[Remedying Effects of a Combined Amendment for Paddy Soil Polluted with Cd for Spring and Autumn Rice]

An in-situ paddy experiment was conducted to study the remedying effects of a combined amendment(calcium carbonate+diatomite+ferric sulfate) on Cd bioavailability in soil and Cd accumulation in rice for spring and autumn rice planted in a certain Cd contaminated paddy soil in Beishan Town, Changsha, Hunan Province. The results showed that:Application of the combined amendment significantly increased soil pH and CEC values in both cultivated seasons, but decreased soil OM contents for the spring rice. During the experiment, the contents of TCLP-extractable Cd and CaCl₂-extractable Cd in soil were reduced by 18.0%-33.0% and 5.4%-57.9%, respectively. The Cd contents in brown rice, husk, leave and root for the spring rice decreased by 29.6%-56.1%, 52.1%-54.0%, 18.1%-80.7% and 24.4%-41.6%, respectively, due to application of the combined amendment. There were significant differences in Cd transport capacity between spring rice and autumn rice, and the transportation of soil Cd in autumn rice was smoother than that in spring rice. For the autumn rice, the effects of the combined amendment were not significant(P>0.05), except that the Cd content in husk increased a little after applying 2 g·kg^-1 of the combined amendment. Significant positive correlations were found between the Cd contents in brown rice and the contents of TCLP-extractable Cd or CaCl₂-extractable Cd in soil. Application of the combined amendment effectively inhibited Cd uptake by rice root and reduced Cd content in brown rice for the spring rice; however, these remedying effects were significantly weakened for the autumn rice due to loss of the combined amendment with the movement of irrigation water in the spring season. Therefore, we suggest that supplement of the combined amendment is necessary between two rice cultivated seasons.