| Summary: | The immediate aim of this study was to relate herbage
availability, liveweight gain and stocking rate to one another
under continuous and rotational grazing so that management
recommendations could be formulated for Coastcross II Bermudagrass
and kikuyu. In addition, these data would be used for an economic
evaluation of growing out young beef animals on these two pasture
species. The broad long term goal was to use this information to
persuade farmers to make more use of planted pastures and thereby
reduce the stocking pressure on the veld. Besides pursuing the
primary objectives, the study offered an opportunity to make an
observational assessment of the put-and-take technique for use in
grazing trials.
In relation to fixed stocking, variable stocking appeared to
have no distinct advantage in this study. This conclusion is
drawn from the fact that little success was achieved in applying
put-and-take at a high level of precision. It was therefore
recommended that future trials should make use of fixed stocking,
except when variation in herbage availability is very large and
predictable.
In such cases the use of put-and-take would be warranted.
Liveweight gain of animals was linearly related to herbage
availability. In two seasons liveweight gain of animals on
Coastcross was higher for continuous grazing than for rotational
grazing at equivalent herbage availability, but in other seasons
there was no difference between the two methods of grazing. At
equivalent levels of herbage availability liveweight gain was
higher in early summer than in late summer. Herbage availability decreased linearly witilin each season
and on average, rotational grazing resulted in increasingly
greater herbage availability than continuous grazing, as stocking
rate was increased on Coastcross. However, no difference between
the two grazing methods was evident on kikuyu.
Finally, the relationship between liveweight gain and
stocking rate was also described by a linear function. On
average, the stocking rate at which maximum liveweight gain per ha
occurred (SRmax) was higher for rotational grazing than continuous
grazing on Coastcross, but not on kikuyu. However, no difference
was evident between the two grazing methods in each season.
During the study period annual rainfall varied from 506 mm to
990 mm. This offered a unique opportunity to examine the relation
between some of the pasture production parameters measured and
annual rainfall. The length of the grazing season and SRmax
increased, but liveweight gain of animals at SRmax declined as
annual rainfall increased. This caused seasonal liveweight gain
at SRmax to increase initially, but then to reach a maximum and
decrease as annual rainfall increased from 500 to 1000 mm.
From this information it was possible to build two models
which can be used to predict liveweight gain per ha and profit per
ha from stocking rate and annual rainfall. These models can
either be built into farm planning programmes or used directly by
agricultural advisors. In tl1is thesis they have been used to show
that there is a wide range in stocking rates and levels of annual
rainfall within which it is possible to make substantial profits
by grazing young beef animals on dryland pastures. This study has
therefore provided forceful information which can be used to
persuade farmers to make more use of planted pastures, and in so
doing, conserve the veld. === Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1983.
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