Grains that grow year after year without having to be replanted could save money, help the environment, and reduce the need for back-breaking labor. Now, the largest real-world test of such a crop—a perennial rice grown in China—is showing promise. Perennial rice can yield harvests as plentiful as the conventional, annually planted crop while benefiting the soil and saving smallholder farmers considerable labor and expense, researchers have found.
“This is the first robust case study” of perennial rice, says Sieglinde Snapp, a soil and crop scientist at the International Maize and Wheat Improvement Center who was not involved with the work.
The results show the crop is “a potential game changer,” adds Clemens Grünbühel, an ecological anthropologist at the Australian Centre for International Agricultural Research who studies agriculture and rural development. The advance could reduce labor or allow China to grow more food, he and others say.
But whether the perennial rice will catch on is hard to predict, says Susan McCouch, a rice geneticist at Cornell University, because seasonal replanting still has some advantages over the new crop.
All rice is perennial to some extent. Unlike wheat or corn, rice roots sprout new stems after harvest. The trouble is that this second growth doesn’t yield much grain, which is why farmers plow up the paddies and plant new seedlings. The improved perennial rice, in contrast, grows back vigorously for a second harvest. Researchers developed it by crossing an Asian variety of rice with a wild, perennial relative from Nigeria. Improving the offspring took decades, and in 2018 a variety called Perennial Rice 23 (PR23) became commercially available to Chinese farmers. This was a “scientific breakthrough,” says Koichi Futakuchi, a crop scientist at the Africa Rice Center.
But how many times PR23 could be harvested before its yield dropped was unclear, as was the magnitude of any economic and environmental benefits. So Fengyi Hu, a geneticist and agronomist at Yunnan University, and others organized longer experiments. They arranged with farmers in three locations to plant the rice and harvest it twice a year for 5 years, while also growing typical rice varieties that were replanted each season.
Over 4 years PR23 averaged 6.8 tons of rice per hectare, slightly higher than the annual rice, they report today in Nature Sustainability. As hoped, the perennial crop tended to grow back again and again without sacrificing the size of the harvest. In the fifth year, however, the yields of PR23 declined for some reason, suggesting it needed to be replanted.
The perennial rice also improved the soil. Compared with annual rice, the crop left more nutrients—organic carbon and total nitrogen—in the soil, which also held water better. Retaining water doesn’t matter for irrigated rice, but it would benefit rice grown in regions that depend on rainfall. By next year, Hu says, the researchers hope to have results from a 6-year trial of another important factor: how much greenhouse gas perennial rice emits. Existing paddy-grown rice is a major global source of methane, for example, which contributes to global warming.
But is the new rice good for farmers? To find out, the researchers compared the effort involved in cultivating PR23 and the annual varieties. Fuel for plowing, the seedlings themselves, and other costs were basically the same the first year, typically $2600 per hectare. But for each following year the perennial rice cost half as much to manage. Each hectare also took between 68 and 77 fewer days of labor.
Those advantages are luring farmers. In southern China, Yunnan University provided seed and training to outreach workers, and the total area planted in 2020 quadrupled to 15,333 hectares last year. (That’s still a tiny fraction of China’s 27 million hectares of rice fields.) The government has also helped promote perennial rice, Hu says. This year, PR23 is on a list of 29 varieties recommended to farmers by China’s Ministry of Agriculture and Rural Affairs.
The largest beneficiary of the labor savings will likely be women and children, who do most of the transplanting of rice seedlings in many rice-growing countries, says Len Wade, an agricultural ecologist at the University of Queensland, St. Lucia, who helped test the rice variety. Mothers will have more time to “look after the family and get the children to school with breakfast and not exhausted,” he says. Farmers could also plant abandoned fields and grow more rice, or they might earn more income in side jobs like construction.
Still, Grünbühel cautions, more study of the impact on households will be needed to see how popular PR23 is likely to be and how the labor savings might affect farmers’ lives.
Researchers note potential risks. Because PR23 enables farmers to till less, fungi and other pathogens can build up in the fields. Insects can persist in the stubble after harvest, because it’s not plowed under, then transmit viruses when they feed on the regenerating sprouts in the spring. And without tilling, weeds can flourish; the researchers found that fields with PR23 needed one to two more herbicide treatments than regular rice. They also note that it’s more work to resow the perennial rice when its yield falters, because its larger and deeper roots need to be killed.
The potential benefits—and any downsides—will soon come into sharper focus. The perennial rice is being tried in 17 countries in Asia and Africa. Another major target is uplands in Asia, where plowing for conventional rise hastens soil erosion in small, terraced rice fields.
The creators of PR23 “have a proof of concept,” Snapp says. “I hope that there’s some momentum building.”
