Effects Of Nitrogen-saving And Density-increasing On Usability Of Upper Leaves And Structure Of Flue Cured Tobacco

The objectives of this study were to understand the mechanism of nitrogen-saving and density-increasing on usability of upper leaves and structure of flue cured tobacco（Nicotiana tabacum L.）.The flue-cured tobacco variety Yunyan 87 was planted at traditional planting pattern CK(13 500plants·hm^-2,150kg·hm^-2),nitrogen-saving pattern T1(13 500 plants·hm^-2,135 kg·hm^-2),density-increasing pattern T2(16 500plants·hm^-2,150 kg·hm^-2),nitrogen-saving and density-increasing pattern T3(16 500plants·hm^-2,135 kg·hm^-2).Experiments were carried out in Changning County of Hunan Province,Hengyang city in 2017.By studying the agronomic characters,the photosynthetic characteristics,the physical characteristics,the appearance quality,the conventional chemical composition,the grade structure of each leaf position,the economic benefit and the sensory quality of tobacco leaves in different cultivation patterns,the effects of nitrogen-saving and density-increasing on the structure of tobacco leaves and the availability of upper leaves were discussed,which could be used as a reference for finding high quality tobacco leaf combination measures showing the characteristic of flavor style.The main results are as follows:（1）The results showed that the net photosynthetic rate of the middle and upper leaves of flue-cured tobacco reduced by 8.12%-30.76%in nitrogen-saving pattern T1,density-increasing pattern T2 and nitrogen-saving and density-increasing pattern T3,and mainly effected by non stomatal limitation.But the effects of different planting patterns on the lower leaves were not the same,wherein the net photosynthetic rate of the lower leaves reduced in nitrogen-saving pattern,increased in density-increasing pattern,but it had no significant changes in nitrogen-saving and density-increasing pattern,and mainly effected by stomatal limitation.（2）Compared with the traditional planting pattern,the leaf thickness,the specific leaf weight and the single leaf weight of the upper leaves all decreased in nitrogen-saving pattern T1,density-increasing pattern T2,nitrogen-saving and density-increasing pattern T3,but the stem content and the leaf openness had no significant changes.In T1,T2 and T3,the leaf thickness decreased by 11.00%,8.14%and 13.15%,the specific leaf weight decreased by7.80%,6.96%and 10.98%,and the single leaf weight decreased by 7.80%,7.37%and13.57%,respectively.（3）Compared with the traditional planting pattern,the SPAD values of the upper 8leaves were significantly reduced in the 1 days before harvesting in nitrogen-saving pattern T1,density-increasing pattern T2,nitrogen-saving and density-increasing pattern T3.In T3treatment,the SPAD values reduced by 9.25%-22.10%significantly.In T1,T2 and T3treatment,the leaf thickness decreased significantly,the degree of porosity increased significantly,and the appearance quality was improved.In T1 and T2 treatment,the maturity of upper leaf tobacco leaves inverted 1-2 leaf increased significantly,all showed up as"mature",and the oil content increased,but there were no significant changes in T2treatment.In the maturity of upper leaf tobacco leaves inverted 3-8 leaf,the oil contents treated by T1 and T2 were all"had"and the identity was"thick to medium"with the structure"slightly dense to loose"and the chroma was"strong to medium",while the oil contents treated by T3 were all"had",and the identity was"slightly thick to medium"and the structure was"slightly dense to loose"and the chroma was"medium".（4）Compared with the traditional planting pattern,the nicotine content reduced,the total sugar content and the reducing sugar content increased,the ratio of total sugar to nicotine and the ratio of total nitrogen to nicotine were closer to the suitable range in nitrogen-saving pattern T1,density-increasing pattern T2,nitrogen-saving and density-increasing pattern T3.In T3 treatment,the content of starch,the content of total nitrogen and the content of chlorine decreased,the content of petroleum ether extract increased,the ratio of total sugar to nicotine and ratio of total nitrogen to nicotine were 5.16and 0.77,and the chemical composition of tobacco leaves was more harmonious.In the sensory quality evaluation,the heterozygosity and irritation of the upper leaves reduced,the aroma quality and aroma quantity improved,the typical flavor style and industrial availability improved in T3 treatment obviously.（5）Compared with the traditional planting pattern,the upper 8 leaf structure improved in nitrogen-saving pattern T1,density-increasing pattern T2,nitrogen-saving and density-increasing pattern T3.In the maturity of upper leaf tobacco leaves inverted 1-2 leaf,the B2F grade tobacco ratio treated by T1,T2 and T3 increased by（14.02-14.97,7.21-8.01,15.91-17.34）percentage points,and the rank structure of other leaves was better than CK..On the whole,in the upper 8 leaf,the（B1F and B2F）grade tobacco ratio treated by T1,T2and T3 increased by 5.11%,2.11%,10.26%,the（C2F and C3F）grade tobacco ratio increased by 2.36%,1.13%,1.71%,the proportion of variegated tobacco reduced by5.37%,2.60%,5.17%.At the same time,the proportion of the upper leaves of the whole plant reduced by 3.48%,3.69%and 8.91%,the proportion of the middle leaves increased by2.52%,4.70%and 6.81%,and the structure of the tobacco leaf area was optimized significantly in T1,T2 and T3 treatment.Nitrogen-saving and density-increasing were generated on the tobacco population structure and ontogeny significantly.The interaction between them changed the ecological conditions of the growth of tobacco plant population,thus affecting the growth and development of tobacco leaves,improving the quality of tobacco leaf appearance,coordinating the chemical composition of tobacco leaves and improving the quality of flue-cured tobacco and the sensory quality of tobacco leaves.