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Energy returns in agriculture, with specific reference to developing countries
ENERGY RETURNS IN AGRICULTURE, WITH SPECIFIC REFERENCE TO DEVELOPING COUNTRIES B. s. PATHAKt and DALJITSINGHS Punjab Agricultural
University,
Ludhiana. India
(Received 21 March 1977) Abstract-Quantitative data are presented for energy inputs and outputs for selected crops in India using either bullock-operated or tractor-operated farms. It is shown that large ratios are obtained for the energ outputs divided by the energy inputs. Preferred allocation of energy resources to the agricultural sector i recommended. INTRODUCTION
The two major constraints faced by the developing countries today are energy and food. The introduction of high yielding varieties, fertilizers and mechanization in agriculture has partially alleviated the food constraint in most of these countries. However, the energy requirements of mechanized agriculture have only accentuated the former constraint. The energy resources of most of the developing countries are very limited and highly inadequate to meet the total demand of all sectors of the economy. It is, therefore, necessary to distribute the energy resources judiciously and to establish a set of priorities for the more beneficial or necessary uses of energy. The allocation of available energy resources between the various sectors depends upon the national priorities and requirements. All the same, it is readily recognised in almost all countries that foremost priority should be given to the agricultural sector. The need to improve the standards of nutrition and the continuing increase in population resulting in a rising demand for food have further reinforced this priority. There is, however, a wide divergence of opinion as to what restrictions, if any, should be placed on energy consumptions in the agricultural sector. The question of appropriate agricultural technology is also being reviewed in the light of the energy constraint. The performance of the agricultural sector is also being evaluated from the energy-returns point of view alone. For most developing countries, such returns are found to be far higher than the energy inputs through conventional resources, implying thereby that agricultural production regenerates more energy than it consumes. Hence, it deserves the foremost priority, not only because it meets our food and raw-material requirements, but also because it represents one of the best uses of our available energy resources. CONSUMPTIVE
VS REGENERATIVE
USES
OF ENERGY
When energy is added to any system, it may either be dissipated in the form of heat or work or stored as intrinsic energy within the system,’ in accord with the laws of thermodynamics. In the former case, which may be called the “consumptive use” of energy, the energy added to a system is reduced to a form which cannot be used further. Transportation, domestic heating and cooking, etc. are examples of consumptive uses of energy. A large majority of the current uses of energy fall in this category and this energy, for all practical purposes, is lost for ever. On the other hand, most chemical uses of energy result in its storage in an intrinsic form, which remains available for further use. The car battery is a classic example of such “regenerative use”. The energy supplied during charging is stored chemically, and nearly 85% of this energy can be reused’ for lighting a lamp or starting an automobile. The energy added to a boiler furnace is stored in steam, which can be used further to run a turbine or to produce electricity. The electrical energy expanded in the hydrolysis of water is available in the form of hydrogen, a very clean fuel. Photosynthetic reduction of carbon dioxide, which results in Wean, College of Agricultural Engineering. SAssociate Professor of Chemical Engineering. 119
I20
B. S. PATHAK and D. SINGH
chemical storage of intrinsic energy in plants, forms the most significant regenerative use of energy. Photosynthesis pirates part of the solar energy available in the environment and adds it to the stored energy of the plants. The energy available from plants is thus greater than the energy supplied to them through conventional energy resources. It is this significant regeneration of energy on a large scale that forms the essential basis of modern agriculture. ENERGYREGENERATIONTHROUGHAGRICULTURE
Modern agriculture depends heavily on five major technologies: seed, mechanization, irrigation, fertilizer application and chemical control of weeds and insects. Each of these technologies has contributed substantially towards increasing the yields of major crops. Each of these also represents a substantial input of energy derived from conventional resources. A part of this energy input is stored as intrinsic energy of the plants. The remaining energy input helps in harnessing still greater amounts of solar energy for storage as the intrinsic energy of the plants. The total energy available from the plants is therefore, far greater than the energy added to them through conventional resources. Quantitative estimates of energy input versus output for various crop combinations for both bullock-operated farms (BOF) and tractor-operated farms (TOF) have been calculated and are reported in Tables l-4. These figures pertain to mechanized and traditional farming for Indian conditions, but should be reasonably representative for most developing countries. The information on energy needs and yields was borrowed from the reports of the scheme “Energy Requirements for Intensive Agril Production” and pertain to the farming areas around Ludhiana (Punjab) and Terai (U.P.). These areas have the common characteristics of high intensity of cropping, high yield levels in the context of average yields of various crops on an all-India basis, and extensive lift irrigation (tubewells). The use of inanimate sources of power (diesel engines, electric motors) is quite common, both for stationary and mobile operations on the farm. Consumption of energy per unit of area is comparatively high in these areas and the proportion of inanimate energy to animate energy would also be much higher than the average for the country. Wheat, maize, paddy, groundnut, and sugarcane are the important crops of the two areas. Information reported is for paddy-wheat, maize-wheat and groundnut-wheat rotation and for sugarcane as a single crop. This procedure takes care of the effects of one crop on the energy requirements of the successive crop for important crop combinations. The energy figures computed for these crop rotations could be considered to be representative of the diierent soil types also because the paddy-wheat combination is common for heavy soils, the maize-wheat rotation and sugarcane are commonly adopted in medium soils, and groundnutwheat rotation is most commonly followed in light soils. The yield figures have been averaged out from a wide range of data. Crop yields as function of fertilizer application are shown in Figs. 1 and 2 for maize and wheat, respectively. The energy inputs into the manufacture of machinery used for the agricultural operations Table 1. Energy balance in agriculture with crop rotation: paddy-wheat in heavy soil. See the text for assumptions and sources.
Item A. ENERGY INPUTS, kWh/ha 1. h4achinery 2. Agricultural Operations: Nursery r&ii Seedbed Sowin 8 gap 8nii Transplanting IDterCullUIC
Fertiker . . application
z HarvcslinR
Tbresbing-
Trnnsoort d Misc. Total -
Paddy BOF TOF
Wheat BOF TOF
391
639
327.5
35.5 122.1
35.5 248.2
65.1 18.9 0.7 201.8
65.1 17.7 0.6 201.8
2z
d:: 42.7 20.1 717.7
28.5
828 584.8
-
598
-
73.8 6.1
238.7 34.1
29.0
32.1 0.2 133.4 0.4 14.2 162.6 54.3 670.1
0.2 129.1 0.4 14.3 188.4 56.2 497.5
Energy
returns Table
121
in agriculture
1. (Contd.) Paddy
Item 3. Fertilizers N P,O, K?O Total 4. Seeds 5. Total 6. Total combined
Table
2. Energy
TOF
560 27.5 25 612.5 175 1763.3
560 21.5 2s 612.5 I75 2144.2 kWh/ha kcabha
input
B. ENERGY OUTPUTS I. Yield, q/ha Wheat Rice Husk Straw 2. Intrinsic energy of grains, kcal/ha 3. Fuel value of byproducts, kcal/ha: Straw Husk 4. Total energy output, kcal/ha 5. Total combined output C. RATIO Energy output/input balance
in agriculture
Wheat
BOF
BOF
TOF
560 27.5 12 599.5 490 1914.5 36778 3.2 x IO6
39.5 16.9 79
35.9 15.4 71.8
15.8 x IO6
14.4 x IO6
560 21.5 12 599.5 490 2357.6 4501.8 3.9 x 10L
25 -
2s
50
50
IO x IOh
IOX IO6
37.1 x IO” 33.3 x IO6 23.5 x IO” 23.5 x lo6 S.6x IO6 5.1 x IO’ 58.5 x IO6 52.8 x IO6 335 x lo6 92 x IO’
with
crop
rotation:
33.5 x IO6 86.3 x IO”
25.6
19.5
maize-wheat
in heavy
Maize Item A. ENERGY INPUTS. kWh/ha I. Machinery 2. Agricultural operations: Seed bed Sowing & gap filling Fertilizer application Interculture Irrigation Spraying Harvesting Thrashing Transport & Misc. Total 3. Fertilizer N PZOS KzO Total 4. Seeds 5. Total 6. Total combined
soil.
Wheat
BOF
TOF
BOF
TOF
288
425
731
916
19.0 11.8 1.9 31.9 172.2 1.2 8.8 60.0 60.5 367.9
109.1 35.5 1.7 27.5 173.8 4.6 7.8 65.0 65.4 490.3
29.8 9.0 0.2 29.0 316.1 0.4 17.6 438.7 102.0 932.9
122.7 34. I 0.2 31.2 316.1 0.4 19.7 418.1 101.3 1043.8
560 27.5 25 612.5 140 1408.4
560 27.5 25 612.5 140 1667.8 kWh/ha kcal/ha
560 21.5 12 599.5
560 21.5 12 599.5 490 3049.3 4717.1 4.1 x 10b
30 -.
30 -
30 54
Input
490 2753.4 4161.8 3.6x IO6
ENERGY OUTPUTS 1. Yield, q/ha Maize #eat Straw Corncobs 2. Intrinsic energy of grains, kcabha 3. Fuel value of byproducts straw, kcal/ha cobs, kcal/ha 4. Total energy output, kcal/ha 5. Total combined output, kcal/ha
-
-
30 54
37 74 -
37 74 -
I2 x IO6
12 x IO6
14.8 x IO6
14.8 x 10”
14.1 x IO -
14.1 x lo6 -
34.8 x IO” -
34.8 x 10” -
26.1 x IO”
26.1 x lo6
49.6~
10” 49.6 x lo6
75.7 x IO6 75.7 x lo6
RATIO Energy
output/input
21
18.5
122
B. S. PATHAK and D.
SINGH
Table 3. Energy balance in agriculture with crop rotation: groundnut-wheat. Item
BOF
TOF
800
1197 1345.6
A. ENERGY INPUTS, kWh/ha
1. Machinery 2. Agricultural operations 3. Fertilizers: N PZGS K# Total 4. Seeds 5. Total B. ENERGY OUTPUTS 1. Yields, q/ha Groundnut Kernels (70%) Shell (30%) Wheat Straw 2. Intrinsic energy of grain, kcal/ha Wheat Groundnut 3. Fuel value of byproducts, kcal/ha Straw Shells 4. Total energy output, kcal/ha C. RATIO Energy output/input
1081.5
kWh/ha kcal/ha
627.2 627.2 45.1 45.1 22 22 694.3 694.3 872 1225 3447.8 4461.9 3.0 x 10” 3.9 x 10”
14 9.8 4.2 30 80
14 9.8 4.2 30 80
I2 x IO” 12x IO” 7.4 x 10” 7.4 x IO” 37.6x IO” 37.6x IO” 14.0x IO” 14.0x IO6 71.0x IO” 71.0x 10” 23.4
18.0
Table 4. Energy balance in agriculture for sugarcane. BOF
Item A. ENERGY INPUTS, kWh/ha I. Machinery 2. Agricultural operations 3. Fertilizers(N) 4. Seed 5. Total B. ENERGY OUTPUTS 1. Yields, q/ha Sugarcane Dry leaves 2. Intrinsic energy of sugars (12.5%),k&/ha 3. Fuel value of byproducts, kcal/ha Bagasse (13%) Leaves 4. Total energy output, kcal/ha C. RATIO Energy output/input
kWh/ha kcal/ha
TOF
590 7%.6 672 9250 11308.6 9.7 x IO6
795 892.8 672 9250 11609.6 10.0x IO”
720.0 240.0 35.5x I06
1050.0 350.0 51.8x IO”
44x IO6 64x lo6 60 x 10” 87.5x IO” 139.5x 106 203.3x IO6 14.4
20.3
have been estimated from Berry and Fels’ as equivalent to 31.%x 10”kcal for 1545kg of machinery. Kahlon4 has reported an average rating of 30 hp for the tractors in this region. The average weight of a 26.5 hp tractor is 1559kgs according to Either.’ The total weight of tractor and implements was therefore assumed to be 4 tonnes. According to the data of Berry and Fels,’ this is equivalent to an energy input of 85.2 x lo6 kcal per tractor including the usual implements. If we assume an average machinery life of 10 yr at 5OOhr of use per year, the energy input into machinery, per hour of operation, is approximately 19.04~ 10’ kcal/hr or 22.2 kWh!hr of operation. On this basis, the energy inputs for various crops have been evaluated and are listed in Table 5. The net energy inputs into the rearing of bullocks have not been incorporated in these calculations but the effect on the final results is likely to be only marginal. The recommended fertilizer dosage for various crops is indicated in Table 6. The energy input into the manufacture of nitrogenous fertiliirs, as reported by Chemical Engineering
Energy
returns
in agriculture
4
Energyinput.
Energy
Ck cd x K&ha m
50
90
input,
(k co1 x 104Jho 6 3
120 --?L--T-L-2
30
60 tt
30
120
0
kg/ha
30
60
P20s,
93
30
kg/ha
60 KzO,
w
kg/ha
Fig. 1. Energy response to fertilizer application; crop: maize
5
Energy Input. (k cd x 104Vha 30 30
60 60
90 90 N, kg/ho
120 120
150 150
0
30
P2D,.
EC
90
kg/ho
Fig. 2. Energy response to fertilizer application; crop:
0
K,O,
kg/ho
wheat.
World, is estimated at 11.2kWh/kg nitrogen.’ Energy requirements for the manufacture of phosphatic fertilizers are estimated from Shreve’s’ data at 1.1 kWh/kg PzO~. The energy input into potash fertilizers has been evaluated from Dryden’s data’ (0.65 kWh/kg of muriate of potash and 1 kWh/kg of KzO). The energy inputs into fertilizers obtained on this basis are summarized in Table 6. It was assumed that both BOFs and TOFs used the recommended dose of fertilizers. Pimentel et al.” in a similar evaluation for corn production in the U.S.A., have found the energy inputs in insecticides etc. to be very small, i.e. less than a fraction of 1% of the total energy input. Consequently, these have been ignored in our analysis. The energy outputs have been estimated on the basis of yields averaged from a wide range of data. The various plant-component ratios assumed are summarized in Table 7. Sugarcane, on the basis of the analysis reported by Spencer Meade,” was assumed to have an average sugar content of 12.5% and an average fiber content of 13%. The calorific value used for wheat, maize and rice was 4000 kcal/kg,12 while for straw a heating value of 4700 kcal/kg was used.13 The intrinsic energy of seeds was assumed to be approx. 5ooOkcal/kg.” The seed rate used for various crops is given in Table 8. Groundnut sheIls and rice husk were assumed to have a heating value of 3300 kcal/kg.13 Dry leaves were assumed to have a heating value of only 2500 kcalfkg. The intrinsic energy of kernel was assumed to be equivalent to the sum of the intrinsic energy of oil contained therein, evaluated” at 100,000kcal/kg, and the remaining cake evaluated at 5000 kcal/kg.‘6 The intrinsic energy of sugarcane was evaluated as the sum of the intrinsic energy of sugars contained therein (3940 kcal/kg)‘6 and the heating value of the fibrous material (4700 kcal/kg).13 The total energy outputs are summarized in Tables l-4. In all cases, the total energy output is greater than the total energy input. ENERGY Vol !. No z--8
B. S. PATHAK and D. SINGH
Energy returns in agriculture
Table 6. Energy inputs in fertilizers for various crops. Fertilizer recommended, kg/ha N GO P203
Crops Wheat
50
Sugarcane Maize Paddy Groundnut
60 50 50 6
25 25 25 I6
12 u 25 IO
Energy input, kWh/ha N PzOs RP 560 672 560 560 61.2
Table 7. Plant-component ratios. Wheat
(semidwarf)
Paddy
(semidwarf)
Sugarcane
Maize
I grain to 1 straw
Groundnut
12 25 25 IO
Table 8. Seed rate for various crops. Wheat Maize Paddy Groundnut Sugarcane
I grain 1 grain
to 2 straw to 2 straw 70 kernel to 30 husk 1.25 pods to 1.75 straw 70 kernel to 30 shell 49 oil to 51 cake 75 cane to 25 dry leaves
21.5 21.5 21.5 17.6
65-75 kg/ha 20 kg/ha 25 kg/ha 100-I 10 kg kernels/ha 70-100 q/ha
EFFECT OF MECHANIZATION
Tables l-3 indicate that the energy outputlinput ratio for a tractor-operated farm is somewhat lower than that of a bullock-operated farm, for the crop combinations investigated here. Although enough data is not available, this is likely to be true in all cases where machinery and agricultural operations account for a substantial portion of the energy input, without resulting in an equivalent increase in the output. Where the other inputs (such as seeds) are most significant, the increased yields from mechanization far outweigh the increase in energy inputs, thus providing greater returns in mechanized farming. Such a case is investigated in Table 4, where the energy output/input ratio for a tractor-operated farm is found to be higher than that for the bullock-operated farm. In these calculations, it has been assumed that the recommended amount of fertilizer is applied both on the BOFs and on mechanized farms. Since the BOFs generally have very limited resources, it is quite likely that the actual amount of fertilizer used on such farms is considerably lower than the recommended dosage. This would cause the energy output/input ratios for BOFs to be still higher. Similar studies have also been carried out for intensive cropping in some of the developed countries.” As expected from the above discussion, the energy output/input ratio in these cases is significantly lower. The effect of variation in individual inputs on the energy returns has not been thoroughly investigated. The variation in energy output with the fertilizer dosage for two crops (wheat and maize) is indicated in Figs. 1 and 2. It would, of course, be necessary to have complete knowledge of the other inpluts as well before any conclusions can be drawn regarding its effect on the energy output/input ratio. Further research in this direction is indicated for optimum utilization of agricultural inputs. CONCLUSIONS
AND RECOMMENDATIONS
is readily apparent from Tables 14 that the total energy output in all cases is far greater than the total energy input through conventional energy resources. The energy output/input ratios vary between 14 and 25.6, depending on the crop combinations, i.e. for every kilocalorie fed into the agricultural system, 14 to 25 kcal are regenerated by the system. These are available for reuse, partly as food and partly as an industrial fuel. These energy returns would be still higher if only the fossil-energy input is taken into account. In such a balance, sugarcane would provide the maximum energy return. In a total balance, the highest returns have been obtained for paddy-wheat rotations on a BOF. The energy returns for corn production on American farms have been evaluated by Pimentel et al.” Their energy output/input ratios are substantially lower than those calculated in this paper, primarily because Pimentel et al. have ignored the energy values of the byproducts. Besides, the American farms are highly mechanized and actually yield a lower energy return. In all cases, however, the energy output is far greater than the energy input. It
126
B. S. PATHAK and D.
SINGH
Analysis of the numerical values in Tables 14 indicates that roughly one third of the energy output is available as the intrinsic energy of the food produced. The remaining energy output is in the form of feed or fuel value of byproducts. If the energy released from these byproducts can be utilized efficiently, one can not only recover the entire energy fed into the agricultural system but can also generate additional amounts of energy. Systematic cropping, therefore, can provide an answer to the two major constraints faced by the developing economies today, viz. energy and food, the excess energy being harnessed from the solar radiations falling on the plants through the process of photosynthesis. The sun, today, is our prime energy source and every year it radiates roughly 8000 kW/person over India alone. This is in tremendous contrast to the present consumption of 0.1 kW/person in this country. Photosynthesis, of course, is the traditional conversion process for harnessing solar energy on a large scale. It fixes the solar radiations through a series of complex biochemical reactions into food and fossil fuels and represents the ultimate fuel source for the entire biomass. Many other forms of collectors and concentrators have also been proposed for harnessing solar energy on a large scale. Although precise data are lacking, the energy efficiencies of these gadgets are likely to be less than that of a well-organized agricultural operation. Thermodynamically, photosynthesis is an efficient system16 but kinetically it may need a fresh look. Apart from retrieval of energy, its gains are manifold-production of food, generation of pure oxygen, production of biomass for animal feed, synthesis of energy-rich fuels such as CH., and C2H50H, etc. Evidently, any energy utilization which manifests itself in regeneration or storage in such varied and useful forms should be given top priority. Therefore, in any allocation of our scarce energy resources, foremost priority should be given to the agricultural sector. REFERENCES 1. B. S. Pathak, Requirements of energy for food production and its conservation. Regional Seminar on Power
Management and Energy Conservation,.PAU, Ludhiana, 12-14, Sept. 1975. 2. A. E. Knowlton. Standard Handbook for Electrical Enaineers. 7th Edn. McGraw-Hill. New York (1957). \- , 3. R. S. Berry and’H. F. Fels, Science 182, 443 (1973). 4. S. S. Kahlon, Energy requirements in intensive agricultural production. Research Publication-S, pp. 7-18, Department of Agril Eng., Punjab Agril University, Ludhiana, 1973-74. 5. Manufacturers Literature, Either Tractors India Ltd., New Faridabad, Haryana, India. 6. Punjab Agricultural Handbook. Punjab April University, Ludhiana, 1975. 1. Anon, Chem. Engng World 10(S),74 (1975). 8. R. N. Shreve, Chemical Process Industries, 2nd Edn. McGraw-Hill, New York (1956). 9. C. 0. Dryden. An Outline of Chemical Technology. 2nd Edn. Affiliated East West Press, New Delhi. IO. D. Pimentel et al., Science 182, 443 (1973). II. G. P. Meade, Spencer Meade Cane Sugar Handbook. Wiley, New York (1%3). 12. D. M. Gates, Energy Exchange in the Biosphere. Harper and Raw, New York (1%5). 13. T. Baumeister (Ed), Marks Standard Handbook for Mechanical Engineers, 7th Edn. McGraw Hill, New York (1%7). 14. K. S. Gill and K. S. Labana, Prog. Farming 11(12),5 (1975). 15. H. Mossel and S. T. Butler. Solar Energy, p. 180.Pergamon Press, Oxford (1975). 16. Anon, Ind. Chem. Engng. 17(2), 1 (1975).
University,
Ludhiana. India
(Received 21 March 1977) Abstract-Quantitative data are presented for energy inputs and outputs for selected crops in India using either bullock-operated or tractor-operated farms. It is shown that large ratios are obtained for the energ outputs divided by the energy inputs. Preferred allocation of energy resources to the agricultural sector i recommended. INTRODUCTION
The two major constraints faced by the developing countries today are energy and food. The introduction of high yielding varieties, fertilizers and mechanization in agriculture has partially alleviated the food constraint in most of these countries. However, the energy requirements of mechanized agriculture have only accentuated the former constraint. The energy resources of most of the developing countries are very limited and highly inadequate to meet the total demand of all sectors of the economy. It is, therefore, necessary to distribute the energy resources judiciously and to establish a set of priorities for the more beneficial or necessary uses of energy. The allocation of available energy resources between the various sectors depends upon the national priorities and requirements. All the same, it is readily recognised in almost all countries that foremost priority should be given to the agricultural sector. The need to improve the standards of nutrition and the continuing increase in population resulting in a rising demand for food have further reinforced this priority. There is, however, a wide divergence of opinion as to what restrictions, if any, should be placed on energy consumptions in the agricultural sector. The question of appropriate agricultural technology is also being reviewed in the light of the energy constraint. The performance of the agricultural sector is also being evaluated from the energy-returns point of view alone. For most developing countries, such returns are found to be far higher than the energy inputs through conventional resources, implying thereby that agricultural production regenerates more energy than it consumes. Hence, it deserves the foremost priority, not only because it meets our food and raw-material requirements, but also because it represents one of the best uses of our available energy resources. CONSUMPTIVE
VS REGENERATIVE
USES
OF ENERGY
When energy is added to any system, it may either be dissipated in the form of heat or work or stored as intrinsic energy within the system,’ in accord with the laws of thermodynamics. In the former case, which may be called the “consumptive use” of energy, the energy added to a system is reduced to a form which cannot be used further. Transportation, domestic heating and cooking, etc. are examples of consumptive uses of energy. A large majority of the current uses of energy fall in this category and this energy, for all practical purposes, is lost for ever. On the other hand, most chemical uses of energy result in its storage in an intrinsic form, which remains available for further use. The car battery is a classic example of such “regenerative use”. The energy supplied during charging is stored chemically, and nearly 85% of this energy can be reused’ for lighting a lamp or starting an automobile. The energy added to a boiler furnace is stored in steam, which can be used further to run a turbine or to produce electricity. The electrical energy expanded in the hydrolysis of water is available in the form of hydrogen, a very clean fuel. Photosynthetic reduction of carbon dioxide, which results in Wean, College of Agricultural Engineering. SAssociate Professor of Chemical Engineering. 119
I20
B. S. PATHAK and D. SINGH
chemical storage of intrinsic energy in plants, forms the most significant regenerative use of energy. Photosynthesis pirates part of the solar energy available in the environment and adds it to the stored energy of the plants. The energy available from plants is thus greater than the energy supplied to them through conventional energy resources. It is this significant regeneration of energy on a large scale that forms the essential basis of modern agriculture. ENERGYREGENERATIONTHROUGHAGRICULTURE
Modern agriculture depends heavily on five major technologies: seed, mechanization, irrigation, fertilizer application and chemical control of weeds and insects. Each of these technologies has contributed substantially towards increasing the yields of major crops. Each of these also represents a substantial input of energy derived from conventional resources. A part of this energy input is stored as intrinsic energy of the plants. The remaining energy input helps in harnessing still greater amounts of solar energy for storage as the intrinsic energy of the plants. The total energy available from the plants is therefore, far greater than the energy added to them through conventional resources. Quantitative estimates of energy input versus output for various crop combinations for both bullock-operated farms (BOF) and tractor-operated farms (TOF) have been calculated and are reported in Tables l-4. These figures pertain to mechanized and traditional farming for Indian conditions, but should be reasonably representative for most developing countries. The information on energy needs and yields was borrowed from the reports of the scheme “Energy Requirements for Intensive Agril Production” and pertain to the farming areas around Ludhiana (Punjab) and Terai (U.P.). These areas have the common characteristics of high intensity of cropping, high yield levels in the context of average yields of various crops on an all-India basis, and extensive lift irrigation (tubewells). The use of inanimate sources of power (diesel engines, electric motors) is quite common, both for stationary and mobile operations on the farm. Consumption of energy per unit of area is comparatively high in these areas and the proportion of inanimate energy to animate energy would also be much higher than the average for the country. Wheat, maize, paddy, groundnut, and sugarcane are the important crops of the two areas. Information reported is for paddy-wheat, maize-wheat and groundnut-wheat rotation and for sugarcane as a single crop. This procedure takes care of the effects of one crop on the energy requirements of the successive crop for important crop combinations. The energy figures computed for these crop rotations could be considered to be representative of the diierent soil types also because the paddy-wheat combination is common for heavy soils, the maize-wheat rotation and sugarcane are commonly adopted in medium soils, and groundnutwheat rotation is most commonly followed in light soils. The yield figures have been averaged out from a wide range of data. Crop yields as function of fertilizer application are shown in Figs. 1 and 2 for maize and wheat, respectively. The energy inputs into the manufacture of machinery used for the agricultural operations Table 1. Energy balance in agriculture with crop rotation: paddy-wheat in heavy soil. See the text for assumptions and sources.
Item A. ENERGY INPUTS, kWh/ha 1. h4achinery 2. Agricultural Operations: Nursery r&ii Seedbed Sowin 8 gap 8nii Transplanting IDterCullUIC
Fertiker . . application
z HarvcslinR
Tbresbing-
Trnnsoort d Misc. Total -
Paddy BOF TOF
Wheat BOF TOF
391
639
327.5
35.5 122.1
35.5 248.2
65.1 18.9 0.7 201.8
65.1 17.7 0.6 201.8
2z
d:: 42.7 20.1 717.7
28.5
828 584.8
-
598
-
73.8 6.1
238.7 34.1
29.0
32.1 0.2 133.4 0.4 14.2 162.6 54.3 670.1
0.2 129.1 0.4 14.3 188.4 56.2 497.5
Energy
returns Table
121
in agriculture
1. (Contd.) Paddy
Item 3. Fertilizers N P,O, K?O Total 4. Seeds 5. Total 6. Total combined
Table
2. Energy
TOF
560 27.5 25 612.5 175 1763.3
560 21.5 2s 612.5 I75 2144.2 kWh/ha kcabha
input
B. ENERGY OUTPUTS I. Yield, q/ha Wheat Rice Husk Straw 2. Intrinsic energy of grains, kcal/ha 3. Fuel value of byproducts, kcal/ha: Straw Husk 4. Total energy output, kcal/ha 5. Total combined output C. RATIO Energy output/input balance
in agriculture
Wheat
BOF
BOF
TOF
560 27.5 12 599.5 490 1914.5 36778 3.2 x IO6
39.5 16.9 79
35.9 15.4 71.8
15.8 x IO6
14.4 x IO6
560 21.5 12 599.5 490 2357.6 4501.8 3.9 x 10L
25 -
2s
50
50
IO x IOh
IOX IO6
37.1 x IO” 33.3 x IO6 23.5 x IO” 23.5 x lo6 S.6x IO6 5.1 x IO’ 58.5 x IO6 52.8 x IO6 335 x lo6 92 x IO’
with
crop
rotation:
33.5 x IO6 86.3 x IO”
25.6
19.5
maize-wheat
in heavy
Maize Item A. ENERGY INPUTS. kWh/ha I. Machinery 2. Agricultural operations: Seed bed Sowing & gap filling Fertilizer application Interculture Irrigation Spraying Harvesting Thrashing Transport & Misc. Total 3. Fertilizer N PZOS KzO Total 4. Seeds 5. Total 6. Total combined
soil.
Wheat
BOF
TOF
BOF
TOF
288
425
731
916
19.0 11.8 1.9 31.9 172.2 1.2 8.8 60.0 60.5 367.9
109.1 35.5 1.7 27.5 173.8 4.6 7.8 65.0 65.4 490.3
29.8 9.0 0.2 29.0 316.1 0.4 17.6 438.7 102.0 932.9
122.7 34. I 0.2 31.2 316.1 0.4 19.7 418.1 101.3 1043.8
560 27.5 25 612.5 140 1408.4
560 27.5 25 612.5 140 1667.8 kWh/ha kcal/ha
560 21.5 12 599.5
560 21.5 12 599.5 490 3049.3 4717.1 4.1 x 10b
30 -.
30 -
30 54
Input
490 2753.4 4161.8 3.6x IO6
ENERGY OUTPUTS 1. Yield, q/ha Maize #eat Straw Corncobs 2. Intrinsic energy of grains, kcabha 3. Fuel value of byproducts straw, kcal/ha cobs, kcal/ha 4. Total energy output, kcal/ha 5. Total combined output, kcal/ha
-
-
30 54
37 74 -
37 74 -
I2 x IO6
12 x IO6
14.8 x IO6
14.8 x 10”
14.1 x IO -
14.1 x lo6 -
34.8 x IO” -
34.8 x 10” -
26.1 x IO”
26.1 x lo6
49.6~
10” 49.6 x lo6
75.7 x IO6 75.7 x lo6
RATIO Energy
output/input
21
18.5
122
B. S. PATHAK and D.
SINGH
Table 3. Energy balance in agriculture with crop rotation: groundnut-wheat. Item
BOF
TOF
800
1197 1345.6
A. ENERGY INPUTS, kWh/ha
1. Machinery 2. Agricultural operations 3. Fertilizers: N PZGS K# Total 4. Seeds 5. Total B. ENERGY OUTPUTS 1. Yields, q/ha Groundnut Kernels (70%) Shell (30%) Wheat Straw 2. Intrinsic energy of grain, kcal/ha Wheat Groundnut 3. Fuel value of byproducts, kcal/ha Straw Shells 4. Total energy output, kcal/ha C. RATIO Energy output/input
1081.5
kWh/ha kcal/ha
627.2 627.2 45.1 45.1 22 22 694.3 694.3 872 1225 3447.8 4461.9 3.0 x 10” 3.9 x 10”
14 9.8 4.2 30 80
14 9.8 4.2 30 80
I2 x IO” 12x IO” 7.4 x 10” 7.4 x IO” 37.6x IO” 37.6x IO” 14.0x IO” 14.0x IO6 71.0x IO” 71.0x 10” 23.4
18.0
Table 4. Energy balance in agriculture for sugarcane. BOF
Item A. ENERGY INPUTS, kWh/ha I. Machinery 2. Agricultural operations 3. Fertilizers(N) 4. Seed 5. Total B. ENERGY OUTPUTS 1. Yields, q/ha Sugarcane Dry leaves 2. Intrinsic energy of sugars (12.5%),k&/ha 3. Fuel value of byproducts, kcal/ha Bagasse (13%) Leaves 4. Total energy output, kcal/ha C. RATIO Energy output/input
kWh/ha kcal/ha
TOF
590 7%.6 672 9250 11308.6 9.7 x IO6
795 892.8 672 9250 11609.6 10.0x IO”
720.0 240.0 35.5x I06
1050.0 350.0 51.8x IO”
44x IO6 64x lo6 60 x 10” 87.5x IO” 139.5x 106 203.3x IO6 14.4
20.3
have been estimated from Berry and Fels’ as equivalent to 31.%x 10”kcal for 1545kg of machinery. Kahlon4 has reported an average rating of 30 hp for the tractors in this region. The average weight of a 26.5 hp tractor is 1559kgs according to Either.’ The total weight of tractor and implements was therefore assumed to be 4 tonnes. According to the data of Berry and Fels,’ this is equivalent to an energy input of 85.2 x lo6 kcal per tractor including the usual implements. If we assume an average machinery life of 10 yr at 5OOhr of use per year, the energy input into machinery, per hour of operation, is approximately 19.04~ 10’ kcal/hr or 22.2 kWh!hr of operation. On this basis, the energy inputs for various crops have been evaluated and are listed in Table 5. The net energy inputs into the rearing of bullocks have not been incorporated in these calculations but the effect on the final results is likely to be only marginal. The recommended fertilizer dosage for various crops is indicated in Table 6. The energy input into the manufacture of nitrogenous fertiliirs, as reported by Chemical Engineering
Energy
returns
in agriculture
4
Energyinput.
Energy
Ck cd x K&ha m
50
90
input,
(k co1 x 104Jho 6 3
120 --?L--T-L-2
30
60 tt
30
120
0
kg/ha
30
60
P20s,
93
30
kg/ha
60 KzO,
w
kg/ha
Fig. 1. Energy response to fertilizer application; crop: maize
5
Energy Input. (k cd x 104Vha 30 30
60 60
90 90 N, kg/ho
120 120
150 150
0
30
P2D,.
EC
90
kg/ho
Fig. 2. Energy response to fertilizer application; crop:
0
K,O,
kg/ho
wheat.
World, is estimated at 11.2kWh/kg nitrogen.’ Energy requirements for the manufacture of phosphatic fertilizers are estimated from Shreve’s’ data at 1.1 kWh/kg PzO~. The energy input into potash fertilizers has been evaluated from Dryden’s data’ (0.65 kWh/kg of muriate of potash and 1 kWh/kg of KzO). The energy inputs into fertilizers obtained on this basis are summarized in Table 6. It was assumed that both BOFs and TOFs used the recommended dose of fertilizers. Pimentel et al.” in a similar evaluation for corn production in the U.S.A., have found the energy inputs in insecticides etc. to be very small, i.e. less than a fraction of 1% of the total energy input. Consequently, these have been ignored in our analysis. The energy outputs have been estimated on the basis of yields averaged from a wide range of data. The various plant-component ratios assumed are summarized in Table 7. Sugarcane, on the basis of the analysis reported by Spencer Meade,” was assumed to have an average sugar content of 12.5% and an average fiber content of 13%. The calorific value used for wheat, maize and rice was 4000 kcal/kg,12 while for straw a heating value of 4700 kcal/kg was used.13 The intrinsic energy of seeds was assumed to be approx. 5ooOkcal/kg.” The seed rate used for various crops is given in Table 8. Groundnut sheIls and rice husk were assumed to have a heating value of 3300 kcal/kg.13 Dry leaves were assumed to have a heating value of only 2500 kcalfkg. The intrinsic energy of kernel was assumed to be equivalent to the sum of the intrinsic energy of oil contained therein, evaluated” at 100,000kcal/kg, and the remaining cake evaluated at 5000 kcal/kg.‘6 The intrinsic energy of sugarcane was evaluated as the sum of the intrinsic energy of sugars contained therein (3940 kcal/kg)‘6 and the heating value of the fibrous material (4700 kcal/kg).13 The total energy outputs are summarized in Tables l-4. In all cases, the total energy output is greater than the total energy input. ENERGY Vol !. No z--8
B. S. PATHAK and D. SINGH
Energy returns in agriculture
Table 6. Energy inputs in fertilizers for various crops. Fertilizer recommended, kg/ha N GO P203
Crops Wheat
50
Sugarcane Maize Paddy Groundnut
60 50 50 6
25 25 25 I6
12 u 25 IO
Energy input, kWh/ha N PzOs RP 560 672 560 560 61.2
Table 7. Plant-component ratios. Wheat
(semidwarf)
Paddy
(semidwarf)
Sugarcane
Maize
I grain to 1 straw
Groundnut
12 25 25 IO
Table 8. Seed rate for various crops. Wheat Maize Paddy Groundnut Sugarcane
I grain 1 grain
to 2 straw to 2 straw 70 kernel to 30 husk 1.25 pods to 1.75 straw 70 kernel to 30 shell 49 oil to 51 cake 75 cane to 25 dry leaves
21.5 21.5 21.5 17.6
65-75 kg/ha 20 kg/ha 25 kg/ha 100-I 10 kg kernels/ha 70-100 q/ha
EFFECT OF MECHANIZATION
Tables l-3 indicate that the energy outputlinput ratio for a tractor-operated farm is somewhat lower than that of a bullock-operated farm, for the crop combinations investigated here. Although enough data is not available, this is likely to be true in all cases where machinery and agricultural operations account for a substantial portion of the energy input, without resulting in an equivalent increase in the output. Where the other inputs (such as seeds) are most significant, the increased yields from mechanization far outweigh the increase in energy inputs, thus providing greater returns in mechanized farming. Such a case is investigated in Table 4, where the energy output/input ratio for a tractor-operated farm is found to be higher than that for the bullock-operated farm. In these calculations, it has been assumed that the recommended amount of fertilizer is applied both on the BOFs and on mechanized farms. Since the BOFs generally have very limited resources, it is quite likely that the actual amount of fertilizer used on such farms is considerably lower than the recommended dosage. This would cause the energy output/input ratios for BOFs to be still higher. Similar studies have also been carried out for intensive cropping in some of the developed countries.” As expected from the above discussion, the energy output/input ratio in these cases is significantly lower. The effect of variation in individual inputs on the energy returns has not been thoroughly investigated. The variation in energy output with the fertilizer dosage for two crops (wheat and maize) is indicated in Figs. 1 and 2. It would, of course, be necessary to have complete knowledge of the other inpluts as well before any conclusions can be drawn regarding its effect on the energy output/input ratio. Further research in this direction is indicated for optimum utilization of agricultural inputs. CONCLUSIONS
AND RECOMMENDATIONS
is readily apparent from Tables 14 that the total energy output in all cases is far greater than the total energy input through conventional energy resources. The energy output/input ratios vary between 14 and 25.6, depending on the crop combinations, i.e. for every kilocalorie fed into the agricultural system, 14 to 25 kcal are regenerated by the system. These are available for reuse, partly as food and partly as an industrial fuel. These energy returns would be still higher if only the fossil-energy input is taken into account. In such a balance, sugarcane would provide the maximum energy return. In a total balance, the highest returns have been obtained for paddy-wheat rotations on a BOF. The energy returns for corn production on American farms have been evaluated by Pimentel et al.” Their energy output/input ratios are substantially lower than those calculated in this paper, primarily because Pimentel et al. have ignored the energy values of the byproducts. Besides, the American farms are highly mechanized and actually yield a lower energy return. In all cases, however, the energy output is far greater than the energy input. It
126
B. S. PATHAK and D.
SINGH
Analysis of the numerical values in Tables 14 indicates that roughly one third of the energy output is available as the intrinsic energy of the food produced. The remaining energy output is in the form of feed or fuel value of byproducts. If the energy released from these byproducts can be utilized efficiently, one can not only recover the entire energy fed into the agricultural system but can also generate additional amounts of energy. Systematic cropping, therefore, can provide an answer to the two major constraints faced by the developing economies today, viz. energy and food, the excess energy being harnessed from the solar radiations falling on the plants through the process of photosynthesis. The sun, today, is our prime energy source and every year it radiates roughly 8000 kW/person over India alone. This is in tremendous contrast to the present consumption of 0.1 kW/person in this country. Photosynthesis, of course, is the traditional conversion process for harnessing solar energy on a large scale. It fixes the solar radiations through a series of complex biochemical reactions into food and fossil fuels and represents the ultimate fuel source for the entire biomass. Many other forms of collectors and concentrators have also been proposed for harnessing solar energy on a large scale. Although precise data are lacking, the energy efficiencies of these gadgets are likely to be less than that of a well-organized agricultural operation. Thermodynamically, photosynthesis is an efficient system16 but kinetically it may need a fresh look. Apart from retrieval of energy, its gains are manifold-production of food, generation of pure oxygen, production of biomass for animal feed, synthesis of energy-rich fuels such as CH., and C2H50H, etc. Evidently, any energy utilization which manifests itself in regeneration or storage in such varied and useful forms should be given top priority. Therefore, in any allocation of our scarce energy resources, foremost priority should be given to the agricultural sector. REFERENCES 1. B. S. Pathak, Requirements of energy for food production and its conservation. Regional Seminar on Power
Management and Energy Conservation,.PAU, Ludhiana, 12-14, Sept. 1975. 2. A. E. Knowlton. Standard Handbook for Electrical Enaineers. 7th Edn. McGraw-Hill. New York (1957). \- , 3. R. S. Berry and’H. F. Fels, Science 182, 443 (1973). 4. S. S. Kahlon, Energy requirements in intensive agricultural production. Research Publication-S, pp. 7-18, Department of Agril Eng., Punjab Agril University, Ludhiana, 1973-74. 5. Manufacturers Literature, Either Tractors India Ltd., New Faridabad, Haryana, India. 6. Punjab Agricultural Handbook. Punjab April University, Ludhiana, 1975. 1. Anon, Chem. Engng World 10(S),74 (1975). 8. R. N. Shreve, Chemical Process Industries, 2nd Edn. McGraw-Hill, New York (1956). 9. C. 0. Dryden. An Outline of Chemical Technology. 2nd Edn. Affiliated East West Press, New Delhi. IO. D. Pimentel et al., Science 182, 443 (1973). II. G. P. Meade, Spencer Meade Cane Sugar Handbook. Wiley, New York (1%3). 12. D. M. Gates, Energy Exchange in the Biosphere. Harper and Raw, New York (1%5). 13. T. Baumeister (Ed), Marks Standard Handbook for Mechanical Engineers, 7th Edn. McGraw Hill, New York (1%7). 14. K. S. Gill and K. S. Labana, Prog. Farming 11(12),5 (1975). 15. H. Mossel and S. T. Butler. Solar Energy, p. 180.Pergamon Press, Oxford (1975). 16. Anon, Ind. Chem. Engng. 17(2), 1 (1975).