A REVIEW OF CARBON AND NITROGEN BALANCES IN SWITCHGRASS GROWN FOR ENERGY

Increased atmospheric CO2, caused partly by burning fossil fuels, is a ssumed to elevate the risk of global warming, while nitrate contaminat ion 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 redu ce atmospheric CO2 accumulation by replacing fossil fuels and sequeste ring C. It could also improve soil productivity by C sequestration, an d reduce NO3-1 contamination of water by absorbing N lost from fertili zer and agricultural waste if planted in filter strips on adjacent lan d. The objective of this study was to assess potential impacts of swit chgrass on C and N balances by reviewing and synthesizing information from current literature, unpublished data and on-going research. Repla cing fossil fuels with switchgrass, or any other biomass, will have a much greater effect on atmospheric CO2 than C sequestration. This is b ecause replacing fossil fuels provides a cumulative effect, while C se questration offers only a one-time benefit. Furthermore, switchgrass w ill provide net gains in C sequestration only if it replaces annual ro w crops, but not if it replaces grazed pasture. Nitrogen recovery by s witchgrass in an Alabama study was 65.6%, which compares favorably wit h the 50% recovery frequently quoted as the norm for wheal (Triticum a estivum L.) and corn (Zea mays L). (C) 1998 Elsevier Science Ltd. All rights reserved.