| Rational Fertilization is an important measure of directional culture for short rotation industrial timber plantation while the implementation of systematic research on forest fertilization and nutrient diagnosis is the precondition of rational fertilization.Now,Eucalypt was one of the most important planting tree species in the world,areas of Eucalypt plantation in china has over 200 hm~2.Planting Eucalypt has become a hot spot of investment and one of the pillar industry in southern Fujian.In this paper, Eucalyptus urophylla×E.grandis clone(DH-3229),one of the main varieties of Eucalypts in the development of Fujian fast-growing and high-yielding plantation was researched for soil degradation because of continuous multigenerational planting and unscientific fertilization in Eucalyptus plantations in the main planting areas in southern Fujian.In such a way that comprehensive investigations for Eucalyptus urophylla×E.grandis plantation woodlands of the main Eucalypt planting areas in southern Fujian were taken to have a deep understanding of status of soil fertility,fertilization,tree growth, nutrition balance and the relations between each other,and based on that,the research of effects on Eucalyptus urophylla×E.grandis growth of indoor pot culture experiments with different proportioning fertilization of N,K,P was made to explore the rules of needs for growth of the objects and primarily establish nutrient diagnosis indexes of the Eucalyptus urophylla×E.grandis,and then,the suitable Eucalypt fertilization formulation should be selected with the purpose of providing scientific fertilization guidance for current Eucalyptus urophylla×E.grandis plantation.Main results are as follows:1.The investigations of fertility condition of Eucalyptus urophylla×E.grandis plantations showed that the fertility condition of Eucalyptus urophylla×E.grandis plantation woodlands in southern Fujian lies between grade 3 and grade 4,it was less middle-level in southern Fujian.In general,the woodland soil were acidity or strong acidity;the content of total N,total K and OM in the soil were at middle level,the content of total P was deficiency,and available nutritions was low,moreover,available P was in serious deficiency,it would be a limited factor for the growth of Eucalyptus.The physical characters of the woodland soil were poorer,it was relatively compact,poor aeration and permeability.There was a certain difference among the 6 different planting areas,the soil fertility status of Eucalyptus urophylla×E.grandis plantations in Changtai and Nanjing was relatively good.However,it was poor in Yunxiao for a low content with total and available nutrient.Compared with other important planting areas,planting area in southern Fujian was at the same level with Guangxi and superior to Guangdong and Hainan.2.Fertilization investigations of Eucalyptus urophylla×E.grandis plantations showed that:the farmers have realized the importance of fertilization during the process of Eucalypt planting,all the plantations had been fertilized with basal fertilizer and top dressing focused on the first two year after it being planted, fertilization was still in disorder with chemical fertilizer mainly used and kinds and application rate greatly at random.3.Growth investigations of Eucalyptus urophylla×E.grandis plantations showed that The first three years was the key period for management after the plantation was founded,during that period,trees grew most rapidly and the influence of soil basic fertility and fertilization on plants growth became more significant as growth period prolonged.Plantations grew most rapidly when they were about 16 months, and became relative slow about 28 months.Among 6 planting areas,the plantations of Changtai country grew best,the secondary was Nanjing,Xianyou and Pinghe,while Nan'an and Yunxiao the worst.4.The result of DRIS nutrition diagnosis showed that:Eucalyptus urophylla×E.grandis plantation in southern Fujian was under poorer nutrition balance with less supply in N,P,Ca and more in K,Mg.so it should enlarge the fertilization amount of N,P and Ca.Through DRIS nutrient diagnosis the optimum ratio range of N,P,K concentration in the leaves of Eucalyptus urophylla×E.grandis plantations was respectively P/N=0.1144±0.0169,N/K=0.9739±0.1997,P/K=0.1074±0.0173.5.The relationship among soil fertility,mineral elements content in leaves and growth of seedling was analyzed by using multifactor interactions stepwise regression method.The results showed that in the Eucalypt planting areas in southern Fujian,there was a strong correlation between the content of OM,total N,hydrolytic N in woodland soil nutrient and tree height,diameter,volume,it showed that N had greater influence on the growth of Eucalyptus urophylla×E.grandis;also,there was a strong correlation between the content of N,K,Ca in leaves and growth of seedling,among them,the content of Ca showed negative correlation with the growth of seedling.For 16 months Eucalyptus urophylla×E.grandis plantations,trees obtained better growth of seedling when the ratio of hydrolytic N,available P and K in the soil was about 6:1:3 or 5:1:5 or when there was amount in the leaves which is N,10.63～12.74 g/Kg;P,1.00～1.42 g/Kg; K,10.64～14.42 g/Kg;Ca,3.52～7.02 g/Kg;Mg,1.93～3.62 g/Kg;and for28months plantations,that was about 5:1:4 or 4:1:4.5 or N,10.69～12.28 g/Kg;P,1.20～1.67 g/Kg;K,12.79～14.73 g/Kg;Ca,2.29～4.1 0g/Kg;Mg,5.34～6.42 g/Kg in the leaves.6.The results of Eucalyptus urophylla×E.grandis growth of indoor pot culture experiments with different proportioning fertilization of N,K,P showed that:different proportioning fertilization of N,P,and K had great influence on tree height,diameter growth,biomass accumulation,and chlorophyll content of Eucalyptus urophylla×E.grandis.Among them,N,P had greater influence but K had less influence.The influence order was N＞P＞K.The accumulation of N,P,K amount in the tissues of roots,stems,leaves has a certain difference,it was great in leaves and less in stems and roots.The accumulation rule of N,P,K amount in the tissues of roots,stems,leaves was leaves＞stems＞roots,representing that leaf is the main organ in nutrients accumulating;The accumulation rule of N,P,K in roots and leaves was N＞K＞P,while in the stems,it was K＞N＞P.The accumulation of N,P,K in roots,stems and leaves which is under different fertilizer treated have a close relationship with fertilization amount,and it would influent the absorption and accumulation in seedling if the amount of fertilizer was too high or too low.7.The results of DRIS nutrient diagnosis of Eucalyptus urophylla×E.grandis leaves under the condition of pot culture showed that:the sequence of fertilizer that seedlings need was at a same order with fertilizer treated sequence.The best ratio scope of N,P,K concentration in the leaf of Eucalyptus urophylla×E.grandis under the condition of pot culture was gained by DRIS nutrient diagnosis and the range was P/N=0.1084±0.0135,K/N=0.4822±0.0864,K/P=5.3726±1.0924.By using regression equation between fertilization amount and growth of seedling,it can be concluded under such experiment conditions that the optimum fertilization amount comfortable for the growth of Eucalyptus urophylla×E.grandis trees is as follows:N,5.48～6.27 g/pot;P,2.94～3.10 g/pot;and K,1.98～2.31 g/pot.Thereby,the ratio of N,P, and K in the pot culture soil shall be 3:1:3 or 3:1:2.6.
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