Effects Of Different Inorganic Fertilizer On Immobilization Remediation Of Farm Soil Contaminated By Cadmium

With the development of industrialization and urbanization, heavy metal pollution in farmland has become gradually prominent. The heavy metal is harmful of human health through the agricultural products into the food chain. As one of important agronomic measures, fertilization can promote the growth of crops and change the quality of soil environment, but also have different effects on the availability of heavy metals in soil and crop accumulation. In addition, the situ chemical stabilization process has the advantages of high efficiency, low cost, simple operation and so on, so it has been widely concerned by researchers. In this study, the effect of fertilization( N, P, K) on the immobilization are studied. The main research results are as follows:1.Pot experiment was conducted to investigate the effects of the two kinds of phosphates(alcium magnesium phosphate and calcium superphosphate) on the rape biomass and Cd content, soil pH and available Cd, and soil enzyme activities. The results showed that the rape biomass increased, but the available Cd content decreased to 0.18 mg·kg-1�'� 0.10 mg·kg-1, compared with the control groups which was 0.61 mg·kg-1, which met with the national food safety standards "the limits of contaminants in food"(GB 2762-2005), the maximum limits of Cd in the leaves and vegetables when the treatments of SSP was up to middle and high concentration. The soil available Cd was observed a certain degree reduction under the addition of calcium superphosphate and alcium magnesium phosphate. Compared with no-phosphate treated soil, the available Cd content in soil decreased under the application of calcium superphosphate and alcium magnesium phosphate. The activities of catalase increased under the treatments of higher level of calcium superphosphate and medium level of alcium magnesium phosphate. The urease activities significantly decreased under different concentrations of calcium superphosphate, while there were no significantly differences in invertase activities under the addition of calcium superphosphate and alcium magnesium phosphate.2. Pot experiment was conducted to investigate the effect of nitrogen fertilizer(urea and ammonium bicarbonate), phosphates(calcium magnesium phosphate and calcium superphosphate) and potash fertilizer(KCl and K2SO4) on the biomass of rice different parts, Cd accumulation, soil pH and soil Cd availability in paddy soil remediation and reveal the influence of different nitrogen fertilizers on the remediation effect and stability by analysizing the results.1) In this experiment of nitrogen fertilizer treatments, the order of Cd accumulation in rice different parts was root > straw > brown rice> rice shell. In stabilization remediation of Cd contaminated soil,application of different doses of urea and ammonium bicarbonate can further increase the biomass of rice, rice shell, straw and leaf. The Cd concentration in brown rice is further reduced and met with the national food safety standards "the limits of contaminants in food". And the effect was more and more obvious with the increasing application of urea. When the medium dose of ammonium bicarbonate was added, the reduction of Cd accumulation in rice is the most obvious, reaching by 0.12 mg·kg-1.2) In this experiment of phosphate fertilizer treatments, the order of Cd accumulation in ricedifferent parts was root > straw > brown rice> rice shell. Under immobilization remediation of Cd pollution farmland, the application of different doses of calcium magnesium phosphate and low and high dose of calcium superphosphate can further promote the rice growth. The Cd availability was increased in some degree under all the calcium magnesium phosphate and calcium superphosphate treatments. The Cd accumulation in brown rice further reduced after calcium magnesium phosphate was added and reached significant level(P < 0.05) at high dose. Although the application of different doses of calcium superphosphate have increased the Cd concentration in brown rice,but the Cd concentration was still below the national food safety standards.3) In this experiment of potash fertilizer treatments, the order of Cd accumulation in rice different parts was root > straw > brown rice> rice shell. In the immobilization remediation of Cd contaminated paddy soil, different doses of KCl reduced the brown rice biomass in some degree. Soil pH decreased and soil Cd availability increased after the different doses of KCl were added.High dose of K2SO4 has activated the soil Cd by 15.80%-33.73%. Application of KCl will further increase Cd accumulation in brown rice, but low doses of KCl treatment does not exceed the limits of China’s food safety standards. K2SO4 treatments increased the Cd in brown rice further, but the Cd content in brown rice is still below the national food safety standards.