The CO_2 concentration and micrometeorological measurements were carried out in a dryland paddy field throughout a growing season, and the relationship between the concentration and soil water flow was examined. Generally, CO_2 concentrations tend to reach maximum values before sunrise under the influence of both plant respiration and soil respiration, and the concentration decreases during the day caused by photosynthesis. Exception of this trend occurs on windy days and during rain in the night. In such instances, the concentration does not peak before sunrise. Early-morning peaks in CO_2 concentration were not detected from the examination of diffusion velocity because the physical effect of falling raindrops did not diffuse the CO_2 gas near the plant canopy. On the other hand, from the comparison between soil water flow with a daily level water balance and CO_2 concentration at 4 : 00 a. m., it was found that the CO_2 concentration near the ground surface increased with an upward soil water movement on clear days. However, CO_2 concentration did not increase when a downward soil water flow occurred during rain in the night. This suggests that the CO_2 concentration decrease before sunrise on rainy nights was mainly caused by the downward movement of soil water, and it restrained the upward emission of soil respiration. The problem is whether the decrease is a temporary phenomena or an everlasting one. It is necessary to chemically investigate the behavior of carbonated water with atmpspheric CO_2 measurement. Also, more detailed experiment with weighing lysimeter are needed, or the same tests applied to drier soil