The effect of defoliation interval and height on growth and herbage quality of kikuyu grass (Pennisetum clandestinum)

A plot study, undertaken on the subtropical north coast of New South Wales, Australia, assessed the effect of defoliation interval (equivalent to time taken to regrow 2, 4, or 6 leaves/tiller) and height (3, 6 or 12 cm) on gr owth and herbage quality of 'common' kikuyu (Pennisetum clandestinum). The pasture had been established for more than 10 years on a red Krasnozem soil . Rainfall and daily temperature during the experimental period were near l ong-term average except for below average rainfall in March and April. In summer, leaf DM yield was maximised (5225 +/- 886 [mean +/-s.e.] kg/ha D M) under the most intense defoliation treatment (2 leaves/tiller to 3 cm he ight) with the lowest yields (1722 +/- 231 kg/ha) under the most lax defoli ation treatment (6 leaves/tiller to 12 cm height). The pro portion of stem and dead material increased significantly with defoliation interval (360, 1 448 and 1956 kg/ha for 2, 4 and 6 leaves/tiller, respectively) but not with defoliation height. In contrast, in autumn-winter, plots defoliated at an interval of 4 or 6 le aves/tiller to 3 or 6 cm gave similar leaf DM yields (3771 +/- 220 kg/ha) w hich were significantly higher than for plots defoliated more frequently (2 436 +/- 220 kg/ha). At all defoliation intervals, defoliation to 12 cm gave the lowest leaf DM yields. In spring, leaf yields of plots defoliated at 3 or 6 cm (3084 +/- 302 kg/ha ) was significantly higher than for plots cut to 12 cm height (1734 +/- 181 kg/ha) with no effect of defoliation interval. The concentration of water-soluble carbohydrate, starch, neutral detergent fibre, metabolisable energy (ME), nitrogen (N), calcium and phosphorus in k ikuyu herbage in summer, autumn-winter and spring were, respectively: 4.2, 3.7 and 5.7%; 5.9, 4.1 and NA%; 56, 52 and 43%; 8.2, 9.3 and 9.1 MJ/kg; 2.8 5, 2.83 and 2.32%; 0.25, 0.34 and 0.26%; and 0.33, 0.27 and 0.26%. Defoliation height influenced NSC concentration (8.4, 9.5 and 10.6% for 3, 6 and 12 cm, respectively), while defoliation interval affected both the ME and N (9.1, 8.8 and 8.6 MJ/kg and 2.8, 2.6 and 2.1% for 2, 4 and 6 leaves/ tiller, respectively) concentration. Although this study was a plot experiment over only one year, the changes i n nutritive value with regrowth interval and the inability of dairy cows to graze below 6 cm height support the recommendation that dairy cattle shoul d graze kikuyu pastures to 6 cm stubble height at 3-4 leaves/tiller interva l in spring and summer, and to the same height but at 5-6 leaves/tiller in autumn-winter.