The effects of planting 4 years of Bromus inermis,Agropyron smithii,Psathyrostachys juncea and oat on soil chemical properties was studied in CAU research station,Saibei Administration District,Zhangjiakou,Hebei,Guyuan.The results showed that from spring to autumn in the fourth year,compare to oat,total nitrogen in 0-10 cm soil in perennial grass was 0.07% higher,0.11% higher in 10-20 cm and 0.09% higher in 20-30 cm.After fertilization in July,total phosphorous in 0-20 cm oat soil was higher than in other p...