Effect of N，P ratios on the growth and absorption, distribution and utilization of 15N-urea of Fuji Apple Saplings

Abstract: The effects of different NP proportions on growth and absorption, distribution and utilization of N were studied using the 15N--labeled tracer method in 3-year-old Fuji apple saplings. Three N levels (110、165、220 kg/hm2，recorded as N1、N2、N3）and three P levels（170、255、340 kg/hm2，recorded asP1、P2、P3）, total 9 treatments were designed in the experiment. The results show that N1P2 fertilization ratio on the total dry weight accumulation and increased Chlorophyll content of Fuji apple saplings in different NP treatments is best, and there are significant differences among the treatments. The transpiration rates in N2P3 ratio is maximum with a value of 2.24 mmol/(m2.s), while the N1P1 and N1P2 ratios are minimum with a value of 1.43 mmol/(m2.s), and the photosynthetic rate of the N1P3 is maximum with a value of 13.46 umol/(m2.s), while the N3P3 ratio is minimum with a value of 9.76 umol.m-2.s-1. The Ndff order and partition rule of 15N of various tree organs are not changed under different NP treatments, while the Ndff and partition ratios of 15N of same organ are different, the 15N requisition ability of Fuji saplings shoot new nutritorium (new shoot, leaf) at the level of N1 was best, and it was stronger than storage organs (roots, trunk); the phosphorus content in N1、N2 levels is proportional to photosynthetic efficiency, while high phosphorus strongly inhibited the photosynthetic efficiency in high nitrogen (N3) levels. The 15N- urea use efficiencies of the N1P2 in different NP treatments are up to 13.6%. In summary, the N1P2 in different NP treatments is optimal, which is recommended to the fertilization in Fuji apple saplings production and cultivation.