Study On High Efficiency Use Technology Of Nitrogen Fertilizer And Its Mechanism In Rapeseed And Sesame Multiple Cropping Pattern

Rapeseed and sesame is one of the main planting patterns in the dry-land of middle reaches of the Yangtze River in China（Hubei and Jiangxi province）.At present,there are two key factors which restrict fast development of this pattern,the first factor is low yield and low nitrogen use efficiency of rapeseed in the dry-land,the phenomenon of unreasonable fertilization is particularly prominent;the second factor is that farmers used continuous cropping of sesame after harvesting rapeseed,and the demand for nitrogen fertilizer is a few for sesame and it often leads to aggravation of sesame disease with increasing of nitrogen fertilizer,and the final yield is obviously decreased.Therefore,in order to solve the above two problems and improve the total yield,total benefit and total nitrogen use efficiency of rapeseed and sesame multiple cropping,these were carried out that effect of application of different nitrogen fertilizer rates,the application period and proportion on the yield of two crops in this study,nitrogen absorption and translocation,nitrogen use efficiency and its related mechanisms.It can provide theoretical basis and technical guidance for high nitrogen use efficient and control sesame disease in this mode.The main results are as follows:（1）On the basis of applying 270 kg pure nitrogen per hectare,the reduction of 45 kg pure nitrogen and 202.5:22.5 of nitrogen distribution ratio for rapeseed and sesame would increase the total output and total benefit.The amount of nitrogen fertilizer significantly affected grain yield at different branches,and first rose and then fallen with the decrease of branch position.The experiment in Wuhan showed that the rapeseed yield increased by 21.2%and 44.2%,with increasing of nitrogen application rate from T₁（180kg/hm²）to T₂（270 kg/hm²）in Huayouza 62 and Huayouza 9,respectively.Meanwhile,total yield of rapeseed and sesame of T₂ treatment were the highest in two test points,and total nitrogen use efficiency of T₂ treatment（44.76%and 52.80%）were significantly increased by 8.61 and 15.45 percentage points than that of T₁ in Wuhan test point.Reducing the nitrogen fertilizer by 45 kg/hm² on the basis of 270 kg/hm²,the highest total yield（3277.9kg/hm²）and total benefit（26455.1 yuan/hm²）were observed in P₃（202.5:22.5,kg/hm²）treatment,which were increased by 41.92%and 56.66%compared with the control（P₀）,respectively.The sesame yield of 21days after sowing（1063.6 kg/hm²）was significantly increased by 69.63%compared with the control（without fertilization）,and the total yield and benefit of rapeseed and sesame of 21days after sowing were the highest among all treatments（3272.4 kg/hm² and 25934.4yuan/hm²）.（2）The nitrogen recovery efficiency of rapeseed under low nitrogen level was significantly higher than that of high nitrogen.The nitrogen transport efficiency of base fertilizer was significantly higher than that of top dressing.About 1.62%of the residual nitrogen of rapeseed was absorbed by the subsequent sesame.¹⁵N recovery efficiency(¹⁵NRE)of HS5 under N₁(0.15 g N.kg^–1 soil)significant increased by 5.89 percentage points compared to N₂(0.30 g N.kg^–1 soil),and the most obvious difference was observed in grain.The ¹⁵N transport efficiency(¹⁵NTE)of the N₁ treatment（37.62%～37.70%）was much higher than that of the N₂ treatment,with the difference mainly observed in stem.The ¹⁵NTE of basal treatment was significantly higher than that of topdressing,with the difference mainly found in leaves.The ¹⁵NRE under topdressing treatment（56.85%～61.60%）increased 8.18 and 8.58 percentage points relative to that under basal treatment,with the main difference observed in grain and pericarp.Additionally,about 1.62%of residual nitrogen from rapeseed season of the two N levels was absorbed by the subsequent sesame,and the average ¹⁵NRE of sesame from basal and topdressing were1.91%and 1.34%,respectively,with signifiant increased in yield compared to the control.（3）There was significant increased in PSII the maximum photochemical quantum yield（Fv/Fm）and PSII potential activity（Fv/Fo）of rapeseed leaf with increasing inorganic nitrogen fertilizer and organic nitrogen fertilizer treatment.Different nitrogen application rate showed significant effects on PSⅡactual photochemical efficiency of different position leaves in the two cultivars,especially for the top second leaf to fourth leaf.Nitrogen addition decreased leaf photosynthetic electron transfer rate during the overwintering stage of rapeseed,especially the top second leaf to fifth.（4）The application of nitrogen fertilizer can increase by 12.8 percentage point of the disease incidence of resistant sesame varieties.The diversity of main phylum in bacterial of rhizosphere soil was significantly affected by diseased.The relative abundance of Ralstonia solanacearum was 0.15 and 0.11 percentage points higher in Diseased sample from rhizosphere soil（D）than in Healthy sample from rhizosphere soil（H）samples for the two cultivars,respectively.N₁ had a significant decrease of 0.708 percentage points in the relative abundance of genus Roseiflexus as compared to N₀ in Jinhuangma with resistant varieties.Compared to N₁,the relative abundance of five genera,such as uncultured-f-Acidobacteriaceae＿Subgroup＿1,Candidatus＿Solibacter,Bryobacter,Rhizo-microbium,and Subgroup＿2＿norank,was significantly increased by 0.593～2.064percentage points in N₀ of Zhongzhi 35 with not resistant varieties.Furthermore,the D samples of Jinhuangma were 0.655 and 0.569 percentage points significant higher than H samples in the relative abundance of Phenylobacterium and Pseudonocardia.The D samples of Zhongzhi 35 were 1.007～1.867 percentage points significant higher than H samples in the relative abundance of Burkholderia,Massilia,Phenylobacterium and Novosphingobium,but it was just the opposite for other six genera.The function potential of bacterial community varied significantly between diseased and healthy samples.The cell motility,signal transduction and translation of bacteria from rhizosphere soil were significantly affected by the sesame disease.In short,without nitrogen fertilizer for sesame,nitrogen application rate for rapeseed should be 270 kg/hm² in rapeseed and sesame cropping pattern,and it can improve the rapeseed and sesame yield and nitrogen use efficiency.Meanwhile,it can also improve chlorophyll fluorescence parameters of rapeseed from pour second leaves to pour fourth leaves.If the total nitrogen application rate of rapeseed and sesame was reduced by 45kg/hm²,then the nitrogen distribution ratio of rapeseed and sesame should be 202.5:22.5（kg/hm²）and it was suitable for rapeseed and sesame under the condition of saving nitrogen fertilizer.Topdressing of 21days after sesame sowing was more appropriate in rapeseed and sesame cropping pattern.Meanwhile,the planting of local sesame variety（Jinhuangma）should be minimized or not fertilized,which can reduce the incidence of sesame and maintain higher yield.It was a simplified and saving nitrogen application technique system in rapeseed and sesame multiple cropping pattern which was worth promoting in the region of rapeseed and sesame multiple cropping.