W.J. FULKERSON and K. SLACK

NSW Agriculture, Wollongbar Agricultural Institute, Wollongbar, NSW, Australia

Abstract

Lotus pedunculatus cvv. Sharnae and Maku and Trifolium repens cv. Haifa were established in a kikuyu (Pennisetum clandestinum) sward on the subtropical north coast of NSW, Australia, in April 1992. Within these pastures, all plots were defoliated at 5 or 12 cm stubble height with a 14 d or 'when ready' (lower leaves commencing to senesce) interval in spring. In autumn-winter, lotus plots were cut at 5 or 12 cm stubble height 'when ready', whereas white clover plots were cut at 5 cm stubble height either every 14 days or 'when ready'. Irrigation replaced evapotranspiration losses at 5–12 day intervals.
Sharnae lotus showed substantially earlier spring growth than Maku, but the annual yields of legume and total herbage (legume plus kikuyu) were similar, with a mean DM yield of pasture over the 2½ years since sowing of 34 080 kg/ha, or 68% of the yield (49 880 kg/ha) of a white clover pasture.
The highest DM yields of legume (15 450 kg/ha for lotus and 24 100 kg/ha for white clover) were obtained by defoliating to 5 cm stubble height when the legume 'was ready' in spring for white clover and also when lotus was again defoliated at 5 cm height in autumn-winter. This treatment had no adverse effect on growth of the kikuyu.
Although there was a significant benefit on total DM from delaying the commencement of severe defoliation of lotus pasture (from 12 to 5 cm stubble height) in autumn — at a time of expected rhizome growth — the effect was small at 4% and was due to an 8% increase in kikuyu, rather than a change in legume yield. In fact, growth of lotus rhizomes was confined to winter-late spring, in contrast to summer-autumn in temperate regions of Australia.
The very low rate of seedling recruitment from natural reseeding, or reseeding white clover in autumn, confirms that attempts to increase its persistence in irrigated kikuyu pastures must focus on strategies that will increase stolon survival, particularly over summer. The impact of root knot nematodes also needs to be quantified.
Management required to establish and maintain a productive legume-kikuyu pasture for 2 years is relatively clear. However, the cause of the decline in vigour of the legume component after 2 years is less clear. Research is at present focused on this problem.