Agriculture as energy producer
Agriculture serves a dual role as both a consumer and producer of energy, utilizing energy for various production processes, including heat and light, as well as generating energy through the cultivation of crops. Historically, energy use in agriculture has evolved from reliance on human and animal labor to significant use of fossil fuels and advanced technologies, particularly since the mid-20th century. This transition has led to remarkable increases in crop yields, as demonstrated by corn production in the United States, which has experienced a fourfold increase in yield due to improved practices and technology.
Direct energy use in agriculture, such as diesel for machinery and electricity for irrigation, represents a small but crucial aspect of overall agricultural operations. Alternative energy sources, such as solar and wind, are being explored, though they currently represent a modest share of energy consumption. Furthermore, dietary shifts towards more animal products raise concerns about energy efficiency, as livestock production requires substantially more energy compared to plant-based food production.
Aquaculture also presents varied energy requirements, with intensive farming demanding higher energy inputs. Additionally, energy crops like corn and soybeans are vital for biofuel production, contributing significantly to the U.S. biofuels market. With the increasing interest in renewable energy, agriculture's role as an energy producer continues to expand, reflecting broader trends towards sustainability.
Agriculture as energy producer
Summary: Agriculture is both a consumer and a producer of energy, using it for heat, light, motor fuel, and other energy required for agricultural production as well as the production of materials such as fertilizer and pesticides. It produces crops, which can act as energy inputs.
History of Energy Use in Agriculture
In preindustrial Europe, as in many developing countries today, agriculture production was labor-intensive and governed largely by the availability of natural resources, including sunlight, water, and regionally available fuels. The primary source of energy was human and animal labor; fuels such as wood were often in short supply, and their use was strictly controlled by law. For instance, in 16th-century England timberlands were protected from poaching by stiff penalties, forcing many farmers to rely on inferior fuels such as peat for their own use. During the “agricultural revolution” of the 17th to 19th centuries, technological advances in agriculture, such as the introduction of the threshing machine, began the process of replacing human and animal labor with machines. However, the widespread use of fossil fuels in agricultural production is a fairly recent phenomenon, with rapid increases seen after 1940.
The shift in types of energy used in American agriculture can be seen by examining trends in the production of corn. Corn yields increased about fourfold from 1945 to 2000, thanks to hybrids, irrigation, commercial fertilizers and insecticides, and other improved technologies, and total energy input has also increased about fourfold. In 1945, the average yield for the US corn crop was 2,132 kilograms per hectare (kg/ha), whereas in 2000, it was 8,590 kg/ha. Labor inputs during that time decreased from 57 hours per hectare to 6.2 hours per hectare, whereas the amount of machinery used increased from 22 kg/ha to 55 kg/ha. The amount of fuel used in corn production has decreased slightly, from about 880 liters per hectare in 1975 to 850 liters per hectare in 2000, despite the large increase in corn produced per hectare, because farm machinery has become more efficient. The type of fuel used has also changed: In 1945, tractors ran primarily on gasoline, whereas today diesel fuel is more common. As a diesel-fueled engine generally performs better in terms of miles per gallon, this switch has contributed to increased energy efficiency in farming.
Changes in the use of fertilizer, pesticides, and irrigation have also increased agricultural productivity while representing another source of energy consumption. Early agriculture depended primarily on nutrients present in the soil, including those from wild vegetation growing on land allowed to lie fallow or from crop rotation. Commercial fertilizers came into use around 1945, and the average use in that year in the United States was 8 kg/ha of nitrogen and phosphorus and 6 kg/ha of potassium. By 2000, this had grown considerably, with an average use of 148 kg/ha of nitrogen, 53 kg/ha of phosphorus, and 57 kg/ha of potassium.
Pesticides also came into widespread agricultural use in the United States in this period. The average quantity of pesticides used in corn production grew from 0.1 kilogram per hectare in 1950 to 1.5 kilograms per hectare in 2000. Irrigation also increased over this period: In 1945, less than 1 percent of the corn crop in the United States was irrigated, versus 16 percent per day. This increase in the use of irrigation in 2000 represents an increased outlay of energy (for example, to pump the water and apply it to the corn) of more than 7.5 times that used in 1945.
Changes in methods of corn harvesting have changed the demands for energy as well. In 1945, most corn was harvested on the cob, but currently it is commonly harvested directly as grain. Because corn can have only 13–15 percent moisture when it is placed in storage, and corn harvested as grain may contain 25–30 percent moisture, corn harvested as grain must be dried before being stored. This process is estimated to require one-third more energy than harvesting the corn on the cob and drying it in corn cribs (in which case wind and solar energy do the drying). However, other agricultural practices have led to reductions in energy use. These include adopting conservation tillage practices and switching to more efficient methods of irrigation.
Energy and Agriculture Production Today
Although the direct use of energy in agricultural production represents a small percentage of the total energy use in the United States, agriculture is dependent on the timely availability of energy, and direct and indirect energy costs are a significant component of total production expenses. Examples of direct energy use include the uses of diesel fuel to operate farm machinery, gasoline to operate smaller farm vehicles, and electricity to produce light and power appliances. Examples of indirect energy use include the uses of natural gas used to produce fertilizer and petroleum or natural gas to produce pesticides; for example, 75–90 percent of the cost of anhydrous ammonia, the principal ingredient in nitrogen-based fertilizers, is due to the natural gas needed to produce it.
There has been some interest in using alternative energy sources in agriculture, although such applications constitute a small percentage of total energy used for agriculture in the United States, and the usefulness of each alternative depends partly on local conditions. Solar energy is currently used on some farms to create electricity (through a photovoltaic system), to heat greenhouses, and for space heating, crop drying, and water heating. Wind energy is also used to create electricity for farms, and both solar and wind systems may also create surplus energy that can be sold back to the local utility provider. Ethanol and biodiesel are used to operate some vehicles and other farm machinery. Geothermal heating is used to heat greenhouses, in aquaculture, and to heat homes and barns.
Livestock Production
One trend seen in many countries as they become more prosperous is a change in diet to include more animal products, including meat. This is a cause for concern, not only because of the health consequences involved as diets shift away from plant products but also because livestock production as compared to grain production requires far more energy inputs to produce the same amount of food.
In the United States, livestock are annually fed about 45 million tons of plant protein—28 million tons of which is grain and 17 million tons of which is forage—producing about 7.5 million tons of animal protein for human consumption.
In terms of energy use, an average of 25 kilocalories is required to produce 1 kilocalorie of animal protein, about 10 times that required to produce 1 kilocalorie of plant protein (although it is worth noting that animal protein is about 1.4 times as nutritious as plant protein).
Aquaculture
Aquaculture—the farming of organisms such as fish, mollusks, and crustaceans—is one of the fastest-growing food production sectors in the world, accounting for about 30 percent of total global fish food production, with more than 220 species currently being produced. The amount of energy required varies widely, depending on the type of aquaculture practiced, and is usually expressed as the ratio of industrial energy input in joules to protein energy output in joules.
Intensive production in tanks—characterized by high stocking density, high dependence on exogenous energy inputs such as feed and chemicals, low inputs of labor, and production of high-value species—tends to have the highest ratio of energy input to protein output, whereas extensive production in a more natural environment tends to have a lower ratio. For instance, tilapia grown in extensive ponds in Indonesia have a ratio of 8, whereas semi-intensive tilapia culture in Africa has a ratio of 18 and intensive shrimp culture in Thailand has a ratio of 67. The highest ratios are for oysters and lobsters grown in tanks in the United States (136 and 480, respectively).
Production of Energy Crops
The largest energy crop in the United States is corn, which is used to produce ethanol. Ethanol has been used as a source of energy in the United States since the 19th century and was also used as a fuel source for early automobiles. However, it was eclipsed by gasoline and did not again become popular as an automotive fuel source and gasoline additive until the late 20th century.
Most ethanol in the United States is created from corn, with one bushel of corn yielding about 2.5 gallons of ethanol. Ethanol production in the United States has shown steady growth from 1980 (175 million gallons produced) to 2000 (1,630 million gallons produced), and by 2010 US ethanol production had increased to 13 billion gallons. About 10 percent of all US gasoline contains ethanol as a fuel additive. Corn stover, the wastes left in the field when corn is mechanically harvested, and crops such as switchgrass also show promise as sources of ethanol. One ton of corn stover yields about 80–90 gallons of ethanol, and a ton of switchgrass will yield about 75–100 gallons of ethanol. Using corn stover for this purpose has two advantages—disposing of waste while creating energy—and using switchgrass has the advantage of not using food crops for energy production.
Biodiesel is created from fats and oils, including those from crops such as soybeans grown specifically for biodiesel production. The US biodiesel market is smaller than the ethanol market but growing. Because biodiesel is created from renewable resources and offers less risk to the environment (it results in lower emissions and is less harmful if spilled), some states and cities have passed ordinances requiring vehicle fleets to use biodiesel or other biofuels or biofuel blends, further increasing demand.
Worldwide, about 6 percent of energy was produced from biomass and waste in 2022. The use of biofuels was growing rapidly, however; for instance, use of biofuels for transportation more than doubled globally between 1990 and 2005 and almost tripled between 2005 and 2015. In 2023, the United States was the leading producer of ethanol, which is considered a type of biofuel, with 15.6 billion gallons. The crops most commonly used to create ethanol worldwide are sugarcane, sugar beet, and cassava.
Bibliography
"Bioenergy." International Energy Agency (IEA), 11 July 2023, www.iea.org/energy-system/renewables/bioenergy. Accessed 29 July 2024.
Food and Agriculture Organization (FAO) of the United Nations. The State of Food and Agriculture 2008. Rome: FAO, 2008. http://www.fao.org/docrep/011/i0100e/i0100e00.htm. Accessed 29 July 2024.
Mousavi-Avval, Seyed Hashem, et al. "Fundamentals of Energy Analysis for Crop Production Agriculture." Ohio State University, 14 Aug. 2018, ohioline.osu.edu/factsheet/fabe-6621. Accessed 29 July 2024.