Recovery of nitrifier populations from inhibition by nitrapyrin or CS2

Summary Nitrifying bacteria from four different soils took approximately 40 days to recover from a 1 μg ml−1 addition of nitrapyrin to aqueous suspensions of the soils, even when the bacteria were cultured under favourable conditions. No evidence was obtained for the development of nitrapyrin-resistant nitrifiers, even after prolonged incubation. Repeated large doses (25μg ml−1) of CS2 had little effect on nitrification by Nitrosolobus sp. and only partially inhibited nitrification by Nitrosomonas sp. Recovery of nitrifying activity was rapid, due to evaporation and hydrolysis of CS2 and not to the development of CS2-resistant nitrifiers. CS2 was an effective nitrification inhibitor at low (ca. 4 μg ml−1) concentrations if a constant concentration could be maintained. Recovery of nitrification after inhibition by a low constant level of CS2 took 40–60 days.

RESP-08196