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 specifically adsorbed (WSA), Fe-Mn oxides bound (OX), organic matter complexed (OM) and residual fractions (RES)] of lead (Pb) and cadmium (Cd) in a red soil. Application of urea at the rate of 200 mg N/kg significantly lowered the 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. However, addition of 100 mg K/kg led to an increase in the SE fraction, but a decrease in the WSA fraction of Pb and Cd. Applying chemical fertilizers had no significant consistent influence on the other fractions of metals. These findings suggest that in heavy metal contaminated red soil, applying fertilizers does not only provide plant nutrients, but may also change the speciation and thus bioavailability of heavy metals.
