CORESTA Congress, Edinburgh, 2010, APPOST 01
Effect of the degree of leaf ripeness at harvest on the yield, quality and chemical characteristics of Oriental (sun-cured) tobacco
Aristotle University of Thessaloniki, Greece; Tobacco Institute of Greece, Chemistry Dept., Drama, Greece
Harvest date is one of the most important crop management practices affecting tobacco yield, quality and usability after curing. In a two-year field experiment, investigations were made into the effect of the degree of leaf ripeness at harvest on several agronomic, physical, and chemical characteristics of Oriental (sun-cured) tobacco (cv. Basma Z/7) grown in Greece. Even though there was no objective and standard method to assess leaf ripeness of Oriental tobacco, a general model of changes of some leaf characteristics (agronomic, physical, and chemical) was constructed to determine the optimal harvest date. The experiment was set up with twelve harvesting treatments at two-day intervals, before (under-ripe), during (ripe) and after (over-ripe) visually empirically judging the full physiological maturity, the stage of maximum accumulation of dry matter. Harvestings were carried out by picking three fully expanded lower leaves from the accurately same stalk position, which were in uniform size and mature stage. Quality, physical and chemical characteristics were calculated at each harvesting time to determine the optimum harvest date. The results showed that yield and quality parameters of leaves both at harvest and after curing were influenced by the degree of leaf ripeness. Leaves harvested after the full physiological maturity stage had the higher quality index (as measured by the grade index) and more desirable chemical composition in comparison with leaves harvested too early or too late. Based on the changes in leaf yield, quality and chemical characteristics after sun-curing, the optimal harvest time for Oriental tobacco leaves was found to be the stage of early senescence, just after the full physiological maturity stage. Preliminary results suggested that changes in nitrate concentration in fresh leaves may provide a simple test for the initiation of harvest. Sap nitrate concentration in the fully expanded bottom leaves should be less than 0.9-1% at the commencement of harvesting for optimal yield and quality. The sap nitrate test, determined by a commercially available field test, can be used as an indicator of fresh leaf ripeness.