Sorption and immobilization of Cu and Pb in a red soil (Ultisol) after different long-term fertilizations

The sorption and immobilization of Cu and Pb in a red soil (Ultisol) treated by no fertilizer (Ck), chemical fertilizer (NPK), a mixture of chemical fertilizer and straw (NPKS), and animal manure (AM) from a long-term fertilization experimental site were studied. Compared to the sorption on Ck soil, the maximum amount of Cu and Pb sorption increased by 16% and 31%, 19% and 42%, and 30% and 45% on NPK, NPKS, and AM soil, respectively. The removal of organic matter from soils decreased the sorption of Cu but increased the sorption of Pb. The sorption of Cu and Pb on the examined soils was reduced by the presence of Ca. However, the inhibition was smaller on the fertilized soils than on non-fertilized soil and was weaker for Pb than for Cu. After the aging of Cu and Pb in the examined soils for 2 months, the proportion of reducible Pb was much higher than that of reducible Cu, whereas that of acid-soluble Cu was much higher than that of acid-soluble Pb in the corresponding soils. The fertilization, especially AM treatment, decreased the percentage of the acid-soluble fraction of Cu and Pb but increased the proportion of the reducible fraction, suggesting that the immobilization of Cu and Pb in the Ultisol was strengthened by the fertilization, especially by the animal manure treatment. These findings could be useful in assessing and controlling heavy metal pollution in Ultisols.