soil nutrient content and organic matter inputs. We conclude that manioc peels improved soil P availability and were an interesting amendment for legume crops. We discuss also the effect of earthworm inoculation.

A study was conducted in order to compare soil faunal activity in four experimental farming systems using different tillage, chemical input and crop rotation practices: A conventional system with deep-ploughing (CT), an integrated system with reduced tillage and minimum chemical input (IN), a system with reduced tillage and high chemical input (RT) and a system with minimum tillage and high chemical input (MT). In nine experimental fields with two sampling points each, earthworms were sampled and biogenic structures were identified and counted in topsoil profiles (0-14 cm depth). Components of these profiles were identified by morphological features. Quantitative analyses of these morphological features provided information about soil compaction, earthworm and enchytraeid activity and distribution of roots and crop residues in the soil matrix. The dominant species in the earthworm community was the endogeic Aporrectodea rosea. Earthworm densities were unexpectedly lowest under reduced tillage (6 specimens per m 2), and highest under deep-ploughing (67 specimen per m 2), the reverse effect being observed with enchytraeid worms, as ascertained by deposition of their faecal pellets in topsoil profiles. Strong very fine granular structure (STVFGR) was most frequent in the integrated farming system (IN). We concluded that in the studied site embracing four farming systems,