Abstract
This research aimed at clarifying the infl-ence of the oxidation-reduction state in soil by ground-water level control on the growth and the yields of soybeans and the uptake of cadmium in soybean seeds. We cultivated soybeans in three devices which could control groundwater levels. In the first and second de-vices, the groundwater levels were fixed at 10 cm and 40 cm, respectively. In the third device the groundwa-ter level could be altered between 10 cm and 40 cm by using a flexible overflow relief well. All three devices were filled with the same 80 % pulverizability soil and the experiment was conducted for three years from 2007 to 2009. 1）In all the three devices, the soil above the ground-water was in an oxidation state （>300 mV） through-out the cultivation period, and soil under the ground-water level was in a reduction state（<300 mV）. In the third device, redox potential in the soil changed quickly when the groundwater level was altered. 2）The volumes of roots in the three devices were the largest between the surface and the 10 cm depth. At a depth lower than 10 cm, the volumes of roots de-creased. Many rootlets were found spread laterally at the 0－10 cm depth in the first and the third devices. In the second device, thick roots existed at as low as the 40 cm depth. In the third device, the volume of roots at a depth lower than 10 cm was less than that in the second device, but they extended down to the 40 cm depth. 3）The yield of the first device was less than those of the others. In the second and third devices, the growth of the soybean plants was similar up to the beginning of the blooming phase. But the yield of the third device was lower than that of the second one. 4）The concentration of cadmium in soybean seeds in the first and third devices was lower than in those in the second device. 5）Our experiment suggested that the groundwater level control after blooming was effective on the con-trol of cadmium uptake.
