Pennisetum clandestinum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Pennisetum clandestinum Hochst. ex Chiov.

Protologue: Ann. Ist. Bot. Roma 8: 41, fig. 5 (2) (1903).

Family: Gramineae

Chromosome number: 2n= 36

Vernacular names

• Kikuyu grass (En)
• Thailand: ya-khikhuyu.

Origin and geographic distribution

Kikuyu grass occurs naturally across the elevated plateaux of East and Central Africa, and has been distributed to other continents and islands with (sub)tropical, humid climates, between latitudes 0°-35°. In South-East Asia, kikuyu grass is restricted to elevated areas (> 1900 m) mainly in Papua New Guinea and the Philippines.

Uses

Kikuyu grass is used for many purposes including lawns and recreational areas, pasture for ruminants under intensive grazing and to prevent soil erosion. It is potentially a weed on arable land and in irrigation channels.

Properties

Nitrogen concentrations range from 1.8-4.3% depending on age and fertilizer application. Digestibility of DM varies from 73% (young leaf) to 50% (mature or frosted material). With advancing maturity the rate of decline in nutritive value of kikuyu herbage is slower than that of other tropical grasses. As kikuyu grass is adapted to very fertile soils, the concentrations of P, K and S are normally adequate for animal growth. On the other hand Na levels are often low (0.02-0.05%), indicating potential deficiencies for very productive lactating ruminants. There are approximately 400 seeds/g.

Description

A perennial, stoloniferous and rhizomatous grass with short culms, 8-15 cm tall, arising from long, prostrate runners, multi-branched and rooting at the nodes. Roots proliferate densely in upper 0-15 cm of soil, from older rhizomes/stolons, becoming less dense towards the growing point; in friable soils, roots can penetrate to 3 m. Leaves arise alternately from multi-branched stolons; leaf-sheath 1-2 cm long, pale green, eventually turning brown on older stolons, densely hairy; ligule a rim of short hairs; leaf-blade linear, 1-15 cm × 1-5 mm, tightly folded when young, flattened when older with sparingly hairy midrib. Inflorescence reduced to a cluster of 2-4 short spikelets each with fine bristles carried close to lateral runners, concealed within the uppermost sheath; spikelets consist of two florets, pale or translucent, one of which is usually fertile; stamens exserted on slender filaments for a short time, often asynchronously with the stigma. Caryopsis develops near stem at ground level, dark brown, ovoid, 2.5 mm long, pointed.

Growth and development

In established swards, kikuyu grass growth is cyclical, dependent on temperature, moisture and fertility. Flowering is indeterminate, being stimulated by defoliation or heavy grazing. After germination and emergence of primary tillers, kikuyu grass seedlings develop a prostrate growth habit as stolons grow radially.

Other botanical information

Early collections of ecotypes in East Africa were distinguished by differences in leaf type and flowering behaviour. Some strains are female fertile (apomictic through aposporic embryos) others are open-pollinated. Several cultivars have been released in Australia. "Whittet", a robust, upright form, was selected in New South Wales from seed introduced from Kenya. "Breakwell" a densely tillered, prostrate strain, was derived from a naturalized stand at Grafton. "Crofts" is fine-leafed with a degree of cold tolerance. "Noonan" seeds prolifically and is tolerant of the disease "kikuyu yellows".

Ecology

Kikuyu grass occurs naturally on the margins of forests on the highland plateaux of Ethiopia, Kenya and Central Africa (1950-3000 m) receiving 1000-1600 mm rainfall per annum. In Kenya at elevations of 2250 m, mean minimum and maximum temperatures range from 2-8 °C and 16-22 °C, respectively. Optimum growth for kikuyu grass is attained at 25/20 °C (day/night temperatures). The grass withstands short duration frosts, but tissue is killed below -2 °C. The present geographical distribution of the grass coincides with mesothermal humid climates, frequently where rain forest was the original vegetation. At higher latitudes (25°-35°) kikuyu grass naturalizes at sealevel. Kikuyu grass is sensitive to water supply; with increasing evaporative demand from 2-5 mm/day growth is reduced and ceases at a water potential of -100 kPa. Kikuyu grass is adapted to free-draining lateritic red loam soils of moderate or good fertility, often with low pH(H₂O) (< 5), and is tolerant of high Al and Mn levels.

Propagation and planting

Kikuyu grass establishes vegetatively and from seed. In vegetative propagation, rooted stolons can be dug or ploughed out mechanically, spread out and pressed in to the ground. Kikuyu grass seed (1-2 kg/ha) is either broadcast or drilled into a prepared seed-bed, usually with companion legumes. Once introduced to a locality, kikuyu grass usually spreads naturally because it offers strong competition with other species or because ingested seed is dispersed in dung by cattle.

Husbandry

After sowing, kikuyu grass forms a dominant sward within 3-9 months, aided by fertilizer application (N and P) and mowing to reduce weeds. It responds vigorously to N fertilizer, yielding 15-30 kg of DM per kg N applied during active growth under a cutting regime, although the response will vary with soil fertility. It responds to P and K if these are in short supply. To improve feeding value and to maintain legumes, the grass needs and responds to intensive grazing which can be either continuous or rotational. In arable land or irrigation channels it is a weed, and intensive control by hand or with herbicides is necessary.

Diseases and pests

In Australia, the major disease is "kikuyu yellows" caused by a soilborne pathogen Verrucalvus flavofaciens ; symptoms are patches of yellow, chlorotic leaves appearing in summer. Larvae of various moths or scarab beetles ( Rhopea magnicornies ) cause temporary damage to kikuyu grass pastures.

Harvesting

Being prostrate, kikuyu grass is suited to grazing, rather than for use as cut-and-carry forage. Repeated mowing to promote flowering is needed for seed production. Seed is harvested by removing all material to ground level, threshing and sieving.

Yield

Dry matter yields of kikuyu grass vary from 9-30 t/ha, indicating a potential for high carrying capacities and animal production by dairy or beef cattle. Stocking rates of 1.5-3.0 dairy cows/ha have been achieved in Australia with high rates of fertilizer, although productivity per head was moderate (9.0-16.6 kg milk/day).

Genetic resources

Although kikuyu grass shows variation in leaf morphology and flowering behaviour in the wild, original clonal introductions have resulted in uniform pastures in many countries. Germplasm collections are available in Australia (New South Wales Agriculture & Fisheries, Grafton) and ILCA (Ethiopia).

Breeding

Improvement in kikuyu disease resistance and cold tolerance has been mainly achieved by selection within natural variation of existing collections. Suitable breeding methods are not available for this species.

Prospects

Kikuyu pastures in South-East Asia are restricted to certain highland areas in New Guinea and the Philippines at present. Widespread soil erosion on steep, cultivated land and degraded catchments in South-East Asia, could be reduced if permanent pastures were established. Kikuyu grass could have an important role for land stabilization and improved animal nutrition in some of these situations.

Literature

• Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London. pp. 222-229.
• Edwards, D.C., 1937. Three ecotypes of Pennisetum clandestinum (Hochst.) kikuyu grass. Empire Journal of Experimental Agriculture 5: 371.
• Mears, P.T., 1970. Kikuyu (Pennisetum clandestinum) as a pasture grass - a review. Tropical Grasslands 4: 139-152.
• Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. pp. 73-76.
• Skerman, P.J. & Riveros, F., 1990. Tropical forage grasses. FAO, Rome. pp. 604-611.

Authors

P.T. Mears