| In order to address the issue of disconnection between seedling cultivation and forestation,the author first puts forwards the concept of directed cultivation of seedlings. The directed seedling cultivation is to use required control technologies to allow the seedlings to meet the forestation requirement in terms of mosphology , physiology and viability so that forestation can be conducted in line with the site condition and seedling type. Targeted on seedlings used under difficult planting site conditions, the article elaborated on a series of modification and control technologies for directed seedling cultivation, including various technological measures taken during the seedling cultivating stage, such as resistant gene and selection of varieties, tree seeds processing technology, seedling resistance modification and control technology, and seedling viability protection and management. It provides theoretical basis for directed and high quality seedlings, and for matching stock to site.Based on the theory of directed seedling cultivation, this article selected Populus euramericana (Dode) Guineird and Purpureus tissue culture seedlings as the material and designed several substrates formula. Studies have been carried out on test of growing substrates, seedling resistance regulator, seedling nurturing, and fertilizer treatment.Depending on the production state of the North National Seed and Seedling Demonstration Base, The results showed that Poplar seedling growth was excellent for the peat moss from northeast of China + vermicukte, the pure peat moss from China, the peat moss from northeast+ammonium fertilizer + NRS fertilizer. They were nearly as good as the Finland peat moss. The Finland peat moss showed the best. Perlite showed bad effects. Vermiculite showed better effect and greatly promoted the growth of the seedlings. The physical and chemical of these substrates have been analyzed, the results showed that the value of maximum water absorbing rate of those good substrates was high and the substrate weight was low. Their particles were mainly in 1 -2 mm diameter and only a few of them less than 1 mm. Suitable pH vable was 3.50-5.65 and that showed the acid environment was suitable to seedling growth. .The suitable content of quick result nitrogen was 969.6mg/kg~2492.6mg/kg and phosphorus as 65.5mg/kg~486.9mg/kg. The content of quick result potassium of Finland peat moss was much higher than that of national peat moss, and the suitable value was 174.2mg/kg~1386.0mg/kg. The content of quick result boron of Finland peat moss wasmuch higher than the national's .The suitable value was 0.9mg/kg~4.5mg/kg.Through test and analysis of the growth indicators, physiology indicators, resistance indicators, and physicochemical characteristics of the Purpureus tissue culture seedlings growing on 17 different substrates, seedling growing substrates suitable for nursery production were selected. The result of the test indicates. The results showed that seedling growth was excellent for domestic peat moss +perlite+ vermiculite (1:1:1), domestic peat moss + Finish peat moss +vermiculite (1:2:2) with strong resistance.Based on the analysis of the physicochemical characteristics of the substrates , The suitable value of the substrate weight was 0. 13g/cm3-0. 47g/cm3, gravity of 1.26-2.81. total gap 80.5%-92%. field water absorbing rate of 117.2%-513%.Purpureus seedlings are suitable for acid environment. Suitable pH value of was 4.5-5.95.Using substrates good for seedling growth as standard, total N content is the best between 0.61-1.05%, quick result phosphorus between 50.67mg/kg-285.12mg/kg and quick result potassium between 430mg/kg-1660mg/kg, the better the substrates promote the seedling growth. ? trace element can promote the growth of the the Purpureus tissue culture seedlings, Trace elements can promote the growth of Purpureus seedlings and the rare elements content in the Finish peat moss is higher than domestic peat moss .especially the effective iron content and the quick result B content have signif...
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