The effects of regrowth and maintenance height on a grass sward with a high density of tillers

Abstract

A perennial ryegrass sward was grazed by sheep in April 1993 to a target sward surface height (SSH) of 3 cm to create a high density of grass tillers. From 3 May, the sheep were removed and small plots were established on the sward, when the average tiller density (± s.e.) was 35 900 + 420 live tillers m~^. Different regrowth treatments were then imposed by allowing plots to regrow to target SSHs of 6 cm (18 g dry matter (DM) m'^), 9 cm (78 g DM m"^), 12 cm (132 g DM m'^) or 15 cm (197 g DM m'^). 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~^ P<0 001) and leaf-stem ratio and in vitro organic matter digestibility were reduced by regrowth beyond 6-1 cm (18 g DM m-2, P<005). The effect on live tiller density was sustained through the remainder 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 leafstem ratio and higher herbage mass (at least P<005). There were significant interactions between regrowth SSH and maintenance SSH, so that leaf-stem ratio, live-dead tiller ratio and live tiller density were reduced by regrowth to a SSH of 16-4 cm followed by maintenance at 9-1 cm, com-