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Poor irrigation has poisoned much of world’s farmland with salts, study finds

REUTERS/David Gray
An aerial photo shows salt-infested dams amid farm fields in Western Australia.

The salt of the earth is a good thing in everyday idiom, but in excess it damages and eventually destroys the productivity of farmland.

And at a time when the world faces relentlessly increasing demand for more food of all kinds  — including a 50 percent increase in cereal grains alone over the next few decades — poor irrigation practices have compromised global cropland acreage equivalent to the land area of France.

That’s the conclusion of a research analysis published Tuesday by a United Nations institute, which concludes that about 20 percent of all irrigated lands from California to Australia have been impaired by accumulating salts, and that the problem continues to expand at the rate of about 5,000 acres per day.

“Economics of Salt-Induced Land Degradation and Restoration” explains that the general problem arises “in arid and semi-arid regions where rainfall is too low to maintain regular percolation of rainwater through the soil and where irrigation is practiced without a natural or artificial drainage system.”

The report was prepared by the Institute for Water, Environment and Health, a unit of United Nations University; its chief author is Manzoor Qadir, a senior scientist of the institute and assistant director of its Water and Human Development Program.

The report is by design a meta-analysis, drawing on more than 20 previous research papers that have assessed the problem of crop losses traceable to excess soil salinity. And while the bulk of the new report is concerned with the intricate economic factors driving this unfortunate trend, and complicating all efforts to reverse it, the institute clearly means for its core message to be heard far beyond the specialist communities.

Institute director Zafar Adeel, in announcing the findings, noted that the Food and Agriculture Organization of the United Nations has projected from current population trends a need for 70 percent more food by 2050 — including that 50 percent increase, to about 3 billion tons a year, just in cereal grains. And yet,

Each week the world loses an area larger than Manhattan to salt degradation. A large portion of the affected areas in developing countries have seen investments made in irrigation and drainage but the infrastructure is not properly maintained or managed. Efforts to restore those lands to full productivity are essential as world population and food needs grow, especially in the developing world.

(I got curious about these big numbers and decided to do a little double-checking. Based on the IWEH estimate of 2,000 hectares or 5,000 acres lost per day, and a gazetteer figure of 33.7 square miles for the island of Manhattan, the world is losing that much acreage every four and a half days.)

Where is this happening?

In at least 75 countries, many of them in the developing world, as Adeel said, but in some highly developed places as well, including our San Joaquin Valley in California and parts of the Colorado River basin. Other regions highlighted in the report include:

  • The Aral Sea Basin of Central Asia
  • India’s Indo-Gangetic Basin
  • Pakistan’s Indus Basin
  • China’s Yellow River Basin
  • The Euphrates Basin in Syria and Iraq
  • Australia’s Murray-Darling Basin

And why is it happening?

In areas where rainfall is insufficient to sustain agriculture, farmers irrigate their fields with surface water or, more often, groundwater. Dissolved minerals in the water contain certain salts that aren’t particularly troubling if they pass quickly through the soil and return to an aquifer.

But soil drainage tends to be poor in dry regions, and water to be precious, especially on the “smallholder farms” that the UN report identifies as a chief source of the problem. These operations produce so little food that farmers have to supplement their agricultural income with other jobs, while teetering persistently at the edge of seeing their farms fail completely.

So they use the water frugally, in ways that cause salts to accumulate even faster in the root zone, poisoning the plants. Sometimes the salt degradation reaches a level that turns the soil surface to a hard, impervious crust, keeping out whatever rain might happen to fall.

And what is the solution?

There are several: Drainage practices can be adopted to carry water through the soil at a pace that prevents soil buildup. Trees can be planted to take salts back out of the ground. Salt-tolerant crops can be grown instead of, or in rotation with, the usual plantings.

All simple enough, except for the costs they impose on an agricultural sector least able to bear them.

Because this is a report with a heavy economics focus, it doesn’t lack for examples that monetize the problem, including an estimate that the annual losses attributable to salt-induced land degradation might amount to $27.3 billion worldwide.

But that’s just a measure of reduced yields, an extrapolation that draws on well-established measures of how salinity and alkalinity reduce crop outputs per acre. It doesn’t account for many other costs listed but not calculated by the authors, including damage to human and animal health, infrastructure decay and other losses associated with failing agricultural sectors.

The main focus, though, remains on the impairment of the soil’s food-producing capacity, and the example statistics are chilling:

In the Indo-Gangetic Basin in India, the crop yield losses for wheat, rice, sugar cane and cotton on salt-affected lands could be 40%, 45% 48% and 63%, respectively.

Multi-location studies undertaken on saline-sodic fields in the Indus Basin in Pakistan … reveal that wheat grain yield losses from salt-affected lands ranged 20-43% with an overall average loss of 32%. For rice, the crop yield losses from salt-affected lands ranged 36-69% with an overall average loss of 48%.

This can be fixed, the authors point out. In addition to tree-planting, excessively salty soils can be amended with gypsum products, and in the wheatfields of Uzbekistan it has been shown that growing a variety of perennial licorice can not only take salt out of the soil but produce an agricultural product useful in making candies, herbal medicines, cosmetics and liqueurs.

Problem is, all of these solutions are expensive to the smallholder farmer on whom they primarily depend, and in most cases will require the involvement of political and social structures that typically have been difficult to engage.

And however much one might enjoy the occasional dram of absinthe or Pernod, converting wheat fields to licorice production can’t really be counted as a contribution to addressing the world’s looming food shortages.

* * *

The IWEH paper was published in the U.N. Sustainable Development Program’s journal Natural Resources Forum and can be read here, with additional materials here.

Comments (4)

  1. Submitted by Ray Schoch on 10/30/2014 - 01:11 pm.


    Some of us…ahem… have never liked licorice, even in childhood.

  2. Submitted by Daniel Collins on 10/31/2014 - 09:21 am.

    Deadly serious

    This is a disaster by any standard. And the scale, the acres being lost estimated to be the size of Manhattan every ~3.5 days scares the beejesus out of me.

    The governor of California is trying to make this worse. Mistakes have been made that need addressing. I’m sure ones taste for licorice won’t be addressed.

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