Annual paddy rice is now available as a long-lived perennial after more than 9,000 years of cultivation. Farmers can now plant once and reap up to eight harvests without sacrificing yield, which is a significant improvement over "ratooning," or cutting back annual rice to obtain a second, weaker harvest.
"Farmers are adopting the new perennial rice because it is economically beneficial to them. Farmers in China, like farmers everywhere, are getting older. Everyone is moving to the cities, and young people are leaving. Rice cultivation is a time-consuming and expensive endeavour. They save a lot of labour and time by not having to plant twice a year "Erik Sacks, co-author of the report and professor in the Department of Crop Sciences at the University of Illinois, agrees.
In a collaboration between the Yunnan Academy of Agricultural Sciences and the International Rice Research Institute, Sacks, senior author Fengyi Hu, and Dayun Tao began working on perennial rice in 1999. In subsequent years, the project expanded to include the Universities of Illinois, Yunnan University, and Queensland University. Another collaborator, The Land Institute, contributed perennial grain breeding and agroecology expertise, as well as seed funding, to ensure the project's long-term viability.
The researchers created perennial rice by crossing an Asian domesticated annual rice with an African wild perennial rice. Using modern genetic tools, the team identified a promising hybrid in 2007, planted large-scale field experiments in 2016, and released the first commercial perennial rice variety, PR23, in 2018.
The international research team spent five years studying the performance of perennial rice alongside annual rice on farms across Yunnan Province. Over the first four years, perennial rice yield [6.8 megagrams per hectare] was roughly equivalent to annual rice yield [6.7 megagrams per hectare]. Due to a variety of factors, yield began to decline in the fifth year, prompting the researchers to recommend re-sowing perennial rice after four years.
Farmers growing perennial rice, on the other hand, used nearly 60% less labour and spent nearly half as much on seed, fertiliser, and other inputs because they didn't have to plant every season.
"The reduction in labour, which is often done by women and children, can be accomplished without the use of fossil fuel-based equipment, which is an important consideration as society seeks to improve livelihoods while reducing greenhouse gas emissions associated with agricultural production," Sacks says.
Perennial rice's economic benefits varied by study location, but profits ranged from 17% to 161% higher than annual rice. Even in locations and years where perennial rice yields were temporarily reduced due to pests, farmers still earned a higher economic return than growing the annual crop.
"That first season, when they planted the annual and perennial rice next to each other, everything was essentially the same: yield is the same, costs are the same, there's no advantage," Sacks says. "However, the second crop and every subsequent crop come at a huge discount because you don't have to buy seeds, you don't have to buy as much fertiliser, you don't need as much water, and you don't have to transplant that rice, which is a huge advantage."
Perennial rice cultivation provides significant environmental benefits by avoiding twice-yearly tillage. The research team discovered increased soil organic carbon and nitrogen storage in perennial rice soils. Other soil quality parameters also improved.
"Modern high-yielding annual crops typically necessitate the complete removal of existing vegetation to establish and frequently necessitate significant inputs of energy, pesticides, and fertilisers. This combination of repeated soil disturbance and high inputs has the potential to disrupt essential ecosystem services in unsustainable ways, particularly for marginal lands,” Hu, professor and dean of Yunnan University's School of Agriculture, says "Perennial rice benefits farmers not only by improving labour efficiency and soil quality, but it also helps replenish ecological systems that are required to maintain productivity over time."
Another component of the research looked at perennial rice's low-temperature tolerance in order to predict its optimal growing zone around the world. Although significant cold exposure hampered regrowth, the research team believes the crop could work in a wide range of frost-free environments.
Although the researchers have already conducted on-farm testing and released three perennial rice varieties as commercial products in China and one in Uganda, they are not finished refining the crop. They intend to use the same cutting-edge genetic tools to rapidly introduce desirable traits like aroma, disease resistance, and drought tolerance into the new crop, potentially expanding its global reach.
"While early findings on the environmental benefits of perennial rice are impressive and promising," says Tim Crews, Chief Scientist at The Land Institute and study co-author.
"There are still questions about carbon sequestration, persistence, and greenhouse gas balances in perennial paddy rice systems." Researchers must also make progress toward perennializing upland rice, which has the potential to reduce highly unsustainable soil erosion on farmlands throughout Southeast Asia. As Dr. Hu's group's work at Yunnan University continues, The Land Institute and an ever-expanding network of collaborators will continue to support global research and scaling efforts for perennial rice."
Sacks continues, "With perennial rice in farmers' fields, I believe we have reached a tipping point. Since the dawn of agriculture, we've been feeding humanity by growing these grains as annuals, but it wasn't always the best way. We can now consciously choose to grow a better crop and a more sustainable agriculture. We have the ability to correct historical mistakes."
