The carbon footprint of grains has become an increasingly important topic as the world grapples with climate change and the need to reduce greenhouse gas emissions across all sectors of the economy becomes urgent.
Agriculture, Forestry, and Other Land Use (AFOLU) is a significant contributor to greenhouse gas emissions accounting for around 21%,17 with agriculture alone responsible for 13.5% of total global emissions.12
With grains like wheat, rice, corn, and soybeans forming the foundation of the global food supply, you most likely consume more grains daily than you care to admit.
This article examines the carbon footprint of grains production in depth, comparing carbon footprints across different countries and production systems and discussing strategies to reduce the climate impact of grain farming through more sustainable practices.
Carbon Footprint of Grains by the Numbers
What is a carbon footprint? A product’s carbon footprint is the total greenhouse gas emissions caused by its production, use, and disposal. It is expressed as grams or kilograms of carbon dioxide equivalent (CO2e).
The carbon footprint of grains refers to the total greenhouse gas emissions associated with the growing, harvesting, processing, transporting, and incidental disposals of grains. This comprehensive life cycle assessment (LCA) approach accounts for all sources of greenhouse gas emissions from “cradle to farm gate.”
This sums all the emissions from each stage and divides the total by the crop yield to determine the carbon intensity per unit produced (e.g. kg CO2 eq. emitted per kg of grain).
Quantifying the carbon footprint of grains is complex as it varies widely based on factors like crop type, location, farming practices, and transportation.
Although data in this field is still lagging, some experts and organizations have attempted to quantify the carbon footprint of individual crops, including grains, which include the full life cycle.
| Carbon Intensity Rank (Highest to Lowest) | Type of Grain | Average Emissions | Key Drivers |
| 1st | Rice | 1.60 CE/kg27 | Methane emissions from flooded paddies, double-cropping, use of nitrogen fertilizers, straw burning |
| 2nd | Wheat | 0.75 CE/kg27 | Low yield levels and high nitrogen fertilzer application rate |
| 3rd | Corn (maize) | 0.48 CE/kg27 | Nitrogen fertilizers, farm machinery, and energy requirements for irrigation |
| 4th | Oilseed rape (canola) | 0.404 CE/kg3 | Lower yield levels and higher nitrogen fertilzer application rate |
| 5th | Soybeans | 0.1 CE/kg5 | Requires little nitrogen fertilizers |
- Rice has the highest carbon footprint, with average emissions of 1.60 kg CE/kg.27
The main reason is methane emissions from flooded paddy fields, which account for 45 to 60% of rice’s total GHGs. Double-cropping of rice, use of nitrogen fertilizers, and straw burning push its footprint even higher. - Wheat has a global average carbon footprint of around 0.75 kg CE/kg.27
Regional differences are driven largely by yield levels and nitrogen fertilizer application rates. China has particularly high emissions which reflect a combination of lower yields and very high N rates. - The carbon footprint of corn production is slightly lower than wheat and rice at 0.48 kg CE/kg.27
This number varies between countries and regions. The key drivers are the use of nitrogen fertilizers, farm machinery operations, and energy requirements for irrigation. - Oilseed rape (canola) has over double the carbon intensity of soybeans and cereals.
This is due to high fertilizer requirements and lower seed yields. Winter oilseed rape in Europe averages over 1.76 kg CO2e/kg.3 - Soybeans have the lowest carbon footprint among the major grains at 0.1 CE/kg.5
As nitrogen-fixing legumes, soybeans require little synthetic N fertilizer, greatly reducing emissions compared to cereals and oilseeds. - Across all crops and regions, the general ranking of carbon intensity from highest to lowest is: Rice > Wheat > Corn > Oilseed Rape > Soybean
While these average values provide a useful frame of reference, it is important to recognize the large country-to-country, region-to-region, and farm-to-farm variability around these estimates.1 For example, individual farms may have carbon footprints 50% above or below the regional averages, depending on their specific management practices, soil types, and local growing conditions.
Regional and Cropping System Comparisons
Globally, carbon footprints for grain production vary substantially across different countries and cropping systems. Developed countries with access to precision agriculture technologies and optimized management practices tend to have lower emissions per unit of production compared to developing countries.
For example, wheat grown in Canada has an estimated carbon footprint of around 0.35 kg CO2e/kg grain,6 roughly half that of the global average at 0.7 kg CO2e/kg. By contrast, wheat emissions in China are over 0.5 kg CO2e/kg grain.27
More broadly, a global meta-analysis found that the mean carbon footprint for grain crops in North America and Europe was 0.25 kg CO2e/kg grain, while South Asia and Sub-Saharan Africa averaged 0.38 and 0.59 kg CO2e/kg respectively.18 Limited access to improved germplasm, precision technology, and optimum management in developing countries hinders their ability to maximize resource use efficiency currently.
The choice of cropping system also has a major influence on grain carbon footprints.
Diversified crop rotations that include nitrogen-fixing legumes and high biomass cover crops tend to have lower emissions than continuous monocultures or rotations with unproductive fallow periods. Including a pulse crop like lentils in rotation with wheat can reduce the carbon footprint by over 30% compared to wheat-fallow.
In China, maize/soybean strip intercropping lowered the system carbon footprint to 0.26 kg CO2e/kg grain,26 compared to 0.36 for a maize/wheat rotation. The complementary root architecture and N transfer from soybeans to maize enhances resource capture and use efficiency.
The Impact of Farming Practices on the Carbon Footprint of Grains
Farming practices have a huge influence on the resulting carbon footprint of the grain produced. Data from the HGCA Project Report 506 in the UK shows this very clearly. Here are the scenarios presented by the report:10
- Low intensity: 130 kg N/ha, very low pesticide, 7.0 t/ha yield
- Medium intensity: 177 kg N/ha, standard pesticide, 8.2 t/ha yield
- High intensity: 261 kg N/ha, standard pesticide, compost application, 8.2 t/ha yield
The low-intensity scenario has the smallest total carbon footprint at 0.244 kg CO2e/kg, compared to 0.361 kg CO2e/kg for the medium intensity and 0.539 kg CO2e/kg for the high-intensity farm. However, the footprints per hectare show a different pattern, with the high-intensity farm having the largest emissions at 2963 kg CO2e/ha, followed by the medium intensity at 1756 kg CO2e/ha and the low-intensity at 1738 kg CO2e/ha.
This difference between the per-kg and per-hectare footprints highlights a key dynamic: more intensive systems tend to have higher emissions per unit area due to greater input use, but lower emissions per unit of output because those inputs are converted more efficiently into yield.
This is particularly true for nitrogen fertilizer. The high-intensity farm applies twice as much N as the low-intensity farm (261 vs 130 kg N/ha) resulting in fertilizer-related emissions being 2.5 times higher per hectare. However, because that extra N boosts yields by 17% (8.2 vs 7.0 t/ha), the fertilizer emissions per kg of wheat are only 54% higher.
Other factors like soil type, tillage regime, and grain drying also play a role in the carbon footprints. The medium-intensity farm achieves the same yield as the high-intensity farm with 32% less N fertilizer but has higher emissions from direct fuel use, likely related to differences in cultivation and drying practices.
Comparing carbon footprints across production systems in this way demonstrates that there is no one-size-fits-all low-carbon farming strategy. Minimizing emissions per unit of output requires optimizing input use efficiency; applying just enough fertilizer and pesticide to reach yield potential while avoiding excess.
Drivers of the Carbon Footprint of Grain Production
Understanding the carbon footprint of any crop requires a comprehensive life cycle assessment (LCA) approach that accounts for all sources of greenhouse gas emissions from “cradle to farm gate.” For grains, the major components of the carbon footprint typically include:
- Fertilizer production and application
- Carbon dioxide (CO2) emissions from farm machinery and irrigation
- Soil disturbance and loss of soil organic carbon
- Methane (CH4) emissions from flooded rice paddies
- Processing, packaging, and transportation
- Emissions from food crop residue management
The manufacturing of nitrogen fertilizers is an energy-intensive process that consumes a lot of fossil fuels and releases significant amounts of carbon dioxide. Additionally, when applied in the field, a portion of the nitrogen in nitrogen fertilizers is converted to nitrous oxide (N2O), a potent greenhouse gas that has a global warming potential (GWP) that is 265 to 298 times that of CO2.23
According to research published in Nature, the global warming potential of nitrogen fertilizer production and use for grain crops ranges from 0.3 to 3.8 kg CO2-equivalent per kg of nitrogen applied.27 For wheat and maize, N fertilizer accounts for over 50% of total emissions on average, split roughly evenly between emissions from manufacturing the fertilizer and nitrous oxide (N2O) emissions when it is applied to fields.
Overuse of N fertilizer is a major issue in China especially, where application rates often exceed crop requirements. It follows that reducing N rates to optimum levels could cut carbon footprints significantly.
Emissions From On-Farm Energy Use (Machinery and Irrigation)
(Image: Lumin Osity29)
Direct energy use for field operations like tillage, planting, spraying, and harvest accounts for 6 to 14% of grain emissions on average.14
Irrigation energy is particularly important for water-intensive crops like rice. Pumping groundwater for irrigation can represent a significant portion of total emissions for wheat in some regions.
Energy use for drying grain to safe storage moisture levels after harvest is another emission source, responsible for 16% of the carbon footprint for some maize in China. A study in the journal Agricultural Systems found that farm operations accounted for 13 to 20% of total greenhouse gas emissions from US corn production.4
Soil Disturbance and Carbon Loss
Intensive tillage is another practice in conventional grain farming that increases carbon emissions by disturbing the soil and accelerating the decomposition of soil organic matter.
(Image: Mario Heller30)
The soil is a major reservoir of carbon, containing more carbon than the atmosphere and plants combined. Tilling the soil stimulates microbes to decompose organic matter, releasing carbon dioxide.
Conventional grain farming also tends to leave soil bare for extended periods, increasing erosion risk and carbon loss. Additionally, when natural ecosystems like forests are converted to farmland, large amounts of carbon stored in the biomass and soil are released as CO2.
The carbon emissions from land use change can be attributed to the crops grown on that land. Historically, converting grasslands and wetlands to cultivated cropland has led to massive losses of soil organic carbon (SOC) to the atmosphere.
(Image: Sandy Ravaloniaina31)
Methane From Rice Production
Rice is unique among the major grain crops in that it is often grown in flooded fields for all or part of its cultivation. When the soil is flooded or saturated, it becomes anaerobic, meaning there is no oxygen available.
This creates conditions for methanogenic bacteria to thrive. As these bacteria decompose organic matter in the soil, they release methane, a greenhouse gas 25 times more potent than CO2.
Rice cultivation is estimated to account for 11% of global anthropogenic methane emissions.11 The amount of methane generated varies depending on how long the fields are flooded, the amount of organic material incorporated into the soil, the rice variety, and the soil type.
A major strategy to reduce methane emissions from rice production is to drain the fields periodically during the growing season, which allows the soil to become aerobic and limits methane production. In China, study results show that using intermittent irrigation and avoiding continuous flooding could substantially reduce methane emissions from rice.27
Using rice varieties that are less susceptible to methane production and transpire less methane from their roots is another way to reduce emissions. Shifting rice production to areas with mineral soils rather than high-organic matter soils can also help.
Other techniques to curb methane from rice cultivation include:
- Removing rice straw after harvest rather than incorporating it
- Using sulfate-containing fertilizers to limit methanogens
- Improving water management to avoid waterlogging
- Planting cover crops to use up soil organic matter in the off-season
With strategic changes to rice production methods, methane emissions could be cut by up to 50% according to some estimates.
Emissions From Processing, Packaging, and Transportation
After harvest, grains undergo various processing steps before reaching consumers. Milling, drying, and other processes require energy inputs that contribute to the overall carbon footprint.
(Image: Julian Andres Carmona Serrato32)
Transportation of grains from farms to processing facilities and then to markets also generates emissions.
Grains are often shipped long distances via truck, rail, and ship to reach processing facilities and markets. The fuel consumption of this transportation contributes to the overall carbon footprint.
At processing facilities, grains undergo additional activities like cleaning, milling, and further refining that require energy inputs and generate carbon emissions. Heating and drying grains to proper moisture levels for storage uses large amounts of propane or natural gas.
A life cycle assessment of wheat flour production in Iran found that post-harvest operations accounted for about 25% of total greenhouse gas emissions.8 Additionally, a study of the US grain supply chain found that transportation accounted for about 10% of total greenhouse gas emissions associated with grain products.16
(Image: Ferdinand Stöhr33)
Crop Residue Management and Grain Wastage
The burning of crop residues like straw is still a common practice in many grain-producing areas which releases CO2, methane, and N2O.
However, alternatives like incorporating crop residue into the soil can help sequester carbon and reduce emissions.
Additionally, a significant portion of harvested grains is lost or wasted before consumption. Estimates suggest that around one-third of all grain intended for human consumption ends up as food waste.
What Are Grains?
Grains are the edible seeds of plants in the grass family.25 They include major staple crops like:
- Wheat
- Rice
- Corn (maize)
- Barley
- Oats
- Rye
- Sorghum
- Millet
Others include pseudo cereals like:19
- Quinoa
- Buckwheat
All these cereal grains have been cultivated by humans for thousands of years and form the foundation of the human diet in many parts of the world, providing carbohydrates, protein, fiber, and other essential nutrients. The three most widely consumed grains worldwide are wheat, rice, and corn.2
Wheat is widely consumed in bread, pasta, noodles, and baked goods. Corn is consumed directly as a vegetable and used to make tortillas, chips, and cornmeal. Rice is a staple for more than 3.5 billion people, particularly in Asia, Latin America, and parts of Africa.15
Grains are also used extensively as animal feed and for industrial purposes such as production of seed oils.
Types of Grains
Grains can be categorized as either whole grains or refined grains:
Whole Grains
Whole grains contain the entire grain kernel: the bran, germ, and endosperm.9 The bran and germ are rich in essential nutrients like B vitamins, minerals, healthy fats, and fiber.
(Image: Daniela Paola Alchapar35)
Examples include:
- Whole wheat
- Whole oats/oatmeal
- Brown rice
- Whole grain corn
- Whole rye
Whole grains provide more nutrients and fiber compared to refined grains.
Refined Grains
Refined grains have been milled to remove the bran and germ, leaving only the endosperm. This gives them a finer texture and longer shelf life but also removes many nutrients. Examples include:
- White flour
- White rice
- White bread
- Degermed cornmeal
While refined grains are easier to chew and have longer shelf lives, many nutrients are lost in the refining process.
(Image: Pierre Bamin36)
As a result, many refined grain products are enriched with some nutrients to replace those lost in processing.
Nutritionally, whole grains have been found to provide more fiber,9 protein, vitamins, and minerals compared to refined grains. However, in terms of carbon footprint, the distinction between whole and refined matters less than the type of grain and how it was grown.
As such, with the carbon footprint calculation of grains in most studies, the starting point is usually the raw harvested grain before any refining.
Whole grains tend to have a lower carbon footprint compared to refined grains. Refining grains to remove the bran and germ requires additional processing, which consumes energy and increases emissions.
Whole wheat flour has been found to have a 3% lower carbon footprint than refined wheat flour for this reason. Eating more whole grains in place of refined grains is one way you as a consumer can decrease the carbon footprint of your diet.
The Global Significance of Grain Production
Grains are fundamental to global food security and agricultural systems. Consider these key facts about grain production and consumption:
- Grains provide about 48% of calories consumed globally.21 According to the World Economic Forum, more than 40% of the global calory intake come from just 3 grain crops: wheat, rice and maize.7
- According to the U.S. Department of Agriculture, close to 3 billion tons of grains will produced globally in 2024.24 In the US, Corn is the most produced grain at 1.23 billion tons in 2023 – 2024, followed by wheat at 787.59 million tons and rice at 520 million tons.22
- According to the Food and Agriculture Organization of the United Nations, the projected global cereal production in 2024 now stands at 2.854 billion tons – a 0.3% increase from 2023.20
- China, the U.S., and India are the world’s largest grain producers.24
Given the massive scale of global grain farming, even small reductions in the carbon footprint per unit of production can have significant impacts on overall agricultural emissions.
How To Mitigate the Carbon Footprint of Grains
Given the significant contribution of grain production to the total greenhouse gas emissions or carbon footprint of agriculture, identifying effective ways to shrink the carbon footprint of these crops is critical to meeting global climate targets.
A mitigation strategy for grain production should aim to maintain or increase yields while reducing emissions intensity.
Some of the most promising levers to pull include:
Optimizing Nitrogen Fertilizer Management
As the single largest emissions source, improving nitrogen use efficiency (NUE) is one of the most powerful ways to cut carbon footprints.
Practices like split application timing, variable rate technology, stabilized/controlled-release formulations, and using soil and tissue tests to match N rates to crop needs can all boost NUE while reducing N2O emissions. Switching to lower-carbon fertilizers (e.g. made with renewable energy) can also provide further reductions.
Conservation Tillage
Reducing or eliminating tillage helps maintain soil structure and prevent the release of stored soil carbon. No-till and minimum tillage practices can significantly lower the carbon footprint of grain production.
Adopting Precision Agriculture
Precision agriculture techniques that use technology like GPS-guided equipment and soil sensors can help optimize inputs like fertilizer and water. By applying only what’s needed where it’s needed, farms can reduce costs and emissions.
Improving Residue Management
Alternatives to field burning, like mulching or incorporation of residues can reduce emissions while building soil organic matter. In some cases, residues can be collected to use as biofuel.
Improving Water Management in Rice
Draining rice paddies midseason and/or using alternate wetting and drying irrigation reduces methane emissions by 20 to 50% compared to continuous flooding.27 Direct seeding rather than transplanting cuts methane emissions as well.
Including Legumes or Cover Crops in Rotations
Diversifying cereal-intensive rotations with nitrogen-fixing legumes like soybeans, peas or lentils reduces the need for fertilizer N inputs. Growing non-legume cover crops also enhances soil health and carbon sequestration.
Renewable Energy Integration
Transitioning farm equipment and irrigation systems to renewable energy sources like solar and wind can lower the carbon footprint associated with energy use in grain production.
Embracing Agroforestry
Integrating trees into grain production systems through practices like alley cropping can increase carbon sequestration and provide additional environmental benefits.
Considering Organic Production
Some studies have found that organic grain production has a lower carbon footprint than conventional, primarily due to the avoidance of synthetic nitrogen fertilizers.
The potential emissions impact of these practices can be substantial. A UK study found that a suite of management changes including no-till, cover crops, controlled-release fertilizers, and nitrification inhibitors could reduce the carbon footprint of bread wheat by 20 to 37%.
In China, adopting all mitigation practices (optimizing N, reduced till, straw return, etc.) could cut grain production emissions by 32 to 47%.27
- Elimination of synthetic fertilizer use and associated emissions
- Increased soil organic carbon through use of cover crops and compost
- Reduced energy use for pesticide and herbicide production
However, organic grain yields are typically lower than conventional yields, which can result in higher land use requirements and potentially higher emissions per unit of grain produced. Studies have found that organic crop yields average 19 to 25% lower than conventional yields.13
The key takeaway is that while organic methods can offer environmental benefits, they are not inherently lower in carbon footprint.
Careful management practices and continued research are needed to optimize the sustainability and lower the carbon footprint of grains of both organic and conventional production systems.
Frequently Asked Questions About the Carbon Footprint of Grains
Do Whole Grains Have Lower Carbon Footprint Than Refined Grains?
Generally, yes. Whole grains tend to have a slightly lower carbon footprint because they require less processing than refined grains. However, other factors like growing location and farming practices also have a significant influence.
How Does Production of Organic Grains Affect Carbon Footprint?
Organic grain production often has a lower overall carbon footprint due to the elimination of synthetic fertilizers and pesticides. However, this can vary depending on yields and specific practices used.
What's the Biggest Contributor to the Carbon Footprint of Grains?
For most grains, the production and application of nitrogen fertilizers is the largest single source of emissions. For rice, methane emissions from flooded fields are often the biggest contributor.
How Does Eating Grains Compare to Meat in Terms of Carbon Footprint?
In general, grains have a much lower carbon footprint than animal-based foods like meat and dairy. Beef has a carbon footprint around 10-50 times higher than most grains per kg of food produced. Pork and poultry have a lower carbon footprint than beef, but still tend to be higher than grains. Eating a more plant-based diet centered on whole grains is an effective way to reduce your dietary carbon footprint.
What Are Some Low Carbon Grains?
While the carbon footprint depends on how and where a grain is grown, some grains that generally have a lower carbon footprint include oats, rye, sorghum and millet. Grains that require less fertilizer, irrigation and processing will tend to have a smaller carbon footprint. Organic grains are also associated with a lower carbon footprint of grains.
References
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28Sidedressing nitrogen on 24 rows of corn in one pass. Photo by James Baltz / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/a-few-farm-machines-in-a-field-ch1kOhA5_XM>
29An Irrigation Rigg in Nebraska sprays a corn crop at regular intervals. Photo by Lumin Osity / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/a-sprinkler-spraying-water-on-a-green-field-6DMht7wYt6g>
30Two tractors are plowing a field in the north of Thailand. Photo by Mario Heller / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/a-couple-of-tractors-that-are-sitting-in-the-dirt-Pu8mQaxqm3U>
31Rice Harvest Photo by Sandy Ravaloniaina / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/brown-wheat-in-close-up-photography-rARwqh9IXEE>
32Sacks of Rice Photo by Julian Andres Carmona Serrato / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/brown-printed-sack-lot-c9AuglIqhes>
33Burning rice field in Hoi An Photo by Ferdinand Stöhr / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/a-field-that-has-some-kind-of-fire-in-it-fLhFJYAU4KA>
34Crop Pesticide Photo by Arjun MJ / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/man-in-white-t-shirt-and-blue-denim-shorts-with-blue-backpack-walking-on-green-grass-792-GkRUtes>
35Corn seeds closeup, yellow and bright Photo by Daniela Paola Alchapar / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/a-close-up-of-a-bunch-of-corn-HRFDmqfmH5Y>
36White Rice Photo by Pierre Bamin / Unsplash License. Cropped, Resized and Changed Format. From Unsplash <https://unsplash.com/photos/white-rice-grains-on-brown-wooden-table--LdilhDx3sk>