Sources of variation in n-alkane concentrations in the cuticular wax of two species of pasture plants

Samples of white clover and ryegrass were collected from 8 sites within an irrigated pasture (40 ha) to determine the extent of variation in the concentrations of individual alkanes (C₂₅⁻C₃₃) between sites, between samples (within site), and within a sample (duplicate analysis). Across both species, between-site variation accounted for 10–35% of the total variation in the concentration of the individual alkanes. There was significant variation between sites in the concentrations of the alkanes C₂₇, C₂₈, and C₃₃ in ryegrass only. Between-sample (within site) variation was significant for most alkanes in both species, accounting for 50–70% of the total variation within white clover and 39–59% within ryegrass. Within the white clover samples, the within-sample repeatability (an indicator of analytical variation) was 0.64 or greater for alkanes present in moderate to high quantities. However, within the ryegrass samples the analytical repeatability was low for all but the C₂₅ (0.71) and C₂₇ (0.62) alkanes. The effects of within-species variation on the estimation of botanical composition of herbage and faecal samples collected from extensive grazing systems are discussed.