2016 年 7 巻 1 号 p. 6-14
Though soil dressing is one of the most effective methods for reducing cadmium (Cd) uptake in rice plants of Cd contaminated paddy fields, it needs large amount of soil and thus often requires a high cost and heavy environmental loads. In this study, we investigated any possibility of minimizing the thickness of soil dressing by utilizing mixing tillage before the soil dressing. 15 cm-thick mixed contaminated soil and overlying 12.5 cm-thick soil dressing (the conventional thickness of soil dressing being 20-30 cm in Japan) were used to form the usual stratified paddy field of the three layers (plow layer, plowsole, and subsoil). Cd concentration of the contaminated soil was adjusted to approximately 2.0, 1.0 and 0.5 mg/kg by mixing tillage. Then rice plants were grown under ponding condition during the cultivation and the experiments of each treatment were conducted under two different water flow systems, open and closed systems. As a result, Cd concentration in brown rice with water flow in an open system was 0.07 mg/kg, 0.05 mg/kg, and 0.17 mg/kg when Cd concentration of soil was 0.5, 1.0 and 2.0 mg/kg, respectively. Cd concentration in brown rice of 2.0 mg/kg soil was 5% significantly higher by 5% than those of other treatments. These results indicated that it was effective to dilute soil Cd concentration to 1.0 mg/kg for reducing Cd uptake of rice plants. There was no significant difference in growth and yield a way these treatments. However, we conclude that mixing tillage may have potential to minimize the thickness of soil dressing to half of the conventional thickness, 20 -30 cm, under ponding condition during the cultivation.
