Maclean et al. - 2002 - Rice almanac source book for the most important e

In these environments, rice yields are low
and extremely variable because of problem soils
and unpredictable combinations of drought and
flood. Although average yields are only about 1.5
t/ha, these areas support more than 100 million
people.
Crucial for survival and production of the
rice crop are the age of plants at the start of
inundation, the rate of water rise, and the
duration of the flood. Many parts of the tidal,
deepwater, and rainfed lowland rice areas are
subject to sudden increases in water level, commonly
called flash floods. These floods occur
after heavy rain, local or remote, and may
completely submerge the crop for several days.
The water is often heavily laden with silt, which
covers the leaves of the plants.
Deepwater rice and floating rice are mainly
grown in fields on the floodplains and deltas of
rivers such as the Ganges and Brahmaputra of
India and Bangladesh, the Irrawaddy of
Myanmar, the Mekong of Vietnam and
Cambodia, the Chao Phraya of Thailand, and the
Niger of West Africa. Flooding occurs in the
later stages of plant growth and can last for
several months.
Tidal wetland rice is cultivated during the
wet season in scattered areas along the coastal
plains of Bangladesh, India, Indonesia,
Myanmar, Thailand, Vietnam, and West Africa.
Tidal rice can tolerate submergence caused by
flash floods or tidal fluctuations. Salt-tolerant
tidal rice is grown in areas where there is salt
water intrusion from the sea. The soils are of
various ages and are complex and diverse,
particularly in river floodplain areas. Many of
these alluvial sediments have undergone little
soil formation. Soil texture varies from medium
to fine. It is usually more coarse on natural
levees and finer in depressions and backswamps.
Although many soils are fertile, problem soils
such as peat, acid-sulfate, and saline soils occur,
particularly near coasts.
Predominant cropping systems
The cropping systems vary depending on the
time, depth, and duration of flooding. Most
varieties of rice can survive complete
submergence for only 3 to 4 d and some rainfed
lowland rice can survive up to 10 d. In floodprone
areas, rice is the only food crop that can be
grown during the rainy season (June to
November in most of Asia). There are four major
cultural conditions in the flood-prone
environments for which rice varieties are
selected: deepwater (up to 100 cm or more); very
Deepwater rice in Cambodia.
The rice plant and its ecology 23