The Application of Nitrogen, Phosphorus, and Potassium Regulate the Growth and Morphological Development of Torreya grandis (Taxaceae) Saplings

Torreya grandis Fort. ex Lindl. cv. "Merrillii" is an important woody oil crop, and the development of plantations relies on the cultivation of high-quality saplings. For this study, 6-year-old grafted T. grandis saplings, which will soon be planted on the mountain, were selected to investigate the regulatory effects of nitrogen (N), phosphorus (P), and potassium (K) on their growth and morphology. To determine the optimal dosage and ratio of N-P-K fertilizer for sapling cultivation, we employed a three-factor four-level L16 (4(3)) orthogonal experiment design. The experiment included a total of 17 treatments-a control group where no fertilizer was applied and 16 treatments with varying levels of NPK supply. We conducted a one-season experiment under a prescribed fertilizer regime and measured root collar diameters and sapling heights, the root, shoot, leaf biomass, total biomass, and the nutritional status of plant organs (root, shoot, leaf). From these measurements, we calculated the root-shoot ratio (RS) and seedling quality index (QI). The application of N-P-K fertilizer exhibited significant benefits for T. grandis sapling cultivation, promoted their growth and biomass accumulation and altered the nutrient allocation patterns in organs. Ultimately, we determined the ideal N-P-K ratio for T. grandis growth to be 1:0.46:0.75, with a fertilizer application of 1.38 gsapling(-1) of N, 0.64 gsapling(-1) of P (P2O5), and 1.04 gsapling(-1) of K (K2O).