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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).
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