Effect of Harvest Time on the Leaf and Essential Oil Yield ofEucalyptus camaldulensis

The effect of time of harvest on the yield of leaves, leaf oil concentration and quality (1,8-cineole percentage), and the total production of essential oil by physiological age class of leaves was assessed in a six-year-old plantation of Petford Eucalyptus camaldulensis over a 12-month period in central Thailand. Leaf dry matter yield (as would be obtained at clear felling) averaged 2.22 tons/ha with a range of 1.41 to 2.62 tons. The proportion of leaves by physiological age class did not vary during the study: 43% were assessed as fully expanded but not fully lignified (Class 1), 31% were fully expanded and lignified (Class 2), 13% were classed as aged leaves (Class 3) and 13% as still expanding (Class 4). Oil concentration (W/W%, DW) and 1,8-cineole percentages were mainly highest in Class 1 leaves (2.6% WAV of 75% 1,8-cineole), and lowest in Class 3 (2.1% WAV of 69% 1,8-cineole) with Class 2 leaves in between (2.3% WAV of 73 % 1,8-cineole). Class 4 leaves were not assessed. Total oil yield from a complete harvest was best during the periods of May to July and January to March when an average of 64 kg/ha was obtained. In the other months the oil yield averaged only 40 kg/ha. Leaf dry matter yield declined appreciably as the wet season progressed, almost certainly as the result of attack on leaves by fungal pathogens. This combined with slightly lower oil concentrations during the wet season led to poor oil yields, particularly in November, at the end of the wet season. These data show a modest yield of oil from Petford E. camaldulensis at this site. There is potential of achieving higher average yields of oil per ha/year from this provenance in Thailand by harvesting younger stands planted at higher stocking densities on selected sites which are least susceptible to disease problems. Further increases in oil yield are possible through selection and breeding to improve both leaf oil concentration and growth rate.