Problem Statement

Rationale. Grazinglands (i.e., rangelands and pastures) and conservation seedings comprise grasslands that make up about 40% of the land area of the U.S. They contain large soil organic and inorganic carbon stores and are important because of their contribution to animal forage production and ecosystem health.

What is known. One of the concerns about the increasing atmospheric concentration of carbon dioxide is the effect on plant community-level responses in natural ecosystems. For example, in some instances, livestock grazing has enhanced carbon storage, but in some cases this increase has been at the expense of undesirable plant community shifts and reduced forage production, a trend that would continue under elevated carbon dioxide. Also, the recent invasion of traditional grasslands by shrubs, generally considered a negative change in the plant community, has been attributed by some to increased atmospheric carbon dioxide levels. This major change in the plant community may alter not only the amount of carbon allocated to below-ground processes, but also the distribution of carbon in the soil profile.

Gaps. We lack information on the potential capacity of grazinglands to store carbon and the rate of carbon accretion under various geographic and climatic conditions across the U.S. Key challenges include devising management schemes to maintain or enhance both grazingland production and carbon storage among diverse soil conditions and types. Management schemes should consider the effects of forage accumulation, grazing management, improved species, and fertility management. Under rangeland conditions, we need to consider the effects of stocking density and changing vegetation structure on processes and interactions that limit carbon storage potential, particularly during periods of stressed growing conditions.

 

Goals

• Quantify the magnitude and rate of change of soil carbon storage with different land use management practices, in different ecoregions, and under different plant communities;
• Determine the rate and extent of soil carbon storage on a regional or soil basis, including the potential of restorative management such as CRP and buffer-strip initiatives;
• Identify and quantify secondary benefits of soil carbon storage; and
• Quantify carbon dioxide fluxes on a seasonal basis under different ecosystems.

Approach

Methodology and parameters in future data collection will be coordinated among locations to fill gaps in existing data on carbon storage in grazinglands, CRP, and buffers and to develop experiments. Existing carbon dioxide flux networks (systems to measure exchanges of carbon dioxide between soil and the atmosphere) should be expanded to regions not currently covered and to other ecosystems and management strategies. Tools must be developed and tested to estimate soil carbon storage in grazinglands, CRP, and buffers. These data then would be provided to develop and verify predictive methods describing the effects of ecosystem changes on soil carbon. Methods must be developed to predict changes in species composition, the range of altered ecosystems, and the resulting differences in potential carbon storage.

Outcomes

• Current and potential soil carbon storage will be estimated for various management and climate conditions.
• The rate of increase in atmospheric carbon dioxide will be reduced.
• Soil resources and air and water quality will be enhanced.

Impact

Enhanced quality of grazinglands, CRP, and buffer strips while attaining maximum potential carbon storage

Linkages to Other ARS National Programs

• Bioenergy & Energy Alternatives
• Food Animal Production
• Rangeland, Pasture, & Forages
• Soil Resource Management