Chinese rice farming trials cut methane emissions

Xia Zhijian

Techniques that use less water, produce more rice and emit less methane are gaining traction in China

In a mountain village in south-west China, the local people are playing a guessing game. A new climate-friendly way of growing rice is being trialled here that will reduce methane emissions. So, what’s the difference in yield between it and the conventional method?

Shortly after the guesses are in, the findings are revealed: the new approach can increase yields by about 20%.

Although it seems far removed, the rice cultivation in this village is connected to a joint statement made by China and the US at the COP26 UN climate conference in 2021. In it, China said that by COP27, which was held in November 2022, it would produce a “comprehensive and ambitious national action plan on methane”, to achieve significant results in controlling and reducing emissions by 2030.

The full text of that plan is not yet available. But during COP27, China’s climate envoy Xie Zhenhua said the text has been written, and that it focusses on three areas: energy and natural gas; agriculture; and waste handling.

Reducing methane emissions is an urgent problem and is viewed as essential to keeping the global average temperature increase below 1.5C. Methane has 86 times more warming potential than carbon dioxide over a 20-year timescale, according to the IPCC (Intergovernmental Panel on Climate Change). While the International Energy Agency has said methane accounts for 30% of global warming since the industrial revolution.

Methane remains in the atmosphere for about a decade, so rapid emission cuts could quickly reduce its contribution to global warming, winning some valuable time to avoid disastrous warming. This is the goal of the Global Methane Pledge, an initiative to voluntarily reduce global methane emissions at least 30% from 2020 levels by 2030, which is currently endorsed by 150 countries. China has not joined the initiative, but as the world’s biggest emitter of methane – accounting for 14.3% of global emissions – its actions, together with other major emitters, will be crucial.

Last year, the government published policy guidance on cutting methane from rice farming, while new planting methods and technologies are being tested in the field. However, as we shall see, the small profits available from small-scale rice farming in the south of China pose problems for promoting climate-friendly techniques.

Meanwhile, the centre of rice farming has been shifting northwards, where less water-intensive techniques are producing less methane. In parts of China’s vast expanses of paddy fields, methane emissions are quietly falling.

Why does paddy farming produce methane?

The microorganisms that produce methane are some of the most ancient forms of life. Known as “methanogens” they are widely found in oxygen-poor environments such as lakebed silt, animal intestines and flooded paddy fields.

Rice can grow in dry ground, but farmers found when domesticating the plant that it also grows well in flooded fields, while the weeds it competes with do not. Paddy field farming therefore developed and has remained largely unchanged for millennia.

The water in paddy fields acts as a barrier between the air and soil, creating the ideal oxygen-poor environment for methanogens, while organic matter excreted by the rice’s root systems provide nutrition. Those ancient organisms thrive in the water-logged soil, emitting methane as they do so.

29%

China produces 29% of the world’s rice and 29% of its methane emissions from paddy fields

China is the world’s largest rice producer, utilising 30 million hectares of land for rice farming in 2021, and producing a harvest of 210 million tonnes, according to the National Bureau of Statistics. Rice is the staple food for 65% of China’s population. The country has 20% of the world’s paddy fields and produces 29% of the rice, according to a paper published in 2018 in the Chinese Journal of Eco-Agriculture.

But those paddy fields are Chinese agriculture’s biggest source of methane emissions. According to the government’s Second Biennial Update Report on Climate Change (2018), China emitted 55.3 million tonnes of methane in 2014, with 22.2 million tonnes of that coming from agriculture. Paddy field rice farming accounted for 8.9 million tonnes, or 40% of all agricultural emissions. Research has found that paddy fields in China produce 29% of global paddy field methane emissions.

Cutting methane emissions from rice farming

In June 2022, the Ministry of Agriculture and Rural Affairs, and the National Development and Reform Commission, published plans for emissions reduction and carbon sequestration in rural areas and the agricultural sector. Paddy field methane reduction was listed as the first of ten priorities in that document, with plans to “promote water-saving rice irrigation where suitable, improve efficiency of water use, and reduce production of methane.”

The best-established method of cutting methane from rice farming is to shift away from traditional flooded-field methods. As the organisms that produce methane can only survive in oxygen-poor environments, letting the soil dry out regularly – exposing it to the air – reduces emissions.

The System of Rice Intensification, which originated in Madagascar in 1981, does this through the use of shallow and intermittent irrigation or alternate wetting and drying. Research has found these techniques can reduce methane emissions from rice growing by 22–64%.

SRI is widely used across Asia, Africa and Latin America. Alongside the environmental benefits, it increases yields and so farmers’ incomes.

But one team working on paddy field methane emissions says SRI isn’t practical for local farmers in China’s south-west. A team member, who preferred to remain anonymous, told China Dialogue: “We haven’t promoted the method as we found the farmers very confused about when they should and shouldn’t flood the fields. In the mountains of the south-west, paddy fields are left flooded year-round, and always have been. This means the fields continue to emit methane over the winter, even though nothing is growing.”

They explained that as the different farmers’ paddy fields are all connected, one farmer adding or removing water affects others, making things more complex.

To accommodate these millennia old practices, the research team has opted for another approach known as furrow flooding. This involves piling up earth into ridges and planting crops on top of them. The furrows between the ridges are then flooded.

“There are clear advantages to furrow flooding,” said the researcher. “The Institute of Soil Science at the Chinese Academy of Sciences found reductions of 60–80% in methane emissions. Managing water levels is easier, as water can be left in the furrows year-round. This saves the farmers a lot of work.”

Elsewhere, other approaches are being tried. In the township of Xitang in Jiashang county, Zhejiang, the China National Rice Research Institute and Alibaba Cloud have built a “smart” farming system as part of a 400 mu (27 hectare) low-carbon farming project.

According to the National Business Daily, the project uses Alibaba’s cloud computing tech and the Internet of Things to connect monitoring instruments with irrigation equipment and automated machinery, allowing more efficient, targeted management. For example, water level sensors are linked to valves that add or remove water from the field as necessary.

Calculations by the institute say the smarter techniques cut water use by 30–50% and methane emissions by 30% or more.

Challenges in popularising the new techniques

Rice farming in the south has been gradually shrinking as people move to the cities. In Hunan, for example, production was 27.6 million tonnes in 2015 and 26.8 million tonnes by 2021. China’s rice production has not been falling overall, however. Production has been shifting to the north. In Heilongjiang, 27.2 million tonnes were produced in 2015, and 29.1 million tonnes in 2021, according to the National Bureau of Statistics.

China has seen 40 years of rapid economic growth, creating many jobs and attracting hundreds of millions of people from the countryside to the cities. In the densely populated south, the remaining farmers tend to work only small patches of land. This makes it harder to achieve economies of scale. It is generally possible to make much more money in the cities. Fewer people are willing stay home and grow rice.

I’ve realised the biggest problem is that the villages are empty and nobody is planting rice

That presents another problem for the team trying to encourage furrow flooding in the south: “When we go into villages to try and talk about rice farming techniques, nobody is interested. A major problem for us is that resistance is in fact a resistance to the idea of rice farming.”

Although furrow flooding can reduce methane and increase yields, the changes aren’t big enough to tempt anyone to quit the factory job and come home to change existing techniques.

“Since joining the team, I’ve realised the biggest problem is that the villages are empty and nobody is planting rice,” said the researcher, who did not wish to be named. “Paddy field rice farming is very tough work and you don’t earn much. Two crops a year on a mu of land earn about 600 yuan (US$89). Why would you do that instead of working in a factory? Our method offers more stable, or even better, harvests. But the difference between 600 and 800 yuan isn’t significant. In some places in Hunan, they’re offering 600 yuan subsidies per mu of rice farming, doubling income, and still nobody is interested. Guangdong’s so close, who wouldn’t choose to work there?”

The team has found that to promote low-methane techniques should involve more than talking to villagers about how to grow rice. How to improve overall economic returns from farmland is the key. They’re investigating involving other more profitable crops too.

“We’re looking at using no-till cover techniques and planting other crops after harvesting [the rice] to add nitrogen and organic matter to the soil. That will increase soil fertility and reduce the need for fertiliser the following year, improving the harvest and reducing costs. We’re looking at a few ways of doing this, including no-till cover planting of broad beans, to see which is most profitable,” the team member said.

Potential for emissions cuts at scale

While rice farming in the south might be shrinking, things are different in the north-east, where there is more arable land per person and higher levels of mechanisation in agriculture. The province of Heilongjiang in particular, with its expanses of dark fertile soil, is becoming a new centre of rice production. Figures from the National Bureau of Statistics show the province grew more rice than any other in 2021 – 2.3 million tonnes more than second-place Hunan.

Rice growing in coastal provinces in the southeast like Guangdong, Fujian and Zhejiang has been shrinking since the early 1980s, according to a paper by Liu Guozhen, Li Zhengguo and others from the Chinese Academy of Agricultural Sciences’ Institute of Agricultural Resources and Regional Planning. Growth, meanwhile, has been mainly in Jilin and Heilongjiang in the north-east.

That shift north has meant changes in techniques. According to news agency Xinhua, Heilongjiang has been researching water-saving methods of rice growing since 2004, with water use reduced by 30–40% and yields up 5–10%. In 2012, that “dry-cultivation” method was used across 4 million mu. That expanded to 30 million mu in 2018, a sevenfold increase over eight years and more than half the area of flooded-field rice growing in the province.

The expansion was due to a combination of government support and significant cost reductions with the new method. One rice farmer, who has 400 mu of land in the Heilongjiang city of Hulin, said in an interview with ChinaNews.com that he had seen costs per mu fall by over 200 yuan, as well as savings on time, labour and water.

The changes rolled out in Heilongjiang have also reduced methane emissions. Research has found the dry-cultivation technique cuts production of methane by over 30%.

But while rice production has been shifting north, paddy fields in the south still produce most of China’s rice. According to the National Bureau of Statistics, only two northern provinces made it into the top ten rice growers for 2021. The other eight were all in the south and they grew 138 million tonnes of rice, about 65% of the total.https://flo.uri.sh/visualisation/12677250/embed

As all provinces have been told by the central government to maintain certain levels of arable land and grain production, there is little chance of a wholesale shift of rice growing to the north in this coming decade – a decade which is crucial for tackling climate change. There is still a lot of scope for climate-friendly techniques to be applied in the paddy fields of the south.

Some experts argue that increased “land transfers” – meaning long-term leases – could help reduce methane emissions from rice cultivation, while warning that smallholders’ land contract rights must be maintained to protect equity. If such transfers were made easier, then an increase in income of only 200 yuan per mu from dry-cultivation would be significant. On a 400 mu farm like that in Hulin, it would be 80,000 yuan per harvest, potentially more with government subsidies. This could increase the likelihood of people leaving factory jobs to implement the new techniques.

There is a parallel to be drawn with fertiliser reduction. In China, larger farms use less fertiliser per unit area, according to a joint study by China Agricultural, Zhejiang and Virginia universities.

The researchers found smallholder farms (less than 0.5 hectares on average) use machinery less and physical labour more, which hampers precise and science-based use of fertilisers. And as smallholder farmers can make more money working in the cities, they are less reliant on their farming income than larger professional farmers (with 30 hectare or more, on average). This makes the latter group more sensitive to changes in fertiliser costs and keener to reduce usage. But 98% of China’s cropland is farmed by smallholders. This led the researchers to recommend policymakers look at systems to facilitate “land transfers” and not just fertiliser application technology.

Chen Mei’an, programme director with the consultancy Innovative Green Development Program (iGDP), studies climate change issues in China. She told China Dialogue: “Farm size is a very important factor. China has smallholder agriculture, but applying better emissions tech costs money, whether it’s in fertiliser use or methane reduction, and that discourages smaller scale farmers. When you have larger farms, you get economies of scale and the costs are spread more thinly. Land transfers and leases would help achieve that.”

Xia Zhijian is Chinese language editor at China Dialogue. He has worked for a range of media outlets reporting on environmental issues.