Salt residue from soil irrigation degrades around 5,000 acres of farmland every day at a global annual cost of $27 billion dollars in lost arable revenues.

Using cheap, short-sighted ways to water land without adequate drainage methods are the chief reason behind the land spoilage, according to the report by the UN University’s Canadian-based Institute for Water (UNU-INWEH). The total area being affected, the report notes, has shot up over the last two decades — from 111 million acres in 1991 to 160 million in 2013, representing some 20 percent of the world's irrigated lands.

Researchers warn that big investment is necessary to reverse the trend.

The authors of the study said the most vulnerable parts of the world are arid regions in developing countries, where pressure to increase crop yields in the short term may lead governments to forgo installing or maintaining the simple, but costly, drainage systems necessary to keep salt away from the soil.

The area around the rapidly shrinking Aral sea, which straddles the Kazakhstan and Uzbekistan border — along with river valleys in Iraq, Pakistan, India and China — are among the areas that have seen crop yields drop because of the accumulation of salt. The problem also affects agriculture in the United States, most notably in California’s San Joaquin Valley.

"Each week the world loses an area larger than Manhattan to salt-degradation,” said Zafar Adeel, director of the UNU-INWEH. “Efforts to restore those lands to full productivity are essential as world population and food needs grow, especially in the developing world."

The study’s authors suggested that the annual loss figure of $27 billion could even be an underestimate. And the amount of land lost is denting efforts to keep a growing population adequately fed.

"To feed the world's anticipated nine billion people by 2050, and with little new productive land available, it's a case of all lands needed on deck," said the study’s principal author Manzoor Qadir, assistant director of water and human development, at UNU.

"We can't afford not to restore the productivity of salt-affected lands," he said.

Source - http://america.aljazeera.com/