Abstract: We examined the contents of total nitrogen (TN) and total phosphorus (TP) in needle, litter, and soil of Pinus armandii forest on the southern slope of the Qinling Mountains in Shaanxi, China. We conducted nutrition diagnosis of P. armandii forest, analyzed nutrient limitation pattern, the fertilization types and amount to increase growth, to provide support for precision fertilization and scientific cultivation of big timber of P. armandii. The results showed that the proportion of big timber (DBH>26 cm) and individuals with the potential to grow into big timber (18 cm<DBH≤26 cm) was 29.0% and 60.6%, respectively. The needle N and P contents were 12.65 and 1.34 g·kg^-1, respectively, and the N:P was 10.24 (<14, unrestricted threshold of forest growth). The N and P resorption efficiency of needle was 33.8% and 48.0%, respectively. In 0-10 cm soil layer, soil N and P contents were significantly negatively correlated with that in the needle, but positively correlated with that in litter. The relationship between the needle N:P and soil N storage was expressed by a quadratic function. The growth of P. armandii was N limited, and an addition rate of 0.42 t N·hm^-2 would ensure normal growth of all individual trees. We recommended the rate of 0.16 t N·hm^-2 to the trees with the potential to grow into big timber to promote them to be big timber in a short period, allocating nitrogen to individual plants in proportion to the biomass of individual trees in the stand per unit area.

Key words: Pinus armandii, big timber, nutrition diagnosis, fertilization, nutrient resorption efficiency