Field plot trial was conducted to study the effects of combined application of organic fertilizer with inorganic fertilizer on the activity of nitrate reductase(NR),root characteristics,yield and quality of lettuce.The results indicated that combined application of organic fertilizer with inorganic fertilizer can promote the activity of NR in lettuce functional leaves and the root vigor of lettuce,significantly increase the yield of lettuce,and increase the contents of vitamin C and soluble sugar in stem and leaves of lettuce,while the conten...