cqvip:Crop production in semiarid regions is always challenging because of the high variability of amount and distribution of precipitation.These regions become more important each year, however, because the rapidly increasing and more prosperous world population seeks greater consumption of animal products(meat, milk and eggs) that requires additional grain to that consumed directly.The dry areas of the developing world where approximately 40% of the world population lives comprise about 40% of the earth's land area.Crop production, particularly cereal grains, must increase in these areas to meet these growing demands.Grain yield of cereal crops is a function of the amount of water used for evapotranspiration(ET), the portion of ET used for transpiration(T), the units of water as T to produce 1 unit of biomass, and the harvest index(HI).The most important factor is the amount of evapotranspiration not only because it is closely proportional to grain yield, but because it tends to also make the other factors more favorable.Therefore, even small increases in ET can be significant.Strategies for manipulating soil and plant conditions for increasing ET, and how additional ET affects the other factors, are discussed for water deficient areas.The use of crop residues as mulch is highly beneficial but often insufficient in dryland regions or is required for animal feed and fuel.Plastic mulch, mainly restricted to China, has significantly increased grain yields in dryland areas by decreasing evaporation from the soil surface.
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