THE LOWEST LIMIT OF PH FOR NITRIFICATION IN TEA SOIL AND ISOLATION OFAN ACIDOPHILIC AMMONIA OXIDIZING BACTERIUM

Investigation to determine the lowest limit of soil pH for nitrificati on were carried out in the laboratory using acid tea soils with pH ran ge of 3.3 to 5.1. A significant linear correlation was observed betwee n the soil pH value and nitrification rate which was measured by the s oil incubation method. It was indicated that the lowest limit of the p H for nitrification was around pH 2.9. Two types of morphologically di stinct strains of chemoautotrophic ammonia-oxidizing bacteria were iso lated from four tested soils. One of them which was acidophilic was fo und to grow in a pH range from 3.5 to 7.0 in pure culture. The optimum pH for growth and ammonia oxidation of the acidophilic strain was pH 5.0. Acidophilic ammonia-oxidizing bacteria presumably play an importa nt role in nitrification in acid tea soils.