2 The effect of different amount of nitrogen fertilizer applied (0, 25, 50, 100 kg urea/667m2) on yield and nitrate content of different pak-choi cultivars was observed .

• 而且增施氮肥增产的效应随着施氮量的增加而呈显著降低趋势，即呈现施肥量的报酬递减，对小白菜菜秧生产以施用25kg/667扩尿素的处理与施用50、100 kg/667m2尿素的处理相比较增产最高，效益最好。