THE EFFECTS OF REGROWTH AND MAINTENANCE HEIGHT ON A GRASS SWARD WITH A HIGH-DENSITY OF TILLERS

A perennial ryegrass sward was grazed by sheep in April 1993 to a targ et award surface height (SSH) of 3 cm to create a high density of gras s tillers. From 3 May, the sheep were removed and small plots were est ablished on the sward, when the average tiller density (+/- s.e.) was 35 900 +/- 420 live tillers m(-2). Different regrowth treatments were then imposed by allowing plots to regrow to target SSHs of 6 cm (18 g dry matter (DM) m(-2)), 9 cm (78 g DM m(-2)), 12 cm (132 g DM m(-2)) o r 15 cm (197 g DM m(-2)). The plots were then maintained by cutting at either 6 or 9 cm SSH until the end of the experiment on 30 September. Live tiller density was reduced by regrowth beyond 8.9 cm (78 g DM m( -2), P < 0.001) and leaf-stem ratio and in vitro organic matter digest ibility were reduced by regrowth beyond 6.1 cm (18 g DM m(-2), P < 0.0 5). The effect on live tiller density was sustained through the remain der of the season. From the beginning of June to the end of September, maintenance of SSH at an average of 9.1 cm compared with 6.4 cm also resulted in lower live tiller density, live-dead tiller ratio and leaf -stem ratio and higher herbage mass (at least P < 0.05). There were si gnificant interactions between regrowth SSH and maintenance SSH, so th at leaf-stem ratio, live-dead tiller ratio and live tiller density wer e reduced by regrowth to a SSH of 16.4 cm followed by maintenance at 9 .1 cm, compared with regrowth to 6.1 cm and maintenance at 6.4 cm.