Impacts Of Heavy Metals Contamination In Soils On Herbages Growth And Their Controls

This paper discusses the impact of heavy metals contamination (copper, zinc and cadmium) on the growth of three common herbages (Festuca arundinacea, ryegrass and alfalfa) by pot experiments. The three typical soils including red soil, yellow brown earth and fluvo-aquic soil were tested with two concentrations of each heavy metal based on the Chinese Soil Environment Equality Standard (CSEES). In order to make better expression of the harmfulness of the heavy metals pollution for different herbages and soils, first, the plant growth characters, heavy metal concentrations of the herbages and in the test soils are determined for their correlation analysis. Then three suggested control methods for polluted soils are described. Finally, the available ion impulse and step regression analysis are selected to express the heavy metals contamination in the situation. The pot experiment results showed that the effects of heavy metals contamination on herbages growth are different according to the type of soils. Festuca arundinacea and ryegrass can抰 grow on tested red soil. In yellow brown earth, the decrease of biomass is more than 10% when heavy metal concentrations in the soil arrive at the value of the second CSEES. In fluvo-aquic soil, heavy metals stress the alfalfa growth when their concentrations are the third CSEES. The following conclusions are obtained from heavy metal content analysis: the heavy metal content of ryegrass on yellow brown earth exceeds the normal growth average, while that of alfalfa on fluvo-aquic soil is below it. The content differences between the first and second stubble are obvious. To alfalfa, the content of zinc in the second stubble is lower than that of the first stubble, but the content of the copper is relatively stable. But to ryegrass, the content of the copper in the second stubble is lower than that of the first stubble, while the content of zinc is reversed. Compared with the single heavy metal pollution, the compound pollution affects the absorption of ryegrass more. The effects are different according to the different plant抯 parts. When the pH of red soil was adjusted to about 5.0 by using calcareousness, the ryegrass grew well. On the light polluted soil (CuSOmg/kg, Znl 00mg/kg, CdO.3mg/kg) the biomass of ryegrass was improved while the ryegrass still couldn抰 grow on heavy polluted soil (Cu 100mg/kg, Zn200mg/kg, CdO.6mg/kg). When the pH of the soil was above 6.0, both emergence rate and biomass of the ryegrass were higher than that under the heavy metal treatments except for the heavy polluted soil. There is obvious improvement by applying Root Growth 78 Promoting Agent (RGPA) to light polluted yellow brown earth(CulOOmgIkg, Zn25OmgIkg, CdO.3mglkg). The suitable dose is 2.5g/kg in the first stubble while the suitable dose is 5.Oglkg in the second stubble. The biomass is much higher and the content of zinc is lower in the ryegrass when using RGPA. But the contents of zinc and cadmium in the ryegrass are still above the normal arrange of plant growth. The improvement by organic matter on polluted soil depends mainly on their sources. The effect of cattle manual is better than that of straw. And the effect of DOM is better than that of the dry organic matter. There is evident correlation between the heavy metal contents of herbages and the available heavy metal concentrations of the soils. And the correlation is much better if available ion impulse is used. After correcting the difference of t...