Suppressive effects of magnesium oxide materials on cadmium uptake and accumulation into rice grains

The objective of this study is to assess the applicability of a commercial magnesium oxide (MgO) and a composite material containing MgO and natural minerals ('MgO-SH-A') as the soil amendments for suppression of cadmium (Cd) uptake and accumulation into rice grains. A cultivation experiment of rice plants (Oryza sativa L. cv. Kinuhikari) was conducted in an actual Cd-contaminated alluvial paddy field to evaluate the effectiveness of these materials. The 'plant available' fractions of Cd in the paddy soil significantly decreased by application of commercial MgO at 2250 kg ha−1 or MgO-SH-A at 4500 kg ha−1. These decreases would be primarily attributed to the increase in soil pH due to applications of the MgO materials because these soil Cd fractions were significantly negatively correlated with the soil pH. Even under a suppressive condition for Cd uptake by rice plants, i.e., continuous flooding of the paddy field around the heading stage, applications of these materials further reduced Cd concentration in brown rice as compared to that from the control. It was concluded that the two MgO materials examined would be effective in preventing Cd contamination of rice grains grown in Cd-polluted paddy fields.