The Nebraska Carbon Study

Author

John Brenner,
Colorado State University

Executive Summary 

Quantifying the change in greenhouse gas emissions due to natural resource conservation practice application in Nebraska. A collaborative effort between CSU-NREL, the State of Nebraska, USDA NRCS and the US DOE

Land managers have long known the importance of soil organic matter in maintaining the productivity and sustainability of agricultural land. More recently, interest has developed in the potential for using agricultural soils to sequester C and mitigate increasing atmospheric CO2 by adopting practices that increase standing stocks of carbon in soil organic matter and vegetation. Practices that increase the amount of CO2 taken up by plants (through photosynthesis), which then enter the soil as plant residues, tend to increase soil C stocks. Likewise, management practices that reduce the rate of decay or “turnover” of organic matter in soils will also tend to increase carbon stocks.

In 2001, we initiated a statewide assessment of how management decisions involving cropping and tillage systems affect soil organic matter. Our approach utilized a variety of resource data (on climate, soils, land use and management), long-term field experiment results, and the Century EcoSystem Soil Organic Matter Computer Model. An initial Phase I study of cropland in Nebraska utilized existing information on climate, soils and management factors (e.g., drainage, crops grown, production levels and tillage systems) to estimate current rates of C sequestration in Nebraska and derived a value of 1.7 million metric tonnes per year (MMT). It was estimated that this annual rate of C sequestration could be maintained and increased to 2.3 MMT of C if all cropland were converted to a no tillage management system. From this Phase I study, it was apparent that the individual counties had land use information, including management histories of cropping rotations, drainage histories, fertilizer rates, and conservation practices that were not available in published databases.

The Phase II study was started in 2001 and involved all 93 counties. This general approach of involving every county within a state had recently been successfully used in similar studies in Iowa and Indiana. To communicate with the local land managers and collect the local data, the Carbon Sequestration Rural Appraisal (CSRA) survey instrument was modified, tested and implemented in each county using an electronic spreadsheet format. Individually tailored spreadsheets were prepared for each county and electronically transmitted to Nebraska. Local data only available at the county level was filled in each spreadsheet. All spreadsheets were electronically transmitted back to Fort Collins, CO when completed. This local data provided additional inputs into the Century Model that were not available in previously published databases, and refined the output for the individual counties and the soils and crop/tillage systems within each county. Century vi estimates for approximately one million different scenarios showing the C changes are now available in the Nebraska CarbOn Management Evaluation Tool (COMET) database. The county summaries for the amounts of C sequestered in 1990-2000 are also available.

The Phase II assessment for Nebraska suggests that agricultural soils are currently (based on 2000 data) sequestering 1.28 MMT of carbon per year (equivalent to 4.7 MMT of CO2 per year), largely through increased adoption of conservation practices over the past 10 to 20 years. Non irrigated systems provide 45% of the sequestration benefit on cropland while irrigated systems provide the remaining 55% of the benefit. The model predicts that rotations that include fallow periods utilizing intensive tillage practices are very close to C neutral or in some case are losing C. Grass plantings continue to sequester C, but the rates are decreasing due to the length of time that they have been in place. The application of sound conservation practices on Nebraska cropland is sequestering C and is equivalent to an offset of 12% of Nebraska’s 1999 fossil fuel carbon emissions. Rangeland has the potential to sequester 5 MMT of C over the next 20 years through the application of grazing management practices on areas identified as being in fair or poor range condition.

Prepared By:
John Brenner, Keith Paustian, George Bluhm, Jan Cipra, Mark Easter, Robin Foulk, Kendrick Killian, Ron Moore, Jill Schuler, Phil Smith, and Steve Williams.

Primary Contacts:
Keith Paustian, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO
John Brenner, USDA-NRCS, Fort Collins, CO