Microbial biomass in paddy soil

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Abstract
The authors investigated the role of microorganisms in paddy soil ecosystems and the influence of fertilizer and manure applications on the soil microbial biomass in paddy soils based on direct count using a fluorescence microscope. The results are summarized as follows. 1) The number of bacteria in the plough layer was 6.6 × 10l0-7.6x 1010/g oven dry soil in the Konosu paddy field, 2.2 × 10l0-2.8 × 1010/g oven dry soil in the Aizu paddy field, and 1.1 × 1010-1.3 × 1010/g oven dry soil in the Shizuoka paddy field. The different fertilizer managements did not influence significantly the number of bacteria in the three experimental fields. 2) In all the experimental fields, the number of cocci predominated accounting for 90% of the total number of bacteria, and the number of rods was less than 10%. Among the cocci, the number of small cocci (diameter=0.5/µm) accounted for 60–70% of the total cocci bacteria. 3) Hyphal length increased in response to long term application of inorganic fertilizer and organic manure in comparison with the plot without fertilizer application. Particularly, in the organic manure plot the hyphal length increased greatly. 4) Bacterial biomass was 235–284 mg/100 g oven dry soil in the Konosu paddy field, 87–102 mg/100 g oven dry soil in the Aizu paddy field, and 60–84 mg/100 g oven dry soil in the Shizuoka paddy field. The different fertilizer managements did not influence significantly the bacterial biomass. Hyphal biomass which amounted to 3.4–13 mg/100 g oven dry soil was one-fifth to one-eightieth that of bacterial biomass, suggesting that the bacterial biomass surpassed remarkably the hyphal biomass in paddy soil. 5) The microbial biomass-C in total soil C was 1.5–6.9%, the microbial biomass-N in total soil N was 0.48–2.3%, and the microbial biomass-P in total soil P was 0.83–3.3%.