Field microclimate characteristics and their effects on the growth and development and quality of wrapper tobacco leaf under shading cultivation

【Objective】This paper explored the effects of microclimate characteristics of wrapper tobacco fields on the growth and development of tobacco plants and the quality of fermented wrapper tobacco leaf under shading cultivation conditions, in order to provide theoretical basis for domestic shading cultivation of wrapper tobacco leaf.【Method】Using the cigar variety Yunxue-1 as the experimental material, three treatments with 100%(CK), 75%(T1), and 65%(T2) light transmittance were set up to analyze the microclimate characteristics of tobacco fields under different treatments and their effects on plant agronomic traits, biomass accumulation and distribution, and main quality characteristics of fermented tobacco leaves.【Result】Shading treatment could reduce the temperature, light intensity, diurnal temperature difference, and effective accumulated temperature ≥10 ℃ in tobacco fields, and increase relative humidity. Shading had significant impact on growth and development indicators such as tobacco plant height, stem circumference, maximum leaf area and biomass accumulation(P<0.05, the same below). Among them, tobacco under T2 treatment had the highest plant height, biggest maximum leaf area, and largest leaf biomass, with the highest increase at 40 d after shading, while tobacco under CK treatment had the longest stem circumference. Tobacco leaf under T2 treatment had the highest scores for appearance quality indicators such as leaf structure, oil content, color uniformity and branch thickness, and its tensile strength was also significantly higher than other treatment groups. The yield and yield rate of wrapper tobacco leaf under shading treatment were significantly higher than those under CK. Compared with CK, the yield of wrapper tobacco leaf under T1 and T2 treatments increased significantly by 5.87% and 13.78% respectively, and the yield rate of wrapper tobacco leaf increased significantly by 8.56% and 18.56% respectively. The correlation analysis results indicated that the decrease in temperature(accumulated temperature, effective accumulated temperature ≥10 ℃ and average temperature) under shading conditions was the main reason for the decreases in leaf thickness, stem circumference, and rhizome biomass accumulation of tobacco plants. The decrease in average light intensity and increase in average relative humidity under shading conditions were key factors in improving the appearance quality and physical properties of wrapper tobacco leaf.【Conclusion】Shading can reduce the environmental temperature and light intensity of wrapper tobacco leaf fields, increase relative humidity, and alter the morphological development and mass accumulation of tobacco plants, thereby increasing the yield and the yield rate of wrapper tobacco leaf. It also makes the appearance and physical indicators of fermented tobacco leaves more suitable for industrial use. Overall, 65% light transmittance is more suitable for shading cultivation of wrapper tobacco leaf in southwestern Henan.