Response of Populations of Lolium perenne cv. S 23 with Contrasting Rates of Dark Respiration to Nitrogen Supply and Defoliation Regime 2. Grown as Mixtures

Abstract

Two populations of perennial ryegrass cv. S 23, selected for contrasting rates of mature leaf tissue respiration, were grown in 50: 50 replacement mixtures to investigate their relative competitive abilities in a range of conditions. The 18 mixed simulated swards were subject to three levels of nitrogen supply (14.5, 32 and 173.5 ppm) from establishment, and to three cutting frequencies (at 1-, 3- and 6-week intervals), 7 weeks after sowing. The slow-respiring population yielded more than the fast. This superiority was greater in mixtures (50%) than in monocultures (10%). Its superiority was as great in weekly-cut swards (51 %), where there was little or no aerial competition, as in 6-weekly-cut swards (50%), where shoot interference was maximal, indicating that its advantage lay in below-ground competition. The limiting resource for which competition occurred could not be positively identified.