6Kavdir Y,Rasse D P,Smucker A J M.Specific contributions of decaying alfalfa roots to nitrate leaching in a Kalamazoo loam soil[J].Agricultural,Ecosystems and Environment,2005,109:97-106.
7Ao J L,Terefeworkb Z,Chen W X,et al.Genetic diversity of rhizobia isolated from astaragalus adsurgens growing in different geographical regions of China[J].Journal of Biontechnology,2001,91:155-168.