| Simplification and aging of flue-cured tobacco varieties are important restrictive factors affecting the production of flue-cured tobacco in the Chongqing tobacco-growing area.It is imperative that we upgrade the varieties and adopt fine varieties combined with suitable cultivation methods.“Yujinxiang No.1”,a local bred variety in Chongqing passed the national cultivar assessment for flue-cured tobacco varieties in 2020,and“Yunyan 116”,a new variety of flue-cured tobacco introduced from Yunnan,show good yield,quality and adaptability in test planning in Chongqing;their intrinsic quality has been recognized by many brands in the cigarette industry.However,in the test planning,it was noticed that the local planting density and nitrogen application in Chongqing could not effectively bring out the excellent characteristics of Yujinxiang No.1 and Yunyan 116.In this research,considering the characteristics of the two varieties,actual production in the Chongqing tobacco-growing area,and the quality requirements of cigarette companies for Chongqing tobacco leaves,an experimental study was conducted on the optimization of the density and nitrogen application for growing Yujinxiang No.1 and Yunyan 116 in Wuxi County,Chongqing at two altitudes.Preliminary trials were carried out in 2019.Through nitrogen increase/decrease and density increase/decrease treatments based on local conventional nitrogen application and planting density,the testing ranges of density and nitrogen application for Yujinxiang No.1 and Yunyan 116 were determined preliminarily.Formal trials were conducted in 2020 and 2021:Yunyan 116 received treatments of less nitrogen application and higher density while Yujinxiang No.1 received treatments of less nitrogen application and lower density.According to the local conventional nitrogen application rate(100.125kg/hm~2)and the local conventional planting density(16500 plants/hm~2)in Wuxi,two nitrogen application levels(N1:100.125kg/hm~2 and N2:92.625kg/hm~2)1.Test results of optimization of nitrogen application and density with Yunyan 116In terms of agronomic traits,at the increased density of 1500 plants/hm~2,Yunyan 116 showed better agronomic traits such as increased average plant height as well as length and width of middle leaves over the two-year period compared with the control.In terms of population development,planting density had a significant effect on the corresponding indicators of Yunyan 116.Under the treatment of density increase and nitrogen reduction,the middle and lower light transmittance was 23.28%and 5.27%,respectively,closer to the ideal than the control(28.61%and 7.62%,respectively).The population photosynthetic rate was significantly higher than the control,indicating improved light utilization.With respect to the activity of key enzymes of carbon and nitrogen metabolism,the activity of nitrate reductase(NR)in Yunyan 116 first increased and then decreased over the growth period.NR activity peaked in the round-top period and bottomed in the middle-leaf maturity period.Under different treatments,NR activity declined as the nitrogen application decreased;NR activity increased as the planting density increased,and peaked under the treatment of conventional nitrogen application and increased density.Amylase(AM)activity in Yunyan 116 gradually increased over the growth period.It peaked in the middle-leaf maturity period and under the treatment of reduced nitrogen application and increased density.With respect to economic traits,planting density was the primary factor affecting the yield and output of Yunyan 116,and nitrogen application was the secondary factor.At the increased density of 1500 plants/hm~2,the average yield of tobacco leaves at the three trial points increased by 21.98%;the average price increased by 8.82%;tobacco output increased by 32.69%;the proportion of intermediate and upper-class leaves increased by 5.73%.At reduced nitrogen application of7.5kg/hm~2,however,leaf yield,average price,output and the proportion of intermediate and upper-class leaves decreased by 1.89%,4.50%,5.70%and 2.58%,respectively.Among combined treatments,the treatment of reduced nitrogen application and increased density and the treatment of conventional nitrogen application and increased density showed a 19.14%and 15.95%increase in leaf yield and a 24.01%and 22.32%increase in output compared with the control,respectively.As for the routine chemical composition of tobacco leaves,under the treatment of reduced nitrogen application and increased density,the CUUI average scores of middle leaves(C3F)and upper leaves(B2F)were 94.25 and 97.43,respectively,higher than the control(91.57 and 87.67).This indicated that the treatment of reduced nitrogen application and increased density could effectively optimize the coordination of chemical components in the cured tobacco leaves of Yunyan 116.As for the content of aromatic compounds in cured tobacco leaves,72 aromatic substances were detected.The total aromatic substances under the treatments of increased density reduced nitrogen application,and reduced nitrogen application combined with increased density were601.331,760.878 and 729.344μg/g,respectively,all higher than the control(594.926μg/g).The totals of phenylalanines,non-enzymatic brown compounds,cembrane degradation products,and carotenoid degradation products under the three treatments were also higher than the control.Therefore,proper densification and nitrogen reduction can increase the content of aromatic substances in Yunyan 116 leaves and improve the intrinsic quality of the leavesTo sum up,under the treatment of reduced nitrogen application and increased density(7.5kg/hm~2,1500 plants/hm~2),Yunyan 116 showed good growth conditions of single plant,good population structure,coordinated carbon and nitrogen metabolic transformation,high yield and the output value of flue-cured tobacco leaves,coordinated chemical components,and the highest content of aromatic substances.Therefore,it is the optimal treatment for Yunyan 116.2.Test results of optimization of nitrogen application and density with Yujinxiang No.1In terms of agronomic traits,under reduced density,Yujinxiang No.1 showed better agronomic traits such as increased plant height,joint distance as well as length and width of middle leaves compared with the control.In terms of population development,under reduced density,the middle and lower light transmittance of Yujinxiang No.1 was 22.04%and 4.39%,respectively,improved than the control(19.27%and 3.94%,respectively).The problem of insufficient light in the middle and lower leaves of the control was improved.The population photosynthetic rate was in order:reduced density>control>reduced nitrogen and density>reduced nitrogen.With respect to the activity of key enzymes of carbon and nitrogen metabolism,the activity of NR in Yujinxiang No.1 peaked in the fast-growing period.Among different treatments,NR activity peaked under the treatment of reduced density and bottomed in the middle-leaf maturity period.AM activity increased over the growth period.It peaked under the treatment of reduced density.With respect to economic traits,under reduced nitrogen application,the average price and the proportion of intermediate and upper-class leaves of Yujinxiang No.1 both dropped.Among four combination treatments,the average price and proportion of intermediate and upper-class leaves were the highest under the treatment of reduced density.The average price under such treatment over the two-year period was 26.715 yuan/kg,and the proportion of intermediate and upper-class leaves 91.33%,both higher than the control(24.34 yuan/kg,89.44%).Although the yield of Yujinxiang No.1 was slightly lower under the treatment of reduced density,the output value was only down by 4.84%because of the higher average price.Under this treatment,the increase in the proportion of intermediate and upper-class leaves is very important for meeting the requirements of the cigarette industry for tobacco grades.As for the routine chemical composition of tobacco leaves,under the treatment of reduced density,the CUUI scores of middle leaves(C3F)and upper leaves(B2F)peaked at 90.22 and 94.25,respectively,higher than the control(86.47 and 88.65).This indicated that the treatment of reduced density could effectively optimize the coordination of chemical components in the cured tobacco leaves of Yujinxiang No.1.As for the content of aromatic compounds in cured tobacco leaves,the total aromatic substances under the treatments of reduced density and reduced nitrogen application and density were680.935μg/g and 702.3695μg/g,respectively,higher than the control(627.109μg/g).The totals of phenylalanines,carotenoid degradation products,and chlorophyll degradation product neophytadiene under the two treatments were also higher than the control.Therefore,the treatment of reduced density is conducive to the formation of aromatic substances in Yujinxiang No.1.To sum up,under the treatment of reduced density(1500 plants/hm~2),Yujinxiang No.1 showed good growth conditions for a single plant,the highest photosynthetic rate,the improved proportion of intermediate and upper-class cured leaves,the highest average leaf price,coordinated chemical components,and the highest content of aromatic substances.Therefore,it is the optimal treatment for Yujinxiang No.1... |
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