YIELD AND CADMIUM CONTENT OF RICE GRAIN IN RELATION TO ADDITION RATES OF CADMIUM, COPPER, NICKEL, AND ZINC WITH SEWAGE SLUDGE AND LIMING

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Abstract
A greenhouse experiment was conducted with an acid soil, with and without lime, pretreated with cadmium at rates up to 10.0 micrograms per gram of soil in factorial combination with low to high amounts of copper, nickel, and zinc. The treated soils were placed in sealed pots, flooded, and cropped to rice under flooded management to have a measure of Cd availability at low addition rates, as influenced by low to high addition rates of Cu, Ni, and Zn under unlimed and limed conditions. Yield of rice grain was related to metal treatments and soil pH through multiple regression analysis. The most significant equation revealed the parameters influencing grain yields to be only soil pH and the Cu addition rate (combining the unlimed and limed soil experiments). Disregarding the high Ni treatment, we found the Cd content of rice grain to be dependent upon the Cd addition rate and soil pH only; additions of Cu, Ni, and Zn had no significant effect on Cd uptake and accumulation in rice grain. The maximum permissible Cd addition rate was found to be strongly pH dependent.