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Wageningen University (2002)

Soil organic matter dynamics in a Cerrado Oxisol

Roscoe, R.

Titre : Soil organic matter dynamics in a Cerrado Oxisol

Auteur : Roscoe, R.

Université de soutenance : Wageningen University

Grade : PhD thesis 2002

Résumé partiel
The Brazilian Cerrado is the second largest biome in the country, spreading over 23 % of the national territory. In the last three decades, it has increasingly contributed to the national production, being responsible in 1995 for 25% of the national agricultural production and sheltering 40% of the cattle flock. Development strategies have stimulated strongly mechanised and intensive agricultural practices, which has raised concerns about soil organic matter (SOM) losses and soil degradation.

Cerrado soils are dominated by low-activity clays and are characterised by high acidity and low pH, cation exchange capacity (CEC), and available nutrients (especially P and N). SOM exerts important functions in these soils, which are closely related to soil quality and sustainability. It is responsible for most of the CEC, and is involved in process of soil aggregation and water dynamics. Losses of SOM due to cultivation may seriously affect these functions, and also represent an important source of CO 2 to the atmosphere. Studying the effects of different management systems on C dynamics in Cerrado soils may help to develop better ways of using these ecosystems.

The initial objective of this thesis was to evaluate the impact of different management systems on SOM dynamics in one of the most representative soil classes in Cerrado, the Dark Red Latosol (18% of the total area ; Oxisol - Soil Taxonomy ; Ferrasol - FAO Legend). The research strategy adopted was to compare, in the same soil unit, paired plots with different management systems (native vegetation, pasture, no-tillage and conventional tillage). The Dark Red Latosol unit (Typic Haplustox) was located in the experimental research institution of EMBRAPA-CNPMS (Brazilian Institute of Agricultural Research - Maize and Sorghum National Research Centre), in Sete Lagoas - MG, Brazil. To assess SOM dynamics, a combination of two methodologies was proposed, (i) the physical fractionation of soil in particle-size and density separates, and (ii) replacement calculations using the natural abundance of the 13C isotope. The physical fractionation aimed at separating SOM pools with different chemistry, location, and turnover, which hypothetically would be more sensitive to soil alterations than total SOM. The natural abundance of 13C was proposed to assess the turnover time of SOM and its fractions. However, as very little data was available about the use of these methodologies in Cerrado ecosystems, the initial focus of the thesis was changed

Mots clés  : soil organic matter / tillage / fire / cerrado soils / carbon / land use / brazil

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