Cadmium availability and uptake by radish (Raphanus sativus) grown in soils applied with wheat straw or composted pig manure

Soil cadmium (Cd) availability and uptake by cherry-red radish (Raphanus sativus) grown in Cd-contaminated soils after addition with wheat straw or composted pig manure were studied. The results indicated that wheat straw application promoted radish growth until the second harvest, while pig manure application improved radish biomass in Acid Ferralsols regardless of harvesting seasons. Application with pig manure might be more effective in lowering the Cd uptake by radish than wheat straw. Especially when pig manure of 11.9 g TOC kg(-1) amended into Acid Ferralsols, Cd contents in leaves and roots of radish decreased by 89.2 and 95.7% at the second harvest, respectively. The changes in Cd fractions distribution in soils after application were contributed to the decline of Cd availability. Furthermore, significantly negative linear correlation (P < 0.05) between the ratio of humic acid (HA) and fulvic acid (FA) in soils and exchangeable Cd was also observed. However, the significantly negative relationship (P < 0.01) between soil pH and exchangeable Cd was merely found in pig manure-treated Acid Ferralsols. The increases in HA/FA ratio or pH values in soils after adding organic materials were also responsible for the decrease of Cd availability in soils and uptake by radish. Thus, it is recommended to stabilize soil Cd and reducing plant uptake by application with composted manure without or slightly contaminated with metals.