Immobilization of Cadmium in Contaminated Soil Using Organic Amendments and Its Effects on Rice Growth Performance

Cadmium (Cd) contamination of rice is a serious public health concern in certain parts of the world. Amendment application based on local organic materials (e.g., manures, compost) is considered effective for reducing plant-available Cd in soil. In this study, two Thai rice (Oryza sativa L) varieties, Chorati and Mali Daeng, were grown in Cd-contaminated soil amended with cow manure, pig manure, organic fertilizer, and leonardite in a mesocosm system. Organic amendment treatments reduced Cd availability in soil. Specific effects of amendments were a function of amendment type and rice variety. Cow manure and leonardite substantially increased growth of the Mali Daeng variety in Cd-contaminated soils; however, there was no significant effect on total biomass of Chorati. Leonardite significantly enhanced grain production of Chorati (12.2 g plant−1) and reduced Cd content in rice grain to 0.14 mg kg−1 which is considered safe for consumption. Leonardite increased CEC in contaminated soil which helped reduce Cd bioavailability to plants. Both rice varieties had ‘excluder potential,’ as they accumulated Cd primarily in roots with translocation factor (TF) values < 1. Root anatomical analysis revealed that leonardite and pig manure treatments increased metaxylem vessel area, which could result in the enhancement of TF in the Chorati variety. However, any increase in TF was not associated with Cd content in rice grains. Our findings indicate that organic amendments immobilized Cd in soil and enhanced rice growth and production while reducing Cd content in rice grain. We emphasize here that the selection of cultivars and amendments plays a key role in the success of low-Cd rice production.