The fluctuation of the surface, or relative depth of water within a paddy field, was related to yield and quality of the rice. A 0.5ha-transplanted paddy field having the fluctuation of elevation of about 100mm was used, and the level of water was monitored at several points of observation in the field. Following conclusions were obtained based upon these measurements for two years.
1) There was a slight tendency of greater yields at lower elevations, although it was not statistically significant. The yield components varied among the elevations; at the lower elevations, the number of panicles per hill-plant and the number of grains per panicle were greater, and vice versa the weight of kernel and the percentage of ripened grains.
2) The protein content in the kernel was significantly greater at lower elevations, which can be related to the smaller weight of the kernel and percentage of ripened grains mentioned above. The greater protein content could be also ascribed to continuous intake of nitrogen, as a result of continuous submergence of water on the soil.
3) There was a case that at poorly drained intermediate elevations in the middle of the field, the protein content was as high as at lower elevations. This implied that the management of the water level or drainage was essential as well as the leveling of the paddy field, so as to produce the rice of as uniform and low protein content as possible within the field.
