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SYSTEMS ANALYSIS AND MODELING IN FOOD AND AGRICULTURE – Energy Use in Production of Food, Feed, and Fiber - D.R. Mears

ENERGY USE IN PRODUCTION OF FOOD, FEED, AND FIBER

D.R. Mears

Bioresource Engineering Department of Plant Biology and Pathology Cook College Rutgers University USA

Keywords: Alternative Energy, Agriculture, Sustainability, Biomass, Solar Energy.

Contents

1. Introduction

2. After the 1973 Oil Embargo

3. Overview of Energy Use and Food Production 4. Agriculture and Alternative Energy

5. Conclusion: Systems Approach to Energy and Food Sustainability Glossary

Bibliography

Biographical Sketch To cite this chapter

Summary

Energy inputs are critical to agricultural production and the increased use of fossil fuel based energy resources has become increasingly important, particularly in developed countries and increasingly in the developing countries. Even though agriculture requires only a very small percentage of all the fossil fuel resources used in the world, long-term sustainability of global agricultural production will require renewable alternative energy resources. Just after the oil embargo of 1973 there was significant research to document the energy flows and requirements in a number of agricultural production systems. Also there was a substantial effort in some countries to develop conservation strategies and alternative renewable energy systems for production agriculture. There are many systems that can provide on-farm energy resources from renewable sources. Solar energy, wind and small-scale hydro systems can provide on-farm as well as off-farm energy resources. Biomass is a resource being used at an increasing rate but still at only a minute portion of its total potential. The derivation of useful energy from waste materials by direct burning, gasification or anaerobic digestion with recycling of the nutrients can replace a substantial portion of current consumption of fossil fuel. Agriculture also has a potential to provide energy to other segments of society, particularly from biomass-based systems. These include biogas from anaerobic digestion and liquid fuels such as ethanol and biodiesel.

1. Introduction

Agricultural productivity has increased with increased use of energy from a variety of sources. Increasing use of inputs to production agriculture of fertilizer, irrigation and pesticides all require commensurate increases in the use of energy. Mechanization of agricultural tasks increases human productivity and improves the timeliness and quality of many operations and also relies on energy inputs. Increasingly the energy for all of

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these inputs to the agricultural production system has been derived from fossil fuels, particularly in the developed countries and increasingly in the developing countries. The requirements of fossil fuel based energy resources for post farm operations including processing, transportation, storage, wholesale and retail distribution and home storage and cooking far exceed production energy requirements in developed production systems.

The energy requirements for production agriculture, less than 3% of global energy use, represent a small portion of the demand for fossil fuels, but are a critically important input to the food, feed and fiber production system. Interest in reducing the dependence on fossil fuel for agricultural production increased dramatically just after the oil embargo of 1973. Many studies were undertaken to quantify the relationships involved in energy flows in various farming systems. Research and demonstration projects focused on reducing dependence on fossil fuel by conservation and replacing fossil fuel resources with solar energy and other renewable alternative sources.

Many renewable energy strategies such as solar thermal energy systems and electrical generation systems such as photovoltaic, wind and small-scale hydro can make a contribution to on-farm as well as off-farm applications. In addition there are possibilities to generate on-farm energy requirements from on-farm sources such as agricultural wastes and other biomass derived energy sources that are particularly effective fossil fuel replacement strategies as the resource is near the place of application.

Beyond the use of farm derived energy sources to meet on-farm energy requirements there are additional opportunities for agriculture to contribute to off-farm energy needs, particularly through biomass derived fuels. Biogas from anaerobic digestion and liquid fuels including ethanol and biodiesel can meet a substantial portion of global energy requirements on a sustainable basis. In order for this to occur the technologies developed must be based on consideration of all aspects of the production and utilization systems. Not only must the energy flows meet all needs on a renewable basis but ultimately all materials must be recycled to achieve long term sustainability.

2. After the 1973 Oil Embargo

As a result of the oil embargo of 1973 and the resultant supply shortages and price increases there was a significant interest in all topics related to dependence on fossil fuel resources. This led to research on a wide variety of energy related topics which included studies of the requirements for energy for food production, the possibilities to reduce dependence on fossil fuel by conservation and alternative energy sources. Also interest grew in the possibilities for agriculture to become a source of energy supply for other societal energy requirements. Many papers, articles and books were produced over the following decade on these topics, three of which are selected as sources for examples in the following discussion.

Energy flows in a variety of food production systems are analyzed by Pimentel in Pimentel and Hall (1984). The gathering of nuts in a hunter-gatherer society is analyzed assuming the inputs are all the energy requirements of one gatherer for his collection

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and transport of the nuts and his daily maintenance energy requirement for other activities and sleep. His total daily energy requirement of 2 680 kcal enabled him to produce 1.75 kg of shelled nuts with a food energy content of 10 500 kcal. Thus the ratio of food energy collected to energy expended is 3.9:1, but significantly all the energy input is human. Another case presented is for Maize production in Mexico using only manpower but includes the energy to produce the tools, (axe and hoe) and the corn seeds for a hectare yielding 1 944 kg of grain. The total energy inputs of 642 338 kcal result in 6 901 200 kcal of food energy produced for a ratio of 10.74:1. In another case example on less productive land with animal power replacing much of the human labor 941 kg of grain are produced from 770 253 kcal total energy inputs and 3 340 550 kcal food output for a ratio of 4.34:1. Clearly the relationship here would have been improved if the land had been more productive. Pimentel points out that the second study was on land that had been cropped for years with a reduction in soil fertility. Significantly the substitution of animal power for human power can enable the use of forage crops for the animal rather than food items normally required for people.

For two additional scenarios for a hectare of maize production in the United States Pimentel uses one case for mechanized production including the use of fertilizer, pesticides, drying and transportation. In the second case he assumes horses replace fossil fuel powered equipment. For both the yield of 7 000 kg per hectare of grain produces a food energy output of 24 500 000 kcal. In these cases the energy input for fertilizers and herbicides and LP gas for drying totaled 4 759 250 kcal per hectare, almost half of which was for nitrogen fertilizer. The total inputs were 6 958 250 kcal per hectare for the mechanized system and 7 219 200 kcal per hectare for the horse based system for output/input ratios of 3.5:1 and 3.4:1 respectively. While there was not much difference in total energy input it is highly significant to note that the human effort was 120 man hours and 70 000 kcal human energy per hectare for the horse based system vs. only 12 man hours and 7 000 kcal for mechanization.

From the sample cases discussed above it is clear that the use of fossil fuels in the production of man’s basic food energy requirements has increased land productivity and the productivity of human labor. One of many interesting and useful charts and tables presented by Stout (1979), p 66, is an overview of the flow of energy in the United States food system to produce 1 kcal of human food. The consumption of 1 kcal of food is composed of 0.38 kcal from animal products and 0.62 kcal from vegetal products. To generate this consumption the total potential food, feed and fiber produced in the field represents 16 kcal of basic energy. Of this amount, 3.9 kcal remains in the field as crop residue 1.1 kcal represents food exports and nonfood items including cotton and tobacco. Of the remaining 11 kcal that enter the food chain 1.2 kcal move directly towards human consumption but 0.5 kcal become processing byproducts that move to animal consumption and an additional 0.08 kcal are waste resulting in the final 0.62 kcal consumed as vegetal products. The remaining 9.8 kcal of the 16 kcal produced plus the 0.5 kcal from processing waste are fed to livestock. Of this energy 5.3 kcal finally reside in the manure produced by the livestock and waste. The remaining energy is used by the animals for their metabolism and for the 0.38 kcal final human consumption.

This chart also indicates the non-solar energy inputs to produce the 16 kcal of food, feed and fiber that ultimately result in human consumption of 1 kcal. The on-farm

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consumption of energy for field production totals 1.39 kcal and on farm livestock operation plus feed manufacturing an additional 0.4 kcal. Food processing requires 1.3 kcal and the transportation of food an additional 0.9 kcal. The energy required by the wholesale and retail distribution system is 1.0 kcal and food preparation from 2 to 5.7 kcal. The total on-farm energy consumption of 1.79 kcal per kcal of food energy produced is an output/input ratio of 0.56. This ratio for the entire food system is less than 1/6 that of mechanized corn production discussed above, a consequence of the high dependence on animal based food production.

It is important to note that there have been a large number of analyses of energy flow in the food systems of a number of countries and for a variety of circumstances. In many cases these analyses are presented to support a particular proposed strategy for change in the food production system or allocation of scarce resources in society or change in human behavior that might result in greater efficiencies of energy conversion from the inputs to the food system relative to the energy content of the food consumed. An argument is often made for changing human diet to reduce or eliminate foods derived from animals thereby substantially improving the efficiency of conversion of energy from that in food and feed produced to human calorie intake.

Pimentel in Pimentel and Hall (1984) pp 18-19 presents an example of such a discussion. The three high protein diets presented include a pure vegetarian diet, a non-vegetarian diet and one, a lacto-ovo non-vegetarian diet that includes eggs, milk and milk products. Each diet is to provide a total of 3 300 kcal and at least 80 g of protein with over 100 g of protein in the animal protein diet. The fossil fuel inputs required to support these are a high of 33 900 kcal for the animal protein diet to 9 900 kcal for the all-vegetarian diet with the lacto-ovo diet in between requiring 18,900 kcal.

In times of a shortage of resources rationing is often used to allocate resources to high priority items and the most visible rationing strategy for many during the oil embargo was a scheduling system for the purchase of fuel for automobiles. Given the relatively low percentage of global energy required for production agriculture, 2.5% in Table 2, and the importance of food production for humans it would be reasonable to argue that production agriculture should receive all the energy resources required. It is significant to note that in highly developed countries this percentage is even lower, i.e. 1.1% for North America. In the discussion above it is noted that in the United States for example, the energy requirement for food processing and transportation exceeds the total for all on farm food production. The energy consumed in the marketing of food and the energy required for storage and food preparation far exceeds that required for production. Thus there is much greater potential for reducing societies dependence on fossil fuel in these areas of the food system than in on farm food production.

A typical example of the efforts to organize information related to energy requirements for agriculture and find ways to reduce dependence on fossil fuel resources was a conference held on the topic of agriculture and energy reported in a conference proceedings edited by Lockeretz (1977). In addition to studies on energy use in various production systems there were focused programs on specific areas that require substantial energy inputs such as: tillage, irrigation, fertilizer, crop drying and livestock

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production. Also covered were topics including the potential for alternative energy systems, the special needs in developing countries and topics on policy.

More recent and increasingly thorough production system energy requirements for various agricultural systems have focused on environmental as well as energy sustainability in many cases. An example of a comprehensive system analysis quantifying all the required energy flows is a study of the energy flow relationships of Asian rice systems (Chancellor 2002). The complete system presented is composed of 12 major entities with 53 linkages representing energy and materials flows. Special emphasis is given to the issues of sustainability related to the nitrogen and water cycles so critical to rice production. The potential to replace all or part of the energy derived from fossil fuels with renewable resources, such as the biomass waste materials, in a number of the linkages are presented. The study concludes that with the advances in knowledge and technology and advances in understanding about energy relationships, there is the possibility that agriculture could not only supply increased yields, but also strengthen its position as a supplier of its own energy as well as of energy to the general economy.

3. Overview of Energy Use and Food Production

A broad overview of the global use of energy in general and the utilization of energy in agricultural production in particular can be obtained by analysis of data posted in a series of tables on the web site of the World Resources Institute. These tables are updated periodically so trends over time can be followed as well as looking at the current situation. Table 1 is a composite of several tables taken from World Resources Institute web site. http://wri.org/ in summer 2004. At this time their data tables were presenting statistics over thewww. range of 1999 through 2002 so the following discussion generally describes the situation approaching 2004. One can reconstruct such an analysis in the future as the basic data tables are updated.

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SYSTEMS ANALYSIS AND MODELING IN FOOD AND AGRICULTURE – Energy Use in Production of Food, Feed, and Fiber - D.R. Mears

Cereals Total (000 metric tons) Pulses Total (000 metric tons) Roots and Tubers Total (000 metric tons) Meat (metric tons) Average Daily per Capita Kilocalories Supply Population Thousands

Year data taken 2002 2002 2002 2002 1999/2000 2002

World 2 029 386 55 165 684 729 236 991 142 2 808 6 211 082

Asia * 922 018 23 140 285 587 89 312 093 2 710 3 493 424

Europe 434 433 8 330 127 764 49 796 566 3 230 725 124

Middle East and North Africa 91 439 3 396 16 567 8 144 354 3 003 423 296

Sub Sahara Africa (SSA) 88 156 8 296 169 110 8 196 212 2 238 683 782

Totals 3 Countries in SSA 4 452 295 3 314 594 562 1 877 46 769

North America 334 184 3 993 26 227 41 916 827 3 696 319 925

Central America and Caribbean 33 427 2 650 4 861 6 988 588 2 850 178 512

South America 104 341 3 953 48 306 25 393 700 2 845 355 695

Oceana 18 648 1 393 3 469 5 285 178 2 969 31 281

Developed Countries 840 806 14 063 168 439 103 564 712 3 242 1 321 286

Developing Countries 1 185 842 41 089 513 453 131 468 806 2 684 4 889 753

* Excluding the Middle East

Data under Cereals, Pulses, Roots and Tubers and Meat are from the Agricultural Production Table in the Agriculture and Food section of the Earthtrends data table from World Resources Institute web site: http://www.wri.org/, their primary source is FAO.

Population data from the Population, Health, and Human Well-Being table from the Earthtrends data table from World Resources Institute web site. http://www.wri.org/, their primary source United Nations Population Division

Table 1: Agricultural Production

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Table 1 shows the basic food supply and food energy supply for the world in total and for various regions. Also shown on the bottom two lines are the same items summarized for the developed and developing countries separately. A row is added which presents totals for three of the Sub Saharan African countries, which have relatively low average daily per capita energy food supply. These three countries, taken together, have an average 1 877 Kilocalories daily per capita food energy supply, well below the average for all the developing countries of 2 684. The total per capita food energy supply in North America is almost double that of these three countries.

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Total Energy used 1000 metric toe Equivalent Energy % Used in Agriculture Agricultural Energy Input 1000 metric toe Equivalent Total Daily Food Energy Millions Kilocalories Energy Efficiency Indicator Food Energy per

Energy Input

Year data taken 1999 1999 1999 1999

1999per Energy Input

World 6 763 082 2.5 169 077 17 441 3.77

Asia * 2 075 416 3.1 64 338 9 467 5.37

Europe 1 785 913 2.9 51 791 2 342 1.65

Middle East and North Africa 366 938 2.2 8 073 1 271 5.65

Sub Sahara Africa no data no data 1 530

TOTALS 3 of above 16 001 4.7 745 88 4.30

North America 1 656 163 1.1 18 218 1 182 2.37

Central America and Caribbean 134 897 2.5 3 372 509 5.51

South America 301 163 4.4 13 251 1 012 2.79

Oceana no data no data 93

Developed Countries 4 016 346 2.2 88 360 4 284 1.77

Developing Countries 2 638 742 2.9 76 524 13 124 6.26

* Excluding the Middle East

Data under Total Energy used and % Used in Agriculture are from the Energy Consumption by Economic Sector section of the Earthtrends data table from World Resources Institute web site: http://www.wri.org/, their primary source is The International Energy Agency, (IEA). The Agricultural Energy Input is calculated from the first two columns.

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The Total Daily Food Energy column for each region is obtained by multiplying Average Daily per Capita Kilocalories supply by Population in

Table 1. Note this is only an approximation as the time basis for these two columns is shifted two years.

The Energy Efficiency Indicator is the total annual food energy divided by the total energy input at 10 exp 7 Kilocalories per toe. Table 2: Food Production and Energy Input Relationships

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Table 2 covers the same regions and addresses the issue of total energy use, energy use for agriculture and the efficiency with which this energy is utilized for agriculture. Taken together these two tables indicate a broad overview of the relationship between energy use in agriculture and agricultural productivity. More detailed analysis of regions or specific countries can be generated from the source tables. This table shows that while developing countries devote 2.9% of their energy consumption to agriculture, the developed countries only use 2.2% while North America uses only half the percentage of all the developing countries, 1.1%. This trend indicates higher uses of energy in other sectors of the economy in the developed countries in general and North America in particular.

The last column in Table 2 relates the total calorific value of the food supply to the energy inputs to the agricultural sector. The energy inputs include all forms of fossil fuel, nuclear energy and both traditional and modern renewable energy sources. As the major energy input to the food system is the solar energy input that drives photosynthesis the energy in the food produced can and should be much greater than the sum of the other energy inputs. The world, taken as a whole, averages 3.77 times as much energy in the food supply as is provided to the food production system from all sources excluding solar energy for photosynthesis. However, there are major differences between regions and countries primarily associated with the general level of economic development.

According to the WRI designation of developed vs. developing countries the developed countries put 3.5 times more energy into their production of food from the energy content standpoint. This analysis only tells a small part of the story as there are important issues in addition to gross energy input and the calorific value of the food produced in the agricultural production system. The productivity of the land is a very important issue for worldwide food production. Significant increases in the productivity of the land are achieved by energy intensive inputs of fertilizer, pesticides and irrigation. Large increases in the productivity of human labor are the result of using energy for the production and operation of farm machinery. Substantial reduction of losses of food between harvest and consumption are achieved by the use of energy for post harvest processing including crop drying and cold storage.

4. Agriculture and Alternative Energy 4.1. Overview

In order to provide mankind’s need for food energy resources must be available to agriculture in a form that is suitable for the application and in sufficient amount for the task. As food production is a very high priority activity relative to many other uses of fossil fuel energy it is rational for society to bear the costs required. However, as the price and scarcity of fossil fuel supplies increase it is prudent and will become essential to look for opportunities to meet the needs of production agriculture from renewable resources. In this regard there have been substantial efforts to understand the energy requirements for agriculture and the patterns of use as well as programs to develop and apply alternative energy technologies.

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To meet energy requirements for agricultural production there are a number of technologies that have been studied and in many cases implemented. In some cases the energy requirements of the farm family and/or others living on the farm may be integrated with the systems being used to provide energy for production. An important aspect of most alternative energy sources is their distributed nature. Wind, solar energy, small-scale hydro systems and biomass based energy supplies all are localized resources. Wind, solar and hydro systems that can be developed and used at the local level will generally be economically competitive with fossil fuel sooner than applications that have to provide energy to distant needs.

Beyond meeting the need for on-farm energy requirements there is also potential for agriculture to provide energy resources for other societal needs. One example is the production of ethanol for use as a fuel or fuel additive. It is generally accepted that biomass derived energy, such as ethanol; biodiesel and biogas are particularly attractive agricultural based energy sources that can be transported and used off-farm as well as on-farm.

4.2. Alternative Sources for on Farm Use

Historically production agriculture was completely dependent upon non fossil fuel based energy resources. Hunter-gatherer societies and some cropping systems depend only on human energy. The use of animal power for production agriculture shifts work from humans to animals but requires feed for the animals, which may be provided primarily from forage crops that can be produced on land that is better suited to forage crops than human food crops. Hydropower has been utilized as an energy source for grain milling, sawmills and other energy requirements. Wind power has been extensively relied on for water pumping and milling also. Early mechanization relied on steam power both for tractors and stationary power units for grain threshing and other operations. Biomass byproducts such as straw could be used as a fuel source as well as wood and later coal. The use of biomass of any sort to provide energy for agricultural production has largely been supplanted by the ready availability of low-cost, easy to handle fossil fuel, primarily petroleum and natural gas.

A number of opportunities to use alternative, renewable energy sources in agricultural production and on farm processing are discussed in Goswami (1986). Wind power has historically been widely utilized for water pumping and is still found to be a practical energy source for this purpose in many locations. As the potential power that can be derived from wind varies with the cube of the wind speed the likely availability of adequate wind at the location and time it is required is a key element in the practicality of wind systems. Water pumping remains one of the most likely applications for wind power as there is the potential to store the water and as the pumping system can be driven directly by the wind machine. When the wind power resource is not completely reliable a hybrid system including another power supply can be used. However, in this case the energy cost savings alone must justify the investment in the wind generation system. So as long as fossil fuel based energy is available at relatively low cost it will generally be simpler and probably more economical to use only that energy source and not make the equipment investment necessary to utilize the renewable resource for part of the work.

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In general there is an advantage when the mechanical power from the wind can be used directly without conversion to electricity and when storage of the energy, (or stored water) is not required or is already an integral part of the system. Wind generated electricity is becoming and will continue to become increasingly competitive with fossil fuel powered electricity generation in some areas, particularly where the power can be used on site and directly. While there are power losses in the conversion of mechanical power to electricity and conversion from electrical power to the final application the versatility of electrical power is often a compelling advantage. Also, if the point of application is near the electrical power distribution grid there is the option to use the grid system to purchase additional power when needed and to which surplus power can be sold when wind supply exceeds demand.

The direct use of solar energy on farms can meet many needs. Traditionally many agricultural crops have been dried using only solar energy but often fossil fuels are used to heat air for crop drying to reduce loses and to increase reliability and product quality. In the analysis discussed earlier, of the 1.39 kcal of energy required in the field to produce a kcal of food, 0.09 kcal of energy is used for drying, Stout (1979), p 66. A modern crop drying system that uses fossil fuel to heat the drying air and purchased electricity to operate fans can be replaced or supplemented by solar collectors for the heat input and/or a photovoltaic source for the electricity for the fans. A hybrid collector of photovoltaic cells incorporated in an air heater array is one example. In some cases it is possible to incorporate the solar collector air-heating component in various farm buildings in such a way as to significantly reduce the investment cost in the system. In addition to crop drying there are other requirements for heat at modest temperatures that can be met with solar thermal collectors. Some animal housing units require heating and, as with solar drying systems, if it is possible to incorporate the solar thermal collection system in the structure itself system economics can be optimized. Some food processing operations require process heat that can be provided with solar collection systems, whether the processing is on-farm or at an industrial processing site off-farm. Solar thermal energy is particularly suited to applications where hot water requirements are met by temperatures under 100oC and the food processing industry uses hot water for many processing applications and for space heating of facilities. One study on the technical and economic feasibility of solar energy indicates that 20% of the energy requirement of the food processing industry could be met with solar energy (Goswami, Vol. 1 pp 156-157).

There is need for domestic energy requirements for on-farm residences including energy for space heating, water heating and food preparation. All of these needs can be met in whole or part with solar energy. Refrigeration needs for cold storage for farm production and for the residences can be met with solar thermal collectors powering absorption refrigeration systems. The technologies required for most of these applications and the economic barriers to their adoption are generally similar for on-farm applications and domestic residential applications. An important consideration in solar thermal systems is the relationship between system economics and the needed operating temperature of the system. In general for solar thermal collectors the efficiency of the collector decreases as operating temperature increases as most losses in the system are directly related to the difference in operating and ambient temperature.

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Thus lower temperature applications, i.e. warm water rather than hotter water, will operate more efficiently and produce more useful energy relative to the capital investment. Therefore absorption refrigeration systems, which require higher operating temperatures than space heating or hot water for food processing, are inherently less economical than those applications.

Greenhouse production of seedlings, vegetables and ornamentals is a particularly highly productive yet energy intensive agricultural production system. Energy is required for heating the greenhouse in cold weather and often for mechanical ventilation systems as well as for operating equipment and cold storage for the crops. Increasing costs of both ventilation systems and electricity to power the fans have led to renewed interest in natural ventilation systems but space heating is also needed in many locations. Several commercial solar heating demonstrations are discussed in Goswami (1986). One of these, developed at Rutgers University (Goswami, Vol. 1 pp 104-107), utilized a floor storage/heat distribution system for the water heated in external collectors and a movable curtain system for insulation to reduce heat loss. The initial emphasis in the development of both the floor heating and movable curtain systems was to provide energy savings.

Curtain materials have been developed that provide appropriate levels of daytime shade and are deployed during high light periods to reduce heat stress on the crop as well as energy conservation on cold nights. Floor and bench heating systems have been found to benefit many crops as the grower can independently control the root zone and plant canopy temperatures. Benefits of root zone heating include better plant growth for some crops, improved disease control due to warmer and drier conditions under the plant canopy and increased energy savings in cases where warmer soil allows for cooler air temperature above the crop. These concepts have been widely applied in greenhouses worldwide even though the relatively low cost of fossil fuels have essentially eliminated the desire for the solar collectors to provide the heat. This case is an example of the integration of systems of crop production and energy management that develop synergies, which produce multiple benefits.

The Energy data set in the World Resources Institute Earthtrends Data Tables indicates that the world production of energy from traditional renewable resources in 1999 was 1 035 039 000 metric toe, (43 EJ), or almost 10% of global energy production from all sources. Traditional renewable resources in this context represent fuelwood, crop residues and biomass left from industrial sources such as papermaking. Over half of this is in Asia, mostly India and China. In this region the traditional renewable energy resource is about 8.7 times the energy input to production agriculture. While some of this energy may be utilized in support of production agriculture, most of it is used for other applications. Cooking and home heating are significant consumers of this resource as are some forms of agricultural product processing such as sugar refining which makes extensive use of bagasse. Sims (2003) points out that many sugar-refining operations use bagasse as a fuel source for generation of electricity needed at the plant and process heat. As this has traditionally been used as much as a method of getting rid of the large amount of waste, as it has been as an energy source, the process has not necessarily been efficient.

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On-farm biogas plants utilize manure and other wet plant or food waste materials to generate methane, which can be used for cooking, heating, process heat or electrical generation. While there is an economy of scale in the use of biogas generators, there have been many workable designs developed for very small-scale applications, even for single-family use, particularly in China and India. Sims (2003) indicates that in both of these countries the trend is to progress from traditional small-scale family biogas plants to more efficient community or industrial operations. Large livestock facilities are attractive sites for biogas generation, particularly when the cropland supporting the livestock operation is close by, making the transport of the sludge left at the end of the biogas generation process to the fields easy. In such an integrated system the biogas generation basically harvests much of the potential energy in the waste while most of the plant nutrients remain in the sludge and can be recycled to the productive fields. Systems integration in on-farm energy programs is and will become an increasingly important concept. The more effectively an alternative energy resource can be implemented and the greater the utilization of the energy produced the more economically attractive and sustainable the technology will become. A biogas plant where the energy in the gas is used productively and the nutrients are returned to plant production is a more attractive application then if the sludge is not recycled. If the biogas is used to power an electrical generator, either with a piston engine or turbine, it is beneficial to find a use for the waste heat. In temperate climates it is often found necessary to heat the digester in cold weather so this is an obvious application of the waste heat. Another byproduct of biogas utilization is the carbon dioxide in the exhaust, which could be used to promote plant growth in controlled environment agriculture if any contaminants deleterious to plant growth are removed.

As an example, the author had an undergraduate student design team conceptualize and analyze materials and energy balances for a particular communal farm in Poland, with a variety of activities. The large farm produced a variety of field and horticultural crops, had a large swine operation utilizing feed grown on the farm, a small food processing plant, some greenhouses producing vegetables year round and a coal fired power plant producing electricity and heat for the processing plant and greenhouses. Manure disposal had become a large problem and the rapidly rising cost of coal was an issue. A system was developed based on plug flow biogas generators located under the benches in the greenhouse. In cold weather the reject heat from the engine on the electrical generator was used to heat the biogas digester, which in turn provided the heat needed for the greenhouses. The heat transfer systems were designed so that the operating temperature of the biogas generator, near the optimum for that process, would match the heat needs for the structure. In summer and fall much of the reject heat would be available for the processing operations. The carbon dioxide in the engine exhaust could be cleaned for use in the greenhouse and the sludge returned to the fields.

The starting point of the analysis was to utilize all of the reported 60 cubic meters per day manure production in the biogas digester. The students utilized data from the literature on the composition of swine manure and found six references on gas production for this amount of manure ranging from 990 to 2763 cubic meters of gas per day. They designed the volume of the digesters based on a 15-day retention time. From this starting point they studied the heat transfer from the engine coolant circulating in

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piping in the digester and the subsequent transfer of this heat into the greenhouse and thence from the greenhouse to the external environment. While this design approach can be used to size system components that provide a workable solution, system optimization will require a simulation approach to evaluate the overall system performance of proposed designs throughout the year.

An example of the use of simulation modeling to study sustainability and economics of whole farm operations is the work at the Pasture Systems and Watershed Management Research Unit of the USDA, (Rotz, C.A. 2004). A model has been developed which can be used to evaluate numerous technologies and management strategies for dairy and beef farms. Factors evaluated include forage harvest and preservation techniques, manure handling methods, cropping systems, and feeding strategies. The model can be used to evaluate the impact of various farming practices on both nutrient losses from the farm and farm profitability. Other farm management options and combinations of options can be evaluated with the Integrated Farm System Model. The model is available from the Internet home page of the Pasture Systems and Watershed Management Research Unit. To obtain a copy of the program, including an integrated help system and reference manual, the home page can be accessed at (http://pswmru.arsup.psu.edu ), where instructions for downloading and setting up the program are provided.

A modeling approach could be used to combine the concepts described in the student project utilizing biogas generation from the manure and the integrated system modeling of Rotz, which includes a materials balance on nutrients. Adding in the systems to generate and utilize energy on the farm could add the features of balancing energy production and needs as well as carbon balance to the nutrient balance. The sizing of the capacities of the various system components and the management strategies employed can be evaluated in terms of the farm’s economic viability and sustainability. While modeling research has been frequently applied to optimizing farm economics, the incorporation of the concepts of energy sustainability is needed.

In addition to direct burning to recover energy from dry biomass waste material gasification is an attractive technology for some applications as the gas can be used to operate an engine as well as be utilized in direct burning applications. Economies of scale favor larger, community based systems as opposed to small, on-farm facilities and therefore much of the application of energy derived from gasification of biomass may ultimately be utilized off-farm.

Liquid fuels for farm operations can also be derived from crops. Ethanol derived from small-scale farm based plants is one option that can replace or supplement gasoline. While there have been limited attempts to develop small scale ethanol production facilities the economies of scale substantially favor larger, centralized plants. As is the case with biogas production, the energy product is only hydrocarbon and all of the nutrients remain in the byproduct, which is generally used for livestock feed. When this is the case the animal will extract some of the nutrients and energy. The energy and nutrients remaining in the manure can then be recovered in a biogas generator as discussed above. Plant based oils can be utilized as a replacement for diesel fuel in engines. As is the case with ethanol production, the residual plant material can be

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utilized as livestock feed. Again, the economies of scale in the processing operation favor large production facilities.

4.3. Agricultural Sources of Energy for off Farm Use

As noted above, there is an economy of scale that can be achieved in some of the production facilities that convert agricultural products into useable energy resources. Therefore, when energy resources are produced in larger, community based or industrial scale settings, the products can be made available to other segments of society besides production agriculture. The suitability of alternative energy resources to particular applications depend significantly upon the relationship between the location of the resource relative to the needed application and the timing of the need relative to the availability. Distributed resources such as solar energy and wind are particularly useful when they can be applied directly on-farm and there is no need to move the energy resource. When solar or wind are used to generate electricity on the farm and the farm is served by the grid the transportation problem is mitigated assuming pricing policies are favorable. However, for the most significant farm produced energy resources that are based on some form of biomass, the conversion process generally favors larger processing facilities so the application of the derived energy resource may well be appropriate for off-farm application, as well as on-farm use.

While there may well be significant opportunities for agricultural enterprises to feed electricity to a national or regional grid that is produced from photovoltaic or wind systems on the farm, a very large potential resource is biomass production for energy as well as feed and fiber. The total biomass resource is large in relationship to all of man’s current energy needs. The energy content of the annual production of biomass on a global scale is well over ten times the total annual production of fossil fuels. Biomass productivity per unit land area is substantially greater on agricultural land than non-farm areas so there is significant global potential to further increase the total production of plant material produced for food, feed energy or a combination. For this productivity to continue indefinitely on a sustainable basis the recycling of nutrients and effective use of water are essential.

A potentially important aspect of turning to biomass as an energy source to replace fossil fuel is the recycling rather than the mining of carbon as the plant material harvested each year has removed the carbon from the atmosphere to which the carbon is replaced when the biomass derived fuel is used. Sims (2003) discusses a variety of biomass energy production scenarios from the standpoint of carbon mitigation as a climate change solution. Agricultural waste is an obvious choice as an energy source, particularly when considering the climate change issue. As noted earlier, in the United States food production system for each kcal of food produced there are 3.9 kcal residing in crop residue, 5.1 kcal in animal manure and 0.2 kcal in processing waste. These waste streams have a potential energy over five times the total on-farm energy requirement.

There are a variety of technologies available for harvesting the energy in agricultural wastes. The most appropriate technology for any given situation will vary depending on the characteristics of the waste material, the desired energy application and

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environmental considerations including the desirability of recycling the nutrients in the waste. Direct burning to fire a boiler or provide process heat is an appropriate option in some situations. In general, dry waste materials are more appropriate for direct burning than wetter wastes, such as manure, unless the waste can be dried before burning. Gasification is an appropriate alternative application, particularly if the end use is to an engine to provide mechanical or electrical power as producer gas can be utilized directly in a spark ignition engine or as a replacement for 80 to 85% of the diesel fuel in a compression ignition engine, (Goswami, Vol. 2 p 97). Gasification efficiency can be 60 to 70% for woody material, (Goswami, Vol. 2 p 89). For higher moisture wastes such as manures, anaerobic digestion may be the most appropriate conversion process. Chang (2004) compares the energy and sustainability characteristics of anaerobic digestion and gasification processes for several types of manures. He calculates the net energy production from 100 tonnes of fresh cattle manure to be 33.642 Gcal by anaerobic digestion and 13.504 Gcal by gasification. Net energy production from 100 tonnes of poultry manure which has a higher solids content initially with air drying before gasification would produce 54.358 Gcal by anaerobic digestion and 71.42 Gcal by gasification.

In addition to extracting energy from waste streams there is significant potential to grow crops specifically for energy production. Sims (2003) projects total world wide energy supplies from crops grown specifically for energy can increase from current levels of 45 EJ per year to a total of 441 EJ per year by 2050. This analysis is based on looking at projections of population, arable land required to meet food needs and the remaining land available for energy crops. Liquid fuels for use in engines are important for many applications and ethanol and biodiesel are particularly useful forms of energy potential in this regard. As noted earlier, ethanol produced from sugar cane can utilize the bagasse as the major processing energy source and with an efficient system can be a net exporter of electrical energy.

Production of ethanol from cereal crops such as maize is of great interest in many developed countries and there have been many studies focused on the net energy production. Ethanol is an attractive liquid fuel that can supplement or replace gasoline in internal combustion engines. While some studies have show a negative net energy production in the past a recent comprehensive study by Shapouri et al (2003) note that the net energy value of ethanol production from corn has been increasing since the early studies of 1970 due in large part to increases in both corn yields and processing efficiency. Their study indicates a net energy output/input ratio averaging 1.34 and up to 1.53 for the best-case scenario. This study indicates that only 17% if the input energy is from liquid fuels such as gasoline and diesel with the rest of the energy inputs coming from other feedstocks. Thus the liquid fuel output/input ratio is 6.4.

The second most widely considered liquid fuel is biodiesel produced from a variety of oil seed bearing crops including soybeans and rapeseed. Biodiesel can be blended with mineral diesel or used directly in compression ignition engines, generally without any needed modification of the engine. Environmental benefits of biodiesel relative to mineral diesel include almost complete elimination of sulfur oxide emissions as well as carbon dioxide emission reduction. As of 2003 there are commercial biodiesel

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production facilities in several European countries and the United States with a total annual production capacity of 1.5 million tonnes, Sims (2003).

5. Conclusion: Systems Approach to Energy and Food Sustainability

Global agricultural energy productivity has been generally increasing over the years. Increases are due to genetic improvement of crops, improved technology including irrigation, fertilizer use, pesticides and mechanization. Improvements in technology and the replacement of human and animal power with mechanization have dramatically reduced the human effort required to provide the global food supply. Fossil fuels have been the major energy source for mechanization, irrigation-pumping power, fertilizer and pesticide production, product processing and transportation and as raw material for some inputs. While the relatively low cost per unit value of fossil fuels their ease of use and general availability have promoted their wide scale utilization in agriculture as well as other aspects of society they are not completely sustainable for ever.

Over the years, and particularly since the energy crisis of 1973, there has been a significant effort to identify alternative and sustainable sources for energy and for raw materials currently provided by coal, oil and natural gas. It has been shown that renewable resources are technically capable of replacing fossil fuel for any application even though current economic conditions make many alternative technologies unable to compete at their current state of development. Given that fossil fuel resources originated as plant material it is clear that agriculture can produce raw materials from which products including fuels can be produced to support any product or energy need currently derived from fossil fuel. It is important to note that in all energy conversion processes, starting with photosynthesis, there are natural laws that establish upper limits on conversion efficiencies. However, there are no immutable laws regarding system economics and the challenge to utilize human ingenuity to develop improved economies for needed energy conversion technologies can be met.

To achieve sustainability in food production and other aspects of production of material goods and services not only must energy be derived from renewable resources but ultimately all materials must be recycled. The systems approach to problem solving is an essential ingredient in efforts to move to a sustainable society in general and a sustainable food supply in particular. Scott (2001) points out the importance of incorporating the systems approach to problem solving relative to the development of sustainable systems into our educational programs. Along with a discussion of the issues involved in a transition to a sustainable world examples of student projects addressing specific case studies in a web based course,

(http://www.aben.cornell.edu/courses/aben299/index.html), are presented.

Glossary Nomenclature

Kcal: kilo (10 exp 3) calories

Gcal: Giga (10 exp 9) calories

EJ: Ecta (10 exp 18) joules [Note: 1 calorie = 4.19 joules]

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TOE: Tons of Oil Equivalents [Note: 1 toe = 10 exp 7 kcal]

Bibliography

World Resources Institute. (2004) web site. http://www.wri.org/ [Representative data from this

website are used, the specific data tables are subject to updating periodically].

Chancellor, W.J. (2002). Energy Flow Relationships in Asian Rice Systems. ASAE Paper No. 028019. St. Joseph, Mich. [This paper presents a comprehensive, quantitative analysis of all energy flows in Asian rice production. This and other research papers are available online at: http://www.asae.org/ ]

Chang, F.H. (2004). Energy and Sustainability Comparisons of Anaerobic Digestion and Thermal Technologies for Processing Animal Waste. ASAE Paper No. 044025. St. Joseph, Mich. [This paper analyzes the theoretical energy recovery from wastes with several technologies and evaluates comparative environmental sustainability. This and other research papers are available online at: http://www.asae.org/ ]

Goswami D.Y. (1986). Alternative Energy in Agriculture. 2 Volumes, 226 and 181 pp. CRC Press, Boca

Raton. [These volumes contain a series of papers outlining the most likely areas of alternative energy sources replacing fossil fuels for agricultural production and as a contribution for additional societal energy requirements]

Lockeretz W. (1977). Agriculture and energy. 750 pp. Academic Press, New York. [This proceedings of a NSF sponsored symposium presents a comprehensive series of papers on energy requirements for many agricultural enterprises]

Pimentel D. and C.W. Hall (1984). Food and Energy Resources. 268 pp. Academic Press, New York.

[This book covers energy flow in the food system with many examples of alternatives including quantitative date and discussions of ethical and social issues relating to energy and the food supply system]

Rotz, C.A. (2004). The Integrated Farm System Model: A Tool for Developing more Economically and Environmentally Sustainable Farming Systems for the Northeast. ASAE Paper No. NABEC 04-0022. St. Joseph, Mich. [This paper describes a modeling approach to research on the sustainability of livestock farms. The model is available from the internet home page of the Pasture Systems and Watershed Management Research Unit: http://pswmru.arsup.psu.edu ]

Scott, N.R. (2001). Transition Toward a Sustainable World: The Roles of Agriculture and Engineering. ASAE Paper No. 017028. St. Joseph, Mich. [This paper discusses the issue of sustainability and the role agriculture can play in contributing to energy supply and other aspects of a global society. This and other research papers are available online at: http://www.asae.org/ ]

Shapouri, H., J. A. Duffield and M. Wang (2003). The Energy Balance of Corn Ethanol Revisited, Transactions of the ASAE, Vol. 46(4): pp 959–968. [This paper presents a comprehensive analysis of the energy inputs into ethanol from corn including inputs for crop production, transportation and processing. This and other research papers are available online at: http://www.asae.org/ ]

Sims R.E.H. (2003) Climate Change Solutions from Biomass, Bioenergy and Biomaterials. 28 pp. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Vol. V. September 2003. [This invited overview paper discusses the availability, technical feasibility, economic and social issues related to replacing many energy requirements with bio-based sources. This and other research papers are available online at: http://cigr-ejournal.tamu.edu/ ]

Stout B.A. (1979). Energy for World Agriculture, 286 pp. FAO Agriculture Series, Rome. [This presents the relationships between agricultural production and energy resources in the late 1970’s].

Biographical Sketch

David Mears is Professor of Bioresource Engineering at Rutgers University where he has concentrated his teaching and research in recent years in the engineering aspects of controlled environment agriculture. The Rutgers University group focused on Horticultural Engineering was intimately involved in a number

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of energy conservation measures resulting in potential savings of 90% for commercial greenhouses relative to average 1970’s requirements. He has long been interested in the relationships between production agriculture and energy and has maintained that through involvement in a wide range of projects from the late 1950’s to the present.

To cite this chapter

D.R. Mears,(2007),ENERGY USE IN PRODUCTION OF FOOD, FEED, AND FIBER, in System Analysis and Modeling in Food and Agriculture, [Ed. David H. Fleisher,K. C. Ting,Luis F. Rodriguez], in

Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss

Publishers, Oxford ,UK, [http://www.eolss.net]