Copper(Cu), arsenic, and cadmium(Cd) are designated as specific substances of the Agricultural Land Soil Pollution Prevention Act in Japan. It has been known that high Cu concentrations in soil layers reduce rice crop production and therefore agricultural practices such as soil dressing have been applied to minimize damage to crops by Cu pollution. In this study, we investigated the effects of percolation patterns of the plowsole and the subsoil on growth and yield, and Cu uptake of paddy rice.

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... Six stratified paddy field models were constructed to conduct growth tests under the condition that the percolation patterns of plowsole and subsoil were in an open or closed system. These models had a plow layer and an upper plowsole made with 12.5cm-thickness of non-polluted soil dressing (3.7 mg/kg) and underlying 15cm-thickness of a polluted lower plowsole and a subsoil layer whose Cu concentrations were either higher (approximately 150 , 250 , 500mg/kg) or lower (approximately 40,70,100mg/kg) than Japanese safety standards (125mg/kg). The two percolation systems were applied to paddy field models by controlling the ground water level at 57.5 cm and 12.5 cm for the open system and closed system model respectively. During the tests, a constant water-ponding system was adopted, and mid-summer drainage was not done. In open system percolation, the pressure head of the plowsole and subsoil were negative but in closed system showed positive pressure. The plow layer of O-40, O-70, O-100, O-150, O-250 and O-500 became reduction layers (under -100mV) while the plowsole and the subsoil became oxidation layers (over 400mV). On the other hand, Eh values of C-40, C-70, C-100, C-150, C-250 and C-500 were gradually decreased after transplanting, and in due time all the layers became reduction layers as Eh values showed under 0 mV. This means that, in this study, the polluted soil layers in O-40, O-70, O-100,O-150, O-250 and O-500 were under oxidation condition while those layers in C-40,C-70, C-100, C-150, C-250 and C-500 were under reduction condition. As a result, Cu concentrations in the rice grains were 5% significantly higher in the open system percolation models regardless of the original amount of Cu in the plowsole and subsoil. On the other hand, we did not recognize the significant difference in growth and yield of rice plants among the models. We concluded that the Cu concentrations in rice plants were affected by percolation patterns of the polluted plowsole and subsoil even though they were covered with non-polluted soil dressing layers.