Pimentel David, et. al. 2008. Reducing Energy Inputs in the US Food System. Human Ecology 36:459–471
[ Here are some excerpts from this paper. I don’t list many of the ideas in the article on how to do this though, read it if you’d like to know more]
Abstract Petroleum and natural gas are the primary fuels in the US food system. Both fuels are now in short supply and significant quantities are being imported into the USA from various nations. An investigation documented that fossil energy use in the food system could be reduced by about 50% by appropriate technology changes in food production, processing, packaging, transportation, and consumption. The results suggest that overall, farmers benefit as well as consumers.
Introduction Petroleum, natural gas, coal, and other mined fuels currently provide the USA with nearly all of its diverse energy needs at a cost $700 billion/year (USCB 2007). Given that more than 90% of US oil deposits have been depleted, the country now imports over 65% of its oil at an annual cost of $200 billion (USCB 2004–2005; Deffeyes 2001). These figures indicate the magnitude of the economic and energy challenges associated with supplying food for the US population.
Further, the usage of oil and natural gas has peaked at a time when oil and gas reserves are predicted to last only 40 to 50 more years (Duncan and Youngquist 1999; Deffeyes 2001). As oil and natural gas supplies decline, the USA will have to depend on coal and a variety of renewable energy technologies. Best estimates are that coal supplies are only capable of providing the USAwith 50 to 100 years of energy (USCB 2007). With the US population continuing to grow close to its current rate, it is projected to increase from 317 million to one billion in about 100 years, further exacerbating strains on coal and oil supplies (Abernethy 2006). However, it is unlikely that such a population could be sustained with the diminishing availability of fossil fuels. The American food supply is driven almost entirely by non-renewable energy sources. In total, each American requires approximately 2,000 l/year in oil equivalents to supply their food, which accounts for about 19% of the total energy use in the USA. Agricultural production, plus food processing and packaging, consumes 14%, while transportation and preparation use 5% of total energy in the USA (Pimentel et al. 2007).
Food Consumed by Americans The fossil energy required to produce the relatively high level of animal products consumed in the average American diet are estimated to be 50% of the total energy inputs, while to produce staple foods such as potatoes, rice, common fruits and vegetables, uses about 20% of the fossil energy inputs. The average American consumes 1,000 kg (2,200 lb) of food per year containing an estimated 3,747 kcal per day (Table 1). A vegetarian diet of an equivalent 3,747 kcal per day requires 33% less fossil energy than the average American diet (Pimentel and Pimentel 1996). The Food and Drug Administration (FDA 2007) recommends an average daily consumption of 2,000 to 2,500 kcal a day, much less than provided by the typical American diet (Vaclavik et al. 2006). Reducing the calorie intake to a lower level would significantly reduce the energy used in food production.
Renewable Energy Supplies The production of 46 quads per year from renewable energy technologies would require at least 17% of total land area not counting cropland in the USA (Pimentel et al. 2002a).
The renewable energy systems that are projected to provide the most energy in the future are photovoltaics, biomass (thermal), and hydroelectric power (Pimentel et al. 2002a). None of these renewable energy sources produce liquid fuels [which is a big problem – tractors, trucks, cars, ships, trains, mass transit, and other essential agricultural and transportation machinery runs on liquid fuels 97% of them oil].
The decline of fossil energy reserves will force the USA to rely on various renewable energy technologies to maintain a viable food supply. These include: hydroelectric, biomass (wood), wind power, solar thermal systems, photovoltaics, passive energy systems, geothermal, biogas, and methanol (Hayden 2001; Pimentel et al. 2002a; Pimentel 2008). Ethanol is not included in this study because it fails to provide renewable energy (Pimentel and Patzek 2005). Together, these systems could provide the USA with an estimated 46 of the 103 quads (quad=1015 BTU) of energy currently used per year (Pimentel 2008; USCB 2004– 2005). The renewable energy systems that are projected to provide the most energy in the future are photovoltaics, biomass (thermal), and hydroelectric power (Pimentel et al. 2002a).
Hydroelectric power already supplies the USA with 269 billion kWh or 7% of the nation’s electricity at a cost of $0.02 per kWh (USCB 2007). One drawback to hydroelectric plants is the substantial land requirement for water reservoirs; 75,000 ha of reservoir land and 14 trillion liters of water are needed to produce 1 billion kWh per year (Pimentel et al. 2002a; Sims et al. 2003).
Land Availability Land is a major concern when attempting to modify fossil energy usage as land provides 99.9% of the human food supply (measured in calories; FAOSTAT 2004). As the population expands, more land is needed to meet nutritional needs, yet the per capita availability of world cropland has declined by 20% in the past decade (Worldwatch Institute 2001). This decrease is due in part to the loss of viable cropland caused by wind and water erosion at a rate of ten million hectares per year (Preiser 2005). In addition, another ten million hectares are abandoned annually worldwide due to severe salinization as a result of irrigation (FAO 2006).
Loss of soil is insidious; one rain or wind storm can remove 1 mm of topsoil and nearly 14 tons of total soil per hectare. This 1 mm of erosion can easily go unnoticed by farmers. Soil erosion occurs at rates ranging from 10 t ha-1 year-1 in the USA and Europe to 30 t ha-1 year-1 in Africa, South America and Asia. Approximately 75 billion tons of topsoil is lost each year worldwide (Pimentel 2006a; Wilkinson and McElroy 2007). Additionally, rapid deforestation (at a rate of 11.2 million ha/year) is occurring as more forest is claimed to replace lost and degraded cropland (Pimentel et al. 2005).
Cropland now occupies 17% of the total land area in the USA, but little additional land is available or even suitable for future agricultural expansion (USDA 2004).
At present, the global availability of land per capita is 0.23 ha for cropland and 0.5 ha for pastureland (Pimentel and Pimentel 2006). However, the USA and Europe have 0.5 ha of cropland and 0.81 ha of pasture available per capita, which is the minimum amount of land required to support their diverse food systems (Pimentel and Wilson 2004; USDA 2004).
As the US population increases to a projected 1 billion people (120 years), US fossil energy resources will run out and reduce per capita land area to only 0.17 ha of cropland and 0.3 ha of pasture land, both values below current global land availability.
There are several different conservation technologies that help control soil erosion, including: crop rotations, cover crops, contour planting, ridge till, mulch, terraces, grass strips, and no-till. Some investigators claim that no-till saves energy but this is usually only accounted for in tractor fuel reductions. These investigations seldom account for the added nitrogen, added corn seed, plus the added pesticides required in no-till production (Pimentel and Ali 1998; Williams et al. 2000; Parsch et al. 2001; Epplin et al. 2005).
In 100 years time, world population is projected to be more than twice as the number is today (6.5 billion)—about 13 billion. A World Health Organization report states that worldwide there are currently more than 3.7 billion malnourished humans, the largest number of malnourished people ever in the history of the Earth (WHO 2005). In light of this report, we should expect food shortage problems to continually worsen.
While the number of malnourished people increased worldwide over the past two decades, per capita grain production simultaneously declined (FAOSTAT 1961– 2005). There are many factors that contributed to this decline, including: a rapidly growing world population (PRB 2006), a 20% decline in cropland per capita in the last decade (Pimentel and Wilson 2004), a 10% decline in irrigated land per capita (Postel 1997) and a 17% decrease in per capita fertilizer use (Pimentel and Wilson 2004). It should be noted that cereal grains make up 80% of the world’s food supply.
Irrigation and Energy Provided there is ample of irrigation water, crop production can be increased significantly in arid regions. Approximately 80% of water used in the USA is solely for irrigation to increase crop production, particularly in arid regions (Pimentel et al. 2004). Plants consume about twothirds of this water while one-third is non-recoverable (Postel 1997). Irrigated corn requires about 14 million liters of water per hectare (500,000 gallons per acre) and uses about three times more energy than rain-fed corn to produce the same yield (Pimentel et al. 2004). Irrigation tends to be expensive both energetically and economically, costing more than $1,200 per hectare when pumping from a depth of only 100 m (Pimentel et al. 2004).
Reducing irrigation dependence in the USA would save significant amounts of energy, but probably require that crop production shift from the dry and arid western and southern regions to the more agriculturally suitable Midwest and Northeast. Also, as noted above, soil salinization due to irrigation causes the abandonment of ten million hectares each year worldwide (FAO 2006). The leaching of salts from the soil into rivers poses another major problem. For example, where the Colorado River flows through the Grand River Valley in Colorado, water returned to the river from irrigated cropland contains an estimated 18 t/ha of salts leached from the soil (EPA 1976), resulting in high salt concentrations in the river.
Conserving Essential Nutrients As fossil fuels become scarce, costs for the production of synthetic fertilizers will rise. This economic pressure will force farmers to seek alternative sources to meet their nitrogen, phosphorus, and potassium demands. Nitrogen is the most vital nutrient in agricultural production and is applied at a rate of 12 million tons of commercial or synthetic nitrogen per year in the USA (GAO 2003; USDA 2004). Although 18 million tons of nitrogen were applied in 1995 in the USA, a 300% increase in the price of nitrogen fertilizer over the past decade has resulted in fewer N applications, highlighting the need to explore alternative nutrient sources. It is of equal commercial importance to provide adequate amounts of phosphorus and potassium, the other essential macro-elements needed by plants to grow well and produce high yields. As will be shown below, leguminous cover crops, manure, and other organic inputs can meet the N, P, and K demands of food production in the USA (Funderberg 2001; Schmalshof 2005).
Cover Crops Conserving soil nutrients is a priority in agricultural production because it reduces the demand for fertilizers and produces high crop yields. A crucial aspect of soil nutrient conservation is the prevention of soil erosion. Cultivation practices that build soil organic matter (SOM) and prevent the exposure of bare soil are a key part of preventing soil erosion. Cover crops help protect the exposed soil from erosion after the main crop is harvested (Troeh et al. 2004). Compared with conventional farming systems, which traditionally leave the soil bare, the use of cover crops significantly reduces soil erosion. Leguminous cover crops also add nutrients to the soil (Drinkwater et al. 1998; Weinert et al. 2002). For example, vetch, a legume cover crop grown during the fall and spring months (non-growing season), can add about 70 kg/ha of nitrogen (Pimentel et al. 2005; Henao and Baanante 2006). Cover crops further aid in agriculture by collecting about 1.8 times more solar energy than conventional farming systems (Pimentel 2006b). Growing cover crops on land before and after a primary crop nearly doubles the amount of solar energy that is harvested per hectare per year. This increased solar energy capture provides extra organic matter which improves soil quality.
Soil Organic Matter Maintaining high levels of soil organic matter (SOM) is beneficial for all agriculture and crucial to improving soil quality. Carter (2002) has shown aggregated SOM to have “major implications for the functioning of soil in regulating air and water infiltration, conserving nutrients, and influencing soil permeability and erodibility” by improving the soil’s water infiltration, structure, and reducing erosion. Maintaining high levels of SOM is a primary focus of organic farming. On average, the amount of SOM is significantly higher in organic production systems than in conventional systems. Typical conventional farming systems with satisfactory soil generally have 3% to 4% SOM, whereas organic systems soil average from 5% to 5.5% SOM (Troeh et al. 2004). Soil carbon increased about 28% in organic animal systems and 15% in organic legume systems, but only 9% in conventional farming systems (Pimentel et al. 2005). This high level of SOM provides many advantages. Increased SOM also provides soil with an increased capacity to retain water. Sullivan (2002) reported that approximately 41% of the volume of organic matter in the organic systems consisted of water, compared with only 35% in conventional systems. The large amount of soil organic matter and water present in organic systems is the major factor in making these systems more drought resistant. Furthermore, 110,000 kg/ha of soil organic matter in an organic corn system could sequester 190,000 kg/ha of carbon dioxide. This is 67,000 kg/ha more carbon dioxide sequestered than in conventional corn systems, and equals the amount of carbon dioxide emitted by ten cars that averaged 20 miles per gallon and traveled 12,000 miles per year (USCB 2004–2005). The added carbon sequestration benefits of organic systems clearly have beneficial implications for reducing global warming.
Manure In 2005, the 100 million cattle, 60 million hogs, and nine billion chickens maintained in the USA produced an estimated 20.5 million metric tons of nitrogen. This nitrogen, most of which is produced by cattle, could potentially be used in crop production. The collection and management of this nitrogen requires special attention. Approximately 50% of the nitrogen is lost as ammonia within 24 to 48 h after defecation, if the animal waste is not immediately buried in the soil or placed in a lagoon under anaerobic conditions (Troeh et al. 2004). The liquid nutrient material in the lagoon must be buried in the soil immediately after it is applied to the land, or again the nitrogen will be lost to the atmosphere. We estimate 70% of cattle manure is dropped in pasture or rangeland and is not included in the total nitrogen estimate, reducing the amount of nitrogen theoretically collected for use per year to 18 million metric tons (Pimentel et al., unpublished data). Because cow manure is 80% water, this manure can only be transported a distance of about eight miles before the energy return is negative. Conserving nutrients will be crucial to farmers in a world of high fertilizer costs. In addition, practices that center on building and conserving soil integrity can greatly improve energy efficiency in food production systems. The use of manure, cover crops, composting, and conservation tillage can contribute to such energy reductions and allow farmers to produce food sustainably.
Reducing energy use in the farm system
Reduced Pesticide Use Currently, more than one billion pounds of pesticides are applied annually to US agriculture (USDA 2004). Certified organic farming systems do not apply synthetic pesticides. Weed control is, instead, achieved through crop rotations, cover crops, and mechanical cultivation (Pimentel et al. 2005). Avoiding the use of herbicides and insecticides improves energy efficiency in corn/soybean production systems. For example, in organic farming, one pass of a cultivator and one pass of a rotary hoe use approximately 300,000 kcal/ha of fossil energy. Herbicide weed control (including 6.2 kg of herbicide per hectare plus sprayer application) requires about 720,000 kcal/ha or about twice the amount of energy used for mechanical weed control in organic farming (Pimentel et al. 2005). In addition, there are a reported 300,000 non-fatal pesticide poisonings (EPA 1992) per year in the USA, and pesticides in the diet have been shown to increase the odds of developing cancer (Horrigan et al. 2002).
Moving Livestock Back to the Grain Farms Another factor in energy usage in farming is the recent proliferation of monocultures, or farms devoting large tracts of land to one crop. The movement of livestock frommixed farming systems was encouraged by the US Government as it began to provide price supports for farmers (NAS 1989). As a result, livestock were moved to concentrated animal feeding operations (CAFOs) where they could be raised in large numbers. This shift resulted in an increase in commercial fertilizer and pesticide use in crop production, plus a significant increase in soil erosion (NAS 1989). It has also raised concern that 76 million hospital cases and 5,000 human deaths may be attributable to pollution associated with CAFOs and poor waste management (CDC 2002).
Crop Rotations Crop rotations are beneficial to all agricultural production systems because they help control soil erosion (Troeh et al. 2004; Delgado et al. 2005). They also help control pests such as insects, plant pathogens and weeds (Pimentel et al. 1993; Troeh et al. 2004). In addition, when legume cover crops are used, essential nitrogen is added to the soil when they are plowed under. As mentioned above, in the Rodale study soil nitrogen levels in organic farming systems were 43% compared with only 17% in conventional systems (Pimentel et al. 2005). Regulatory actions and market-based incentives could encourage the movement of livestock manure away from pollution causing CAFOs and back to the mixed farms where it can be incorporated into the soil. They could also encourage the agricultural practice of crop rotation, the use of cover crops, and reduced pesticide applications, all of which would result in increased energy savings and reduced hazards to human health.
Labor and Mechanization
Raising corn and most other crops by hand requires about 1,200 h of labor per hectare (nearly 500 h per acre; Feeding the World 2002). Modern mechanization allows farmers to raise a hectare of corn with a time input of only 11 h, or 110 times less than required for hand-produced crops (Pimentel et al. 2007). Mechanization requires significant energy for both the production and repair of machinery (about 333,000 kcal/ha) and diesel and gasoline fuel (1.4 million kcal/ha; Table 4). About one-third of the energy required to produce a hectare of crops is invested in machine operation (Pimentel and Patzek 2005). Mechanization decreases labor significantly, but does not contribute to increased crop yields. Organic corn production requires mechanization. Economies of scale are still possible with more labor and the use of smaller tractors and other implements. Reports suggest that equipment quantity and size is often in excess of requirements for the tasks. Reducing the number and size of tractors will help increase efficiency and conserve energy (Grisso and Pitman 2001).
Return to Horses and Mules
A horse can contribute to the management of 10 ha (25 acres) per year (Morrison 1946). Each horse requires one acre of pasture and about 225 kg of corn grain. Another 1.5 acres of hayland is necessary to produce the roughly 800 lbs of hay needed to sustain each animal. In addition to the manpower required to care for the horses, labor is required to drive the horses during tilling and other farm operations. The farm labor required per hectare would probably increase from 11 hours to between 30 and 40 h per hectare using draft animal power. Nevertheless, an increase in human and animal labor as well as a decrease in fuel-powered machinery is necessary to decrease fossil fuel use in the US food system.
Energy Inputs in Meat, Poultry and Dairy Production
Each year an estimated 45 million tons of plant protein are fed to US livestock producing approximately 7.5 million tons of animal protein (meat, milk, and eggs) for human consumption (Pimentel 2004). The livestock feed is comprised of about 28 million tons of plant protein from grains and 17 million tons from forage. In the USA, the average protein yield of the five major grains (corn, rice, wheat, sorghum, and barley, plus soybeans) fed to livestock is about 700 kg/ha. For every kilogram of high quality animal protein produced, livestock are fed nearly 6 kg of plant protein (Pimentel 2004). Major differences exist in the inputs of feed and forage between animal products. For example, production of 1 kg of beef requires 13 kg of grain and 30 kg of forage (fossil energy input 40 kcal per 1 kcal beef protein), 1 kg of pork requires 5.9 kg of grain (14:1 kcal), and 1 kg of broiler chicken requires only 2.3 kg of grain (4:1 kcal). A kilogram of conventional milk produced in the USA requires 0.7 kg of grain and 1 kg of hay (14:1 kcal; Pimentel 2006b). In Norway, organic milk production was reported to be 43% more energy efficient (Refsgaar et al. 1998), since the cattle were grazed on pasture land.
When converting plant protein into animal protein, there are two principal categories of energy and economic costs:
(1) the direct production costs of the harvested animal including the grain and forage fed; and (2) the indirect costs of maintaining the breeding herd. Diverse combinations of grains, forages, and legumes (including soybeans) are fed to livestock to produce meat, milk, and eggs. The major fossil energy inputs required to produce grain and forage for animals includes fertilizers, farm machinery, fuel, irrigation, and pesticides. The energy inputs vary according to the particular grain or forage being grown and fed to livestock. On average producing one kcal of plant protein for livestock feed requires about 10 kcal of fossil energy (Pimentel 2004). Of the livestock systems evaluated, broiler-chicken production is the most energy efficient, with 1 kcal of broiler protein produced with an input of 4 kcal of fossil energy (Pimentel 2006b). Broilers are a grain-only livestock system. Turkey production is also a grain-only system and is next in efficiency with a 1:10 ratio. In addition, conventional milk production, based on a mixture of grain and forage feed, is also relatively efficient, with 1 kcal of milk protein requiring 14 kcal of fossil energy (Pimentel 2006b). Nearly all the feed protein consumed by broilers is from grain, while milk production uses about two-thirds grain and one-third forage. Of course, 100% of milk production could be achieved using hay and/or pasture as feed.
Food Processing and Packaging
In the USA, processed foods account for 82% to 92% of food sales (Murray 2005; Putman et al. 2002; SixWise 2006). Of the energy used for the total food system, 16% is used in processing and 7% is used in packaging. [Pimentel then has a long list of how to use less energy]
Transport of Food
In the US food travels an average of 2,400 km (1,500 miles) before it is consumed, a practice which is obviously energy intensive. A very energy intensive part of the American diet is the large quantity of fruits and vegetables that are transported by aircraft. The amount of energy required to ship 1 kg of food by aircraft is 6.63 kcal/km. On the other hand, shipping by rail is only 0.12 kcal/kg/km (Pimentel 1980).
Conclusion and References: see the original paper