Ráðunautafundur - 15.02.1989, Page 30

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During this period feeding of hay or silage should commence. Fertilizer nitrogen
applied early (when the 10 cm soil temperature reaches 5.5°C-usually early March)
will assist in encouraging early growth. Fields selected for lambing and early
grazing should be the most sheltered and free draining. It is important that
following lambing and turn out on to pasture that a sward height of 4 cm is
achieved as quickly as possible. For swards less that 4 cm, supplementary feed
should be given on a declining scale as the target sward height is approached.
During early summer and mid-lactation a sward height of between 4-6 cm should be
maintained. This can be achieved by closing up areas for conservation (hay or
silage) or by the use of grazing cattle. A flexible approach is required making full
use of the variability that exists within the in-bye. Careful management in this
early period is crucial for (a) controlling pasture quality by limiting seed head
formation and (b) allowing for maximum production of hay or silage.
In late lactation and after June sward height can be increased beyong 6 cm - (6-
8 cm) when there is little problem with seed head production - to ensure adequate
lamb growth as their grazing attains greater importance. Higher sward heights are
particularly important on low density silage aftermaths. Following weaning, ewes can
be kept according to their condition, fat ewes on swards at 2 - 3 cm, thin ewes on
swards 4-6 cm. Lambs for finishing are kept at sward heights of 6 - 8 cm while
store lambs can be kept at higher densities on sward heights of 4 - 6 cm. In the
autumn, ewes are flushed on swards of 6 - 8 cm. The importance of maintaining
adequate sward heights before, during and just after mating has been clearly
established in its effect on ewe fertility. If this cannot be achieved then
supplementary feeding is necessary. Finally swards are grazed down to heights of 3-
4 cm prior to the onset of winter conditions.
A practical problem emerges when decisions have to be made over changes in
stocking rate which are necessary to maintain target sward heights.
Methods based on ’percentage’ adjustment (Hodgson et al„ 1986) or absolute
change, Hutchings (1988) have not proved entirely satisfactory, although the latter
has greatest promise. Ideally a predictive model which takes into account forecasted
weather, fertilizer use and current status of soil nutrients (nitrogen) and moisture
could lead to greater precision. While this would be of immense value in research it
represents a level of sophistication that would be difficult to adopt on a hill farm.
A similar approach is being developed for the summer management of suckler
cows at grass (Wright, 1988).
Most of research has been directed to grass dominant pastures. There is now an
increasing interest in the potential use of legumes, particularly white clover, for
environmental, nutritional and economic reasons. Many problems exist in developing
robust guidelines for grazing management aimed at maintaining clover in the sward