Root System Formation in Rice Plant and Soil Environment

[摘要] Root system formation in rice plant was studied by means of an improved monolith method in relation to soil conditions of seventeen paddy fields of the farmers at Yamagata, Akita, and Gifu prefectures in Japan. It was found in every paddy field that root system formation is greatly affected by the plow-sole in paddy. As to the distribution rate of crown roots into the direct foot-layer of soils, it was proved that the distance from the "center" of the root system (not from the soil surface, × mark in fig. 1) to the plow-sole in paddy soils is a positive factor in deciding it, regardless of such differences as soil texture, variety of rice plant, cultural methods, districts, and etc. In addition to the effect of the plow-sole on the root distribution, the effect of vertical water percolation in paddy soils on it was clarified. When the distance from the "center" of the root system to the plow-sole is the same, root systems at the paddies of very remarkable water percolation (8∼13 cm per day) have the higher distribution rates into the direct foot-layers than those of comparatively low water percolation (0∼5 cm per day). More detailed observations on crown root distribution into three layers of paddy soils (namely, top-, side-, and oblique foot-layer, fig. 1) reveal the following facts: The distribution rate into the top-layer seems to be dominant when the distance from the "center" of the root system to the plow-sole is short (4∼7 cm); and into the side-layer, when it is moderate (10∼12 cm); and then into the oblique foot-layer, when it is long (14∼16 cm). Furthermore, it was found that when vertical water percolation is very remakable (8∼13 cm per day.), crown roots (primary roots) with many secondary roots are densely distributed within a limited region (fig. 4, B1∼B4), and when the percolation rate is comparatively low (0∼5 cm per day), long crown roots with few secondary roots are sparsely distributed within a larger region (fig. 4, A1∼A5). In future, another investigations should be continued into the mechanism of such effects mentioned above on root distribution, together with phenomenon of geotropism of each crown roots.

[学科分类] 农业科学（综合）