The American Society of Agronomy, the Crop Science Society of America and the Soil Science Society of America published a report titled “Agriculture’s Role in Greenhouse Gas Emissions and Capture” that reports that agriculture is responsible for 6% of U.S. greenhouse gas emissions.
In a summary by Penn State University soils scientist Sjoerd Duiker, the report highlights the following ways to reduce emissions or increase capture of greenhouse gasses in agriculture:
- Reduce fuel consumption
- Enhance soil carbon sequestration
- Improve nitrogen-use efficiency
- Increase ruminant-digestion efficiency
- Capture gaseous emissions from manure and other wastes.
Reduce Fuel Use
Fuel consumption in crop production can be reduced if farmers use conservation tillage to cut back on trips over the field. Farmers can also use cows (or buffaloes, sheep or horses) to harvest forages by grazing instead of mechanically harvesting alfalfa and grass with equipment running on fossil fuel.
Drying grain crops naturally in the field instead of in the grain bin using natural gas is another important method to reduce fossil-fuel use. Reducing the use of irrigation water also reduces greenhouse gas emissions because pumps run on fossil fuel.
Finally, precision fertilizer application and using more legumes in crop rotations can help to reduce nitrogen fertilizer use in crop production. The report states that this is an important way to reduce greenhouse gas emissions in agriculture, because more than 30% of fossil fuel consumption in crop production is due to the energy needed to make nitrogen fertilizer.
Enhance Soil Carbon Sequestration
Carbon sequestration is the transformation of crop residues and roots into long-lived carbon compounds in the soil through the process of microbial decomposition. Farmers have a unique opportunity to store carbon in their soils by increasing soil organic matter content, the report says.
Carbon sequestration can be increased by using conservation agricultural practices, including conservation tillage, winter cover crops, crop residue and waste management; diverse crop rotations, perennial pastures and land idling programs such as CRP.
According to the report, conservation tillage can sequester around 900 pounds of carbon dioxide per acre per year, and well-aerated soil with high surface organic matter can consume methane from the atmosphere.
Improve Nitrogen-Use Efficiency
While nitrogen-use efficiency reduces fossil-fuel consumption directly, it's also important because part of the nitrogen applied for crop production is converted into nitrous oxide, a very potent greenhouse gas.
Some 1% to 2% of nitrogen applied as fertilizer or manure is lost as nitrous oxide. The most effective way to reduce nitrous oxide emissions is to increase nitrogen-use efficiency by more accurate nitrogen applications based on soil and tissue tests, and by timing nitrogen applications to crop need.
Specifically, the report lists the use of soil nitrate tests; precise timing of fertilizer to match crop needs; adaptive management to monitor plant health; GIS and variable-rate technology; leguminous cover crops to fix atmospheric nitrogen; winter cover crops to avoid nitrate leaching; and filter strips to intercept nitrogen.
Increase Ruminant-Digestion Efficiency
Agriculture is a large emitter of methane, a greenhouse gas that is 21 times more potent than carbon dioxide. Agriculture is responsible for 34% of U.S. methane emissions, primarily by enteric fermentation in ruminants.
The report says farmers can reduce methane emissions by adjusting portions of animal feed to decrease digestion time; using edible oils and other feed additives to reduce metabolic activity of rumen bacteria that produce methane; by capturing methane from manure storage and using it to generate electricity; and, finally, by applying manure to soil as a nutrient source rather than storing it as a waste.