Flood of potential on water-saving rice

Rice fields. Image: Polina Polina Kuzovkova / Unsplash

New approaches to managing rice production in Latin America are proving effective at reducing water usage and cutting back the high greenhouse gas emissions.

Rice is a crop that feeds nearly half the world’s population. Using traditional production techniques, paddy fields are flooded to stop weeds growing, which then produces methane as organic matter decays underwater without access to oxygen.

“Rice consumption is increasing as global population increases, and the main concern is how we will maintain production without depleting natural resources."

Eduardo Graterol Matute, Latin American Fund for Irrigated Rice.

Methane is a potent greenhouse gas, and global rice production generates 12% of all manmade methane, contributing 1.5% of overall global warming, according to the Asian Development Bank. Rice researchers have now found a way to adapt a method of intermittent irrigation known as alternate wetting and drying (AWD), where rice paddies are flooded and then left to dry.

“Colombia is an agricultural country that has set out to reduce its greenhouse emissions by 50% [by 2030] and techniques such as adapted AWD can help meet that goal, at least when it comes to rice production,” explains Sandra Loaiza, from the alliance between Bioversity International and the International Centre for Tropical Agriculture (CIAT), who led the research.

Laughing gas

AWD was developed in Asia by the International Rice Research Institute in the 1970s. The original version reduces methane release, but promotes the formation of nitrous oxide – also known as a laughing gas – a potent contributor to global warming. Loaiza and her team faced the challenge of inhibiting both gases simultaneously.

Under standard AWD, the water level is allowed to fall to 15cm below the soil, whereas in the new approach, developed in the Saldaña Municipality in the Tolima region, in the west of Colombia, the water is replenished sooner, resulting in lower stress and greater yields for the variety of rice used – Fedearroz 67.

“We adjusted the AWD to allow water to descend five and ten centimetres below the soil,” explains Loaiza.

Normally fertilisation is carried out when the field is flooded, but this means fertiliser is dissolved, resulting in the release of nitrous oxide. Under the adapted method, fertilisation is carried out when the soil is damp, reducing nitrous oxide emissions.

Ready for replication

Now Colombia's National Federation of Rice Producers, Fedearroz by its acronym in Spanish, is conducting additional tests to validate the outcomes on a larger scale. The approach has the potential to be replicated in other Latin American countries, as it reduces water demand and greenhouse gas emissions, without sacrificing yields.

“The relevance of this work is that it generates local hard data,” explains Edwin Barrios Gómez, from the National Institute for Forestry, Agriculture & Livestock Research in Mexico, acknowledging that the bulk of information on rice management is primarily obtained from Asia.

Image: Inkiipow / Unsplash

He says that the experience shows that rice does not need to be flooded all the time and that “we could reserve water for the most critical stages of the crop”.

According to the researcher, who didn’t take part in the experiment, it stands out for facilitating knowledge transfer.

“It is said that the problem with technologies like AWD is the lack of adoption, but many times it is because the solutions stay in universities or greenhouses,” adds Barrios Gómez.

According to the database of the UN's Food & Agriculture Organization, 117 countries and territories cultivate rice, with 25 of them located in Latin America and the Caribbean. Agriculture consumes 70% of the global freshwater supply and the rice sector hoards up to 43% of that.

Changing the paradigm

Rice is one of more attacked crops for its water consumption and the methane it emits, says Jorge Ayala Filigrana, an agronomist engineer and former organic rice producer in Palizada, Campeche in south-east Mexico, “but when you use the correct production system, such paradigm can change.”

Currently, between 12 and 75% of the daily calorie intake for the Latin American population comes from rice, as reported by the Alliance Bioversity International and CIAT. This emphasises the crucial role of rice in the region, especially considering that 70 million people lack the financial means to meet their food needs. The importance of rice for regional food security is undeniable.

“It is a staple food for those with limited economic resources because, for less than a dollar a day, you can feed four people,” says Eduardo Graterol Matute, executive director of the Latin American Fund for Irrigated Rice.

The average Latin American consumes 45kg per year, but in some countries, such as Panama and the Caribbean, consumption is as high as 70kg per person annually. This demand, although far below the 230kg consumed annually per capita in South Asia, where consumption is the highest globally, is constantly increasing.

For Graterol Matute this trend keeps him awake at night, “Rice consumption is increasing as global population increases, and the main concern is how we will maintain production without depleting natural resources,” he says. “This is where science, technology and organizations have a crucial role to accomplish.”

Climate change was one of the reasons why Mexican former rice producer Jorge Ayala Filigrana stopped producing rice in 2021, “Extreme rains impacted us, and higher temperatures affected the fertility of plants,” he says.

Jesús Solís, a farmer in the southern part of the state of Morelos, Mexico, is not planning to change his crop. He sows rice for three years, then switches to sugarcane for another three years, and repeats the cycle.

“Before we used pesticides, but now the cane’s stubble helps us control weed growth, and after five or six months, the grains [of rice] are already mature,” he says.

However, he admits that maintaining production is becoming more difficult over time. When he became a rice producer 45 years ago, there was enough water to sow 3,000 hectares. Today, he and the other producers in the region cannot even reach a third of that amount.

“We’ve devastated the flora, the urban sprawl has increased, temperatures that used to be 38-40 degrees now rise to 45 degrees, and there is less rainfall,” he says.

This article was produced by SciDev.Net’s Latin America & The Caribbean desk.