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Graminae
Common names
Rice.
Description
An annual grass with erect culms 0.6-2 m tall usually with
four to five tillers. Inflorescence a loose terminal panicle of perfect
flowers; each panicle branch bearing a number of spikelets, each with a
single floret. Each flower is surrounded by a lemma and palea at the base
of which are two small glumes. The lemmas may be awnless or variously awned.
The rice grain enclosed by the lemma and palea (hull) varies in size, texture
and colour. Each panicle holds 100-150 seeds.
Distribution
Throughout the tropical world as a crop.
Season of growth
Summer.
Rainfall requirements
Rain-grown rice usually requires an annual rainfall in excess
of 1 500 mm. Most of the world's rice is grown under irrigation and water
is supplied as required. The amount may be in the vicinity of 7-9 million
litres per hectare.
Drought tolerance
It has little drought tolerance.
Soil requirements
Upland varieties need fairly good drainage but japonica varieties
need a heavy, relatively impervious soil. The pH is generally not important,
as rice has the capacity to neutralize the soil on which it is growing.
Sowing methods
The seed may be drilled into dry land or sown in nurseries
and the seedlings later transplanted into a wet paddy-field. Also, seed
may be pre-germinated and broadcast into the mud in the paddy-field.
Number of seeds per kg.
About 40 000.
Tolerance to herbicides
Rice tolerates the herbicides used to control its main grassy
weed pest, Echinochloa crus-galli (barnyard or water grass). It will tolerate
the use of 2,4-D amine at 1-1.5 kg AI/ha and 2,4,5-T amine at 1-1.5 kg
AI/ha at the late tillering stage before panicle initiation for the control
of broad-leaved weeds.
Dry-matter and green-matter
yields
Yields of paddy straw after harvest varies considerably. A
yield of 5 000-15 000 kg/ha may be expected.
Suitability for hay and
silage
Practically all the paddy straw from rice crops in the tropics
is conserved as hay for animal feeding and is usually stacked around poles
in the house compound. Medling, (1972) under high rainfall conditions (3
997 mm) at Gualaca, Panama, found that baling the straw with large roller
balers was effective and that the straw bales would stay in the field without
major deterioration, while grass hay (Hyparrhenia rufa and other grasses)
suffered serious deterioration.
Toxicity
Excess feeding of rice straw leads to toxicity because of high
oxalates, which will bind the calcium in the diet. This effect can be reduced
by soaking the straw in water or neutralizing it with a weak solution of
calcium carbonate or calcium hydroxide (Göhl, 1975).
Seed yield
Japonica varieties, 4 000-4 500 kg/ha; indica, 1 000-1 500
kg/ha of milled rice.
Cultivars
There are numerous cultivars, each suited to a particular ecological
niche.
Diseases
Numerous diseases occur, affecting the leaves for use as straw
for feeding animals. The more important ones are blast, caused by Piricularia
oryzae, leading to brown and shrivelled leaves; brown spot, caused by Cochliobolus
miyabeanus; and narrow brown leaf spot, caused by Cercospora oryzae.
Optimum temperature for
growth
A mean temperature above 21°C.
Frost tolerance
It will not stand frosts.
Maximum germination and
quality required for sale
70 percent germinable seeds, 98.8 percent purity in Queensland.
Pests
Army-worms and grasshoppers cause major leaf damage, and stem
borers affect the stalk.
Palatability
The hay is fairly palatable, but not nutritious enough for
maintenance.
Response to photoperiod
It flowers over short and medium day lengths (Evans, Wardlaw
& Williams, 1964).
Chemical analysis and
digestibility
Göhl (1975) records analyses of vegetative material.
Natural habitat
Swampy areas.
Tolerance to flooding
The japonica or paddy varieties are aquatic and grow in water
at various depths. Deep water varieties will grow in up to 6 m of water.
Upland or indica varieties are not adapted to flooding.
Fertilizer requirements
In paddy rice, land preparation for planting usually involves
some incorporation of organic matter, either from a previous grass/ legume
pasture, green manure crop or from plants cut and transported to the field.
A basic phosphorus and potash dressing may be required but nitrogen fertilization
is a main determinant of yield. Half the nitrogen may be applied at transplanting
with the remainder at ear initiation, and the application may be 150-250
kg/ha.
Genetics and reproduction
2n=24 (Fedorov, 1974). Some tetraploid (2n=48) exist, but the
diploid are more numerous.
Seed production and harvesting
The rice is either hand harvested and later threshed or mechanically
harvested with combines and hulled and cleaned.
Economics
Rice is one of the world's two major human food crops, the
other being wheat. Rice straw is retained for feeding draught animals in
most rice-producing countries in the tropics. Rice bran is fed to domestic
animals when not required for human consumption in dry years. Paddy straw
provides 80 percent of the organized roughage for India and a large part
of the roughage for animals in other rice-producing countries where draught
animals are used.
Animal production
The inclusion of urea and molasses improved the voluntary intake
of paddy straw from 1.5 to 2.1 kg/100 kg live weight and dry-matter intake
was 1.9-1.98 kg/100 kg live weight. Molasses-urea also increased digestibility
coefficients of crude fibre and crude protein. This supplement increased
body weight from 3.5 to 5.5 kg per head in 100 days. Paddy straw plus 1
percent urea and 18-20 percent molasses on a dry- matter basis is maintenance
(Singh & Kushwaha, 1974). Sunn hemp (Crotalaria juncea) hay, with 12.7
percent digestible crude protein and 65 percent total digestible nutrients,
provided maintenance for bullocks as a supplement to paddy straw in the
proportions of 1:3 and 1:2. The bullocks consumed 1.952.11 kg DM/50 kg
live weight (Ready & Murty, 1962).
Further reading
Chandraratna, 1963; Finlay, 1975.
Dormancy
The seeds of indica (upland) varieties have post-harvest dormancy
for up to three months, which can be broken by storage at 8°C under
very moist conditions immediately after harvest. The seeds of japonica
varieties have no dormancy period.
Tolerance to salinity
Its extensive root system not only loosens the soil and renders
it more permeable, to facilitate leaching, but also creates an acidic environment
which reduces pH values in alkaline soils to neutrality. The improved cultivars
'IR-8' 'IR-8-68' and 'Jaya' exhibit high tolerance to salinity as do the
tall indica cultivars 'Jhona 349', 'Damodor' and 'MCM' (Yadav, 1975).
Land preparation for planting
Upland rice and large-scale paddy cultivation where the seed
is drilled prior to flooding need a well-prepared seed-bed, as for wheat.
Paddy rice fields are usually ploughed and harrowed several times in the
wet state as a "mudding-up" operation which incorporates organic matter
and levels the land.
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