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1.Methanogenic Microbial Ecosystem in Paddy Field Soil

-Distribution of Methanogenic Activity in Soil Fraction, Rice Roots and Plant Residue and their Seasonal Changes in Paddy Soil-

Atsuko Ueki and Nobuo Kaku(Faculty of Agriculture, Yamagata University)

Distributions and seasonal changes of methanogenic activities in soil fraction, rice roots and plant residue in rice paddy soil were investigated. Methanogenic activity was usually detected in every fraction during the cultivation period of rice plants. The activity of soil fraction was rather low until late June and then it rapidly increased. Rather high activity was maintained during July and then it decreased to much lower levels by late September. Methanogenic activity on rice roots increased also at late June and rather high activities were detected during August. As for plant residue, a rather high activity was detected even just after the transplanting of rice plants and the high level of activity was kept until early July. The activity of plant residue dropped earlier than those of other fractions during July. Changes of amounts of rice roots and plant residue in paddy soil during the cropping season were measured using hill plots which were amended with rice straw and placed in the same paddy field. From the changes of methanogenic activity and the amount of each fraction, the changes of contribution of each fraction to the total activity in paddy soil during the cropping season were estimated. It appeared that plant residue largely stimulated the methanogenic activity early in the cropping season and inversely rice roots stimulated late in the cropping season.

Keywords: methane, Paddy soil, Anaerobic bacteria, Greenhouse gas, Flooded soil