Studies On The Effects Of Planting Densities And Nitrogen Fertilizer On Development And Nitrogen Utilization Of Direct-seeding Oilseed Rape (brassica Napus L.)

To solve the problem of low nitrogen utilization efficiency and heavy labor force in transplantingwhich seriously restrict the development of rapeseed industry,,plot experiment,pillar experiment and potexperiment were confined to evaluate the effects of density and nitrogen fertilizer on the soilenvironment, nitrogen uptake and utilization,parameter of root morphological, plant growth anddevelopment above ground,grain yield and economic benefits of fertilization of rapeseed (zhongshuang NO.11)in this research. The main results are listed as follows:(1) The net income of nitrogen fertilizer on rapeseed decreased with the increase of nitrogenapplication rate while increased with higher planting densities. The economic nitrogen application rateon rapeseed under high planting density is126.6kg/hm2, which resulted in a relevant grain yield2231.5kg/hm2;the economic nitrogen application rate on rapeseed under low planting density was149.2kg/hm2, which resulted in a relevant grain yield2169.5kg/hm2. Under the same objective yield, thenitrogen rate would be saved obviously at the range of22.9%-30.6%.(2) Nitrogen derived from fertilizer and soil increased with the increasing of nitrogen applicationrate and planting density. The amount of nitrogen accumulation in plant and grain increased with theincreasing of nitrogen application rate less than180kg/hm2; when the nitrogen application rate increasedto270kg/hm2, it improved obviously mainly on the part of non-economic grain. Nitrogen utilizationefficiency of rapeseed decreased with the increasing of nitrogen application rate, while it increased withplanting density. By the method of subtraction, the NUE under low planting density was58.4%, while itwas63.5%under high planting density. By the method of tracer, the15NUE under low planting densitywas41.8%, while it was43.2%under high planting density.(3) The green leaves number, root crown diameter, plant height and dry matter accumulation aboveground increased with the increasing of nitrogen application rate at different growth stages. The greenleaves number and dry matter accumulation above ground unit area increased with higher plantingdensity while the root crown diameter was converse at different growth stages. The order of dry matteraccumulation under low planting density at harvesting stage was: nutshell>stalk>grain>root, the orderof dry matter accumulation under high planting density at harvesting stage was: stalk> nutshell>grain> root. The effective branches numbers and effective pod per plant increased with the increasingof nitrogen application rate less than180kg/hm2, it would be a trend of decreasing if increased more.The effective branches numbers per plant under high planting density decreased by50.6%than lowplanting density, but the effective branches numbers unit area under high planting density increased by49.5%than low planting density. Higher planting density reduced the effective pod per plant and seedper pod while improved the1000-seed weight obviously. The grain yield unit area of rapeseed increasedwith the increasing of nitrogen application rate at the range of0~180kg/hm2, when the nitrogen rateincreased to270kg/hm2, it declined. The order of effects of yield components on the grain yield was:1000-seed weight>effective pod per plant>seed per pod.(4) The increasing of nitrogen application rate mainly improved the total root surface unit area, and higher planting density mainly enhanced the total root length and volume unit area at all growthstage. The total root length, root surface and root volume unit area were higher under high plantingdensity than low except average root diameter. The root biomass and root activity increased with theincreasing of nitrogen application rate under both planting density at Ten-leaf and early flowering stages,higher planting density could improve the root activity. Under the same level of nitrogen applicationrate, the root biomass in the layer from0to10cm of the soil under high planting density was higherthan low, which was opposite to the root biomass in the layer from10to40cm of the soil., it indicatedthat higher planting density would induce the extend of the root to the deep layer in the soil.The inorganic nitrogen in the soil of rapeseed mainly exist in the form of NO-3-N, nitrogenapplication mainly increased the content of NO-3-N in the layer from0to20cm of the soil. The effectof planting density and nitrogen application rate on the content of NO-3-N in the layer from0to60cmof the soil was that: it enhanced by31.2%under a nitrogen application rate of270kg/hm2than180kg/hm2.and decreased by12.1%under high planting density than low. The content of NO-3-N underhigh planting density decreased by12.1%than which under low planting density. The increasing ofnitrogen application rate and planting density could enhance the activity of urease, sucrase andphosphatase during the whole growth period.(5)The total root length, root surface and root volume of rapeseed were in significant positivecorrelations with nitrogen accumulation at all growth stages except average root diameter. The total rootlength was the main factor which affected the nitrogen accumulation. The total root length, root surfaceand root volume of rapeseed were in significant positive correlations with grain yield at Ten-leaf stageand harvesting stage; the total root length, root surface, root volume and average root diameter ofrapeseed were in significant positive correlations with grain yield at early flowering stage. Thecorrelation between root surface and grain yield was the highest at Ten-leaf stage and early floweringstage, while the correlation between root length and grain yield was the highest at harvesting stage. Thetotal root length, root surface and root volume of rapeseed were in significant positive correlations withnitrogen accumulation at all growth stages except average root diameter. The total root length was themain factor which affected the nitrogen accumulation. The total root length, root surface and rootvolume of rapeseed were in significant positive correlations with grain yield at Ten-leaf stage andharvesting stage; the total root length, root surface, root volume and average root diameter of rapeseedwere in significant positive correlations with grain yield at Early flowering stage. The correlationbetween root surface and grain yield was the highest at Ten-leaf stage and early flowering stage, whilethe correlation between root length and grain yield was the highest at harvesting stage.