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Crop Establishment

Method of establishment of rice can be broadly divided into direct sowing of pre germinated or ungerminated seeds and transplanting of seedlings. The choice of the method of establishment depends on factors such as,

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 leveled 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.

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Last updated: February 27, 2007