Microflora related to the nitrogen cycle in the tropical paddy soils

Abstract Paddy soils collected in 103 sites of Thailand consisted of surface soil (0-1 cm) and subsurface soil (1-10 cm). Collections were made twice, in the middle of the rainy season and in the middle of the dry season. The counts of 12 groups of microbes related to the nitrogen cycle were determined. In the soils sampled in the rainy season the population level of aerobic bacteria per 1 g of dry soil ranged from 107 to 106. For other microorganisms, the values were as follows: actinomycetes—l04 to 104, anaerobic bacteria—l05, cellulose decomposer—104, denitrifier—105, ammonifier—104 to 104, nitrite oxidizer—103, ammonia oxidizer-105, Clostridium-105 to 104, nitrogen-fixing blue green algae, Azotobacter and purple nonsulfur bacteria-103, respectively. Populations of all 12 groups examined were larger in the oxidized surface soil than in the subsurface soil and, in particular, the populations of aerobic nitrite oxidizer and photosynthetic purple nonsulfur bacteria were more than 4 times higher than those...