| This experiment was made on three cultivars:Qiuyu,Qinglong and Tailai which were wide-spreaded in Heilongjiang province in silkworm mulberry production . It adopted random sample in the areas, was divided into 4 densities and designed stubs to be 45 000, 60 000, 75 000 and 90 000 stubs/ hm2 respectively , which showed mulberry growing characteristic under the condition of different planting densities, the length of leaves ,the production of mulberry leaves and the influence mechanism on leaves quality. The article aimed at discussing the reasonable growing densities of having no trunk mulberry fleetness park in the high and cold region in Heilongjiang province, provided theoretical consult and references for Heilongjiang province silkworm mulberry production to improve silkworm mulberry yield, economy cost and increase die benefits .Research results show:The reasonable dense plantation in mulberry was viable in such high and cold region as Heilongjiang province, different cultivars contained different and suitable cultivation density.The appropriate increment unit area mulberry stub counts, Qiuyu and Qinglong under the density of 60 000 stubs/ hm2 and the Tailai under the density of 75 000 stubs/ hm all could increase the leaves production, attain to the highest leaf production and wouldn't reduce leaves quality, won't affect the silkworm quantity. The reasonable dense plantation in mulberry could produce the stanza and increase the effect.Density affects yield greatly. The effect on composing factors of single stub yield . from the three experimental cultivars ,the branches of single stub , the length of single stub and leaves yield per meter reduced along with the increase of density. The branches number and the length of branches increase along with the increase of date and density. The density had obviously relativity to the length of branches, relativity to the branches number, and obviously mined relativity to the leaves yield .It showed density influences greatly to the yield composing factors of the above three cultivars. Qiuyu ,at the density of 60 000 stubs/ hm2, its quantity of single stub as 3.2 stubs, length of single stub as 4.8 meters, the leaves yield on the length of single stub as 32.3g, would reach the highest yield. Qinglong, at the density of 60 000 stubs/ hm2 , its quantity of single stub as 3.3 stubs, length of single stub as 4.9 meters, the leaves yield on the length of single stub as 31.4g, would reach the highest yield. Tailai, at the density of 75 000 stubs/ hm2, its quantity of single stub as 4.1 stubs, length of single stub as 4.0 meters, the leaves yield on the length of single stub as 29,8g, would reach the highest yield. Above three treatment combination should be adopted in Heilongjiang province silkworm mulberry production.From the three experimental cultivars , under different densities, the branches number and length of branches in unit area increased along with the increase of density.The change in branches numbers of Qinglong was similar to Tailai: at the desity of 75 000 stubs/hm2, Qiuyu increased to 90 000 stubs/ hm2 with the density, the ability of ramification was restrained, the branches number reduced. At A4 density the length of branches unit area was always over and above other density, the bigger the density was , the less that the length of branches increment was . At last the density unit area became near to, the growth of the length of branches of mulberry suffered to repress. The branches number and length of branches in unit area in the three experimental species increased along with the increase of dates. The leaves yield per meter expressed for Al > A2> A3> A4; The change of leaves yield unit area was contrary with leaves yield per meter in preperiod , all for A4> A3> A2> Al, entering the prosperous growing period, leaves yield unit area of Qiuyu and Qinglong was A2> A3> A4> Al, but Tailai was for A3> A4> A2> Al. The density that a cultivation needs was different when different cultivars attain the plentiful producing.
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