Energy production from corn

Jessica Zhang • Sarah Palmer • David Pimentel

Received: 20 April 2011 / Accepted: 28 July 2011 / Published online: 27 August 2011� Springer Science+Business Media B.V. 2011

Abstract Several physical and chemical factors limit the production of biofuels, such as

the complex process required for the conversion of plant biomass into ethanol. For

example, fossil energy inputs needed for the production of ethanol from corn is 1.59 liters

per liter of ethanol. One of the many factors limiting energy output from biomass is the

extremely low fraction of sunlight reaching a hectare that is captured by the plants. On

average only about 0.1% of the sunlight is captured by green plants per year.

Keywords Corn ethanol � Fossil fuel � Deforestation � Fermentation/distillation �Dry distillers grains (DDG) � Environmental impact

1 Introduction

1.1 Perhaps the most famous method of ‘‘going green’’ is the use of corn ethanol

Seeing that corn and its derivatives are ingredients in 75% of our groceries, it may come as

no surprise that corn would find its way into our engines as well (farmersfeedus.org 2010).

At first, this development seems to rid us of our dependence on fossil fuel. Through careful

analysis of the energetic, economical, and environmental costs and payoffs of corn pro-

duction for ethanol, however, this paper shows that corn ethanol does not meet the effi-

ciency, cost, and ethical standards that would merit its label as a superior alternative to

fossil fuel but rather leads to ethical and economical roadblocks. With the global popu-

lation on the rise and food prices increasing, justifying the allocation of some corn for

ethanol production will become more and more difficult. Through this analysis, we come to

the conclusion that, rather than investing in subsidized corn for ethanol, the US

Readers should send their comments on this paper to BhaskarNath@aol.com within 3 months of publicationof this issue.

J. Zhang � S. Palmer � D. Pimentel (&)College of Agriculture and Life Sciences, Cornell University, Ithaca 14853, NY, USAe-mail: dp18@cornell.edu

123

Environ Dev Sustain (2012) 14:221–231DOI 10.1007/s10668-011-9318-4

government, investors, and consumers would better meet their energy goals by abandoning

corn ethanol.

In this article, we examine the potential for improving the efficiency of converting corn

grain into ethanol. In summary, we attempt to define the impact of biofuel production on

greenhouse gas emissions and the prevention of malnutrition and hunger.

2 Ethanol production from corn grain

2.1 Energy inputs in corn ethanol production

In this analysis, the most recent scientific data for corn fermentation/distillation were used.

All current fossil energy inputs were used for corn production and for the fermentation and

distillation to determine the entire energy cost of ethanol production. Additional costs to

consumers include federal and state subsidies (Koplow and Steeblik 2008) plus costs

associated with environmental pollution and/or degradation that occur during the entire

production process.

In a large ethanol conversion plant, the ethanol yield from 2.69 kg of corn grain is 1 l of

ethanol (approximately 9.5 l pure ethanol per bushel of corn). The production of corn in

the United States requires a significant energy and monetary investment averaging 14

inputs including labor, farm machinery, fertilizers, irrigation, pesticides, and electricity. As

listed in Table 1, the production of an average corn yield of 9,500 kg/ha (151 bu/ac) using

up-to-date production technologies requires the expenditure of about 7.4 million kcal of

energy inputs (mostly natural gas and oil), the equivalent of about *743 l of oil equiv-

alents expended per hectare of corn. The production costs total $835/ha for the 9,500 kg/ha

or approximately 11¢/kg ($2.34/bushel) of corn produced (Table 1).

Full irrigation (when there is insufficient or no rainfall) requires about 100 cm/ha of

water per growing season. Because from 15 to 19% of US corn production is irrigated

(USDA 1997; Supalla 2007), only 8.1 cm per ha of irrigation was included for the growing

season. On average, irrigation water is pumped from a depth of 100 m (USDA 1997). On

this basis, the average energy input associated with irrigation is 320,000 kcal per hectare

(Table 1).

Table 1 Energy inputs and costs of corn production per hectare in the United States

Inputs Quantity kcal 9 1,000 Costs $

Labor 11.4 ha 520b 148.20c

Machinery 55 kgd 1,018e 110.00f

Diesel 62 lg 620h 46.42

Gasoline 9 li 90j 7.14

Nitrogen 150 kgk 2,475l 85.25m

Phosphorus 55 kgn 228� 48.98p

Potassium 62 kgq 202r 26.04s

Lime 1,120 kgt 315u 28.64

Seeds 21 kgv 520w 74.81x

Irrigation 8.1 cmy 320z 123.00aa

222 J. Zhang et al.

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Table 1 continued

Inputs Quantity kcal 9 1,000 Costs $

Herbicides 2.3 kgbb 230ee 35.29

Insecticides 0.7 kgcc 70ee 32.55

Electricity 103.2 kWhg 34ff 7.22

Transport 107 kggg 122hh 61.20

Total 7,438 $834.74

Corn yield 9,500 kg/haii 34,200 kcal input/output 1:4.60

a NASS (2005)b It is assumed that a person works 2,000 h per year and utilizes an average of 9,000 l of oil equivalents peryearc It is assumed that labor is paid $20 an hourd Pimentel and Pimentel (2008)e Prorated per hectare and 10 year life of the machinery. Tractors weigh from 6 to 7 tons and harvesters8–10 tons, plus plows, sprayers, and other equipmentf Estimatedg William McBride, Personal Communication, USDA 2010h Input 11,400 kcal per li Estimatedj Input 10,125 kcal per lk NASS (2003)l Cost $.55 per kgm Patzek (2004)n NASS (2003)o Input 4,154 kcal per kgp Cost $.62 per kgq NASS (2003)r Input 3,260 kcal per kgs Cost $.31 per kgt Estimatedu Input 281 kcal per kgv Pimentel and Pimentel (2008)w Pimentel and Pimentel (2008)x Estimatedy USDA (1997)z Batty and Keller (1980)aa Irrigation for 100 cm of water per hectare costs $1,000 (Larsen et al. 2002)bb NASS (2005)cc USDA (2002)dd USDA (1991)ee Input 100,000 kcal per kg of herbicide and insecticideff Input 860 kcal per kWh and requires 3 kWh thermal energy to produce 1 kWh electricitygg Goods transported include machinery, fuels, and seeds that were shipped an estimated 1,000 kmhh Input 0.34 kcal per kg per km transportedii Average. USDA (2007), USCB (2008)

Energy production from corn 223

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2.2 Energy inputs in corn fermentation/distillation

The average costs in terms of energy and dollars for a large, modern dry-grind ethanol plant

are significant and are listed in Table 2. In the fermentation/distillation process, the corn is

finely ground and approximately 8 l of water are added per 2.69 kg of ground corn. Some of

this water maybe recycled. After fermentation, the mixture is distilled to obtain a liter of

Table 2 Inputs per 1,000 l of 99.5% ethanol produced from corn

Inputs Quantity kcal 9 1,000 Dollars $

Corn grain 2,690 kga 2,106b 634.14

Corn transport 2,690 kgb 264c 27.63d

Water 7,721 le 46f 3.86g

Stainless steel 3 kgi 42p 8.52q

Steel 4 kgi 40q 2.39q

Cement 8 kgn 9q 1.52r

Steam 2,564,764 kcalq 2,362r 59.94j

Electricity 395 kWhq 2,863q 27.65k

95% ethanol to 99.5% 9 kcal/ll 9l 40.00

Sewage effluent 20 kg BODm 69h 6.00

Distribution 331 kcal/lo 331 375.00

Total 8,141 $1185.38

a Output: 1 l of ethanol = 5,130 kcal (Low heating value). The mean yield of 9.5 l pure EtOH per bushelhas been obtained from the industry-reported ethanol sales minus ethanol imports from Brazil, both mul-tiplied by 0.95 to account for 5% by volume of the #14 gasoline denaturant, and the result was divided by theindustry-reported bushels of corn inputs to ethanol plants. (Patzek, T. W. 2006. Personal Communication)b Data from Table 15.1 (See Pimentel and Patzek 2008)c Calculated for 144 km roundtripd Pimentel et al. (2009)e 7.7 l of water mixed with each kg of grainf Pimentel et al. (2009)g Pimentel et al. (2009)h 4 kWh of energy required to process 1 kg of BOD (Blais et al. 1995)i Estimated from the industry-reported costs of $85 millions per 65 million gallons/year dry grain plantamortized over 30 years. The total amortized cost is $43.6/1,000 l EtOH, of which an estimated $32 go tosteel and cementj Calculated based on coal fuel. Below the 1.95 kWh/gal of denatured EtOH in South Dakotak $0.07 per kWh (USCB 2004)l 95% ethanol converted to 99.5% ethanol for addition to gasoline (T. Patzek, personal communication,University of California, Berkeley, 2004)m 20 kg of BOD per 1,000 l of ethanol produced (Martinelli 2009)n Newton (2001)o DOE (2002)p Johnson et al. (2008)q Venkatarama Reddy and Jagadish (2003)r Portland Cement Association (2011) http://www.bipac.net/page.asp?g=pca&content=issue_energy&parent=PCA

224 J. Zhang et al.

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95% pure ethanol from the 8–12% ethanol beer. The 1 l of ethanol must be extracted from

approximately 11 l of the ethanol/water mixture. Although ethanol boils at 78�C, and water

boils at 100�C, the ethanol is not all extracted from the water in the first distillation, which

obtains 95% ethanol (Maiorella 1985; Werekoo-Brobby and Hagen 1996; S. Lamberson,

personal communication, Cornell University, 2000). To be mixed with gasoline, the 95%

ethanol must be further processed and more water removed, requiring additional fossil

energy inputs to achieve 99.5% pure ethanol (Table 2). Thus, a total of 8 l of wastewater is

required for the production of 1 l of ethanol, and the disposal of this relatively large amount

of sewage effluent comes at an energetic, economic, and environmental cost.

The production of a liter of 99.5% ethanol, including the energy to produce the corn,

requires 158% more fossil energy than the energy present in 1 l of ethanol and costs $1.19

per l ($4.48 per gallon) (Table 2). The corn feedstock requires more than 26% of the total

energy input. In this analysis, the total cost, including the energy inputs for the fermen-

tation/distillation process and the apportioned energy costs of steam, electricity, and

stainless steel tanks and other industrial materials is substantial (Table 2).

2.3 Net energy yield

The largest energy inputs in corn ethanol production are corn feedstock production energy,

steam energy, and electricity used in the fermentation and distillation process. The total

energy input to produce a liter of ethanol is 8,141 kcal (Table 2). However, a liter of

ethanol has an energy value of only 5,130 kcal. Based on a net energy loss of 3,011 kcal of

ethanol produced, 58% more fossil energy is expended than is produced as ethanol.

2.4 Economic costs

Current corn ethanol production technology uses more fossil fuel and costs substantially

more to produce in dollars than its energy value is worth on the market. Without the more

than $12 billion annual federal and state government subsidies, US ethanol production

would be reduced or cease, confirming the basic fact that ethanol production is uneco-

nomical and does not provide the United States with any net energy benefit (Koplow and

Steeblik 2008).

Federal and state subsidies for ethanol production that total more than $12 billion/year

for ethanol are mainly paid to large corporations (Koplow and Steeblik 2008), while corn

farmers are receiving a minimum profit per bushel for their corn (Pimentel and Patzek

2008). Senator McCain reports that direct subsidies for ethanol, plus the subsidies for corn

grain, amount to 79¢ per l (McCain 2003).

About 80% of the ethanol in Brazil is also heavily subsidized (Berg 2004). Even with

heavy subsidies, about half of the fuel burned in autos in Brazil is gasoline, only about 50%

is ethanol (Berg 2004). Sugar subsidies have a major impact on ethanol production from

sugarcane (Pimentel and Patzek 2008).

If the production cost of a liter of ethanol were added to the tax subsidy cost, then the

total cost for a liter of ethanol would be $1.54. The mean wholesale price of ethanol was

almost $1.00 per l without subsidies. Because of the relatively low energy content of

ethanol, 1.6 l of ethanol have the energy equivalent of 1 l of gasoline. Thus, the cost

of producing an amount of ethanol equal a liter of gasoline is about $2.33 ($8.82 per gallon

of gasoline). This is more than the 53¢ per l current cost of producing a liter of gasoline.

The subsidy per liter of ethanol is 60 times greater than the subsidy per liter of gasoline!

This is the reason why ethanol is so attractive to large corporations.

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2.5 Corn land use

In 2008, about 34 billion l of ethanol (9 billion gallons) was produced in the United States

(EIA 2008). The total amount of petroleum fuels used in the United States is about

1,270 billion l (USCB 2008). Therefore, 34 billion l of ethanol (energy equivalent to

22 billion l of petroleum fuel) provided only 1.7% of the petroleum utilized. To produce

this 34 billion l of ethanol, about 9.6 million ha or 34% of US corn land was used.

Expanding corn ethanol production to 100% of US corn production would provide just 4%

of the petroleum needs of the United States while reducing and degrading cropland needed

for food production.

However, US corn cultivation may continue to increase because of the ethanol targets

(36 billion gallons) set by the most recent Energy Bill (Donner and Kucharik 2008) of

which 15 billion gallons which are to be produced from corn grain.

Corn production is the prime cause of the ‘‘dead zone’’ in the Gulf of Mexico (NAS

2003). Increased corn ethanol production will increase the nitrogen fertilizer pollution in

the Gulf of Mexico (Donner and Kucharik 2008).

2.6 By-products

The energy and dollar costs of producing ethanol can be offset partially through by-prod-

ucts, like the dry distillers grains (DDG) made from dry-milling of corn. From about 10 kg

of corn feedstock, about 3.3 kg of DDG with 27% protein content can be harvested (Stanton

and LeValley 1999). The DDG is suitable for feeding cattle that are ruminants, but has only

limited value for feeding hogs and chickens. In practice, this DDG is generally used as a

substitute for soybean feed that contains 49% protein (Stanton and LeValley 1999).

However, soybean production for livestock feed is more energy efficient than corn pro-

duction because soybean production for animal feed needs little or no nitrogen fertilizer

(Pimentel et al. 2002). In practice, only 2.1 kg of soybean meal provides the equivalent

nutrient value of 3.3 kg of DDG (or nearly 60% more DDG is required to equal the soybean

meal protein). Thus, the credit DDG provides in fossil energy per liter of ethanol produced is

about 445 kcal. Factoring this, credit for a nonfuel source in the production of ethanol

reduces the negative energy balance for ethanol production from 158 to 151% (Table 2).

The high energy credits for DDG given by some are unrealistic because the production of

livestock feed from ethanol is uneconomical given the high costs of fossil energy plus the

costs of soil depletion to the farmer (Patzek 2004). The resulting overall energy output/input

comparison remains negative even with the large credits for the DDG by-product.

2.7 Environmental impacts

Some of the economic and energy contributions of the by-products are negated by the

widespread environmental pollution problems associated with ethanol production. First,

US corn production causes more soil erosion than any other US crop (Pimentel et al. 1995;

NAS 2003). In addition, corn production uses more herbicides, insecticides, and nitrogen

fertilizer than any other crop produced in the United States. Consequently, corn causes

more water pollution than any other crop since a large quantity of these chemicals invades

ground and surface waters, thereby causing more water pollution than any other crop (NAS

2003).

Another environmental impact of biomass crop production is the land use change that

they demand. Nabuurs et al. (2007) reports that the limit for biomass crops is the

226 J. Zhang et al.

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availability of arable land; the massive scale of agricultural land expansion for biofuels

necessary will require deforestation. However, an important consideration when evaluating

the environmental effects of biofuels is whether the emissions avoided are higher and in

favor of biofuel production or in favor of forest preservation and expansion (Righelato

2007). According to the International Energy Agency forests converted to cropland have a

negative environmental impact because the land change destroys the carbon sink that the

forest provides (IEA 2004). Righelato (2007) of the World Land Trust investigated the

impacts of land use changes from forest to biofuel cropland, and found that the amount of

carbon sequestered, emissions avoided, by tropical forests is 3–4 times more than the

emissions avoided by bioethanol production. Only after the forest area reaches maturity in

50–100 years, would the emissions avoided from cropland conversion be able to surpass

the amount of carbon stock that is accumulated and calculated according to models for the

power of age in a forest structure (Righelato 2007; Alexandrov 2007; Sylvester-Bradley

2008).

As mentioned, the production of 1 l of ethanol requires 1,700 l of freshwater both for

corn production and for the fermentation/distillation processing of ethanol (Pimentel and

Patzek 2008). In some Western irrigated corn acreages, like some regions of Arizona,

ground water is being pumped 10-times faster than the natural recharge of the aquifers

(Pimentel et al. 2004). Ethanol production using sugarcane requires slightly more water per

ethanol liter than corn ethanol or about 2,000 l of water.

In addition, 1.59 l of fossil fuel is required to produce 1 l of ethanol, confirms that

ethanol production significantly contributes to global warming problems (Pimentel and

Pimentel 2008). All these factors confirm that the environmental and agricultural system in

which US corn is being produced is experiencing major degradation. Further, it substan-

tiates the conclusion that the US corn production system, and indeed the entire ethanol

production system, is not environmentally sustainable now or for the future, unless major

changes are made in the cultivation of this major food/feed crop. Corn cannot be con-

sidered a renewable energy source when used as a raw material for ethanol production.

Pollution problems associated with the production of ethanol at the chemical plant sites

are also emerging. The EPA (Cosgrove-Mather 2002) has already issued warnings to

ethanol plants to reduce their air pollution emissions or be shut down. Another pollution

problem concerns the large amounts of wastewater produced by each ethanol plant. As

noted, the production of 1 l of corn ethanol produces 6–12 l of wastewater. This polluting

wastewater has a biological oxygen demand (BOD) of 18,000–37,000 mg/l depending on

the type of plant (Kuby et al. 1984; Patzek 2004). The cost of processing this sewage in

terms of energy (4 kWh/kg of BOD) was included in the cost of producing ethanol

(Table 2).

The major problem with corn and all other biomass crops is that they collect on average

only 0.1% of the solar energy per year (Pimentel et al. 2009). At a fairly typical gross yield

of 3,000 l of ethanol per hectare per year, the power density achieved is only 2.1 kW/ha.

That is compared with the gross power density achieved via oil, after delivery for use, on

the order of 2,000 kW/ha (Ferguson 2008).

2.7.1 World malnutrition and use of food for biofuel

The Food and Agriculture Organization (FAO) of the United Nations estimated that there

were 1.02 billion undernourished people worldwide in 2009, representing approximately a

sixth of the world population. In its 2009 report, The State of Food Insecurity in the World,

the FAO (2009) defined undernourishment as being ‘‘when caloric intake is below the

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minimum dietary energy requirement (MDER)’’, where MDER ‘‘is the amount of energy

needed for light activity and a minimum acceptable weight for attained height’’. Caloric

intake is certainly not the only measurement of malnourishment; micronutrient deficiencies

can also have severe health impacts. In 2000, the World Health Organization (WHO 2000)

estimated that the number of people who have iron deficiency anemia is around 2 billion.

Anemia can result in extreme fatigue, impairment of physical and mental development in

children, and higher maternal deathrate. The WHO also estimated that 740 million people

have iodine deficiency disorder, which can have severe impacts on children’s brain

development. Finally, up to 140 million children are Vitamin A deficient, putting them at

higher risk for blindness and making them more susceptible to illnesses.

As more land and crops are devoted to the production of biofuels, rather than to human

consumption, concerns have been raised that malnutrition will worsen (Pimentel et al.

2009). Jacques Diouf, head of the FAO, stated in 2007 that he feared that a number of

factors, including the production of crops for biofuels, create ‘‘a very serious risk that

fewer people will be able to get food’’ and the poor will suffer (Rosenthal 2007). The

president of the World Bank, Robert Zoellick, shared a similar apprehension, asserting that

demand for biofuels has been a ‘‘significant contributor’’ to ballooning food prices.

According to Zoellick, ‘‘It is clearly the case that programs in Europe and the United States

that have increased biofuel production have contributed to the added demand for food’’

(NPR 2008) and increased food prices (Congressional Budget Office 2009). Ziegler (2007),

the UN Special Rapporteur on the Right to Food, has taken a more extreme stance. In 2007,

he claimed biofuels to be a ‘‘crime against humanity’’ and called for a 5-year moratorium

on their production (Ferrett 2007).

3 Conclusion

Each year, the United States and other nations import more than 60% of their oil at a

tremendous cost to themselves (USCB 2008). In the United States alone, oil represents

nearly 40% of the United States’ energy consumption, leading the EIA (2008) and other

organizations to estimate that cheap world oil supplies will be depleted by 2040 (Murray

2004; Green et al. 2006; Hodge 2008; W. Youngquist, Personal Communication,

December 8, 2009). Such a forecast has created an urgent need for an alternate liquid fuel

and has stimulated many nations to seek diverse ways to produce liquid fuels. As a

consequence, corn ethanol production has become a popular feedstock for ethanol pro-

duction. Unfortunately, the production of ethanol from corn grain has proven to be ener-

getically and environmentally costly in terms of the subsidies which now total $12 billion

per year (Koplow and Steeblik 2008). Producing ethanol using corn in the United States,

for instance, requires 1.59 l of fossil energy but only supplies 1 l of ethanol. This is a

tremendous cost and is certainly not making the United States oil independent.

In addition, converting corn into ethanol has increased US food prices (Pimentel et al.

2009). Using food as a source of ethanol seems to present important ethical problems.

Producing ethanol using corn in the United States requires 1.59 l of fossil energy but

only supplies 1 l of ethanol. This is a tremendous cost and is certainly not making the

United States oil independent.

Acknowledgments This research was supported in part by the Podell Emeriti Award at CornellUniversity.

228 J. Zhang et al.

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References

Alexandrov, G. A. (2007). Carbon stock growth in a forest stand: The power of age. Carbon Balance andManagement, 2, 4.

Batty, J. C., & Keller, J. (1980). Energy requirements for irrigation. In D. Pimentel (Ed.), Handbook ofenergy utilization in agriculture (pp. 35–44). Boca Raton: CRC Press.

Berg, C. (2004). World fuel ethanol analysis and outlook. http://www.distill.com/World-Fuel-Ethanol-A&O-2004.html. Accessed January 12, 2010.

Blais, J. F., Mamouny, K., Nlombi, K., Sasseville, J. L., & Letourneau, M. (1995). Les mesures deficaciteenergetique dans le secteur de leau. In J. L. Sasseville & J. F. Blais (Eds.), Les Mesures deficaciteEnergetique pour Lepuration des eaux Uses Municipales. Scientific Report 405. Vol. 3. Quebec: INRS-Eau.

Cosgrove-Mather, B. (2002). More pollution than they said: Ethanol plants said releasing toxins. CBS News.May 3, 2002. http://www.cbsnews.com/stories/2002/05/03/tech/main508006.shtml. Accessed April 15,2011.

DOE. (2002). Review of transport issues and comparison of infrastructure costs for a renewable fuelsstandard. Washington, DC: US Department of Energy. http://tonto.eia.doe.gov/FTPROOT/service/question3.pdf. Accessed April 15, 2011.

Donner, S. D., & Kucharik, C. J. (2008). Corn-based ethanol production compromises goal of reducingnitrogen export by the Mississippi river. Proceedings of the National Academy of Sciences, 105(11),4513–4518.

EIA. (2008). International energy statistics: Renewables. Washington, DC: Energy Information Agency, USDepartment of Energy. http://www.eia.doe.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=79&pid=79&aid=1. Accessed April 15, 2011.

FAO. (2009). The state of food insecurity in the world. Rome: Food and Agricultural Organization of theUnited Nations. http://www.fao.org/docrep/013/i1683e/i1683e.pdf. Accessed April 15, 2011.

Farmersfeedus.org. (2010). Against biofuels. http://www.farmersfeedus.org/ia/our-farm-families/. AccessedNovember 21, 2010.

Ferguson, A. R. B. (2008). The power density of ethanol from Brazilian sugarcane. In D. Pimentel (Ed.),Biofuels, solar and wind as renewable energy systems: Benefits and risks (pp. 493–498). New York:Springer.

Ferrett, G. (2007). Biofuels ‘crime against humanity’. BBC News (October 27, 2007). http://news.bbc.co.uk/2/hi/7065061.stm. Accessed April 15, 2011.

Green, D. L., Hopson, J. L., & Jia, L. (2006). Have we run out of oil yet? Oil peaking analysis from anoptimist’s perspective. Energy Policy, 34(5), 515–531.

Hodge, N. (2008). Future sources of energy: What is a cubic mile of oil? http://www.energyandcapital.com/articles/future-sources-energy/787. Accessed April 15, 2011.

IEA. (2004). Biofuels for transport: An international perspective. Paris: International Energy Agency,OECD/IEA. http://www.iea.org/press/pressdetail.asp?PRESS_REL_ID=127. Accessed April 15, 2011.

Johnson, J., Reck, B. K., Wang, T., & Graedel, T. E. (2008). The energy benefit of stainless steel recycling.Energy Policy, 36(1), 181–192.

Koplow, D., & Steeblik, R. (2008). Subsidies to ethanol in the United States. In D. Pimentel (Ed.), Biofuels,solar and wind as renewable energy systems: Benefits and risks (pp. 79–108). Dordrecht: Springer.

Kuby, W. R., Markoja, R., & Nackford, S. (1984). Testing and evaluation of on-farm alcohol productionfacilities. Cincinnati: Acures Corporation, Industrial Environmental Research Laboratory, Office ofResearch and Development. US Environmental Protection Agency.

Larsen, K., Thompson, D., & Harn, A. (2002). Limited and full irrigation comparison for corn and grainsorghum. http://www.colostate.edu/depts/prc/pubs/LimitedandFullIrrigationComparisonforCorn.pdf.Accessed April 15, 2011.

Maiorella, B. (1985). Ethanol. In H. W. Blanchm, S. Drew & D. I. C. Wang (Eds.), Comprehensivebiotechnology, Vol 3, Chap 43. New York: Pergamon Press.

Martinelli, L. A. (2009). BOD in sugarcane waste. (p. 24). http://www.fapesp.br/eventos/bioen0809/martinelli.pdf. Accessed April 15, 2011.

McCain, J. (2003). Statement of senator McCain on the energy bill. press release. Wednesday, November 21,2003. http://mccain.senate.gov/public/index.cfm?FuseAction=PressOffice.Speeches&ContentRecord_id=faed0c9b-6d5c-46dd-acd2-3163891b6685&Region_id=&Issue_id=79a48974-2bd4-4888-be97-e8a445366a84. Accessed April 15, 2011.

Murray, B. (2004). Dispelling ‘‘urban myths’’ about the oil market: Energy economist explains basicoperating conditions of world oil markets. FACS (Foundation for American Communications). Posted

Energy production from corn 229

123

December 8, 2004. http://www.facsnet.org/index.php?com_content&view=article&id=183:oil-urban-myths-12-04&catid=75. Accessed April 15, 2011.

Nabuurs, G. J., Masera, O., Andrasko, K., Benitez-Ponce, P., Boer, R., Dutschke, M. E., et al. (2007).Forestry. In B. Metz, et al. (Eds.), Climate change 2007: Mitigation (pp. 541–584). Contribution ofWorking Group III to the Fourth Assessment Report of the Intergovernmental Panel on ClimateChange Cambridge: Cambridge University Press.

NAS. (2003). Frontiers in agricultural research: Food, health, environment, and communities. Washington,DC: National Academy of Sciences.

NASS. (2003). Agricultural chemical usage: 2002 field crops summary (p. 6). May 2003. United StatesDepartment of Agriculture, National Agricultural Statistics Service. http://usda.mannlib.cornell.edu/usda/nass/AgriChemUsFC//2000s/2003/AgriChemUsFC-05-14-2003.pdf. Accessed 15 April 2011.

NASS. (2005). National agricultural statistics service: Farm labor. http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1063. Accessed April 15, 2011.

NASS. (2008). Ch XIV statistics of fertilizers and pesticides. http://www.nass.usda.gov/Publications/Ag_Statistics/2008/Chap14.pdf. Accessed March 1, 2010.

Newton, P. W. (2001). Human settlements theme report. Australian state of the environment report 2001.Melbourne: CSIRO Publishing.

NPR. (2008). World bank chief: Biofuels boosting food prices. National Public Radio. 11 April, 2008.http://www.npr.org/templates/story/story.php?storyId=89545855. Accessed April 15, 2011.

Patzek, T. W. (2004). Thermodynamics of the corn-ethanol biofuel cycle. Critical Reviews in Plant Sci-ences, 23(6), 519–567.

Patzek, T. W. (2010). A probabilistic analysis of the switchgrass ethanol cycle. Sustainability, 2, 3158–3194.Patzek, T. W., & Pimentel, D. (2005). Thermodynamics of energy production from biomass. Critical

Reviews in Plant Sciences, 24(5–6), 327–364.Pimentel, D., Berger, B., Filiberto, D., Newton, M., Wolfe, B., Karabinakis, E., et al. (2004). Water

resources: Agricultural and environmental issues. BioScience, 54(10), 909–918.Pimentel, D., Doughty, R., Carothers, C., Lamberson, S., Bora, N., & Lee, K. (2002). Energy inputs in crop

production in developing and developed countries. In R. Lal, et al. (Eds.), Food Security and envi-ronmental quality in the developing world (pp. 129–151). Boca Raton: CRC Press.

Pimentel, D., Harvey, C., Resosudarmo, P., Sinclair, K., Kurtz, D., McNair, M., et al. (1995). Environmentaland economic costs of soil erosion and conservation benefits. Science, 267, 1117–1123.

Pimentel, D., Marklein, A., Toth, M. A., Karpoff, M., Paul, G.S., McCormack, R., Kyriazis, J., & Krueger,T. (2008). Biofuel impacts on world food supply: Use of fossil fuel, land and water resources.Energies, 1, 41–78. doi:10.3390/en1010041, online, open access. http://www.mdpi.org/energies/papers/en1020041.pdf.

Pimentel, D., Marklein, A., Toth, M. A., Karpoff, M., Paul, G. S., McCormack, R., et al. (2009). Food versusbiofuels: Environmental and economic costs. Human Ecology, 37, 1–12.

Pimentel, D., & Patzek, T. (2008). Ethanol production: Energy and economic issues related to US andBrazilian sugarcane. In D. Pimentel (Ed.), Biofuels, solar and wind as renewable energy systems:Benefits and risk (pp. 357–371). Dordrecht: Springer.

Pimentel, D., & Pimentel, M. (2008). Food, energy and society (3rd ed.). Boca Raton: CRC Press (Taylorand Francis Group).

Portland Cement Association. (2011). Environment and energy. Government affairs: Tools for concretethinking. Portland Cement Association. http://www.bipac.net/page.asp?g=pca&content=issue_energy&parent=PCA. Accessed April 20, 2011.

Righelato, R. (2007). Biofuels or forests? Scitizen, August 23, 2007. http://scitizen.com/authors/Renton-Righelato-a-809_s_5c85358b289831dc490e29b55191d47e.html. Accessed April 15, 2011.

Rosenthal, E. (2007). World food stocks dwindling worldwide, UN warns. New York Times, December 17,2007. http://www.nytimes.com/2007/12/17/world/europe/17iht-food.html?_r=1&scp=1&sq=world%20food%20stock%20dwindling%20rapidly,%20UN%20warns&st=cse. Accessed April 15, 2011.

Roushey, J. (2010). A new standard in steam measurement: Rising energy costs and pending regulationscalls for a better way. Plant Services.com. http://www.plantservices.com/articles/2010/01SteamMeasurement.html. Accessed April 15, 2011.

Stanton, T. L., & LeValley, S. (1999). Feed composition for cattle and sheep. Colorado State University.Cooperative Extension, Report No. 1.615. http://www.ext.colostate.edu/pubs/livestk/01615.pdf.Accessed April 15, 2011.

Supalla, R. (2007). Biofuels: An emerging water resources hazard. University of Nebraska, Lincoln,Agricultural Economics Department, Presentations, Working Papers, and Gray Literature: AgriculturalEconomics. http://digitalcommons.unl.edu/ageconworkpap/40/. Accessed April 15, 2011.

230 J. Zhang et al.

123

Sylvester-Bradley, R. (2008). Critique of Searchinger (2008) & related papers assess indirect effects ofbiofuels on land-use change. ADAS Support of the Gallagher Review. http://www.globalbioenergy.org/uploads/media/0806_ADAS_-_Seachinger_critique.pdf. Accessed April 15, 2011.

USCB. (2004). Statistical abstract of the United States: 2004–2005 (124th ed.). Washington, DC: UnitedStates Census Bureau, US Government Printing Office.

USCB. (2008). Statistical abstract of the United States: 2009 (128th ed.). Washington, DC: US GovernmentPrinting Office. United States Census Bureau.

USDA. (1997). Farm and ranch irrigation survey (1998). 1997 Census of agriculture. Vol. 3, SpecialStudies. Part 1. http://www.agcensus.usda.gov/Publications/1997/Farm_and_Ranch_Irrigation_Survey/fris97.pdf. Accessed April 15, 2011.

USDA. (2007). Agricultural statistics 2007. Washington, DC: US Government Printing Office. USDepartment of Agriculture.

USDA. (2008). Agricultural statistics 2008. Washington, DC: US Government Printing Office. USDepartment of Agriculture.

Venkatarama Reddy, B. V., & Jagadish, K. S. (2003). Embodied energy of common and alternative buildingmaterials and technologies. Energy and Buildings, 35(2), 129–137.

Werekoo-Brobby, C., & Hagen, E. B. (1996). Biomass conversion and technology. Chichester: John Wiley& Sons.

WHO. (2000). Turning the tide of malnutrition: Responding to the challenge of the 21st century. Geneva:World Health Organization. http://www.who.int/mip2001/files/2232/NHDbrochure.pdf. AccessedApril 15, 2011.

Ziegler, J. (2007). UN rapporteur calls for biofuel moratorium. http://www.swissinfo.ch/eng/index/UN_rapporteur_calls_for_biofuel_moratorium.html?cid=6189782. Accessed April 15, 2011.

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