Rice is the staple food of 18.6 million Sri Lankans and is the livelihood of more than 1.8 million farmers. More than 30 percent of the total labour force is directly or indirectly involved in the rice sector. The annual per capita consumption of rice was around 92 kg in 1998 and is dependent on the paddy production in the country and the price of imported wheat flour. In 1998 total production was 2.69 million mt of rough rice (paddy), which is about 96 percent of the national requirement. With the present population growth rate of 1.2 percent, slightly increasing per capita consumption, requirements for seed, and for wastage in handling, Sri Lanka needs about 3.1 million mt of paddy by the year 2005 (Annex 1). Hence, it is projected that the national average yield should increase to 4.1 t/ha to feed the population of Sri Lanka in 2005.1
In Sri Lanka, rice is grown under a wide range of physical environments such as different elevations, soils and hydrological regimes. There is a wide range of climatic and soil conditions in the country. The annual rainfall ranges from 600 mm in the arid areas to 6,000 mm in the very wet areas. Elevation ranges from mean sea level (MSL) to 2,575 m above MSL and the average temperature ranges from 30 °C at the MSL to 15 °C at the upper most elevations. Rice lands are distributed in almost all the above agro-ecological environments except for elevations above 1,200 m MSL. Hence, compared to many other rice growing countries, Sri Lanka grows rice under a wide range of environmental conditions.
Based on the total annual rainfall, Sri Lanka is broadly divided into three climatic zones:
|Dry Zone (DZ)||Rainfall < 1,500 mm|
|Intermediate Zone (IZ)||Rainfall 1,500 - 2,500 mm|
|Wet Zone (WZ)||Rainfall > 2,500 mm|
Similarly, the island is divided into three major elevation zones:
|Low Country (LC)||MSL 0 - 300 m|
|Mid Country (MC)||MSL 300 - 800 m|
|Up country (UC)||MSL 800 and above|
By combining the two parameters above (rainfall and elevation), seven major agro-ecological zones (AEZ) have been identified (LCDZ, LCIZ, LCWZ, MCIZ, MCWZ, UCIZ and UCWZ). These AEZ were further subdivided into 24 agro-ecological regions, considering the rainfall distribution, soil type and the landform. Rice is grown in all the agro-ecological regions except in WU1, WU2, WU3 and IU2. If water conditions are right, almost all kinds of soils could be used for rice cultivation. In Sri Lanka, the hydromorphic associates of almost all its great soil groups are used for rice cultivation.
The rice lands in Sri Lanka are further categorized either as irrigated (major and minor irrigation systems) or as rainfed and are cultivated in two distinct cultivation seasons. The major cultivation season (Maha) which is from late September to early March is fed with inter-monsoon rains and with the Northeast monsoon, which is well distributed in the Island. The minor cultivation season (Yala), which is from early April to early September, brings rain mostly to the Southwest region of Sri Lanka.
Dry sowing of paddy in aswedumised fields is known as kekulama in Sri Lanka. When dry sowing is done in highland under shifting cultivation it is called vee hena. In the past for kekulama, the fields were ploughed with a new country plough first to get a somewhat deeper tillage then kept for a few days and dry seeds were sown with the anticipation of rains soon. Having sown seeds again, farmers ploughed the land with an old worn out plough to cover the seeds. When the fields are wet the same operations are done but sprouted seeds are sown instead. In some paddy tracts and under some tanks certain sections were sown to kekulama and then when the tanks were full with rains other sections were sown having done the normal wetland land preparation which includes:
This combination of above cultural practices apparently has been adopted for centuries with the aim of controlling weeds. Weed menace is unavoidable because of depletion of soil fertility mainly caused by soil erosion inherent to wetland paddy cultivation. In depleted soil, weeds grow much more vigorously than paddy because the fertility level and other physical conditions are ideal for weeds. If and when other means of weed management are available most of the said practices can be got rid of. One of the main attempts of nava kekulama is to manage weeds with other innovations not requiring more water than for an ordinary highland crop. Main features of nava kekulama are as follows:
Minimal or zero tillage:
Observations in zero tillage shows patchy good results. Experiments were conducted on zero tillage in three different methods including Fukoka method modified to suit tropical conditions. Mulching the fields soon after sowing: This is the most striking innovation which has not been given any thought by scientists for many decades or even centuries. By mulching alone a yield increase of five to eight bushels or 100 to 160 Kg. per acre per season has been observed in Sri Lanka. The yield increase of the crop depends on the initial fertility level of the soil. Mulching completely checks the soil erosion. It is the main factor contributing to soil fertility. Adds organic matter substantially without much effort. Enhances and increases the soil microbes and particularly the earthworm population. Earthworms not only make the soil fertile but also pulverize the soil so that it paves way for zero tillage. Improves organic matter content of the soil season after season and as a result improves the water holding capacity enabling the crop to withstand short water stresses. When a mulch is applied to a thickness of about 7 to 8 cm (3 inches), complete weed control can be expected. Picking the sown seeds by birds is prevented. Though not scientifically proved, it appears that wet straw fixes nitrogen as in the rice roots. With a material like straw with very high C/N ratio when applied as mulch, yellowing of the crop due to nitrogen starvation is expected. This condition does not occur with nava kekulama but vigorous green growth is observed for about one month. One might wonder whether the paddy seeds would germinate and emerge through the thick mulch. The seeds , however, germinate almost 100 %.
Water Management: In nava kekulama all attempts in water management is to keep the soil at field capacity and avoid inundated situation except at the panicle initiation stage which falls around two months before the expected harvesting. This practice of water management results in an extensive root system growth.
Primordial protection: If drought occurs when the paddy crop is around four to five weeks old, the shoot dries but the underground stem and some roots with primodia remain intact ,hardened and dormant or in hibernated condition. As in the case of germinated dried seeds with rains or when there is sufficient water is available plant begins to grow. Dormant period gets added up to the age of the crop. I and II above brings forward a strong case to change cultural practices now adopted in order to save water and bring about a natural crop protection measure.
Ecological and environmental impact of nava kekulam:
Social and economic advantages of nava kekulam
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 determined 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 in 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 increases 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 shade 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 anywhere 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 midrib 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.