AVAILABILITY AND THE RELATED MECHANISMS OF CADMIUM IN SOILS AS INFLUENCED BY THE APPLICATION OF STRAW OR PIG MANURE

A pot experiment was conducted to study the effects of straw or composted pig manure application on availability of cadmium(Cd) in soil and the related mechanisms.Results showed that application of straw increased Cd uptake and pig manure decreased Cd uptake of leafused lettuce.It was mainly because that straw increased exchangeable Cd and pig manure decreased exchangeable Cd.The effect of straw or pig manure on exchangeable Cd was related to the changes of humic acid(HA) and fulvic acid(FA).When straw was applied the increase of FA in the soil was more than HA and HA/FA ratio decreased,while application of pig manure increased HA/FA.Statistical analysis showed that soil HA/FA ratio was negatively correlated with soil exchangeable Cd(P0.05).Results also showed that the aromatization of humic substance was higher in soil applied with pig manure than the soil amended with straw.It was concluded that the availability of Cd in soil could be influenced by the changes of organic fractions after application of organic materials.