Sorghum (perennial)


Scientific name

Sorghum x almum Parodi
Sorghum spp. perennial hybrids

Synonyms

Sorghum x almum Parodi = S. bicolour x S. halepense

Family/tribe

Family: Poaceae (alt. Gramineae) subfamily: Panicoideae tribe: Andropogoneae.

Common names

For S. x almum:
almum grass, almum sorghum, Columbus grass , five-year sorghum;  sorgho d’Argentine (French);  Columbusgras (German);  sorgo negro, pasto colon (Spanish);  batag, gau (Philippines).

For Sorghum spp. hybrids:
Commonly known by cultivar names, e.g. ‘Silk’, ‘Krish’.

Morphological description

An erect, robust, tussocky perennial with numerous tillers and thick short rhizomes which curve upwards to produce new shoots near the parental stool.  Culms solid and pithy, about 1 cm thick, sometimes reaching a height of 3–3.6 m.  Internodes of culm may have a thickened ring.  Leaves 2.5–4.0 cm wide, generally glabrous except for hairs near the liguleInflorescence is a large pyramidal panicle with secondary and tertiary branches, generally drooping as seed ripens.

Distribution

For Sorghum x almum:
Native:
South America:  Argentina, Paraguay, Uruguay.
Natural hybrid arising from cultivated and weedy Sorghum in Argentina.

Man-made hybrids confined to locations where purposefully sown or have since naturalised.  Widely sown on fertile soils in semi-arid northern Australia.

Uses/applications

Vigorous medium-term (3–5 years) pasture forages for grazing by cattle, or conservation as hay or silage.  Can be used as pioneer species when sown with other more persistent, but slower establishing, perennial grasses for quick cover and feed.  Can be used for cut and carry but seed of hybrids is expensive for smallholders in developing countries.

Ecology

Soil requirements

Adapted to fertile soils from clay to loam with neutral to high pH (pH 5–8.5).  Some tolerance of salinity but not waterlogging .

Moisture

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Good drought tolerance and best in semi-arid conditions with 500–800 mm rainfall .  Poor tolerance of flooding.

Temperature

Seed planted for summer growth when soil temperatures are above 15°C.  Established stands can survive mild frosts and regrow from root bases or short rhizomes.  Planted at latitudes between 25°N and 30°S.

Light

Full sunlight.

Reproductive development

Short-day response.  Begins flowering 7–8 weeks after planting.  Reliable seed producer.

Defoliation

Tolerant of heavy grazing with coarse stems remaining, and with regrowth from axillary buds, but does not stand trampling.  Short-lived perennial will weaken after about 3 years.  Should be grazed heavily when it reaches 50 cm high to prevent development of coarse stems and early flowering.  Should not be grazed below 15 cm if good regrowth is expected.

Fire

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Not normally subjected to fires.

Agronomy

Establishment

Planted with seed sown into (5–7 kg/ha) or onto (20 kg/ha) arable seedbed.  Also sown at light seed rates (<5 kg/ha) with other grasses into ash after clearing bush, or after blade ploughing shrubby regrowth. Large seed germinates and establishes vigorously.

Fertiliser

Should be grown only on fertile soils where little extra fertiliser is required.

Compatibility (with other species)

May be sown as a pioneer with more permanent grass species or with winter- or summer-growing legumes.

Companion species

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Grasses:  Sown with more permanent grass species such as Panicum, Chloris and Cenchrus to take over as the sorghum declines.
Legumes:  Medicago sativa , annual medics (Medicago spp.), Neonotonia wightii , Lablab purpureus .

Pests and diseases

Good resistance to rust and blight, and to sugar cane virus.  Planting sorghums near sugar cane is generally discouraged for fear of cross transmission of disease.

Ability to spread

Can spread from seed dropping onto suitable arable land.

Weed potential

Sale of seed of S. x almum has been restricted for fear of reversion to the rhizomatous parent, S. halepense.  Likewise, seed of cv. Silk has been restricted in some states of Australia for fear of contamination with seed of rhizomatous S. halepense which is similar in appearance to that of cv. Silk.

Feeding value

Nutritive value

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Nutritive value greatly depends on soil fertility.  It provides good feed only on soils which are at least moderately fertile.  Total free sugars in the stem average about 20%.

Palatability/acceptability

Moderate to very palatable.

Toxicity

Leaf can be poisonous because of high concentrations of hydrogen cyanide (prussic acid), especially in young dark-blue coloured regrowth after a dry spell.  Provision of a supplement block containing sulphur may reduce the risk of poisoning.

Production potential

Dry matter

DM yields up to 20 t/ha/yr, but more normally around 4–10 t/ha.

Animal production

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Under continuous grazing in sub-humid Australia, steers grazing at stocking rates of 1.5–3 steers/ha averaged LWGs of 150 kg/head/year.

Genetics/breeding

Cv. Krish is a hybrid between S. halepense (L) Pers. and S. roxburghii Stapf.
Cv. Silk is a hybrid between ‘Krish’ and S. arundinaceum (Desv) Stapf.
These sorghums are cross-pollinating.
S. x almum is predominately cross-pollinated, but also self-fertile.  Has largely been replaced by the artificial hybrids.
2n = 40.

Seed production

Seed does not shatter readily and can be harvested easily.  No dormancy .
Since seed of ‘Silk’ and that of the noxious weed S. halepense are of similar colour, care must be taken with the purity of seed crops.

Herbicide effects

Seedlings and young plants are easily eradicated with non-residual contact herbicides such as glyphosate.

Strengths

  • Easy establishment and rapid growth.
  • Very productive on fertile soils.
  • Pioneer species with other perennial grasses or legumes.

Limitations

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  • Demands high soil fertility .
  • Prussic acid poisoning.
  • Seed cannot be distinguished from that of S. halepense.

Other comments

Will quickly strip nitrogen from marginal soils making it difficult to plant following permanent pastures.  Difficult to eradicate from subsequent grain crops.

Selected references

Catalogues from commercial seed companies such as:
The Forage Book (ISBN 0 9594231 1 7). (Pacific Seeds, Toowoomba, Queensland, Australia).

Internet links

Cultivars

Cultivars

Country/date released

Details

‘Krish’ Australia (1967) Better resistance to leaf diseases and better palatability than Sorghum x almum.
‘Silk’ Australia (1978) Resistance to leaf diseases;  holds green leaf longer into early winter.

Promising accessions

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Promising accessions

Country

Details