Study On The Fertilization Diagnosis And Nitrogen Utilization Characteristics Of Acacia Melanoxylon Seedling

One-year-old Acacia melanoxylon seedlings for fertilization experiment were selected to design 23 groups of different N,P and K fertilization ratios by using quadratic regression orthogonal rotational combing design with three factors.The effects of different N,P and K fertilization ratios on growth,biomass accumulation,root characteristics,N,P and K nutrient accumulation and distribution in Acacia melanoxylon seedlings stage were studied.Through principal component analysis of seedling height,ground diameter,biomass and root morphology of 23groups of Acacia melanoxylon seedlings with different fertilization ratios,the best fertilization ratio of seedling height,ground diameter,biomass,root morphology and the best combination ratio of comprehensive index performance of Acacia melanoxylon seedlings were revealed.We diagnosed the nutrition of Acacia melanoxylon leaves treated with different fertilization ratios by DRIS diagrammatic method and index method respectively and combine the results of principal component analysis,then obtained the optimum N,P and K fertilization ratios corresponding to the optimum growth at seedling stage.We also used ¹⁵N isotope tracer to study the absorption,utilization and distribution characteristics of nitrogen fertilizer in Acacia melanoxylon under different nitrogen application levels,in order to provide reference for scientific fertilization of Acacia melanoxylon seedlings.The results are as follows:1.Different fertilization treatments have significant effects on seedling height,ground diameter and biomass of Acacia melanoxylon seedlings in different months.The seedling height,ground diameter and biomass of Acacia melanoxylon seedlings under most fertilization treatments were higher than those of the control group.Among the 23fertilization treatments,the seedling height of treatment23、4 was the best,and the seedling height of treatment 10 was the worst;the ground diameter of treatment 12 and 13 was the best,and the ground diameter of treatment20 was the worst;the biomass of treatment 13 was the largest to 20.89g,followed by treatment 4,19.61g and treatment 3 was the smallest 11.94g.The growth rate of seedling height of all fertilization treatments reached the highest in July-August,and the ground diameter increased the fastest in August-September.2.Most proportion fertilization treatments can promote root growth.Among the 23 treatments,treatment 4 was better in the root morphology of Acacia melanoxylon seedlings.Root length,root diameter,root surface area and root volume were 3123.22 cm.,7.1 mm.（Plant）^-1,700.04cm².（Plant）^-1,12.52 cm³.（Plant）^-1 respectively.However,nine zero-level treatments（15-23 treatments）showed poor overall performance in root length,root diameter,root surface area and root volume.3.Principal component analysis of the characters of Acacia melanoxylon seedlings（seedling height,ground diameter,biomass and root morphology）treated with different fertilization proportions showed that:Treatment 13（N:P:K=1.2:1.5:1）was the most favorable for the growth of ground diameter and root length of Acacia melanoxylon,Treatment 4（N:P:K=0.6:2.2:0.2）was the most favorable for the growth of all characters of Acacia melanoxylon（except ground diameter and root length）,and ranked first in the comprehensive ranking,for the growth character of Acacia melanoxylon seedlings,treatment 4 was the best fertilization proportions.4.The accumulation and distribution of N,P and K in different organs of Acacia melanoxylon seedlings were significantly affected by different fertilization proportions.The distribution of nutrients in roots,stems and leaves was quite different.The contents of N and K in leaf organs were higher than those in stem and root organs.The content of P in stem organs was higher than that in leaf and root organs,the content of K was higher than that in root organs.The content of N in root organs was higher than that in stem organs.Distribution rates of N,P and K in leaf organs were above 50%.The distribution rates of N,P and K in stems ranged from 20%to 30%,and the distribution rates of nutrients in root organs were below20%.In 23 groups of fertilization treatments,the N,P and K nutrient accumulation of treatment 4 reached the maximum,the accumulation of N was 668.29 mg per plant,the accumulation of P was 13.08 mg per plant,the accumulation of K was 190.7 mg per plant.5.Through graphic method,it was found that the N,P and K elements of treatment 1,4,12,16 and 20～21 reached equilibrium state in 23 groups of fertilization treatments.Through the index method,it was found that the nutrient index of treatment 4 was closest to"0",indicating that the nutrient of treatment 4 was the most balanced.Therefore,combining the growth index and root morphological index of seedlings with DRIS nutritional diagnosis,it can be concluded that treatment 4 can most promote the growth of Acacia melanoxylon seedlings,and the corresponding N,P and K fertilization rates are 0.6g.（plant）^-1,2.2 g.（plant）^-1 and 0.2 g.（plant）^-1,respectively.6.The characteristics of N uptake,distribution and utilization of Acacia melanoxylon seedlings under different nitrogen application levels were studied by¹⁵N isotope tracer.It was found that the absorption of fertilizer nitrogen by Acacia melanoxylon under different treatments increased rapidly in the second week of fertilization,and stabilized after January.The absorption of fertilizer nitrogen by Acacia melanoxylon seedlings and organs increased with the increase of nitrogen application rate,while the utilization rate of fertilizer nitrogen decreased with the increase of nitrogen application rate.When nitrogen application rate was0.46g per plant.The maximum utilization rate was 37.095%.The distribution of ¹⁵N in roots,stems and leaves was significantly different,and the overall trend was leaf>stem>root.