Abstract: The optimum nutrient requirements (macronutrients) for maximum growth rate of Paulownia elongata and Robinia pseudoacacia have been studied based on the principles of steady state nutrition, by using a growth technique that the nutrients consumed were compensated by means of daily determinations and adjustments of pH and conductivity titrition.The seedlings were grown under controlled conditions, the nutrient status in seedlings and its maximum growth rate remained stable during the experimental period. To obtain a high relative growth rate over 25% per day in Paulownia elongata and about 15% per day in Robinia pseudoacacia, suitable proportions by weight may be 100N:75K:18P:7Ca:8.5Mg and 100N:60K:15P:8Ca:9Mg respectively.The optimum nutrient requitements by weight and its perspective of applications in fertilizations of nursery and young forest stands were also discussed in this paper.

Key words: Paulownia elongata, Robinia pseudoacacia, Steady state nutrition, Optimum nutrition, Nutrient proportions, pH and conductivity titrition