ABSTRACT
MICROORGANISMS OF SOIL AND OF ORGANIC SUBSTRATES Immobilisation of Mineral Elements Fresh organic matter is rapidly colonised. Part of it is assimilated by microorganisms, another part mineralised, while a more recalcitrant fraction participates in the formation of humic acids. The proportion of mineral elements released and immediately available for plants depends on the nature of the substrate. If the contents of nitrogen, sulphur and phosphorus are
in the compared to their carbon composition, all these will be immobilised in the microbial biomass. The addition of mineral salts would be necessary in this case to preclude competition between the plants and the microorganisms (see page 125). However, this immobilisation is only temporary and the mineral elements that could be leached are conserved in the fertile soil horizons. Renewal of the biomass ensures progressive mineralisation of these elements that gradually become available for the plants.
