The study was carried out in field experimental plot of Qingdao Agricultural University, in Shandong
Province, located in Chengyang District, Qingdao City (36° 15′N, 120°20’ E). The experimental plot
belongs to temperate and monsoonal climate. The annual mean temperature is 12.6ć and the average
frost-free date is 179 days over the past years. The soil at the experimental site is loam texture and the
plow soil layer of 0-20cm contains 1.35% of total organic matter, 0.09% of total nitrogen, 105.42 mg· kg-
1 of available nitrogen, 24.58 mg·kg-1 of available phosphate and 85.72 mg·kg-1 of available potassium.