| Brassica napus is the main cultivation species of rapeseed in China,accounting for about90%of the total planting areas of rapeseed,and the application of hybrid varieties has been popularized and applied basically,and the application of hybrid varieties has a great effect on the increase of rapeseed production and income.However,with the development of society,the high input of traditional rapeseed production mode has seriously restricted the development of rapeseed,and it is urgent to carry out whole-process mechanization in rapeseed production to achieve cost reduction and efficiency increase.At the same time,in order to ensure the quality of cultivated land,the state has proposed the policies of"reducing nitrogen and increasing efficiency"and"increasing agricultural efficiency and farmers’income".Therefore,it is of great theoretical and practical significance to carry out research on cultivation technology measures of suitable crop(High density planting),reduce nitrogen,and increase efficiency for rapeseed hybrid.Three excellent rapeseed hybrid cultivars:Shaanyou1831(V1),Shaanyou1832(V2)and Shaanyou975(V3),were selected as material to carry out the three-factor split zone test of nitrogen application rate and planting density.Four nitrogen levels(N0(0 kg/hm~2),N1(108 kg/hm~2),N2(144 kg/hm~2)and N3(180 kg/hm~2))were set as main regional factors,and three planting densities(D1=150,000 plants/ha,D2=300,000plants/ha and D3=450,000 plants/ha)were set as secondary regional factors.The variety is splitting area.We studied the effects of different nitrogen application rates and densities on photosynthetic characteristics,dry matter accumulation,nitrogen accumulation and absorption,yield and yield component factors of three new rapeseed hybrids to reveal the rules of dry matter and nitrogen accumulation and distribution during the growth and development of rapeseed,and to provide a new theoretical basis for achieving the cultivation goal of"high yield and high efficiency"of rapeseed hybrids.The results are as follows:(1)Nitrogen application rate and density significantly affected the photosynthetic characteristics of rapeseed.Before pod setting,high nitrogen application rate and low density could promote photosynthesis of the three varieties at seedling stage and flowering stage.Compared with seedling stage and flowering stage,chlorophyll content and photosynthetic efficiency were the highest at flowering stage.At the grain filing stage,high nitrogen and high density could significantly increase the pod area index of group,the effective photosynthetic area,the photosynthetic rate,the photosynthetic performance,and the dry matter accumulation of plants.The results showed that the content of chlorophyll content,net photosynthetic rate,transpiration rate and PAI of V3 were significantly higher than those of V1 and V2 at the grain filing stage.(2)Nitrogen application rate and density significantly affected the accumulation and distribution of dry matter at different stages of rapeseed:the dynamic dry matter accumulation of the three varieties was in line with the Logistic growth function model(S curve)at the whole growth stage,and the dry matter accumulation per plant reached the maximum under the treatment of maximum nitrogen application rate and minimum density,and the effect of density on the shoot was greater than that of nitrogen application rate.The distribution of dry matter to vegetative organs increased with the increase of nitrogen application rate at bolting stage and final flowering stage.At the ripening stage,the proportion of dry matter allocation to reproductive organs increased with the increase of nitrogen application rate,and the proportion of dry matter accumulation in seeds increased under nitrogen application.(3)Nitrogen application rate and density significantly affected nitrogen accumulation,distribution and utilization at different stages of rapeseed.During the whole growth stage,nitrogen accumulation of stem reached its maximum value at the final flowering stage,while that of leaf reached its maximum value at the initial flowering stage.The nitrogen accumulation of siliques accounted for about 90%of the whole plant,and the seeds accounted for about 60%of the whole plant at the ripening stage.The above-ground nitrogen accumulation in V1,V2 and V3 was significantly increased with the increase of nitrogen application rate,but significantly decreased with the increase of density.In addition,the response of above-ground nitrogen accumulation to density in V2 was small,while was more obvious V1 and V3.Increasing density could significantly improve the recovery efficiency of applied nitrogen and seed nitrogen accumulation of the three varieties,and V3 varieties were significantly higher than V2 and V1.In the range of 0～180 N kg/hm~2,increasing nitrogen application rate could significantly increase the nitrogen harvest index and seed nitrogen accumulation of the three varieties.(4)Nitrogen rate and planting density significantly affected the resistance of the three varieties:high nitrogen rate and high density both increased lodging risk and Sclerotinia sclerotiorum of the three varieties.The net photosynthetic rate of the three varieties significantly decreased after inoculation for 10 days.Combined with the investigation of the incidence indices of artificial inoculation and natural sclerotinia disease in field,lodging resistance and disease resistance in V1 were significantly superior to those in V2 and V3.(5)Nitrogen application and planting density significantly affected the yield and yield component factors of rapeseed:The increase of density decreased the plant height,the length of main inflorescence,the number of siliques and yield per plant,and increased the effective branch height.The increase of nitrogen fertilization could effectively improve the number of siliques,the number of seed per siliques,thousand-seed weight and protein content in a certain range(0-180 kg/hm~2),thus increasing the yield of per plant,but reducing oil content of rapeseed.Increased nitrogen application and reasonable planting density could significantly improve yield.Shaanyou 1831 could achieve the maximum yield potential of 295-297 kg per mu at nitrogen application of 180 kg/hm~2 and density of 360-450,000 plants/ha.Shaanyou1832has a maximum yield potential of 308-310 kg per mu at nitrogen application rate of 176-180kg/hm~2 and density of 370-44,000 plants/ha.Shaanyou 975 has a maximum yield potential of310-313 kg per mu at 176-180 kg/hm~2 of N and 350-450,000 plants/ha.We provide a high-yielding and efficient cultivation measure for hybrids of Brassica napus in the drought region of northwest China:nitrogen application of 175-180 kg/hm~2 and density of 370-440,000plants/ha. |
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