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Title: Conversion of grazed pastures to energy cane as a biofuel feedstock alters the emission of GHGs from soils in Southeastern United States

item GOMEZ-CASANOVAS, NURIA - University Of Illinois
item DELUCIA, NICHOLAS - University Of Illinois
item HUDIBURG, TARA - University Of Idaho
item Bernacchi, Carl
item DELUCIA, EVAN - University Of Illinois

Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2017
Publication Date: 1/1/2018
Citation: Gomez-Casanovas, N., DeLucia, N.J., Hudiburg, T.W., Bernacchi, C.J., DeLucia, E. 2018. Conversion of grazed pastures to energy cane as a biofuel feedstock alters the emission of GHGs from soils in Southeastern United States. Biomass and Bioenergy. 108:312-322.

Interpretive Summary: Bioenergy production is likely to lead to changes in how land is used. Pastures on high organic soils in the subtropics are presently used for primarily grazing, however, the economics of bioenergy feedstock production, for example sugar cane bred for bioenergy production, may favor conversion of this land. Before this can occur, it is important to understand how changing land from grazed pastures to bioenergy sugar cane production will impact productivity as well as other important components of ecosystem function. In this experiment, we analyzed how changing the land to bioenergy feedstocks in Central Florida would impact the rate in which greenhouse gases, which have a net impact on warming the global and changing climate patterns, will change. We found two important results – first that the measured release of greenhouse gases was greater than what was predicted using models. Second, we discovered that removing grazed pastures and planting bioenergy sugar cane resulted in greater increases in greenhouse gases than if the land was to remain in grazed pastures. Finally, we discovered that the release of greenhouse gases was highly variable, but was linked to fertilization or precipitation. However, these this experiment was limited to transition phase from grazed pastures to bioenergy sugar cane, so long-term responses might vary from our observations.

Technical Abstract: 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 (CO2, CH4, and N2O) 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 N2O 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 N2O 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 CH4 and CO2 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.