| It is necessary to make full use of winter fallow field to grow winter oilseed rape and increase the yield per unit area to ensure the edible oil safety in China.Nitrogen(N)fertilizer deficiency or excess occurred frequently in farmer’s practice.Since the benefit for simplified production,direct sown of winter oilseed rape became the primary establishment.Direct-sown winter oilseed rape was more sensitive to N deficiency comparing with transplanted establishment.However,that how does N nutrition affect direct-sown winter oilseed rape yield components remained unknow.Different N fertilizer rates field experiments were conducted in this study to analysis the dry matter and N accumulation characteristics under different yield levels,and identify the quantitative relationship between N accumulation and yield and its components.The mechanism of how does N nutritions regulate the yield components was studied,to identify the efficient N managements to target yield.The main results are summarized as follows.(1)N fertilizer application significantly increased dry matter and N accumulation,enhanced pods per plant and seeds per pod and adjusted plant population density at harvest(PPDh),to increased yield of direct-sown winter oilseed rape.Compared with common urea(CU)split application,the accumulation of dry matter and N and N concentration were increased notably of controlled release urea for winter oilseed rape(CRUrape)one-off application with the N rate≥180 kg N/hm~2.The yield and N use effiency(NUE)of CRUrape increased by 11.7%and 15.7%,respectively,comparing with that of CU at 180 kg N/hm~2.Regional recommended N application rate of CU and CRU were 201 and 203 kg N/hm~2,respectively.However,the profit achieved at the recommended N rate of CRU increased by 17.8%relative to that of CU.(2)Improving dry matter and N accumulation at seedling stage by N application was critical for high oilseed rape.High yield(>3000 kg/hm~2)direct-sown winter oilseed rape had larger proportion of dry matter and N accumulation at overwinter(90 accumulation proportion at overwinter of 3000 kg/hm~2 was averaged 56.9%,while it was less than 35.4%of low yield level.With the dry mater at seedling before overwinter(50 days after sowing)increasing 100 kg/hm~2 or 0.1 g/plant,yield increased by 222 and 256 kg/hm~2,respectively,and NUE increased by 3.0%and 3.5%(absolute value),respectively.High yield oilseed rape had advanced initial N rapid accumulation(T1),delayed end of dry matter and N rapid accumulation(T2),with prolonged rapid dry matter and N duration(△T),comparing with low yield level.Additionly,growth duration of high yield oilseed rape was longer by 18-27 d than that of low yield.Recommended N application increased maximun accumulation rate of dry matter and N accumulation by 166%and 300%,respectively.Average accumulation rate of dry matter and N during seedling increased by 499%and 689%by the recommended N,respectively.Additionly,T1 of dry matter and N accumulation were also advanced by 1.8 d and 10.8 d,respectively.The N accumulation proportion at overwinter were increased by N supply,with the proportion of 33.7%,50.5%and 63.2%under dificent,recommended and excessive N supply conditions,respectively.(3)N application regulated leaf number before overwinter,affecting branch number and pods per plant,to affect yield.The leaf number before overwinter was positively correlated with the seedling dry matter and N accumulation.With dry matter each increase of 1 g/plant,the leaf number increased by 0.7-0.9 leaf/plant.With N accumulation each increase of 50 mg N/plant,the leaf number increased by0.5-1.0 leaf/plant.Within the plant population density(PPD)of 50-130 plant/m~2,the leaf number increased by 0.4-1.1 leaf/plant and 1.0 leaf/plant by dry matter and N accumulation every increase of 1000 kg/hm~2 and 50 kg N/hm~2,respectively.Yiled varied in a parabola curve with leaf numer before overwinter increase.Branch number increased by 1.6 with leaf number each increase by 1 leaf/plant.Increased branch improved the branchy pods and pods per plant,to increase yield.With the leaf number each increase of 1 leaf/plant within the range of 2.6-6.7 leaf/plant,yield increased by622-981 kg/hm~2.The yield increase was higher when the base leaf number was less.(4)Among the four yield components,pods per plant had the greatest effect on yield,followed by PPDh.While seeds per pod and 1000-seed weight had a litter contribution to oilseed rape yield.Seed yield(y)increased linearly with pods per plant(x)(y=36+25.6x).High yield oilseed rape had smaller ranged PPDh with 45-70plant/m~2 of 3000 kg/hm~2.Increasing the pods per plant under proper PPDh is the key to improve the direct-sown winter oilseed rape.The pods number was under the regulation of N nutrient over whole growing season.N nutrient at seedling affected branch formation to afftect yield.While it affected pods number directly of N nutrient at bolting,flowering and pod stage.There showed parabolic relationships between pods per plant and the N accumulation per plant at the three stages.With each increase of 10 mg N/plant at these three stages,pods per plant increased 2.8-7.6,0.2-5.7 and 2.1-4.4 pod/plant,respectively.PPDh was affected by N application.The PPDh increased or decreased by N addition when indegious nitrogen supply capacity was less or more than 690 kg/hm~2,respectively,to maintain optimal PPDh.(5)N nutrient regulated PPD decrease and determined PPDh.The decrease in PPDh accounted for 9.3%-36.6%of the yield loss induced by N deficiency,indicated that optimal PPDh was critical for high yield of direct-sown winter oilseed rape.PPD decreased since seedling emergency.Emergency-60 days after sowing(DAS)and 150DAS-harvest were the critical stages for PPD decrease.When the N concentration was higher than 4.11%at seedling and 2.44%at flowering,the PPD was maintained at80-120 plant/m~2 and 50-80 plant/m~2,respectively,to achieve optimal PPDh.More precipitation during seedling(sowing to 60 DAS)or less precipitation during flowering(150 DAS-180 DAS)increased the plant mortality.The plant mortality was increased with accumulative temperature(>645℃d)addition.(6)Based on the quantitative relationship between N nutrition and yield and the yield components,a strategy for active N mannagement for target yield of direct-sown winter oilseed rape was designed.Yield components of target yield of 3000 kg/hm~2were identified.The PPDh was 45-70 plant/m~2,pods per plant was 104 pods,seeds per pod was 19-24 seed/pod and 1000-seed weight was 2.8-3.8 g.The N supply at seedling,overwinter,bolting and flowering stage was determined as 29.0,87.8,8.7and 33.7 kg N/hm~2,respectively,based on the average indegious nitrogen supply capacity of the field experiments.This study identified theoretical yield components of varying target yields and the characteristics of N accumulation,and clarified the regulation process of seedling N nutrition–leaf number-branch-pods per plant.This process revealed significance of N uptake at seedling satge on the high yield formations.That how does N nutrition regulating the PPDh was also clarified.In view of these knowledge,N regulation strategy under target yield was proposed,which provided specific nitrogen index at critical stages.The result could provide a theoretical knowledge and specific guidance for improved yield and NUE production of direct-sown winter oilseed rape. |
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