Ecosystem Studies and Management
Measurements of Greenhouse Gases in an Agricultural Field in North Dakota
Sources and Sinks
Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the most important human-produced greenhouse gases.
While most human-produced CO2 is derived from fossil fuel combustion, soils are the dominant natural source of N2O, and fertilized agricultural soils are a major source of increasing N2O in the atmosphere. Sources of CH4 include rice cultivation; while wetlands are a significant natural source, and upland soils are a natural CH4 sink (they remove CH4 from the atmosphere). A significant fraction of human-produced CO2 is also derived from land use change, including converting land agricultural purposes, which often results in a loss of carbon stored in the soils.
Methods and Measurements
Instrumentation to easily measure carbon dioxide (Infrared Gas Analyzer) have been available for many years, however instrumentation to easily measure methane and nitrous oxide in field settings has only recently become obtainable. Thanks to funding from NASA, we are one of the first organizations to purchase a Quantum Cascade Laser (Aerodyne Research http://www.aerodyne.com/), a device used to measure methane and nitrous oxide. Using this new laser in conjunction with our previously developed system for measuring carbon dioxide release from soils, we now lead the field with the ability to simultaneously measure the three most important greenhouse gases produced by soils. Our test site is located in an agricultural field in North Dakota, where we are measuring fluxes of carbon dioxide, methane and nitrous oxide, every half hour over the spring alfalfa growing season (early March to early June).
Left: The Quantum Cascade Laser (QCL) and the Infrared Gas Analyzer (IRGA) measure all three of the most important greenhouse gases simultaneously. Right: Automated chambers used to sample carbon dioxide, methane and nitrous oxide from an agricultural soil. The two chambers in the foreground are in the open position and the chamber in the background is in the closed position.
Results for the 2012 Season
- These soils are sources of carbon dioxide and nitrous oxide to the atmosphere, whereas they are a sink for methane.
- All three greenhouse gases are highly dependent on soil moisture conditions. High measures of soil moisture correspond to increased release of these gases.
- High frequency measurements show that these gases have a short lived, transient response to changes in soil moisture.
- This system, which measures the most important human-produced greenhouse gases, carbon dioxide, methane and nitrous oxide, will provide invaluable information to future efforts to curb their release into the atmosphere.
Figure 3: Fluxes measured every 30 minutes of carbon dioxide, nitrous oxide and methane, along with concurrent measures of water-filled poor space (a measured of soil moisture), precipitation, and soil and air temperature.