Conclusions

The growth and productivity of all crops is directly related to the amount of water they transpire. Differences in productivity among the primary cereal crops under water-limited conditions may be explained by differences in physiology, morphology, crop duration, and management. Physiologically, 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 environments, 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 appropriate times of planting. Crops cannot grow without water, but we certainly can improve their performance under drought-prone conditions by selecting appropriate crops and management practices.

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