Thousands of farmers in China have started to grow a remarkable new version of rice, one that realizes an old scientific dream. It's a perennial form of the grain, which doesn't have to be planted anew each season, but emerges year after year from long-lived roots in the soil just as many wild grasses do.

Researchers at Yunnan University in Kunming, China, worked for more than two decades to create this rice, and have now revealed details of their success in the journal Nature Sustainability. Their perennial rice, they report, requires much less labor, dramatically reducing a farmer's costs while producing about the same amount of grain. Its long-lived roots may deliver big environmental benefits, too, although scientists need more data to confirm that.

"This is a really big deal. This is a change in the way that we think about agriculture," says Erik Sacks, a plant geneticist at the University of Illinois who collaborated with the Chinese scientists and co-authored the new study.

Some scientists, including Sacks, are hoping that this version of rice is a foretaste of future perennial crops that will transform agricultural landscapes, preserving vulnerable soil and enriching natural ecosystems. Other scientists are skeptical that this success can be replicated in other major crops such as wheat or corn.

Shilai Zhang, one of the leaders of the Yunnan University research group, wrote in an email to NPR that Chinese researchers first tried to create a perennial version of rice in the 1970s, but failed. They achieved a crucial breakthrough in 1996 by cross-pollinating a conventional rice variety with a relative of rice that grows wild in Africa, and is perennial. The resulting embryo wouldn't normally survive, but scientists used a laboratory technique called tissue culture to grow a new, hybrid rice plant from it. This plant had permanent living roots, like its African parent, but could also be cross-bred with standard cultivated rice.

Zhang and his colleagues grew thousands of offspring from this hybridization, trying to find a variety that was perennial, yet also delivered bountiful harvests of top-quality rice. "We failed again and again," Zhang wrote. Local farmers thought that they were only planting weeds, rather than true rice.

In 2018, however, the researchers finally had a perennial variety in hand that passed muster, and they released it to farmers in China. Other varieties went on the market two years later. They appear to be catching on. According to the researchers, about 11,000 small farms planted perennial rice in 2020, on a total area of roughly 9000 acres. A year later, the number of farms willing to try the new varieties had quadrupled, and the planted area jumped to 38,000 acres.

According to Zhang, many farmers are attracted to perennial rice because it takes less work. In some rice-growing areas of China, he wrote, "young people are moving away, and the rest of the rice producers are old." Perennial rice allows them to avoid the hard work, and the cost, of planting seed and transplanting seedlings into paddies each year. The Yunnan University researchers say that this cuts the cost of raising a crop roughly in half during the years when farmers don't have to plant it.

The new rice doesn't keep producing a bountiful harvest forever, though. In field trials, yields dropped off after four years of production, which included eight growing seasons. At that point, farmers need to replant.

Perennial rice still accounts for a vanishingly small portion of China's total harvest. According to Zhang, it's too early to estimate how widely it could spread. In theory, at least, it could thrive across the tropics. It is best adapted to places with plenty of water, such as irrigated lowland paddies, and it can't survive freezing winters.

Perennial rice could have the biggest environmental payoff, however, on hillsides which lack irrigation, and where rain can wash away exposed soil. Permanent living roots in the soil could preserve that valuable soil. The current versions of perennial rice aren't adapted to such conditions, but Zhang says his research group is working on varieties that could thrive there. The International Rice Research Institute (IRRI) in the Philippines tried to create perennial rice for upland, drought-prone areas in the 1990s, but shelved the program due to slow progress and lack of funding.

For some researchers, including Sacks, the Chinese rice varieties are a sign that it's possible to create perennial alternatives to today's major crops. Wheat, rice and corn, which have to be replanted each year, have nourished humanity for centuries, but growing them takes a heavy toll on the environment. Farmers generally clear their fields for planting by tilling the soil, which degrades it and exposes it to water and wind erosion.

The Land Institute, a nonprofit group in Salina, Kansas, has led the push for perennial crops. It provided financial support for research on perennial rice at Yunnan University, and has been promoting a perennial relative of wheat, which it has named Kernza.

Some other crop experts, such as Kenneth Cassman at the University of Nebraska, are skeptical that there's broad potential for perennial crops. In an email, Cassman argued that rice is a special case. Growing it in many parts of the world involves a lot of hand labor, so eliminating the work of planting is more valuable than it would be for other crops. In addition, even traditional rice is able to grow a second, smaller crop after being harvested, so it's not a huge genetic leap to achieve true perenniality.

A large Chinese company called BGI Genomics has thrown its weight behind perennial rice, promoting it in an online video. The company has announced field trials of the new rice in Uganda, in cooperation with that country's Academy of Agricultural Sciences.