Microbiological response to Ca(OH)₂treatments in a forest soil

Lime was added to a forest acid soil rich in organic matter. During five weeks of initial incubation at room temperature (until the various limed soil samples reached stabilized pHs of 5.5, 6.0 or 6.5), there were rapid increases in the bacterial population, denitrifiers, and fungal mycelia, particularly in the heaviest limed sample. Conversely, nitrite oxidizers decreased to undetectable numbers regardless of the lime dose applied. At this time soil samples were amended with 5% of fresh soil. During 12 weeks of subsequent incubation at 28°C, the bacterial population was favoured by increasing soil pH; nevertheless, at the end of the incubation the positive effect was only significant at pH 6.0 and 6.5. By contrast fungi were depressed by raising the pH. Nitrifiers and denitrifiers were more numerous in the limed than in the unlimed soils but only in samples at pH 6.5 were the differences significant throughout the incubation period.