Drought-Related Characteristics of Important Cereal Crops - Monitoring and Predicting Agricultural Drought: A Global Study - page 20

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Table 2.3 Global wheat production and area harvested

Country Area (%) Production (%)

India 11.7 11.9

China 11.5 16.4

Russian Federation 9.9 7.4

United States 9.3 9.3

Australia 5.2 3.5

Canada 5.2 3.6

Turkey 4.1 2.8

Pakistan 3.8 3.3

Argentina 3.2 3.1

Others 36.1 38.8

World total 212 Mha 576 Tg

[20],

Source: FAO (2001).

ge rmplasm for high yield under full irrigation would lead to increased yield
un der drought conditions.

Line
——
5.3
——
Norm
PgEn

Ir rigation

Though most wheat is produced under rain-fed conditions, the area of
irrigated wheat is increasing. In the subtropical wheat production areas
of South Asia, wheat is often grown during the cool season in rotation
with irrigated lowland rice and may receive several irrigations during the
season. Where declining water quality or water abundance restricts irri-
gation, some irrigated wheat production areas in the Great Plains of the
United States are being converted to rain-fed production, although it is
most economical to combine crop rotations (wheat-sorghum-fallow) with
limited amounts of irrigation rather than to convert entirely to rain-fed
production (Norwood, 1995). Irrigation generally increases wheat yield,
but it may also lead to diseases. For example, in Denmark, Olesen et al.
(2000) found that irrigation increased wheat yield, but it also increased
the incidence of mildew disease.
Where wheat is irrigated, farmers generally apply irrigation amounts be-
low levels of potential evapotranspiration. Schneider and Howell (1997) re-
ported that deficit irrigation at a level of 33 or 66% replacement of the wa-
ter lost by ET generally increased grain yield per unit irrigation more than
did a late start or early termination of irrigation. Stegman and Soderlund
(1992) used infrared thermometry to estimate a crop water satisfaction
index (CWSI) for spring wheat. They found minimal yield reductions for
CWSI less than 0.4-0.5 and maintaining available soil moisture above 50%
of total root zone moisture availability. Garrot et al. (1994) showed that
a CWSI could be used to schedule irrigation of durum wheat for increased
WUE in an arid zone and recommended irrigation to maintain CWSI values
less than 0.3-0.37. The relationship between yield and ET changes from

[20],