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Production constraints
Uncertainty characterizes rice farming in rainfed
lowlands. Crops suffer from droughts, floods,
pests, weeds, and soil constraints. Since most
rainfed lowlands depend on erratic rainfall,
conditions are diverse and unpredictable.
Understanding how farmers’ practices help
reduce risk and assure some production is
essential to developing improved technologies
for the rainfed lowlands.
Most rainfed lowland rice farmers are poor
and must cope with unstable yields and financial
risks. They adapt their cropping practices to the
complex risks, potentials, and problems they face.
They typically grow traditional, photoperiodsensitive
cultivars and invest their labor instead of
purchasing inputs. Farmers bund the fields to store
water. They weed, may redistribute seedlings to
ensure good crop stands, and usually harvest by
hand. Suitable modern varieties and associated
production technologies have been limited.
Although new technology developed in the
1960s and 1970s focused on the irrigated sector,
rainfed lowland rice farmers were not forgotten.
Researchers have tried to produce new varieties
and improved farming practices for nutrient
management, crop establishment, on-farm water
collection, and weed and pest control. These
practices can potentially contribute to higher
yields, especially in the favorable rainfed
subecosystem.
Rainfed lowland rice farmers in less
favorable areas use traditional varieties that do
not respond well to higher fertilizer rates. In
Bangladesh, eastern India, Indonesia,
Philippines, and Thailand, however, adoption of
new rice varieties is increasing as scientists are
now developing new breeding lines with single
or combined traits adapted to rainfed lowland
stresses. Rice varieties that are bred for tolerance
for submergence, late transplanting, and
resistance to lodging allow farmers to apply
fertilizers and use more intensive weed
management practices. Decentralized regional
breeding programs developed in northeastern
Thailand and eastern India, focusing on droughtand
submergence-tolerant improved lines,
respectively, now have advanced lines under
evaluation in farmers’ fields.
Rainfed lowland rice varieties of the future
will need to respond to improved management
while retaining the tolerance of the traditional
varieties for drought, floods, and soil stresses.
Such varieties should perform well under
favorable conditions and still equal the
productivity of traditional cultivars under
adverse conditions. Farmers would then be able
to invest money and labor in potentially more
productive land preparation and fertility
management practices that will assure higher
yields.
Upland rice ecosystem
Physical description
Upland rice is grown in Asia, Africa, and Latin
America. Of about 150 million ha of world rice
area in the mid-1990s, about 14 million ha were
planted to upland rice: 8.9 million ha in Asia, 3.1
million ha in Latin America, and 1.8 million ha
in Africa. Although upland rice constitutes a
relatively small proportion of the total rice area,
it is the dominant rice culture in Latin America
and West Africa. In Asia, the area of the upland
ecosystem is much larger than the area under
rice, because rice is grown in rotation with many
other crops.
Upland rice is grown in low-lying valley
bottoms to undulating and steep sloping lands
with high runoff and lateral water movement. In
Southeast Asia, most upland rice is grown on
rolling and mountainous land with slopes
varying from 0% to more than 40%. In eastern
India, upland rice is grown on several million
hectares in permanently cultivated, level fields at
the top of a toposequence ranging from rainfed
lowland to upland. In West Africa, upland rice
grows on hills in the humid zone and on flatland
in the drought-prone and moist forest zones.
Most upland rice in Brazil is on level to gently
rolling (0–8% slope) land, much under
mechanized cultivation. In northern and
northeastern Brazil, some upland rice is grown
on rolling topography under shifting cultivation.
Upland rice soils range from erodible, badly
leached Alfisols in West Africa to fertile volcanic
soils in some areas in Southeast Asia. Their
texture, water-holding capacity (WHC), cation
exchange capacity (CEC), nutrient status, and
soil-related problems vary greatly. In Southeast
Asia, many upland soils in high-rainfall areas
where rice is grown are erodible, acidic, and
highly P-fixing. Subsoil acidity and Al toxicity
are common additional constraints, along with
severe nutrient deficiency and poor WHC. In
Brazil, where upland rice is a major crop, soils
have extremely low CEC values, high P fixation,
20 Rice almanac