The study was conducted in Tarik Sub-district in Sidoarjo Regency, an area of more than 1,300 hectares of irrigated rice fields pressed up against the industrial sprawl of the Surabaya metropolitan region. Researchers from Wijaya Kusuma University and Universitas Pembangunan Nasional Veteran Jawa Timur spent 2026 monitoring a single hectare of productive farmland across two harvest seasons, one in January and one in June. Working with local farmers and agricultural extension officers, they measured everything that moves carbon into and out of the field: the biomass of plants, the grain that leaves at harvest, the straw that returns to the soil, the manure spread on the paddies, and the methane and nitrous oxide that escape into the air.

The technical heart of the study lies in its use of the Net Ecosystem Carbon Balance, or NECB, a framework that ecologists consider far more honest than the simple productivity numbers often cited in favor of rice as a climate solution. Net primary productivity, the total carbon fixed by plants through photosynthesis, looks impressive on paper. In this study it reached 13.75 tonnes of carbon per hectare per year, squarely within the range reported for tropical double-cropping rice systems worldwide. But the researchers warn that most of that carbon is essentially transit carbon. It is fixed by the plants, packaged into grain and straw, and then hauled off the field at harvest rather than permanently stored in the ecosystem.

When the researchers accounted for every flux, the picture changed dramatically. Of the 13.75 tonnes of carbon fixed annually, 10.99 tonnes left the field through harvest, since all the grain carbon and roughly 69 percent of the straw carbon were removed. Ecosystem respiration, the combined exhalation of plants and decomposer microbes, released another 4.37 tonnes of carbon as carbon dioxide. Methane emissions carried off a further 0.10 tonnes. Against those losses, the only meaningful carbon import was 2.30 tonnes from cattle manure applied to the field. The resulting NECB was a slim positive 0.59 tonnes of carbon per hectare per year, technically a carbon sink, but only barely, and only because of that narrow margin between enormous gross inflows and outflows.

Then came the gases that change everything. Because the field was irrigated intermittently rather than continuously flooded, methane emissions were relatively moderate at 134.40 kilograms per hectare per year, equivalent to 3.63 tonnes of carbon dioxide when scaled by the 27-fold warming power of methane under the IPCC AR6 standards. Nitrous oxide, driven largely by the 561 kilograms of nitrogen applied annually through urea, NPK fertilizer, manure, and returned straw, added another 0.72 tonnes of carbon dioxide equivalent, thanks to its staggering 273-fold warming potential. Total emissions reached 4.35 tonnes of carbon dioxide equivalent per hectare per year, which overwhelmed the 2.17 tonnes of carbon dioxide equivalent represented by the carbon sink surplus. The final annual net greenhouse gas balance was a positive 2.18 tonnes of carbon dioxide equivalent per hectare, meaning the field is a net source of warming.

This divergence between the two accounting frameworks is the study’s most striking finding. A field can simultaneously be a carbon sink and a greenhouse gas source because methane and nitrous oxide pack vastly more warming power per kilogram than carbon dioxide. Small mass fluxes of these gases, just 134 kilograms of methane and a mere 2.64 kilograms of nitrous oxide per hectare, still generate a climate burden that the carbon surplus cannot offset. The researchers note that this trade-off is well known in rice systems: shifting from continuous flooding to intermittent irrigation slashes methane but can nudge nitrous oxide upward, and in this study nitrous oxide contributed 16.6 percent of the net balance, slightly higher than the 12 percent reported in some earlier work.

The team translated that net emissions figure into money using Indonesia’s carbon tax of 30,000 rupiah per tonne of carbon dioxide equivalent, established under the country’s 2021 tax harmonization law. The result: an environmental liability of 65,400 rupiah per hectare per year, roughly 3.67 US dollars. That sounds trivial for a single hectare, but scale it across Tarik Sub-district’s 1,332 hectares of paddies and the annual environmental cost climbs to about 87 million rupiah, nearly 4,900 dollars. Across the millions of hectares of Indonesian rice land, the aggregate figure becomes a serious policy consideration, particularly for a nation that has already legislated a carbon tax and committed to ambitious climate targets.

The findings carry direct implications for two United Nations Sustainable Development Goals. For SDG 13, on climate action, the message is that rice mitigation strategies cannot lean on the comforting story of photosynthetic capacity. They must explicitly target methane and nitrous oxide at their sources, for example by optimizing the dose and timing of nitrogen fertilizer to curb nitrous oxide without sacrificing yields, and by expanding intermittent irrigation regimes, which the study confirms can suppress methane substantially compared with continuous flooding. For SDG 15, on life on land, the alarm concerns soil health: with nearly 70 percent of straw removed from fields and external organic inputs minimal, the long-term trajectory of soil organic carbon is at risk, threatening the land degradation neutrality targets embedded in the goal.

The researchers propose a three-part prescription for low-emission rice farming. First, farmers should return a larger, but carefully proportioned, share of straw and organic matter to their fields, which would strengthen the ecosystem carbon balance and gradually rebuild soil carbon stocks, though the additions must be balanced against the methane that fresh organic matter can stimulate in flooded soils. Second, nitrogen fertilization should be fine-tuned so that emissions fall without productivity suffering, a critical constraint in a crop that underpins food security for billions. Third, periodic or intermittent irrigation should be actively encouraged, since the study’s own emission calculations showed that the water regime was the single most powerful lever keeping methane in check at the site.

The authors are candid about the limitations of their work. Ecosystem respiration was drawn from a comparable study in the same region of East Java rather than measured directly, methane emission factors came from IPCC guidelines and Indonesian Ministry of Environment standards, and the carbon balance did not yet incorporate periodic measurements of changing soil organic carbon stocks. They call for multi-season monitoring, direct gas flux measurements, and multi-year assessments to validate the flux-based estimates. Even so, the study’s central lesson stands and resonates far beyond one Javanese sub-district: whether a rice paddy helps or harms the climate is not an intrinsic property of the ecosystem but the outcome of management choices, and national greenhouse gas inventories should judge farmland by its full annual balance rather than by snapshots of stored carbon. For a world that depends on rice and on a stable climate, getting that accounting right may be one of the most consequential calculations of the decade.

Subject of Research: Net carbon sequestration and annual greenhouse gas balance of Indonesian paddy fields and their economic-ecological implications for SDGs 13 and 15

Article Title: Carbon sequestration and the annual net greenhouse gas balance of paddy fields, and their economic-ecological implications within the framework of sustainable development goals 13, 15

Article References: Patiung, M., Wisnujati, N. S., & Leilasariyanti, Y. (2026). Carbon sequestration and the annual net greenhouse gas balance of paddy fields, and their economic-ecological implications within the framework of sustainable development goals 13, 15. Frontiers in Environmental Economics, 5, Article 1906407. https://doi.org/10.3389/frevc.2026.1906407

Image Credits: AI Generated

DOI: 10.3389/frevc.2026.1906407

Keywords: carbon sequestration, paddy fields, greenhouse gas balance, methane emissions, nitrous oxide, NECB, carbon tax, Indonesia, sustainable development goals, climate action, soil organic carbon, intermittent irrigation