Effect Of Nitrogen Reduction On Winter Rapeseed And Difference Of Nitrogen Efficiency Among Different Varieties

Winter rapeseed is mainly distributed in the Yangtze River Basin of China.The phenomenon of excessive application of nitrogen fertilizer in the planting process is very common,which not only increases the production cost of farmers,but also pollutes the environment.Nowadays,under the background of green and sustainable development of agriculture,how to ensure food security and realize green and efficient production of crops is one of the most severe challenges we face in this century.First of all,while stabilizing or even increasing yield,formulating a reasonable amount of nitrogen fertilizer and reducing the phenomenon of excessive application of nitrogen fertilizer can improve the efficiency of nitrogen fertilizer utilization and reduce the risk of ecological environment to a certain extent;In addition,screening the corresponding nitrogen efficient varieties in the region,and trying to reveal the physiological and agronomic characteristics of different nitrogen efficient varieties,so as to further guide the future breeding work,which can maximally solve a series of problems caused by the serious consumption of natural resources and excessive input of nitrogen fertilizer,and realize the sustainable development of agriculture.This study is carried out in Hanzhong,Shaanxi Province,the main production area of Winter Rape in the upper reaches of the Yangtze River.The field experiment is a split plot design.The main treatments are different nitrogen application rates,including no nitrogen application treatment（N0）,nitrogen reduction treatment（N180）and farmer model treatment（N231）;Five local cultivated rape varieties were selected for secondary treatment:Shaanyou28（SY28）,Qinyou 28（QY28）,Fengyou 737（FY737）,Qinyou 10（QY10）and Zhongyouza19（ZYZ19）.The main results are as follows:（1）Compared with no nitrogen application treatment,nitrogen application significantly increased Leaf SPAD value,number of green leaves,leaf area,net photosynthetic rate,root length,rhizome diameter,nitrate reductase activity and glutamine synthase activity in winter rape at seedling stage,before flowering and full flowering stage.There was no significant difference between local farmers’model treatment（N231）and nitrogen reduction treatment（N180）.There was no significant difference in aboveground nitrogen absorption,winter rape yield and main quality indexes in different periods after nitrogen fertilizer reduction.（2）After the reduction of nitrogen fertilizer,the distribution of nitrate nitrogen reserves in the soil profile of Winter Rape in different periods was significantly different only in the surface soil layer（0～20cm）after harvest.In addition,under the condition of reduced nitrogen application,the nitrogen recovery efficiency,nitrogen partial productivity and nitrogen use efficiency of winter rape increased by 4%～7%,4～5kg kg^-1 and 2.5～3.0 kg kg^-1 respectively.（3）Compared with nitrogen inefficient Winter Rape varieties（nitrogen double low variety QY10）,there was no significant difference in nitrogen uptake before seedling stage of nitrogen efficient varieties（low nitrogen tolerant variety QY28 and nitrogen efficient variety FY737）.The total nitrogen uptake before and after flowering and at harvest was one of the main reasons for the difference in nitrogen efficiency among varieties.（4）By measuring the transcriptome of post flowering leaves,it was found that the gene members of nitrate transporter family（NRT）,ammonium transporter family（AMT）and the gene expression of key enzymes in nitrogen metabolism pathway were significantly up-regulated in nitrogen efficient varieties compared with nitrogen inefficient varieties,indicating that nitrogen efficient varieties have stronger activity in nitrogen absorption and metabolism in leaves after anthesis.（5）The proportion of nitrogen allocated to inflorescences at flowering and grains at harvest of nitrogen efficient Winter Rape varieties was significantly higher than that of nitrogen inefficient Winter Rape varieties.The number of pods per plant,yield,harvest index and nitrogen harvest index of Winter Rape are closely related to the nitrogen use efficiency of rape,which can be used as the main index for screening nitrogen efficient rape varieties.In addition,our study also found that there is a negative correlation between grain nitrogen content and plant height and the nitrogen use efficiency of rape.In conclusion,it is feasible to reduce the nitrogen application rate of farmers in the winter rape planting system from 231kg ha^-1 to 180 kg ha^-1;Variety QY 28 is a local low nitrogen tolerant variety,which has high yield and nitrogen efficiency without nitrogen application.Variety FY 737 is a local nitrogen efficient variety,which has the highest yield and nitrogen efficiency under high nitrogen conditions.Variety QY 10 is a local double low variety,which has the lowest yield and nitrogen efficiency under all nitrogen application treatments;In terms of nitrogen absorption and metabolism,compared with nitrogen inefficient Winter Rape varieties（nitrogen double low variety QY10）,high nitrogen absorption and nitrogen metabolism activity before and after flowering were found in high nitrogen efficient Winter Rape varieties（low nitrogen tolerant variety QY28 and nitrogen efficient variety FY737）;In terms of agronomic characteristics,higher pod number per plant,harvest index and nitrogen harvest index,lower plant height and grain nitrogen content can be used as auxiliary screening indexes for nitrogen efficient utilization varieties.