Impact of crop management, and climate and soil variability on corn ethanol production and net energy value

Summary

Computer models were used evaluate the potential of corn for biofuel and to determine the variation in the net energy value of ethanol from corn grain as function of management inputs and weather variability

Situation

Ethanol from corn and other agricultural crops is regarded as an important alternative to fossil fuels to increase energy independence and attain positive environmental effects, notably in form of decreased emissions of carbon dioxide. The natural conditions for producing corn for ethanol in the southeastern USA are favorable. However, within Georgia and other states in the southeastern USA, there is a natural variability in soil and climate conditions that affects the corn yield. Also corn management practices e.g. irrigation, nitrogen fertilizer application and planting dates vary within that region. However, the impact of natural soil and climate variability as well as crop management on energy aspects of corn-ethanol is not well known. In an energy system in which fossil fuels to a large extent are substituted by biofuels from agriculture, it is probable that the impact of environmental factors on feedstock supply would increase. Fossil fuel production is normally relatively insensitive to environmental variability. It is probable that also the long-term sustainability of a biofuel based energy system would be impacted by variability in soil, climate and crop management. The net energy value (NEV), defined as the output energy in the produced biofuel and co-products minus all non-renewable energy inputs in the production chain, is a measure of the energy sustainability. A negative NEV means that more non-renewable energy is used in the product than what is generated. Consequently, a production with a negative NEV is not sustainable in a long-term perspective. Knowledge about impact of climate and soil variability, and crop management practices on ethanol feedstock productivity and NEV would be valuable to identify biofuel energy systems that serve for an even feedstock supply and that are also sustainable in a long-term perspective.

Response

Studies with the aim of determining the impact of crop management practices and climate and soil variability on corn ethanol feedstock production and NEV are being conducted. In these studies corn production as a function of soil weather and crop management factors has been simulated with a dynamic crop simulation model (CSM-CERES-Maize). The simulations represent weather conditions for a time period of 68 years and soil and weather conditions for about 100 counties in Alabama, Florida and Georgia. Weather input data to the simulations were obtained from the National Climatic Data Center (NCDC) and soil input data from the United States Department of Agriculture National Resources Conservation Service (USDA-NRCS). Ethanol NEV was calculated based on the simulated yields. Information about energy requirements in the ethanol production chain including crop management practices, ethanol processing and grain transportation used in the NEV calculation was taken from the literature. The specific impact of spatial soil and climate variability on the difference in NEV among four important corn producing counties in different regions of Georgia has also been investigated. In that study, simulations of corn production under conditions with exchanged soil and weather conditions among the four counties were conducted. To determine the impact on net energy balance of a substantially increased corn production in the southeastern USA, average NEV was calculated based on grain yield simulations for 94 counties in Alabama, Florida and Georgia. In these calculations, each county was given the weight representing its proportion of the total grain acreage within the region in two production scenarios which represented the 1976 and 2006 production acreages. Also the total net energy yield (NEY) as defined as the NEV times the total ethanol produced from a part of the corn grown in the two scenarios was calculated. The impact of irrigation on NEV and NEY in the two scenarios was evaluated by simulating different proportions of irrigation corn.

Impact

Results showed that corn ethanol feedstock productivity and NEV vary with crop management practices. Especially irrigation has a positive effect on both feedstock productivity and NEV. Moreover, irrigation decreased the inter-annual variation in feedstock yield and ethanol NEV. The impact of irrigation was significant under specific planting dates and nitrogen fertilizer levels in a single location as averaged under a long time series. The impact of irrigation on ethanol feedstock productivity and NEV was also significant under conditions representing an averaged crop management, as well as for average soil and climate conditions over a larger are of southeastern USA. Temporal climate variability in form of El Niño Southern oscillation (ENSO) significantly affected ethanol feedstock productivity and NEV in a single location. La Niña had a positive impact on NEV under most crop management scenarios tested in that location. However, averaged over a larger production region of the coastal plains of Alabama, Florida and Georgia the impact of ENSO on ethanol feedstock productivity and NEV was small. Differences in ethanol feedstock productivity and NEV among four geographically distant major corn production counties in Georgia were partly due to spatial climate variability and partly to spatial soil variability. Simulation scenarios representing two historical production corn acreages in the Coastal Plain area of Alabama, Florida and Georgia showed only small differences in ethanol NEV and average feedstock yields between the two production scenarios. Consequently, the total net energy yield from those scenarios was correlated to their respective area of corn production. These results indicate that there is a possibility to substantially increase the ethanol feedstock production in the southeastern USA in an energy sustainable way. Irrigation had a positive impact on ethanol NEV for both scenarios of corn production.

State Issue

Agricultural Profitability and Sustainability

Details

• Year: 2008
• Geographic Scope: Multi-State/Regional
• County: Spalding
• Program Areas:
  • Agriculture & Natural Resources