Amelioration of Cadmium Polluted Paddy Soils by Porous Hydrated Calcium Silicate

Abstract

Porous hydrated calcium silicate (PS) is a by-product of autoclave light weight concrete and is being used as a silicon fertilizer in Japan. The impacts of this amendment on the yield and cadmium content of rice (Orzya sativa L. var. Kokoromachi), soil pH and the extractability of soil cadmium assessed by 1 M NH4OAc were compared with those of silica gel and CaCO3 by pot experiments. The application of PS at the rate of 2.0% and silica gel at the rate of 1.0% in Andosol and PS at the rate of 0.75% in Alluvial soil significantly increased the grain weight of rice. PS and CaCO3 treatment significantly increased soil pH, decreased the 1 M NH4OAc extractability of cadmium and reduced cadmium content in straw and brown rice in the two soils. However, cadmium content of rice of PS treatments was not significantly different from that of CaCO3 treatments in Andosol, while was significantly lower than that of CaCO3 treatments in Alluvial soil. Soil analysis showed that it was less effective in increasing soil pH and decreasing the extractability of cadmium by 1 M NH4OAc than CaCO3 at the same application rate in Andosol. Soil pH and 1 M NH4OAc extractability of cadmium were not significantly different between 2.0% of PS and CaCO3 treatments in Alluvial soil. The application of silica gel did not improve soil pH nor decrease the extractability of soil cadmium, but resulted in a significant decline of cadmium content in brown rice. These results demonstrate that the supply of silicon together with an increase in soil pH, as obtained by PS application, shows potential to reduce the cadmium content of rice.