ESSENTIAL OIL YIELD IN <em>EUCALYPTUS</em> <em>CITRIODORA</em> IN RELATION TO FOLIAGE AGE AFTER POLLARDING AND TREE AGE

Abstract

In a series of field experiments in subtropical south China, Eucalyptus citriodora leaf biomass, essential oil yield and composition were measured in relation to tree age, different pruning treatments and foliage age following pollarding. The dominant compounds in the essential oil included citronellal (76.9%), citronellol (7.5%), isopulegol (6.4%) and neoisopulegol (3.1%). The 3- and 5-year-old trees yielded the most essential oil (4.4 and 4.7% respectively) and citronellal (82.6 and 82.5% respectively), and yield decreased with tree age. One year following the pruning treatments, foliage biomass was three times greater from 1, 2 and 3 m high stumps than from coppiced trees and 0.5 m high stumps. Oil yield was highest for trees pollarded at 1 m (equivalent to 5.9% from dry leaves) and lowest from coppiced trees (3.2%). All pollarding treatments yielded more citronellal (79.3–81.9%) than coppiced trees (66.0%). Oil yield and citronellal content were higher (5.9 and 77.7% respectively) when harvested at 12 months than at 6 months, 2, 3, 4 and 5 years after pollarding. Based on our results, harvest of fresh E. citriodora leaves should begin 3–5 years after planting, with a 1-year harvest interval, and pollarding above 1.0 m for optimal oil yield.