Flooded rice fields increasingly contribute to greenhouse gases

Rice is a dietary staple for billions of people worldwide, grown everywhere from the terraced paddies of Southeast Asia to the irrigated plains of China and India. But the same flooded conditions that allow rice to thrive also create the perfect environment for microbes that release climate-warming gases.

A team of environmental and agricultural scientists has found that greenhouse gas emissions from rice paddies have nearly doubled globally since the 1960s, as an article by The Conversation platform highlighted.

According to the study, they reached an average of around 1.1 billion tons of carbon dioxide-equivalent emissions annually during the 2010s, which is roughly equal to the yearly emissions produced by 239 million cars.

The findings mean rice cultivation is now the largest agricultural emissions source outside of livestock production, while global demand for rice is expected to continue rising in the coming decades.

Researchers say farmers already have tools available to reduce emissions without sacrificing yields. If all growers adopted the best currently available “climate-smart” practices, global rice emissions could be cut by around 10% by midcentury. However, scientists caution that much larger reductions will ultimately be needed to meaningfully slow climate change.

Why emissions are rising

The study identified two main drivers behind the increase in emissions: the expansion of rice-growing areas and the intensification of farming practices.

More than half of the global rise comes from the expansion of cultivation itself. In parts of Africa, for example, rice-growing areas have roughly doubled since the 1960s, contributing to a sharp increase in methane emissions across the region.

At the same time, farmers are using larger amounts of fertilizers and organic materials such as straw and manure, planting higher-yield rice varieties, and growing crops more densely. These methods increase rice production but also generate more greenhouse gases.

Researchers found that one practice in particular — leaving rice stalks in fields after harvest and plowing them back into the soil — accounted for around 18% of the increase in rice-related emissions since the 1960s.

While the method improves soil fertility, it also increases the amount of organic material decomposing underwater, creating ideal conditions for methane-producing microbes.

Rising global temperatures further intensify the problem by accelerating microbial activity in flooded soils.

Synthetic fertilizer use has also played a major role. Nitrogen fertilizer application increased by roughly 76% after 2000, boosting emissions of nitrous oxide, another potent greenhouse gas. The study estimates it contributed about 9% of the increase in total global net emissions from human activity.

Measuring rice’s climate footprint

Researchers note that assessing the full climate impact of rice production is more complicated than measuring a single greenhouse gas.

Rice paddies release methane and nitrous oxide from flooded soils, while rice plants themselves absorb carbon dioxide during growth. Fields also lose stored carbon between growing seasons.

To better capture the full picture, the research team combined multiple methods to analyze emissions from 1961 to 2020, identify the factors driving them, and test the effectiveness of mitigation strategies under future climate conditions.

The scientists concluded that reducing fertilizer use, limiting excessive crop residue applications, introducing periodic dry intervals between flooding cycles, and reducing tillage could together lower global rice emissions by around 10% by midcentury.

The team said they were surprised to find that replacing chemical fertilizers with organic alternatives is not always better from a greenhouse gas perspective, despite its popularity in organic farming systems.

Maintaining moderate levels of straw and crop residue can improve soil fertility, but excessive amounts increase methane emissions and accelerate soil carbon loss.

One promising alternative is converting part of the residue into biochar — a charcoal-like material created by burning organic matter under low-oxygen conditions before mixing it into flooded soils. Researchers say biochar can help stabilize soil carbon while reducing methane emissions.

Managing fertilizer use more carefully is also seen as a highly effective strategy, particularly in heavily fertilized agricultural regions such as parts of China and South Asia.

Excess nitrogen application often increases nitrous oxide emissions and water pollution without significantly improving crop yields. Reducing overuse could therefore cut emissions, improve water quality, and lower costs for farmers at the same time.

By Nazrin Sadigova