Variations in composition and yield of leaf oils from alley-farmed oil mallees (Eucalyptus spp.) at a range of contrasting sites in the Western Australian wheatbelt

Variations in the amount and composition of leaf oil of alley-farmed 'oil m allees' were examined at wide-ranging sites across the Western Australian w heatbelt. Of four particularly promising species studied at six locations i n respect of oil composition, 1,8-cineole comprised 65-92% of the total oil . Up to 32 constituent oils were present in proportional amounts ranging fr om 0.01 to 13%. A further 26 trace components were recorded in certain spec ies. Relative abundances of cineole, limonene, alpha-terpineol and terpinen -4-ol varied significantly between sites for all four species, with evidenc e of reduced levels of cineole being compensated for by increases in the la tter three compounds. Foliar yields of cineole of all nine taxa were assess ed for 2.5- or 3-year-old saplings cut respectively in summer or winter, an d for corresponding coppice biomass produced over the following 12 months f rom the same trees. Average leaf cineole yields for the five best performin g taxa varied widely between species and sites, with sapling harvests produ cing 12-130 (mean 49) kg cineole per kilometre of twin-row hedge compared t o 1-68 (mean 23) kg km(-1) for subsequent coppice harvests. While genotype was primarily important in determining leaf cineole concentration, modifyin g effects of season and leaf age balance were evident for both sapling and coppice canopies. Cineole concentrations were generally greatest in early s ummer when particularly high proportions of recently matured leaves were pr esent. Of the. nine taxa studied, two provenances of Eucalyptus vegrandis w ere discounted on grounds of poor growth and low cineole concentrations, an other (E. kochii subsp. kochii) rated unsuitable due to inbreeding depressi on in available seed sources, and a further species (E. angustissima) deeme d useful only at winter-wet, saline, sandy sites. The remaining taxa (E. ko chii subsp. plenissima, E. horistes, E. polybractea, E. loxophleba subsp. l issophloia and E. gratiae) showed general ability to yield well at favourab le sites. With such large ranges in cineole yields between taxa and sites, the study advocated that successful commercial culture of oil mallees would require careful selection of species for location of planting, and adoptio n of management practices conducive to maximum possible biomass and build u p of foliar oils in coppice growth at harvest. (C) 2000 Elsevier Science B. V. All rights reserved.