Orthogonal fertilization tests designed to optimize the quality of Eucalyptus seedlings

To improve the quality of Eucalyptus grandis × E. urophylla seedlings, L9(3⁴) orthogonal tests on nitrogen supplementation (10, 15, and 20 g/plant), phosphorus supplementation (3, 6, and 9 g/plant), and potassium supplementation (6, 9, and 12 g/plant) were conducted to select the most effective combined measurement. The results revealed that Eucalyptus had the highest values for total biomass (737.20 ± 32.74 g/plant), specific leaf area (196.73 ± 23.16 cm²/g), soluble sugar content (8.33 ± 0.75%), protein content (1.16 ± 0.19 g/L), and photosynthetic rate (20.02 ± 1.67 μmol/m²/s) under different combined conditions. Combination effects were observed under nitrogen, phosphorus, and potassium supplementation. Nitrogen was the most influential factor in the quality of the Eucalyptus seedlings, followed by phosphorus and potassium. We suggest that a combination of 15 g/plant nitrogen, 9 g/plant phosphorus, and 6 g/plant potassium produces the highest quality Eucalyptus seedlings.