Elsevier

Biomass and Bioenergy

Volume 14, Issue 4, 1 April 1998, Pages 379-384
Biomass and Bioenergy

A review of carbon and nitrogen balances in switchgrass grown for energy

https://doi.org/10.1016/S0961-9534(97)10074-5Get rights and content

Abstract

Increased atmospheric CO2, caused partly by burning fossil fuels, is assumed to elevate the risk of global warming, while nitrate contamination of surface runoff and groundwater from fertilizer and agricultural wastes constitutes a serious environmental hazard on a regional scale. Switchgrass (Panicum virgatum L.) grown as an energy crop could reduce atmospheric CO2 accumulation by replacing fossil fuels and sequestering C. It could also improve soil productivity by C sequestration, and reduce NO−13 contamination of water by absorbing N lost from fertilizer and agricultural waste if planted in filter strips on adjacent land. The objective of this study was to assess potential impacts of switchgrass on C and N balances by reviewing and synthesizing information from current literature, unpublished data and on-going research. Replacing fossil fuels with switchgrass, or any other biomass, will have a much greater effect on atmospheric CO2 than C sequestration. This is because replacing fossil fuels provides a cumulative effect, while C sequestration offers only a one-time benefit. Furthermore, switchgrass will provide net gains in C sequestration only if it replaces annual row crops, but not if it replaces grazed pasture. Nitrogen recovery by switchgrass in an Alabama study was 65.6%, which compares favorably with the 50% recovery frequently quoted as the norm for wheat (Triticum aestivum L.) and corn (Zea mays L).

Introduction

Switchgrass is the herbaceous energy crop species chosen by the Biofuels Feedstock Development Program of the United States Department of Energy for major research focus in the immediate future.1, 2 Among the many reasons for this choice are the expected positive impacts that switchgrass could have on C and N balances when grown for energy.[3] More specifically, switchgrass could:

  • 1.

    reduce CO2 emissions and the associated risk of global warming by replacing fossil fuels and sequestering C;

  • 2.

    improve soil productivity by C sequestration; and

  • 3.

    reduce NO3 contamination of surface runoff and groundwater by absorbing N lost from fertilizer and agricultural wastes if it is planted in filter strips on adjacent land.

However, the extent of these benefits has not been well documented. Therefore, the objective of this study was to assess potential impacts of switchgrass on C and N balances by reviewing and synthesizing information from current literature, unpublished data and on-going research. This synthesis will document the current state of knowledge and help focus future research.

Section snippets

Carbon accumulation

Two important concerns about current trends in the C cycle are:

  • 1.

    increased atmospheric CO2 (caused largely by burning fossil fuels) and the associated risk of global warming; and

  • 2.

    loss of C from soils (caused mainly by annual cropping) and the associated loss in soil productivity.

Nitrogen accumulation

Although relatively little information is available on the ability of switchgrass to accumulate N from the soil, this species is already being promoted as a suitable candidate to plant in filter strips aimed at preventing chemicals from contaminating surface runoff and groundwater.[18] The traditional approach for measuring percent recovery of applied N is by the difference method, in which total N recovered in above ground biomass of unfertilized plots is subtracted from that in biomass of

Conclusions

Studies presented and reviewed in this paper suggest the following:

  • 1.

    C sequestration benefits from switchgrass will depend mainly on what enterprise is replaced by switchgrass;

  • 2.

    switchgrass will likely be superior in C sequestration to annual crops, but no better than grazed pasture;

  • 3.

    since profits from pasture-based beef production are lower than for row crops, switchgrass will likely replace pasture first, providing little or no net gain in C sequestration;

  • 4.

    C sequestration is relatively unimportant

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