Effects of transplanting period on the growth and development of cigar tobacco and the yield and quality of wrapper leaves in the central growing area of Shandong Province

Objective This study aimed to determine appropriate transplanting dates for wrapper tobacco leaf production in the central Shandong’s tobacco-growing areas， with the goal of optimizing climate resources allocation and promoting high-quality wrapper tobacco leaf production.Method Field plot trials were conducted using QX103 as the experimental material， with five treatments of transplanting dates： May 10^th （Y1）， May 15^th （Y2）， May 20^th （Y3）， May 25^th （Y4）， and May 30^th （Y5）. The time for main growth stages and temperature conditions were investigated， and agronomic traits were determined during the budding stage. In the budding period and maturity stage， the contents and accumulations of nitrogen， phosphorous and potassium in parts of tobacco plant were determined； after curing， physical properties and major chemical component contents of the wrapper leaves were measured； and yield， production value， and wrapper leaf output rate were calculated.Result As transplanting period was delayed， the field growth period was shortened， with the central flower blooming-final harvesting stage showing the most pronounced reduction； compared to Y1 treatment， delayed transplanting increased the average temperature and reduced the effective accumulated temperature during the whole growth period. As transplanting period was delayed， agronomic traits of tobacco plant in the budding stage， dry matter accumulation in different parts in maturity stage， and accumulations of nitrogen， phosphorus and potassium in leaves exhibited a trend of first increasing and then decreasing， with the highest leaf size， accumulations of dry matter and nitrogen， phosphorus and potassium in maturity stage observed in treatment Y3. The transplanting period had a significant effect on physical properties： Y3 showed a significantly lower leaf thickness compared to that in other treatments， and a significant greater tensile force compared to that in treatments Y4 and Y5， and a significantly lower stem ratio. The contents of reducing sugars， total sugars， nicotine， total nitrogen， and chlorine were lower in leaves of Y3， while its potassium content was the highest. As transplanting dates were delayed， the total yield of tobacco leaves was decreased， and the yield and yield value of wrapper tobacco leaves first increased and then decreased， with Y3 showing increases in wrapper yield （14.53% -145.07%）， yield rate （5.55% -163.88%）， and yield value （2.85%-44.58%） compared to that in other treatments.Conclusion Delaying the transplanting could increase the leaf size of cigar tobacco and dry matter accumulation in leaves， and improve the coordination of physical properties and chemical component， so as to improve the yield， output rate and output value of wrapper tobacco leaves. Based on comprehensive analysis， the suitable transplanting period is from May 15^th to 20^th for cigar tobacco leaves in the central growing area of Shandong Province.