| Field experiments with rice straw, pig manure and green manure were conducted in the polluted soil in Miaoyunao Village, Daye City, Hubei Province. The total Cd and Cu content in the surface soil (0～15cm) is 4.55 mg kg-1 and 289.9mg kg-1 respectively. Rice straw and green manure were added to the soils at the rate of 5.2,10.3 and 15.4 t ha-1 and the application rate for pig manure was 2.2,4.4 and 6.5 t ha-1. The effect of organic materials on the growth of Chinese cabbage, bioavailability of Cd and Cu, soil Cd and Cu fractions, enzyme activities and microbial biomass was evaluated. The main results are described as follows.1. The concentration of Cd and Cu in cabbage dropped the most obviously in the treatment of rice straw and decreased by 46% and 17% respectively at the highest application rate of rice straw (15.4 t ha-1). The concentration of Cd and Cu in Cabbage decreased by 19% and 17%, respectively, when the soil was amended with the largest amount of green manure (15.4 t ha-1). No significant decreases in the concentration of Cd and Cu were observed for the treatment of pig manure.2. Treatment of three organic materials increased cabbage yielded which was 0.4-1.4 times greater than those of the control. The yield of cabbage increased with increasing amounts of organic amendends. Total P and soluble sugar in cabbages were increased by 12.9% and 135% respectively in the soils amended with the highest rate of rice straw (15.4t ha-1). Total P, K, soluble sugar and total proteins in the cabbage tissues were increased by 69%,13%,20% and 135%, respectively, when pig manure was applied at the highest level (6.5t ha-1).3. The distributions of Cd and Cu in soils were altered for all the three organic treatments. Rice straw showed the better effect than green manure in decreasing the content of soluble & exchangeable heavy metals, while pig manure increased the content of soluble & exchangeable heavy metals. Soluble/exchangeable and organic bound Cd were decreased by 65% and 48% respectively when rice straw was applied at the largest amount, while both inorganic bound and residual Cd were increased by 20%. Meanwhile, soluble/exchangeable Cu was decreased by 48% and organic bound Cu was increased by 14%. No obvious changes were obatined for inorganic bound and residual Cu fractions.4. All the three organic materials improved the activities of soil enzymes as well soil microbial biomass. The activities of soil invertase, protease, urease and acid phosphatase were significantly enhanced by treatment of rice straw and green manure. The activity of soil cellulase was improved exclusively with treatment of pig manure. Activities of urease and acid phosphatase increased when pig manure was applied. Both rice straw and pig manure treatments increased more significantly than green manure treatment the amounts of soil microbial biomass.In summary, rice straw showed best performance in the in situ immobilization of Cd, Cu in polluted soils as well as in the inhibition of uptake of Cd, Cu by cabbages plants. Therefore, rice straw can be selected as a right organic material for the in situ remediation of heavy matals-polluted soils. However the subsequent effect of its application in field soils and the combination with other techniques deserve future investigations. |
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