Rice is transplanted or direct seeded in puddled soil on level to slightly sloping, bunded or diked fields with variable depth and duration of flooding, depending on rainfall. Soils alternate from flooded to nonflooded, Yields vary depending on rainfall, cultivation practices, and use of fertilizer. Rainfed lowland rice makes up 25 percent of the world's harvested rice area and 17 percent of world production. Areas where rainfed lowland rice is the predominant ecosystem are among the world's most densely populated rural regions and home to some of the world's poorest rural and urban populations. The rainfed lowlands must contribute to the production needed to feed expanding urban areas while preserving natural resources and improving the well being of farm families.
Crops suffer from lack of moisture and inadequate nutrition, and current yields are very low.
Upland rice makes up 13 percent of the world's harvested rice area and 4 percent of rice production. The uplands support millions of people, most of them at the subsistence level. Improved technology is needed that will help rehabilitate degraded uplands and transform them into sustainable agroecosystems. Soils cycle from flooded to non-flooded and may have severe problems of salinity and toxicity. The rice crop grows as flood water rises, with harvest after the water recedes.