Effects of various inorganic soil amendments containing alkalinity and soluble silicate on cadmium uptake by lowland rice [Oryza sativa]

This study was conducted to evaluate the effects of various inorganic soil amendments containing alkalinity and soluble silicate on Cadmium (Cd) uptake by lowland rice from the viewpoint of the ability in amendment of soil pH and silicon-supplying. Lowland rice (Oryza sativa L. cv. Koshihikari) was cultured in frames (0.3m x 0.3m) set in paddy field slightly polluted with Cd in Jinzu River basin. The most effective amendment to restriction of Cd uptake was fused silicate phosphate fertilizer (FSP) and Cd content in brown rice and straw was reduced to each 52% and 40% equivalency of control plot. Cd uptake in brown rice and straw was also restricted to 61% equivalency of control plot with FSP. As to the ability in amendment of soil pH FSP showed high performance, and it maintained soil pH around 6.7 after 14th day before heading. Though autoclaved lightweight concrete fertilizer (ALC) rose soil pH to 7.13 until heading stage, since then in ripening period pH decreased to 5.63. Since in the high range of the average soil pH in latter growth stage Cd contents in brown rice were reduced below 0.4mgkgsup(1), it was considered that inorganic soil amendment had high ability to amend soil pH in latter growth stage reduced Cd content in brown rice efficiently. As to the ability in silicon-supplying, FSP and ALC were more effective and silicate content in straw with FSP and ALC application were 35gkgsup(1) higher than control plot (71.3gkgsup(1)). Cd contents in brown rice were reduced with increase of silicate content in straw, so this tendency hinted at the possibility that Cd uptake by lowland rice was restricted with the accumulation of silicate in straw. Because positive correlation was recognized between average soil pH in latter growth stage and silicate content in rice straw (r=0.915**), it was considered that inorganic soil amendment had high ability to amend soil pH also had high ability in silicon-supplying.