The impact of energy shortages on the timeliness of agricultural operations

Agriculture, Ecosystems and Environment, 38 ( 1992 ) 167-178 Elsevier Science Publishers B.V., Amsterdam

167

The impact of energy shortages on the timeliness of agricultural operations A. Shahbazi North Carolina Agricultural and Technical State University, 1601 East Market St., Greensboro, NC 27411, USA (Accepted 3June 1991 )

ABSTRACT Shahbazi, A., ! 992. The impact of energy shortages on the timeliness of agricultural operations. Agric. Ecos:l,stems Environ., 38:167-178. This report provides a review of energy requirements for various agricultural operations. As most agricultural operations are time dependent, the timeliness of energy supplies is the second most important concern, after availability. Failure to supply adequate fuel at the right time can delay planting and harvesting, thereby reducing quality and quantity of the yield. The effect of energy shortages on agriculture could be minimized by implementation of the following practices: ( 1 ) developing alternative energy sources such as solar energy; (2) using energy management practices and energy efficient equipment; (3) using energy conservation practices.

INTRODUCTION

Production of most agricultural crops is seasonal. Tillage operations, planting, cultivation, irrigation, spraying, harvesting, post-harvest processing, etc. are all seasonal operations and time dependent (Attwood, 1980; Audsley, 1984; Fletcher and Featherstone, 1987 ). Fieldwork, scheduled to conform to the needs of the crop, must be performed at the proper time. Each crop requires a certain amount of field preparation which takes place sometime before planting. In a conventional production system, the performance of the crop and the yield is a function of the type of field preparation and the planting date. Adequate tillage operation followed by timely planting is essential. Any deviation from the normal operation is bound to affect the quantity and the quality of the crop yield. Growing crops also need a continuous supply of water. Where the rain is insufficient, water - - when available - - may be provided mechanically via pumps and irrigation systems. Irrigation pump operations require large amounts of diesel fuel. If there is an interruption in the fuel supply and water is in short supply, the plant will develop moisture stress. The crop yield and

168

A. SHAHBAZi

quality will be lowered, depending on the degree of the stress and the plant growth stage where stress has taken place. When a crop is ready for harvest, it should be harvested within a reasonable amount of time. If the crop is not harvested during this time, serious losses may occur. Thus, agricultural planting and harvesting operations require direct and indi,'ec~: energy inputs. This means that adequate quantities of fuel and energy must be available at the proper time to assure successful crop production. As a result of effects of timeliness, agriculture is vulnerable to fuel shortages and interruptions in the supply of other forms of energy. Because crop production is a continuous biological process, it cannot be temporarily slowed or accelerated. Losses from fuel shortages and energy interruptions are not proportional to the down time, but may be severe depending upon the stage of the production. To better understand the importance of timely energy supplies to agriculture, this assessment will: ( 1 ) review energy dependency in agricultural operations; (2) assess the impact of inadequate fuel supplies on agricultural production. TILLAGE

Plowing and field preparation is a farm activity which enhances and improves soil condition for crop planting. As in any other field activity, field preparation is closely dependent on soil type, weather conditions, drainage system, and threshold soil water content. Mechanical work on soil is not possible unless the soil has adequate warmth and moisture. Moisture content of soil is dependent on time and the amount of rain and irrigation. Field work should be performed when soil contains an optimum moisture content (field capacity). Otherwise, the task will be difficult and will require much higher energy inputs. For example, fuel requirements for para-piowing in a dry soil ( 15.8% moisture) is 12.2 i ha -~, whereas in moist soil (8.5% moisture), it is 9.5 ! ha -t (A. Khalilian, personal communication, 1989). These requirements are 84% and 44% higher than the requirement at field capacity, respectively. Therefore, tillage should be performed when soil conditions are as close to optimum as possible. Nolte et al. (1983) reported that the number of days available for fieldwork between April and November are dependant on soil, weather, location, and threshold soil water content. Dumas and Renoll ( 1983 ) studied the fuel and time requirements for cotton production using a moldboard plow operation compared with a subsoil-bedding operation. They reported that the moldboard plow production system required 103.1 I ha-t of fuel and 9.2 h ha- ~of time, while the subsoil-bedding production system required 87.2 1 ha-~ of fuel and 8.0 h ha- ~of time. Plowing, employing subsoil bedding can be com-

IMPACTOF ENERGYSHORTAGESON TIMELINESSOF AGRICULTURALOPERATIONS

169

p!eted more quickly and with less energy. This could be useful strategy during an energy shortage. Another strategy for dealing with energy shortages is the use of minimum-till or no-till procedures. These operations originally were used to reduce soil erosion, but they were soon rediscovered by energy-conscious scientists and farmers owing to their low tractor fuel requirements. There are some studies that suggest that in the production of certain crops, reduced and no-tillage operations are more energy efficient than conventional systems (Rak and Forester, 1976; German et al., 1976). However, the total energy consumption in no-till crop production may be higher than in the conventional method of production because of the use of larger amounts of chemicals. One might ask whether human or animal-powered equipment are better choices. Humans have a very limited power output. A healthy adult can produce 75 watts of power continuously. Working l0 h day-t, one person can produce 750 watt-hours work or 2.7 MJ. The net energy analysis of labor gives a value of 594 MJ d a y - i for energy used in agricultural labor in the United States (Fluck and Baird, 1980). Using this value (594 MJ day- t ) for input energy, the efficiency of human labor can be calculated as 0.5%. If we utilize the most widely used energy value for labor, 12 MJ day-i based on food caloric energy consumption, the efficiency is calculated to be 20%. Under current economic conditions in the US, the use of draft animals in agriculture would be inefficient, even if the animals were available. In discussing this matter, Gavett (1973) stated that 61 million draft animals would be required to power US agriculture in 1977, and that half of the cropland would be required to feed those animals. PLANTING AND CULTIVATION

Crops have to be planted at the proper time to obtain optimal crop yields. The Arkansas Extension Service has reported for every day that soybeans are planted after 20 June, yields are reduced by 67.3 kg ha-~ (United States Senate, 1979). In addition, the timeliness of planting operations has a great deal to do with weed control and olther cultural practices which in turn require energy. Excessive rain during planting time will delay planting. When the soil dries sufficiently, planting must take place as soon as possible. This means that all the fuel energy required has to be available at that time. As all farmers are forced to do the same thing and they all need the fuel at the same time, there might be local fuel shortages if fiLeldistribution is not properly planned. Blackshaw et al. ( 1981 ) reported that late seeding of Narquay wheat reduces the competitive ability of green foxtail plants which grow among wheat crops. This indicates that there is an ideal planting time for wheat. If the planting is not completed at the proper time, there may be qualitative and

170

A. SHAHBAZi

quantitative reduction in the yield. Alessi et al. ( 1981 ) studied the effect of seeding date on water-use efficiency and safflower yield. They reported that early seeding (mid-May) produces highest safflower seed yield and oil concentration. This again emphasizes the importance of timely availability of fuel needed for planting operations. Crops such as corn require a high chemical input. Large amounts of energy are consumed in the production of such chemicals (Pimental, 1980). During 1973 and 1979, when there was a fuel shortage in the United States, the farmers in the corn belt were switching to the production of soybean which requires a lower chemical input than corn. Farming systems with organic input to replace nitrogen fertilizer and other chemicals are recommended to conserve energy. In this system, not only are the energy inputs low but there is a significant impact on preventing environmental pollution. Lockeretz et al. (1976) studied 14 organic farms (average field size of l 01 ha) and 14 farms with conventional production systems (average field size of 140 ha) in corn belt states. The organic farms had already gone through the transition to organic production. Lockeretz et al. determined the energy, labor, and chemical inputs and concluded that: ( l ) the organic group consumed appreciably less energy (67% less); (2) the organic farms required 12% more labor; (3) the profitability of crop production per acre of cropland was comparable for the two groups of farms. Thus, organic farming is a less chemically intensive method and may enable farmers to reduce the vulnerability of their agricultural systems to oil price increases and fuel shortages. IRRIGATION

Crops need a continuous supply of water in order to grow. Water is provided naturally by rainfall or by irrigation. The timely supply of fuel to power pumps and irrigation systems is essential to some crops growing in arid environments. For example, a rice crop, because of its characteristics, needs an uninterrupted supply of water. Delay in irrigation can cause severe reductions in both the quality and quantity of the rice harvest. According to an Arkansas farmer, "a small cut in the amount of farm fuel can be afforded, while a small delay in the time of supply cannot be afforded" (United States Senate, 1979). From 1964 to 1984, irrigated farmland in the United States increased from 16.8 to 24.9 million ha - - a 48.9% increase. The sprinkled irrigated area increased from 2.2 to 9.0 million h a - more than a 300% increase (Goldstein, 1985). The trend is toward increased irrigated production and that means more energy consumption on the farm. The recent droughts ( 1987-1988 ) in the US have encouraged the shift toward irrigation. The irrigated areas using diesel fuel grew rapidly during 1974-1983, fol-

IMPACT OF ENERGY SHORTAGES ON TIMELINESS OF AGRICULTURAL OPERATIONS

! 71

lowed by electricity and natural gas. The majority of increases during this time are accounted for by the use of energy consuming distribution systems such as sprinklers (Sloggett, 1985 ). Rising energy costs for pumping and dis:ribution of irrigation water may be absorbed by energy conservation practices (improving the energy efficiency of the pumps), using less water, more efficient water application, and by switching to crops such as soybeans, which have lower water requirements. Other techniques for overcoming the high cost of energy include using less expensive sources of energy such as solar water pumps, energy management practices such as irrigating at night to avoid peak load electrical costs and evaporation (Abernathy and Mancini, 1977; Anschultz and Lipper, 1977; Larson, 1978; Twersky and Fischback, 1978, Anschultz et al., 1978; Larson et al., 1978 and Larson, 1982). Water requirements of trees and some deep-rooted crops and forages are lower than crops and vegetables with shallow root systems. For instance, Irish potatoes have an irrigation schedule of "every other row every other day" (United States Department of Agriculture (USDA), 1977 ). This kind of irrigation schedule shows a continuous need for energy to run pumps and irrigation systems throughout the season. Therefore, switching from shallow rooted crops to deep rooted crops will reduce both water and energy requirements. HARVESTING

The timely availability of fuel is absolutely essential for harvesting success. Almost all major field crops - - fruit, and vegetables such as beans, carrots, onions, and tomatoes m grown in the United States are harvested by machine (R. Kumar et al., unpublished data, 1978). This directly affects the energy demancls of these crops. The harvesting time period for most crops is short. If the harvest of a field crop is delayed as a result of unavailability of fuel, there will be crop losses. A relationship is established between the delay in harvesting and the yield loss for barley (Fig. 1 ). Huisman (1983) has calculated the timeliness loss for two cereal farms which ranges from 55.8 to 63.9% of the total crop when the harvesting rate of the combine is 2 m 2 s - l. If the harvesting rate of the combine is increased to 10 m e s-i, the timeliness loss can be reduced to 1.041.56% of the total crop. This loss is based on the probability of lost work hours during the season owing to weather conditions. As we move away from the normal harvest time, the risk of bad weather increases and the number of workable days decreases. The timeliness loss in the study by Huisman (1983) was calculated on the basis of 40 years of data. The timeliness loss is found to be directly proportional to operating speed. When the speed is low, the harvest will require more time; it will increase vulnerability to bad ~veather and reduce the number of the workable days.

172

30

A. SHAHBAZI

_

u

•

go

/

0

I

I

I

I

I

10

20

30

40

50

Days after flfsl cut

Fig. l. Losses in barley as affected by time in harvesting: upper, cv. 'Emma': lower, cv. 'Midas' (Robinson and Mollan, 1982, p. 147).

Also, the delay in harvesting will severely limit the speed of harvesting operations. This is because the harvest loss (header loss) of over-ripe crops is proportional to the machine speed. The higher the speed, the higher the loss. Is a labor-intensive harvesting system less susceptible to energy problems? Labor-intensive harvesting systems are being utilized in certain areas of agriculture such as fruit and vegetable production. This less ms the impact of fuel shortages. However, those who have been involved with labor-intensive production systems know well that agricultural labor is becoming less available and more expensive. In fact, this is one of the main reasons for the ever-increasing automation of harvesting in various fields of agriculture. Singh and Singh ( 1978 ) have reviewed the energy requirements of several pieces of hand grain harvesting equipment, including the European scythe, American grain cradle, Japanese portable reaping machine, and an Indian sickle. They stated that the energy requirements of the European scythe and American cradle are about the same and equal to 56, 67, and 75 kJ ha- ~ for rye, oat and buckwheat, respectively. In spite of these low energy inputs, hand grain harvesting equipment has major limitations. Two of these limitations are their low harvest rate and high labor requirements, neither of which modern agricultural production systems can afford. However, if a small farmer owns only a fraction of a hectare, he or she can harvest that crop more profitably using hand harvesting equipment than by hiring a combine. The combining cost for a hectare in most developing countries would be about onehalf of the total income of some poor rural farmers. Few people, if any, are

IMPACT OF ENERGY SHORTAGES ON TIMELINESS OF AGRICULTURAL OPERATIONS

173

willing to spend one-half of their income on equipment just for harvesting. Therefore, it is more economical for small farmers to harvest their crops using hand tools rather than comtfines. White (1979) estimated the fuel consumption of combine harvesters to be 17.86 l ha-i. A survey in Ireland by An Foras Taluntais (1980) yielded a slightly lower fuel consumption - - 15.6 l ha- ~ for grain combines but, with an additional 7.2 1 ha-i for transporting the grain, the total is even higher at 22.8 ! ha-i. New combine harvester designs which utilize rotary separation units consume more fuel. Robinson and Mollan (1982) stated that an IH 1460 rotary combine in Switzerland used about 80% more fuel than a conventional class Dominator 85. New combines have a better field performance, but use more fuel per unit area. With energy being the critical component of crop production, it is unlikely that the increased crop recovery will justify additional fuel use. Therefore, we ought to consider redesigning our machinery for better fuel efficiency. Timeliness is especially important in harvesting fruits and vegetables owing to the perishable nature of these crops. For most fruits and vegetables, the optimal time for harvest is very short. DRYING AND COOLING

Grain is usually harvested at a moisture content of 20-28%, which is higher than the storage moisture content of I l - 13%. To prevent the grain from spoiling in storage, it needs to be dried. The recommended storage moisture contents are 13%, l 1%, 12% and 12% for shelled corn, soybeans, wheat, and sorghum, respectively (Midwest Plan Service, 1980). Drying must take place at a rate fast enough to prevent spoilage. The time allowed for drying depends on grain temperature and moisture content; these two parameters are interrelated. The higher the temperature of the air, the higher the moisture-carrying capacity. In a low-temperature drying process, drying begins when daily temperatures drop below l0 ° C; it stops when average daily temperatures fall below 0°C. Owing to variations in weather conditions in various states throughout the US, drying times fluctuate. For instance, the typical drying time in Indiana (a major corn producing state), spans the first week in September and the end of the third week in December a 14 week period (USDA, 1977). Drying rice is a seasonal process and is performed after the harvest in late summer and early autumn. During the drying process, a continuous supply of energy is needed (24 h day- i ). Peanut drying is an energy-consuming operation which requires a timely supply of heating energy. The south and southeast are the major peanut-producing regions in the United States. Peanuts are usually harvested during September and October in the southeast region, and during mid-August to Octo-

174

A. SHAHBAZI

ber in the south. When drying facilities are available, peanuts can be harvested greener in order to reduce the field loss. Peanuts are normally harvested at about a 45% moisture content on wet basis. It is left in the field under the sun until the moisture content reduces to about half the original value. Then it is picked up and artificially dried to about 10%. In conventional drying systems, 7000-7500 kJ of energy are required to remove 1 kg of water. Young (1988) has been able to reduce this drying energy requirement by 30%. About one-third of this can be attributed to the use of solar energy and the other two-thirds to recirculating hot exhaust air. Drying is a seasonal process which is performed at different times of the year for different crops. But, in general, most of the drying is performed during harvest time prior to storage and during *,he winter (Fig. 2 ). If we are able to reduce the drying load, or use dryers that run on non-petroleum energy sources, or redesign the drying systems to increase their efficiency, we will help reduce the impact of energy shortages on agriculture. Solar energy is the least expensive and most abundant source of energy in most parts of the world. It has been used extensively in agriculture to dry 120 _

Diesel

I10 _

-o-o.-o-o-

Gasoline

.....

Propane

I00

£

~ 8o

~

70

l I

~L 60

l

_

I I

5O

l I i

40

l 1

30

I

2o 10

// I

I

I

I

I

I

I

I

I

I

I

Jan Feb Mar Al:)r May June July Aug Sepl Ocl Nov Dec

Fig. 2. Energy co.sumption per hectare is depicted by fuel type and time of year for corn grain with drying. Fertilizers and pesticides are not shown in the graph (Robinson and Mollan, 1982, p. 78).

IMPACT OF ENERGY SHORTAGES ON TIMELINESS OF AGRICULTURAL OPERATIONS

175

grain crops, forage crops, peanuts, fruits, and vegetables, and many other products. Solar energy is sometimes used to provide 100% of the drying energy requirements. Most of the time, however, it is used as a supplemental heat source (Troeger, 1986; Young et al., 1988 ). A major limitation of solar drying systems is the lack of effective thermal storage facilities for use during cloudy days or at night. A short application period each year is another limitation of solar drying systems. The season for drying most crops is very short and specific. Therefore, it is necessary to develop multiple uses for solar drying systems in order to make them economically attractive. One such facility has been designed by Huang ( 1986); it is a greenhouse type structure used both for plant production as well as for fruit and vegetable drying. PROCESSING, TRANSPORTATION, AND STORAGE

Adequate energy supplies are needed for food processing. Timeliness is essential in preserving the quality of harvested crops. For example, many vegetable and fruit canning plants operate for only a few weeks a year, and a critical shortage of fuel during this period would have a major negative impact on the industry. Food processing plants consume large quantities of energy. The most convenient source of fuel for processing has been natural gas piped directly to the plant. Food processing plants can be expected to be hit harder if there are shortages in the gas supply. If we look at the employment picture in agriculture, we notice a shift in employment from agricultural production to food processing and marketing. There is a significant drop in the number of people involved in agricultural production and an increase ofthe same magnitude in food marketing employment. Consumer spending on food can further illustrate this point. In 1986, $345 billion was spent on farm foods: of this, 24% was spent on production activities, 28% on food processing and 48% on food marketing (D.M. Edwards, unpublished data, 1987). Energy use within the food system in the USA is distributed as follows: production, 18%; processing and packaging, 33%; preparation, 30%; transportation and retail, 19% (Stout, 1984). By growing our own food, or buying locally grown produce by season, nearly 80% of the energy requirement can be eliminated, and so can our dependence on fossil fuels. Movement of food depends on adequate transportation facilities. Transportation by waterways requires the least amount of energy, but waterways are not available everywhere. Most states depend on trucking which is the least energy efficient means of transportation (USDA, 1980). At the present time, 50% of the trucks on the highway carry food and agricultural products. To protect food supplies, the entire food system must prevent fuel shortages

176

A. SHAHBAZI

from turning into food shortages. Although the availability of fuel is the primary concern, it must also bc available at a reasonable cost. The energy cost today in the food industry, is the second highest cost below that of labor. The two most important conservation practices a~e: ( 1 ) redesigning the machinery and increasing their efficiency; (2) reducing wasted heat. For example, Young et al. (1988) has designed a peanut drier that uses natural gas supplemented with solar energy. Conventional peanut driers exhaust hot air after a single pass through the drier. The newly designed energy-efficient drier recycles the exhaust heat and supplements it with solar energy. This drier saves 70% of drying energy. Thirty percent of this saving is attributed to solar energy and 40% is attributed to recycling. Another example is electrical motors. They arc very inefficient and waste a lot of energy. By using various control devices, their efficiency can be improved. A considerable amount of heat loss occurs at every stage of food processing. By implementing a heat recovery program throughout the plant, energy demand can bc reduced significantly. For example, consider the pasteurization process for milk. Milk is pumped through a heat exchanger for pasteurization; then it is cooled down to a safe storage temperature. The heat contained in the hot milk after pasteurization is wasted unless it is transferred to the incoming cold milk and reused. This way, heat extracted from hot milk reduces heat loss and improves energy efficiency.

CONCLUSIONS

Five conclusions can be drawn from this assessment. ( l ) Alternative energy sources such as solar energy can substitute for conventional fossil energy supplies. (2) Conservation can reduce the dependency of agriculture of fossil fuels. (3) Minimum-till and no-till operations can reduce the tractor fuel requirements for tillage operations. On the other hand, chemical and seed requirements are higher for these production systems. As a result, these practices may require quantities of energy equal to those required by conventional operations. (4) Although labor-intensive harvesting systems can be helpful in reducing the effects of energy shortages in certain agricultural crops, it cannot be used as a substitute for mechanized harvesting. It is only practical in small rural farms and for certain vegetable crops. (5) The use of energy management practices and energy-efficient equipment can significantly reduce the energy requirements of many agricultural

activities.

IMPACT OF ENERGY SHORTAGES ON TIMELINESS OF AGRICULTURAL OPERATIONS

177

REFERENCES Abernathy, G.H. and Mancini, T.R., 1977. Design and installation of a solar-powered irrigation pump. ASAE Pap. 77-4020, Am. Soc. Agric. Eng., St. Joseph, MI, pp. 1-4. Alessi, J., Power, J.F. and Zimmerman, D.C., 1981. Effects of seeding dates and population on water-use efficiency and safflower yield. Agron. J., 73: 783-787. An Foras Taluntais, 1980. Annual research report, Ireland. In: D.W. Robinson and R.C. Mollan (Editors), Energy management and agriculture, Royal Dublin Society, Dublin Ireland, 145 pp. Anschultz, J.A. and Lipper, R., 1977. Scheduling irrigation by temperature to manage electric loads. ASAE Pap. 77-3045, Am. Soc. Agric. Eng,, St. Joseph, MI, pp. i-2. Anschuitz, J.A., Ginther, C. and Lipper, R.J., 1978. Experiences with irrigation scheduling for electric load. ASAE Pap. 78-501, ~m. Soc. Agric. Eng., St. Joseph, MI. Anwood, P.J., 1980. The importance of timeliness in field operations. Farm management, 4 (3): 117-123. Audsley, E., 1984. Use of weather uncertainty. Compaction and timeliness in the selection of optimum machinery for autumn field work - - a dynamic program. J. Agric. Eng. Res., 29: 141-149. Blackshaw, R.E., Stobbe, E.H. and Sturko, A.R.W., 1981. Effect of seeding dates and densities of green foxtail (Setaria viridis) on the growth and productivity of spring wheat ( Triticum aestirum). Weed Sci., 29:212-217. Dumas, W.T. and Renoli, E., 1983. Fuel and time data for A~abama cotton production practices. Trans. Am. Soc. Agric. Eng., 26: 399-400. Edwards, D.M., 1987. Project 1999, a strategic plan. Department of Agricultural Engineering, Michigan State University, East Lansing, MI, pp. 1-15 (unpublished). Fletcher, J.J. and Featherstone, A.M., 1987. An economic analysis of tillage and timeliness interactions in corn-soybean production. N. C. J. Agric. Econ., 9 (7): 207-215. Fluck, R.C. and Baird, C.D., 1980. Agricultural Energetics. AVI, Westport, CT, p. 10. Gavett, E.E., 1973. Agriculture and energy use. In: R.C. Fluck and C.D. Baird (Editors), Agricultural Energetics. AVI, Westport, CT, pp. 112-115. German, L., Schneeberger, K., Workman, H. and McKinsey, J., 1976. Economic and energy efficiency comparisons of soybean tillage systems. In: W. Lockeretz (Editor), Agriculture and Energy. Am. Soc. Agric. Eng., St. Joseph, MI, pp. 277-279. Goldstein, A., 1985. 1984 Irrigation survey, lrrig. J., 35 ( I ): 2-6. Huang, B.K., 1986. Use of solar energy for drying and curing. In: D.Y, Goswami (Editor), Alternative Energy in Agriculture, Vol. I. CRC Press, Boca Raton, FL, pp. 117-121. Huisman, W., 1983. Optimum cereal combine harvester operation by means of automatic machine and threshing speed control. Doctoral Thesis, Dep. Agric. E:lg., Agricultural University, Wageningen, The Netherlands, pp. 217-220. Kumar, R., Chancellor, W. and Garrett, R., 1978. Estimates of the impact of agricultural mechanization developments on in-field labor requirements for California crops, Department of Agricultural Engineering, University of California, Davis, CA, pp. 7-9 (unpublished). Larson, D.L., 1978. Utilization of an on-farm solar powered pumping plant. Ser. 2901, Ariz. Agric. Exp. St., Tucson, AZ, pp. !-3. Larson, D.L., 1982. Operational evaluation of a solar power plant for irrigation pumping. ASAE Pap. 82-2523, Am. Soc. Agric. Eng., St. Joseph, MI, pp. 1-4. Larson, D.L., Sands, C.D., Towle, C. and Fangheier, D.C., 1978. Evaluation of solar energy for irrigation pumping. Trans. Am. Soc. Agric. Eng., 21:110-1 ! 5. Locke~ctz, W., Klcr ~er, R., Commoner, B., Gertler, M., Fast, S., O'Leary, N. and Biobaum, R., 1976. Econom,c and energy comparison of crop production on organic and conventional turn belt farms. In: W. Lockeretz (Editor), Agriculture and Energy. Am. Soc. Agric. Eng,, St. Joseph, MI, pp. 85-87.

178

A.SHAHBAZI

Midwest Plan Service, 1980. Low temperature and solar grain drying. Midwest Plan Service, Iowa State University, Ames, pp. 25-28. Nolte, B.H., Fausey, N.R. and Skags, R.W., 1983. Time available for field work on two Ohio soils. Trans. Am. Soc. Agric. Eng., 26: 445-447. Pimentel, D. (Editor), 1980. Handbook of Energy Utilization in Agriculture, Chap. I. CRC Press, Boca Raton, FL. Rask, N. and Forester, D.L., 1976. Corn tillage systems-- will energy costs determine the choice? In W. Lockeretz (Editor), Agriculture and Energy. Am. Soc. Agric. Eng., St. Joseph, MI, pp. 289-292. Robinson, D.W. and Mollan R.C., 1982. Energy Management and Agriculture. Royal Dublin Society, Dublin, 147 pp. Singh, M.S, and Singh, K.N., 1978. Force requirements of different sickles. J. Agric. Eng., 15: 11-18. Sloggett, 1985. Energy and U.S. agriculture - - irrigation pumping, 1974-80. Rep. No. 545, Nat. Resourc. Econ. Div., Econ. Res. Serv., USDA, Washington, DC, pp. 4-6. Stout, B.A., 1984. Energy Use and Management in Agriculture. Breton, North Scituate, MA, pp. 15-16. Troeger, J.M., 1986. Peanut drying models. Annu. Rep., Regional project S-196, USDA-ARS, Coastal Plain Exp. Stn., Tifton, GA, p. 1. Twersky, M. and FischbPzk, P.E., 1978. Consideration of irrigation systems in solar photovoltalc energy program. ASAE pap. 78-255 l, Am. Soc. Agric. Eng., St. Joseph, MI, pp. 1-2. United States Department of Agriculture, 1977. Solar energy applications in agriculture: potential, research needs and adoption strategies. NSF/RA -76002 l, Agric. Res. Serv., Agric. Exp. Stn., University of Malyland, College Park. United States Department of Agriculture, 1980. Cutting energy costs. The 1980 Yearbook of Agriculture, Sect. 1. USDA, Washington, DC, pp. 10-14. United States Senate, 1979. Impact of fuel shortages during harvest, hearings before the committee on agriculture, nutrition, and forestry. 96 Congress, US Government Printing Office, p. 2, 8, 71. White, D.J., 1979. Efficient use of energy in agriculture and horticulture. Agric. Eng., 34: 6773. In: D. Robinson and R.C. Molland (Editors), Energy Management and Agriculture, 1982, Royal Dublin Society, Dublin, Ireland, p. 67. Young, J.H., Tutor, J.C. and Cain, Jr., G.L., 1988. Recirculation and solar energy collection assist peanut drying. Pap. 88-6584, Am. Soc. Agric. Eng., St. Joseph, MI, pp. 1-2.