Paspalum dilatatum Poir.

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Graminae

Common names

Paspalum (Australia), dallis grass (United States).

Description

A leafy, tufted perennial with clustered stems arising from shortly creeping rhizomes; culms to 1 m; inflorescence of 3-5 racemes; spikelets ovate, about 3 mm long, fringed with silky hairs (Henty, 1969). The racemes have spikelets overlapping in rows along one side of a flattened axis (Chippendall & Crook, 1976).

Distribution

Native to the humid subtropics of southern Brazil, Argentina and Uruguay; now widely distributed.

Season of growth

Spring and summer, declining at flowering in summer.

Altitude range

Sea-level to 2 000 m.

Rainfall requirements

It requires a minimum of about 750 mm of annual rainfall; does best in a rainfall of about 1 250 mm, and in irrigated pastures. Maximum recorded, 1 650 mm (Russell & Webb, 1976).

Drought tolerance

The underground root-stock gives it considerable drought tolerance once it is established.

Soil requirements

It grows best in heavy, moist, fertile, alluvial and basaltic clay soils.

Ability to spread naturally

It spreads readily by seed where conditions are suitable for germination.

Land preparation for establishment

A good, fine seed-bed prepared by ploughing, discing and harrowing gives best results. In favourable conditions a rough ploughing may suffice.

Sowing methods

It is generally drilled or broadcast as seed. It is often seeded into rice stubble in Texas and Louisiana (Bennett, 1973).

Sowing depth and cover

Surface sowing or drilling to a depth of 1-1.5 cm, and lightly covered is the usual practice.

Sowing time and rate

It is best sown just before the expected rainy season, at 9- 14 kg/ha, but it can be sown at any time from spring to late summer.

Number of seeds per kg.

500 000 to 750 000.

Seedling vigour

Good.

Vigour of growth and growth rhythm

It begins growth in the spring and grows vigorously in early summer. At Samford, Queensland (lat. 27°22'S) the growth rate declines rapidly in midsummer, is low in late autumn and dormant in winter (Shaw et al., 1965). It flowers throughout the growing period.

Response to defoliation

Paspalum will withstand heavy defoliation and, having an underground root-stock, it is protected from heavy grazing and trampling by livestock. Grazed no shorter than 5-7.6 cm it will produce up to three times the forage that it would if grazed lower (Bennett, 1973). Increasing frequency of defoliation reduces yields, but some recovery occurs with increasing application of nitrogen (Colman & Lazenby, 1970).

Grazing management

It should be kept grazed during the growing period to prevent if from flowering and becoming relatively unpalatable. This will also prevent ergot infection of the seed-head, which can cause poisoning. If cattle graze infected plants in the sphacelial stage, the sticky ergot clings to the face and legs of animals, assisting its spread and soiling the skin. As the paspalum sward ages it often becomes sod-bound and should be renovated periodically by ploughing, disc- harrowing or deep ripping. In some cases, a mole drainer will help to aerate and drain wet soils growing paspalum.

Response to fire

Paspalum pastures are seldom subject to fire, but, if burnt, they quickly recover from the root-stock when conditions are again favourable.

Dry-matter and green-matter yields

At Samford, Queensland, an annual yield of 15 000 kg dry matter was recorded by Davies (1970). In Fiji an average yield of 5 311 kg DM/ha with a crude protein content of 9.9 percent was obtained over a three-year period (Roberts, 1970a, b). In the United States yields from 1 230-12 000 kg/ha are obtained (Bennett, 1973).

Suitability for hay and silage

Paspalum is suitable for both purposes. It should be cut before flowering to obtain the best quality hay. Paspalum which has gone to seed has a low feed value. Paspalum made good silage, but the pH was about 4.8 and the concentration of volatile acids below 5 percent of the dry matter, while NH3-N accounted for nearly 20 percent of the nitrogen (Levitt et al., 1962, 1964, 1965).

Value as a standover or deferred feed

As the grass matures it declines markedly in feeding value, so it is best cured as hay or silage rather than left as standing material in the field.

Toxicity

The grass itself is not known to be toxic, but seed-heads parasitized by the ergot fungus Claviceps paspali can be toxic due to pyridine alkaloids in the sclerotia, which appear in late summer or autumn. Affected animals at first show excitement, distrust of people and a tendency to attack. Later they tremble, appear to lack muscular control, stagger and may fall. They recover in a few days if removed from infected areas in the early stages of excitement (Everist, 1974).

Seed yield

90-500 kg/ha. The seed remains viable for two years (Jones, 1973).

Cultivars

Bashaw and Forbes (1958) found three distinct cytological groups in the species: a yellow-anthered, erect type with pubescent spikelets and 40 chromosomes, in which the meiotic behaviour was regular and the mode of reproduction sexual; a semi-prostrate, purple-anthered strain with 40 chromosomes and extremely irregular meiotic behaviour, reproducing apomictically; and the common type with purple anthers and 50 chromosomes, reproducing apomictically. The second type has been recognized as a variety under the name of 'Prostrate' by the Georgia Coastal Main Experiment Station, United States. Two other varieties were released by the Louisiana Agricultural Experiment Station, United States, namely 'B-230' and 'B-430'. Both are alleged to have better seed production than the common type, and 'B-230' has a longer growing period. No varieties are registered in the United States nor on the OECD list for 1967 (Barnard, 1969).

Diseases

The main disease of paspalum is ergot, caused by Claviceps paspali. The disease first appears in the form of a dark, sticky exudate from each spikelet or "seed". This sticky mass, produced during the "sphacelia" stage, contains many tiny spores which spread the disease to clean seed-heads. This stage gives rise to the "sclerotia", a kind of dormant spore that lodges in the infected spikelets, replacing the ovaries and grain. These are round, yellowish-grey bodies, 3 mm across, dry and firm. In autumn they ripen and fall to the ground, remaining dormant until the following spring. These are toxic. Preventing the paspalum from seeding helps to control the disease (Everist, 1974). Anthracnose (Colletotrichum graminicola) and leaf blight (Helminthosporium microplus) also attack paspalum.

Main attributes

Its palatability, productivity, ability to stand heavy grazing and trampling. Its compatibility with white clover.

Main deficiencies

Its heavy seeding and ergot susceptibility, low productivity and tendency to become sod-bound. Its short grazing season has led to its replacement by Setaria spp.

Optimum temperature for growth

Adapted to the humid subtropics. 30°C is optimal for leaf growth (Mitchell, 1956), 27°C for tillering and 22.5°C for flowering (Bennett, 1959).#

Minimum temperature for growth

Seed production is inhibited at temperatures below 13°C (Knight, 1955). Mean temperature of coldest month, 2-10°C (Russell & Webb, 1976).

Frost tolerance

It is susceptible to frost but more tolerant than Rhodes grass. Its underground root-stock allows it to persist and recover from frost.

Latitudinal limits

About 28°N and 35°S (Russell & Webb, 1976).

Response to light

It does not grow well in shade.

Ability to compete with weeds

When fully established, paspalum competes well with broad-leaved weeds, but as fertility declines weedy grass species, e.g. Axonopus spp., invade.

Maximum germination and quality required for sale

60 percent germinable seed, 60 percent purity in Queensland. It is germinated at 20-35°C, moistened with KNO3 solution. Germination is increased by exposure to light.

Pests

On Queensland's Atherton Tableland it is attacked by root-destroying white grubs (Lepidiota caudata and Rhopaea paspali), which reduce pasture productivity (Quinlan & Edgley, 1975). The sugar cane borer (Diatraea saccharalis) sometimes attacks it (Bennett, 1973).

Palatability

Paspalum in the pre-flowering stage is very palatable, but when infected at flowering by ergot its palatability declines rapidly.

Response to photoperiod

It is generally unresponsive to photoperiod, but a day length of 14-16 hours is best for seed production.

Natural habitat

Moist grassland.

Tolerance to flooding

It is sensitive to flooding when actively growing, but is less so during its dormant period, when it tolerates inundation of up to one week's duration. Its density increased slightly under periodic 48-hour flooding (Squires & Myers, 1970).

Fertilizer requirements

Paspalum needs high fertility and responds to a basic complete fertilizer mixture and subsequent dressings of nitrogen. Adequate nitrogenous fertilizer will stimulate the competitive ability of paspalum over associated Axonopus spp., whereas lack of fertilizer gradually allows Axonopus spp. to dominate. Linear nitrogen responses occurred up to applications of 135 kg N/ha, with recoveries of 72-80 percent (Colman & Lazenby, 1970). Cassidy (1971) obtained substantial growth increases when nitrogen at 224 kg/ha was applied during early summer (October-November), and a large growth rate increase from 7.8 to 56 kg DM/ha per day when applied at the height of its growing season (November to January). In another case, 89 kg. N/ha were applied in April (early autumn) and increased dry-matter production from 39.2 to 54.9 kg/ha per day; in mid-May (late autumn) dry matter increased from 20.2 to 31.4 kg/ha per day. The use of strategic applications of nitrogen to paspalum can thus play an important role in extending the grazing season of this grass. The critical value for phosphorus expressed as a percentage of the dry matter at the immediate pre-flowering stage is 0.25.

Compatibility with other grasses and legumes

As fertility declines paspalum pastures can be invaded by Axonopus spp. In planted pasture mixtures it is often sown with temperate grasses and clovers which make maximum growth when paspalum is comparatively dormant. It becomes sod-bound, and clovers can be sod- seeded into it during the dormant period with adequate fertilizer. It forms a very productive pasture with white clover (Trifolium repens).

Genetics and reproduction

The chromosome number of the common type is 5x=50. It is an obligate apomict by apospory and pseudogamy (Barnard, 1969). Bashaw and Forbes (1958) list it at 2n=40 (sexual and apomictic) and 2n=50 (apomictic).

Seed production and harvesting

Paspalum seeds freely, but the seed ripens from the tip of the racemes downwards and shatters as soon as it is ripe. It is thus hard to harvest, and viability is often low. Seed production is also affected by ergot infection. A day length of 14-16 hours and high temperatures are best for seed production, which is inhibited by temperatures below 13°C (Knight, 1955). Seed is rather slow to establish, but will remain dormant in the ground for months awaiting satisfactory germination conditions (Whittet, 1965). Harvesting should begin when 60-80 percent of the seed-heads are a light brown colour (Bennett, 1973). For storage, dry the seed at 60°C to a moisture content of 7-10 percent.

Economics

Paspalum is one of the most important summer forage grasses, and was one of the earliest species adopted for improved pastures.

Animal production

In the Murrumbidgee Irrigation Area in Australia, P. dilatatum pastures can carry 25 sheep per hectare during the growing season. At Badgery's Creek near Sydney (mean temperature of the coldest month 11.5°C, hottest 23.5°C) by planned irrigation, fertilizer supply and adding winter-growing species by sod- seeding, unsupplemented Friesian cows consistently produced more than 10 000 litres of milk per hectare per year. The paspalum content ranged from less than 5 percent in winter to 70 percent in spring and summer (September to February); the pastures supported all the nutritional needs of 2.5 cows per hectare in winter and 5 cows per hectare in spring and summer (Crofts & Pearson, 1977). Squires and Myers (1970) showed that paspalum was better than other warm-season grasses (Cenchrus ciliaris, Eragrostis curvula, Panicum coloratum and Sorghum almum) under irrigation as a pasture for sheep at Deniliquin, New South Wales, Australia (35°30'S).À#

Further reading

Gardner, 1956; Whittet, 1965.

Dormancy

There is some post-harvest dormancy (Whittet, 1965).

Value for erosion control

Where paspalum is effectively established it exerts almost full erosion control. It is used to stabilize mine dumps in South Africa (Chippendall & Crook, 1976).

Tolerance to salinity

It has little tolerance to salinity.

Response to herbicides

To control paspalum in the young stage, use paraquat at 570 ml of a 200 g AI/litre product (e.g. Gramoxone) per 200 litres of water plus surfactant at 250 ml/200 litres water. Spray to the point of run-off. Mature plants can be sprayed with glyphosate at 2 litres of a 360 g AI/litre product (e.g. Round- up) per 200 litres of water in three applications, ten days apart (Tilley, 1977).