Drought-Related Characteristics of Important Cereal Crops - Monitoring and Predicting Agricultural Drought: A Global Study - page 18

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Table 2.2 Global rice production and area harvested

Country Area (%) Production (%)

India 29.4 22.5

China 18.9 31.0

Indonesia 7.7 8.4

Bangladesh 7.2 5.9

Thailand 6.5 4.3

Vietnam 5.0 5.5

Myanmar 4.3 3.5

Others 21.0 18.9

World total 151 Mha 585 Tg

Source: FAO (2001).

[18],

da maging roots and restricting root growth (Ingram et al., 1994). Although
th e roots systems of direct-seeded lowland rice plants appear to be better
ab le to supply water to the plants during periods of drying and rewetting,
m any farmers continue to transplant rice to improve weed management
(Ingram et al., 1995). Upland rice roots generally do not form aerenchmya
and perform much like the roots of other cereal crops. Upland rice soils
often have low pH and high aluminum saturation, both of which restrict
rice root growth and increase susceptibility to drought. Because of frequent
water and nutrient deficits, upland rice generally yields 1 Mg/ha or less,
with genetic improvement coming largely through growing rice varieties
with developmental rates that match the average length of the rainy season
(Ingram et al., 1995).
Rice is most susceptible to drought during panicle emergence, largely
because this is the crop stage at which the leaf area has reached a maximum
and plants transpire the most water (Yambao and Ingram, 1988; Singh
et al., 2001). Rice varieties differ in sensitivity to drought during panicle
emergence, which may be explained by the ability of some varieties to
store nonstructural carbohydrate in vegetative tissues before drought and
remobilize those substrates to maintain seed set and growth during drought
(Ingram et al., 1995).

Line
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0.6
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Norm
PgEn

[18],

W ater Production Functions

Yambao and Ingram (1988) developed a drought stress index for rice based
on growth stage and the cumulative difference between actual and potential
transpiration. They found that most of the difference in growth stage sen-
sitivity to water deficit could be explained by the differences in crop water
demands. Rice is most sensitive to water deficit during panicle emergence
largely because that is when potential transpiration is greatest. Building
on this concept, Singh et al. (2001) tested a range of water production
functions for rice. In general, those that considered differential sensitivity
to water deficit at different growth stages performed better than those that