Remediation of the application of intercropping system to the farming soil contaminated with PAHs

The paper is aimed to present its author's experimental results of the effects of the application of intercropping system to remedy the farming soil contaminated by the polycyclic aromatic hydrocarbons (PAHs), one of the most widespread organic pollutants distributed primarily in the soil, sediment and oil-residues. To remove the aged PAHs from the farming soil, we have done experiments with phytoremediation in-situ to study the effect of mono-cropping and intercropping treatments on the removing. Some economic crops and remediation crops, such as maize, castor, soybean, ryegrass and alfalfa, have been used in our experiments. The results of our experiments show that the removing rate of PAHs stands between 25 % and 30%, whereas the removing rate of high rings PAHs can be as high as between 26% and 35% in maize/alfalfa intercroping and that of maize/ryegrass, which proves significantly higher than done by means of other treatments. At the same time, maize/alfalfa and maize/ryegrass intercropping proves to be able to increase the amount of soil microbes, with their amount of bacterium, fungi and actinomycete in soil going up as follows: 9 × 10~6 - 12 × 10~6 CFU· g~(-1), 7 × 10~4 - 9 × 10~4 CFU· g~(-1) and 4 × 10~5 - 14 × 10~5 CFU· g~(-1), respectively. Moreover, the greatest increase has been gained in the account of PAHs-degrading bacteria from the two treatments, that is, 1.3 × 10~5 - 1.8 × 10~5 cell· g~(-1) and occupied 6% - 8% in the total amount of bacteria in the soil, thus greatly enhancing the crops-microbial interaction as a result of improvement of the remediation to the soil PAHs pollution under the new intercropping system. Furthermore, the improved interaction of root and soil tends also to influence the bioavailability of PAHs. In addition, the pollutant removing effect in the contaminated soil can also be enhanced by such potential application. Hence, the results of our experiments suggest the feasibility of the multi-species phytoremediation to improve the remediation effects of PAHs, which helps to reduce the accumulation of PAHs in the crops,