Although its parent species are native to Asia (Oryza sativa) and certain parts of Africa (Oryza glaberrima), centuries of trade and exportation have made rice commonplace in many cultures worldwide. The process of diffusion has carried rice in all directions and today it is cultivated on every continent except Antarctica. Well-suited to countries and regions with low labor costs and high rainfall, as it is labor-intensive to cultivate and requires ample water, rice can be grown practically anywhere, even on steep hills or mountains. Rice can grow in wet environments that other crops cannot survive in. Irrigated lowland rice, which makes up three-quarters of the world rice supply, is the only crop that can be grown continuously without the need for rotation and can produce up to three harvests a year—literally for centuries – on the same plot of land. Farmers also grow rice in rainfed lowlands, uplands, mangroves, and deepwater areas.
Rice has been cultivated in Asia for between 8 and 10,000 years in parts of present day Thailand, Myanmar, and China. Rice has been cultivated in the Niger delta and other regions of Africa for approximately the same period, beginning with wild rice species and as of 3500 years ago, what is today called African rice O. glaberrima. The African species shows more tolerance to fluctuations in water depth, iron toxicity, infertile soils, severe climatic conditions and human neglect, and a better resistance to various pests and diseases. However, it also suffers easy shattering, brittle grain and poor milling quality, and consistently shows lower yields thanO. sativa. Scientists from the Africa Rice Center have managed to cross-breed African rice with Asian rice varieties to produce inter-specific cultivars called NERICA, an acronym for "New Rices for Africa", which merges the best qualities of the two species – developed to tolerate the low input and harsh growing conditions of African agriculture while enhancing productivity.
World production of rice is over 700 million tonnes, with developing countries accounting for 95 percent of the total production. China and India are responsible for nearly half of the world output, being the largest and second largest producers respectively, followed by Indonesia. Together with Pakistan, Bangladesh, Vietnam, Thailand, Myanmar, Philippines, and Japan, Asian farmers account for 92% of the world's total rice production. India has the largest absolute farm area under rice production, though it has the lowest productivity per hectare of the top three producers. By proportion of cultivated land, Cambodia leads – with 90% of the total agricultural area used for rice production.
Rice production in Africa has not kept pace with increasing demand. Only 54% of the Sub-Saharan Africa rice consumption is supplied locally. Drought is considered the most important factor reducing rice yield - affecting 80% of the total rice area in Mali, 67% in Burkina Faso and 48% in Nigeria, Sub-Saharan Africa’s leading producers. In addition to the gap in farming system technology and knowledge, many rice grain producing countries have significant post-harvest losses due to poor roads, inadequate storage technologies, inefficient supply chains and farmer's inability to bring the produce into retail markets dominated by small shopkeepers. Post-harvest losses can be as high as 40%, amounting to tens of billions of US dollars.
Only about 5–6% of rice produced is traded internationally. Many producer countries consider the crop a strategic food staple, and subject its trade to a wide range of restrictive controls. The global rice trade constitutes just 1% of world trade. Developing countries are the main players in the world rice trade, accounting for 83% of exports and 85% of import. Major importers include Nigeria, Indonesia, Bangladesh, Saudi Arabia, Iran, Iraq, Malaysia, the Philippines, Brazil and other African and Persian Gulf countries. The exporters of rice are limited. Five countries – Thailand, Vietnam, India, the United States and China – account for about three-quarters of world rice exports.
Rice is central to the food security of over half the world’s population – it is vital for the nutrition of much of the population in Asia, as well as in Latin America, the Caribbean and in Africa, totaling over 3.5 billion people worldwide that eat it every day, and depend on it for more than 20% of their daily calories.It is the grain with the third-highest worldwide production, after maize and wheat. Since a large portion of maize crops are grown for purposes other than human consumption, rice is the most important grain with regard to human nutrition and caloric intake, providing more than one fifth of the calories consumed worldwide by the human species – it is the predominant dietary energy source for 17 countries in Asia and the Pacific, 9 countries in North and South America and 8 countries in Africa, providing over 20 percent of the world’s dietary energy supply, while wheat supplies 19 percent and maize 5 percent.
It is a major economic mainstay for many rural populations, being mainly cultivated by small farmers in holdings of less than 1 hectare. Asia has more than 200 million such farms. It is also a wage commodity for workers in the cash crop or non-agricultural sectors. The world’s top consumers of rice are China, India, Indonesia, Bangladesh, Vietnam and Thailand in that order. Brazil and the United States are the leading consumers in the Americas, while South Africa leads in Africa. In Africa, rice is the fastest growing staple by consumption, and this increase in demand is also true for Latin America and Caribbean countries.
There are many varieties of rice and culinary preferences tend to vary regionally. For example in India, there is a saying that "grains of rice should be like two brothers, close but not stuck together” while in the Far East there is a preference for softer, stickier varieties. All the varieties of rice – white, brown, black, red and purple – provide dietary protein, minerals and vitamins, carbohydrates, fibre and fat. However the quality and quantity of these vary significantly – depending on variety, the soils on which the crop was grown, the manner in which it was processed, and the method of preparation for consumption. However, none is a complete nutrition source.
In 2008 when rice prices tripled, the World Bank estimated that an additional 100 million people were pushed into poverty. For the extremely poor in Asia, rice accounts for as much as half of their food expenditures and a fifth of total household expenditures. Rice of necessity therefore features prominently in poverty alleviation strategies targeting enhanced economic development and improved livelihoods. NERICA is an example of this. Ongoing research in China to develop perennial rice could result in enhanced sustainability and food security. Bio-fortified golden rice, a product of genetic engineering, is targeting vitamin A deficiency in people who obtain most of their calories from rice.
Other genetic engineering research efforts have produced rice varieties that express proteins usually found in breast milk that have antiviral, antibacterial, and antifungal effects. These varieties are proposed as a component in oral rehydration solutions, and other emergency nutrition preparations, which are used to treat diarrheal diseases, thereby shortening their duration and reducing recurrence. Such supplements may also help reverse anemia.
Beyond its obvious significance as a vital staple, rice plays an important role in many cultures. For thousands of years different parts of the rice plant have been used in religious and ceremonial occasions, as medicine, and as inspiration and medium for a great number of works of art. Rice shortages affect society far beyond the cold statistics of price, caloric intake, yield growth rates, and international trade. Any significant disruptions of rice supplies can and do have far-reaching social and political ramifications. In most of the developing world, rice is equated with food security and closely connected to political security. Changes in rice availability, and hence price, have caused social unrest in several countries. Developing drought-tolerant cultivars that have a high yield potential in normal years and provide a good yield under drought and other major stresses will help sustain rice production in the large rain-fed lowland ecosystem across Africa. Drought tolerance is also compounded by soil stress so comparative genomics approaches need to be used to pyramid genes for aluminium tolerance, phosphorus uptake efficiency and drought tolerance for improved cultivars.
To keep rice prices stable and affordable, IRRI estimates that an additional 8-10 million tons of rice needs to be produced every year. The challenge is to produce these additional quantities with less land, less water, and less labor, in more efficient, environmentally-friendly production systems that are more resilient to climate change.