Effect of continuous cropping duration on soil nematodes structure in cotton field of Xinjiang, China

Long-term continuous cropping of cotton had lead to substantial agricultural losses. However, continuous cotton cropping could maintain high yields of cotton for many years in some areas. To explore the effect of continuous cropping and soil depths on soil nematodes communities, the composition and structure of soil nematodes community were investigated. Soil samples at depths (0-20cm and 20-40cm) were collected from cotton fields with a history of 5, 10, 15 or 20 years of cotton cropping in the Karamay region. The results show that 36 genera were found. Significant differences in the numbers of total nematodes and trophic groups were observed among continuous cropping times. The highest number of total nematodes was observed at 20-40cm depth under continuous 10-planting years and the lowest number at 20-40cm depth under continuous 5-planting years. There was significant soil depth effect on the abundances of fungivores and plant parasites. Continuous cropping effect on soil nematode communities could be reflected by values of ecological index. Continuous cropping times, soil depths and their interaction significantly influenced H´, λ, WI, PPI, MI, PPI/MI, F/B and NCR. Shannon index (H´) was higher in 10-year cotton field than other-year fields, while the Simpson index was the lowest in 10-year cotton field. The lowest value of WI appeared at 20-year cotton field, where had the most plant parasites. The obviously decreased trend of NCR and increased trend of F/B were found with the increasing of planting times. The bacterial decomposition pathway was more important in the 5-year situations, and the fungal decomposition pathway was more important in the 20-year situations. Nematode analysis showed that the changes of soil nematode communities and trophic groups could indicate the change of the soil environment and nematode community structure with the changes of continuous cropping times.