NITROGEN NUTRITIONAL DIAGNOSIS AND RECOMMENDATION AS TOPDRESSING FERTILIZER N FOR SEVERAL CROPS IN NORTH CHINA Ⅳ. Nitrogen nutritional diagnosis and recommedation as topdressing fertilizer N in wheat-corn rotation

Two quick test methods (diphenylamine method and nitrate test strip) for diagnosising nitrogen nutritional status under condition of rotatiori cropping with winter wheat-summer corn were studied in field expriment. The results suggested that the optimum diagnosis parts of plants was the stem base for wheat arid the midrib of near matured leaf for corn, both just prior to jointing stage, arid the critical values of nitrate was considered to be 2.00(diphenylamine method) and 1500mgkg-1No3- (nitrate test stripe) for wheat and 2. 40(diphenylamine method) and 1240mgkg-1NO3-(nitrate test stripe) for corn. Based upon the results from nitrogen nutritional diagnosis, series fertilizer N topdressing recommendation model was set up as following:wheat:Nd=220. 2-95. 8Td(diphenylamirie method) Nd=220. 2-0. 147Tr(nitrate test strip) corn:Nd=185. 9-72. 5Td(Yuncheng, diphenylamine method) Nd=185. 9-0. 13Tr(Yuncheng, nitrate test strip) Nd=176. 2-80. 5Td(Yongji, diphenylamine method)