Life cycle assessment of corn grain and corn stover in the United States

Abstract

Background, aim, and scope The goal of this study is to estimate the county-level environmental performance for continuous corn cultivation of corn grain and corn stover grown under the current tillage practices for various corngrowing locations in the US Corn Belt. The environmental performance of corn grain varies with its farming location because of climate, soil properties, cropping management, etc. Corn stover, all of the above ground parts of the corn plant except the grain, would be used as a feedstock for cellulosic ethanol. Materials and methods Two cropping systems are under investigation: corn produced for grain only without collecting corn stover (referred to as CRN) and corn produced for grain and stover harvest (referred to as CSR). The functional unit in this study is defined as dry biomass, and the reference flow is 1 kg of dry biomass. The system boundary includes processes from cradle to farm gate. The default allocation procedure between corn grain and stover in the CSR system is the system expansion approach. County-level soil organic carbon dynamics, nitrate losses due to leaching, and nitrogen oxide and nitrous oxide emissions are simulated by the DAYCENT model. Life cycle environmental impact categories considered in this study are total fossil energy use, climate change (referred to as greenhouse gas emissions), acidification, and eutrophication. Sensitivities on farming practices and allocation are included. Results Simulations from the DAYCENT model predict that removing corn stover from soil could decrease nitrogenrelated emissions from soil (i.e., N 2 O, NO x , and NO 3 − leaching). DAYCENT also predicts a reduction in the annual accumulation rates of soil organic carbon (SOC) with corn stover removal. Corn stover has a better environmental performance than corn grain according to all life cycle environmental impacts considered. This is due to lower consumption of agrochemicals and fuel used in the field operations and lower nitrogen-related emissions from the soil. Discussion The primary source of total fossil energy associated with biomass production is nitrogen fertilizer, accounting for over 30% of the total fossil energy. Nitrogen-related emissions from soil (i.e., N 2 O, NO x , and NO 3 − leaching) are the primary contributors to all other life cycle environmental impacts considered in this study.Conclusions The environmental performance of corn grain and corn stover varies with the farming location due to crop management, soil properties, and climate conditions. Several general trends were identified from this study. Corn stover has a lower impact than corn grain in terms of total fossil energy, greenhouse gas emissions, acidification, and eutrophication. Harvesting corn stover reduces nitrogenrelated emissions from the soil (i.e., N 2 O, NO x , NO 3 − ). The accumulation rate of soil organic carbon is reduced when corn stover is removed, and in some cases, the soil organic carbon level decreases. Harvesting only the cob portion of the stover would reduce the negative impact of ...

Exploring impacts of process technology development and regional factors on life cycle greenhouse gas emissions of corn stover ethanol

“…These counties are selected to correspond with counties evaluated previously by Kim et al (2009) as there is now a body of relevant data for corn and corn stover production in these counties. It is assumed that a bioethanol plant (biorefinery) located in each county obtains and processes stover harvested in the same county.…”

“…System expansion is the most common approach used in previous studies (e.g., Sheehan et al 2004;Kim et al 2009;Spatari and MacLean 2010;Hsu et al 2010). In the system expansion approach, only emissions related to the additional activities required to harvest stover are assigned to the stover.…”

“…For this approach, the GHG emissions assigned to stover presented in Kim et al (2009), who used the DAYCENT model and system expansion to calculate the GHG emissions assigned to stover for the eight counties considered in this study, are utilized directly.…”

“…Graham et al (2007) and Nelson et al (2002) discuss that corn stover could be used for ethanol production in the U.S., provided it is removed from the field in a sustainable manner, e.g., with minimal soil erosion and preservation of soil carbon. In the U.S. most of the corn stover is left in the fields; Kim et al (2009) reported that only 5% of the total corn stover is removed, and that it is used as animal feed and bedding. The amount of stover which could be removed without soil organic carbon loss is dependent upon geography and local/regional soil conditions (Luo et al, 2009).…”

“…The amount of stover which could be removed without soil organic carbon loss is dependent upon geography and local/regional soil conditions (Luo et al, 2009). Kim et al (2009) suggest that the stover removal rate ranges from 25% to 50% in the U.S.…”