Differences in the influence of cadmium on the decomposition of various types of organic materials in soil

The influence of Cd on the decomposition of various types of organic materials in soil was studied. CdCl2 or CaCl2 (control) was added to a Gley soil at a level of 10 mmol kg(-1) soil. Three days later, organic materials including glutamic: acid, glucose, casein, starch, cellulose, lignin, rice straw, rice straw compost, or 3 kinds of sludges mere mixed with the soil in a proportion of 1%, respectively. During an 8-week period of incubation at 28 degrees C, CO2 evolution was measured periodically. At the end of the incubation period, the form of Cd in the soil was analyzed by successive extractions with water, CaCl2, CH3COOH, Na4P2O7, and with hot HCl after HNO3-HClO4 digestion. The decomposition of all the organic materials mas inhibited by the addition of Cd, but the degree of inhibition varied considerably among the types of organic materials. The decomposition of rice straw, rice straw compost, and sludges was markedly inhibited by Cd. The amount of mater-soluble Cd was less in the soils treated with rice straw, rice straw compost, and sludges than in the soils treated with other types of organic materials, while the amounts of CaCl2-extractable Cd were much larger in the latter soils. In the case of rice straw, rice straw compost, and sludges Cd was easily adsorbed from the CdCl2 solution. These results suggest that the inhibition of organic matter decomposition by Cd is caused by the adsorption of Cd onto organic matter.