The SHIFT-Program ENV 44 tries to maintain soil fertility in the Bragantina area (Pará) by production of mulch material from fallow vegetation. A main focus with respect to sustainability deserves to be agroforestry

CRAVO, M. da S.

GLASER, B.

LAABS, V.

LEHMANN, J.

LILIENFEIN, J.

PINTO, A.

TEIXEIRA, W.

ZECH, W.

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New approaches towards sustainability of land-use systems in Tropical Brazil.

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German-Brazilian Workshop on Neotropical Ecosystems – Achievements and Prospects of Cooperative ResearchHamburg, September 3-8, 2000Biotic and Abiotic Interactions in Soil and Sediment – Summaries of Lectures, Session 2Zech, W., Cravo, M. da Silva, Laabs, V., Pinto, A., Lilienfein, J., Glaser, B., Teixeira, W. and Lehmann, J.:New Approaches towards Sustainability of Land-use Systems in Tropical Brazil1183 Uptake of mineral elements in the fine rootsThe influx of calcium from an external source into primaryroots of 3-year-old Carapa guianensis plants was monitoredwith the stable isotope 44Ca of this macro-nutrient calcium.The uptake of calcium into the fine roots of Carapa guianensis for example is strongly determined by the finestructure of exodermis and endodermis. The time series forlabeling with 44Ca started with two minutes, followed by 16min and 64 min respectively. The structural characteristics of the exodermis apparentlyinfluence the uptake of calcium, which is particularlyobvious in the outer cortex. In Carapa the uptake of the44Ca-labelling into the outer cortex amounts to about 3%after 2 min. Only at longer time of application,  the transportinto the central part of the fine root is evident. After 64 minthe 44Ca-label amounts about 58% of the total Ca content inthe primary xylem. Obviously the relationship of structure and barrier behavioris in the exodermis and endodermis different, indicating aspecific strategy in adapting to site conditions.4 Conclusions• The fine roots of C. guianensis are remarkably well adapted to dry periods to maintain tree growth.• C. guianensis Aubl. exhibits a specialized fine root structure, expressed in particular in the development ofthe cell wall layers of the exodermis and endodermis.These structural characteristics of fine roots coincide withthe special kinetics for the uptake of mineral elementssuch as calcium.• The results on structure and function of the fine roots support the findings on water and mineral element balan-ce, which indicate a good adaptation of C. guianensis tothe site conditions at the "terra firme” in CentralAmazonia.Traditionally, tropical soils have been frequently used in asustainable way by slash and burn. But currently, thismethod accelerates land degradation due to increasingpopulation pressure. Fallow periods are therefore shortened,thus reducing the potential for soil regeneration. There is,without doubt, an urgent need to develop new approachesfor sustainable land-use in tropical regions. In the followingsome interesting activities on this subject are referred on,partly developed within the SHIFT-program.The SHIFT-program ENV 44 tries to maintain soil fertilityin the Bragantina area (Pará) by production of mulch mate-rial from fallow vegetation. A main focus with respect tosustainability deserves to be agroforestry. It could be shownby the SHIFT project ENV 45 that individual trees havefundamentally different effects on sustainability, e.g. bydifferent root activity patterns allowing different access tosubsoil nutrients (especially nitrogen) and different nitrateleaching rates. In collaboration with the University ofUberlândia and CIAT it was shown that intensive tree fallowusing pines strongly enhances soil acidification. If the soilnutrient status allows, the introduction of high qualitytimber into agroforestry systems, as studied by SHIFTproject ENV 42, would enhance the commercialproductiveness of the system. An interesting approachtowards sustainability of acid soils in South America wasdeveloped by CIAT, rotating acid tolerant crops withimproved pasture using nitrogen fixing plant species likepueraria. Analyzing the soil solution it could be shown thatthe nutrient status of these systems is comparable to the oneof the natural Cerrado Vegetation. The introduction of theimproved pasture rotation also strongly contributes to land-use sustainability by increasing soil organic carbon con-tents. Recently, we could identify charcoal as an importantsoil organic carbon constituent contributing to thesustainability of the Terrae Pretae in Amazonia. This findingoffers new approaches to soil organic carbon and nutrientmanagement concepts for sustainable agriculture in thetropics.Up to now the mulch and agroforestry systems are not fullyaccepted by land-users. Especially large scale farmers andNew Approaches towards Sustainability of Land-use Systems in Tropical BrazilZech, W.1, Cravo, M. da Silva2, Laabs, V.1, Pinto, A.3, Lilienfein, J.1, Glaser, B.1, Teixeira, W.1, 2 and Lehmann, J.11 Institut für Bodenkunde und Bodengeographie, Germany2 Embrapa-CPAA, Manaus, Brazil,3 Universidade Federal de Mato Grosso, Cuiabá, BrazilGerman-Brazilian Workshop on Neotropical Ecosystems – Achievements and Prospects of Cooperative ResearchHamburg, September 3-8, 2000Biotic and Abiotic Interactions in Soil and Sediment – Summaries of Lectures, Session 2Altstaedt, A., Amelung, W., Pinto, A., Laabs, V. and Zech, W.:Biocide Pools in Tropical Soils of the São Lourenço River Basin -Implications from Dissipation Studies in Soil Density Fractions119partly also small-holders prefer mechanized farming withconsequent application of mineral fertilizers and biocides.Some of these chemicals are persistent and may accumulatein soil, water, and crops. Since the application of biocides ispart of most land-use practices in humid and sub-humidBrazil, the investigation of their environmental behaviorand their effects on biodiversity are important issues in theevaluation of sustainability. First results of the SHIFTproject ENV 54 show that the dissipation time of frequentlyused biocides in the Cuiabá (Mato Grosso) region isastonishing short; but nevertheless biocide leaching withinthe soil does still take place.All these research lines do contribute to a better under-standing and management of tropical land-use systems.Only with a sustainable land management a continuouseconomic development can take place and at the same timeecological risks on the local and global scale are minimized.2.0-2.4, 2.4-2.6 and > 2.6 g cm3), in which we measured thebiocide concentrations. The biocide concentrations weresignificantly correlated to the carbon contents of thefractions, underlining the importance of soil organic matterfor biocide sorption. The dissipation of endosulfan,chlorpyrifos and trifluralin in the bulk soil as well as in thefractions was described best using a bi-exponential model,which is the sum of two first-order kinetics. Since the rateconstants of dissipation were the same in all fractions, it isconcluded that the processes causing the decrease of rateconstants were present in all fractions and cannot be relatedto the organic C-pools of density fractions. However l-cyhalothrin disappeared more slowly in the light fractions< 2.0 g cm3 than in other fractions, but only incidentally. Afew days later, the rate constants were comparable in allfractions. It is concluded that density fractions in an oxisolrepresent pools of different biocide accumulation but not ofdifferent biocide dynamics.Various studies show that biocide degradability decreaseswith residence time in soil. Thus, a slow enrichment ofpesticides could take place, though half-lives of biocides arevery short in the tropics. Some studies indicate a biphasic dissipation kinetic: In afirst phase higher rate constants (of an first order kinetic) areobserved than in a second phase. The biphasic dissipationkinetic implies that pesticides distribute between pools ofdifferent degradability in soil. Since pesticides interactpreferably with the soil organic matter, we aimed toelucidate if pesticide pools are related to different soilorganic constituent such as represented by soil densityfractions.In our field experiment we applied endosulfan, chlorpyrifos,l-cyhalothrin and trifluralin on a Humic Acrustox of the SãoLourenço river basin and studied the dissipation in differentdensity fractions. Soil samples were collected repeatedlyduring the whole Experiment (28 d) and fractionated byphysical means into five density Fractions (< 1.6, 1.6-2.0,Biocide Pools in Tropical Soils of the São Lourenço River Basin Implications from Dissipation Studies in Soil Density FractionsAltstaedt, A.1, Amelung, W.1, Pinto, A.2, Laabs, V.1 and Zech, W.11 Institute of Soil Science and Soil Geography, University of Bayreuth, D-95440 Bayreuth, 2 Projeto Ecologia do Gran Pantanal, Universidade federal de Mato Grosso, 78060 Cuiaba, MT, Brazil

New approaches towards sustainability of land-use systems in Tropical Brazil.

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