A Growing World Will Need More Irrigation
* Some Environmentalists Want To Burst Dams, But Feeding The 21st Century May Require Building More
May 2, 2001
by Dennis T. Avery
THE BridgeNews FORUM: Viewpoints on farming, farm policy and related agricultural issues.
CHURCHVILLE, Va.--The World Bank is no longer funding dams. Eco- activists are blocking new dams. More and more of the water from existing dams is being released for fish management instead of irrigation or electricity.
Irrigation wells are drawing down water tables in places such as the Ogallala Basin in the Western United States. Can farmers produce three times as much food for the world of 2050 without irrigation? Probably not, according to David Seckler, one of the world's top irrigation experts at the International Water Management Institute in Sri Lanka.
Seckler notes that 60 percent of the world's grain comes from irrigated land. As high-yield farming doubled the world's grain production between 1960 and 2000, more than 90 percent of the increase came from the irrigated land (working synergistically with high-yield seeds, fertilizers and pesticides).
The irrigated land, farmed by more than 46 million families, kept food prices low for billions of poor people in the Third World.
Why don't we just concentrate on the land that gets enough rainfall from nature, so we won't need dams? Seckler says the variability of rainfall is the biggest problem in trying to wrest more of our food from marginal rain-fed farmlands.
Neither humans nor livestock can take a year off from eating just because the rains didn't come. North America is the biggest chunk of prime farmland in the world, but even the famed Corn Belt gets barely enough rain to grow corn most years and it suffers a serious drought about one year in ten.
Most of the other prime farmlands in the world are even more vulnerable to drought.
A secondary impact of rainfall variability is that farmers have to manage for average rainfall. They don't dare manage for peak yields, investing in extra seeds and plant food, and risk losing most of that investment to dry weather.
But when the rainfall is good, that also means the farmer hasn't planted enough seeds with enough plant nutrients to get the peak yield. Compounding the problem, when a major drought hits, farm prices rise dramatically because there is little to sell.
When the rain is plentiful, the farms often produce more than we can immediately eat, and prices collapse. Biotechnology may give us drought- resistant crops one day, but Seckler isn't looking for an early victory.
He points out that the drought-resistant crops in nature tend to be low-yield grains such as millet and sorghum and such low-nutrient root crops as cassava.
Nor is there a single gene or set of genes that researchers can work with to get drought tolerance. Seckler notes that dry-land farming takes just as much moisture as irrigation.
In some cases, he says, the dry-land farming may use up water that would otherwise be used downstream on higher-value uses such as domestic water supplies or even higher-yield irrigated farming.
Low-yield dry-land farming too often wastes the rain that does fall, says Seckler. Low cropping densities means most of the soil in the field is exposed to direct sunlight.
Seckler points to an African study that found only 5 percent of the water in the field benefited crop production. Most of the moisture simply evaporated.
Fortunately, lots of rain-fed crops are planted with some moisture- conserving system such as conservation tillage, mulching or terracing.
Such systems concentrate the water, boost yields, make inputs such as fertilizer cost-effective and get more "crop per drop." Seckler does see a major role for expanding "supplemental irrigation." He says there are lots of farming regions where the average rainfall over the cropping season is adequate, but yields are often greatly reduced by short, 15-to-30 day droughts at critical stages of crop development.
"Water stress at the flowering stage of maize, for example, will reduce yields by 60 percent, even if the water is adequate for the rest of the year," he says.
Perhaps the single most promising supplemental irrigation system, says Seckler, is the "percolation tank," which is already being widely adopted in India.
The percolation tanks are small underground reservoirs that capture runoff and store it. The water is only pumped onto the fields when it is most critical for the crops. Groundwater storage avoids the high evaporation losses of surface storage. Where the water tables are shallow, even the percolation losses can be recaptured and reused.
Such percolation tanks can be combined with highly efficient sprinkler and drip irrigation systems to achieve very high levels of water efficiency.
Seckler expects the world will need more irrigation, not less, in the 21st century, in order to feed more people from less land. He says high- efficiency supplemental irrigation "absolutely has to happen if sub- Saharan Africa is to produce enough food to feed its rapidly growing population."
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Dennis T. Avery is based in Churchville, VA, and is director of the Hudson Institute's Center for Global Food Issues.