Drought-Related Characteristics of Important Cereal Crops - Monitoring and Predicting Agricultural Drought: A Global Study - page 24

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Using crop-water production functions by growth stage for corn, sor-
ghum, and wheat grown in the Texas High Plains area of the United
States, Hoyt (1982) found that it would be possible to reduce irrigation
by 20% without significantly reducing profitability, thereby extending the
life expectancy of the Ogallala aquifer.

C rop Management

According to Payne (1997), soil fertility rather than water availability is the
factor that most limits yield of pearl millet in the Sahel of West Africa. In a
four-year experiment, Payne found that increasing plant population density
to at least 20,000/ha and fertilizer applications to at least 40 kg N/ha
an d 18 kg P/ha increased total evapotranspiration by 50 mm. Moderate
pl ant population densities of 10,000/ha and fertilizer rates of 20 kg N/ha
an d 9 kg P/ha tripled WUE and substantially increased yield. Similarly,
ov er a four-year experiment in Niger, which included three dry years and
on e wet year, Sivakumar and Salaam (1999) found that P and N fertilizer
ap plication increased the WUE of pearl millet by an average of 84%. At
the same time that P and N fertilizer applications may increase productivity
of pearl millet, few farmers in the Sahel have access to the cash or credit
needed to purchase such inputs. Instead, they apply small amounts of
farmyard manure collected from their livestock (Roncoli et al., 2001).

[24],

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C onclusions
The growth and productivity of all crops is directly related to the amount
of water they transpire. Differences in productivity among the primary ce-
real crops under water-limited conditions may be explained by differences
in physiology, morphology, crop duration, and management. Physiologi-
cally, the WUE ranges from 0.01 Mg ha -1 mm -1 or less for rice to 0.03
Mg ha -1 mm -1 for maize. Thus, maize can produce three times as much
biomass as rice from the same amount of water. Wheat grows well under
rain-fed conditions because its deep root system provides access to a larger
soil volume. Millet and sorghum are grown in the most drought-prone envi-
ronments, largely because they have either very rapid development to take
advantage of a short growing season or because they produce something
with relatively low input levels when other crops produce nothing at all.
Plant breeding efforts have enabled some crop plants to escape drought by
developing varieties whose duration better matches the length of the rainy
season. Both plant breeding and crop management efforts have succeeded
to some extent in improving root system depth, thereby allowing plants
greater access to soil moisture.
Irrigation can alleviate drought stress in areas where water resources and
infrastructure are available. Deficit irrigation generally increases both WUE
and economic returns. Other management practices that can improve crop
productivity under water-limited conditions include tillage to allow deeper
root growth, fertilizer applications, inoculation with mychorrhizae, and

[24],