Andropogon gayanus Kunth.

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Graminae

Common names

Gamba grass (Africa), Sadabahar (India), Rhodesian andropogon (southern Africa), Rhodesian blue grass (Zimbabwe), onaga (north-west Africa).


Description

A perennial species which in Africa grows in large tufts up to 2 m high with a reedlike habit. It is blue, with a waxy bloom. The leaves are distinctive because the many blades appear to be petioled. In the lowest leaves the laminar tissue is greatly reduced, almost to the midrib, above the ligule. The leaf widens gradually and then narrows again, so that the blade is finely pointed (Chippendall & Crook, 1976). Fifty percent of its roots are fibrous, and less than 0.5 mm in diameter, growing laterally at an angle of 10-15° to the surface for the first 50 cm, and then growing parallel to the surface for 1 m. These collect the early falls of rain. Forty percent are cord roots up to 2 mm in diameter which grow downwards at 30-40° and rarely measure 50 cm long. Ten percent of the roots are 0.5 mm in diameter, branch rarely, and form ropes. These grow vertically down to 80 cm and give drought tolerance (Bowden, 1963a).#

Distribution

Native to tropical Africa and now introduced to many countries.

Season of growth

Summer.

Altitude range

Sea level to 2 000 m, but grows best below 1 000 m.

Rainfall requirements

It grows in the 400-1 400 mm rainfall regime but prefers a rainfall of 750-1 260 mm and more than three months dry season ­ up to six months.

Drought tolerance

Excellent. Ten percent of its roots form ropes 0.5 mm thick which go down to more than 80 cm (Bowden, 1963a). In an oxisol at Carimagua, Colombia it dried the profile to 120 cm (CIAT, 1978).

Soil requirements

It will grow on a wide range of soils including those of low fertility, from sands to black cracking clays, but prefers sandy clays of medium to high fertility. In South America it has shown outstanding results in oxisol-ultisol soils (CIAT, 1978). In the Sudan it is common on sandy loams to loamy sands.

Ability to spread naturally

It spreads slowly by seed.

Land preparation for establishment

A clean, firm seed-bed is required.

Sowing methods

Cleaned and de-bearded seed is drilled in shallow rows or broadcast and rolled. It can be planted also from root-stocks (splits), the best being mature woody stumps.

Sowing depth and cover

Sow seed at 1-2.5 cm below the surface.

Sowing time and rate

Sow at the beginning of the rainy season at 5 kg/ha (35-70 kg/ha uncleaned).

Seed treatment before planting

De-beard the seed ­ a machine has been developed at CIAT, Colombia (CIAT, 1978).

Seedling vigour

Good.

Vigour of growth and growth rhythm

Dry-matter yield increased during the wet season from June to October in Nigeria, reaching a maximum of about 3 800 kg/ha in October, declining then until February. Cutting in early October gave best balance of bulk and quality (Haggar, 1970).

Response to defoliation

At Fashola Livestock Farm, Nigeria, A. gayanus required intervals of more than six weeks between cuttings, and a cutting height of about 4 cm to maintain productivity and a good stand (Ahlgren et al., 1959). It cannot stand heavy grazing until it is well established, but requires high stocking rates to maintain reasonable height.

Grazing management

It should be utilized when young, as once flowering stems appear it becomes harsh and of little nutritional value. Burning during the dry season is universal. However, it is important to maintain some residual dry matter and leaf area after grazing in such erect grasses (CIAT, 1978).

Response to fire

It tolerates fire and in Ghana and elsewhere it is burnt every year. Early dry-season burning promotes its growth, whereas late burning promotes the unpalatable Loudetia acuminata (Ramsey & Rose-Innes, 1963).

Dry-matter and green-matter yields

Adegbola (1964) recorded 14 800 kg DM/ha per year at Agege (Lagos), Nigeria. In India 3 300 kg/ha fresh grass was obtained. Hendy (1975) obtained a production of 40 000 kg DM/ha per year at the Livestock Research Station, Tanga, United Republic of Tanzania, from a fertilizer application of 44 kg P2O5, 30 kg K2O and 50 kg N/ha per year. A selection of A. gayanus, No. 621 from Shika, Nigeria, yielded 4 000 kg DM/ha at Quilichao, Colombia without fertilizer nitrogen but with adequate phosphorus (CIAT, 1978).

Suitability for hay and silage

It has been conserved as silage and hay, but its low nutritive value (Ademosun, 1973) does not justify the work involved (Miller, Rains & Thorpe, 1964).

Value as a standover or deferred feed

It is coarse and of low nutritive value after maturity, with only 1.5 percent crude protein (Miller, Rains & Thorpe, 1964).

Toxicity

No toxicity has been reported by Everist (1974).

Seed yield

Haggar (1966) recorded 21-86 kg/ha. Caryopses constitute 10 percent of this figure. At CIAT, Colombia, 34 kg/ha of pure live seed was harvested manually. Collection of shattered seed from the ground increased yield and germination capacity, when not affected by the weather (CIAT, 1978).

Cultivars

There are several different types of plants and four varieties:

  • Var. bisquamulatus (Hochst.) Hack 

common in the savannahs from Senegal to the Sudan, colonizing denuded and waste land. It is very palatable to livestock.

  • Var. gayanus 

in periodic swamps in the same region. Good for erosion control in damp places.

  • Var. squamulatus (Hochst.) Stapf 

occurring also in this area and extending to the United Republic of Tanzania, Zimbabwe, Mozambique, Transvaal and Angola (Bowden, 1963b).

  • Var. tridentatus 

confined to Ghana (Rose-Innes, 1977). Bisquamulatus and squamulatus grow best on well-drained sandy clays of medium to high fertility. Pasto Carimagua cv. 621 was to be released by CIAT in 1980.

Diseases

It has no disease problems.

Main attributes

Its excellent growth and dry-matter production in acid infertile soils with minimum inputs, exceptional tolerance to drought stress, burning, and high levels of aluminium saturation; low P and N requirements; no known disease or major insect attacks; excellent seed-producing ability; compatibility with legumes; adaptability to low-cost pasture establishment systems, acceptable nutritional quality and high intake due to high palatability; high animal production levels during the first year (CIAT, 1978). Its adaptability to low-lying tropical areas which have low to moderate rainfall and its ability not only to survive a long dry season of several months but also to remain green for much of it and begin regrowth very early in the following rains to provide an early bite (Bowden, 1963b).

Main deficiencies

As it approaches and reaches maturity, it coarsens and is also of low nutritional value.

Optimum temperature for growth

The optimum temperature for flowering is 25°C (Tompsett, 1976).

Frost tolerance

It is probably not tolerant of frost.

Latitudinal limits

Probably about 20°N and S.

Response to light

It prefers to grow in full sunlight.

Ability to compete with weeds

It could suppress weeds by shading and root competition in dry areas.

Pests

It may be attacked by the Brazilian spittle bug (CIAT, 1978).

Palatability

It is palatable when young and cattle will eat it up to flowering. Palatability ranking was A. gayanus > Panicum coloratum > P. maximum > Pennisetum purpureum (Bowden, 1963b).

Response to photoperiod

It is a short-day plant with a critical day length for flowering between 12 and 14 hours. Flowering increased as day length shortened from 12 to eight hours (Tompsett, 1976).

Chemical analysis and digestibility

Göhl (1975) lists its feeding analysis in Table 15.2, to which Boudet's (1970) figures are added. Crude protein content in all categories of leaf and stem rose to a maximum at ear emergence. Maximum yields of digestible nutrients can be obtained by cutting at that time (Haggar & Ahmed, 1971). A. gayanus selection 621 gave low digestibility but high nitrogen levels in Colombia (CIAT, 1978).

Natural habitat

Open woodland and savannah.

Tolerance to flooding

Rains (1963) lists A. gayanus var. gayanus among grasses growing in seasonally flooded places.

Fertilizer requirements

A. gayanus performs very well without fertilizer nitrogen or phosphorus (CIAT, 1978) and thus is a valuable grass for low-input pasture production. Haggar (1975) found the highest return of dry matter per unit of fertilizer (14.4 kg DM/kg N) was from only 28 kg N/ha and there was only a modest increase in crude protein up to 10.5 percent of the dry matter with increasing nitrogen. However, Haggar (1975) obtained almost linear increases in dry- matter production with increasing amounts of sulphate of ammonia up to 112 kg N/ha, but from 112 kg to 896 kg N/ha yields were curvilinear with maximum yield at 500 kg/ha. Falade (1975) determined the optimum phosphorus content of the dry matter for growth was 0.19 percent in a sandy loam soil at Ibadan, Nigeria when fully fertilized. Andrew and Robins (1971) obtained a critical percentage of 0.185 in Queensland. Some basic potassium may be required. It tolerates high aluminium (Spain, 1979). On the Quilichao ultisol in Colombia, A. gayanus gave maximum yield in the establishment year without fertilizer, and on the Carimagua oxisol the maximum yield was obtained with 50 kg P2O5/ha. Phosphorus fixation in the Carimagua oxisol is about half that of the Quilichao ultisol (CIAT, 1978).

Compatibility with other grasses and legumes

It combines naturally with Stylosanthes fruticosa in the Sudan and the United Republic of Tanzania and with Stylosanthes spp. and Desmodium ovalifolium and other legumes in Colombia (CIAT, 1978).

Genetics and reproduction

2n=40 (20, 35, 40, 42, 43, 44; Fedorov, 1974).

Seed production and harvesting

Generally it is a good seed producer. Manual harvest produces more than 100 percent more than mechanical methods. In India, Mishra and Chatterjee (1968) obtained the highest yield by cutting twice a year (in mid-January and early July) and fertilizing with 38.9 kg N/ha plus 22 2 P2O5/ha. It maintained its seed yield with a third cut late in August.

Economics

A. gayanus (gamba grass) is a dominant constituent of large areas of natural and sown grasslands in Nigeria and other savannah areas of tropical Africa. It especially suits low-lying tropical areas which have moderate to low rainfall and a long dry season. When incorporated into a rotation it has been found to be a fertility builder. The stems are used for weaving grass mats and for thatching (Bowden, 1963b). It is a promising grass in northern Australia.

Animal production

In Nigeria, natural grassland containing 60 percent of A. gayanus resulted in a weight gain of 0.31 kg per day when grazed by N'Dama and Keteku cattle, but when consumed as silage the weight gain was 0.11 kg/ day (Adegbola, Onayinka & Eweje, 1968).

Further reading

Bowden, 1963b; CIAT, 1978.

Dormancy

Germination improves for a time with storage.

Value for erosion control

It has been used in Kano, Nigeria for reclaiming badly overgrazed and eroded land (Bowden, 1963b).