[Effects of different potassium fertilizers on the phytoavailability of Pb in soil and its mechanisms].

Effects of four kinds of potassium fertilizer (KH2PO4, K2SO4, KNO3 and KCl) in its conventional application rate as K, 0.11 g x kg(-1) on the Pb absorption by rape and speciation of Pb in paddy soil were examined by pot trial. Results showed that the Pb content in rape decreased with using KH2PO4 and K2SO4, and in the second season of pot trial for KH2PO4 treatment, Pb content in rape shoots under Pb1 (300 mg x kg(-1)) and Pb2 (500 mg x kg(-1)) level decreased by 35.6% and 45.4% respectively compared with control treatment. Applied KNO3 in soil also decreased Pb content in rape shoots to some extent, but KCl had adverse effect. At lower Pb level (300 mg x kg(-1)), KH2 PO4 and K2SO4 caused Pb in soil transformed from non-residual fractions to residual fraction substantially and for higher Pb level (500 mg x kg(-1)) only KH2PO4 application had similar effect. Under two contaminated Pb levels, exchangeable and carbonate fraction Pb in soil by using KCl were all enhanced, which indicated that KCl could promote the phytoavailability of Pb. As thus one of the most important mechanisms of potassium fertilizers influencing Pb phtoavailability was changing the speciation of Pb in soil.