Heavy metals mixed with toxic organics are increasingly contaminating soil with the development of the industry and the modernization of agricultural production

making remediation of the contaminated soils an urgent and challenging task. In this study

we set up 4 treatments with sandy loam as the test object:(1) Control group

co-contaminated soil (CK); (2) No fertilizer group

co-contaminated soil + ryegrass (NF); (3) Nitrogen fertilizer group

co-contaminated soil + ryegrass + nitrogen fertilizer (F1); (4) Nitrogen fertilizer and phosphate fertilizer group

co-contaminated soil + ryegrass + nitrogen fertilizer and phosphate fertilizer (F2). In order to provide a preliminary theoretical basis for remediation of contaminated soil and environmental impact assessment

we studied the effects of ryegrass and fertilization on microbial activity in oil

lead and cadmium co-contaminated soil. The results showed that both ryegrass and fertilization had positive effects on the soil basal respiration and microbial biomass carbon in the co-contaminated soil. Compared with the control

the peaks of basal soil respiration in NF

F1 and F2 increased by 20.94%

24.41% and 42.69%

respectively. The effects of nitrogen and phosphate fertilizer (F2) on soil basic respiration were most significant. On the 10th day

the peaks of soil microbial biomass carbon in NF

F1 and F2 increased by 26.92%

127.43% and 181.89%

respectively

indicating that fertilization treatments were better than non-fertilization. Various soil enzymes had different responses to ryegrass and fertilizer application. The activities of FDA hydrolysis were restrained in NF

F1 and F2

while the application of nitrogen fertilizer could maintain the dehydrogenase activity in the oil-lead-cadmium co-contaminated soil at a certain time. Fertilization could continuously and effectively improve and maintain the activity of urease in the oil-lead-cadmium co-contaminated soil. But there was little impact on the catalase activity. These findings implied that the soil microbial biomass

soil microbial biomass carbon and soil enzyme activity were enhanced by the application of nitrogen and phosphate fertilizer. It meant that planting ryegrass with nitrogen and phosphate fertilizer could promote soil pollutant removal and soil quality improvement.