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The cultivation of energy cane throughout the Southeastern United States may displace grazed pastures on organic soil (Histosols) to meet growing demands for biofuels. We combined results from a field experiment with a biogeochemical model to improve our understanding of how the conversion of pasture to energy cane during early crop establishment affected soil GHG (CO 2 , CH 4 , and N 2 O) exchange with the atmosphere. GHG fluxes were measured under both land uses during wet, hot and cool, dry times of year, and following a fertilization event. We also simulated the impact of changes in precipitation on GHG exchange. Higher fertilization of cane contributed to greater emission of N 2 O than pasture during warmer and wetter times of the year. The model predicted that energy cane emitted more nitrogen than pasture during simulated wetter than drier years. The modeled emission factor for N 2 O was 20 to 30-fold higher than the default value from IPCC (1%), suggesting that the default IPCC value could dramatically underestimate the consequences of this land conversion on the climate system. Predicted soil CH 4 and CO 2 fluxes were higher in pasture than energy cane, and this difference was not affected by increasing precipitation. Model simulations predicted that soils under first year cane emit more GHGs than pasture, particularly during wet years, but this difference disappeared two years after energy cane establishment. Our results suggest that management practices may be important in determining soil GHG emissions from energy cane on organic soils particularly during the first year of cane establishment. [ABSTRACT FROM AUTHOR]

Abstract: Loblolly pine plantations are the most important source of forest products in the US and the slash remaining after conventional harvest represents a significant potential source of bioenergy. However, slash removal in intensive harvests might, under some circumstances, reduce site productivity by reducing soil organic matter and associated nutrients. Two complimentary studies in the Gulf Coastal Plain of the southeastern US were designed to test whether harvest intensity (level of biomass removal) could have a negative long-term impact on site productivity. Harvesting tree crowns in addition to the merchantable bole had a negative impact (18%) on pine biomass accumulation by age 7–10 years on 15 of 19 research blocks. Sites at risk of harvest-induced reductions in productivity were relatively unproductive prior to harvest and had low soil phosphorus (P) concentrations. Intensive harvesting, fertilization, and chemical control of non-crop vegetation were all energy efficient; the additional biomass energy gained through these practices was two-orders of magnitude greater than the energy needed to conduct the activities. Harvest of slash for bioenergy in the Gulf Coastal Plain of the southeastern US has the potential to reduce productivity on infertile soils, but fertilization has the potential to restore and even improve productivity on those sites in an energy-efficient way. [Copyright &y& Elsevier]