Abstract: The method of simulating diagnosis was derived for the research of foliar optimum nutrient status from the sample plots which were the treatments of experiment on amelioration and increasing fertility with Ⅰ-69 poplar (Populus deltorides Bartr. Cv. "Lux") on Sajong black soil. By canonical correlation analysis, sampling time was selected, and foliar mutriment elements closely related to forest tree growth were determined.Parabolic function was taken as the diagnosis function of optimum nutrient status in foliar. While selecting the variable of diagnosis function,content of foliar nutrient and the proportion of nutrients were considered. It was concluded that optimum foliar nutrient status for Ⅰ-69 poplar was as follows: The leaf content of P₂O₅ was 0.55—0.75% in July in the first year after plantation; N was 3.20—4.20% in the next year; N was 3.00—3;70% in May in the third year; N/K was 1.00—1.60 in the fourth year.

Key words: Poplar forliage nutrient, Nutrition diagnosis, Foliar nutrient critical valu, Nutrition model