Life cycle assessment of corn grain and corn stover in the United States |
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Authors: | Seungdo Kim Bruce E Dale Robin Jenkins |
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Institution: | (1) Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910-8396, USA;(2) DuPont Engineering Research and Technology, 1007 Market Street, Wilmington, DE 19898, USA |
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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 corn-growing 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 nitrogen-related emissions from
soil (i.e., N2O, NO
x
, and NO3
− 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., N2O, NO
x
, and NO3
− 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 nitrogen-related emissions from the soil (i.e., N2O, NO
x
, NO3
−). 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 stover removal on
soil organic carbon sequestration rate while still bringing the benefit of lower nitrogen-related emissions from the soil.
No-tillage practices offer higher accumulation rates of soil organic carbon, lower fuel consumption, and lower nitrogen emissions
from the soil than the current or conventional tillage practices. Planting winter cover crops could be a way to reduce nitrogen
losses from soil and to increase soil organic carbon levels.
Recommendations and perspectives County-level modeling is more accurate in estimating the local environmental burdens associated with biomass production than
national- or regional-level modeling. When possible, site-specific experimental information on soil carbon and nitrogen dynamics
should be obtained to reflect the system more accurately. The allocation approach between corn grain and stover significantly
affects the environmental performance of each. The preferred allocation method is the system expansion approach where incremental
fuel usage, additional nutrients in the subsequent growing season, and changes in soil carbon and nitrogen dynamics due to
removing corn stover are assigned to only the collected corn stover. |
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Keywords: | Biorefinery Cob Corn Life cycle assessment Soil organic carbon Stover Tillage Winter cover crop |
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