Management and productivity of white clover in a kikuyu grass sward in subtropical Australia.
A field trial plot-cut study, on heavy clay soil, evaluated the establishment, productivity and persistence of Trifolium repens cv. Haifa sown into a vigorous sward of Pennisetum clandestinum. After T. repens had become dominant, 4 m2 plots were randomly allocated to cutting treatments at 5 or 12 cm stubble height in spring at an interval of 14 d or when ready (lower leaves beginning to senesce) in spring and autumn. During the summer, the grass was managed to provide the maximum amount of leaf by cutting to 5 cm stubble height and applying 100 kg urea/ha each month. Over the 2.5 years of the study and under optimal cutting treatment in the summer, the total yield of forage was 19.95 t DM/ha, of which 57% was T. repens. Haifa yield declined significantly in years 2 and 3 and the DM yield in 1994 was composed almost entirely of naturalized T. repens. The invasion of naturalised T. repens was paralleled in the control plots. The loss of T. repens vigour observed in year 3 may have been due to the heavy infestation of the root knot nematode Meloidogyne sp. or to the cutting management over the second summer, or both. Extensive monitoring suggested that the reduction in vigour was not caused by a decline in soil fertility, pH, moisture stress or damage by stock. It is suggested that management at the transition phases between the dominance of the 2 pasture components in early autumn and late spring is critical to T. repens success in relation to stolon survival over the critical late summer/early autumn period. It is concluded that success relies upon the following procedures: removal of the P. clandestinum sward by heavy grazing, forage harvesting or mulching; repeated grazing after sowing whenever new shoots of P. clandestinum exceed 5 cm; cessation of N fertilizer application 3 weeks before sowing T. repens; infrequent but severe grazing of T. repens once established; and alteration of management practices to favour P. clandestinum growth in late spring.