| Rational fertilization is one of the key techniques of high quality and strong seedling cultivation of fast-growing and high-yield plantation, especially the poplar seedlings fertilization. Soil potted cultivation experiments, pot exponential fertilization experiments under sand culture and field orthogonal rotary regression fertilization experiments were conducted in this research. Through comparing the variation laws of the growth, biomass, nutrition, net photosynthesis rate, root growth of poplar cutting stock and soil nutrition in different experimental methods and treatments, the annual growth rule and fertilizer requirement rule of Populus×euramericana cv. '74/76' cutting stock was revealed and the proper fertilization time and rational fertilization amount was also proposed. Besides, this study established a fertilization technical system for Populus×euramericana cv. '74/76' cutting stock breeding in nursery. The specific results are as follow:(1) The annual variation rule of seedling growth was revealed by studying the height and basal diameter growth of seedlings cultured in pot filled with soil. The Logistic growth models for seedling height and basal diameter of Populus×euramericana cv. '74/76'cutting stock were (?) and (?), respectively. According to theparameters, a, b, K which were determined by solving the growth model, it was found that the survival, seedling, fast growing and hardening stage of poplar seedlings were April, May-June, July-August and September-October, respectively.(2) Under the conditions of soil potted cultivation, the average biomass of single Populus×euramericana cv. '74/76' cutting stock was 347.71g and about 3.4984g pure N and 0.7271g pure P were absorbed by the seedlings during the whole year. The total root length, absorption area and root volume of single seedling were 92113.02cm, 7870.34 cm2 and 179.10 cm3, respectively.(3) Under the conditions of sand potted cultivation with exponential fertilization, the optimum experimental treatment was T3 for seedling stage, T2 for previous fast growing stage(July) and T1 for terminal fast growing period(August), and the maximum and economical fertilization amount were 15.08g and 9.13g, respectively. At the end of hardening stage, the average seedling height was 204cm, average basal diameter 22.67cm and average biomass 231.56g, and the summit of net photosynthesis rate at 12:00 was up to 24.32μmol CO2·m-2·s-1. The rational fertilization period was June-August among witch August is the most critical. Consequently, it is advisable to fertilize 15 days before the achievement of seedling growth summit.(4) Under exponential fertilization conditions of sand culture, total nitrogen content of the treatment T2 was the highest, of which total nitrogen content in September was up to 3.26g.However, total nitrogen content of the treatment T1 was 2.72g. In root ecology research, T1 was the optimal treatment. Root absorbing area of single cutting stock in the treatment T1 was 17558.78cm2, and root length was 193291.2cm, root volume was 132.6cm3.(5) Under test conditions of field orthogonal rotary regression, according to the field biomass,regression model was built: W=354.12+0.486N+0.22P-2.82×10(4)NP-1.98×10-4N2, rational fertilization rate was obtained, i.e nitrogen fertilizer 780.14 kg/hm2, phosphate fertilizer 1174.72 kg/hm2, maximum biomass 612.91g could be obtained.(6) Combined sand cultivation and soil cultivation with the filed experiment, the nutrient utilization efficiency of sand culture treatment and the field experiment are 25.43%, 16.99% respectively. And it can calculate that 595.68kg/hm2 N fertilizer should be dressed in the growing seasons,i.e.39.71kg/mu, compared with the convention fertilizer volume which is 50-60kg/mu, 20.58%-33.82% of the urea can be saved.The conclusion is that at the time of land land preparation in the beginning of the year, each acer of cutting stock need to fertilize organic fertilizer, which contain the same amont of N content equal to 395.18kg urea.Meanwhile, topdressing fertilization nitrogen are 98.52 kg/hm2, 96.56 kg/hm2, 400.60 kg/hm2 respectively in June, July and August.
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