AUTOTROPHIC NITRIFICATION IN ACID TEA SOILS

Investigations to analyze the nature of nitrification in acid soils we re carried out in the laboratory using 2 soil types from a tea field. The optimum temperature for the nitrification activity in these soils was 25-degrees-C and the activity was inhibited above 35-degrees-C, su ggesting that the nitrifying bacteria became adapted to the soil condi tions. The optimum NH4+-N concentrations for nitrification ranged betw een 20 and 200 mg N/100 g of soil and the activity decreased at a conc entration above 300 mg N. The effect of acidity on nitrification was s tudied by using soil samples amended with various amounts of CaCO3. Al though the pattern of NO2- production changed, the rate of ammonia oxi dation was not influenced by the addition of CaCO3. The nitrification activity was completely inhibited by the addition of nitrapyrin or ace tylene. These results suggest that acid-tolerant or acidophilic autotr ophic nitrification occurs in acid tea soils in Japan.