The mechanism of reduction in waterlogged paddy soil

Elucidation of the laws governing the reduction process in flooded rice paddy soil is indispensable for developing the lowland rice cultivation system by which the oxidation-reduction conditions for optimum growth can be maintained throughout the growth of the crop. The authors’ efforts have been focussed on the microbial metabolism of the reduction process in paddy soil, using waterlogged soil incubated in closed syringes as a simplified model of rice paddy field soil under flooded conditions. Such conditions can be assumed to occur throughout the plowed layer of field soil under flooding, except for the uppermost layer to which oxygen is supplied. One may conclude from the results of this investigation that the type of microbial metabolism in waterlogged soil changes successively according to the oxidation-reduction state from aerobic respiration in the presence of molecular oxygen, which is the most efficient energy-yielding reaction, to methane fermentation, which appears to be a less efficient energy-yielding reaction.