Comprehensive effects of N, P, K, and Zn formulated fertilization on growth, physiology, and seedling quality of Carya illinoensis.

Optimizing fertilizer application is critical for balancing plant growth promotion, economic efficiency, and environmental sustainability. For Carya illinoensis (pecan), a high-value nut tree, balanced nutrient management of nitrogen (N), phosphorus (P), potassium (K), and zinc (Zn) is essential to enhance seedling vigor and establishment success. However, the optimal formulations of N, P, K, and Zn for maximizing seedling quality remain undetermined. This study employed an L9(34) orthogonal design to evaluate the integrated effects of N, P, K, and Zn combinations on growth, physiological traits, and seedling quality index (SQI) of pecan seedlings. The results demonstrated that fertilization generally promoted growth and nutrient uptake, with responses varying across parameters. Specifically, the N1P3K3Zn3 treatment (low N, high P, high K, high Zn) achieved the greatest total biomass accumulation and SQI, while the N1P2K2Zn2 treatment (low N, medium P, medium K, medium Zn) maximized ground diameter growth. Physiological analyses revealed that fertilization enhanced leaf chlorophyll content and non-structural carbohydrate accumulation during the active growth phase (June-August). Furthermore, distinct formulations differentially modulated stress responses; for instance, N2P1K2Zn3 minimized malondialdehyde content, while N2P2K3Zn1 optimized leaf membrane stability. Principal component analysis of 14 integrated indicators identified N1P2K2Zn2 as the treatment yielding the best overall seedling performance. These findings underscore that nutrient interactions, rather than single-element effects, drive seedling quality in pecan. The study provides a quantitative basis for formulating balanced N-P-K-Zn fertilizers to cultivate high-quality pecan seedlings, thereby supporting sustainable nursery management and afforestation practices. Future work should validate these formulations in long-term field trials and assess their impacts on orchard productivity and soil health.