Effects Of Transplanting Dates On Growth, Yield, Quality Of Flue-cured Tobacco And Its Biological Mechanisms In Tobacco Growing Regions Of Southern Shaanxi Province

Flue-cured tobacco is one of important economic crops in China, which occupies about1million hm2cultivated area. Southern Shaanxi is one of main planting regions of high-qualityflue-crued tobacco. It has been known that yield and quality of flue-crued tobacco aresignificantly influenced by different transplanting date. However, systematical investigationsare seriously lacking on studies that how does transplanting date affect on yield and quality offlue-crued tobacco by biological mechanisms such as nitrogen (N) and potassium (K)nutrition status, photosynthetic characteristics and anatomical structure of leaf tissue. Thisstudy was conducted to investigate effects of different transplanting dates i.e.30th-April(4-30),5th-May (5-5),10th-May (5-10),15th-May (5-15) and20th-May (5-20) treatments on Nand K contents, photosynthetic characteristics, anatomical structure of leaf tissue, growthperiod, disease incidence, agronomic and economic traits and chemical quality of flue-curedtobacco in southern Shaanxi province by selecting three different typical ecological zones(Luonan, Xunyang, Nanzheng) to elucidate the best transplanting date and their biologicalmechanisms based on the comprehensive analysis method. Three main planted flue-curedtobacco cultivars i.e. Qinyan96, K326and Yunyan97, were used in the current study inLuonan, Xunyang and Nanzheng respectively. The aim of this study is to provide importanttheory and practice basis for production of high-quality tobacco leaf. The main results are asfollowing:1. Contents of N, K, chlorophyll and carbohydrate as well as net photosynthesis rate (Pn)were increased at earlier period and then decreased at later period due to the postponement oftransplanting date in both Xunyang and Luonan. The best effect recorded in treatment of10th-May. The above parameters were decreased gradually in Nanzheng, and the better effectwas obtained in treatments of5-10and5-15(no-significant between them). In addition, thefunction of N on yield and quality of flue-cured tobacco exhibited the trend from weak tostrong, but the reverse was true on Pn and chlorophyll. Potassium and carbohydrates played akey role in the whole growth period. The functions of N, K and carbohydrates were greaterthan those of Pn and chlorophyll.2. Effects of different transplanting date on leaf tissue structure at flower budding stage were greater than that at harvesting stage. With tobacco leaf senescence, leaf and palisadetissue as well as sponge tissue thickness became thin, palisade tissue became loose andspongy tissue cell gap became bigger. Significant positive correlations were obtained betweenpalisade, sponge tissue thickness and leaf thickness. Effects of leaf tissue on leaf thicknessindicated a trend of sponge tissue>palisade tissue>lower epidermis>upper epidermis. Withpostponement of transplanting date, leaf tissue thickness declined gradually at flower buddingstage, and leaf, palisade tissue thickness decreased firstly, and increased later at harvestingstage in Luonan, decreased gradually in Nanzheng, increased firstly and then declined inXunyang. The biggest leaf tissue thickness in Luonan, Nanzheng and Xunyang was obtainedby4-30,5-5and5-10treatments at flower budding stag, and recorded in4-30,5-10and5-15treatments at harvesting stage, respectively.3. With postponement of transplanting date of flue-cured tobacco, main growth periodswere put off; and field growth period after transplant became shorter. Changes in days of eachgrowth stage varied with differences in cultivars and ecological conditions. In addition, therewas a significant impact of transplanting date on middle leaf area. Leaf area slightly increasedfirstly, and decreased later in Luonan and Nanzheng, but declined gradually in Xunyang whentransplanting date was postponed. Both incidences of disease incluing black shank and brownspot and disease index declined firstly and then rose in Luonan and Xunyang. Incidence oftobacco masaic decreased slightly in Nanzheng when transplanting date was postponed.Moreover, economic traits of flue-cured tobacco were significantly influenced bytransplanting date. With postponement of transplanting date, yield, average price, output valueand percentage of medium and superior tobacco from Luonan and Xunyang increased firstlythen declined. Yield and output value decreased gradually, and average price increased firstlyand then declined. The highest percentage of medium and superior tobacco was obtained in5-10and5-20treatments (non-significant between them).4. Different transplanting date could affect chemical quality of flue-cured tobacco variedwith cultivars and ecological regions. With postponement of transplanting date of flue-curedtobacco, chemical quality of flue-cured tobacco from four leaf position increased firstly andthen decreased. The better transplanting date treatments were as following: tips,5-10and5-20;leaf,5-10and5-20, cutters,5-10, lugs,5-10and5-20. Comprehensive effect indicated a trendof5-10>5-20>4-30>5-30in Luonan. Reducing sugar, total sugar and nicotine content, ratio ofK to chlorine enhanced firstly and then declined, and K content rose slowly, ratio of reducingsugar to nicotine and ratio of total N to nicotine declined gradually when transplanting datewas postponed. The optimal transplanting dates were treatments of5-5and5-10. Thechemical indices of tobacco were perfect and the chemical compositions were reasonable in cutters from Xunyang. With postponement of transplanting date for flue-cured tobacco, bothreducing sugar and total sugar content increased firstly, and decreased later. And the contentsof nicotine and total N, ratio of K to chlorine declined slightly, ratio of reducing sugar tonicotine increased gradually. And the optimal treatment was5-10due to the most reasonablechemical compositions of flue-cured tobacco in Nanzheng.Innovations points were as following in this study:(1) Different transplanting date couldfunctioned on output and quality of flue-cured tobacco by biological mechanisms in view ofN and K nutrition in tobacco leaf, photosynthetic characteristics and leaf tissue structure;(2)We differentiated and confirmed effect degree and change trend of each biological indicators;(3) Appropriate transplanting date could provide suitable climatic conditions to promote somephysiological metabolism, improve N and K nutrition of leaves and photosyntheticperformance and dry matter accumulation and disease resistance resulting in better yield andquality formation of flue-cured tobacco. In this study, the optimal transplanting date was5-10in these three ecological regions based on comprehensive analysis.