Reversing the impact of salt on cropland

Reversing the impact of salt on cropland

Study looks at impact of salt on world's irrigated cropland. Degraded cropland now size of France. Can the process be reversed?

Mid-South farmers are well aware that turning on an irrigation system doesn’t mean strictly pure freshwater will reach the crop. Often, salts are part of the liquid package and, if allowed to accumulate, future yields will be hampered.

The same is happening in irrigated fields around the world. The scope and solutions to the problem are the subjects of a newly-released study by the United Nations’ Institute for Water, Environment and Health.

“Food security concerns coupled with the scarcity of new productive land have put productivity enhancement of degraded lands back on the political agenda,” reads the study. “In such a context, salt-affected lands are a valuable resource that cannot be neglected nor easily abandoned even with their lower crop yields. This is especially true in areas where significant investments have already been made in irrigation and drainage infrastructure…

“Simple extrapolation suggests that the global annual cost of salt-induced land degradation in irrigated areas could be $27.3 billion because of lost crop production.”

Manzoor Qadir, leading author of the study, spoke with Farm Press in early November. Among his comments:

The impetus behind the study?

“There are two main drivers behind it. One is food security concerns across the globe.

“Second, we don’t have much more productive land in irrigated areas. When I speak of ‘irrigated areas’ it’s referencing those areas where rainfall isn’t sufficient and irrigation is necessary to produce a crop. That’s mostly in arid and semi-arid regions where rainfall is typically much less.

“In such regions, there are often large-scale irrigation schemes in place. They tend to be very productive. For example, 18 to 20 percent of the global cropland is irrigated and that produces between 36 and 40 percent of the world’s food. That means 80 percent of the cropland depends solely on rainfall and produces just 60 percent of the food.

“With those numbers it becomes clear that it is very important we pay close attention to the irrigated agriculture. Currently, there is about 310 million hectares of irrigated cropland. Of that, some 20 percent has gone to salt-induced land degradation with compromised productivity. Some of that 20 percent has extremely low yields.

“So, we wanted to check the actual size of the salt-affected areas and how we might rehabilitate these lands.”

Accumulation

On salt accumulation…

“Once the process starts, it’s a snowball rolling downhill -- it only gets faster and larger.

“Whenever we irrigate in arid and semi-arid areas, we can’t help but add salt to the soil. Even freshwater contains salts. If we grow, say, cotton or wheat with good quality freshwater irrigation we’re adding salts in the range of one to two tons per hectare.

“Salts mainly accumulate in soils two main ways. When we irrigate, part of the water evaporates into the atmosphere and leaves behind the salts. The second manner is when plants take up water, which is largely pure, leaving salts in the root zone.

“If we don’t have a mechanism in place to ensure that, after a period of time, the salts are somehow removed from the root zone, they’ll go to deeper soil depths. Gradually, the salts will reach a level where they retard plant growth.”

On where the problems are worse…

“The major examples of large-scale degradation include some of the former states of the Soviet Union, like Turkmenistan. There are some huge cotton-producing regions that are backed by large scale irrigation systems. More than 50 percent of their irrigated area is basically salt-affected.

“The Soviet Union did install drainage systems in some of these states. However, in later years, the states didn’t keep up with the maintenance of the drainage systems. The systems became choked and that exacerbated the salt issues.”

An illustration of how big is the salt-affected area is…

“So, of the 310 million irrigated hectares about 62 million is salt-affected. The extent of salt-affected lands in 1990 was about 45 million hectares. Over 23 years, simple math shows that every day about 2,000 hectares of productive land is affected by salt-induced land degradation.

“Speaking about ‘millions of hectares’ is not always easy for people to grasp. It’s easier to say the affected area is about the size of France.”

Future impacts

How might this impact movement of populations in the future?

“In some areas that’s already happening. This type of land degradation is a gradual process. It doesn’t happen in just a few months. But if the early warning signs aren’t heeded and the situation is left alone then crop yields drop.

“When they drop far enough, the farmers move out. Often, they go to nearby cities. These are usually smaller farmers and are unable to handle the problem by themselves. They’re forced to leave and begin work in another industry.”

On ‘fixing’ the problem…

“There are several techniques available.

“One being researched is growing highly salt-tolerant crops. They can withstand the conditions in some of the impacted areas.

“The truth is there are a wide range of things that can be done to deal with the salts. We aren’t lacking technologies. There are other factors beyond biophysical interventions.

“Most of the problems with this are occurring in developing nations and their governments aren’t moving very quickly to address them. There aren’t relevant policies in place to trigger action on the ground. Most of the countries don’t even have salinity program frameworks in place to move forward to mitigate the problems.

“Further, in most of these areas, there is no economic analysis to help policymakers justify dealing with salts.

“Another aspect is the lack of capacity. Most of the researchers and professionals involved with salinity management in developing countries are still using very old methods in their assessments. In this era, when other researchers use GIS and remote sensing tools they’re still using conventional tools. That may mean the scope of the problem is actually worse than we believe.

“Lastly, we should address the role of the private sector. Somehow, reversing salt-induced land degradation hasn’t taken ahold in the private sector. Businesses should have been attracted to this much more -- especially in a private/public partnership.”

We’ve spoken about areas having trouble with salts. Have there been any success stories of cropland coming back from bad salt problems?

“There are examples. One is in the Australian Murray Darling Basin. In the 1970s, there was large-scale salinization there because of changing land-use patterns. Then, in the 1980s, the Australian government developed a management plan for the area and successfully reversed the problem.

“It can be done if you have the proper prioritizing, planning and implementation.”

Response to your report?

“We were hoping the press would pick up on this and it has. The education effort we were hoping for has begun through the international media.

“The study will hopefully be a big push to have policymakers’ eyes opened. This issue is absolutely important when considering global security and food needs of a growing population.”

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