A
paddy field is a flooded parcel of
arable land used for growing
semiaquatic rice. Paddy cultivation should not be confused with cultivation of
deep water rice, which is grown in flooded conditions with water more than 50 cm (20 in) deep for at least a month. Genetic evidence shows that all forms of paddy rice, both
indica and
japonica, spring from a domestication of the wild rice
Oryza rufipogon that first occurred 8,200–13,500 years ago South of the Yangtze River in present-day China. However, the domesticated
indica subspecies currently appears to be a product of the introgression of favorable alleles from
japonica at a later date, so that there are possibly several events of cultivation and domestication. Paddy fields are the typical feature of rice farming in
east,
south and
southeast Asia. Fields can be built into steep hillsides as
terraces and adjacent to depressed or steeply sloped features such as rivers or
marshes. They can require a great deal of labor and materials to create, and need large quantities of water for irrigation.
Oxen and
water buffalo, adapted for life in
wetlands, are important working animals used extensively in paddy field farming.