Carbon Balance and Greenhouse Gases in Agricultural Systems
Concerns about the impact of rising atmospheric concentration of carbon dioxide (CO2) on global climate have inspired efforts to identify ways in which changes in farming practices might reduce emission rates and even promote removal of CO2 from the atmosphere by increasing carbon storage in soils as organic matter. Proposed practices include reduced tillage and modified cropping systems that include winter cover crops and perennial living mulch crops. This approach that we are using involved continuous measurement of surface/atmosphere exchange in neighboring fields with the same soil type, but different farming practices. CO2 exchange and water use are measured by eddy covariance, using a sonic anemometer and open-path infrared gas analyzer.
Eddy covariance installation at Rosemount
One field is managed in conventional fashion for southern Minnesota, which means a corn/soybean rotation, with fall tillage consisting of chisel plowing. In an adjacent field we test alternative farming practices. Our field site at Rosemount, MN has been a part of the Ameriflux program since 2004. This is a network of research sites throughout North America where continuous measurements of CO2 and H2O exchange are made. The data are made available to researchers throughout the world for use in the development and testing of climate and crop models. A link to the data can be found on our biometeorology web site.
Our Rosemount site is also now part of the USDA - ARS LTAR program, which focuses not only on CO2 and H2O, but also on nutrient cycling, particularly nitrogen, both in air and water. The overall focus is on developing systems that reduce the environmental impact of agriculture while preserving and even increasing productivity. Fluxes of nitrogen gases of concern (N2O and NH3), for which open-path analyzers are not available, are measured by continuously sampling air from 2 heights in each field, routing it to a centrally located instrument trailer where trace gas analyzers are used to sequentially measure the constituent concentrations, from which emission rates can be calculated.
Automated chambers for measuring CO2 and N2O emissions.