Saltwater-loving plants could open up half a million square miles of previously unusable territory for energy crops, helping settle the heated food-versus-fuel debate, which nearly derailed biofuel progress last year.

By increasing the world's irrigated acreage by 50 percent, saltwater crops could provide a no-guilt source of biomass for alt fuel makers and tone down the rhetoric of U.N. officials worried about food prices, one of whom called the conversion of arable land to biofuel crops "a crime against humanity."

While growing crops in saltwater has been on the fringes of horticulture for decades, the new demand for alternative energy has pushed the idea onto the pages of the nation's most prestigious scientific journal and drawn the attention of NASA scientists.

Citing the work of Robert Glenn, a plant biologist at the University of Arizona, two biologists argue in this week's Science that "the increasing demand for agricultural products and the spread of salinity now make this concept worth serious consideration and investment."

Glenn has been arguing for the value of all kinds of saltwater farming to a small but growing audience for nearly thirty years, but it is the demand for biomass to turn into fuel that brought NASA calling. His team's report for the agency estimates that salt-loving crops could be used to produce 1.5 billion barrels of ethanol annually on a swath of new agricultural land almost five times the size of Texas.

"I'm convinced that saltwater agriculture is going to open up a whole new expanse of land and water for crop production," Glenn said. "Maybe the world hasn't needed a 50 percent expansion in irrigated agricultural land because we've had enough food, but now that biofuels are in the mix, I think it's the way crop production should go."

The world's population has grown by five billion people since 1900 to an astounding 6.7 billion today. Despite the population explosion, food production — primarily animal feed and commodity cereals like wheat and rice — has been able to keep pace. But the food system has been severely stressed by a variety of factors, including the increasing use of arable land to grow energy crops to turn into biofuels.

Even if energy crops didn't cause all or even most of the precipitous rise in food prices in 2007, most social and environmental groups agree that the best location for bioenergy crops would be on currently unusable land. That would ensure that land used to grow food crops in poor countries wasn't converted to growing energy crops to power cars in developed nations.

A key question has remained, though: where exactly will humans find a whole bunch of unused land that is still good for growing crops?

Overly salty land could play a large and previously underappreciated role. That's because there's plenty of previously uncultivated territory in the world's coastal deserts, inland salty soils, and over-salinized agricultural land.

After taking into account environmental protections and other factors, Glenn's report estimates that 480,000 square miles of unused land around the world could be used to grow a special set of salt-tolerant plants — halophytes. Glenn's team calculated that this could produce 1.5 billion barrels of oil equivalent per year. That's 35 percent of the United States' liquid fuel needs.

Halophytes thrive in saltwater. While salt damages most plants, these salt-loving plants actually use the saltwater to draw in fresh water. In essence, they make themselves saltier than the surrounding water, which, through osmosis, drives fresh water into the plant.

These plants are attractive candidates for both food and fuel because they have very high biomass and oil seed yields. The Science authors note that one leading halophyte-candidate, Salicornia bigelovii, produces 1.7 times more oil per acre than sunflowers, a common source of vegetable oil.

"[Some halophytes] yield even more than things like switchgrass and they'll be grown on land that's just not used right now," said Glenn.

Of course, turning halophyte biomass into fuel will require further cost reductions in the production of biofuel from cellulose. Research into cellulosic ethanol continues around the world at a breathtaking pace and many industry observers expect the next five years to yield enough breakthroughs to make the technology economical.

Halophytes could also be part of the solution to another environmental problem: heavily-salinated wastewater from large farms. Right now, that water is dumped into manmade wetlands. For example, in California, the Imperial Valley authorities dump their salty water into the Salton Sea.

"That's a huge ecological problem waiting to happen," said Glenn.

After absorbing 80 years of agricultural runoff, the Salton Sea is 25 percent saltier than the ocean, and is facing serious ecological problems. Instead of pumping salinized water into these wetlands, the farms could capture that wastewater and use it to grow halophytes. Already, Sharon Benes, a plant scientist at Fresno State, has been planting test plots in the San Joaquin Valley.

But even if halophytes can help solve some of the world's environmental problems, Glenn is realistic about the difficulties of changing agricultural systems.

"I started in aquaculture back in the early 70s and we thought, golly, aquaculture is going to save the world. Looking back, it's been 35 years, but over half of the key fisheries products come from aquaculture, it just took longer than people thought," Glenn said. "I think it's the same thing with saline crop production."

Citation: "Crops for a Salinized World" by Jelte Rozema and Timothy Flowers. Science, doi 10.1126/science.1168572

Image: Salicornica bigelovii and Salicornica virginica growing in Galveston, Texas. flickr/Anna Armitage

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