| Heavy metal pollution not only destroys the quality and fertility of the soil,but is also potentially harmful to humans due to its toxicity,bioaccumulation and non-biodegradability.Now it is a key issue that remediation and safe utilization of heavy metal contaminated soil in the agricultural and environmental fields around the world.The complexation and adsorption with heavy metal ions of humic acid can reduce the content of water soluble and exchangeable state heavy metals,and enhance the stability of heavy metals.The main research direction of humic acid in soil heavy metal pollution is soil improvement by using humic acid or modified humic acid.In this paper,two kinds of humic acid fertilizers(sodium humate and ammonium fulvic acid)were used as materials to study effects of humic acid fertilizers on heavy metal speciation,content of heavy metal absorbed into Chinese cabbage and soil enzyme activity in soil contaminated by Zn,Pb,Ni and Cd.The main findings are as follows:(1)Sodium humate of different content could significantly reduce the content of weak acid extraction state of Zn in soil,and significantly increase it of residual state.Ammonium fulvic acid of different content could reduce the content of weak acid extraction state of Zn in soil and increase it of the residual state.However,the effect not significant.Sodium humate or ammonium fulvic acid of different content or ammonium fulvic acid can could significantly reduce the content of weak acid extraction state of Pb in soil and significantly increase the content of residual state.In comparison,the best passivation effect of Pb was obtained with additons of 0.6 g/kg-0.8 g/kg sodium humate or 0.8 g/kg ammonium fulvic acid.Sodium humate or ammonium fulvic acid of different content could reduce the content of extraction state of weak acid and reducible state of Ni in soil.The content ofresidual state of Ni increased at low content of sodium humate and ammonium fulvic acid,and then decreased with the content of them rising.It was the best passivation effect on Ni that addition of sodium humate was 0.6 g/kg-0.8 g/kg,or addition of ammonium fulvic acid was 0.6g/kg.Sodium humate of different content could significantly reduce the content of weak acid extraction state of Cd in soil,and increase the content of residual state significantly,while had little effect on the content of reducible and oxidizable states.Ammonium fulvic acid of different content could small reduce the content of weak acid extraction state of Cd in soil,significantly reduced the content of the reducible state,and remarkably increased the content of the reducible state and the residual state.It was the best passivation effect on Cd that addition of sodium humate was 0.8 g/kg,or addition of ammonium fulvic acid was 0.6g/kg.(2)Sodium humate of different content could inhibit the absorption of Zn and Ni by pakchoi,and ammonium fulvic acid of different content has no significant effect on the content of Zn and Ni in pakchoi;Sodium humate or ammonium fulvic acid of different content could significantly inhibit the absorption of Pb in pakchoi.With a maximum inhibition with a dosage of 0.8 g/kg.Sodium humate or ammonium fulvic acid of different content could significantly inhibit the absorption of Cd by pakchoi.When the dosage was 0.8 g/kg,the inhibitory effect was the best.(3)Sodium humate or ammonium fulvic acid of different content could promote urease activity in soil contaminated with Zn.The urease activity was the highest when the dosage was 0.8 g/kg.Sodium humate or ammonium fulvic acid of different content could promote urease activity in soil contaminated with Pb.The urease activity was the highest when the dosage was 0.6 g/kg.Sodium humate or ammonium fulvic acid of different content could promote urease activity in soil contaminated with Ni,but the change was not significant.The application of different dosages of ammonium fulvic acid could promote the activity of urease in soil.The urease activity was the highest when the addition dosage was 0.8 g/kg.Sodium humate of different content could promote invertase activity in soil contaminated with Zn and Ni,and the change is not significant,but the application of 0.8 g/kg and 1.0 g/kg of ammonium fulvate to soil invertase enzymes have a significant effect;Sodium humate or ammonium fulvic acid of different content could promote invertase activity in soil contaminated with Pb.When the dosage was 0.6-0.8 g/kg,the activity was the highest.Sodium humate or ammonium fulvic acid of different content could promote invertase activity in soil contaminated with Cd.When the dosage was 0.6-0.8 g/kg,the activity was the highest.Sodium humate or ammonium fulvic acid of different content could promote the activity of alkaline phosphatase in soil contaminated with Zn.When the dosage was 0.6-0.8 g/kg,the activity was the highest.Sodium humate or ammonium fulvic acid of different content could promote the activity of alkaline phosphatase in soil contaminated withPb?Ni.When the dosage was 1.0 g/kg,the activity was the highest.Sodium humate or ammonium fulvic acid of different content could promote the activity of alkaline phosphatase in soil contaminated with Cd.but the change is not significant.In summary,in the soil contaminated by Zn,Pb,Cd,Ni,the application of different amounts of sodium humate or ammonium fulvic acid can have different passivation effects on heavy metals,and can reduce the number of pakchoi The absorption of heavy metals enhances the activity of soil enzymes.However,for different heavy metals,the effect is quite different.Therefore,in the practical application of the two fertilizers,different types and different amounts of fertilizer should be selected according to different heavy metal pollution. |
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