Effect of delaying harvest on tobacco quality of upper six leaves and climatic requirement in central Henan of China
Upper tobacco leaves have higher quality potential and play an important role in low tar cigarette production. Upper leaves being rich in organic matter and tight in structure, high maturity is the key to produce high quality cured leaves. According to the current harvesting standards, the maturity of upper leaves is generally low in reality and the degradation is not complete, so delaying harvest of upper leaves to increase maturity is an important approach to improve availability of upper leaves. A series of experiments were carried out in central Henan Province from 2017 to 2018 to investigate the effect of delaying harvest time on leaf quality, and to establish climatic indexes required for high quality upper tobacco production. Harvesting date experiment included five treatments (normal date, delayed 4, 8, 12, 16 days). Another two-factor field experiment included transplanting date and harvesting date, and the relationship between climatic parameters during upper six leaf growth and cured leaf quality was investigated. The results showed that with the delay of harvesting date, the soil plant analysis development (SPAD) value, weight per leaf and yield of the upper six leaves showed a continuous downward trend. The output value and sensory evaluation quality increased to a point before declining, reaching maximum values at delayed 10 to 12 days with 19.03 % and 7.36 % higher than that of normal harvest control, respectively, characteristic of richer aroma, better taste and more satisfaction. SPAD value of 5.0-6.1 was proved to be a proper index to decide the optimum maturity. The analysis on the relationship between quality of upper six leaves of flue-cured tobacco and temperature and other climatic indexes revealed that the full flavour style was more significant when the average daily temperature during the mature stage of the upper six leaves was between 25.3~27.1 °C. The quality was the best when the accumulated > 20 °C temperature was between 263.0313.3 °C for the mature period of upper six leaves and between 497.9544.5 °C for the whole growth stage of upper six leaves, respectively. This study provided technical standards and climatic indicators for high maturity and high availability of upper tobacco leaf production.