Rising Temperatures Effect On Rice Yields, Growth And Quality


Various Korean rice yields types were tested in 2010 to see how they would grow in higher temperatures brought about by climate change.

Various Korean rice types were tested in 2010 to see how they would grow in higher temperatures brought about by climate change.

The testing was based on general circulation model (GCM) scenarios and virtual models called crop environment resource synthesis (CERES). It was conducted by agro-climate change and ecology researchers from the state-run National Institute of Agricultural Sciences.

The results were startling. Compared to Korea’s average temperature between 1971 and 2000, a test scenario with a rise of 2 degrees Celsius showed rice yields would fall by 4.5 percent. The figure was 8.2 percent with a three-degree rise.

When the test used the United Kingdom Meteorological Office’s carbon dioxide-based scenario ― known to forecast higher temperatures than other virtual climate models ― the rice yields fall was 15 percent.

One of the Intergovernmental Panel on Climate Change’s future climate trajectories, which incorporated intensifying greenhouse gas concentrations worldwide, also showed that Korea’s rice production would sustain a huge hit, according to the Gyeonggi Province Agricultural Research and Extension Services.

Under the Representative Concentration Pathway (RCP) 8.5 ― a scenario in which greenhouse gas emissions continue to rise throughout the 21st century ― rice yields were expected to drop by almost 14 percent by 2040 compared to 2020.

“If the temperature keeps surging and we don’t come up with any measures, we could see our rice yields fall by as much as 40.1 percent at the end of this century,” Kim Joon-hwan, from the National Institute of Crop Science’s (NICS) Crop Production and Physiology Division, told The Korea Times.

The forecasts are frightening in a country where rice has been a food staple for centuries.

In fact, Korea is experiencing a greater rise in average temperatures than many other countries. According to Choi Byung-yeol from Gyeonggi agricultural services’ Crop Research Division, Korea saw a 1.5 degree Celsius rise in average temperature in the 100 years from 1912, whereas the global average was 0.7 degrees.

The country’s food self-sufficiency in 2018 stood at just 21 percent ― down from 94 percent in 1965 ― according to the Ministry of Agriculture, Food and Rural Affairs. It means Korea relies heavily on other countries and could suffer a huge impact if there are hiccups in the global food chain.

“The COVID-19 global pandemic has brought fears of a global food crisis,” Choi told The Korea Times. “The United Nations World Food Programme has forecast that the global population in food poverty will jump from 130 million to 260 million by the end of 2020.

“We have also seen news that major agro-exporters like Vietnam, Russia, Serbia, Pakistan, Cambodia and Thailand started limiting exports to protect their own food security. This so-called ‘food nationalism’ lockdown is becoming real. But what poses a greater threat is not something instantaneous like COVID-19. It is agro-environmental changes due to climate change’s impacts that have been happening for much longer terms.”

Rising heat

The country’s agro-experts have been monitoring rising temperatures in Korea because of their effect on rice growth, yields and quality.

In Suwon, in Korea’s central province of Gyeonggi, average temperatures during the rice growing period from May to October rose by 1.5 degrees Celsius between 1964 and 2018. During 2000-2019, the figure rose by 1.1 degrees Celsius. Choi said temperatures throughout Gyeonggi had risen by 0.3 degrees every 10 years since 1970, but recently the trend has accelerated.

While climate change’s two most defining effects are elevated atmospheric carbon dioxide and temperature, it is the latter that seriously affects rice production.

During rice’s heading stage ― when panicles are fully visible ― when the temperature is 35 degrees or higher, it affects pollens and makes pollination unlikely to succeed, according to Jung Jong-tae from Chungcheongnam-do Agricultural Research and Extension Services. He told The Korea Times that extreme heat had increased the unsuccessful pollination rate in 2018.

“For Japonica rice in Korea, the right temperature for 40 days of the ripening period following its heading stage is 21-22 degrees Celsius,” Jung said. “But if higher temperatures persist during that period, alpha-amylase, an enzyme in rice, becomes more active and dissipates starch inside the grains. It affects the rice’s quality and yield as more grains become smaller and opaque in color, the grains’ protein level increases and fewer grains become available for polishing.”

According to Ahn Gyu-nam from South Jeolla Agricultural Research and Extension Services, rising temperatures affect rice ripening. Higher temperatures, especially during the 20 days following the heading stage, severely damage rice yields.

“Rising temperatures shorten the grain’s growth period, especially for those that take longer than other types to ripen,” Ahn told The Korea Times. “Although we alternated timings for seeding to accommodate climate change’s impacts, it eventually shortens the growth period before heading.”

Citing NICS’s 2018 research that forecast climate conditions for Jeonju, North Jeolla Province, during 2051-60 based on the RCP8.5 scenario, Ahn said increased temperatures “sped up the grains’ growth rate and reduced days taken for the grains to reach the heading stage by five days.” This ultimately “decreased the proportion of ripened grains significantly whereas unripe grains greatly increased.”

‘Super rice’

It takes 15 to 20 years to develop and introduce a new genetically improved rice type to weather harsher climate conditions. Korea has seen some new types developed that have proven stronger than their predecessors.

But doubts remain whether these improved types will keep up with future climate conditions, prompting experts to urge faster research and development for a “super rice” before it is too late.

“Despite climate change’s effects in Korea, our rice production has so far been on the rise because of our new rice types,” Joo Ok-jung from Gyeonggi agricultural services told The Korea Times. The agency found that Samgwang, a rice type developed during the 2000s, yielded more than those from the 1990s, and even more than earlier types.

Joo planted Chucheong (a rice type developed before 2000) and Samgwang ― two major types in Gyeonggi ― in a 1,000 square meter plot and compared their yields from 2009 until 2019. The average annual yield for Samgwang was 574 kilograms, while that of Chucheong was 519, meaning the former had better adaptability to rising temperatures.

“Better rice types are born after their strength is proven in a number of encounters with high temperatures, typhoons, blight and harmful insects,” Joo said. “So the more recently developed types are equipped with a stronger nature.”

Gyeonggi agricultural services has begun developing rice types that pollinate and ripen well in high temperatures and can withstand diseases in the heat like bakanea. This makes the infected seeds grow at least 1.5 times higher than normal and die within the first two weeks.

“One of the new rice types we are working on will withstand the tropical climate Korea might experience in future, so we are researching genes that allow grains to ripen at high temperature,” Joo said. “Our other upcoming new breeds have been designed to withstand a shortage of water and fertilizers, so to be more effective for the future climate than the present.”

Other super breeds have been created by Chungcheongnam-do agricultural services. Bbareumi buds and ripens before summer’s extreme heat arrives in Korea in June. Baekokhyang, in contrast, starts to grow after late August when summer is almost over. Sebi, another super rice developed by a Sejong University professor’s team, has genes that allow pollination at 40 degrees Celsius, according to Jung.

“Future rice types must pollinate well under extreme heat, not trigger alpha-amylase to keep grains healthy and transparent, and have low protein levels,” Jung said. “Each of these traits means a defense against climate change’s various impacts like extreme heat, drought and flooding.”

Korean researchers’ hunt for stronger rice types dates back more than a decade. Seoul National University’s Department of Plant Science tested Hwaseong and Dasan in 2008 and 2009, respectively, and found the former superior. They saw that Hwaseong had a significant number of grains failing to ripen and a loss in yields when the temperature was raised by 5 degrees Celsius, whereas Dasan showed such signs between 1.5 and 3 degrees.

“Nurturing rice types that are not sensitive to high temperatures or developing new ones with such traits will reduce the risk of yield loss due to climate change,” the school researchers concluded.

Kim said NICS has also recently found that Jowun, Manan, Dongan and Ilmi are particularly strong Korean rice types ― with little change in quality or yield ― under high temperatures.

“We have been paying more attention to high temperature’s detrimental effect of reducing rice yields because of grains’ shortened growth period and increased respiration volume than CO2’s positive effect of increasing the grains’ photosynthesis volume and thereby increasing its yields,” Kim said.

But “super rice” cannot be a silver bullet by itself. Agricultural methods specialized for helping rice grow under extreme conditions are also required for future production.

Planting rice later than the conventional season of spring to see its budding past summer’s extreme heat is one way, according to Joo. This method is possible as spring and fall in Korea become shorter and summer comes earlier. Chungcheongnam-do agricultural services found that under temperatures of 26 degrees Celsius or higher for 20 days following the heading stage, irrigation with flowing water increased yields up to 14 percent compared to stagnant water.

The experts also recommended against using nitrous fertilization. Joo said the chemical hampers budding at high temperatures and lowers resistance to harmful insects.

Restricting arsenic in any form of fertilization is another key. Unlike the United States and China, where arsenic levels have often been high, in Korea, the chemical in over 1,100 rice samples was found at an average of 0.06 milligrams per kilogram, below the country’s standard of 0.2, according to the Ministry of Food and Drug Safety’s 2015 finding.

Arsenic and extreme heat were found to cause double the threat to rice production, according to Stanford University Earth System Science Department’s 2019 study.

“Korean rice so far seems safe from arsenic,” Jung said. “But if Stanford’s study is true, the chemical under high temperature could pose a new threat.”

The article is originally published at korean times.



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