This study investigated the effects of fertilization on the growth and physiological characteristics of Quercus chungi seedlings to screen out a set of suitable fertilization formula for the growth of Quercus chungis seedlings, and provided a scientific theoretical basis for the cultivation of high-quality and strong Quercus chungi seedlings.

This paper applied the quadratic generalized rotary regression design on three fertilization factors (N,P, K) with five levels (-1.682, -1, 0, 1,1.682) using one-year-old container seedlings of Q. chungii, resulting in a total of 21 treatments (including the CK ), to investigate the seedlings responses on the parameters of the growth and physiological characteristics under different fertilization treatments based on the measurement on the indicators of growth (seedling height, ground diameter, total root length, average root diameter, number of root tips, total biomass) and physiological indexes (total chlorophyll, soluble sugar, soluble protein) of the Quercus chungi seedlings in each treatment, and then established regression equations between the effects of N, P, K factors and each indicator of the growth and physiological parameters for effect analysis.

Compared to the no-fertilizer treatment of CK, a reasonable fertilization could promote the growth of Quercus chungi seedlings and improve the physiological activity of leaves. The main effects among the three fertilizer factors were in order of N > K > P on the seedling height, diameter, total biomass, soluble protein and total chlorophyll, while the main effects were in order of N > P > K on total root length, average root diameter and number of root tips, and the main effect was in order of K > N > P on soluble sugar, based on the main effect analysis results. The one-way effect analysis results revealed that there were significant promoting and regulating effects with the application of moderate N and K fertilization on seedling height, ground diameter, total biomass growth, as well as the accumulation of total chlorophyll, soluble protein, and soluble sugar, while there was no significant effect with P fertilization on the above indicators. There were significant effects of N and P fertilization on total root length and root tip number, while the average root diameter was only significantly responded to N fertilization. Among the coupling effects of NPK, there were significant effects in NK interactions fertilization on seedling height, root tip number, and soluble protein, while there were significant effects in NP interactions fertilization on ground diameter and total root length, as well as there were significant effects in PK interactions fertilization on total chlorophyll and soluble sugar. There were significant effects with moderate levels of N, K fertilization on seedling height, ground diameter, total biomass growth, and total chlorophyll, soluble protein, and soluble sugar accumulation, while there was no significant effect with P fertilization, based on the single-factor effects analysis results. There was a trend of increasing firstly and then decreasing on the single and two-factor significant effects of the growth and physiological indicators with the increase of N, P and K fertilization, in which it was in line with the law of “diminishing returns”.

Reasonable NPK formula fertilization was beneficial to the cultivation of high-quality and strong Q. chungii seedlings and promoted the growth of Quercus chungi seedlings and the accumulation of physiological characteristics indicators, enhancing the growth and physiological resistance. Using principal component analysis and frequency analysis, with a total biomass of ≥ 27.66 g as the thresh goal, the optimal fertilization interval for Q. chungi was determined as N fertilizer (urea) 2.12-3.71 g per plant, P fertilizer (superphosphate) 5.16-7.34 g per plant, and K fertilizer(potassium chloride) 1.56-2.75 g per plant.