2.1 Experimental materials
The Stevia rebaudiana Bertoni variety is Qingtian 3 ( bred by Qingdao Agriculture University) and
cultivated in experimental plots in Qingdao Agricultural University (north latitude36°.11', east longitude
120°17') in 2009. The soil nutrient is: available nit rogen 116.68mg/kg; rapidly available potassium 104.51
mg/kg; rapidly available phosphorus 28.68mg/kg; organic matter 1.85%; pH is 6.82,respectively.