Effects of Combined Application of Nitrogen, Phosphorus and Potassium on the Growth and Physiological Characteristics of Container Seedlings of Cyclobalanopsis

To investigate the effects of nitrogen (N), phosphorus (P), and potassium (K) ratio fertilization on the growth of Cyclobalanopsis container seedlings, a study was conducted using 3-year-old seedlings of Cyclobalanopsis glauca (C. glauca), Cyclobalanopsis myrsinifolia (C. myrsinifolia), and Cyclobalanopsis multinervis (C. multinervis) as experimental materials. An orthogonal experimental design was employed, examining changes in growth and physiological indicators under nine N-P-K ratio treatments. Principal component analysis (PCA) and membership function method were used for comprehensive evaluation to screen the optimal fertilization ratio. The results show that: (1) Based on a comprehensive analysis of height increment, ground diameter increment, aboveground dry weight, and underground dry weight, treatment T6 (High N, Medium P, Medium K) yielded higher values across all four indicators for C. glauca. For C. myrsinifolia, treatments T1 (High N, High P, Low K) and T6 resulted in higher values. Treatment T7 (Medium N, Medium P, Low K) produced higher values for C. multinervis. (2) Comprehensively analyzing leaf length, leaf width, and leaf area, treatments T3 (High N, Low P, High K) and T8 (Medium N, Low P, Low K) yielded higher values for C. glauca. Treatment T4 (Low N, High P, High K) resulted in higher values for C. myrsinifolia. Treatments T5 (Medium N, High P, High K), T8, and T9 (Low N, Low P, Medium K) yielded higher values for C. multinervis. (3) The comprehensive evaluation index was highest for C. glauca and C. multinervis under treatment T8, and highest for C. myrsinifolia under treatment T4. Therefore, the optimal fertilization ratio for 3-year-old C. glauca and C. multinervis seedlings is urea 0.217 g + calcium superphosphate 0.160 g + potassium chloride 0.154 g per container/plant. For 3-year-old C. myrsinifolia seedlings, the optimal ratio is urea 0.109 g + calcium superphosphate 0.640 g + potassium chloride 0.231 g per container/plant.