PRODUCTIVITY AND NITROGEN UPTAKE OF AGING AND NEWLY SOWN SWARDS OF PERENNIAL RYEGRASS (LOLIUM-PERENNE L) AT DIFFERENT SITES AND WITH DIFFERENT NITROGEN-FERTILIZER TREATMENTS

A field trial was conducted on 8 sites for 3 years to compare the prod uctivity and nitrogen (N) uptake of ageing sown leys (5-12 years old) with newly sown diploid perennial ryegrass at a range of N-fertilizer rates (0, 125, 250, 375 and 500 kg N ha(-1)) and with a diploid-tetrap loid mixture of perennial ryegrasses (at 250 kg N ha(-1) only). All pl ots were cut at 6-weekly intervals. Mean annual DM yields at 500 kg N ha(-1) were 12.3 and 13.2 t ha(-1) for ageing and newly sown swards, r espectively. There were differences between sites in the relative prod uctivity of sward types: on some sites, particularly at low rates of N fertilizer, ageing leys gave greater production than newly sown sward s. Three-year mean DM production varied by over 200 per cent between s ites, and the 8-site mean was ca. 45 per cent greater in year 1 than y ear 3, for both sward types, due to seasonal differences in weather. S wards resown with a diploid-tetraploid perennial ryegrass mixture had greater early season production than the diploid (cv. Vigor) sown alon e, although not at all sites. Mean N yield of herbage, at 0 fertilizer N, was 20 per cent higher from ageing leys than resown swards. Appare nt N recovery was higher from resown swards and highest in year 1. Res ults are discussed in relation to previous multi-site trials, and rela tionships between sward type, DM yield, N uptake and N supply are pres ented for sites with different response patterns. Implications for gra ssland management are considered.