Species composition of ryegrass (<i>Lolium perenne</i>) and tall fescue (<i>Festuca arundinacea</i>) mixtures using various combinations of <i>n</i>‐alkanes

Abstract

Abstract This study was conducted to evaluate the reliability of the n ‐alkane technique for estimating the species composition of Lolium perenne (ryegrass, L) and Festuca arundinacea (tall fescue, F) mixtures. Samples of L and F were collected in May (period 1) and June 2003 (period 2) on mono‐specific swards that were maintained at a height of 9 cm. Seven sets of mixtures containing controlled proportions of L and F were then prepared: 1·00:0, 0·80:0·20, 0·60:0·40, 0·50:0·50, 0·40:0·60, 0·20:0·80 and 0:1·00 of L:F, respectively, in the mixture. The proportion of each species in the mixtures was estimated from measured n ‐alkane concentrations, and then compared with the actual known proportion. Various n ‐alkane combinations were tested and compared to establish which combination gave the best estimate. Total n ‐alkane concentrations, and especially C 29 ‐ and C 31 ‐alkane concentrations, were higher in period 1 than in period 2 for both species. The best n ‐alkane combination varied between periods, as did the effectiveness of C 29 ‐alkane in discriminating between L and F. The species composition of the mixtures was satisfactorily estimated for the majority of n ‐alkane combinations, providing the combination included n ‐alkanes with contrasting profiles between both species. A systematic overestimation of the proportion of ryegrass was observed for the 0·50:0·50 mixture.