Carbon is a building block of life, a key component of the soil organic matter that helps crops grow. Carbon naturally cycles between the soil and the atmosphere through plants, but when too much carbon is released from the soil into the atmosphere it does no one any good. It hinders farmers’ ability to remain productive and profitable. It also reflects poorly in terms of greenhouse gas emissions, which the U.S. and other countries are on a mission to reduce in an effort to address climate change and leave a healthier planet for future generations.
The Inventory of U.S. Greenhouse Gas Emissions and Sinks, which has been published by the Environmental Protection Agency annually since 1990, offers a look at how U.S. industries—including agriculture—are doing on their emissions. For agriculture, the latest report, released in April, coupled with additional data from the latest Census of Agriculture, tells a story of progress and opportunities for continued improvement.
First Look: Agriculture as a GHG Source
Agriculture contributed approximately 9.4% of total greenhouse gas emissions from the U.S. in 2021, according to the latest report. That’s 598.1 million metric tons out of 6,340.2 million metric tons in gross emissions. The U.S. netted an estimated 5,586 million metric tons of carbon dioxide equivalent.
Agriculture’s emissions have held relatively steady, remaining under 10%, with some ups and downs to be expected due to year-to-year changes in weather and markets, which affect numbers of acres and animals in production.
Major sources of U.S. emissions are:
- Transportation (approx. 28%)
- Electric power (approx. 25%)
- Industry (approx. 23%)
- Commercial and residential (approx. 13%)
- Agriculture (approx. 10%)
While the report notes there have been increases in emissions from agricultural sectors since 1990, emissions per unit of food have generally decreased as the industry becomes more efficient and gears up for the need to feed an increasingly populated planet. For example, dairy cattle emissions increased 13.4% in the past 30 years while milk production has increased by 62%. In any discussion on climate, we must remember to balance the need for food security.
The Big 3 Emissions
The three major greenhouse gas emissions of concern are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Most (79.4%) of the U.S.’s overall emissions are carbon dioxide, followed by methane (11.5%) and nitrous oxide (6.2%).
Agriculture leads the way as a source of methane (primarily through enteric fermentation and manure management; enteric fermentation is the natural digestion of livestock, especially ruminants like cattle) and nitrous oxide (primarily through soil management practices). Other, smaller sources of agricultural emissions, include carbon dioxide from liming and urea application, methane from rice cultivation, and methane and nitrous oxide from burning crop residues.
Agriculture as a Solution
Some might view these facts as bleak, but there is good news.
Agriculture—led by the land stewardship of farmers and ranchers—is not just a carbon source, it’s a carbon sink, meaning it has the ability to not just release but sequester carbon. This gives agriculture a unique story in the climate change conversation, one not obvious in an initial look at the EPA report. Agriculture is part of the solution.
Through their management practices, farmers and ranchers can decrease emissions and increase sequestration while improving their ability to produce food, reduce dependency on costly inputs, provide ecosystem services, and gain resilience in drought and flooding.
Example: Fertilizer Management
Take nitrous oxide, for example. It’s the bulk of agriculture’s emissions and is largely tied to the efficiency of nitrogen fertilizer use in fields.
Jerry Hatfield, Ph.D., Solutions from the Land senior adviser and former director of the USDA-ARS National Laboratory for Agriculture and the Environment, says when farmers fertilize with precision—using the right source at the right time with the right rate and at the right place—they can save themselves costly inputs while reducing potential for emissions.
Some farmers may find value in split applications of fertilizer or delayed applications. Those with low-yielding sections of fields may decide to significantly reduce or not apply fertilizer on those sections until they can improve the organic matter with strategies like reduced tillage, cover crops and integration of livestock grazing. Applying more nitrogen to low-yielding acres does not necessarily increase yield because often the real issue is an ability for the land to hold water, another indicator of soil health, Hatfield says. In this case, applying more nitrogen only adds cost to the farmer and increases potential for emissions.
“If we can get much more efficient in how we apply that nitrogen, or change the timing of that nitrogen application, we could dramatically reduce that nitrous oxide emissions number while improving crop productivity,” Hatfield says.
To reduce methane emissions, agriculture can continue to Improve forage quality and digestibility in livestock, Hatfield continues.
“The report helps us see the areas agriculture can leverage,” Hatfield says. “The dialogue we need to create now is, ‘How do we implement practices that reduce emissions and have a tremendous impact on our producers’ ability to efficiently produce food?’ These practices that can reduce emissions are not just for the environment. They are good for the farmer. They build resilience and help farmers be more efficient with their resources, including their finances.”
We Must Equip Farmers
Farmers need continued research, tools and technologies, and opportunities to collaborate among themselves and with agricultural partners to enable them to find and adopt innovative solutions for building soil health and improving the overall sustainability of their operations.
The latest Census of Agriculture shows us that farmers have already been adopting practices that, among many soil health benefits, are connected to reduced emissions, like reduced tillage and no-till as well as planting cover crops. States including Iowa, Missouri, Nebraska, Ohio and Illinois more than doubled their acres with cover crops from 2012 to 2017.
“The more we improve our organic matter in the soil, the better we can store more water in the soil,” Hatfield says. “But we’re also making that system more aerobic and reducing potential for nitrous oxide emissions.”
Agriculture is complex, he adds, and the EPA report should be reviewed with attention to the variability rates and uncertainty values. A biological system like agriculture is difficult to pin down with numbers, meaning there is a wide range of uncertainty over the data. Still, the report points out areas of opportunity for agriculture to focus on with an eye toward achieving win-win solutions for farmers, ranchers and foresters, and society and the planet.
“There’s still room for improvement, but in terms of our overall production system, we’re getting better and better all the time,” Hatfield says.
