Luizão, R.C.C.; Barros, E.; Luizão, F.J.; Alfaia, S. 2002. Soil biota and nutrient dynamics through litterfall in agroforestry system in Rondônia, Amazônia, Brazil. Documentos, 182:93-97.

Abstract: Agroforestry systems are presented as a valuable alternative to pastures to sustain crop production in forested areas. In order to evaluate their effect on soil macroinvertebrate communities, sampling was conducted during the rainy season at four localities located in the Rondônia and Acre states of Brazil. Four land-use systems were selected (fallow, annual crop, agroforestry systems and pasture), and compared to nearby disturbed forests. We used the sampling method recommended by the Tropical Soil Biology and Fertility Programme. Soil macrofauna responded more readily than soil parameters to different cultivation practices. Co-inertia analysis, however, showed a relationship between soil parameters and soil macrofauna. Comparison of communities showed a significant impact of land-use practices. All systems had quite abundant invertebrate communities with relatively low densities in the forest (884 ind. m^-2) and in pastures (841 ind. m^-2), and higher densities in fallow, agroforestry system and annual crop (1.737-1.761 md. m^-2). Earthworms were dominant in pastures (155 ind. m^-2 and 56.2 g m^-2 on average), whereas termites thrived better in annual crops and fallows (with respective densities of 1.287 and 816 and biomasses of 2.32 and 1.38 gm^-2). Macrofauna communities in agroforestry systems were rather similar to the forest, in spite of higher densities of social insects. The termite: earthworm ratios were very low in pastures (0.2), had similar values in the forest (7.9) and the agroforestry system (8.8), which is much lower than in fallows (20.4) and annual crops (21.4) This study showed that all land-use practices were able to sustain sizeable macrofaunal communities with agroforestry communities rather similar to those of a distributed forest.

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Lavelle, P.; Barros, E.; Blanchart, E.; Brown, G.; Desjardins, T.; Mariani, L.; Rossi, J.P. 2001. Soil organic matter management in the tropics: why feeding the soil macrofauna. Nutrient Cycling in Agroecosystems, 61:53-61.

Abstract: This paper synthesizes information on the food requirements of soil macro invertebrates and some of their effects on soil organic matter dynamics. Some clues to techniques that would optimize their activities through organic matter management are suggested. Soil macro invertebrates can consume almost any kind of organic residues in mutualistic association with soil microflora. Significant amounts estimated at several T per ha of predominantly easily assimilable C are used yearly in natural ecosystems as energy to sustain these activities. Sources of C used are highly variable depending on the feeding regime. The largest part of the energy assimilated (e.g., 50% by the tropical earthworm Millsonia anomala) is actually spent in burrowing and soil transport and mixing. Bioturbation often affects several thousand tons of soil per hectare per year and several tenth of m3 of voids are created in soil. A great diversity of biogenic structures accumulate and their nature and persistence over time largely controls hydraulic soil properties. The OM integrated into the compact biogenic structures (termite mounds, earthworm globular casts) is often protected from further decomposition. Most management practices have negative effects on the diversity and abundance of macro invertebrate communities. Structures inherited from faunal activities may persist for some weeks to years and the relationship between their disappearance and soil degradation is rarely acknowledged. When SOM supply is maintained but diversity is not, the accumulation in excess of structures of one single category may have destructive effects on soil. It is therefore essential to design practices that provide the adequate organic sources to sustain the activity and diversity of invertebrates. Special attention should also be paid to the spatial array of plots and rotations in time.

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Barros, E.; Curmi, P.; Hallaire, V.; Chauvel, A.; Lavelle, P. 2001. Role of macrofauna in the transformation and reversibility of soil structure of an oxisol in the process of forest to pasture conversion. Geoderma, 100:193-213.

Abstract: In a central Amazonian pasture, a single earthworm species, Pontoscolex corethrurus, becomes very abundant (400 ind. m^-2) after forest clearing. Its casts form a compact, continuous and impermeable crust with a thickness of 20 cm. To analyze the structural modifications, we established a field experiment in which soil blocks from the forest were implanted in the pasture, and soil blocks from the pasture were implanted in the forest. The objectives were (1) to verify the formation of the compact crust at the soil surface in pasture environment; (2) to evaluate the time necessary for the formation and the destruction of this crust, and (3) to find out if the crust formation was a reversible process. We used quantitative morphology to identify the biogenic structures formed by different fauna groups and to quantify the modifications in the solid phase as well as the resulting porosity. For the soil depth 0-5 cm, the measured porosity was 48% in the forest and 16% in the pasture. After 1 year, the blocks of forest soil installed in the pasture presented a porosity of 26%, and the blocks of pasture soil installed in the forest presented a porosity of 34%. There were significant differences between the control blocks and the exchanged blocks. The results demonstrate that the processes of formation and destruction of the biogenic structures are reversible. Approximately, 1 year is necessary to re-establish the equilibrium between the exchangedd blocks and the control blocks.

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Desjardins, Th.; Lavelle, P.; Barros, E.; Brossard, M.; Chapuis-Lardy, L.; Chauvel, A.; Grimaldi, M., Guimarães, F.; Martins, P.; Mitja, D.; Muller, M.; Sarrazin, M.; Tavares Filho, J.; Topall, et O. 2000. Dégradation des pâturages amazoniens : description d'un syndrome et de ses déterminants. Étude et Gestion des Sols, 7(4):353-378.

Résumé: En Amazonie bresilienne, la presque totalité des zones déforestées depuis une trentaine d’années a servi à l‘installation de pâturages dont une moitié a été depuis abandonnée dans un etat de dégradation souvent avancé. Plusieurs hypothèses ont été émises pour expliquer cette dégradation, parmi lesquelles la détérioration de certaines propriétés physiques et chimiques des sols, le développement incontrôlé des adventices, l?effet des changements des peuplements de la macrofaune du sol, les attaques parasitaires, les effets de la gestion des parcelles. Afin de vérifier ces hypothèses, une étude comparative de plusieurs pâturages a éte réalisée, associant leur historique, l‘analyse de leur végetation (graminée plantee et vegétation secondaire), de leur macrofaune et de quelques proprietés des sols. Deux groupes de pâturages ont été sélectionnés en fonction de leur état apparent de dégradation, sur des Oxisols en Amazonie centrale et des Ultisols en Amazonie orientale. La dégradation des pâturages, caracterisée par une diminution de la phytomasse de la graminée introduite et l’augmentation de celle des adventices, n?apparait pas directement liée à l’age du pâturage ni à une dégradation marquée des sols. La déforestation et le brûlis qui la suivent provoquent généralement un tassement des horizons superficiels, une augmentation du pH, de la somme des bases at du taux de saturation. Au cours des années qui suivent l’installation du pâturage, ces caractéristiques évoluent très peu, independamment de l’etat de dégradation des pâturages. La quantité de phosphore extractible et les teneurs en carbone organique at azote total n’evoluent pas de façon sensible en fonction de l’age at de la dégradation des pâturages. Las peuplements de la macrofaune du sol sont en géneral fortement modifies par la mise en pâturage. Dans un cas, nous avons pu mettre en évidence des changements de fonctionnement du sol liées à ces modifications de peuplements. Il apparáit que les pratiques de gestion, comme le choix des graminées introduites, le contrôle de la pression exercée par le bétail, l?utilisation des feux ou de la coupe pour contrôler les espèces adventices exercent une influence considérable sur l’evolution des pâturages.

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Desjardins, Th.; Lavelle, P.; Barros, E.; Brossard, M.; Chapuis-Lardy, L.; Chauvel, A.; Grimaldi, M., Guimarães, F.; Martins, P.; Mitja, D.; Muller, M.; Sarrazin, M.; Tavares Filho, J.; Topall, et O. 2000. Hydraulic conductivity measurement by the disc infiltrometer: practical and theoretical aspects. Étude et Gestion des Sols, 7(4):353-378. (In French).

Abstract: During the last 30 years, pastures become the main land use following deforestation in Brazilian Amazonia. About 50% of these areas are now abandoned and degraded. Several assumptions were advanced to explain degradation changes in some chemical and physical properties of soils, variations in soil macro fauna populations, parasitic attacks, and management practices. Vegetation (graminaceous planted and secondary species), soil macro fauna and soil characteristics of different pastures were studied to verify the accuracy of these assumptions. Two groups of pastures were selected according to their apparent state of degradation in central and eastern Amazonia (respectively on oxisols and ultisols). The phytomass of the planted graminaceous decreased in degraded pastures whereas those of secondary species increased. No correlation was observed between these changes and the age of pasture or a marked soil degradation. Slash and burn induced a compaction of the soil surface layer, an increase of soil parameters such as pH, sum of bases and saturation degree. During the years following installation of pastures, these characteristics remained rather stable in all pasture types, degraded or not. The contents of total carbon and nitrogen and extractable phosphorus remained also quite stable. The populations of soil macrofauna were largely modified by the installation of pasture, but without visible effects on soil functioning, except in one case. Pasture management i.e. choice of the graminaceous species, control of the carrying capacity use of fire or cut to control the secondary vegetation strongly influenced, the evolution of pastures.

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Schroth, G.; Lehmann, J.; Rodrigues, M.D.R.L.; Barros, E.; Macedo, J.L.V. 2001. Plant-soil interactions in multistrata agroforestry in the humid tropic. Agroforestry Systems, 53:85-102.

Abstract: Multistrata agro forestry systems with tree crops comprise a variety of land use systems ranging from plantations of coffee, cacao or tea with shade trees to highly diversified home gardens and multi-storey tree gardens. Research on plant-soil interactions has concentrated on the former. Tree crop-based land use systems are more efficient in maintaining soil fertility than annual cropping systems. Certain tree crop plantations have remained productive for many decades, whereas home gardens have existed in?the same place for centuries. However, cases of fertility decline under tree crops, including multistrata agroforestry systems, have also been reported, and research on the causal factors (both socioeconomic and biophysical) is needed. Plantation establishment is a critical phase, during which the tree crops require inputs but do not provide economic outputs. In larger plantations, tree crops are often established together with a leguminous cover crop, whereas in smallholder agriculture, the initial association with foodcrops and short-lived cash crops can have both socioeconomic and biological advantages. Fertilizers applied to, and financed by, such crops can help to “recapitalize” soil fertility and improve the development conditions of the young tree crops. Favorable effects on soil fertility and crop nutrition have been observed in associations of tree crops with N2-fixing legume trees, especially under N-deficient conditions. Depending on site conditions, the substitution of legume “service” trees with fast-growing timber trees may lead to problems of competition for nutrients and water, which may be alleviated through appropriate planting designs. The reduction of nutrient leaching and the recycling of subsoil nutrients are ways to increase the availability of nutrients in multistrata systems, and at the same time, reduce negative environmental impacts. These processes are optimized through fuller occupation of the soil volume by roots, allowing a limited amount of competition between associated species. The analysis of temporal and spatial patterns of water and nutrient availability within a system helps to optimize the use of soil, resources, e.g., by showing where more plants can be added or fertilizer rates reduced. Important research topics in multi-strata agroforestry include plantation establishment, plant arrangement and management for maximum complementarity of resource use in space and time, and the optimization of soil biological processes, such as soil organic matter build-up and the stabilization and improvement of soil structure by roots, fauna and microflora.

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