Salt Is Turning Farmland Into Wasteland Around the World
Much like a salt-heavy diet will eventually kill people, it will also kill the environment.
A Central Valley farm suffering from salinization. Image: Scott Bauer/Wikimedia
Eating too much salt in your diet can beget a litany of adverse health effects—blood pressure, stroke, heart disease, cancer. That's well documented. It's not as well known that consuming too much salt can have similarly dire effects on the environment, and, by extension, our food supply. Salt degradation has caused tens of billions of dollars worth of damage, mars an area of cropland the size of Manhattan every week, and has hit nearly one-fifth of the world's farmland so far.
"Salts have damaging effects whether they are in excess amounts in the human body or in agricultural lands," Manzoor Qadir, the lead author of an eye-opening new study on the subject, published by the United Nations' Institute for Water, Environment and Health, told me in an email conversation.
"If salt degradation goes on unchecked, more and more land will be highly degraded leading to wasteland," he said. "Restoring such lands will not be economically feasible at all."
When farmers irrigate crops with water—even "good quality" freshwater—salt comes along for the ride. Without proper drainage systems, the salt can then accumulate in soil whenever water evaporates and leaves it behind, or plants suck out the 'pure water' and leave salt concentrated in the root zone. Once enough salt accumulates, it can cause a host of problems to the crops—not entirely unlike how a salt-heavy diet adversely impacts people.
"In terms of effects on crops, salt-induced land degradation results in reduction in plant growth rate, reduced yield, and in severe cases, total crop failure," Qadir told me. This happens especially quickly in arid regions, which suggests the process may be accelerated by climate change.
The UN report brings some fairly astonishing findings—his team estimates that 2,000 hectares of farmland (nearly 8 square miles) of farmland is ruined daily by salt degradation. So far, nearly 20 percent of the world's farmland has been degraded, an area approximately the size of France.
Naturally, this carries some serious implications for food security, as well as a hefty price tag. The report notes that "the global annual cost of salt-induced land degradation in irrigated areas could be US $27.3 billion because of lost crop production."
Right now, the problem is only growing worse, and Qadir worries that in some cases, once-arable farmland will be ruined permanently.
To halt the trend, Qadir says we need to implement solutions at both the local and national levels: "irrigation and drainage schemes must account for water quality impacts, and farmers must be motivated to irrigate efficiently, with minimum leaching fractions." Countries should also adopt Salinity Management Action Plans to help ensure farmers can get the support and resources they need to both restore degraded crops and keep healthy ones from overdosing on salt.
The stakes are high here—the world will be home to nearly 10 billion people by 2050, and feeding everyone is going to be one of the great projects of the 21st century (surviving and adapting to climate change being the other). It's going to be additionally hard to keep the world fed—and from rioting—if we're rapidly losing our most important cropland to reversible processes like salt degradation.
Because Qadir is such a good communicator on this issue, I'm appending our email interview below, for those interested in diving in a bit deeper.
Motherboard: How does salt degradation happen?
Manzoor Qadir: Salt is a natural content of soils and water. Even the good-quality water (freshwater) contains salts and irrigation with such water also adds salts to the irrigated land. So irrigation with freshwater to grow and complete growth cycle of a crop like cotton or wheat may add salts to the soil between 1 to 2 tons per hectare. The salts accumulate in soil by two main processes when irrigation water is applied: (1) evaporation from the irrigated land where by water evaporates and leaves behind salts on the soil surface; and (2) crop plants take up almost 'pure' water and the salts are left behind in the root zone and eventually begin to accumulate and concentrate there. Since soil salinity makes it more difficult for plants to absorb soil moisture, these salts must be leached out of the plant root zone by applying additional water. This water applied in excess of crop needs is called the leaching fraction. Salt-induced land degradation is also greatly increased by poor drainage system. In terms of effects on crops, salt-induced land degradation results in reduction in plant growth rate, reduced yield, and in severe cases, total crop failure.
Salt-induced land degradation is common in arid and semi-arid regions where rainfall is too low to maintain a regular percolation of rainwater through the soil and irrigation is practiced without a natural or artificial drainage system. Such irrigation practices without drainage management trigger the accumulation of salts in the root zone, affecting several soil properties and crop productivity negatively.
Why is it happening at such a large scale?
Efficient farm-level water management is essential to minimize the accumulation of salts in the irrigated soils. Irrigation water must be used sparingly, particularly in arid and semi-arid areas, as each unit of irrigation water adds salt that contributes to higher salinity levels in surface streams and groundwater. Too often, planners of irrigation schemes do not account sufficiently for the downstream effects of excessive irrigation. They assume that the surface runoff or deep percolation from one farm is beneficial to other farmers. Yet water quality inevitably degrades along the sequence of subsequent water uses. In case of no or inadequate drainage system, salts tend to accumulate in the root zone, thereby leading to salt-induced land degradation. Most irrigation schemes, particularly in developing countries, have inadequate drainage systems, leading to extension in salt-induced land degradation and extent of salt-affected lands over time.
Well known examples of salt-induced land degradation include the Aral Sea Basin (Amu-Darya and Syr-Darya River Basins) in Central Asia, the Indo-Gangetic Basin in India, the Indus Basin in Pakistan, the Yellow River Basin in China, the Euphrates Basin in Syria and Iraq, the Murray-Darling Basin in Australia, and the San Joaquin Valley in the United States. The anthropogenic environmental changes resulting from salt-induced land degradation in the Aral Sea Basin are considered to be the largest in recent times.
What is the most promising way to efficiently solve the problem?
In terms of bio-physical strategies, irrigation and drainage schemes must account for water quality impacts, and farmers must be motivated to irrigate efficiently, with minimum leaching fractions. Wide adoption of minimum leaching fractions will minimize the cost of a regional drainage system for removing saline drainage water and maintaining sufficient depth to shallow water tables. There are a number of site-specific options available to reverse salt-induced land degradation and restore salt-affected lands.
The actions and investments needed to restore salt-affected lands require action at the national level (for example, developing a Salinity Management Action Plan) to address action at the farm level are: (1) pertinent policies to facilitate availability, price control, transportation, and application of soil amendments along with the allocation and supply of additional amounts of water for salt removal from affected areas; (2) involvement of supportive institutions and skilled human resources to undertake soil and water quality testing and mapping in the degraded areas and advice on selecting pertinent soil management approaches; (3) provision of facilities and infrastructure for disposal of salts removed from salt-affected lands during restoration; (4) capacity development of farmers to follow up on recommended salinity management approaches; (5) utilization of locally available resources and indigenous knowledge of communities in combating salt-induced land degradation; (6) comprehensive economic analysis of salt management options (cost and benefits of 'action' vs. 'no action'); and (7) involvement of private sector, particularly those businesses in close connection with natural resources but potentially at greater risk with significant effects directly or indirectly. These businesses may deal with basic resources such as forestry, wood, pulp, and paper.
Does climate change play a role and/or accelerate the process?
In the process of salt-induced land degradation, the salt-affected soils have lost a significant fraction of their original carbon pool. The magnitude of the loss may range between 10 and 30 tons of carbon per hectare, depending on the original size of the carbon pool and the severity of degradation. The soil carbon pool, which consists of both organic and inorganic carbon, is not only important with regard to productivity and the environmental functions soil performs; it also plays an important role in the global carbon cycle by sequestering carbon. It is possible to enhance soil carbon sequestration by restoring salt-affected soils. Studies undertaken along these lines have demonstrated that by reducing salt-induced land degradation and cultivation of appropriate crops, shrubs, and trees on such soils have the potential to mitigate the greenhouse effect by increasing the amount of carbon present in the soil through the production of biomass.
In addition to carbon sequestration, there are additional benefits stemming from ecosystem services resulting from the restoration of the degraded lands, such as recreation and aesthetic values; and reduction in environmental degradation through improvements in soil health and structure, surface and groundwater quality, and air quality. Valuation of such ecosystem services is expected to result in favorable environmental and economic benefits, although functional markets for many of the ecosystem services are currently embryonic or nonexistent.
What's the worst-case scenario if salt degradation goes on unchecked, both on local scales and globally?
If salt degradation goes on unchecked, more and more land will be highly degraded leading to wasteland. Restoring such lands will not be economically feasible at all.
A related but slightly different aspect of salt-induced land degradation, which may help further in understanding the effects of salts. When we talk about salts in agricultural lands, we refer to a mix of salts, including sodium chloride (table salt) in significant amounts/proportions. Here is an interesting dimension with lot common with regard to sodium effects on human body and irrigated lands.
In case of human body as sodium accumulates, the body holds onto water to dilute the sodium. This increases both the amount of fluid surrounding cells and the volume of blood in the bloodstream. Increased blood volume means more work for the heart and more pressure on blood vessels. Over time, the extra work and pressure can stiffen blood vessels, leading to high blood pressure or even heart attack, stroke.
The soils where sodium salts accumulate in the root zone exhibit unique structural problems as a result of certain physical processes (slaking, swelling, and dispersion of clay) and specific conditions (surface crusting and hardsetting). These problems can affect water and air movement, plant available water holding capacity, root penetration, seedling emergence, runoff and erosion, as well as tillage and sowing operations. In addition, imbalances in plant nutrition occur and these may result in deficiencies of several nutrients. In severe cases, the soils are degraded to the level that convert them to salt-affected wastelands.