A Prickly Proposition

Can an overlooked succulent help salvage toxic soils?

  • The cactus requires little water, thrives in toxic conditions that kill other plants, and even improves soil by sucking selenium up through its roots and releasing it as a harmless gas, a process known as volatilization.
    Photo by Flickr/John Tann

California’s San Joaquin Valley might seem like an agricultural paradise. Nearly 90 percent of America’s processed tomatoes and 99 percent of our raisins are produced there, in broad fields that tumble from the Sierra Nevada and stretch to the Coast Range. But the valley is also an ancient seabed high in salt, selenium, and boron, and for much of the last century, farmers used irrigation to flush those minerals out of their soil and into groundwater or rivers—out of sight, out of mind.

By the mid-1980s, though, the selenium had concentrated in toxic levels in Kesterson Reservoir, causing deformities like missing eyes and protruding brains in birds and fish. Regulations were implemented to prevent farmers from sending briny irrigation water downstream, and wildlife health gradually improved. But because farmers were forced to reuse water again and again, the toxic elements built up on their fields instead of in wetlands. As the soil became ever saltier, farmers had to take swaths of once-fertile cropland out of production.

It was about that time that an energetic young soil scientist named Gary Bañuelos arrived. An early proponent of phytoremediation—using plants to improve contaminated soil—he’d helped Chinese villagers dealing with selenium poisoning and Chilean farmers with arsenic in their
irrigation water. In 1987, he was analyzing vegetables for radioactivity outside Chernobyl when the U.S. Department of Agriculture asked for his help: They wanted “the plant doctor” to figure out what could be done for the San Joaquin’s swiftly deteriorating soil.

But when he arrived in his home state, Bañuelos was stumped. “The nastier the soil, the more exotic you have to go with your plant selection,” he explains. “But you can’t go too exotic, because if the farmer can’t pronounce its name, they definitely won’t grow the crop.”

He considered Australian saltbush, but cattle that ate it became too thirsty and drained water supplies. Then he experimented with selenium-loving broccoli, but the hot, dry soil proved too harsh for it. Mustard seemed like an option, but as water in central California became increasingly scarce, no farmer wanted to spend precious drops on something they might not be able to sell.

It wasn’t until 2005 that a graduate student working under Bañuelos suggested Opuntia ficus-indica, better known as prickly pear. The cactus requires little water, thrives in toxic conditions that kill other plants, and even improves soil by sucking selenium up through its roots and releasing it as a harmless gas, a process known as volatilization. Plus, its juicy pears are beloved by chefs around the world. A tool to fix the San Joaquin’s soil problem was already there—Bañuelos just needed to fine-tune it.

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