Climate change imposes new directions on rice cultivation – 05/29/2023 – Environment

Climate change imposes new directions on rice cultivation – 05/29/2023 – Environment


As the Earth warms and endangers the food supplies and livelihoods of billions of people, rice is in trouble. Sometimes there is a lack of rain at a time when young plants need water. Or it rains too much when they’re needing to protrude above water. With the sea advancing inland, the brackish water ruins the plantations. With the warmer nights, the productivity of rice fields decreases.

These dangers are all forcing the world to look for new ways to grow one of its most important grains. Rice growers are modifying their planting schedules. Growers work to create seeds capable of withstanding higher temperatures or salty soils. Resistant creole varieties are being reintroduced.

And when water becomes scarcer, as it has in so many parts of the world, farmers are intentionally letting their fields dry out, a strategy that also reduces the emission of methane, a potent greenhouse gas emitted by rice paddies.

The climate crisis poses special problems for smallholders with little land, as is the case for millions of farmers in Asia. “They will have to adapt,” said Phan Tan Dao, director of irrigation for Vietnam’s coastal Soc Trang province, one of the world’s biggest rice producers. “Otherwise they won’t be able to survive.”

One study found that extreme rainfall in China has reduced rice production over the past 20 years. India has limited its rice exports, for fear of not having enough to feed its own population. Heat and floods have destroyed crops in Pakistan, and in California prolonged drought is causing many farmers to leave their fields idle.

Today’s challenges are different from those of 50 years ago. At the time, the world needed to produce a lot more rice to avoid large-scale famine. High-yield hybrid seeds grown with chemical fertilizers helped. Farmers in the Mekong River Delta are now producing up to three crops a year, feeding millions of people in their region and around the world.

Today, this very intensive production system has created new problems all over the world. It has reduced aquifer levels, increased fertilizer use, reduced the diversity of rice varieties grown, and polluted the air with smoke from burning straw remaining in the fields. Compounding all of this is climate change, which has altered the rhythm of sunshine and rain that rice depends on.

Possibly the most worrying problem of all, given that rice is consumed daily by some of the world’s poorest populations, is that high concentrations of carbon dioxide in the atmosphere deplete the nutrients in each grain.

Rice faces another climate problem: it is responsible for an estimated 8% of global methane emissions. It is a small part of coal, oil and gas emissions, which together account for 35% of the total. But fossil fuels can be replaced by other energy sources. The rice, not so much. Rice is the staple food of 3 billion people. It’s biryani and pho, jollof rice and jambalaya—a source of translation and sustenance.

“We are living in a fundamentally different time,” said Lewis H. Ziska, professor of environmental health sciences at Columbia University. “You have to produce more with less. How do you do that in a way that’s sustainable? How do you do that in a changing climate?”

a risky balance

In 1975, faced with the risk of widespread famine after a war, Vietnam decided to grow more rice.

The effort was tremendously successful, as the country became the world’s third largest exporter of rice, after India and Thailand. The green patchwork of the Mekong delta has become its most prized rice-growing region.

At the same time, however, the Mekong River was modified by human hands. From its source in southeastern China, the Mekong runs through Myanmar, Laos, Thailand and Cambodia, being interrupted by many dams. Today, when it reaches Vietnam, there is little fresh water left to flush out the seawater seeping inland. Rising sea levels bring in more seawater. Irrigation channels begin to contain brackish water. The problem will only get worse as the temperature rises.

“Today we accept that rapidly rising salt water is normal,” said Pham, the director of irrigation. “We need to prepare to deal with this.” He said that in the past, salt water used to seep about 30 kilometers inland during the dry season, but now it reaches distances of 70 kilometers.

Climate change carries other risks as well. It is no longer certain that the monsoon season will start in May, as was the case in the past. So in dry years, farmers rush to plant rice 10 to 30 days earlier than normal, researchers have found. In coastal areas, many of them alternate between rice and shrimp production, which do well with a little seawater.

But to do so, you have to limit greed, said Dang Thanh Sang, 60, who has been growing rice in Soc Trang forever. Shrimp farming is profitable, but it carries great risks. Diseases can spread easily. The land becomes infertile. He has seen this happen with other producers.

So, on his 2.8 hectares of land, Dang grows rice when there is fresh water in the canals and raises shrimp when sea water infiltrates them. Rice cleans the water. Shrimp nourish the soil. “It doesn’t make a lot of money, like when you just raise shrimp, but it’s safer,” he said.

In a recent paper, researchers concluded that rice farmers in other regions will have to modify their growing schedules for rice and other grains. Scientists are trying to help them with this.

Argelia Lorence’s lab is full of rice seeds—310 different varieties.

Many of them are old varieties, which are rarely grown today. But they have genetic superpowers that Lorence, a botanical biochemist at Arkansas State University, is trying to identify, especially those that allow rice plants to survive hot nights, one of the most acute dangers of climate change.

She has identified two such genes so far. They could be used to produce new hybrid varieties.

“I am convinced that within a few decades farmers will need very different types of seeds,” said Lorence.

Less water in rice paddies?

Rice played a fundamental role in the history of the United States. He enriched the country’s southern coastal states, all with the labor of enslaved Africans who came with generations of knowledge of rice cultivation.

Today, the country’s main producing region lies on hard clay soil near where the Mississippi River meets one of its main tributaries, the Arkansas River. It bears no resemblance to the Mekong delta. The fields in this region are completely flat. The work is done by machines. The rice farms are immense, some covering over 8,000 hectares.

What these rice paddies have in common with those in the Mekong Delta are the hazards created by climate change. The nights are warmer. The rains are inconsistent. And then there is the problem created by the very success of so much intensive rice cultivation: the water table is dangerously low.

Benjamin Runkle is a professor of engineering at the University of Arkansas at Fayetteville. He suggested that instead of keeping rice paddies constantly flooded, as has always been done, Arkansas farmers let them dry out a bit. Then let the water in again and then repeat the process. And he asked them to let him measure the methane being emitted from their fields.

Mark Isbell, a second generation producer, agreed to do the experiment.

At the edge of his paddy field, Runkle set up a tall white device that a crane might mistake for a similar bird. The device measured the gases produced by the bacteria that reproduced in the flooded fields. “It’s like putting the earth to a breathalyzer test,” Runkle said.

Conducted over seven years, their experiment concluded that by not continually flooding fields, farmers can reduce methane emissions from rice paddies by more than 60%.

For producers who can demonstrate a reduction in their emissions, the Biden administration is offering federal funding for what it calls “climate intelligence” projects.

Agriculture Secretary Tom Vilsack came to Isbell’s farm last fall to publicize the program. Isbell thinks the incentives will persuade other rice farmers to adopt the alternate flooding and drying system.

“People look over the hill to see what’s coming to the future and learn now,” said his father, Chris Isbell.

Translated by Clara Allain



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