A COMPARISON OF THE OUTPUT FROM PERMANENT SWARDS CONTAINING CLOVER ORRECEIVING NITROGEN-FERTILIZER WHEN CONTINUOUSLY GRAZED BY EWES AND LAMBS

A 2-year experiment was designed to compare the output from a permanen t grass sward, either containing clover (GC) or receiving 200 kg N ha- 1 (GN), when continuously grazed by sheep stocked at 12 and 15 ewes ha - 1 on GC and 15 and 18 ewes ha-1 on GN. Sward surface height (SSH) wa s controlled within designated guidelines by adjusting the size of the grazing area with an electrified 'buffer' fence; the herbage surplus to grazing requirement was cut and conserved. A dried grass supplement was offered to the sheep during periods of low herbage availability. The experiment was carried out during 1989 and 1990. No silage was mad e on GC15 in either year compared with 28 and 90 kg DM ewe- 1 on GN15 in 1989 and 1990 respectively; supplementation was consistently and si gnificantly greater on GC15 than on GN15. Clover proportion was genera lly higher on GC12 than GC15 (significant (P<0.01) in September 1989) and reached a maximum level of 14% on GC12 in August 1990. Herbage org anic matter digestibility was little affected by the inclusion of clov er in the sward. Differences in lamb growth rate were not significant and, at the common stocking rate, there was no difference in lamb outp ut between GC and GN. In 1990, GC12 and GN15 treatments proved to be s uccessful after weaning in balancing the increasing nutritional requir ements of the ewes during the period prior to mating, the requirements of a declining lamb population as the lambs satisfied the criteria fo r slaughter and were sold, and a continuing need to conserve surplus h erbage. The metabolizable energy requirements of the ewes and lambs ov er 2 years were 75-8 and 74.7 GJ ha-1 for GC15 and GN15 respectively, and the differences in total utilized metabolizable energy output of t he two systems were due to the amounts of herbage conserved and supple ment consumed. The 2-year mean total UME output on GC 1 5 was 80% of t hat on GN 1 5 (67-8 and 84.4 GJ ha- 1 for GC 1 5 and GN 1 5 respective ly) and the experiment provided further evidence that grass/white clov er swards with no fertilizer N applied are capable of producing about 80% of the total output of grass swards receiving 200 kg N ha-1.