Much as aquaculture has eclipsed wild fisheries, salt-tolerant plants could close the gap between escalating hunger and limited freshwater supplies
By James Workman
The ancients annihilated rivals by sowing conquered lands with salt. Modern agriculture has voluntarily inflicted this fate on itself. Today, half of all irrigated crop production is limited by the effects of salinity, according to the US Department of Agriculture, slashing the world’s harvest by a fifth. Worse, soil salinisation has been called both an ‘inevitable’ and ‘irreversible’ consequence of irrigation, even as humans seek to grow more food on less land while demanding 40 percent more freshwater than the world can provide.
The response has been an intensive global effort to balance freshwater supply and demand through efficiency, reuse, recovery, conservation and desalination.
But a small band of researchers, largely ignored as they labour in the margins, are looking beyond the usual resource-scarce recipe. With evidence that the Earth has more than enough ingredients to thrive, humans must simply think differently, they say, about what kind of land, water, or crops we should cultivate.
“Some 10,000 natural plants could produce just about everything we need in terms of food, fodder, feed and fuel,” says Dennis Bushnell, Chief Scientist at NASA Langley Research Center, and among the most vocal champions of the expanding discipline of saline agriculture.
The keys to resource abundance, he explains, come from halophytes. These make up the 2 percent of all plant species on the planet that have evolved through natural selection to cope with highly saline soils, salt pans, marshlands or even tidal flats. The most common names of the thousands of halophytic species include dwarf glasswort, sea spinach, date palms, pickleweed, or saltbush.
To be sure, these varieties rarely sound mouth-watering. Few halophytic plants can be found in your grocery store, and may never land on your dinner plate. But that also applies to standard irrigated crops; the bulk of freshwater-dependent, or ‘glycophytic’ grains are not eaten by us either. More than 76 percent of US corn harvests are consumed by cars and animals, not people. Indeed, North America grows its largest irrigated ‘crop’–lawns– simply to feed power mowers.
So as ‘normal food’ crops hit the wall of freshwater scarcity, halophytes offer a win-win alternative. They grow in marginalised landscapes, heal damaged saline soils, relieve pressure on rivers and aquifers, and provide vital resources and local resilience. But obstacles remain.
“The technical feasibility has been demonstrated,” says Edward P Glenn, a pioneering researcher in the field of saline agriculture, and Professor Emeritus at the University of Arizona. “A number of demonstration farms have been operated in different parts of the world. What has prevented wide-scale adoption is political, cultural and economic inertia.”
In other words, it took 11,000 years for civilisations to master freshwater farming, and decades more to develop our current globally productive agro-industrial complex. Saline agriculture can’t disrupt this deeply entrenched system overnight.
Some worry that halophytes will linger just out of reach. “Saline agriculture has a future when the need arises,” says Jacob Kijne, a global consultant in irrigation management to development aid agencies. “When sources of freshwater become scarce, societies appear to work hard to get there as soon as possible. Only then will it be a vital alternative.”
That future may be arriving. Salt-tolerant seeds–having been sown and harvested in demonstration projects–have begun spreading through the winds of change, and putting down roots in degraded landscapes. Some even export. Small-scale halophyte farms produce for the fresh vegetable market in Europe. Saltbush and orache species are being cultivated for animal feeds.
The question is, can it scale?
One key to the gates of saline agriculture can be found in oil. Perhaps the most commercially promising halophyte is dwarf saltwort, Salicornia bigelovii, which consists of 33 percent oil, rich in linoleic acid. That makes it a competitive alternative to the sunflower for cooking oil, and while it won’t replace other sources overnight, disruption has begun.
“The ideas haven’t been around for so long compared to the time required to launch a new agricultural industry,” says Glenn. He points out how the US Department of Agriculture “worked for 20 years or more to make sunflower a viable oilseed crop. Same story for canola oil which started out as rapeseed, which had toxic properties”.
Halophytes also hold out a tantalising source of clean energy. While corn ethanol converts rich soil and precious freshwater into a petrol additive, halophytes can unlock fuel without either. University of Delaware researchers found seashore mallow seeds comparable to soybeans as a source for biofuel. Last year, Yvonne Ventura, an Israeli researcher at the Jacob Blaustein Institutes for Desert Research of Ben Gurion University, concluded that, “time will ultimately be the determining factor advancing halophyte cultivation, when prices for fossil and alternative energy resources will exceed the halophyte biofuel production costs”.
Another option lies in forage. In the heyday of desalination (even in some parts today) arid coastal countries burn fossil fuels to purify seawater, to provide irrigation, to grow alfalfa and to feed livestock. Halophytes can help eliminate the first three steps. In the 1990s, Glenn recalled, his team discovered that “sheep raised on a diet supplemented with salt-tolerant plants such as saltbush, sea blite and glasswort gain at least as much weight and yield meat of the same quality as control sheep fed conventional grass hay.”
Halophytes still exist on the margins–of public minds and lands. Yet the genetics revolution could nudge them mainstream. Two decades ago, when biotechnology was still in its infancy, researchers struggled to make barley more salt tolerant. Today, with 107 Nobel laureates endorsing genetically modified organisms (GMOs) as demonstrably safe, halophytes appear to be gaining traction as technically feasible, commercially viable and socially acceptable food.
In this respect, NASA brings a planetary view toward food security. It is currently supporting research into a hundred drought-resistant potato varieties, many of them genetically modified to boost tolerance to salt. Astrobiologists express confidence that their calorie-rich plants can sustain humans on other planets, let alone the increasingly harsh conditions right here on Earth.
“Genomics would make halophytes much more productive, use less water, boost nutrients, and be designed for various fuel processing approaches,” says Bushnell. “But many do not like (the culture of) ‘Frankenfood’” due to our “terminally conservative fear of change.”
Cultural tastes and social fears present a barrier to adoption. So does political inertia. Established food industries resist halophytes as an existential threat to their current investments, says Bushnell. But opposition appears weakest where hunger and thirst are most acute. Government officials in Chile, Australia, Aruba, California, Saudi Arabia and the US are all exploring salt-tolerant crops. Even the UK government is weighing an investment into a saline agriculture research centre, to unlock its large scale potential.
“There are many energy options but no alternative to food, land and water,” says Bushnell. “As the water and food shortages deepen we will have to shift to halophytes. The raw need will outweigh inertia.”
As a global model for this tectonic shift, saline agriculture advocates the long opposition to, followed by explosive growth of, another saline food source: aquaculture.
Glenn became an optimist when his career began half a century ago in marine work at the University of Hawaii. “Our goal was to develop aquaculture to supplement wild fisheries, which were stressed,” he recalls. “We used to think it was hopeless. Then, slowly at first but then faster and faster, the world turned to aquaculture products over wild fisheries.”
Today half of fishery products are farmed; in 14 years the ratio will be two thirds. Halophytes may be a natural extension of this development, and indeed aquaculture runoff feeds salt-tolerant plants.
In Asia, vast seaweed farms dot the coastlines and shrimp, fish and shellfish are grown in ponds. “Saline agriculture in general, including aquaculture, has been advancing in importance globally,” adds Glenn. “All that seawater is a resource that can be used to grow halophytes on land and I do think it will eventually happen.”
