Effects Of Coal-based Humic Acids On The Activity And Bioavailability Of Copper In Soil

Leaching experiment, greenhouse pot culture experiment, and germination experiment were conducted to study the effects of coal-based humic acids on the activity of exogenous copper. The effects of coal-based humic acids and exogenous copper on soil and plant were studied to provide a theoretical basis for using coal-based humic acid to alter the activity and bioavailability of soil heavy metal Cu and then to realize the safe utilization of agricultural land or repairing Cu-contaminated soil. The results obtained are as follows:(1) The results of leaching test showed that:The application of exogenous copper increased the concentration of heavy metal copper in eluent. The concentration of copper was the highest in eluent in the treatment of No.11humic acid among the experimental coal-based humic acids. It means that the No.11coal-based humic acid generated soluble complexes with copper ions and promoted the mobility of copper ions. Therefore the No.11coal-based humic acid had a certain activation to copper. The second coal-based humic acid was No.10. But the concentration of Cu was much higher in deionized water eluent in EDTA treanment than in all experimental coal-based humic acids treatments. No.6and No.9coal-based humic acids both had stronger fixation effect to exogenous copper and reduced the migration of copper. The leaching effect of KC1salt solution to copper in soil was much better than deionized water. The interception effects of soil to Cu migration enhanced and the concentration of Cu in eluent decreased as the thickness of soil increased. Finally, the No.6, No.9, No.10, and No.11were screened out from11coal-based humic acids as experimental material for further research.(2) The pot experiment showed that:Adding exogenous copper significantly increased soil total copper content. The No.6and No.10coal-based humic acids had no significant effect on soil total copper, but the No.9and No.11coal-based humic acids as well as EDTA significantly decreased the copper content in soil on the basis of adding exogenous copper. Application of exogenous copper increased the contents of different copper forms in different degree. On the basis of adding exogenous copper, the No.6and No.9coal-based humic acids both reduced the contents of soil exchangeable copper and carbonate-bound copper, but increased the content of the residual copper. The No.10and No.11coal-based humic acids and EDTA all increased the contents of soil exchangeable copper and carbonate-bound copper, but reduced residual copper in soil. All experimental coal-based humic acids and EDTA reduced the content of copper as iron and manganese oxidation state, but increased the content of organic bound copper. It means that No.6and No.9coal-based humic acids had a certain inactivation to soil Cu. The No.10and No.11coal-based humic acids and EDTA had a certain activation to soil Cu and EDTA is best.Adding exogenous copper significantly reduced the phosphorus content in soil, but the effect on the contents of soil organic matter, total nitrogen, and available potassium was not significant. On the basis of added exogenous copper, the No.10coal-based humic acid and EDTA significantly increased soil organic matter content, the No.9coal-based humic acid significantly increased soil nitrogen content, the No.11coal-based humic acid significantly improved the soil available potassium content, and the No.6, No.9, and No.11coal-based humic acids and EDTA all significantly increased soil available phosphorus content, but EDTA significantly reduced the nitrogen content in soil.Adding exogenous copper increased the contents of total nitrogen, total phosphorus, and total potassium in pak-choi, and also had a role in promoting the growth of pak-choi. On the basis of adding exogenous copper, the effect of the experimental coal-based humic acids and EDTA on the growth of pak-choi was not significant, the No.9, No.10, and No.11coal-based humic acids and EDTA significantly inhibited the absorption of pak-choi to nitrogen, while the effect of the four experimental coal-based humic acids and EDTA on the contents of total phosphorus and total potassium in pak-choi was not significant.The copper content increased in pak-choi after added exogenous copper. On the basis of adding exogenous copper, the No.6coal-based humic acid significantly reduced the copper content in pak-choi. It means that the No.6coal-based humic acid had significant inhibiting effect on the absorption of pak-choi to copper. The copper content of pak-choi increased in the treatments of No.10and No.11coal-based humic acids. It means that the No.10and No.11coal-based humic acids had a certain promoting effect on the absorption of pak-choi to copper. (3) The germination experiment showed that:Application of experimental coal-based humic acids improved the germination rate of pak-choi seed, and exogenous copper with low concentrations had stimulated effect on the germination of pak-choi seed, but exogenous copper with high concentrations had a certain inhibitory effect on the germination of pak-choi seed.