Effects of the Percolation Patterns and the Thickness of Soil Dressing on Reducing Cadmium Uptake and and Yields of Rice Plants （Oryza Sativa L.）

The objective of this study is to clarify the effects of the thickness of soil dressing, the percolation patterns of plowsole and subsoil on reducing cadmium （Cd） uptake, and growth and yields of rice plants. Six stratified paddy field models, three patterns of soil dressing layer and two percolation patterns were used for the experiments. These models had 12.5 cm, 15.0 cm and 25.0 cm thickness of soil dressing layer and 15 cm thickness of underlying polluted soil layer, whose Cd concentration was about 1.81 mg·kg^-1. As a result Cd concentration of brown rice was lower than 0.04 mg·kg^-1 for the models with the close system percolation, while that in the open system percolation models were lower than 0.17 mg.kgl.When the thickness of soil dressing became lower, Cd concentrations with the open system percolation models showed significantly higher values than those of the other models （5% of significant level）. But any significant difference was not found in the growth and yield among these models. As above mentioned, it was found that Cd concentration in rice grains was affected by the thickness of soil dressing and percolation patterns.

Groundwater Level Effect on Redox Potential, on Cadmium Uptake and Yield of Soybean

In this greenhouse experiment, we investigated the effects of two constant groundwater levels: 10 cm groundwater level (GW-10) and 40 cm groundwater level (GW-40) and one change groundwater level, which was 40-10-40 cm (GW-40-10-40) on Cadmium (Cd) uptake and seed yield of Soybean plant in Cd contaminated soils (1.57 mg·kg-1). The experimental soil layer was made with gravel layer (14 cm), non-polluted soil (15 cm) and polluted soil (25 cm). The redox potential of every soil layer was measured from sowing to harvesting. The soil layer (10 – 40 cm) of GW-10 was always in reduction condition and that of GW-40 was always in oxidation condition. First 50 days of GW 40-10-40 were in oxidation and next 50 days in reduction and final 20 days again returned in oxidation condition. Soybean seed Cd concentration was significantly highest in GW-40-10-40 (1.16 ± 0.13 mg·kg-1) and lowest in GW-40 (0.81 ± 0.12 mg·kg-1). Cd concentration of stem was found significantly higher in GW-40 (1.7 ± 0.2 mg·kg-1) than GW-10 (0.91 ± 0.08 mg·kg-1) and GW-40-10-40 (1.28 ± 0.13 mg·kg-1). There was no significant difference in root Cd concentration among these 3 treatments. Main stem height of soybean plant and 100 seed weight of GW-40 were significantly higher than those of GW-10. The result revealed that, soil redox condition is an important factor for Cd uptake in soybean plant and seed yield of soybean. This study will help to manage the farming process more appropriately with the aim of minimizing uptake of Cd and other toxic metals in grain crops.

Influence of Percolation Patterns and Soil Copper Concentration on Copper Uptake,and Growth and Yield with Copper-Polluted Stratified Paddy Fields

Copper(Cu)was designated as a specific substance in 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 thus agricultural practices such as soil dressing have been applied to minimize the damages to crops by copper pollution.In this study,authors investigated the effects of percolation patterns of the under-plowsole and subsoil on growth and yield,and copper uptake of paddy rice.Six stratified paddy field models were constructed to conduct the growth tests under the condition in which the percolation patterns of the under-plowsole and subsoil were in an open and closed system.These models have a plow layer(10 cm thickness)and upper-plowsole(2.5 cm thickness)made with 12.5 cm-thickness of non-polluted soil dressing(3.7 mgCu?kg-1)and an underlying 15 cm-thickness of polluted under-plowsole(7.5 cm thickness)and subsoil whose Cu concentration was higher or lower than Japanese safety standard(approximately 100 mgCu?kg-1,150 mgCu?kg-1 and 500 mgCu?kg-1,respectively).During the tests,a constant water-ponding system was adopted,and mid-summer drainage was not done.As a result,Cu concentrations of the rice grains were 5%significantly higher in the open system percolation models regardless of the original amount of Cu in the under-plowsole and subsoil.On the other hand,authors did not recognize any significant differences in growth and yield of rice plants among the models.Authors concluded that the Cu concentrations in rice plants are affected by percolation patterns of polluted plowsole and subsoil even though they are covered with non-polluted soil dressing layers.