Keywords: 
• bioremediation /
• oil contamination /
• soil /
• in-situ remediation /
• degradation

Abstract: The degradation microbial communities which were lab selective enrichment cultured from oil polluted soil of Zhongyuan Oil Field could fast grow using crude oil as carbon source. These microbial communities binding with Ryegrass and Alfalfa were used in experiments on combined in-situ bioremediation of oil contaminated soil. The experimental area was divided into five: microbial communities with Ryegrass， microbial communities with Alfalfa， only microbial communities， only Ryegrass and blank. After 99 d bioremediation， the cumulative degradation rate of petroleum hydrocarbon could reach 43.27% to 67.38%， which were much higher in the two areas of microbial communities with Ryegrass or Alfalfa. Whereas the cumulative degradation rate of blank area was lower than 2.5%.Those results showed that the selected microbial communities could obviously degrade the oil polluted soil in central plains oil field. The experimental results indicated that the inoculated degradation microbial communities generally need 1~3 d adaptive phase then being active，few nutriment such as soluble salt， NO-3， Cl-，etc could infiltrate into the lower soil layer(50 cm). The nitrogen fixation of Alfalfa roots may cause the distinct increase of NH+4. In addition， some factors containing temperature， water， oxygen， nutriment and mini-geo-envirorment were optimized in the experiments.