Trifolium semipilosum (PROSEA)
Trifolium semipilosum Fresen.
- Protologue: Flora 22: 52 (1839).
- Family: Leguminosae
- Chromosome number: 2n= 16
- Kenya white clover, Kenya clover (En).
Origin and geographic distribution
T. semipilosum occurs naturally in the humid and equatorial high altitude areas of Kenya, Uganda, Tanzania, Yemen and Ethiopia. Now it is cultivated elsewhere in the high altitude tropics and in the subtropics and sometimes it is naturalized locally.
Kenya white clover is mainly used for grazing ruminants, although it is also fed to pigs, chickens and ducks in Papua New Guinea.
The N concentration and digestibility of Kenya white clover leaves and stems are only slightly lower than white clover ( Trifolium repens L.) and higher than for almost all tropical legumes. Nitrogen concentrations range from 2-5% and P concentrations from 0.2-0.5%. Sodium percentages are often below 0.1%. There are 700-900 seeds/g.
A perennial herb, initially with a crown and taproot, with prostrate pilose stems radiating from this, which root at the nodes if in contact with moist soil. Leaf trifoliolate with pilose petiole much longer than the leaflets; leaflets cuneate-obovate to elliptical or orbicular, 0.4-2 cm × 0.4 -1.1 cm, glabrous above and pilose on the margins, midrib and usually on the lower half of the two lateral leaflets; petiole length varies with grazing pressure, from 2-20 cm. Inflorescence globose, 5-40 flowered, about 2 cm across; flowers white to pale pink; calyx 4-6 mm long, corolla 8-10 mm long. Pods oblongoid, 5-6 mm long with 2-6 seeds. Seed irregularly discoid, ca. 1.5 mm across, dull yellow, light brown or olive green to black.
The primary taproot usually only lives for 1-2 years and the prostrate stems then persist through continuing development of nodal roots.
Two varieties are distinguished:
- var. semipilosum (synonyms var. microphyllum Chiov. and var. kilimanjaricum Baker), with leaflets twice as long as broad and silky pilose underneath; pods pilose at least at apex.
- var. glabrescens Gillett, with leaflets about as long as broad, glabrescent underneath and glabrous pods.
Var. glabrescens naturally occurs in rather more humid areas than var. semipilosum , often in association with Pennisetum clandestinum Hochst. ex Chiov.
Cultivar "Safari" is described as being var. glabrescens .
Kenya white clover grows in the low altitude subtropics and elevated tropics (1000-3000 m). In its natural habitat in East Africa, annual rainfall is 550-1400 mm. Temperature requirements for growth are intermediate between those of most tropical legumes and white clover. It grows very well in Papua New Guinea at sites with a diurnal temperature range of 10-20 °C and at elevations as low as 1300 m, provided the soil is fertile. It can flower and set seed on the equator and also at latitudes in excess of 30°. In the subtropics, flowering occurs mainly during the cooler months. Plants of "Safari" can resist moderate frosting but top growth is killed by heavy frosts. It grows at pH range of 5-7.5 with greater tolerance of low Ca and high Al and Mn than white clover. It requires levels of available soil P > 20 mg/kg. It cannot tolerate very dry or waterlogged sites. In Papua New Guinea it grows very well in abandoned gardens and along roadsides.
Seed of "Safari" can be very hard-seeded, particularly when hand-harvested, and scarification is usually required. Seed should be inoculated with the appropriate rhizobium inoculum (e.g. CB782). Although it can be established by surface broadcasting into undisturbed swards, it is best established into a seed-bed. In the subtropics, it is best to sow in autumn when temperatures are falling yet soil moisture is often favourable. First year pastures often go through a period when growth is poor and leaves pucker and turn yellow, orange or red. The reasons for this are not clear, although sometimes ascribed to "rugose leaf curl", but the plants often or usually grow out of the condition. However, new plants arising from seedling recruitment in an established sward can also be affected.
The main disease described for "Safari" has been rugose leaf curl. This was initially ascribed to a virus and then to a Rickettsia -like organism. However, the symptoms on young stands may not necessarily be caused by that disease. Slugs can severely defoliate swards of "Safari" during sustained periods of wet weather, and weevils can damage swards by damaging or severing larger roots. Rotting of roots and stolons by Pythium spp. has been recorded during hot, moist conditions.
"Safari" combines well with a wide range of tussock and stoloniferous grasses in mixed pastures. Although "Safari" stems can grow upwards from the soil surface, "Safari" pastures should be well grazed, particularly when the grasses are growing actively. This ensures that stolons remain close to the ground and continue to develop new nodal roots to make up for the death of older roots. "Safari" swards can develop high reserves of soil seed, of over 10 000 seeds/m2, but recruitment of new seedlings is not reliable. "Safari" can spread through seed dispersed in faeces. Given levels of above 10-20% legume in the sward, "Safari" pastures can give high production of milk or liveweight gain.
Genetic resources and breeding
Germplasm collections are held by ATFGRC (CSIRO, Australia) and ILCA (Ethiopia). Attempts to cross "Safari" with T. repens have been unsuccessful. Some plants in Ethiopia and Kenya look like intermediates between T. semipilosum and T. burchellianum Ser., and var. glabrescens might be originally a natural hybrid of these 2 species.
It is highly unlikely that the zone of adaptation will be extended beyond the wetter subtropics and elevated tropics. Even within this zone, the main limitation of "Safari" is its unreliability of successful establishment and persistence, which is partly related to the condition described as rugose leaf curl. Although it is showing considerable promise in Papua New Guinea highlands, this unreliability will continue to limit its use in many areas unless the problems can be defined and solutions found.
- Cook, B.G., Mulder, J.C. & Powell, B., 1985. A survey to assess the influence of environment and management on frequency, vigour and chemical composition of Trifolium semipilosum in south eastern Queensland. Tropical Grasslands 19: 49-59.
- Gillett, J.B., 1971. Trifolieae. In: Milne-Redhead, E. & Polhill, R.M. (Editors): Flora of tropical East Africa. Leguminosae 4 - Papilionoideae 2. Crown Agents for Oversea Governments and Administrations, London. pp. 1027-1028.
- Jones, R.M. & Cook, B.G., 1981. Agronomy of Kenya white clover cultivar Safari. CSIRO, Australia, Division of Tropical Crops and Pastures. Information service. Sheet 41-3. 4pp.
- Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. pp. 163-164.
- Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 456-462.
- 't Mannetje, L., 1966. A punched card key to species of Trifolium L. in Africa, south of the Sahara, excluding Ethiopia. East African Agriculture and Forestry Journal 31: 261-270.
- Zohary, M. & Heller, D., 1984. The genus Trifolium. The Israel Academy of Sciences and Humanities, Ahva Printing Press, Jerusalem. pp. 176-177.
R.M. Jones & A.K. Benjamin