As a main source of nourishment for over half the worlds population, rice is by far one of the most important commercial food crops. Its annual yield worldwide is approximately 535 million tons. Fifty countries produce rice, with China and India supporting 50% of total production. Southeast Asian countries separately support an annual production rate of 9-23 million metric tons of which they export very little. Collectively, they are termed the Rice Bowl. Over 300 million acres of Asian land is used for growing rice. Rice production is so important to Asian cultures that oftentimes the word for rice in a particular Asian language also means food itself.
Rice is a member of the grass family (Gramineae). There are more than 10,000 species of grasses distributed among 600 genera. Grasses occur worldwide in a variety of habitats. They are dominant species in such ecosystems as prairies and steppes, and they are an important source of forage for herbivorous animals. Many grass species are also primary agricultural crops for humans. As well as rice, they include maize, wheat, sorghum, barley, oats, and sugar cane.
There are three different types of rice: japonica, javanica, and indica. Japonica rice varieties are high yielding and tend to be resistant to disease. Javanica types of rice fall between japonica and indica varieties in terms of yield, use, and hardiness. Although quite hardy, indica yield less than japonica types and are most often grown in the tropics.
Because cultivation is so widespread, development of four distinct types of ecosystems has occurred. They are commonly referred to as irrigated, rainfed lowland, upland, and flood-prone agroecological zones. Irrigated ecosystems are the primary type found in East Asia. Irrigated ecosystems provide 75% of global rice production. Irrigated rice is grown in bunded (embanked), paddy fields. Rainfed lowland ecosystems only sustain one crop per growing season and fields are flooded as much as 19.7 in (50 cm) during part of the season. Rainfed low-land rice is grown in such areas as East India, Bangladesh, Indonesia, Philippines, and Thailand, and is 25% of total rice area used worldwide. Production is variable because of the lack of technology used in rice production. Rainfed lowland farmers are typically challenged by poor soil quality, drought/flood conditions, and erratic yields. Upland zones are found in Asia, Africa, and Latin America. It is the primary type of rice ecosystem in Latin America and West Africa. Upland rice fields are generally dry, unbunded, and directly seeded. Land utilized in upland rice production runs the gamut of descriptions. It can be low lying, drought-prone, rolling, or steep sloping. Usually, crops are either sown interspersed with another crop, intermittently with another crop, or the crop is shifted every few years to a new location. Lastly, flood-prone ecosystems are prevalent in South and Southeast Asia, and are characterized by periods of extreme flooding and drought. Yields are low and variable. Flooding occurs during the wet season from June to November, and rice varieties are chosen for their level of tolerance to submersion.
Rice is mostly eaten steamed or boiled, but it can also be dried and ground into a flour. Like most grains, rice can be used to make beer and liquors. Rice straw is used to make paper and can also be woven into mats, hats, and other products.