Drought-Related Characteristics of Important Cereal Crops - Monitoring and Predicting Agricultural Drought: A Global Study - page 21

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year to year, and the CWSI for wheat must be calibrated separately for
each variety and location (Stegman and Soderlund, 1992).
Water production functions have been developed widely as guides for
the efficient use of irrigation water for wheat. In Saudi Arabia, Helweg
(1991) modeled the water-yield relationship of wheat, and in Turkey, Ozs-
buncuoglu (1998) tested water production functions to analyze the eco-
nomic value of water. Though both Helweg (1991) and Ozsbuncouglu
(1998) were able to develop accurate water production functions, math-
ematical relationships differed greatly between the two countries. To be
useful, water production functions must be tested and calibrated separately
for each location of interest.

C rop Management

[21],

R ain-fed wheat must be sown early enough to assure that the root system
is well developed before there is a significant probability of water deficit.
Sa unders et al. (1997) found that sowing wheat in autumn under rain-
fe d conditions produced yields similar to sowing wheat in spring under
irrigation in the Canterbury Plains of the United Kingdom. Thus, autumn
sowing could promote the efficient use of scarce water resources. Similarly,
delay in the sowing date from November to January consistently reduced
yields and responses to inputs of supplemental irrigation and nitrogen for
wheat cultivated in Syria (Oweis et al., 1998).
Plant nutrition also affects responses to water deficit. Application of
fertilizer nitrogen generally increases the productivity of rain-fed wheat,
although in some regions supplemental irrigation may be needed for wheat
to fully benefit from the applied nitrogen (Frederick and Camberato, 1995).
In contrast, it is important not to apply nutrients at levels so high that
shoot growth increases more than root growth. In the Coastal Plain of the
United States, increase in the amount of nitrogen applied to winter wheat
increased the severity of drought stress during the grain-filling phase and
reduced yields (Frederick and Camberato, 1995).
In hot and relatively arid environments such as Sudan and Mexico,
mulch and irrigation increased wheat yields, but mulch and irrigation
did not affect yields in hot and humid environments such as Bangladesh
(Badaruddin et al., 1999). Farmyard manure, which both provides nutri-
en ts to the crop and increases the water-holding capacity of soils, increased
yi elds in both arid and humid environments (Badaruddin et al., 1999).

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[21],

Sorghum and Millet

D istribution

Global production of sorghum and millet is 85.8 million tons (tables 2.4
and 2.5), one-seventh of the total wheat production. Still, sorghum and