EFFECT OF ACIDULATION OF HIGH CADMIUM-CONTAINING PHOSPHATE ROCKS ON CADMIUM UPTAKE BY UPLAND RICE

Little information is available in literature on Cd uptake by crops fr om either phosphate rock (PR) or partially acidulated PR (PAPR). The p urpose of this greenhouse experiment was to study the effect of acidul ation of two PRs having high Cd content (highly reactive North Carolin a PR and low-reactive Togo PR) on Cd uptake by upland rice. The degree s of acidulation with H2SO4 were 100% for North Carolina PR (NC-single superphosphate [SSP]) and 50% or 100% for Togo-PR (i.e., Togo PAPR or Togo-SSP). Separation of the confounding effect between P uptake and Cd uptake from various P sources was made by adding 200 mg P/kg as KH2 PO4 to all the treatments. Rates of Cd added from various P sources we re 50-400 mu g Cd/kg. Upland rice (Oryza sativa L.) was grown on two a cid soils (Hartsells, pH 5.0 and Waverly, pH 5.6) to maturity. The res ults show that Cd uptake by rice grains followed the order of NC-SSP > NC-PR and Togo SSP > Togo PAPR > Togo PR. The results also showed tha t most of the Cd uptake was retained in rice roots and straw. Total up take of Cd, Ca, and P by rice plant (root, straw, and grain) was highe r from NC-PR than from Togo-PR. Cd concentration in rice grains showed no significant difference between NC-PR and Togo-PR, whereas Cd conce ntrations in root and straw were higher with NC-PR than that with Togo -PR. There was a significant relationship between total Cd uptake by r ice plant and Cd extracted by DTPA from soils treated with various P s ources at 400 mu g Cd/kg.