Effects of N/P Ratio and Loading on the Growth of Container Seedling of Three Precious Tree Species

Objective  To study the effect of slow-release fertilizer (SLF) N/P ratio and loading on the growth of Taxus wallichiana var. mairei, Phoebe chekiangensis and Cinnamomum chekiangense.

Method  In this study, with two factors of N/P ratio (1.75:1, 2.25:1, 2.75:1 and 3.25:1) and SLF loading (1.5 kg·m^-3, 2.5 kg·m^-3, 3.5 kg·m^-3 and 4.5 kg·m^-3), a factorial experimental design was applied to study the Growth (seedling height, root diameter and biomass accumulation), growth rhythm and SPAD of two-year-old container seedlings of the three species.

Result  The growth and SPAD value of the container seedlings (two-year-old) of the 3 species as affected by N/P ratio and SLF loading were different. The biomass accumulation and root-shoot ratio of T. wallichiana var. mairei, Ph. chekiangensis and C. chekiangense varied slightly in N/P ratio. With the increase of N/P ratio, the growth of Ph. chekiangensis was promoted, but the growth of T. wallichiana var. mairei was inhibited. The effect of SRF on the growth and biomass accumulation of 2-year-old container seedlings among the three species all reached the extremely significant level, and with increasing SRF loading, the seedling height, ground diameter and biomass accumulation were obviously enhanced, coupled with the below-ground biomass accumulation of T. wallichiana var. mairei and above-ground of Ph. chekiangensis increased, but which had no statistically significant effect to root-shoot ratio of C. chekiangense, with the optimum of SLF at F3 (3.5 kg·m^-3). The growth and biomass accumulation of the three species were affected slightly by N/P ratio and the interaction with SLF loading, and vice versa. With the increase of N/P ratio, the sustainable growth of T. wallichiana var. mairei was extended and the total linear growth of Ph. chekiangensis was also enhanced, while the same situation was not found for C. chekiangense. The APAD value of the seedling leaves of the tree species differed a lot, but the APAD value was not affected by N/P ratio and SLF loading. However, as the N/P ratio and SLF loading added, the fluctuation strength of SPAD value of T. wallichiana var. mairei and C. chekiangense increased, so did the dynamic variation rule of SPAD among all the three species.

Conclusion  The optimum ratio was 1.75:1 or 2.25:1 to T. wallichiana var. mairei, 2.75:1 to Ph. chekiangensis and C. chekiangense, Loading amount of 3.5 kg·m^-3 could enhance the growth and SPAD value of all the three species evidently, but it would have the side effects once overcommitted.