The diverse rice ecosystems
The environmental and socio-economic conditions of rice production vary greatly from country to country as well as from location to location. The diverse environmental and socio-economic conditions have affected the performance of rice production in the past 45 years. They also influence the opportunities for increasing rice production in the future. Environmentally, rice is grown under different climates including temperate, sub-tropical and tropical. Within a climate the weather varies from arid and semi-arid to sub-humid and humid. Based on soil-water conditions rice production ecosystems include irrigated lowland, irrigated upland, rainfed lowland, rainfed upland and deepwater/floating ecosystems.
Socio-economically, farm size cultivated by a household in South Asia, Southeast Asia, East Asia, and Africa is generally small, which varies from less than one hectare to few hectares. The ratio of rice land to arable land is high in South Asia, Southeast Asia, and East Asia (Table 2). With the exception of Japan and Korea Rep, rice cultivation in South Asia, Southeast Asia, East Asia, and Africa still uses enormous amounts of human labour, in spite of strikes made in mechanization of rice production. On the other hand, farmers in Europe, America and Australia cultivate large farms and rice cultivation is highly mechanized with large expenditures of energy from fossil fuels.
Irrigated Lowland Rice Ecosystems
In recognition of the important role of water to the productivity of rice crops, efforts have been made to assure adequate water supply to rice cultivation throughout human history through irrigation development. Irrigated lowland rice is grown in bunded fields with assured water supply for one or more crops per year. In temperate and most of the sub-tropical climate areas, rice is grown mostly under irrigated lowland ecosystems, once a year during the warm months; when temperature regimes are suitable for growth and development of rice plants. However, with available irrigation water, rice could be grown more than one crop per year in tropical climate areas. In arid and semi-arid zones of tropical climates, rice is planted under irrigated conditions only, but in humid and sub-humid zones, rainfall supplement irrigation water during the rainy season. In South Asia, Southeast Asia, and East Asia, irrigated lowland rice is dominant in the vast, flat and low-lying flood plains and deltas of many of the world’s major rivers, which are flooded annually during the rainy season.
The irrigated lowland rice production systems had benefited from substantial investment during the second half of the 20th century for the building of dams to divert the flow of the river and/or to store surface water and then channel it onto rice fields as well as the drainage systems to convert large part of deepwater and floating rice areas into irrigated rice production. In late 1960s, farmers in a number of countries turned to underground sources and millions of irrigation wells were drilled to provide water to rice production. The irrigated lowland rice systems have benefited much from modern or high-yielding and hybrid rice varieties and associated improved rice technologies. The FAOSTAT Agriculture database counts the harvested area not the area that is planted to rice. Therefore, one hectare of rice land could be counted two or three times if it is planted two or three rice crops in a year. In recent years, the harvested area worldwide from irrigated lowland rice systems was about 88 to 90 million hectares. Because the risk of crop failure is lower than in the other ecosystems, irrigated lowland rice farmers use more production inputs to increase rice yield. The average yields of irrigated lowland rice vary from about 3 tonnes/ha in some countries in Sub-Saharan Africa to 10 tonnes/ha in Egypt.
Irrigated Upland or Aerobic Rice Ecosystems
There were efforts in the 1980s to develop and popularize the irrigated upland rice or aerobic rice production in Brazil using sprinkler irrigation systems. Aerobic rice production was recently practiced in northern China as a response to water shortage. Soils of irrigated upland rice fields are freely drained. The adoption of irrigated upland rice production systems so far has been very limited. It is estimated that the areas planted with aerobic rice varieties was about 80,000 hectares in China and 250,000 hectares in Brazil.
Rainfed Lowland Rice Ecosystems
Rainfed lowland rice ecosystems are found mainly in tropical climate areas; in river deltas, flood plain and inland swamps. Bunds and dikes are built around rainfed lowland fields to capture and conserve rainfall for growth and development of rice plants. Water supply to rice crops comes principally from rainfall, but in some places water may come from diverted small water courses (e.g. streams), or swollen rivers. Rice fields are covered with a layer of standing water up to 50 cm during half of the growing season or more. Variability in rainfall and its distribution normally cause either flood or drought stresses in rainfed lowland rice production.
In Asia the expansion of the irrigated lowland rice area has contributed negatively the total harvested area of rainfed lowland rice, while farmers’ efforts to do double cropping in areas with long rainy season have positive contributions. Also, the development of inland valley swamp for rice production in Sub-Saharan Africa contributed to the increase in the harvested area of rainfed lowland rice. In the recent years, worldwide, the harvested area of rainfed lowland rice is estimated to be about 44 to 46 million hectares. Yields of rainfed lowland rice remain low, about 1.5 to 2.5 tonnes/ha in most cases, in spite of series of modern and high yielding varieties that were made available by international and national institutions worldwide.
Rainfed Upland Rice Ecosystems
Rainded upland rice fields are found mainly in tropical climate areas; on flat land or on slopes of hills and mountains. They are normally not surrounded by bunds or dikes. Soils of rainfed upland rice fields are freely drained during most of the growing season. Rainfall is the only source of water supply to rice growth and development. Rice yield and production, therefore, vary considerably from year to year depending on the amount of rainfall and its distribution. Drought stress is a major factor affecting rice yield and production. In spite of series of modern and high yielding varieties that were made available by international and national institutions worldwide yields of rainfed upland rice remain very low about 1.5 tonnes/ha or less in most cases. Harvested area of rainfed upland rice in Brazil decreased significantly since the 1980s, but that in Sub-Saharan Africa increased steadily. In the recent years, the harvested area of rainfed upland rice is estimated to be about 15 to 16 million hectares.
Deepwater/Floating Rice Ecosystems
Deepwater/Floating rice ecosystems are found in low lying areas in deltas, estuaries, swamps, and rivers’ valleys in tropical Asia and sub-Saharan Africa, where the water is stagnant for some time during rice growing season. During the early part of the rice growing season, water supply to rice crop comes mainly from rainfall. However, as the cropping season progresses, water from swollen rivers and from high-lying ground inundated rice fields for considerable period of time. Depth of standing water in rice fields during considerable period of the cropping season could be up to 100 centimetres in deepwater rice ecosystems and to more than 1 m and sometimes were up to 6 m in floating rice ecosystems. Most of tidal affected rice area belongs to deepwater rice ecosystems. Varieties planted in deepwater rice ecosystems could elongate 2-3 cm per day when submerged, while those planted in floating rice ecosystems could elongate rapidly sometimes up to 20 cm per day when submerged. Varieties planted in tidal affected rice areas have good tolerance level to salinity. In the past, there were about 11 million hectares of deepwater and floating rice. However, large areas have been converted for irrigated rice production through the development of irrigation and drainage systems. In recent years, it is estimated that the harvested area of deepwater and floating is about 3 to 4 million hectares. Rice production in these ecosystems has not benefited much from research and development in the past. Yields of deepwater/floating rice are about 2 tonnes/ha or less.
Climate change
Flooded rice is a major source of methane emission, while the use of nitrogen fertilizers produces nitrous oxide; both are greenhouse gases linked to global warming. On the other hand, temperature increase, variability in rainfall and its distribution, and rise in ocean water potentially have important effect on rice production. High atmospheric temperature could reduce rice yield in tropical climate areas, while variability in rainfall and its distribution could lead to more frequent and severe floods and droughts. Rising ocean water could expand substantially rice area influenced by tidal waves in low-lying flood plains and deltas of rivers where rainfed lowland, irrigated lowland and deepwater/floating rice are widely cultivated, especially in East Asia, Southeast Asia and South Asia. In addition to the above mentioned-technologies, generations of new rice varieties would most likely be needed for sustainable rice production under climate change.
Malnutrition in rice consuming populations
Although malnutrition in rice-consuming population is caused by problems associated with socio-economic and developmental factors rather than rice consumption alone, proteinenergy malnutrition (PEM), vitamin A deficiency, anaemia due to iron deficiency, iodine disorder (IDD), and zinc deficiency are still found in populations, which consume rice as staple food. Considerable efforts have been given to the development of high-yielding varieties with better nutrition values, especially the content of iron, zinc, and vitamin A in rice grains. It is also expected that improvement in income would lessen the malnutrition in rice consuming population. For example, beriberi, a nutrition problem associated with the deficiencies of thiamine and riboflavin among rice-consuming populations, especially in Asia, has gradually disappeared with increased income that could afford the population to have more varied diets. On the other hand, prices of the high quality rice such as Basmati and Jasmine in the international rice markets are normally high and this encourage farmers to shift away from producing high-yielding rice to producing high-quality rice, although yield potential of high-quality rice is generally low.
Policy and institutional environment
The majority of rice farmers are poor and caught in the endless cycle of poverty and food deficit, but national policies in countries, where rice is the staple food crop, usually favour the rice consumers, not the farmers; by limiting the prices of rice in the market. With the increase in prices of inputs and low rice prices, rice production does not provide farmers with high income. Rice food security needs clear national policy that allows right investment in all phases of rice development. There must be right policies on input availability, output marketing and prices. Furthermore, investment in rural infrastructure such as road, irrigation, communication and credit must match the growing demand for rice production. The rice Green Revolution in the 1970s and 1980s was possible thanks to the investment in research and extension services to build capacity and expertise in rice production. The success of rice Green Revolution has led to reduction in public investment in rice research and extension in general. Policy must be readjusted to provide more support to the development and transfer improved technologies for sustainable rice production.
Maximizing the Value of Rice Harvests
High yields will only lead to additional production if accompanied by improvements in post-harvest operations. Losses from post-harvest operations range from 10-30 %. Although technologies for post-harvest operations are available, post-harvest handling of rice in much of South Asia, Southeast Asia and Sub-Saharan Africa is still not substantially improved due to poverty, lack of credit, and absence of efficient systems for supply and repair of equipment and implements for post-harvest handling of rice. About 60 % of output from rice production is in the form of straw and husk. The burning of rice straw and husks has caused air pollution and contributed to global warming. Although they are not consumable as food, rice straw and husk are good sources of energy and could be used as feed to ruminants. Reduction of post-harvest losses and conversion of rice straw and husks to value-added products could increase farmers’ income and reduce environmental pollution.
