Combined Effects Of Nitrogen And Plant Density On Grain Yield,Quality And Nitrogen Use Efficiency In Wheat

Wheat（Triticum aestivum L.）provides energy and protein for world human and animals.Wheat grain productivity is easily affected by environmental factors.In the current field study,we studied the combined effects of nitrogen（N）and seed rate（SR）on physiological characteristics,dry matter（DM）and N accumulation and translocation as well N use efficiency（NUE）and end-use quality in winter wheat.This experiment was conducted in two successively growing seasons（2017-2018 and 2018-2019）under different N and SR treatment.The N was applied at the rate of N235 and N290 kg ha-1,and N0,N180,N235,N290 kg ha-1,in the first and second growing seasons,respectively.SR was applied at 135,180 and 225 kg ha-1 in both growing seasons.The main findings of current experiment were as follow:1.Optimized N and SR combination for balancing high grain yield and N uptake efficiency（NUPE）in winter wheatN and SR are two crucial factors which affect physiological characteristics,agronomic traits,dry matter（DM）and N accumulation,partitioning and translocation as well N use efficiency in winter wheat.In this experiment,we try to clarify the combined effect of N and SR to improve simultaneously grain yield（GY）and NUE.The result showed that by increasing N,physiological traits such as photosynthesis rate,chlorophyll content（SPAD value）,enzyme activities,leaf are index（LAI）,and number of tillers,GY,DM and N accumulation were significantly increased in response to increasing N fertilizer up to N235 kg ha-1.There was no significant difference between N235 and N290 for all above mention parameters.However,by increasing seed rate,photosynthesis,SPAD value and enzyme activities were decreased while GY,DM and N accumulation and LAI were increased.The highest value of tillers,GY,pre-anthesis DM and N translocation,N agronomic efficiency（NAE）,N recovery efficiency（NRE）,and N uptake efficiency（NUPE）among the combined treatments of N and SR,were obtain from N235+SRI 80 treatment.Moreover,increasing N beyond N235 kg ha-1 significantly decreased NAE,NRE and NUPE.The present study clarified that overuse of N application as well as seed rate do not lead to increase.Therefore,we suggested to use suitable combined treatment of N and SR（N235+SR180）or an increase in SR up to optimum level instead of increasing N level,to achieve maximum GY and improved NUE parameters.Increasing SR from 135 to 180 kg ha-1 the increment was shown by 12.9%and 9.1%for GY and NUPE,respectively.Based on this finding,we estimated that 1 kg ha-1 N would be replaced approximately by increasing SR of 0.6 kg ha-1.Finally,to make balance between GY and NUE,as well as to decline the risk of environmental pollution,suitable combined treatment or to increase SR up to suitable rate instead of increasing N would be the best method.2.Combination of nitrogen and seed rate affected quality traits of winter wheatThe quality of wheat flour mainly depends on the available amount of protein,protein composition,starch and starch component（amylose and amylopectin）.The result of our study showed that baking quality parameters were significantly affected in response to N and SR,whereas the effect of N was greater than SR.Grain volume weight（GVW）,grain hardness（GHD）,protein content,gluten protein,GMP,HMW-GS,H/L and Zeleny sedimentation value,were significantly increased and decreased by N and SR,respectively.The ratio of gliadin/glutenin was also significantly increased by N application rate.The effect of N application rate for above mention parameters was significant up to N235,beyond that level there was no further effect.Total protein,gliadin and glutenin percentage increased over N treatment by 32.5,49.7,and 34.3%respectively compared to control（N0）treatment.The percentage of protein,gliadin and glutenin were decreased by 5.5,6.2 and 6.4%when SR increased from SR135 to SR225 kg ha-1 respectively.Total starch,starch components i.e.,amylose and amylopectin,and pasting properties traits,except peak time（PT）and gelatinization temperature（GT）,were significantly decreased in response to N and increased by increasing SR.PT was not affected by N and SR and GT was affected by both（N and SR）but had same trend with protein i.e.,it was increased by increasing and decreasing N and SR respectively.Moreover,metabolic protein（albumin and globulin）,LMW-GS,were not statistically affected by N and SR.The key finding of current experiment,increasing N up to N235 kg ha-1 with decreasing SR significantly increased wheat baking quality traits,and there was no variable difference between SR treatments under high dose of N application.To sum up,optimizing N and seed rate combination would be better for improving grain yield and improve N use efficiency.The maximum GY（8.3 t ha-1）,NAE（14.4 kg kg-1）,NRE（55.2%）,and NUPE（1.02 kg kg-1）were obtained from the combination of N235+SR180 treatment.As well,the result shown that instead of increasing N rate,it would be better to increase SR up to suitable amount,particularly for N use efficiency.Protein and other quality traits were significantly increased in response to increasing N and reducing SR.Further increasing N rate（N290）,do not further improve the values of physiological traits,GY and quality traits but it decreased NUE.