Effects Of Planting Density On The Development And Yield Of Rapeseed (Brassica Napus L.) Under Different Sowing Dates

The effects of planting density on the development,plant height,total leaf numbers of main stem,number of green leaves,dry matter accumulation,chlorophyll,soluble sugar content,groups of branches,pod numbers as well as yield and quality of rapeseed were investigated under different sowing date(traditionally suitable sowing date and delayed sowing date)in this paper.The results are as follows:1.Increasing planting density could accelerate the reproductive process of the rapeseeds,especially under early sowing date.Whole growth period of rapeseed sown during the first ten-days of October shorted about 3d and 5d of late variety-HuaShuang No.5 and early variety-HuaYouZa No.10,respectively,as the planting density increasing. Sown in the early November,the days that rapeseed need to become mature had little difference between the two,but the bolting and blooming had an advanced tendency.2.Increasing planting density weakened the growth and development of the individual of rapeseed,especially under the early sowing date.Plant height,the numbers of main stem leaves and green leaves,dry matter weights of whole plant,roots,stems, branches,leaves and pods all were decreased as the planting density increasing under the early sowing date.In the condition of s delaying the sowing date,the plant height increased at first and then reduced while the planting density was increaseding.Under different sowing date,planting density had little effect on the dry matter allocation in rapeseeds.The seeds,branches and pod covers,stems accounted for about 30%,40-50%, 20-30%,respectively.Individual growth vigor was different between hybrid rape and conventional rape,individual development caused by planting density was also different.3.Increasing planting density,the chlorophyll content of the physiological characteristics of the functional leaves of rapeseeds decreased but soluble sugar content increased.The trend of chlorophyll content of the two varieties were as follows:it was higher on second and third 10 days of December,decreased as the temperature decreasing during over-wintering period,ascended in the mid of February,reached peak at full-bloom stage,the effect of planting density on the chlorophyll content was also the most obvious at this stage.The soluble sugar content of leaves was at a low level at the seedling stage when vegetative growth was mainly processed,the soluble sugar content increased with the enhancement of the reproductive growth,reached peak at full-bloom stage.The soluble sugar content increased under the adversity conditions(such as low temperature of 0℃).The increasing tendency of soluble sugar content as the planting density increased was more obvious at the early sowing date.4.The regularity of the effect of different density,sowing date on the quality of oilseed was not strong.The range of the oil content,glucosinolate content and protein content of different treatment were 40.02-45.44%,17.37-38.22%,16.97-24.26% separately.The analysis of variance indicated that the effect of planting density on the indicators of quality was not obvious.5.As the planting density increased,the planting height,the stem diameter,the numbers of effective branches and the length of the main inflorescence all decreased gradually but the location of the branches on the stem rose.The numbers of the effective pods of individual plant,biomass and yield of seeds showed declining trends,while the numbers of the effective pods of individual plant,the numbers of seeds in one pod and the weight of one thousand seeds change little.Under the early sowing date,the number of branches and pods of rapeseed populations increased with the increase in planting density.In the conditions of early sowing date,yield-increasing effect of increasing the planting density was not obvious,but yield showed a deceasing tendency as the planting density increased especially in the conditions of high soil fertility.Rapeseed sown before October 11,the tendency that yield increased with the increase in planting density gradually became strong.For example,the yield of rapeseed sown at October 30 of 3.2-4.0×10~4 plants/667m~2 increased by 11%-14%compared with 1.6×10~4 plants/667m~2.6.Technical scheme for rational close planting and obtaining stable and high yield of rapeseed.In the conditions of high soil fertility of middle and lower Yangtze,the yield of direct sowing rapeseed before October 10 had little difference from 8000 to 16000 plants/667m~2.In the conditions of low soil fertility,planting density could be raised to 1～2×10~4 plants/667m~2.Sown after October 10,the effect of the difference of population size on yield was more obvious as the sowing date postponed,planting density could be raised to 2～3×10~4 plants/667m~2.Postponed to November 1,conventional rape could obtain the yield of 153～173kg/667m~2 at the density of 2.5～4×10~4 plants/667m~2,hybrid rape could obtain the yield of 162～181kg/667m~2 at the density of 1.6～3.2×10~4 plants/667m~2;In the conditions of low soil fertility,no matter conventional or hybrid rape could raise the planting density to 4×10~4 plants/667m~2.Postponed to November 15 or so, if the rapeseed could keep normal germination and water and fertilizer management was strengthened,planting density was more than 3×10~4plants/667m~2,then seed yield about 100kg could be still obtain.