Effects Of Nitrogen Application Rate And Planting Density On Growth And Quality Of G80 Flue-cured Tobacco

In order to find out the best combination of cultivation measures for flue-cured tobacco,a two-factor experiment was carried out in Liuyang City of Hunan Province in 2019 and2020 using flue-cured tobacco G80 as the test variety.In order to initially define the suitable nitrogen application rate and planting density of Liuyang G80,four nitrogen application levels 0,135,165 and 195kg/hm²and three planting densities 15750,17250 and 18750plants/hm²were set in 2019,with a total of 12 treatments.In order to further explore the effects of nitrogen application rate and planting density on the upper leaves of flue-cured tobacco,three nitrogen application levels were set in 2020,namely 135,165 and 195kg/hm².The planting density was set at three levels of 15750,17250 and 18750 plants/hm²,with a total of nine treatments.The main research results of this paper are as follows:（1）The interaction of nitrogen application rate and planting density had significant effects on agronomic traits of flue-cured tobacco during growing period;Nitrogen application rate had significant effect on agronomic traits of flue-cured tobacco at clumping stage and maturity stage.Increasing the amount of nitrogen fertilizer and decreasing the density in a certain range were more beneficial to the growth and development of tobacco plants.The agronomic traits of flue-cured tobacco were better when the nitrogen application rate was 195kg/hm²and the planting density was 15750 plants/hm².The nitrogen application rate was the main factor affecting the agronomic traits of upper leaves.The nitrogen application rate of 135kg/hm²was beneficial for pour 1 leaf of tobacco opening.Appropriate increase of nitrogen fertilizer was beneficial to leaf opening of P2,P3 and P4.（2）Nitrogen application rate mainly affected relative chlorophyll content and LAI of flue-cured tobacco;The planting density mainly affected the light transmittance of flue-cured tobacco population.With the increase of nitrogen fertilizer,the relative relative chlorophyll content in flue-cured tobacco leaves increased,and LAI increased,while the population light transmittance showed a general downward trend.With the increase of planting density,the population light transmittance generally decreased first and then increased,showing the medium density of low density>and high density>,and the medium density of medium density>and high density>and low density of LAI.The activities of nitrate reductase and glutamine synthetase in the upper leaf of G80 were stronger with higher nitrogen fertilizer and lower density.From day 60 to day 70,the enzyme activity of nitrogen metabolism showed an upward trend,and after day 70,the enzyme activity gradually decreased.（3）With the increase of nitrogen application rate,the yield of cured tobacco increased,the output value and the proportion of quality tobacco increased first and then decreased;The density increased,the yield increased,the output value increased first and then decreased,the average price and the proportion of quality tobacco decreased.The yield and economic benefit of the combination of 165kg/hm²and 17250 plants/hm²were the highest.（4）The physical properties of the upper and middle leaves after curing showed that the density decreased with the increase of nitrogen fertilizer,while the leaf length,leaf width,leaf thickness and single leaf weight showed an increasing trend.The cultivation combination of nitrogen application rate of 195kg/hm²and planting density of 15750 plants/hm²showed better physical properties after curing.With the increase of nitrogen application,the sugar content decreased and the nicotine content increased.With the increase of density,sugar content increased and nicotine content decreased.The chemical composition content of1-4 leaves of the treatment G80 with nitrogen application of 135kg/hm²was more coordinated after roasting.The chemical composition of B₂F and C₃F was more coordinated after roasting with 165kg/hm²of nitrogen application.（5）The lower the N application rate or the higher the planting density,the higher the N use efficiency.The combination of 135kg/hm²and 18750 plants/hm²had the highest N use efficiency.The main period of N accumulation was 45-60 days,accounting for about60%of the total uptake.（6）The combination of 165kg/hm²and 17250 plants/hm²for flue-cured tobacco G80in Liuyang tobacco area showed better economic characters,chemical composition of tobacco leaves,appearance quality and sensory quality,so it is suggested to be popularized and applied.Considering N use efficiency,output value,economic benefit and tobacco quality after curing,the suitable N application rate for G80 in Liuyang tobacco area is 165kg/hm²,and the planting density is 17250 plants/hm².