Agriculture Reference
In-Depth Information
attraction of Voisin's book is that he goes some way towards explaining how to 'think like
a cow' with less of the anthropomorphism that pervades some other attempts to unveil the
secret thoughts of bovines. But the reason why the topic has a cult following is that it is the
first attempt to analyse in detail the principles behind what Voisin called 'rational grazing',
and has since come to be known as 'pulse grazing', 'mob grazing', 'short duration grazing'
or even 'controlled overgrazing'.
Pulse grazing involves carefully rotating livestock around paddocks so that they eat grass
at the optimum moment in its growth, and for the optimum period of time. If they are left
for more than two or three days days in the same paddock, they will return to the favoured
plants that were eaten on day one and have now begun to grow back to take a second bite,
while ignoring the less palatable grasses, resulting in excessive grazing pressure on the
higher quality grass, and inefficient use of the lesser. This is hardly a radical observation,
but Voisin has a keen eye for detail and he goes on to propose some sophisticated methods
of managing and fencing land to ensure 'rational grazing'.
Voisin's book was largely ignored until it was picked up in the 1970s by a biologist, Al-
lan Savory, who was working with buffalo, elephant and other big game in what was then
Rhodesia, and was dismayed that cattle were 'overgrazing my beloved Africa to death'.
Savory was approached for help by some cattle ranchers who themselves were becoming
worried by the deterioration in their rangelands:
Although my antagonism to cattle was well known, what I was saying publicly at the
time made sense to them … In tackling this new challenge to manage cattle and wildlife
together while improving the land I dusted off my copy of
Grass Productivity
and was
astounded to find that Voisin had already solved the riddle of
time
. He had proven that over-
grazing had little relationship to the number of animals but rather to the time plants were
exposed to the animals, the time of exposure being determined by the growth rate of plants.
If animals remained in any place for too long, or returned to it too soon, they overgrazed
certain plants. Suddenly I could see how trampling also could be either good or bad. Time
determined that too. The disturbance needed for the health of the soil became an evil if pro-
longed too much or repeated too soon.
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Savory surmised that the ecology of natural rangelands had evolved to favour pulsed
grazing. In wide open grassland, large herbivores herd together for safety from predators
who escalate the numbers game by hunting in packs. Wildebeest and zebra in Africa do
not amble across the savannah in family groups sampling the vegetation, picking out the
choicest morsels. They move like an army upon one location kicking up dust and spewing
out methane, and graze close to the ground before moving on. It sounds like a scorched
earth policy, but the volume of dung deposited on the areas they have grazed deters them
from returning until the grass has recovered. Their migration patterns are as much a care-
fully timed rotation as Voisin's tidy fences, while their hooves break up soil crusts and
