Impact of Irrigation on the Net Energy Value of Corn-Ethanol in the Southeastern USA.

There is an increasing interest in corn as a bio-ethanol crop throughout the USA, including the Southeast. For the bio-ethanol industry to be sustainable, it is important that a sufficient amount of feedstock can be supplied and that the ethanol production has a positive net energy value (NEV), i.e. the energy output in the ethanol and co-products minus all energy inputs in the ethanol production chain. Currently, corn is produced both under rainfed and various types of irrigated conditions in the southeastern USA, with higher average grain yields under irrigated conditions. The relative abundance of water in the region would make an increase in irrigation possible. The objective of this study was to determine the average corn yield and ethanol NEV under different scenarios of irrigation and corn cultivation in the southeastern USA. Yield for three corn varieties grown under both irrigated and rainfed conditions in a region representing southeastern Alabama, northern Florida and southwestern Georgia was simulated for a time period of 68 years with the CSM-CERES-Maize model. Weather and soil input data for the simulations were obtained from the National Climatic Data Center and the USDA- National Resources Conservation Service, respectively. The calculation of the ethanol NEV took into account energy requirements for farm management practices, grain transportation and ethanol processing, and ethanol and co-product energy output. Corn grain yield and ethanol NEV were calculated based on different scenarios of irrigation. In general, the larger the proportion of irrigated corn, the higher the corn grain yield and ethanol NEV, and the lower the inter-annual variation in corn yields and ethanol NEV. The results from this study suggest that corn for ethanol purposes should preferably be grown under irrigated conditions to enhance the ethanol NEV and to provide for a higher and more even ethanol feedstock supply.