Abstract
Topsoil samples derived from a granite parent material were taken from a 9 years old burned forest and incubated at different moisture contents. The soil is bare and its ash bed was already depleted by runoff. A close relationship was found between the factors of soil water content, nitrogen (N) mineralization rate and CO2 release resulting from the activities of soil microorganisms. The samples incubated at relatively high initial moisture content had a high mineralization rate. After the increase of soil moisture content to 70% of its MWHC (Maximum Water Holding Capacity), the rate of increase was higher in samples with low initial moisture content. In other terms, the dryer the soil samples were, the higher was their N mineralization rate after being moistened at the same final level. The peak recorded in the rate of nitrogen mineralization during the first 3 days after the increase of soil moisture content was followed by a gradual decrease. The increase of soil moisture content had more effect on N mineralization in the case it happened 7 days after the beginning of the incubation than 14 days later. As far as carbon dioxide was concerned, the drier the soil samples were, the higher were their CO2 release after a sudden accretion of their initial water content adjusted to a final 70% MWHC. Instead of decreasing in the same way N mineralization did, the amount of CO2 released from soil augmented, suggesting a regain in soil microbial activity which may have led to N immobilization.
