Objectives (according to project's initial proposal)

Aim of the project is to investigate how manipulations of quantity and quality of plant residues in agricultural systems might be used for a melioration of soil fertility, as indicated by an increase of soil organic matter quantity and quality, soil moisture and biogenic soil microstructures. The causal relationships between increased input of plant litter, a more stable microclimate at the soil surface, increased abundance of the decomposer macrofauna, stable decomposition rates and resulting soil organic matter and nutrient release will be demonstrated.

The investigations on management of plant residues seek to obtain practical recommendations for farmers such as selection of crop and intercrop plant species and their spatial distribution, use of legume species for intercropping and regular mulching and the management of woody residues (e.g. by chopping). Because the use of pesticides in tropical agriculture systems may be a relevant factor affecting the regarded biological soil processes, the side effects of chemicals on soil organisms and litter decomposition are being investigated in parallel.

The research activities are organised in four modules:

Module 1:Three field experiments about the effects of the manipulations of quantity and quality of legume plant residues in an exemplary already degraded agricultural system will show howto an optimization of the conditions in and on the soil, such as microclimate, biomass and abundance of soil fauna, soil organic matter content, soil structure and nutrient availability can be reached. Another experiment tests alternatives to the usual slash-and-burn treatment of woody residues during the preparation of a plantation and its effects on soil macrofauna abundance, wood decomposition and soil organic matter quantity and quality and production of manioc.

Module 2: Studies in microcosms (Terrestrial Model Ecosystem TME) under controlled conditions in laboratory are conducted in order to investigate quality-dependent consumption rates of organic matter by soil macrofauna, the nutrient release and especially the interactions between fauna and microorganisms.

Module 3: Intensive surveys of soil fauna in different agroecosystems will determine whether the species composition and the litter decomposition rates of autochthonous and introduced material (standard) influence the soil structure and nutrient availability. The results will improve the database for an evaluation of the outcome of the experiments and increase the chance for generalizations.

Module 4: Studies in laboratory and field about the ecotoxicological effects of pesticides on soil fauna and litter decomposition. Toxicity tests for organisms are performed taking into account the relevance of these species for the soil biological processes. Besides the risk assessment of pesticides for soil compartment, the results will contribute to new methods and protocols of toxicological tests suitable for tropical regions.

First goal of the project is to produce scientific and technical knowledge regarding the management of plant residues aiming at the optimization of decomposition and nutrient cycling processes and leading to a melioration of soil fertility., Second goal is to provide the basis for the installation of on-farm-research in rural properties. In the long term the project research should lead to the development of recommendations for recuperation of abandoned, while degraded areas using alternatives to slash-and-burn preparation of plantations and methods for soil amelioration like introduction of legumes in agricultural systems and qualitatively differentiated application of mulch.

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Modul 1: Field Experiments

The experimental manipulations of plant residue quantity and quality in this project have been designed to reveal causal mechanisms and define the manageable factors strongly acting on soil fertility - independent from the agricultural system. Emphasis is put on a scientifically sound design and statistical power.Therefore a maximum of regional conditions and management practices relevant in Amazonia was taken into consideration.

Under a practical viewpoint, three legume species (Pueraria phaseoloides, Tephrosia candida and Flemingia macrophylla) are cultivated since 2001 in an alley-cropping system in order to evaluate their agronomic aspects and to produce enough material to test the effect of the mulching on the soil fertility.

One experiment compares the different effect of the three legume species, when planted between the crop species, the second experiments tests different quantities of one mulch quality and the third tests different qualities (C/N ratio, lignin, polyphenols) in equal quantities.

Another experiment using woody residues from the original vegetation cover is realized in close cooperation with trials of different management practices (mineral fertilization, legume mulching) after initial preparation of areas of primary or secondary forest for manioc plantations. In this experiment, the slash-and-burn practice is compared with alternatives of using the autochthonous wood. It was installed in areas formerly covered by primary and secondary forest, which were slashed and prepared for manioc cultivation in 2001.

The woody residues experiment were installed in areas formerly covered by primary and secondary forest, which were slashed and prepared for manioc cultivation under different management systems.

Modul 2: Microcosm Experiments

During the first phase of the project (1996-99) one of the main results was that the microbial decomposition is strongly dependent from the macrofauna activity. On the other hand it is well known that the microflora is essential for mineralization. Therefore, the interactions between macrofauna and microorganisms are studied in microcosms. The method is named Terrestrial Model Ecosystem, TME. In order to establish this new test system several tests without pesticides have been run so far. They are aimed to assess the decomposition of leaf litter under controlled laboratory conditions. The intact soil cores -TME were taken from the field by means of a heavy dredger and are kept in the laboratory under controlled conditions.

Modul 3 Screening:
Part A: Studies on macrofauna and decomposition processes in different agrosystems

The idea that the decomposition process is regulated by the macrofauna and that the use of plant residues is important for soil fertility management is based on studies in few agroforestry systems at Embrapa Amazônia Ocidental, and on data from literature. The degree of similarity in the decomposition process, soil physics and chemistry in relation to the soil fauna of different agroecosystems is being investigated in the "screening" part in several important cultures of central Amazonia.

Part B: Importance of ants in the decomposition process, nutrient recycling and soil chemistry and physics

The results of the first phase in SHIFT project 52 showed that velocity and quality of the decomposition process strongly depend on the presence of five groups of soil macrofauna: earthworms, diplopods, isopods, termites and ants. While the first four groups are well known as decomposers, the functional connections between the number and biomass of ants and the speed of decomposition is still not understood, because only a small fraction of the total of ants species act at least partly as decomposer (e.g. small Attini). Therefore the positive influence of ants i.e. on soil physics by nest digging, accumulation of nutrients in soil nests, and enhancement of soil microbial activity will be studied.

Modul 4 Ecotoxicological studies: Effects of pesticides on soil fauna and decomposition

Agriculture, especially in the Amazon region, requires a high input of chemical products due to the high diversity of pests and diseases. The large increase of agricultural activities in this area, including the use of pesticides, demands urgently the adaptation of existing test methods for tropical regions to assess the ecotoxicological hazard potential of pesticides.
Therefore, ecotoxicological tests determining the effects of chemicals on soil macrofauna species and decomposition processes under tropical conditions are developed. The main effort is put on the laboratory scale. In addition the effects of pesticides on site-specific Oligochaeta and Isopod species and on organic matter decomposition will be determined in terrestrial microcosms (intact soil cores) and in the field (an abandoned rubber plantation). The results of all three levels will be used to assess the extrapolation from data gained in standardised tests to the field situation.

A field test was started by applying a fungicide (Derosal) and an insecticide (Karate) in various concentrations on selected plots (including litter-bags). The main measurement endpoint is the litter mass loss within the litter-bags. In addition, the abundance of the macrofauna will be determined.

In the national (Brazilian) scenario the main approach of this research is the Management and improvement of degraded soils, that can give answers for demands like :

- The sustainable use of natural resources in the Amazon region.

- Training of human resources to develop research in Amazonia.

In the international scenario this research project is included in demands like:

- The better knowledge of the natural and agricultural ecosystems in tropical regions.

- Development of new technologies for sustainable development, environmental protection and conservation of biodiversity.

- Improved management of Soil Organic Matter in low input systems.

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Contractors

Germany

SMNK Staatliches Museum für Naturkunde Karlsruhe

ECT Oekotoxikologie GmbH, Flörsheim

IfGG Institut für Geographie und Geoökologie, Universität Karlsruhe

ZEF Zentrum für Entwicklungsforschung, Universität Bonn

Brazil

Embrapa Empresa Brasileira de Pesquisa Agropecuária Embrapa Amazônia Ocidental, Manaus

FUA Fundação Universidade do Amazonas, Manaus

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