An area of farm soil the size of France has been lost to salinisation of soils, according to experts at the UN University.

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The problem is mainly affecting soils in arid and semi-arid areas. UN University experts said on Wednesday that across 75 countries, 2,000ha of arable soil have been damaged by salt each day for the past 20 years.

Scientists at the UN University's Canadian-based Institute for Water, Environment and Health warned that this creeping degradation has led to an area the size of France becoming degraded. This is around 62 million hectares, or 20% of the world's irrigated lands. The figure has risen from 45 million hectares in the early 1990s.

Regions where rainfall is too low to allow rains to percolate through the soil, and where irrigation is practiced without a natural or artificial drainage system, are prone to salt degradation. Irrigation systems without drainage management lead salts to accumulate in the root zone, which reduces soil life and fertility.

"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 Manzoor Qadir, Assistant Director at Institute in Hamilton, Ontario. "We can't afford not to restore the productivity of salt-affected lands."

Zafar Adeel, director of the UN INWEH, added, "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."

Research looks at benefits of preserving land, reversing degradation

Research released this week by scientists at the institute, based in Canada, Jordan, Pakistan and Sri Lanka, details crop productivity losses at farm, regional, and global levels. The researchers also investigated the cost of doing nothing, and the net economic benefit of preventing and/or reversing land degradation.

They found that the inflation-adjusted cost of salt-induced land degradation in 2013 was estimated at $441 per hectare (almost £275), or a global cost of $27.3 billion (£17bn) for the year.

Giving the example of India's Indo-Gangetic Basin, the researchers note in their report that crop yield losses for wheat, rice, sugarcane and cotton range from 40% to 63%. As well as the cost of lost crops, the degradation could also have social and health costs, researchers warned.

"It is important to note that the above numbers on global cost of salt-induced land degradation refer to economic losses based on crop yield losses only," they warn in their report.

Even in the USA's Colorado River Basin, studies have shown the annual economic impact of degradation caused by salinisation of irrigated land to be $750 million (£466m).

Impact of salinisation could be underestimated

The researchers also note that "There may be larger gaps in crop yields harvested from salt-affected and non-affected areas under similar agro-ecosystems, suggesting an underestimation of the economic cost of salt-induced land degradation."

In addition to socio-economic impacts, such as deteriorating infrastructure, falling land values and the social costs of failing farm businesses, salinisation could even carry environmental consequences, as "Degraded lands… emit more greenhouse gases, thus contributing to global warming."

Though the threat form soil degradation is serious, there are solutions, including tree planting, mixing harvested plant residues into topsoil and improving drainage or growing salt tolerant crops.

The researchers said that – as they are not factored into market decisions – 'ecosystem services' such as healthy soil are at risk of being overlooked. They recommend that, although there is a cost of investing to prevent or reverse land degradation, or restore degraded land, these costs (of action) are "much less than the costs of letting land degradation continue and intensify."

They said a supportive policy framework, better infrastructure, help for farmers, use of locally available resources and respect for indigenous knowledge of communities will all prove crucial in combating salinisation.

One method advocated by the UN researchers has received a great deal of attention in the past week; Dutch farmer Marc van Rijsselberghe has reportedly produced potatoes which can be irrigated with salt water, which he claims could reduce pressure on water availability and food security.

Worldwide, well known salt-degraded land areas include:

• Aral Sea Basin, Central Asia,
• Indo-Gangetic Basin, India
• Indus Basin, Pakistan
• Yellow River Basin, China
• Euphrates Basin, Syria and Iraq
• Murray-Darling Basin, Australia, and
• San Joaquin Valley, United States