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Graminae
Common names
Giant button grass (Australia).
Description
It is similar to D. aegyptium but stouter and taller. It is
an erect annual with broad leaves and a tendency to root at the nodes under
favourable moisture conditions. The plant produces a profusion of tillers
which lead to numerous inflorescences. The spikes are 4.5-10 cm long in
groups of four to eight, often unequal.
Distribution
Found throughout tropical Africa, especially southern Africa.
The Queensland introduction Q.10091 was collected by Dr J.P. Ebersohn from
southern Zimbabwe.
Season of growth
Predominantly summer growing, but will overwinter if frosts
are light.
Rainfall requirements
The seed was collected in southern Zimbabwe in a rainfall regime
of 450 mm spread over the months of October to April.
Drought tolerance
Once it germinates it generally escapes drought because of
its short growing season.
Soil requirements
It prefers sandy soils and is a strong pioneer on the Kalahari
sands in Africa. Under good moisture conditions it will establish on lateritic
red earths and heavy self-mulching soils.
Ability to spread naturally
It spreads well by seed under favourable conditions of soil,
moisture and nutrients.
Land preparation for establishment
A rough seed-bed is usually sufficient, especially with sandy
soils.
Sowing methods
The seed is broadcast on the surface and uncovered.
Sowing time and rate
At the beginning of the wet season at about 5 kg/ha.
Number of seeds per kg.
About 2 million.
Vigour of growth and growth
rhythm
It flowers in 30-45 days and ripens seed in 60-80 days in latitudes
26-25°S in Queensland.
Dry-matter and green-matter
yields
Yields of air-dried matter ranged from 6505 500 kg/ha, the
latter figure when fully fertilized.
Suitability for hay and
silage
It makes good, soft, leafy hay.
Toxicity
No nitrate poisoning has been reported.
Seed yield
190 kg per hectare seed were harvested in four harvests in
south-eastern Queensland in one year.
Optimum temperature for
growth
Germination is highest at 40-42°C.
Frost tolerance
It is killed by heavy frosts (-6°C) during June and July
in Zimbabwe, but it retains its leaf.
Latitudinal limits
It occurs commonly between latitudes 25°N and S.
Palatability
It is very palatable.
Chemical analysis and
digestibility
The percentage of nitrogen in the tops of D. giganteum was
0.3-0.35 without fertilizer and 0.3 and 0.4 with 500 kg/ha superphosphate.
The percentage of phosphorus was 0.03 without and 0.050.08 with superphosphate.
Natural habitat
On disturbed or sandy areas.
Tolerance to flooding
It does not tolerate flooding.
Fertilizer requirements
It is not usually fertilized but good yields were obtained
by Bishop (1973) at Normanton, Queensland, in trial plots receiving 500
kg/ha of superphosphate and 250 kg urea per hectare.
Seed production and harvesting
It seeds heavily and is easily harvested.
Economics
In Africa it is useful in quickly providing ground cover and
grazing on cultivated land going out of production. In Kordofan Province,
Sudan it is used as a cut and carry grass for feeding livestock in the
villages.
Dormancy
There is some after-ripening, the maximum germination in Queensland
being obtained with two-year-old seed germinated at 40-42°C, with a
figure of 68 percent. The germination figures for 1969 are shown in Table
15.23. Germination is stimulated by a submergence in water up to eight
days from 11.3 percent after one day to 15.2 percent after eight days.
Treatment with 1 percent Thiourea for 15 hours gave a germination of 40
percent; the control was only 9.2 percent (Batianoff, personal communication).
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