FIELD VARIATIONS IN ALKANE SIGNATURES AMONG PLANT-SPECIES IN DEGRADEDAND PERENNIAL PASTURES ON THE NORTHERN TABLELANDS OF NEW-SOUTH-WALES

Differences in concentrations of n-alkanes in the cuticular waxes of p lants can be used to estimate the species composition of herbage mixtu res or the diet consumed by grazing animals. The objectives of this st udy were (i) to provide information on the n-alkane (C-25-C-35) 'signa tures' or patterns of pasture species occurring in 'degraded' and pere nnial pastures of the Northern Tablelands, New South Wales, and (ii) t o examine the extent of the field variation in the signatures. There w ere considerable differences in odd-numbered alkanes and in their tota l content between species. There were also significant differences in n-alkane concentrations among species within grasses, legumes, and wee ds. For the individual odd-numbered alkanes, differences between speci es accounted for 87-93% of the total variance in alkane concentration over 3 samplings. Variable results for the temporal effect suggest tha t time-specific herbage samples are needed in animal diet studies. Ana lyses of the spatial effect indicate that random cuts over each treatm ent plot can obtain representative samples of each species. Multivaria te statistical analyses using principal component and discriminant ana lyses indicated that the patterns of alkanes in species occurring on b oth degraded and perennial pastures were readily distinguishable. Thes e results confirmed that the alkane technique could be used for estima tion of diet composition in grazing sheep on the Northern Tablelands, NSW, where differences in n-alkane signatures between species were suf ficient and persistent over time.