不同钾肥对土壤铅植物有效性的影响及其机制

采用盆栽试验,观测了水稻土上钾常规用量(K,0.11 g·kg-1)下施用4种钾肥(KH2PO4、K2SO4、KNO3、KCl)后小油菜对铅的吸收量及土壤铅的形态转化.结果表明,与不施钾肥的对照相比,施用KH2PO4和K2SO4能够抑制植株吸收铅,其中施用KH2PO4作物生长第2季在铅低污染(Pb1=300 mg·kg-1)和高污染水平(Pb2=500 mg·kg-1)下植株体内铅含量分别降低了35.6%和45.4%;KNO3对植物铅吸收也有一定的抑制作用,KCl则促进了植株的铅吸收.在铅低污染水平时,施用KH2PO4和K2SO4降低了水溶交换态和碳酸盐结合态的铅,而铁锰氧化态、有机结合态和残渣态则显著增高;对于铅高污染土壤,仅在施用KH2PO4时表现出和铅低污染水平下相似的效果.在2种铅污染水平下,施用KCl的土壤水溶交换态或碳酸盐结合态铅都明显提高,说明其能增加铅的植物有效性.钾肥影响铅植物有效性的机制之一是改变了土壤中铅的赋存形态.

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.