Yasuo Takai

THE MECHANISM OF METHANE FERMENTATION IN FLOODED PADDY SOIL

Abstract Methane is a gas occurring ap~ndantly in .nature as a product of anaerobic bacterial decemposition of organic matter under water. Methane arises not. only from stagnaat and putrescent, pools but also from soils used in rice culture during summer (1,2.3).

Rapid degradation of γ-HCH in upland soil after multiple applications

Since 1973, the authors have carried out a long-term upland field experiment by applying γ-HCH (γ-BHC, lindane) every year in the same field in order to examine how the fate of γ-HCH was afrected in the long run. The disappearance-rate of γ-HCH increased with the increasing period of application. After the third and fourth applications of γ-HCH, more than 80% of the applied γ-HCH was lost within 1 month. The rapid loss of γ-HCH in the field was considered to be principally due to the degradation by microorganisms accumulated in the field for the long-term experiment. This asssumption was supported by several laboratory experiments: which indicated that the γ-HCH-decomposing microorganisms could survive and decompose γ-HCH in other soils to which γ-HCH had never been applied and that the active γ-HCH-decomposing microorganisms were aerobic or facultative anaerobic bacteria.

Effect of fertilizer and manure application on microbial numbers, biomass, and enzyme activities in volcanic ash soils: I. Microbial numbers and biomass carbon

Abstract Fertilizer and manure application affected the microbial numbers and biomass in topsoil and subsoil fields consisting of volcanic ash upland soil. 1. Microbial numbers (bacteria, spore-forming bacteria, actinomycetes, and fungi) were the largest in the farmyard manure plot, followed by the chemical fertilizer plot, and smallest in the no-fertilizer plot in both fields. The numbers of all the microorganisms except fungi in the samples from the topsoil field were larger than in the samples from the subsoil field in the respective plots. Microbial numbers obtained here were several times as large as the mean values of microorganisms in volcanic ash upland soils, presumably due to the use of a Waring blender for dispersing the soil samples. 2. Soil microbial biomass carbon was the largest in the farmyard manure plot, followed by the chemical fertilizer plot, and smallest in the no fertilizer plot in both fields. Microbial biomass carbon in the samples from the subsoil field was larger than that in th...

Organic debris as micro-site for nitrogen fixation

Abstract The importance of non-symbiotic N2 fixation in the reduced layers of submerged paddy soils was stressed in previous papers by field surveys (1, 2) and model experiments in the laboratory (2, 3). In these investigations, the activity of the non-symbiotic N2 fixation in the manured plots was found to be higher than that in the non-manured plots. Now, it is rather well established that fairly large part of soil organic matter exists in the form of organic debris in paddy soils (4), that the amount of organic debris is larger in manured plots than in non-manured plots (5) and that soil microbial activities are high on and around the organic debris (6). The organic debris might be the active micro-sites for non-symbiotic N2 fixation. The experiment conducted on this assumption will be described in the present paper.

Application of N2/Ar ratio method for N2 fixation studies in submerged soil

Abstract Recently there has been developments in the measurement of N2 fixation due mainly to the C2H2 reduction method (1). This method, however, has several disadvantages, especially for submerged soil, and the estimated amount of fixed N2 on the basis of the C2H2 reduction activity is not very reliable. The tracer 15N2 technique which gives a reliable estimation of the fixed N2 is too expensive for common use. Development of an alternative method suitable for submerged soil would therefore be desirable. The present authors expected that the measurement of the ratio N2/Ar in the soil solution might provide advantages for the estimation of the fixed N2 in submerged soil.