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Review of rice production methods has shown that practices range from very primitive to highly mechanized (De Datta, 1981; Luh, 1980; Yoshida, 1981). Tractors and two-wheeled power tillers are the most important agricultural machines used for rice production (Barker, Herdt and Rose, 1985). In 1980 the number of power tillers used per 1 000 ha was from 0.1 to 26 in tropical Asia, 56 in China, 73 in Taiwan (province of China), 198 in the Republic of Korea and 1158 in Japan. In Asia, animals (buffalo and water buffalo, carabao) are still used for ploughing and harrowing. Land preparation may be carried out while the soil is dry or wet, depending on the water supply. For irrigated rice, the soil is prepared wet or puddled in Asia, but puddling is not generally practiced in America, Europe and Africa. In areas without a hard pan, where animals and tractors sink in the mud, the soil is prepared with hand hoes. Regardless of whether the land is prepared wet or dry, the water is always held on the lowland fields by bunds.
Most irrigated rice is transplanted, although direct seeding is becoming more extensive. The seeds are pregerminated and grown in wet seed-beds for 9 to 14, 20 to 25 or 40 to 50 days after sowing and are then transplanted either by hand or by mechanical transplanters. The number of seedlings per hill may vary from one to eight. Direct seeding is done by broadcasting the pregerminated grain by hand in Asia or by water-seeding by airplane in the United States and Australia. The seeds may also be machine-drilled in puddled soil or drill-seeded into dry soil. Deep-water rice is commonly dryseeded, but it is occasionally transplanted or double transplanted.
Ideally, water is maintained in the rice field to suppress weed growth during the growing season. Hand weeding and mechanical or rotary weeders are popular. Herbicides are also economical and effective. Fertilization is normally practiced for increased yield, particularly with the modern, semi-dwarf or high-yielding varieties which respond well to fertilizer without lodging. Both inorganic and organic fertilizers are used, including green manures such as the leguminous shrub Sesbania spp. and the water plants Azolla and Anabaena spp. Modern rice varieties increase in grain yield by 6 kg per kg of applied fertilizer in the wet season and by 9 kg per kg of applied fertilizer in the dry season. Total fertilizer nutrients range from 10 to 100 kg/ha in tropical Asia and from 200 to 350 kg/ha in Japan, Taiwan and the Republic of Korea (Barker, Herdt and Rose, 1985).
Other rice ecosystems
Rain-fed lowland rice is grown on puddled soil in fields bounded by dykes that can pond water to depths of 0 to 25 cm (shallow) and 25 to 50 cm (medium), depths seldom exceeded in such areas (Huke and Huke, 1990). The irrigation water is not received from river diversions, storage reservoirs or deep wells, but from rainfall or runoff from a local catchment area. The prevailing climatic and soil conditions in shallow rain-fed rice areas are extremely variable. In deep-water (50 to 100 cm) rain-fed lowland rice, modern semi-dwarf varieties cannot be used. Fertilizer use is low, stand establishment difficult and pest control almost impossible, and yields are poor. Rain-fed lowland rice is next to irrigated rice in importance in terms of harvested area and production of rice (Table 5).
Upland rice is grown in fields that are not bunded but are prepared and seeded under dry conditions and depend on rainfall for moisture (Huke and Huke, 1990). In Brazil, a major part of the rice crop is upland. In India and throughout Southeast Asia, upland cultivation is common along river banks as waters recede at the end of the rainy season. Soils are commonly heavy and residual moisture alone sustains growth. Upland rice farming ranges from shifting cultivation of forested hilly or mountainous areas that are cleared and burned to large-scale mechanized operations. Between these two extremes is farming of sloping hill regions that are subject to serious erosion and frequent drought, by hundreds of thousands of the poorest of rice farmers. The environmental damage here is very serious. In South and Southeast Asia some 13 percent of the total rice area is upland, but in some countries in Africa and Latin America upland rice exceeds 50 percent of the national total rice area. Yields are lowest in upland rice (Table 5).
TABLE 5 - Harvested area, yield and rough rice production in 37 major rice" producing developing countries, by ecosystem, 1985
|(million ha)||(%)||(million t)||(%)|
a Weighted average. Source: IRRI, 1989.
In deep-water rice, water depth is at least 1 m during a significant portion of the growing season. In large parts of Bangladesh as well as in portions of the Mekong and the Chao Praya Deltas, water depth may exceed 5 m, but it is normally between 1 and 3 m in other regions (Huke and Huke, 1990). Where water rises rapidly after the start of the monsoon rains, rice is commonly broadcast in unpuddled fields that are seldom bounded by dykes of any sort. The varieties planted are tall and leafy, with few tillers. They are photoperiod sensitive and mature only after the rainy season. They can elongate and float as the water level rises. Major dyking and flood control projects in the last two decades have upgraded many former deep-water rice areas into the rain-fed or irrigated category in Bangladesh, India, Thailand and southern Viet Nam.
Tropical rice is usually harvested at 20 percent or more moisture about 30 days after 50 percent flowering, when grains will provide optimum total and head rice yields. Moisture content at harvest is lower during the dry season than in the wet season because of sun-drying while the grains are in the intact plant. The actual period of dry-matter production is no more than 14 to 18 days, after which the grain undergoes drying.
Harvesting is carried out by cutting the stem, sun-drying and then threshing by hand by beating the rice heads on a slotted bamboo platform, by having animals or people tread on the crop or by the use of mechanical threshers. Combine harvesters are used in large areas such as the Muda estate in Malaysia and in the United States, Australia, Europe and Latin America.
Sun-drying to 14 percent moisture is a common practice but is unreliable during the wet season. Many mechanical dryers have been designed but have not been popular with farmers and processors. After drying, the rough rice is winnowed to remove the chaff using either a hand winnower or a manually operated wooden winnower.
More labour may be used by Asian farmers growing modern varieties than by those growing traditional varieties (Barker, Herdt & Rose, 1985). The contribution of family labour and hired labour is quite variable with location.
The various steps in rice cultivation include seed selection, seed-bed and land preparation, transplanting, weeding, fertilizing, pest management, harvesting, threshing, drying and marketing. Huke and Huke ( 1990) estimated that the labour requirements for one hectare of low-intensity rice production relying on rainfall for water and using improved IR36 seed and 50 kg of urea fertilizer are about 84 person-days and 14 animal-days to yield 2.5 tonnes of rough rice. In obtaining the 2.5 tonne yield, harvesting with a sickle and hand threshing against a log will consume at least 22 person-days. By contrast, labour input in high-technology California rice production of about 350 ha is 40 person-days (Herds, 1986).
Huke and Huke (1990) calculated the energy efficiency of low-intensity rice production at a specific site in the Philippines to be 12 calories per calorie expended. Under medium and high inputs, output ratios were 7 to 8 calories per calorie expended.
While women make up 25 to 70 percent of the labour in rice farming systems in Asia, their role has not been recognized until recently and their needs have remained unaddressed in technology development (Feldstein and Poats, 1990). They participate in rice and rice-related production, marketing and processing activities. It is now widely appreciated that women are often active in agricultural production and that they, as well as men, are potential users and beneficiaries of new technology. Gender analysis is now integrated into research projects and priority is given to technologies that reduce the burden of rural women without displacing their income-generating capacities. These technologies include integrated pest management, seed management and post-harvest rice utilization and processing (Unnevehr and Stanford, 1985).
The total cost of producing one tonne of rough rice in 1987-89 is compared for irrigated upland and rain-fed rice in Table 6. Total cost per hectare and grain yield were highest for irrigated rice and lowest for upland rice.
In the 1950s, growth in rice production in most Asian countries was due to expansion of the area planted, but in the 1960s and 1970s yield increase was more important (Barker, Herdt and Rose, 1985). Contributing factors were the introduction of semi-dwarf varieties and higher fertilizer inputs.
The semi-dwarf varieties developed at the International Rice Research Institute (IRRI) have a plant type that contrasts with that of the tall, traditional, photoperiod-sensitive varieties. They have erect leaves, are heavy tillering and have low photoperiod sensitivity. Their plant architecture allows them to absorb nutrients without lodging and allows sunlight to penetrate the leaf canopy. Growth duration is shorter in the modern varieties and is close to 100 days from seeding, which allow three crops per year. At low input levels, they yield comparably to traditional varieties. However, in all cases, modern varieties outperform traditional varieties, given additional inputs of energy, insecticides and fertilizers.
TABLE 6 - Cost of producing one tonne of rough rice, 1987-89 (US$)
|Korea, Republic of||939||-||-|
Source: FAO. 1991.
By 1981-84, modern varieties covered 13 percent of the total rice area in Thailand, 34 percent in the Republic of Korea, 25 percent in China, 25 percent in Bangladesh, 36 percent in Nepal, 54 percent in Malaysia, 46 percent in Pakistan, 49 percent in Myanmar, 54 percent in India, 82 percent in Indonesia, 85 percent in the Philippines and 87 percent in Sri Lanka (Dalrymple, 1986). The low adoption rate in Thailand is due to the requirement in that country for long-grain varieties (brown rice length greater than 7 mm) for export. More than 60 percent of the world's rice area is now planted to varieties of improved plant type.
The yield potentials of the new modern varieties are no better than those of the first modern variety, IR8, but they show improved resistance to insect pests and diseases and increased tolerance to environmental stresses. However, their increased resistances are single-gene characteristics which are overcome by the pests in a few years. insect resurgence has been documented in which insecticide spraying increased the insect population instead of reducing it (Chelliah and Heinrichs, 1984). Alternative approaches of horizontal or multiline resistance are considered necessary, as there is a rapid breakdown of resistance to the brown planthopper because of the appearance of new insect biotypes. No source of resistance to tungro virus disease has been identified in cultivated rice, O. saliva. However, resistance sources have been identified in wild species and are being introduced through wide crosses to O. saliva.
The mean size of the rice farm is less than 1 ha in Bangladesh, Japan, the Republic of Korea and Sri Lanka, over 1 ha in Indonesia and Nepal, about 2 ha in Malaysia, Pakistan and the Philippines and about 3 ha in Thailand (IRRI, 1991a). The most common types of tenure are share-cropping and fixed rent (Barker, Herdt and Rose, 1985). Share-cropping is widely practiced in Bangladesh, India, Pakistan and Indonesia. Fixed-rent systems exist in all countries of the region, but are less common than share rents. In land reform in China, North Korea, Viet Nam and Myanmar, land has been expropriated by governments and held in public ownership; in Japan and Taiwan, former tenants were deemed owners. In the Philippines, the 1972 land reform for fixed-rent tenants was rapidly implemented, but land ownership transfer has been slow.
About 4 percent of the world's rice production enters international trade. The major exporters in 1988 were Thailand, the United States and Pakistan, while the major importers were Iraq, the Soviet Union, Hong Kong, Saudi Arabia, Malaysia, Singapore, Sri Lanka, Nigeria, Bangladesh and Brazil (FAO, 1990a, Table 2). Viet Nam became the third largest rice exporter in the world in 1989, with 1.38 million metric tons of milled rice (IRRI, 1991a).
Pests and diseases are major problems in the tropics, particularly with rice monoculture, since hosts are continuously present in the environment. Rodents, birds and golden snails all reduce rice yields. The major insect pests are the yellow stem borer, the green leafhopper, which is the vector of the tungro virus, and brown planthoppers, which cause hopperburn. Insect control has been attempted by breeding varieties with improved resistance to the pests. Integrated pest management is becoming more popular in view of the problem of insect resurgence from the excessive use of insecticides.
The major diseases of rice plants in tropical Asia remain the rice blast fungus and bacterial leaf blight. The existence of many races of the blast fungus makes control difficult. Blast is a particular problem in upland rice. The major virus disease is the tungro virus, transmitted by the green leafhopper. The rice weevil and hoja blanca are the main problems in Latin America, while yellow mottle virus and diopsis predominate in Africa.
The incorporation of resistance into rice varieties is complicated by the presence of many races of diseases, as in blast, and the existence of biotypes of pests, as in the brown planthopper.
The great production gains in the 1960s and 1970s occurred in the irrigated and favourable rain-fed lowland areas, where short-duration, semi-dwarf varieties could express their high yield potential. Mean farm yields of irrigated rice in many countries are still about 3 to 5 tonnes per ha, but some farmers can obtain twice that. Irrigated land now comprises about half of total harvested area, but it contributes more than two-thirds of total production and is expected to continue to dominate the sector (Table 5). The less favourable environments (unfavourable rain-fed lowland, upland, and deep-water and tidal wetland) produce 20 to 25 percent of the world's rice. These rice ecosystems must sustain farmers and consumers who so far have received little benefit from modern advances in rice technology.
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