Distribution of the Method of Establishment of Rice in Sri Lanka
99/00 Maha 2000 Yala Broadcasting 79 % 85.8% Row seeding 0.3% 0.1% Transplanting in rows 3.3% 1.4% Transplanting (random) 15.7% 12.6%
Direct sowing
This method is becoming more popular among rice farmer
as it is economical than transplanting. The yields are also comparable with
transplanted rice if crop is properly managed. Direct seeding methods could
be divided into Wet seedling and Dry seeding. In Wet seeding pre-germinated
seeds are broadcasted into puddled and leveled field which are free from standing
water. At the time of puddling basal fertilizer mixture should be added. After
germination of seed, seedling desiccation due to water stress should be avoided
by intermittent wetting of the field. When the seedlings are of about 5 cm tall
(about a week after sowing) water is impounded to prevent germination of weeds
and desiccation of the seedlings. The stand establishment by this method vary
with the quality of land preparation, weed competition, water management and
the rainfall during the initial period after sowing. Row seeding of germinated
seeds could also be done but it is practiced in limited scale because of the
cost and the difficulty in obtaining implements. This method of sowing will
help controlling weeds, especially mechanical control and management of the
crop. This system will also help to maintain optimum density of seedlings whereas
random broadcasting often lead to low or high seedling density. Selection of
a suitable variety for direct seeding is important as there is a genotypic variability
in germination under submerged conditions. However, if field can be maintained
at or below field capacity for about 5 days, focus should be on varieties which
process good initial seedling vigour. Seedling vigour is mainly determined by
the seed quality and other cultural practices. Stand establishment is often
poor with direct seeding because of poor quality seed paddy, poor land preparation,
weed competition, poor water management, unfavourable environmental conditions
and physical damages. Therefore seed rates should be adjusted accordingly to
have the desired panicle number. Components of yield could be divided into panicle
number, seeds per panicle and seed weight. Panicle number is mostly determine
by the tillering ability of a variety which is a function of the number of seedlings
per unit area. In general a healthy crop of new improved rice variety, under
optimum condition, should bear about 350-400 panicles per sq., meter. Thus seed
rate should be adjusted accordingly to meet this requirement. A variety with
a seed weight of about 26-28g/1000 seeds have a seed rate of about 18 g/m2.
Seed rate decreases with seed weight thus, "Samba" type varieties have lesser
seed rates. Decreasing seed rate would increase unproductive tillering. Increasing
seed rate would also increase density, which increases unhealthy seedlings with
small panicles due to competition for resources, and increase susceptibility
to pest and diseases. Seeds can also be sown as ungerminated dry seeds in Kakulan
or Manawari sowing. In this method dry seeds are sown to dry soil either in
rows or in random. Seed rate generally vary with the severity of the environment
and the type of physical damages to the seeds. Depending on the level of weed
infestation in dry seeded rice the seed rate also varies from 150 kg/ha to 300
kg/ha. However if conditions for rice seed germination and subsequent operations
are favourable the seed rate for dry seeding could be reduced.
Transplanting
The extent of transplanted rice is decreasing due to
the scarcity of labour and other resources and the decrease cultivation of 4-4
1/2 month rice varieties. Transplanting will also decrease rice plants ability
to withstand moisture stress. Transplanting is generally recommended for 4 -
4 1/2 month varieties and if 3 month variety is transplanted it should be planted
with young (12-14 days old) seedlings. Transplanting is also recommended when
land preparation is not up to the standard and water management is poor. It
has been reported that transplanting increase the yield of long age varieties
when compared with broadcasting because transplanting reduces the excessive
build up of vegetative biomass due to transplanting shock. In transplanted rice,
spacing between hills vary with the age of the variety. A spacing of 20 x 20
cm2 and 20x15 cm2 is recommended for a long age (4-4 1/2 month) and short age
(3-3 1/2 month) varieties. A hill should be planted with 2-4 healthy seedlings.
If random transplanting is practiced hill density of about 25 m-2 for 4-4 1/2
month varieties and 30-35 m-2 for 3-3 1/2 month varieties is optimum. For transplanted
rice seedling age is a major factor in determining yield. Transplanting shock,
which is the set back of growth due to uprooting and replanting of seedling,
increases with the increase age of seedling and with decrease age of the variety.
In general the effect of transplanting on yield increases with decreasing age.
Seedling age (in calendar days) also vary with the environmental condition and
the type of nursery. The physical and bio-chemical factors would set a minimum
and maximum age for a particular nursery. Minimum age of a seedling for transplanting
would be about 12-14 days. For a three month age crop seedling age should not
increased beyond 15 days while for a 4 month crop it is about 21 days. Seedling
age of a dapog nursery should not exceed 14 days.
Nursery Systems
Raising seedlings for transplanting could be done in
either wet bed, dapog or dry bed methods. For mechanical transplanting seedling
boxes could be used. The choice of a particular nursery system depends on the
availability of water labour, land and agricultural implements.
Wet-Bed Method
Wet seed bed nursery is mainly used in areas where water
is adequate for nursery establishment. before sowing of germinated seeds soil
is thoroughly puddled and levelled and construct drainage canals between seed
beds for proper removal of water. Addition of organic manure (decomposed) and
small amount of inorganic fertilizer as basal dressing will increase easiness
of uprooting of seedlings and seedling vigour. Total seed bed area is about
1/10 of the area to be transplanted and requires about 100 kg of seed paddy
per ha. Seed rate should be adjusted for small grain varieties. Nursery site
should be without shade and with adequate irrigation and drainage facilities.
Quality rice seeds should be soaked in clean water for a minimum period of 24
hrs. and incubate in a warm dry place for about 48 hrs. Sprouted seed should
then be broadcasted uniformly on the nursery bed. Before seeding the nursery
should be drained completely. There after nursery should be maintained in moist
condition for about 5 days. Once the seedlings are established, the nursery
is impounded with water and raise the level gradually. The best stage of transplanting
seedling is about 15-21 days. Nursery should be free from weeds, any pest or
disease incidence and nutrient deficiencies. If such conditions occur it must
be treated at the nursery level.
Dry-bed method
This system of nurseries are prepared in dry
soil conditions. Seed beds of convenient dimensions are prepared by raising
the soil to a height of about 5-10 cm. A this layer of half burnt paddy husk
could be distributed on the nursery bed mainly to facilitate uprooting. In this
method dry or in just sprouted seeds are sown in rows, which are about 10cm
apart to the dry nursery bed. Sowing of seeds could also be done as random but
random sowing should be discouraged as the weed control is difficult. The site
should be free of shaded and with adequate irrigation facilities. Nursery area
should be about 1/10 of area to be transplanted. Seed rate should be higher
than for wet-bed (about 150 kg/ha) as the germination could be lower. Uprooting
of seedlings should be done between 15 - 21 days after germination. Nursery
should be maintain without any moisture stress. A basal fertilizer mixture could
be applied and incorporated between rows if the soil nutrient supply is low.
The advantage of this method is that seedlings are short and strong, has longer
root system than wet bed and can be raised even during heavy rains which is
not possible with wet bed. However roots may get damaged during pulling. Seedlings
of upland nurseries may also get infected with blast and are more prone to pests
such as rodents etc.
Dapog method
Dapog nurseries could be located any where on a flat
surface. However, if low land paddy field is used, water supply/control should
be very reliable. Area needed is about 10 m2/ha of the transplantable land which
is much smaller than conventional nurseries. Seed rate is about 125 kg/ha. Seed
bed should be levelled and make the centre slightly higher than the edges to
permit water to drain off the surface. Cover the surface with either banana
leaves with the mid rib removed, poly ethylene sheets or any flexible material
to prevent seedling roots penetrating to the bottom soil layer. Cemented floors
can also be used for this purpose. Cover the seed bed with about 1/4" layer
burnt paddy husk or compost. Sow pre-germinated seeds uniformly on the seed
bed to a thickness of 2-3 seeds. Splash the germinating seeds with water and
press down by hand or with a wooden flat board in the morning and afternoon
up to 3-4 days to prevent uneven growth. Too much watering should be prevented.
More frequent irrigation is necessary if seed were sown with out the bedding.
The nursery should be transplanted in 12-14 days after germination of seeds.
The advantage of the "dapog" over wet/dry bed nursery is that less area is needed
and the cost of uprooting of seedling is minimal. However since the seedlings
are small transplanting is difficult. Very young seedlings from dapog nurseries
are subjected to less transplanting shock than of other nurseries, thus these
seedlings are more suitable for short aged varieties. Other disadvantage of
dapog seedling was the field should be very well levelled and free of water
since the seedlings are very short. For mechanical transplanting, nurseries
should be about 1.2m wide (may vary with the type of transplanter). A sheet
of polythene is place on the levelled nursery bed and a compost layer to a height
of 1.5 - 2cm is placed on it. Sprouted seeds are then sown to a density of 700-1000
g/m2. Irrigation should be done to prevent water stress. Seedlings are ready
for transplanting after 14 days.