Abstract
Accolding to the author's view, the superficial roots of rice plants develop near the surface, to a depth of up to 5 cm, beginning in the spikelet differentiation stage and extending to the full-ripe stage, but the formation of superficial roots is greatly affected by differences in water management of a paddy. The root systems used in paddy fields in this study were obtained from the University of Tokyo, the Agricultural Experiment Stations of Aomori and Fukushima prefectures, and farmers in Akita, Yamagata, Saitama, Chiba, Fukui and Saga prefectures in Japan. The systems of water management used for the paddy fields involved several techniques for flooding, midseason drainage, and intermittent irrigation. The result of observations of the superficial roots showed that primary roots growing in the fields of intermittent irrigation and midseason drainage increased in number, and the roots glowing in the fields of flooding decreased in number. Moreover, the former consisted of upper roots in the upper three shoots units, most of roots being distributed in the soil layer at the depths of (2-3) cm to (4-5) cm. The latter consisted of both upper and lower roots also appearing in the upper shoot units, most being concentrated in the soil layer at the depths ranging from (0-1) cm to (1-2) cm. It has been already shown by the authors that secondary roots on the primary roots of plants were divided into two types, i.e. thick secondary roots branched out tertiary roots and thin secondary roots branched out non-tertiary roots. In this study, it was found that the density of the formation of the thick secondary roots in the fields of intermittent irrigation and midseason drainage was also higher than that of fields of flooding. Superficial roots also showed the formation of additional lateral roots in the following ways: teriary roots in the fields of flooding, and forth roots in the fields of intermittent irrigation and midseason drainage. From the above-mentioned results, it is clear that a comparison of superficial roots formation in the fields of intermittent irrigation and midseason drainage, with that of superficial roots in the fields of flooding, the former showed more improvement than the latter.
