The amount of irrigation needed to grow feedstock for ethanol depends on what is being grown—and where.
During the Washington International Renewable Energy Conference held in March in Washington, D.C., U.S. Department of the Interior Secretary Dirk Kempthorne said that crops used for ethanol take an enormous amount of water. "To reach our ethanol production target of 7.5 billion gallons per year by 2012 will require 30 billion gallons of water a year to process," he said, "or the amount of the annual water needs of Minneapolis, Minn. And if just 25 percent of the new corn crop requires irrigation, ethanol will demand more water than the combined annual usage of all cities in Arizona, Colorado, Idaho and Nevada. As we increase ethanol production, we must have a holistic approach that takes into account its impact on water supply."
During World Water Week, an international meeting held in Stockholm, Sweden, in August, the Stockholm International Water Institute concluded that bioenergy demands are diverting water from food production and that by 2050, the amount of water used to grow and process feedstocks for energy in the world will equal the amount of water used to grow crops to feed the world.
Also in August, the Roundtable on Sustainable Biofuels, a Switzerland-based think tank that is helping the European Commission to define sustainability criteria for biofuels in the European Union, released the first version of its criteria. The group said that water used for irrigation must not be withdrawn beyond the replenishment capacity of the water table and that water-intensive energy crops must not be established in water-stressed areas. Crops that fit local conditions must be used for the most efficient use of water, the criteria said.
In September, with support and advice from the World Wildlife Fund and Natural Resources Defense Council, members of the international airline industry—including Air France, Air New Zealand, All Nippon Airways, Cargolux, Gulf Air, Japan Airlines, KLM, SAS and Virgin Atlantic Airways—formed the Sustainable Aviation Fuel Users Group, demanding that the cultivation of jet fuel plant sources should not jeopardize drinking water supplies. While ethanol is not a source of jet fuel, it is clear that both government and industry around the world are concerned that the irrigation of crops for energy production might lead to water shortages.
Ethanol and Water Use
Using corn ethanol to power a vehicle consumes more water than using petroleum gasoline. In a report titled "Water Intensity of Transportation" published in the November 2008 edition of the journal Environmental Science & Technology, researchers in the Bureau of Economic Geology and also the Center for International Energy and Environmental Policy in the Jackson School of Geosciences at the University of Texas in Austin, Texas, report that driving a petroleum gasoline-fueled light-duty vehicle—which includes cars, trucks and sport utility vehicles—typically consumes between 9 and 18 ounces of water per mile. However, driving an E85 ethanol-fueled light-duty vehicle can consume between 1 and 62 gallons of water (28 gallons of water on average) per mile—up to 882 times as much as petroleum gasoline—if the ethanol in the E85 blend is processed from corn grain that is harvested from irrigated fields, depending on where the corn is grown. In fact, the amount of water used to irrigate the corn crop has the greatest impact on how much water is used per mile.
Approximately 50 million acres of land worldwide is used for the production of biofuels and about 11.6 trillion gallons of water is used throughout the world annually to irrigate energy crops, according to a report entitled "Biofuels and Implications for Agricultural Water Use: Blue Impacts of Green Energy" published by the International Water Management Institute. However, the global impact of irrigating crops for biofuel production is minor, the IWMI said, and the amount of water that is needed to irrigate energy crops varies widely, depending on which crops are being grown and where.
Individual countries and regions need to assess the local impact of energy crop irrigation, the IWMI said. For example, both China and India might not have enough water resources to grow energy crops for ethanol if they use traditional crops such as corn or sugarcane. China withdraws approximately 2,400 gallons of water for irrigation to grow enough corn to produce 1 gallon of ethanol. India withdraws approximately 3,500 gallons of water for irrigation to grow enough sugarcane to produce 1 gallon of ethanol.
Meanwhile, very little irrigation is used in Brazil to grow sugarcane. According to an IWMI report entitled "Water Use and Impacts Due to Ethanol Production in Brazil," the total rainfall in the savannahs of Brazil is enough to grow crops there without irrigation. Meanwhile in the United States, only 3 percent of all irrigation is used to grow corn for ethanol, the report said. Overall in the United States, approximately 17 percent of U.S. corn for grain or seed is irrigated, based on the latest available USDA data from 2002, according to Carey King, co-author of the UT study and a research associate at the school.
The IWMI said if all national targets for biofuels production are to be met worldwide, an additional 74 million acres of land and 47.5 trillion gallons of water for irrigation will be needed. Meanwhile, water constraints will limit the potential for growth in the production of energy crops in some parts of the world. According to a report entitled "The State of Food and Agriculture 2008-Biofuels: Prospects, Risks, and Opportunities" published by the Food and Agriculture Organization of the United Nations, the most potential for expansion is in Latin America and sub-Saharan Africa.
U.S. Energy Crop Irrigation
When ethanol is processed from corn grown in nonirrigated fields, driving an E85 ethanol-fueled light-duty vehicle consumes only between 19 and 45 ounces of water per mile—or eight times as much as petroleum gasoline—compared with an average of 28 gallons of water per mile for irrigated corn, the UT study said.
According to the USDA's Natural Resources Conservation Service Resource Economics and Social Sciences Division, the majority of producing ethanol plants in the United States—and those that are planned or in construction—are located in the heart of the Corn Belt where little irrigation is needed to grow corn. For example in 2002, between 500 and 1,000 gallons of water was used on average to grow one bushel of irrigated corn in Iowa (when the corn was irrigated at all). Between 1,000 and 2,000 gallons of water per bushel were used in Minnesota, South Dakota, Wisconsin and Illinois.
However, as you move to the outer edges and away from the center of the Corn Belt, the irrigation requirement for corn starts to increase. For example, in Nebraska and Kansas, the average irrigation needed per bushel of corn is between 2,000 and 3,000 gallons of water. The National Research Council cited the Ogallala aquifer, which runs through Kansas and Nebraska, as a resource under stress. According to Daniel O'Brien, an extension agricultural economist at Kansas State University, Ogallala aquifer groundwater supplies have been declining since irrigation began in the 1960s. He said increased demand for corn for ethanol might result in more corn acreage and more intensive irrigation, which might accelerate the decline of the aquifer.
Kansas farmers planted 4.1 million acres of corn in 2008, a 5 percent increase over 2007 and the largest planting in the state since 1936, according to the Kansas Corn Growers Association. Nebraska farmers planted 9 million acres of corn in 2008, a 4 percent decrease from the highest-ever planting of 9.4 million acres in 2007, according to the Nebraska Corn Board. The University of Nebraska-Lincoln Extension Institute of Agriculture and Natural Resources reports the consumption of water by irrigated crops is the biggest user of water in Nebraska. Nebraska has 22 ethanol plants in production and four under construction; Kansas has 13 plants in production and one under construction, according to BBI International's U.S. & Canada Fuel Ethanol Plant Map.
According to King, only Kansas and Nebraska are above average in the 10 Corn Belt states in terms of the amount of water that is used to irrigate corn. "The average for the 10 corn states is similar to the average for the entire U.S.," King said, "but heavily weighted by Kansas and Nebraska, which have over half of the total irrigation for corn in gallons of water. They dominate the irrigation."
The 2002 USDA irrigation census data indicates that the 10 major corn states used 3,812 billion gallons of water for the irrigation of corn for grain or seed, with Nebraska using 1,800 billion gallons and Kansas 560 billion gallons. King said a light-duty vehicle powered by E85 ethanol from irrigated Kansas corn consumes 52 gallons of water per mile; the same vehicle powered by E85 ethanol from irrigated Nebraska corn consumes 43 gallons per mile. King's calculations are based on 2002 USDA census data, he said, and would not reflect the impact that the 2005 renewable fuels standard might have had on the amount of water used to irrigate corn in those states. The USDA 2007 census data is scheduled to be released in February.
The push to grow corn outside of the Corn Belt is a cause for concern, according to a report by the NRC entitled "Water Implications of Biofuels Production in the United States." The NRC found that shifting agricultural land from other crops to grow corn or expanding corn production into regions with little agriculture, especially dry areas, might greatly increase pressure on water resources in those regions. The amount of water that goes through the corn plant and into the atmosphere as transpiration is directly related to corn grain yields, according to the Nebraska extension service.
Because irrigation is such a large factor in the amount of water used to produce ethanol, there is a "tremendous amount of need" for proper water resource planning, said the UT researchers. Historically, using petroleum-based fuels has had a small overall impact on U.S. water resources, they said, and the United States must consider the supply of water needed for irrigating existing and future energy crops. They said comparing the amount of water supplied by rainfall to the amount supplied by irrigation provides a measure for sustainability.
Future Ethanol and Water Use
If corn continues to expand to the edges and outside of the Corn Belt, water conservation, erosion prevention, and the efficient use of fertilizer can help to mitigate the impact of water use for growing energy crops, the NRC said. No-till planting practices, where crops are planted into the previous year's crop residues, might be employed. The corn stover from these areas is less likely to be available for the production of cellulosic ethanol in the future, the NRC said.
The UT study also looked at the impact on water usage if cellulosic ethanol made from corn stover is used in a light-duty vehicle. If the ethanol is processed from corn stover from irrigated fields, driving an ethanol-fueled light-duty vehicle consumes between 3 and 46 gallons (an average of 19 gallons) of water per mile, depending on where the corn is grown, which is generally less than ethanol processed from corn grain-only that is harvested from irrigated fields. Meanwhile, driving a vehicle using ethanol processed from corn stover from non-irrigated fields consumes about 32 ounces of water per mile.
If the entire corn plant is used to make ethanol, the UT report said, a light-duty vehicle will consume between 2 and 38 gallons of water per mile for irrigated corn and between 28 and 49 ounces of water per mile for non-irrigated corn, depending on where the corn is grown.
However, because crop residues on the soil surface absorb water from rainfall and snow and also reduce the evaporation of water from the underlying soil, using corn stover for the production of cellulosic ethanol might also have an impact on the amount of irrigation needed to grow corn, according to Andrew Sharpley, a soils and water quality researcher at the University of Arkansas.
"Immediately, it wouldn't have a major impact," Sharpley says. "But long-term, over several years, you would be removing a lot of organic matter from that soil that would [normally] get recycled back in. If you're harvesting it continuously and removing it, then the organic matter in the soil tends to slowly decline. One of the major benefits of organic matter is that it increases the water-holding capacity and potential of soils."
Policies to promote the production of cellulosic ethanol using nonfood crops, such as switchgrass and native grasses, should be expanded, the NRC said, because the large-scale production of those feedstocks could be irrigated with wastewater that otherwise would be unsuitable for irrigating food crops.
Ryan C. Christiansen is an Ethanol Producer Magazine staff writer. Reach him at firstname.lastname@example.org or (701) 373-8042.