Chloris gayana Kunth

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Graminae

Common names

Rhodes grass (Australia, United States, Africa), pasto Rhodes (Peru).

Description

A glabrous, usually stoloniferous perennial up to 90 cm high, but very variable. Inflorescence up to 15 spikes, occasionally in two whorls, but usually one. Its roots descend to 4.7 m; 47 m of roots occur in the first 30 cm3 of soil, but they are sparse beyond 2.4 m (Hosegood, 1963).

Distribution

Native to Africa, introduced to the United States in 1902 and now widely grown in tropical countries.

Season of growth

Spring and summer.

Altitude range

600-2 000 m in the equatorial zone, lower to the north and south (Bogdan, 1969); sea-level to 500 m in Queensland.

Rainfall requirements

It grows best in the 600-750 mm rainfall area and Russell and Webb (1976) gave its range as 691-1 597 mm. It is widely used in irrigated pastures in Israel and the United States.

Drought tolerance

Good. Rhodes grass roots can extract water to a depth of 4.25 m.

Soil requirements

It grows on a wide range of soils, but may have some establishment problems on acid soils. It prefers loose-textured loams of volcanic origin.

Ability to spread naturally

Excellent. It produces stolons which creep over the ground, rooting at the nodes, and also produces abundant seed to give rise to new plants.

Land preparation for establishment

The better the seed-bed preparation the better the establishment, although a rough ploughing will help provide some plants from which to slowly build a sward. In Australia most seed is aerially sown into ashes left after a scrub burn.

Sowing methods

Aerial sowing into ashes one week after a fire is usual. Drilling seed through a modified seed drill mixed with sawdust and sown through the fertilizer box with the delivery chutes removed is another method. Seed can also be undersown in maize, thus giving good grazing after the maize is harvested.

Sowing depth and cover

It is sown on the surface, or no deeper than 2 cm, and covered by rolling or with a bush or a light metal harrow. Mulching after sowing with up to 5 000 kg/ha of hay has significantly increased herbage production in Zimbabwe (Smith, 1966).

Sowing time and rate

It should be sown into ashes as soon as the ashes have cooled and just ahead of the normal wet season. Severe erosion of ashes and loss of seed will result if a storm occurs over sloping sown land before the seedlings stabilize the soil. Seeding rate is 1-4 kg/ha.

Number of seeds per kg.

7 250 000 to 9 500 000 most cultivars 4 250 000 for cv. Katambora.

Seed treatment before planting

Treat the seed with lindane dust, 20 percent dust at 1 kg per 80 kg of seed, if seed-harvesting ants are prevalent.

Tolerance to herbicides

It can be killed by cultivation or a heavy spraying with paraquat at 570 ml of a 200 g AI/l product (e.g. Gramoxone) per 200 l water plus surfactant at 250 ml/200 l water. Spray until the solution runs off the leaves (Tilley, 1977). Pre-emergence treatment with atrazine at 1 and 4 kg/ha severely affected emergence of Chloris gayana and the 4 kg/ha treatment also adversely affected survival after emergence on Mywybilla clay on the Darling Downs, Queensland (Scateni, 1978).

Seedling vigour

Excellentbetter than Makarikari grass (Lloyd, 1970).

Vigour of growth and growth rhythm

Growth commences early in the spring. A newly sown field will be ready to graze four to six months after planting and reaches its highest production in the second year. Feeding value is low at flowering.

Response to defoliation

Rhodes grass stands a good deal of defoliation, but in Israel, Dovrat and Cohen (1970) showed that in irrigated and fertilized fields, dry-matter production was some 50 percent higher at 28-day cutting intervals than at 14-day intervals.

Grazing management

It should be allowed to establish and then grazed to prevent flowering, as the nutritive value declines rapidly toward maturity. Fertilizer nitrogen should be added as necessary, or farmyard manure applied.

Response to fire

Rhodes grass usually recovers well after a fire.

Dry-matter and green-matter yields

In Zambia, Rhodes grass alone yielded 58 000 kg DM/ha. Under irrigation in Texas, a yield of air-dried herbage of 15 775 kg/ha was recorded, cv. Callide yielded 6 084 kg/ha cut at 50 days, 11 350 kg at 90 days, 11 817 kg at 153 days and 14 157 kg at 188 days. The leaf percentages were 52, 28, 30 and 20 percent respectively and nitrogen in the dry matter 1.4, 0.78, 0.52 and 0.50 percent. In south-west Australia, a yield of 23 639 kg/ha was obtained from an irrigated Rhodes grass pasture treated with three dressings of fertilizer at eight-week intervals during the summer (November to April), each dressing providing 56, 22 and 45 kg/ha of nitrogen, phosphorus and potassium, respectively (Roberts & Carbon, 1969).

Suitability for hay and silage

It makes quite good hay if cut just as it begins to flower or a little earlier. Old stands give low-quality hay. Silage has been made successfully in Nigeria, Zambia and northern Australia, but generally it does not give satisfactory silage (Catchpoole, 1965).

Value as a standover or deferred feed

It can be used as low-quality roughage in conjunction with urea-molasses licks.

Toxicity

No toxicity has been recorded in Australia. Ndyanabo (1974) recorded 0.44 percent total oxalic acid in the dry matter, but no toxicity in India.

Seed yield

100-650 kg/ha.

Cultivars

  • 'Giant Rhodes Grass' 

robust with thick stems, long awns (6-9 mm) and a long tuft of hairs at the awn base. Drought resistant and productive. In Kenya it is known as 'Mpwapwa', in Tanzania as 'Kongwa', and in Australia as cv. Callide. It is a tetraploid. It flowers from January to May in Queensland.

  • 'Katambora' 

originating from the banks of the Zambesi River, Zimbabwe, it is leafy, dense- growing and a good seed producer. It suppresses nematodes in soil. It is a diploid and flowers from January to May in Queensland.

  • 'Mbarara' 

from Uganda. Somewhat stemmy, very productive, and gives the highest seed yield and has high seedling vigour.

  • 'Pioneer' 

the first Rhodes grass introduced to Australia. It is early flowering and hence of lower nutritive value. It flowers from November to May in Queensland.

  • 'Rongai' 

not a cultivar but a regional group of types in the Rongai area near Nakuru, Kenya. Drought-resistant and stemmy.

  • 'Nzoia' 

of African origin. Very leafy and has good seed yields but is susceptible to Helminthosporium infection and hence has low persistence.

  • 'Samford' 

introduced to Australia as CPI 16144 in 1952 from Musaia, Sierra Leone. A tetraploid (2n=40) with vigorous stolon development, it flowers late in Australia (April-May), is less frost-tolerant than 'Pioneer' and responds well to nitrogen. Its seed production is good and its palatability outstanding, even in the mature dry state (Barnard, 1972).

  • 'Pokot' 

a single plant selection from the Pokot district in Kenya. Leafy and vigorous, high yielding and late-flowering.

  • 'Masaba' 

first introduced into Kenya as 'Endebess' but later renamed 'Masaba', it is leafy and productive but seed production is affected by smut.

  • 'Karpedo' 

suited to the drier areas of Kenya.

Diseases

The cultivar Nzoia is susceptible to Helminthosporium and cv. Masaba is affected by a smut.

Main attributes

Its wide adaptability, ease of establishment, persistence and early nutritive value.

Main deficiencies

The short season of nutritive peak in many cultivars.

Optimum temperature for growth

Ivory (1976) recorded 30/26C to 40/29C day/night temperatures, Russell and Webb (1976) suggested a range of 16.9 to 22.3C, and Bogdan (1969) suggested 35C. Ludlow (1970b) found growth at 30C was 5.85 times greater than at 20C for cv. Samford.Jm 

Minimum temperature for growth

Ivory (1976) determined the critical mean temperature for growth as 8C. Russell and Webb (1976) gave the mean temperature for the coldest month for Rhodes grass at 2.6 to 12.4C. In the USSR minimum temperatures of-10C and in Texas, United States, of -9.4C have been recorded, but there is usually no growth below 0C. Ivory (1976) recorded -2.6 to -3.5C.mancy

Frost tolerance

It can survive sub-zero temperatures. In Uruguay it survived the intense and repeated frost of 1942 (Bogdan, 1969). Plants usually survive and grow the next season. On the Darling Downs, Queensland, Australia, it was one of the most frost-tolerant grass species during its first winter, with cv. Pioneer having 97 percent survival (Jones, 1969).

Latitudinal limits

A range of 18-33.4N and S with a mean of 25.7 (Russell & Webb, 1976).

Response to light

It does not grow well in shade.

Ability to compete with weeds

Rhodes grass is of prime importance in pasture mixtures for the brigalow (Acacia harpophylla) scrub soils in Queensland because of its vigorous early growth after the scrub has been burnt. Rhodes grass seed sown in the ashes helps suppress sucker regrowth unless suckers are well established before the Rhodes grass, in which case it cannot compete.

Maximum germination and quality required for sale

60 percent germinable seeds and 50 percent purity in Queensland. Germinate at 20-30C moistened with water. Germination is increased by exposure to light.

Pests

In Uganda thrips have damaged Rhodes grass seed.

Palatability

Young growth is very palatable, but after the plants have seeded they are less attractive.

Response to photoperiod

Optimum day-lengths are ten to 13 hours (Bogdan, 1969).

Chemical analysis and digestibility

In Rhodes grass the contents of organic compounds usually vary as follows: crude protein 4-13 percent, crude fibre 30-40 percent, ether extract 0.8-1.5 percent, nitrogen-free extract 42-48 percent (Bogdan, 1969). In Australia crude protein increased from 6.3 percent unfertilized to 9.5-9.8 percent when fertilized with 440 kg N/ha. Sodium chloride content may be high. Digestibility is usually 40-60 percent of the dry matter. Ghl (1975) recorded seven sets of analyses.

Natural habitat

Open woodland and grassland on a wide range of soils.

Tolerance to flooding

It tolerates seasonal waterlogging, but is killed by root submergence over 30 cm (Colman & Wilson, 1960).

Fertilizer requirements

Rhodes grass rarely gives a response to potash, gives an increased response to phosphorus in some areas and usually a spectacular linear response to nitrogen in the presence of adequate phosphorus and potassium, both in yield and in crude protein content. Split applications after each cut or after grazing cycles are better than one basic application with the usual rate of 275-400 kg/ha. The critical value for phosphorus as a percentage of the dry matter at the immediate pre-flowering stage is 0.23.

Compatibility with other grasses and legumes

Rhodes grass does grow with legumes, though experiences have been erratic. In Zambia, when grown with Stylosanthes guianensis, yields were increased by about 20 percent and with Neonotonia wightii the increase was nearly 100 percent. In Kenya Medicago sativa and Trifolium semipilosum also stimulated yields (Bogdan, 1969). In Australia there has been a tendency to grow Rhodes grass and Medicago sativa separately but Christian and Shaw (1952) showed that M. sativa at two to four plants per m2 enhanced Rhodes grass production on a black clay soil.

Genetics and reproduction

2n=20, 30, 40 (Fedorov, 1974). The diploids (2n=20) include cvs. Pioneer and Katambora and the tetraploids (2n=40) include cvs. Callide and Samford. Breeding and selection aim at plants that are leafier and late flowering. Rhodes grass is cross-pollinating.

Seed production and harvesting

Rhodes grass seed matures 23-25 days after flowering. It is a short-day plant and may flower over a long period making seed harvesting difficult and also reducing its nutritive value. A harvesting cycle of 60-70 days gives seed of better viability and spikelets with a higher caryopsis content (Humphreys, 1973). In cv. Mbarara anthesis is completed in three weeks. Seed is harvested with a combine with a threshing drum operating at 1 100-1 400 rpm and the blast reduced to prevent loss of seed. Harvest ten to 14 days after "smoking" (pollination) has ceased. The crop can also be cut with a reaper and binder a little earlier and the seed cured in the field before threshing, or the heads stripped off with a stripper harvester. The seed must be subsequently cleaned. Hand picking is satisfactory for small areas, and this seed needs minimal cleaning. The seed should be stored carefully. Its viability lasts for up to two years with mature seed (Jones, 1973) but rarely past the first year for immature seed. Pure seed plots should be isolated by 30- 60 m.

Economics

Rhodes grass has been used as a short-term pasture ley in East Africa, the United States and Australia where it restores soil structure and provides organic matter.

Animal production

In Kenya, live-weight gains in cattle were 382 kg/ha in the first year of Rhodes grass growth, 228 kg/ha in the second, and 167 kg/ha in the third. In Zimbabwe, Rhodes grass fertilized with 220 kg/ha superphosphate + 440 kg/ha ammonium sulphate supported five steers per hectare for four months of peak growth in summer while they gained 117 kg/head, or 234 kg/ha. When only 220 kg/ha of sulphate of ammonia was used, the stocking rate had to be reduced to 2.5 steers/ha for the same level of live-weight gain (Bogdan, 1969). In Zimbabwe, Rhodes grass fertilized with 270 kg and 38 kg P/ha gave live-weight gains of 230 kg/ha from a stocking rate of 12.4 heifers per hectare (Rodel, 1970).

Further reading

Bogdan, 1969.

Value for erosion control

It effectively controls erosion when well established. It is rather tall and needs management by light grazing or hay production. Cv. Katambora establishes and covers rapidly and persists well even at low fertility.

Tolerance to salinity

Excellent. A "salt-pan" strain comes from the salt-pan near Hammanskraal, Pretoria, where it flourishes on the bottom of the pan, in granite soil impregnated with brine (Chippendall, 1955). In Italy it grows on land previously under saline water, and it grows on saline soils in Mississippi, United States. It is tolerant to CaCl2 and NaSO4, less so to NaNO3 and NaCl, and sensitive to MgCl2 (Bogdan, 1969). In the Sudan C. gayana seed germinated in soil containing 0.4M NaCl (Abd el-Rahman & El-Monayeri, 1967).