Aristida adscensionis L.

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Graminae

Synonyms

A. sub-micronata Schumach.

Common names

Six-weeks three-awn (United States), common needle grass (Kenya).

Description

An annual growing up to 90 cm high. Culms many-noded, few. Leaf- sheath tight. Leaf-blade linear, long-pointed. Upper glume always distinctly emarginate or two-fid at the summit and with a very distinct mucro or short awn between the acute or obtuse lobes. Awns scabrous, about 1.5 cm long (Andrews, 1956). The culms are yellow to bright green, curing to a straw colour. The seed- heads may be purple.

Season of growth

Summer, but can grow out of season if temperature and moisture are suitable.

Altitude range

Sea-level to 2 250 m. It is dominant in Zimbabwe at altitudes below 600 m.

Rainfall requirements

It is dominant in Zimbabwe in a rainfall regime of 300380 mm falling mainly between November and March. It requires a rainfall in excess of 250 mm.

Drought tolerance

Being an annual, it usually escapes drought once it has had sufficient rain to germinate.

Soil requirements

It prefers sandy soils but has a wide tolerance.

Land preparation for establishment

It will establish on roughly prepared ground and can be oversown into unprepared land.

Sowing methods

Broadcast the seed on to the surface and, where possible, cover lightly.

Main attributes

A common pioneering species on disturbed soil, waste land, rocky places and fallows.

Main deficiencies

Its short life and severe decline in nutritive value soon after it dries.

Palatability

It is a late-flowering, unpalatable annual in the United Republic of Tanzania (Wigg, Owen & Makurasi, 1973). The sharp seeds and stiff awns repel animals when mature. It provides an abundance of feed for a short time in Arizona.

Chemical analysis and digestibility

Göhl (1975) has listed its chemical analysis in Table 15.4.

Genetics and reproduction

2n=22 (Fedorov, 1974).

Seed production and harvesting

It will grow and set seed at any time of the year in Arizona when moisture and temperature are favourable, but is predominantly summer-growing.

Economics

It is one of the better annual grasses in Arizona ranges, but provides poorer forage than most perennials.

Animal production

It is used for semi-arid cattle ranching in Zimbabwe. At Tuli station in southern Zimbabwe, the natural veld was estimated by Rattray (1962) to carry one animal per ten hectares. When the carrying capacity was increased to one animal per eight hectares an almost pure stand of Aristida adscensionis was induced, which is unpalatable and provides little ground cover during the dry season.

Further reading

Humphrey, 1960a.

Value for erosion control

It easily colonizes bare ground.

Natural habitat and distribution

Occurs in any disturbed poor soils in grassland and open bush throughout tropical Africa. Introduced to the United States.