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Understanding the cultivar
I
n South Africa’s arid and semi-arid areas, it is the lower rain-
fall and water shortages that force livestock producers to grow
drought-tolerant pastures. Forage sorghums fall perfectly into
this category by only requiring 350 mm - 400 mm rainfall per
season. This depends on distribution and soil moisture conservation
techniques.
Forage sorghums, similar to grain sorghums, are able to enter into
a dormancy phase during dry and unfavourable conditions, which
would otherwise damage plants. During this dormancy phase,
growth stops, while survival becomes the primary objective. This
ability, together with a well-developed root system, gives forage
sorghum its hardiness.
Forage sorghums are hybrids with many different crossings. The
most common planted types in South Africa are sweet-sorghum x
sweet-sorghum crossings and sorghum x sudan grass crossings,
which are grouped into different flowering dates (early to ultra-late).
Early flowering hybrids usually grow fast, but have a short grow-
ing season, while late flowering hybrids grow slower, but have a
longer growing season. The high sugar content of sweet-sorghum
x sweet-sorghum crossings makes them highly suitable for silage
production. They can also be used later as foggage.
In grazing systems, there is however nothing that beats an early
flowering sorghum-sudan grass crossing with regards to the days-
to-first-graze and regrowth after each graze. These hybrids produce
abundant leaf material with thin stems, which makes them suitable
to utilise as green chop. It is however very important to manage
early flowering types to prevent the onset of the reproductive stage,
which results in inferior quality and poor regrowth. Establish it over
an extended period, ranging from early November through to mid-
December. This will spread the production and make the fodder flow
more manageable. Bear in mind that for early plantings, soil tem-
perature should be at least 18°C.
Grazing can commence when the stand is 750 mm - 800 mm in
height (1 000 mm at the highest), and grazed to no lower than
250 mm. This will keep the stand producing good quality leaf
material. By keeping the stand vegetative, waste caused by
trampling is also reduced. A soil analysis should be done before
establishment to ensure that optimal soil pH, phosphate and
cation levels are present. Depending on the water availability, forage
sorghum should be established with
40 kg N/ha, with additional applications of
20 kg - 40 kg N/ha after each grazing.
Under stressful growing conditions, any for-
age sorghum can cause prussic acid poison-
ing. Avoid grazing young plants when under
stress. Nitrate poisoning can also be a prob-
lem, especially when high N applications have
been made and where these plants are sub-
jected to drought stress or extended periods
of overcast weather. Consult nutritionists or
veterinarians about supplements to reduce
these risks.
Advance Seed is the exclusive distributer of
Supergraze 1 000, an early flowering sorghum
x sudan grass cultivar. The 50% flowering
stage can be reached within 70 - 80 days when
established early in spring. This is however
subject to climate, the growing environment
and how it is managed.
DIRK COETZEE,
agronomist: Advance Seed
ANNUAL RAINFALL
ROW ESTABLISHMENT
BROADCASTING
Low
<500 mm
4 kg/ha - 8 kg/ha
(1,2 m - 1,5 m rows)
Medium
500 mm - 700 mm
8 kg/ha - 15 kg/ha
(0,8 m - 1,2 m rows)
High and irrigation
>700 mm
15 kg/ha - 25 kg/ha
(0,4 m - 0,8 m rows)
25 kg/ha
Each kilogram of Supergraze 1 000 seed can have between 30 000 and 45 000 seeds, depending on the seed lot
TABLE 1: SOWING DENSITIES.
Supergraze 1 000 forage sorghum available from Advance Seed.
27
October 2015
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