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Carbon Sequestration in Forage Systems

February 2009
Maria L. Silveira - Range Cattle Research & Education Center, Soil & Water Scientist

Rising atmospheric CO₂ concentrations and the potential effects on climate change are important environmental issues worldwide. The increasing amounts of CO₂ released to the atmosphere are largely influenced by the combustion of fossil fuel, agriculture, and changes in land use. This trend is expected to continue into the future, leading to very complex interactions between the biosphere, hydrosphere and atmosphere.

Soil carbon (C) sequestration has been promoted as a means by which substantial amounts of CO₂ could be removed from the atmosphere. The definition of C sequestration is often unclear and somewhat controversial. To be sequestered, C should be converted from the active pools (i.e. atmospheric CO₂) to less reactive intermediate or passive pools, and, consequently, sustained in the soil for decades or longer.

Pasturelands can be important sinks of atmospheric CO₂ and play a major role in the overall C cycle fluxes. Unlike tropical forests, where the majority of the C is the vegetation, as much as 90% of the C pools in pastures are located in the soil. Researchers have estimated that from 29.5 to 110 Tg C (Tg = 1 million metric tons) can be annually sequestered in pastureland in the USA.

Current pasture management strategies are generally aimed at increasing forage yield. However, pasture management may also promote C storage in the soil. The key is determining how management can be manipulated to enhance soil-C sequestration potentials, without negatively affecting forage yield or ecosystem function.

Because of the increasing global demand for alternative energy sources, pasturelands may potentially become an important source of biomass fuel. This trend can further enhance the importance of pasturelands in terms of global C sequestration potentials. The potential of pasturelands for generating synergies between C management and sustainable energy source has not been fully explored and science-based information that addresses the ecological benefits of enhancing C sequestration in pastureland ecosystems is critically needed. We hope that in the near future science will identify pasture management strategies that promote long-term C sequestration and also enhance the economic feasibility of C sequestration in pasturelands throughout the USA.