Drought-Related Characteristics of Important Cereal Crops - Monitoring and Predicting Agricultural Drought: A Global Study - page 17

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46

of the experiment. The challenge is whether farmers are willing to accept
low yields during dry years for the greater potential yields of maize during
the wet years.

Rice

D istribution

Rice's center of origin is in Southeast Asia. Though rice ranks third in total
production, it provides more than half of the daily dietary calories for the
majority of the world's population. This is because most rice is consumed
directly by humans in countries where it is produced. Generally, less than
5% of the global rice production is traded internationally. Although rice is
cultivated from the equator to 55° latitude, one of the widest production
zones of any crop, only 15 countries produce more than 90% of the annual
total rice production. Less than 20% of total rice production lies outside
of Asia (table 2.2).
The flood-irrigated lowland rice ecosystem accounts for 75% or more
of the total rice production, though it occupies only 55% of the produc-
tion area (IRRI, 2002). In contrast, rain-fed lowland and upland rice,
which occupies about 38% of the total rice area, produces only 21% of
the world's total rice production. Although there has been some success
in efforts to improve the drought resistance of rice through breeding (In-
gram et al., 1995), because of genetic limitations and because soils and
soil management practices often restrict rice root growth, rice is arguably
the most drought susceptible of the important food crops. Under tropical
growth conditions rice plants have a transpiration WUE of about 0.010 Mg
ha -1 mm -1 (Yambao and Ingram, 1988), and an evapotranspiration WUE
about half of that, giving rice a WUE less than half of the most inefficient
maize plants.

[17],

Line
——
-0.0
——
Norm
PgEn

[17],

D rought in Rice Ecosystems

For the most part, irrigated rice only experiences drought when irrigation
systems break down or when a regional drought restricts the amount of
water available for irrigation. Though both rain-fed lowland and upland
rice ecosystems suffer from frequent droughts, there are important differ-
ences between the two.
In the rain-fed lowland ecosystem, roots must be able to function un-
der both flooded and drained soil conditions. Thus, roots of rain-fed low-
land rice often have a mix of aerenchyma and non-aerenchymatous tissue
(Ingram et al., 1994). Farmers generally puddle the soils of rain-fed low-
land rice fields, like those of the irrigated lowlands. This puddling creates a
hard soil layer about 10-15 cm below the soil surface. When these puddled
soils drain, they often become very hard and develop deep cracks, thereby