| Organic fertilizer plays a positive role in producing grain and vegetables all over our country and the world. In recent years, heavy metal pollution has taken a great part of environmental pollution. The heavy metal content of grain and vegetables growing in heavy metal contaminated soil outnumbers the national standard dramatically. It is an extreme threat to people's health when heavy metals entering human bodies through various channels with triggering a variety of diseases afterwards. Therefore, How to reduce the toxicity of heavy metals in soils and improve the quality of crop is indispensable for controlling heavy metal pollution and producing unpolluted crops.The content of Cu and Cd as different forms detected by using Sposito sequential extraction in non-rhizosphere soil and rhizosphere soil, the changes of production and quality of garland chrysanthemum, the activities of urease, Catalase, sucrase and neutral Phosphatase, and the content of microbial biomass carbon(MBC) in heavy metal contaminated soil are studied by pot-experiment with an intention of evaluating the effect of applying compost in heavy metal contaminated soil in terms of changes of enzymes activities as well as transformation of Cu and Cd, wihch provides a scientific support for cultivating unpolluted vegetables in heavy metal contaminated soil.The main results are outlined as follows:(1) The increase of compost amount comes to the rise of production, crude protein, Vc and total content of P and K of chrysanthemum, which attains to maximum when compost comes up to 40-60 g kg-1 basically, while reversely for the content of soluble sugar of chrysanthemum with being up to minimum when compost is 60 g kg-1.(2) The content of Cu in chrysanthemum was significantly reduced due to the increase of compost amount, with 36% more than that of the control when the amount of compost is 100 g kg-1. Moreover, the content of Cd in overground part of chrysanthemum and that of Cu, Cd in its root showed a trend of significant decrease at first and increase in the sequel, meanwhile they are up to minimum as compost amount reaches 20 g kg-1, 40 g kg-1, 40 g kg-1 respectively.(3) The content of soluble and exchangeable Cu was significantly increased 6.0 times that of the control in non-rhizosphere and rhizosphere soil attributed to applying different amounts of compost. With increase of compost amount, the content of organic-bound Cu was significantly increased in non-rhizosphere soil, but apparently increased first and decreased afterward in rhizosphere soil. The highest values were 16%, 13% higher than that of the control respectively. Precipitated Cu decrease at first and then increase in non-rhizosphere soil, while increase then be stable in rhizophere soil. Residual Cu was increased at first and then stabilized in non-rhizosphere and rhizophere soil.(4) With increase of compost amount, in non-rhizosphere soil, soluble and exchangeable Cd was significantly reduced with 33%-83.3% lower than that of the control. Organic-bound Cd was significantly increased with 82.3%-129% higher than that of the control. Residual Cd were increased significantly 8.5%-26.8% compared with the control. However, precipitate Cd changed slightly. In rhizosphere soil, soluble and exchangeable Cd was decreased at first and increased afterward apparently with 14.3%-85.7% lower than that of the control. Organic-bound Cd was increased significantly by 33.3%-129% compared with the control. Precipitate and residual Cd were increased at first and reduced afterward with the highest values being 8.0%,31.5% higher than that of the control respectively.(5) With increase of compost amount, urease and Catalase significantly increased in heavy metal contaminated soil. When the amount of compost was at the range of 20-100 g kg-1, the maximal activity of urease and Catalase significantly increased by 134%, 53.5% compared with that of the control respectively.(6) With increase of compost amount, sucrase and neutral Phosphatase were increased at first and then reduced in heavy metal contaminated soil. When the amount of compost was at the range of 20-60 g kg-1 , the maximal activity of sucrase and neutral Phosphatase significantly increased by 22.3%, 88.9% compared with that of the control respectively.(7) With increase of compost amount, MBC was increased significantly in heavy metal contaminated soil. When the amount of compost was at the range of 20-100 g kg-1, MBC increased by 28.6-171% compared with the control.(8) With the cooperative reaction of chrysanthemum and compost, there are differences among the content of Cu, Cd as various forms in non-rhizosphere soil and rhizosphere soil. In the practical production, compost application is feasible by after considering volume of compost, price, forms and toxicity changes of heavy metals in heavy metal contaminated soil. The best choice of the volume of compost is 40g kg-1 for planting chrysanthemum in contaminated soil. |
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