Tao Li, a researcher at the International Rice Research Institute (IRRI) in the Philippines, has just taken a significant step toward transforming how the world accounts for greenhouse gas emissions from rice farming. Rice paddies are a major source of methane—a greenhouse gas 28 times more potent than carbon dioxide over a century—contributing roughly 10% of all human-driven methane emissions. Yet, until now, tools used to model rice systems have largely ignored the soil processes that drive both carbon storage and gas release.
Li and his team have upgraded the ORYZA model—a widely used platform for simulating rice growth, water use, and nitrogen dynamics—into ORYZA 3.5. The new version is the first to integrate soil organic carbon and nitrogen cycling with real-time simulation of methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) emissions. This makes it possible for the first time to use ORYZA for Tier 3 greenhouse gas inventories, the most detailed level of reporting under international climate guidelines.
“Farmers and policymakers have been flying blind when it comes to the carbon footprint of rice,” said Li. “With ORYZA 3.5, we’re not just predicting yields—we’re tracing the flow of carbon from soil to plant to atmosphere, and back again.”
The team tested the model using two years of field data from IRRI’s irrigated rice systems. Through sensitivity analysis and machine learning, they identified which soil and crop parameters most strongly influence emissions and yield. Surprisingly, soil hydraulic properties—how water moves through the soil—had the greatest impact on both rice yield and biomass. Meanwhile, seasonal methane emissions were most sensitive to methanogenesis potential, soil bulk density, and decomposition rates.
“What we’re seeing,” Li explained, “is that small changes in soil structure or water management can swing emissions dramatically. That’s not just academic—it’s a lever we can pull to reduce greenhouse gases without sacrificing food production.”
The model also revealed trade-offs and synergies. In simulations, 22–38% of parameter combinations simultaneously increased rice yield and reduced methane emissions—results that held up under statistical scrutiny. This suggests that targeted management, such as adjusting water regimes or residue incorporation, could deliver climate benefits while maintaining productivity.
For the energy and climate policy sectors, ORYZA 3.5 offers a powerful new tool. National greenhouse gas inventories often rely on default emission factors, which can over- or underestimate emissions from rice systems. With this model, governments and agribusinesses can now simulate region-specific scenarios, test mitigation strategies, and report emissions with greater accuracy.
Published in *Agricultural Water Management* (formerly known as the *Agricultural Water Management* journal in English), ORYZA 3.5 represents a leap toward climate-smart agriculture. As global demand for rice rises and pressure mounts to cut emissions, tools like this one could help align food security with climate goals—turning paddies from carbon emitters into part of the solution.