Comparative herbage characteristics and sheep production (ewes and lambs until weaning and lambs thereafter) from swards of Aurora (very early flowering), Frances (early flowering), Talbot (intermediate flowering) and Melle (late flowering) varieties of perennial ryegrass {LoUum perenne) were studied under a continuous variable stocking management based on sward surface height guidelines. The varieties were assessed as grass-only (215 kg N ha""' fertilizer) and grass/clover (83 kg N ha"' fertilizer) pastures.Over 2 years (1985-86) total annual lamb production per hectare from grass-only swards of Aurora was 19% more than that from Frances despite similar herbage productivity. Differences between the varieties in lamb output were more pronounced as grass/clover swards, with Aurora producing 29 and X^'^n more Iamb than Melle and Talbot respectively and with Frances also giving 16% more than Melle. Overall lamb production from grass/clover swards was 10% more than that from the grassonly pastures, mainly due to 69% advantage in individual Iamb growth rates after weaning. Herbage organic matter digestibility, during the post-weaning period, was higher on grass/clover than on grass-only swards, and similarly with Aurora versus the other varieties. Under a frequent cut simulated grazing regime the relative herbage productivity of the four Correspondence: Mr J. M. M. Munro, IGER, Bronydd Mawr Research Centre, Trecastlc, Brecon, Powys, LD3 8RD, UK.varieties differed, with Aurora 13% less productive than Frances.The results are discussed in relation to the limitations of assessing performance under cutting, and the significance of the interaction in animal productivity between the two sward types.
Study of the growth of heavily fertilized swards of S23 pereimial ryegrass {Lolium perenne) at a hill and a lowland centre in mid-Wales during 1968-69 demonstrated that lower productivity in the uplands could only be partiaUy attributed to a shorter growing season and poorer summer growth conditions. Comparison of yields with potential transpiration estimates indicated that winter damage had an important bearing on production during the following year. In 1969, the adverse combination of a mild autumn and a severe winter led to a spring tiller density which was less than 25% of normal at the hill centre.
The DM and N contribution of S184 wbite clover in mixed ryegrass/dover swards was recorded at Pant-y-d^r Hiil Centre (305 m) for 4 years, 1967-70. By direct comparison with fertilized grass swards it was estimated that the clover N contribution on peaty gley soil averaged 100 kg N/ha per year (89 Ib N/ac) under cutting and 98 kg N/ha (87 ib/ac) under grazing with faecal return. On more fertile acid brown earth the corresponding contributions were 81 and 90 kg N/ha (72 aud 80 Ib/ac). Full replacement of clover by N fertilizer would require average annual applications of 268, 229, 156 and 128 kg fertilizer N/ha, respectively (239, 204, 139 and 114 lb N/ac).
Detailed soil and vegetation analysis at Pant-ydVVr Hill Centre illustrated the main physical, chemical and biological factors involved in low output from rough grazing on 5 soil series, ranging from acid brown eartb to undifferentiated peat, wbich are representative of most of upland mid-Wales. Wbile all tbe soils, derived from Silurian sbale, bad low pH and base saturation status and bJgb lime, pbospbate and potasb requirements, tbe principal restraint on tbe productivity of resown grassland, particularly on tbe wet peaty gleys, was low available N status.
A small flock of 16 Blackface ewes occupying 40 acres of hill ground grazed as a fairly tight community. From observations over a complete year, 1960, it has been shown that sheltering behaviour was largely dependent on wind speed exceeding 24 m.p.h. Sheltering increased markedly at temperatures below freezing. Temperature above freezing, except for rapid falls in temperature exceeding 4° F., exerted little effect on sheltering. No relationship could be found between sheltering behaviour of the sheep and other factors which included rain, relative humidity, wind direction or season of the year.It would appear therefore that the sensitivity of sheep to exposure is influenced more by wind speed than any other climatic factor.
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