Today’s rice farmers must plant new seedlings every year, a process that requires time, energy and expensive inputs like fertilizer and pesticides. But a promising new option may be on the horizon: perennial rice plants that grow back again and again.
Perennial rice isn’t a cure-all. But researchers say it can help growers do less work and spend less money, while also providing benefits to the environment. They shared more details about the innovative crop in a paper published this month in the journal Nature Sustainability.
Grown for millennia, rice is a staple crop that feeds an estimated four billion people around the world. But current production methods are labor-intensive and expensive. Many rice growers in China are aging, while the young people are moving away from farms and into cities. Moreover, rice is grown in flooded fields that are habitat for methane-producing microbes. Rice production currently releases an estimated 34 million tons of methane per year.
With these problems piling up, scientists suspected there was room for improvement.
“We have been feeding humanity by growing these grains as annuals since the dawn of agriculture, but it wasn’t necessarily the better way,” Sacks says in a statement. “Now we can consciously choose to make a better crop and a better, more sustainable agriculture. We can fix the errors of history.”
The road to perennial rice has been long and bumpy. The first attempt at developing this variety took place in the 1970s, but it wasn’t successful. Then, in the mid-1990s, the researchers managed to cross a conventional, annual rice variety (Oryza sativa) with a wild perennial relative grown in Africa (Oryza longistaminata). Using a laboratory technique called tissue culture, they prompted the hybrid embryo to grow into a plant with permanent living roots, NPR reports.
From here, researchers spent years tinkering with the hybrid variety to develop a perennial plant that produced lots of high-quality rice. After much trial and error, they released a successful candidate—known as Perennial Rice 23 (PR23)—to farmers in China in 2018.
As expected, PR23 grew back year after year, but researchers wanted more long-term data to fully understand its pros and cons. They asked farmers in three locations to plant PR23, then harvest it twice a year for five years. (All rice can be harvested twice, though the second harvest produces a much lower yield.) For comparison, they also asked the farmers to plant and harvest typical annual rice varieties.
During the first year, both varieties performed equally as well. But after that, the perennial plants began to show advantages. Over the first four years, they produced an average of 6.8 tons of rice per hectare, slightly more than the annual plants’ 6.7 tons per hectare. With perennial rice, farmers spent about half as much money on fertilizer, seed and other inputs as they did with the annual crops. They also did 60 percent less labor. As a result, growers’ profits increased 17 to 161 percent with perennials.
The new rice also boosted soil health, leaving behind more nutrients like organic carbon and total nitrogen compared to their annual counterparts. The soil also held water better.
But the perennials’ success isn’t infinite. Their yields started to drop in the fifth year, suggesting that farmers will need to replant periodically, though still not as often as with annuals. Researchers also don’t know if the perennial plants emit less methane than conventional ones do, though they’re conducting studies to answer that question by next year.
There may be other risks involved with growing perennial rice, too. Since the plants’ roots are deeper and larger, farmers have to work harder when they do eventually replant the perennials. Because farmers don’t till and plow as frequently with perennial rice, fungi and pathogens may build up in the soil, and weeds and insects can prosper in the fields. During the experiment, farmers needed to spray herbicide treatments more often on fields planted with PR23. As Sieglinde Snapp, a soil and crop scientist at the International Maize and Wheat Improvement Center who was not involved in the study, tells Science’s Erik Stokstad, perennial rice is still only in the “proof of concept” phase.
Potential drawbacks aside, more and more farmers in China are taking the leap and going perennial, though the new variety still accounts for a small fraction of the country’s 27 million hectares of rice. As a result of outreach and education efforts, farmers planted an estimated 15,333 hectares of perennial rice in 2021, a fourfold increase from 2020.
Farmers in 17 countries across Africa and Asia are also trying the rice, which may help address some of the existing research’s unanswered questions.
“While early findings on the environmental benefits of perennial rice are impressive and promising, more research and funding are needed to understand the full scope of perennial rice’s potential,” says study co-author Tim Crews, a scientist at the nonprofit The Land Institute, in the statement.