Study On Interaction Of Phosphate And Heavy Metal (Zinc,Cadmium) In Calcareous Soils

The interaction of P-Zn and P-Cd in soil-plant system were researched by pot experiment; the interrelationship of P-Zn in calcareous soils and the effect of phosphate on sorption & desorption of Zn2+ were researched by soil incubation and sorption & desorption in lab; and discussed the mechanism of P-Zn interaction in calcareous soils. The results were as follows:1. In calcareous soils, applying phosphorus fertilizer increased the concentration of DTPA-extractable zinc in soil, and zinc fertilizer addition increased the concentration of available phosphorus in soil too, that is, the interaction between phosphorus and zinc in calcareous soils is synergism. But this synergism works under a certain limitation. When p & Zn added too much, the synergism would be weaken, and even become antagonism.2. Zn2+ adsorption by the soil with different phosphorus concentration (or sorption) were simulated with classical Langmuir equation, showing that the Zn2+ maximum sorption (Xm) and the constant of sorption (K) become small with the increase of phosphorus concentration (or sorption) in soil. Which indicated that the increase of both phosphorus concentration and phosphate sorption in calcareous soil could decrease the Zn2+ maximum capacity and capability of Zn2+ sorption. Besides, with the increase of phosphate sorbed, Zn2+ desorbed by KCl increased obviously, on the contrary, Zn2+ desorbed by HCl decreased. It showed that phosphorus addition could increase the availability of sorbed zinc, which indicated further that addition phosphorus could enhance the availability of zinc in calcareous.3. The availability of zinc in soils changed markedly with the different kinds of phosphates applied. Ca1-P,Ca2-P and Ca8-P increased the availability of Zinc in the follow order: Ca1-P>>Ca2-P>Ca8-P. On the contrary, Fe-P decreased the availability of zinc in soils. Ca10-P and Al-P has no significant effect on availability of zinc.4. The results of pot trail showed that applying phosphorous and zinc promoted the growth of wheat. Applying zinc increased significantly the zinc concentration and accumulation in wheat plant. On the background of low level phosphorous, zinc addition has no significance effect on P concentration and accumulation in wheat plant; On the background of high level phosphorous, zinc addition increased the P concentration and accumulation in wheat plant. Applying phosphorous fertilizer increased significantly the P concentration and accumulation in wheat plant; Phosphorous addition decreased P concentration in wheat plant, but increased P accumulation in wheat plant.5. In calcareous chao soil, the interrelationship between phosphorous and cadmium is similar with between phosphorous and zinc. When low level of p & Cd were added, the interaction is synergism, but is antagonism when addition p & Cd exceeded a certain level. P addition in different degrees of Cd contaminated soil promoted the growth of vegetable, and increased the amount of uptake to Cd,Cu,Zn,Mn by vegetable plant, but decrease the concentration of Cd,Cu,Zn,Mn in plant. The concentration of Cd in plant has a positive correlation with the concentration of Cd addition into soils. Low level of Cd addition promoted the growth of vegetable, and increased the amount of uptake to phosphorous by plant, but decreased phosphorus concentration in plant; High level of Cd addition restrained the growth of vegetable, and decreased the amount of uptake to phosphorous of plant, but increased phosphorus concentration in plant. With the increase of Cd added into soil, the amount of uptake to Cu,Zn and Mn ascended at first and descended later.