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ROLE OF MICROBIAL BIOMASS IN SOIL |
Pôle d'Aspach has been studying soils for many years to understand their biological functioning and the impact of cultivation practices.
INRA laboratories, and more especially the laboratory of Soil Microbiology in Dijon (Côte d'Or, France) have been working on the measurement of biological activity of soil (Chaussod, 1996).
Biotransformations of many elements take place in soil. These elements, such as carbon (Chaussod et al., 1986; 1988) and nitrogen (Hoffmann et al., 1997), are of major importance in parcel fertility.
Microbial biomass of soil is constituted of microscopic organisms. These microorganisms take part in the degradation of organic compounds into mineral elements that are assimilable by plants.
Recent work also indicate that microorganisms take part in aggregation characteristics of soils (Chantigny et al., 1997).
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Thanks to fondamental research, reliable techniques have been developped to measure the microbial biomass. However all these laboratory techniques are not easy for a routine use.
Among these techniques, SADEF-Pôle d'Aspach has chosen to develop the method of measurement of carbon extracted from the microbial biomass, or microbial carbon.
It is measured by the "fumigation-extraction" method. This technique has been developped by Vance et al. (1987) and adapted by Wu et al. (1990) for routine analyses.
First, the soil is treated by chloroform vapors, intended to kill almost the totality of microorganisms. The cellular content spills in the soil and the organic carbon can be extracted and measured.
This technique, developped by Rémi Chaussod (INRA Dijon) in France, is easy to implement for the fumigation and extraction stage, and requires specific apparatus for the measurement of soluble carbon extracted.
Moreover, results are accurate, reliable and reproducable.
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Microbial biomass is one of the most sensitive parameter from those analysed in soils (Filip, 16th International Soil Science Society
Congress, Montpellier (France), Août 1998).
Microbial biomass changes as soon as its environment changes. As a consequence, any change in the agronomic management of a parcel will have an impact on microbial biomass.
For this reason, the measurement of microbial biomass can allow to check for the impact of agricultural practices on the biological state of soils.
Studies have shown changes in soil biomass after :
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changes in cropping systems (Hoffmann et al., 1997 ; Hu et al., 1997 ; Ritz et al., 1997 ; Staben et al., 1997 ; Salinas-Garcia et al., 1997 ; Moyano et al., 1989),
fertilizer inputs (McCarty ; Meisinger, 1997 ; Salinas-Garcia et al., 1997 ; Nohrstedt et al., 1997 ; Wanner et al., 1997),
pH changes (Wanner et al., 1997),
pollutions (Harden et al., 1993)
stress (drought...) (Garcia et al., 1997a and b).
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