Response of alkaline functional fertilizer on Cd absorption and transportation in soil-rice system

Reduction of cadmium accumulation in rice grain is of great significance for food safety. The purposes of this study were to investigate the efficacy and mechanism of alkaline functional fertilizer (AFF) on soil acid, available cadmium (Cd) and its and accumulation in rice through three field experiments in Hunan province with different soil type by use of conventional fertilizer as control. Results showed that soil pH value was increased with the amount of the AFF, the maximum increment of the pH was 1.65 units. Soil available Cd was reduced with increase of the AFF and soil pH value, and it decreased by 12 %, 38 % and 44 % in the three sites, respectively. The rice yield was related to the original or basal soil pH and available cadmium content. The yield increased by 4–16 %, 12–27 % and 9–24 %, respectively. Cd content of root, stem, leaf and polished rice reduced by 78.75 %, 88.05 %, 84.05 % and 80.38 % by use of the AFF in the three sites, respectively. The Cd content of polished rice would be declined below the allowable limit of food safety standard in China (0.2 mg·kg−1). The Cd enrichment coefficient (ERC) was in the order of root > stem > leaf > polished rice. The results of index of transport coefficient (TC) showed that Cd in polished rice mainly came from stem and leaf. The Cd content in the leaf and stem should be reduced first to reduce the Cd content of polished rice. The mechanism of the AFF reducing Cd uptake and accumulation lies in the fertilizer neutralizing both active and potential soil acid by slow release of OH–. The fertilizer was capable to increase soil cation exchange capacity and passivate Cd to reduce its bio-availability. Development and promotion of the AFF are significance to decline Cd transport in the soil–plant ecosystem and ensure food safety. The recommended economic fertilization rate of the AFF is 3000 to 4500 kg/ha