The Technology And Mechanism Of Nitrogen Nutrient Regulation In Winter Oilseed Rape

Oilseed rape is a dominant oil crop in China.The Yangtze River Basin(YRB),with 90% of the state’s oilseed rape planting area and total yield,is the largest winter oilseed rape planting area in China,which is of great significance in ensuring edible oil safety in China.Winter oilseed rape has a great demand for nitrogen(N).Excessive and insufficient of N fertilizer rates were existed.Improper fertilizer management,unitary species structure,extensive application and so forth are very common phenomena in filed practice.Unreasonable N application can cause several problems such as poor exertion of yield potential,N use efficiency decline,which can influence high yield and high efficiency of oilseed rape.Therefore,this research was carried out in multiple years and sites in the main winter oilseed rape production areas in YRB.By means of studying and comparing technical methods in different production scenarios such as N application rate,N management,N fertilizer force,N fertilizer application methods and soil N regulation in topsoil and so forth,we analyze the mechanism of winter oilseed rape yield formation and N uptake from oilseed rape yield and yield components,dry matter accumulation,N uptake and N use efficiency perspective,aiming to provide scientific basis for establishing winter oilseed rape management strategies.The main research results are as follows:(1)Precisely regulating of reasonable N fertilizer amount according to cultivation mode,rotation mode,plant density,ecological condition and so forth.Cultivation mode leads winter oilseed rape to different responses to N fertilizer.Transplanting winter oilseed rape(TP)shows a significant higher yield than Direct-seeding winter oilseed rape(DS),with an increase rate of 15.3%.Higher pod number per unit area is crucial guarantee for TP obtaining a high yield.Pod number per unit area of TP are 178.9 pod /m2 higher than DS.N fertilizer significantly increases dry matter and N accumulation of both TP and DS,especially after stem elongation stage.Comparing with CK treatment,average yield increasing rate and N accumulation increasing rate of DS are 255.9% and 279.1%,which are significantly higher than TP.Agronomic nitrogen use efficiency of DS is also higher than TP,which indicates DS is more sensitive to N fertilizer responses.When the target yield is 1000~2000 kg/hm2,recommended N amount of DS and TP are 151.5 kg/hm2 and 149.0 kg/hm2,respectively.When the target yield is 2000~3000 kg/hm2,recommended N amount of DS and TP are 208.3 kg/hm2 and 214.7 kg/hm2,respectively.Clearly,under the same target yield,TP can reduce 35.7 kg/hm2 as compared with DS.Differences of soil N supplying capacity in different rotation modes can influence nitrogen efficiency and suitable N application rate of oilseed rape.Winter oilseed rape yield in cotton-oilseed rape rotation(C-R)is significant higher than that of rice-oilseed rape rotation(R-R),with an average increasing rate of 27.9%.The treatment of no N fertilizer treatment in R-R shows significant lower yield than that in C-R,indicating that C-R has a better soil N-supplying capacity than R-R.Averaged yield increasing rate and N agronomic efficiency of R-R are 84.0% and 6.0 kg/kg,respectively,which are significant higher than that of C-R.The results indicate that winter oilseed rape in R-R is more dependent on N fertilizer.N application plays an important role in rotation system.Properly increasing N fertilizer amount can compensate for N-supplying deficiency in rice-oilseed rape rotation,thus narrowing yield gap between the two rotation modes.Suitable N application rate of winter oilseed rape in rice-oilseed rape rotation is 210.8 kg/hm2.Under the same target yield,cotton-oilseed rape rotation can reduce N fertilizer amount by 35.7 kg/hm2.Plant density and N application significantly influenced seed yield and yield components.Optimal plant density is the prerequisite for a high rapeseed yield.High plant densities affected the dry matter accumulation of individual plants and reduced the number of pods per plant.N fertilization substantially improved pods per plant and enhanced seed yield.At low plant densities,rapeseed yield increased as the N fertilizer application rate increased.At high plant densities,excessive N fertilizer inputs played only a minor role in seed yield.The farmers’ practice of transplanted density is 9.0×104 plant/hm2 in this region.When the target yield is set at 3000 kg/hm2,if density could increase to 10.0-12.0×104 plant/hm2,the optimal N fertilizer application rate could be cut down with 10.3%-23.7%.On the contrary,it was essential to increase N fertilization rate with 13.9%-34.8% to gain the target yield when the density was decreased to 7.0-8.0×104 plant/hm2.The growth of winter oilseed rape was obviously inhibited by waterlodging at seedling stage.Leaf number,leaf area and the SPAD values are reduced at different degrees.Waterlogging reduced dry matter accumulation and N absorption and utilization of winter oilseed rape,which caused unrecoverable influence on winter oilseed rape growth.The grain yield was significantly decreased by 23.6% under the waterlogging stress,and the decreased seed yield resulted from a decrease in density at the five leaf stage and the number of siliques per plant,which are reduced by 7.6% and 20.4%,respectively.N application promotes oilseed rape growth and development,improves population quality,alleviates yield loss caused by waterlogging at seedling stage,and there was a direct relationship between alleviation effects and N fertilizer input.Therefore,within certain limits,increasing N application rate could show compensation effect on direct-sown winter rapeseed growth and recovery after seeding stage waterlogging.Compared with the waterlogging treatment,59.2 kg/hm2 of N fertilizer was reduced in the drainage treatment when the seed yield remains unchanged.(2)Reasonablely managing N fertilizer according to cultivation modes and soil N-supplying capacity.Compared with one-off application treatment,split application proportions of TP were 60% basal fertilizer and 40% overwintering fertilizer and split application proportions of DS were 60% basal fertilizer,20% seeding fertilizer and 20% overwintering fertilizer can obtain better results,which increase seed yield and N use efficiency.Yield increasing rates are 14.7% and 21.7%,N accumulation increasing rates are 19.8% and 27.8%.Different trial sites show different effects of N split application due to different soil N apply capacities.(3)Control-released urea(CRU)makes one-off application and reduce N fertilizer amount possible.And CRU combines with common urea at a certain proportion can reduce oilseed rape production costs.Compared with common urea,CRU shows an average increasing rate of 7.4% and 11.5% in TP and DS seed yield,respectively.CRU shows a better yield-increasing effect under low N level than which under medium and high N levels,which indicates reducing CRU application rate is possible.Under low N level,dry matter and N accumulation increase significantly after anthesis is the main reason of seed yield increasing in CRU treatments.Comparing with common urea,the increasing rates of CRU treatments decrease when N application rate increases.Therefore,when CRU application rate is 180 kg/hm2,high yield and reduction in N fertilizer amount can be obtained at the same time.CRU combines with common urea not only can reduce production costs,but also integrate soil,fertilizer N-supply and winter oilseed rape N demand through a proper proportion,thus increasing yield and N use efficiency.Based on yield and linear plus plateau relationship between CRU and common urea application proportion,the best ratio of CRU and common urea of TP are 42% and 58%,while DS are 60% and 40%.(4)The optimal N fertilizer application methods were established based on the cultivation patterns and soil N-supplying techniques.Different N application methods show significant influence on seed yield,dry matter and N accumulation,following as concentrating> ploughing > broadcasting.Compared with broadcasting method,the concentrating method could increased yield by 18.2%-23.8% in both TP and DS;concentrating method can also significantly increase dry matter accumulation in winter oilseed rape in both TP and DS,especially synchronously increases dry matter accumulation in shoot and root after anthesis,thus increasing seed yield.Combined with winter oilseed rape cultivation modes,TP and DS was suggested to use bunch fertilization and drill fertilization as N concentrating application techniques in practice production conditions.(5)A soil-based N strategy can regulate the soil N supply to match the crop N uptake based on the soil Nmin test in the root zone before fertilization.Using a logarithmic function to describe the relationship between the N supply and the relative shoot N uptake,the optimal N target value was determined to be 105-128 kg N/hm2 from transplanting to over-wintering,95-105 kg N/hm2 from over-wintering to stem elongation,94-102 kg N/hm2 from stem elongation to flowering and 71-73 kg N/hm2 from flowering to maturity.Recommendations based on the soil Nmin test will be more efficient in warmer or normal winter seasons compared with the fixed fertilizer recommendation.