Comparison of physical separation and alkane concentrations to estimate the species composition of herbage samples from a pastoral environment

Abstract

The botanical composition of simple herbage mixes has been successfully estimated using the alkane profiles of pasture species. In this report, the ability of the n-alkane technique to identify the component species in more complex herbage mixes from a pastoral environment was examined. Herbage samples (quadrat cuts), collected from 3 heterogeneous pastures at Condobolin, were sorted by hand to identify the botanical components and their proportional representation. Within each pasture, 19-20 individual species were identified. Groups of species were subsequently formed on the basis of a principal components analysis of their alkane profiles. The botanical composition determined by hand sorting was then compared with the estimates obtained from a least-squares optimisation of the alkane profiles, and significant differences between the techniques were found. In general, the proportions of the Medicago spp. component, and of the component including Avena spp., in the herbage mixes were underestimated.