Axonopus affinis Chase

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Graminae

Common names

Mat grass (Queensland), compressum, Durrington grass (New South Wales), narrow-leaved carpet grass (Australia).

Description

A glabrous perennial, 25-75 cm high, having short rhizomes and slender to moderately stout arching stolons with short internodes. The grass often forms a dense mat. Leaf-blades are 5-20 cm long, 2-6 mm wide, flat or folded with a rounded or obtuse apex. The inflorescence consists of two to three slender, sessile, erect spikes, the upper pair approximate and the third a little remote. The spikes are straight and the rachis is 0.5 to 0.75 mm wide. The spikelets, each 2 mm long, are arranged in two neat rows. The fertile floret almost equals the spikelet in length, and is white to pale yellow in colour. It differs from A. compressus in having more slender culms and stolons, narrower leaves and shorter (2 mm) spikelets which are more obtuse; it has wavy or flexuous peduncles and fertile lemmas with glabrous apex or only a very reduced tuft of apical hairs (Barnard, 1969) (see Fig. 15.8).

Distribution

A. affinis is believed to have originated either in the southern United States, the West Indies or Central America. It is now found in the tropical and subtropical regions of America, Africa, Asia, Australia and the Pacific islands.

Season of growth

Summer growing, with peak growth in late summer.

Rainfall requirements

Usually in excess of 750 mm per annum.

Drought tolerance

It is more drought-resistant than A. compressus and will invade hilly, as well as flat, country.

Soil requirements

It prefers a sandy, moist soil and will flourish in sandy and heath soils too infertile for Paspalum dilatatum. It will respond however to more fertile conditions.

Ability to spread naturally

Under favourable conditions this grass will rapidly spread by stolons and rhizomes, and the abundance of light seed enables it to spread quickly also from seed spread by grazing animals.

Land preparation for establishment

It can be established on a well-prepared seed-bed or broadcast into ashes after a scrub burn.

Sowing methods

Usually broadcast on the surface and harrowed or rolled in.

Sowing depth and cover

Surface sowing with the minimum of cover.

Sowing time and rate

In the United States it is sown at 6-12 kg/ha from spring to midsummer.

Number of seeds per kg.

Approximately 2 860 000.

Tolerance to herbicides

Bromacil at 1.8 kg of an 800 g AI/kg product (e.g. Hyvar X) per 200 litres water plus 250 ml surfactant sprayed at a minimum of 450 litres water per hectare will control it (Tilley, 1977). 2,2-DPA at 4.8 kg/ha sufficiently restrained the growth of carpet grass to allow sod-seeding of white clover in Alabama, United States (Searcy & Patterson, 1961).

Seedling vigour

It has a very vigorous seedling stage.

Vigour of growth and growth rhythm

It has a short growing season, extended by early nitrogen application.

Response to defoliation

It stands heavy defoliation. Under high cutting height its yield is reduced.

Grazing management

It should be kept in the vegetative state by frequent grazing and periodically renovated and fertilized with nitrogen, especially in spring to prolong its feeding value.

Response to fire

It recovers quickly from fire.

Dry-matter and green-matter yields

Yields of fertilized carpet grass ranged from 812-5 197 kg/DM/ha per year in the south-eastern United States with nitrogen applications from 56-370 kg N/ha per year (Martin, 1975).

Suitability for hay and silage

It makes poor-quality hay, since when it is high enough to harvest it is low in nutritive value.

Value as a standover or deferred feed

In its mature state it is really only poor-quality roughage.

Toxicity

No toxicity has been reported with this grass.

Cultivars

No cultivars are recorded.

Diseases

No major diseases occur.

Main attributes

It grows on poor soil and covers the ground against erosion, and it tolerates overgrazing. It is considered a good horse feed, as horses eat the masses of seed-heads avoided by cattle (McLennan, 1936).

Main deficiencies

It has very low nutritive value, especially after seeding, low dry-matter yield and response to fertilizer, short growing season, poor root development and low animal production.

Optimum temperature for growth

Top growth was maximum at a temperature of 27-32°C with a day length of 15 hours.

Minimum temperature for growth

Temperatures below 12.8°C inhibited flowering (Lovvorn, 1945). In Australia it is found further south than A. compressus.

Frost tolerance

It has some degree of tolerance to frost.

Ability to compete with weeds

It dominates annual weeds in a pasture. It is often a weed itself.

Maximum germination and quality required for sale

60 percent germinable seeds, 97 percent purity (Queensland) germinated at 20-35°C with KNO3 moistening agent.

Pests

No major pests are evident.

Palatability

It is fairly palatable till flowering, after which its palatability declines.

Response to photoperiod

It flowers in all day lengths from eight to 16 hours, but seed production is greatest under 12- to 14-hour day lengths (Knight & Bennett, 1953).

Chemical analysis and digestibility

Its forage is generally of much poorer quality and lower feeding value than Paspalum dilatatum. Its copper levels are much lower than those of the latter. After seed set, the crude protein level in mat grass may fall as low as 4 or 5 percent. Grain or urea-molasses supplements need to be fed to lactating dairy cattle in this case, and phosphorus should be available.

Natural habitat

Subhumid and humid woodland and savannah.

Tolerance to flooding

It prefers moist-soil but does not withstand prolonged flooding or permanently swampy conditions very well, though better than Paspalum dilatatum.

Fertilizer requirements

It has a low fertility requirement but will respond to fertilizers, particularly nitrogen, but its efficiency of use of applied nitrogen is low compared with other pastures. Its shallow root system (96 percent of roots in the 0- 5 cm layer), lack of root response to fertilizer, and distribution, suit carpet grass to infertile, moist sandy soils. Apply 224 kg/ha superphosphate at sowing and annually (McLennan, 1936).

Compatibility with other grasses and legumes

It is a low-fertility grass; as soil fertility declines it can successfully invade Paspalum dilatatum pastures, as well as Cynodon dactylon lawns. Few legumes will grow with it to compete with its dense sod.

Genetics and reproduction

2n=80, 54 (Fedorov, 1974).

Seed production and harvesting

A. affinis is a prolific seeder and seed is shed easily. If seed were required it could be beaten off with revolving beaters on to a tray. It is harvested mechanically in Mississippi and Louisiana, United States.

Economics

It is a low-quality pasture which indicates declining fertility throughout the tropical world.

Animal production

Animal live-weight gains from carpet grass are low compared with other pasture species, and live-weight losses occur in winter. Live-weight gains from pure pasture alone have been 84-98 kg/ha per year unfertilized; with white clover and fertilized a peak of 693 kg/ha per year (Martin, 1975). When A. affinis replaces Paspalum dilatatum as a pasture butter production will drop 33 percent in northern New South Wales (McLennan, 1936).

Further reading

Barnard, 1969; Martin, 1975.

Value for erosion control

In the United States it is widely used to prevent erosion and stabilise road banks (Bennett, 1962).