Effect of applying chemical fertilizers on forms of lead and cadmium in red soil

A three-month incubation study was undertaken to examine the influence of N , P and K on the various forms (soluble plus exchangeable (SE), weakly spec ifically adsorbed (WSA), Fe-Mn oxides bound (OX), organic matter complexed (OM) and residual fractions (RES)) of lead (Pb) and cadmium (Cd) in a red s oil. Application of urea at the rate of 200 mg N/kg significantly lowered t he SE fraction, but raised the WSA or OX fraction of both metals. Supply of 80 mg P/kg caused a decrease in the SE fraction of the two metals. The WSA fraction of Pb was reduced, whereas that of Cd increased by adding P. Howe ver, addition of 100 mg K/kg led to an increase in the SE fraction, but a d ecrease in the WSA fraction of Pb and Cd. Applying chemical fertilizers had no significant consistent influences on the other fractions of metals. The se findings suggest that in heavy metal contaminated red soil, applying fer tilizers does not only provide plant nutrients, but may also change the spe ciations and thus biovailability of heavy metals. (C) 2000 Elsevier Science Ltd. All rights reserved.