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  3. Growing More Food with Less Water [A]Six thousand years ago farmers in Mesopotamia dug a ditch to divert water from the Euphrate

Growing More Food with Less Water [A]Six thousand years ago farmers in Mesopotamia dug a ditch to divert water from the Euphrate

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问题                 Growing More Food with Less Water
[A]Six thousand years ago farmers in Mesopotamia dug a ditch to divert water from the Euphrates River. With that successful effort to satisfy their thirsty crops, they went on to form the world’s first irrigation-based civilization. Sumerian farmers harvested plentiful wheat and barley crops for some 2,000 years thanks to the extra water brought in from the river, but the soil eventually succumbed(沦为)to salinization(盐化)—the toxic buildup of salts and other impurities left behind when water evaporates.
[B]Far more people depend on irrigation in the modern world than did in ancient Sumeria. About 40 percent of the world’s food now grows in irrigated soils, which make up 18 percent of global cropland. Farmers who irrigate can typically reap two or three harvests every year and get higher crop yields. As a result, the spread of irrigation has been a key factor behind the near tripling of global grain production since 1950. Done correctly, irrigation will continue to play a leading role in feeding the world, but as history shows, dependence on irrigated agriculture also entails significant risks.
[C]Fortunately, a great deal of room exists for improving the productivity of water used in agriculture. A first line of attack is to increase irrigation efficiency. At present, most fanners irrigate their crops by flooding their fields or channeling the water down parallel furrows, relying on gravity to move the water across the land. The plants absorb only a small fraction of the water; the rest drains into rivers or aquifers(地下蓄水层), or evaporates. In many locations this practice not only wastes and pollutes water but also degrades the land through erosion, waterlogging(水浸)and salinization. More efficient and environmentally sound technologies exist that could reduce water demand on farms by up to 50 percent.
[D]Drip systems rank high among irrigation technologies with significant untapped potential. Unlike flooding techniques, drip systems enable farmers to deliver water directly to the plants’ roots drop by drop, nearly eliminating waste. The water travels at low pressure through a network of perforated(穿孔的)plastic tubing installed on or below the surface of the soil, and it emerges through small holes at a slow but steady pace. Because the plants enjoy an ideal moisture environment, drip irrigation usually offers the added bonus of higher crop yields. Studies in India, Israel, Jordan, Spain and the US have shown time and again that drip irrigation reduces water use by 30 to 70 percent and increases crop yield by 20 to 90 percent compared with flooding methods.
[E]Sprinklers can perform almost as well as drip methods when they are designed properly. Traditional high-pressure irrigation sprinklers spray water high into the air to cover as large a land area as possible. The problem is that the more time the water spends in the air, the more of it evaporates and blows off course before reaching the plants. In contrast, new low-energy sprinklers deliver water in small doses through nozzles(喷嘴)positioned just above the ground. Numerous farmers in Texas who have installed such sprinklers have found that their plants absorb 90 to 95 percent of the water that leaves the sprinkler nozzle.
[F]Despite these impressive payoffs, sprinklers service only 10 to 15 percent of the world’s irrigated fields, and drip systems account for just over 1 percent. The higher costs of these technologies(compared to simple flooding methods)have been a barrier to their spread, but so has the prevalence of national water policies that discourage rather than foster efficient water use. Many governments have set very low prices for publicly supplied irrigation, leaving farmers with little motivation to invest in ways to conserve water or to improve efficiency. Most authorities have also failed to regulate groundwater pumping, even in regions where aquifers are over-tapped. Farmers might be inclined to conserve their own water supplies if they could profit from selling the surplus, but a number of countries prohibit or discourage this practice.
[G]Efforts aside from irrigation technologies can also help reduce agricultural demand for water. Much potential lies in scheduling the timing of irrigation to more precisely match plants’ water needs. Measurements of climate factors such as temperature and rainfall can be fed into a computer that calculates how much water a typical plant is consuming. Farmers can use this figure to determine, quite accurately, when and how much to irrigate their particular crops throughout the growing season. A 1995 survey conducted by the University of California at Berkeley found that, on average, farmers in California who used this tool reduced water use by 13 percent and achieved an 8 percent increase in yield—a big gain in water productivity.
[H]Developing new crop varieties offers potential as well. In the quest for higher yields, scientists have already exploited many of the most fruitful farming options for growing more food with the same amount of water. The hybrid wheat and rice varieties that spawned the green revolution, for example, were bred to allocate more of the plants’ energy—and thus their water uptake—into edible grain. The widespread adoption of high-yielding and early-maturing rice varieties has led to a roughly threefold increase in the amount of rice harvested per unit of water consumed—a tremendous achievement. No strategy in sight—neither conventional breeding techniques nor genetic engineering—could repeat those gains on such a grand scale, but modest improvements are likely.
[I]Yet another way to do more with less water is to reconfigure our diets. The typical North American diet, with its large share of animal products, requires twice as much water to produce as the less meat-intensive diets common in many Asian and some European countries. Eating lower on the food chain could allow the same volume of water to feed two Americans instead of one, with no loss in overall nutrition.
[J]Reducing the water demands of mainstream agriculture is critical, but irrigation will never reach its potential to alleviate rural hunger and poverty without additional efforts. Among the world’s approximately 800 million undernourished people are millions of poor farm families who could benefit dramatically from access to irrigation water or to technologies that enable them to use local water more productively. Most of these people live in Asia and Africa, where long dry seasons make crop production difficult or impossible without irrigation. For them, conventional irrigation technologies are too expensive for their small plots, which typically encompass fewer than five acres. Even the least expensive motorized pumps that are made for tapping groundwater cost about $ 350, far out of reach for farmers earning barely that much in a year. Where affordable irrigation technologies have been made available, however, they have proved remarkably successful.
[K]Costing less than $ 35 , the treadle(踩踏板)pump has increased the average net income for these farmers—which is often as little as a dollar a day—by $ 100 a year. To date, Bangladeshi farmers have purchased some 1. 2 milliontreadle pumps, raising the productivity of more than 600, 000 acres of farmland. Manufactured and marketed locally, the pumps are injecting at least an additional $ 350 million a year into the Bangladeshi economy.
[L]Bringing these low-cost irrigation technologies into more widespread use requires the creation of local, private-sector supply chains—including manufacturers, retailers and installers—as well as special innovations in marketing. The treadle pump has succeeded in Bangladesh in part because local businesses manufactured and sold the product and marketing specialists reached out to poor farmers with creative techniques, including an open-air movie and village demonstrations. The challenge is great, but so is the potential payoff. Paul Polak, a pioneer in the field of low-cost irrigation and President of International Development Enterprises in Lakewood, Colo. , believes a realistic goal for the next 15 years is to reduce the hunger and poverty of 150 million of the world’s poorest rural people through the spread of affordable small-farm irrigation techniques. Such an accomplishment would boost net income among the rural poor by an estimated $ 3 billion a year.
The new low energy sprinklers are positioned just above the ground, so they can help plants absorb more water.
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