Energy usage in British agriculture—A review of future prospects

Energy usage in British agriculture—A review of future prospects

AgrwulturatS),~tem.~ 5 (1980) 51 70 E N E R G Y U S A G E IN BRITISH A G R I C U L T U R E - - A REVIEW OF F U T U R E PROSPECTS P. N. WILSOY & T. D...

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AgrwulturatS),~tem.~ 5 (1980) 51 70

E N E R G Y U S A G E IN BRITISH A G R I C U L T U R E - - A REVIEW OF F U T U R E PROSPECTS

P. N. WILSOY & T. D. A. BRIGSTOCKE

BOCM Silcock Ltd, Basing View, Basingstoke, Hants RG21 2EQ, Great Britain

S UMMA R Y The sudden increase in theprice of oil in 1973/74 drew attention to the fact that energy resources are not inexhaustible. Since then Jossil fuel consumption has risen and is currently close to the 1973 peak level. While agriculture has become technologically more efficient, it has become less efficient in its use of energy during the last fi'w decades. Agricultural production up to the farm gate utilises less than 4 % of national power energy consumption while it provides over 55 ~o of the nation's unprocessed food. However, when the total foodprocessing part of this o'cle is taken into account nearly 16 ~,,, of total national energy consumption is used in the overall production and preparation o f f ood. When the b iological and industrial energetics are considered, it is apparent that intensive agricultural production has both a low biological efficien O' and a comparatively high usage of energy, apart from ruminant meat production under natural grazing conditions. What is needed is a planned use of resources coupled with a reduction in energy inputs without significantly depressing the high current levels of agricultural productivity. The possibility of achieving this objective is discussed. Reference is made to an earlier review by the same authors in which three potentially difJerent sources oJ energy--straw, livestock wastes jor use as Jertilisers and livestock wastes for the production o[" methane--were examined. This paper discusses in detail glasshouse heating, power station waste heat utilisation and the possible exploitation of wind power. The paper concludes that the future for energy usage in agriculture is full of interesting possibilities requiring continuing R&D inputs. Nevertheless, investment in new energy forms must come from government sources, because of the high capital costs and attendant risks. 51 AgriculturalSystems 0308-52 IX/80/0005-0051/$02.25 © Applied Science Publishers Ltd, England, 1980 Printed in Great Britain

52

P.N.

WILSON,

T. D . A. B R I G S T O C K E

INTRODUCTION

The sudden increase in the price of oil in 1973-74 drew attention to the fact that energy resources, particularly fossil fuels, are not inexhaustible. However, in m a n y ways the energy situation is still as critical as it was in 1973 74 and it is vital that intensive efforts are made at conserving this resource. As a D e p a r t m e n t of Energy Consultative Green Paper (1978) stated, d e m a n d for oil has returned close to the pre-1973 level. The governments o f energy consuming countries now regard imported oil as the buffer source of energy to the e c o n o m y in the sense that it fills the gap between national d e m a n d and indigenous supply. TABLE 1 ESTIMATED LIFE IN YEARS OF WORLD FUEL RESERVES RELATED TO PROJECTED CONSUMPTION RATES FOR THE YEARS GIVEN

Fuel

1975

1980

1985

1990

Coal Oil Gas Uranium (thermal reactors) Uranium (breeder reactors)

698 48 31 14

535 31 20 6

409 19 Il

301 l0 4

523

399

304

230

Source: Bowman (1975). M a n y analyses have been made of the extent o f the world fuel reserves and how long they will last at projected rates o f consumption. In Table 1, it is assumed that each fuel is used exclusively and that 'support' energy (support energy = energy other than that derived directly f r o m solar radiation) d e m a n d will increase at 5.3 ~o per a n n u m , so that by 1990 only coal reserves will remain in any significant a m o u n t (Bowman, 1975). The situation is similar in the U K . Over the 20 years preceding the energy crisis in 1973, primary energy c o n s u m p t i o n in the U K increased at an average rate o f nearly 2 ~ (White, 1977). Table 2 presents an estimate of the U K indigenous TABLE 2 ESTIMATES OF THE UK INDIGENOU~SENERGY RESOURCES (1976)

Resource

Coal Oil Natural gas Uranium

Estimated recoverable reserves Unit given Coal equivalent (G t)

45 Gt 3 4-5 Gt (1.6-1.8) x 103 km 3 --

45 4.5-6.7 2.2-2.6 20

Consumption per annum in 1973

Estimated life (years)

134 Mt 95 Mt 39.7 kmat --

336 32-47 39-46 100-200

# Given by Gray (19"76)as 'current consumption'. Sources: Department of Energy (1976); Digest of UK Energy Statistics (1974); White (1977).

ENERGY USAGE IN BRITISH A G R I C U L T U R E - - F U T U R E PROSPECTS

53

TABLE 3 NATIONAL ENERGY CONSUMPTION IN THE UK (1973)

Resource

Consumption

Energy equiealent PJ t

'~o of total energy

134 Mt 95 Mt 28.3 km 3

3500 4300 1170 240 50

37.8 46.5 12.6 2.6 0-5

9260

100-0

Coal Petroleum Natural gas Nuclear-electricity Hydro-electricity Total t PJ = peta joule = 1015 J. Sources: JCO (1974); White (1977).

energy resources. It will be noted that by the end of the 1980s production of North Sea oil and gas will have peaked. Estimate-s for coal and uranium production indicate that these sources could meet an increasing proportion of energy needs. However, the amount of energy derived from nuclear- and hydro-electricity is insignificant at present (White, 1975), as is shown in Table 3. Thus it is essential that each industry should reconsider its dependence on energy consumption. This will become increasingly difficult as more complex industrial technology is involved (Wilson & Brigstocke, 1977). Indeed it has been argued (Kenward, 1976) that the key to safeguarding future supplies is to create a sensible "portfolio' of energy research and development so as to obtain the maximum future flexibility. Whatever the outcome, it is evident that at present a high energy use correlates with a high gross national product (Cook, 1971).

HISTORICAL REVIEW

The ! 950s and 1960s were the decades of cheap and assured fuel supplies, when oil cost some 1-5 US dollars per barrel, equivalent to having one human 'energy slave' working for 4000 hours for a US dollar (4000 M J/dollar) (Leach, 1976). Thus it was understandable that agricultural strategies stressed the need to increase yield and reduce manpower, by increasing fertiliser usage and more intensive use of machinery (Wilson & Brigstocke, 1977). Indeed during the period 1956-70, fertiliser inputs increased dramatically. The use of nitrogen increased 2½ times, phosphate by one third and potash by one third (Cooke, 1971). During a similar period, White (1976a) noted that increased fertiliser usage produced increasing yields and outputs of metabolisable energy. It is also interesting that until 1950 the number of horses exceeded the number of tractors, and it was not until 1962 that the latter began to exceed the number of fulltime agricultural workers (MAFF, 1968). In this respect, Stansfield et al. (1974)

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P. N. WILSON, T. D. A. BRIGSTOCKE

dismissed the idea of re-introducing draught animals, noting that when the horse provided motive power in British agriculture one tenth of the total farm acreage was used to feed them. Table 4 sets out in historical perspective the energetics of corn production (Osbourn, 1976). It is instructive to compare a corn area cultivated with the use of mechanisation with an area of similar size cultivated by hand, in terms of the number of men theoretically sustained per hectare. TABLE 4 A HISTORICALPERSPECTIVEOF THE ENERGET1CSOF CORN PRODUCTION

One man and his hoe

Area cultivated (ha) Annual grain yield (t/ha) Total annual output of grain tonnes per man MJ x 103 Total annual input (MJ x 103) food for man and animals b fossil fuels Surplus food MJ x 103 man years Ratio MJ output/MJ input No. men sustained with food/ha

System o f corn production One man One man and and his tractor two horses in USA 1970"

0.5 2

10 2

40 5

1-0 16-6

20 332

203 3378

4.5

134

4.5 1198 3373 749 2.82 18-7

12.1 2-7 3-68 7-4

198 44 2.48 4.5

aData from Pimentel et al. (1973). bData from Brody (1945). Source: Osbourn (1976).

It follows that, while agriculture has become more efficient technologically, it has become less efficient in its use of energy. Indeed Black (1971) has pointed out that modern methods of agriculture, which may appear much more productive than primitive methods, are probably very similar in terms of the efficiency with which the total energy resources are used. Therefore it is desirable that the partition of energy usage is investigated to discover the degree of energy-dependence of different systems of agriculture, and how this dependence can be sensibly reduced without adversely affecting food output (Wilson & Brigstocke, 1977). It should, however, be noted that this paper does not attempt to discuss in detail food processing, packaging and distribution, or domestic consumption of energy for food preparation in the home. APPRAISAL OF ENERGY USAGE IN AGRICULTURE I f t h e e n e r g y u s e d in a g r i c u l t u r e is c o m p a r e d w i t h t h e o t h e r m a j o r e n e r g y d e m a n d s in the U K , the d a t a indicate that agriculture has a relatively low energy requirement.

ENERGY USAGE IN BRITISH AGRICULTURE--FUTURE PROSPECTS

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TABLE 5 USE OF PETROLEUM FUELS IN UK INDUSTRIES

1973

Sector

Energy equit'alent ( 1 0 9 M J)

Energy (°/o)

75 218 2325 375 1179 128

1-7 5.1 54.1 8-7 27-4 3-0

4300

100-0

Agriculture Steel Transport and other industries Domestic Electricity, oil and gas Miscellaneous Total Source: JCO (1974).

Table 5 shows the distribution of usage of petrol fuels in the UK in 1973 and illustrates agriculture's relatively small support energy demand. This is also true of electricity consumption on farms since some of the electricity included in this category will be used for domestic purposes. Indeed it is likely that, of an agricultural electricity consumption of 14.2 x 109 MJ, only 8.4 x 109 MJ is actually used for specific agricultural purposes (JCO, 1974). A break-down of the components of power energy input into agriculture in 1973 is given in Table 6. It is interesting to note that the total energy required to produce our national requirements for fertiliser is about the same as the energy used.on farms as oil, and that the energy required to produce machinery and feed exceeds that used directly as on-farm electricity. The most important users of petroleum-type fuels within the TABLE 6 PRIMARY ENERGY CONSUMED IN UK AGRICULTURE

(1973)

Solid fuel Petroleum Electricity Fertiliser Machinery Feedstuff processing (off-farm) Chemicals Buildings Transport, services Miscellaneous Total Source: White (1977).

P J

~ of total

4.1 85.0 33.1 83.5 52.0 51- 3

1.1 23.6 9.2 23.1 14.4 14.2

8.5 22.8 16.3 4-3

2.4 6.3 4-5 1-2

360.9

100.0

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P. N. WILSON, T. D. A. BRIGSTOCKE

TABLE 7 USE OF PETROLEUMFUELS IN AGRICULTUREIN THE UK MAY TO JUNE 1972-73

Consumption (kt) Tractors and self-powered machines Vehicles, lorries, vans and cars Glasshouse heating Heating, drying and lighting Total

Energyequivalent (PJ)

~ of total energy

925 293 496 198

42-1 13.7 21-8 9.1

48-5 15.8 25-2 10.5

1912

86.7

100.0

Source: J C O (1974).

agricultural sector are tractors and self-powered machines, accounting for roughly 50 ~ of consumption, with glasshouse heating using a further 25 ~o (Table 7). It is important to place the total energy consumption of the agricultural sector in perspective. Agriculture utilises less than 4 ~ of national power energy consumption while it provides over 55 ~o of the nation's unprocessed food (White, 1977). The agricultural industry, therefore, has a good claim on valuable energy resources even if these should become yet scarcer. However, when the food processing part of this cycle is taken into account the situation appears very different. Several estimates (e.g. Gifford & Millington, 1973; Hirst, 1974) have also been made of the total consumption of energy involved in the overall food production and processing system. Table 8 compares energy consumption in the production and preparation of food as a percentage of total national energy consumption in three countries. There is surprising similarity between the UK, Australia and the USA and it will be noticed that agriculture requires less support energy input up to the farm gate than that required in the processing, distribution and preparation of food. TABLE 8 PRIMARY ENERGY CONSUMPTION IN THE PRODUCTION AND PREPARATION OF FOOD AS PERCENTAGES OF TOTAL NATIONAL ENERGY CONSUMPTION

Energy consumption in Agriculture, fishing# (to farm gate) Food processing and distribution Food preparation (domestic)

UK (White, 1977)

% of total national consumption Australia USA (Gifford, 1973) (ASAE, 1974)

3.9

2-1

2.2 2-7

7.0

5-8

6.2 7-8

4.9

7.1

3.6-4.5

15.8

15.0

12.0-15.0

t White (1977) does not include any allowance for fishing.

ENERGY USAGE IN BRITISH A G R I C U L T U R E - - F U T U R E PROSPECTS

57

Jacques & Blaxter (1978) assessed the support energy required to produce meat food products. Their investigation estimated the support energy required to transport live animals from farm to abattoir, to slaughter, process and package them and to deliver the final products to the retailer. They concluded that when the relationship between the support energy input and food energy output was evaluated, values of 7 and 9 J/J were found for pigs and cattle respectively. These compared with values for processed cereals and root vegetables, which ranged from 3 to 5 J of input/J of human food. The effect of the increase in energy prices on food production costs has been to increase farm gate food prices by 20 ~ in real terms and by more if one counts indirect inflationary effects (Leach, 1976). As Odum (1971) said some years ago of American intensive farming, 'We do not eat food, we consume oil!'.

THE ENERGETICS OF AGRICULTURE

Although all energy sources are basically solar in origin, the fossil fuels--coal, petroleum and natural gas--represent forms of long-term energy storage whilst the photosynthates of the plant kingdom are forms of short-term energy storage (Wilson, 1976). The quantity of incoming solar energy 'captured' by plants represents only some 1-2 ~o of the incident solar radiation falling on the land area they occupy (Cooper, 1970). Indeed the daily photosynthetic productivity for a specific geographical location depends upon the crop surface, available latitude, season and sky conditions (Monteith, 1972). Of the amount recovered in harvested crops, only part provides edible food for man. Many crops, especially grass, are fed to farm livestock so that the actual 'farm gate' output of food for human consumption of all crops is only 11% of the energy originally recovered in the harvested plant material, while 70~o of the primary output, including grass, is destined for animal feed. The efficiency with which livestock convert this feed into edible products is relatively low (Holmes, 1970). Part of the reason for this low efficiency is that ruminant animals consume herbage, and other cellulosic materials, which are not efficiently digested. In addition, ruminants are able to graze remote areas unsuitable for crop production due to topography, climate, etc. Furthermore, extensive ranching systems consume very little support energy and may therefore be considered energetically efficient. Several authors have adopted a positive approach to evaluating ruminants as producers of human food (Blaxter, 1975; Pimentel et al., 1975; Wedin et al., 1975). Bartlett & Clawson (1978) were less optimistic and noted the difficulties facing meat production from ranching and the considerable difficulties in achieving an optimal balance between maximising red meat production, minimising the use of fossil fuel based energy and maximising profit. Osbourn (1976) has stated that the grass crop compares favourably with root and

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P. N. WILSON, T. D. A. BRIGSTOCKE TABLE 9 ESTIMATES OF AGRICULTURALUSE OF SUPPORT ENERGY

1 Commodity or product

2 Energy input or support energy G J/ha yr

Wheat Barley Potatoes Carrots Brussels sprouts Tomatoes (glasshouse) Milk Beef (from beef herd) Pigs (pork and bacon) Sheep (lamb and mutton) Poultry (eggs) Poultry (broilers)

19.6 18.1 52.0 25.1 32.4 1300.0 17.0 10.6 18.0 10.1 22.5 29.4

3 Energy output or ME G J/ha yr

4 E= Co/. 3/ Col. 2

5 Protein output kg/ha yr

6 Energy input to produce protein MJ/kg

61.0 60.6 69-3 32-5 10.9 62-0 12.0 2.4 11.4 2.5 6.0 4.3

3.11 3.36 1.33 1.30 0.34 0.05 0.70 0.23 0.63 0.25 0-26 0.15

435 310 460 234 296 945 145 31 76 22 113 145

45 58 113 107 109 1360 118 348 238 465 200 203

Source: White (1975).

grain crops in terms of energy and protein yield per unit of support energy input. However, a change of crop may require a change of animal. Beef cattle fed on whole maize silage are energetically far less efficient than broilers fed on maize grain (Greenhalgh, 1976) and clearly neither pigs nor chickens produce very efficiently when grazing grass alone. Table 9 presents data for the energetic efficiencies of the production of some temperate-region agricultural products up to the farm gate. Table 10 reveals a different picture when the efficiency of support energy use in less

T A B L E l0 EFFICIENCY OF SUPPORTENERGY USE IN LESSDEVELOPED AGRICULTURALSYSTEMS

Product Upland rice Sweet potatoes Cowpeas Sugarcane Sweet potatoes Rice Dryland rice Maize Cassava Banana t E ratio =

Location Gambia Zambia Zambia Mauritius African rain forest Fiji Sarawak Zambia Fiji Fiji

Gross energy in food end-product

Energy input Source: Spedding & Walsingham (1975).

E ratiot 3 4-9 9 l1 16 20 34 40 71 130

ENERGY USAGE IN BRITISH AGRICULTURE--FUTURE PROSPECTS

59

developed tropical agricultural systems is quantified. The very favourable efficiency ratios achieved with cassava, maize and bananas should be particularly noted. This paper does not examine energy flows in agricultural production systems. Work by Slesser (1973), Leach (1974, 1976) and White (1975) should be studied for details of the evaluation of energy accounting methodology. However Table 11 shows that the overall energy conversion (E) ratio for British agriculture is 0.4 (White, 1976a). Other authors, such as Leach (1974) and Blaxter (1974, 1975) have TABLE 11 OVERALL ENERGY BUDGET FOR UK AGRICULTURE UP TO THE FARM (;ATE ( P J PER ANNUM)

Input or energy subsic(v

Solid fuels Petroleum Electricity Fertilisers Machinery Feedstuff processing (off-farm) Chemicals Buildings Transport distribution and services Miscellaneous Imported feedstuffs

Total

Output or energy available to man

4. I 85.0 33.1 83.5 52.0 51.3 8.5 22.8 16.3 4.3 53.2

Cereals Potatoes Sugar beet

56-8 13.0 14.6 Arable crops

Vegetables Fruit Milk Beef Pigs (pork and bacon) Sheep (lamb and mutton) Poultry (eggs) Poultry (chicken) Poultry (turkey)

2.4 Horticulture 0.8 38.0 13.8

4.5 4.5 1.9 0.6 Livestock 168.2

Output energy

168.2

Input energy

414-1

3.2

17.3

414-1 E=

84.4

80.6 168.2

-0.4

Source: White (1976a).

suggested similar figures. In order to obtain the energy consumed in the 50 ~o of unprocessed food that is produced in the UK, an energy input is required which is 2½ times as great. This input is in the form of fossil fuels and imported feedstuffs (White, 1976a). Besides regarding agriculture as a biological process of solar energy conversion, farming can also be considered as an industry consuming raw materials brought to the farm. The direct consumption of energy and fossil fuels on farms, including contributions from mining, refining and electricity, accounts for 43 ~o of the energy input. Fertilisers and lime account for 38 ~o and the next largest item is the energy cost of maintaining machinery on farms (Blaxter, 1975). Thus taken together the biological and industrial energetics illustrate both a low biological efficiency and a comparatively high usage of energy, apart from

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WILSON, T. D. A. BRIGSTOCKE

ruminants grazing natural grassland. Although British agriculture is technically and economically very efficient, it is energetically inefficient. The major factor for the low biological and land use efficiency of the UK food system is the high proportion of food production in the form of animal meat, especially pig and poultry products. It has been estimated (MAFF, 1974) that of all the farm land in the UK only 8 ~o provides food directly for man. The remaining 92 ~ is devoted directly or indirectly to feeding livestock, which also consume about 7 Mt of imported feedstuffs per year (Leach, 1976; White, 1976b). Even if one excludes rough grazing, the proportion of land used directly for human food rises only to 13 ~ (Leach, 1976). Theoretically the biological efficiency could be increased by a reduction in the relative size of the animal sector. In recent years several studies have been made of the comparative efficiencies of animal and crop production, and work by Spedding (1973) and Holmes (1970, 1975) should be consulted. Furthermore it is known that more people could be fed in the UK if fewer resources were devoted to animal production (Duckham, 1974; Mellanby, 1975). However animal production systems can be well justified as they provide high-quality food demanded by man and they also utilise parts of plants and waste plant products which man cannot eat. Thus what is needed is a planned use of resources coupled with a reduction in energy inputs without significantly depressing current levels of agricultural production. A saving in energy can be accomplished by either economising on the energetics of present production methods or by producing fuels and power from organic materials on the farm or other natural sources of energy and thus reducing total support energy consumption (Wilson & Brigstocke, 1977). THE FUTURE

The prospect of achieving a greater utilisation of solar energy is currently a topic of much debate. One report (Department of Energy, 1977) has stated that solar energy could contribute about 2 ~ of present national requirements within the next 25 years. Any exploitation of this source of energy must be by interception and conversion of part of the existing total radiation before it is dissipated. There are wide seasonal variations in the monthly mean daily energy flux with average daily totals varying from about 16 MJ/m 2 in summer to 2 MJ/m 2 in winter for the southern UK. Indeed the total energy received by the horizontal surface of the UK in a year is about 3500 MJ/m 2, whilst the corresponding figure for a country such as Australia is about 6500 MJ/m 2 (Brinkworth, 1976). Alternative energy sources, such as wind and tidal power, might be used with solar energy to supplement traditional forms of power in the foreseeable future (Wilson & Brigstocke, 1977). In agriculture, there is a need to increase the photosynthetic efficiency of plants. The efficiency of solar energy conversion by crops will depend on such agronomic factors as plant spacing, cell structure, temperature and the availability of water and nutrients, which may affect the photosynthetic process.

ENERGY USAGE IN BRITISH AGRICULTURE--F U TU R E PROSPECTS

61

On a practical note the Built Environment Research Group (1977) produced a report giving details of receptacles for storing collected solar energy. Bailey (1976) noted the possibility of using solar energy to meet glasshouse heat demand. Various methods are proposed such as solar flat plate or concentrating collectors, or solar ponds using a heat exchange mechanism. Much interesting work has already been conducted in the USA. Studies have included the solar heating of water for glasshouse heating and crop drying (e.g. Tabor, 1963; Bauman et al., 1975; Short et al., 1976: Vaughan, et al., 1976). The problem in the U K is that only 42 o / o f the total solar radiation is direct so that, at present fuel prices, solar heating is not cost effective. To become economic, costs must decrease to one third of the present level (Bailey, 1976). Nevertheless Brinkworth (1976) noted that 505o of incident solar energy could be collected at 55 °C for British summer conditions. The technology of extracting and using geothermal energy already exists and is in widespread use in certain parts of the world (Armstead, 1977; Barbier & Fanelli, 1977). The problem is to assess how this overseas experience can be exploited in the UK. The difficulty is the cost of an operation to exploit such resources and it is unwise to extrapolate from overseas results to British conditions (Garnish, 1978). In an earlier paper, Garnish (1976) calculated the heat content of the earth's crust at all depths within the reach of drilling technology (8 10 km). This heat content exceeds 1018 J/kin in the UK. How much, if any, of this resource will ever be exploited in the UK is dependent upon the final cost of the energy which could be available to users relative to that from other energy sources (Garnish, 1978). Nevertheless the Energy Technology Support Unit intend to carry out a survey to assess the possible market for geothermal energy in agricultural and horticultural industries (Fuller, personal communication, 1978). In the UK, population densities are relatively high so the potential land area for agricultural fuel production is limited. If the entire land surface of the U K was to grow crops for fuel with a photosynthetic efficiency as high as 1 "~/o,and with the utilisation of all crop energy as fuel, then the UK could probably provide all its energy requirement by this method (Leach, 1976). Using a different approach, Blaxter (1978) noted that if every acre of crop and grassland in the U K was used for biological fermentation it would only meet 8 ~o of the country's primary fuel supply need. Such a novel system of agriculture would allow no space for food production, but it has been argued (Department of Energy, 1976) that there is much marginal land not suitable for agriculture that could be used for growing fuel crops. Graham (1975) suggested that in the USA some crops may be grown which can serve the dual function of being food sources as well as a source of cellulose for converting into hydrocarbon fuels by fermentation, pyrolysis or hydrogenation. His calculations would appear to be highly optimistic for U K production conditions. Afforestation for this purpose is a possibility and White (1977) has calculated that evergreen forests can have a dry matter yield of 22 t/ha per annum. This yield could be raised in the Tropics where a crop such as Napier grass (Pennisetumpurpureum) can produce

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WILSON, T. D. A. BRIGSTOCKE

85 t D M / h a per annum with a photosynthetic efficiency of 2-4 ~ . Table 12 presents data for selected carbohydrate production rates by plants and illustrates the very high productivity of Spartina grass and U K pine forests (Heslop-Harrison, 1975). Vlitos (1978) has drawn attention to the potential of Leucaena as a rapidly growing tree for use as fuel. This tree crop could be harvested within 3 to 5 years after planting.

T A B L E 12 CARBOHYDRATEPRODUCTION BY PLANTS

Crop

Annual CHO production (g/m 2)

Wheat Hay Sugar beet Sugar cane Potatoes Spartina grass U K pine forest Deciduous wood US prairie Nevada desert Seaweed beds

344 497 1470 3430 845 3300 3180 1560 446 40 358

After Heslop-Harrison (1975).

Another interesting possibility has been suggested by Chapman (1973) who argued that in the USA 'chemical farming' ought to be discontinued. This would results in a much reduced yield, necessitating much of the soil bank in the USA being brought back into production, but it would be more energetically efficient. An earlier review (Wilson & Brigstocke, 1977) evaluated three potential sources of energy--straw, livestock wastes for fertilisers, and the production of methane. It has been estimated (JCO, 1974) that the energy input to U K agriculture could be reduced by 4 0 ~ from the 1972 levels if all these wastes were used efficiently. Nevertheless there are many other sources of energy conservation which are pertinent and these are discussed in the following sections.

GLASSHOUSE HEATING

Glasshouse heating accounts for 25 ~o of the petroleum fuels used in agriculture and is the sector hardest hit by rising fuel prices, because heating costs form such a large proportion of the total costs of glasshouse crop production. Stansfield et al. (1974) estimated that the annual fuel consumption of glasshouses in the U K was 0.8 Mr, more than one third of the agricultural total. To give an example, for a crop such as

ENERGY USAGE IN BRITISH AGRICULTURE--FUTURE PROSPECTS

63

early tomatoes, fuel and power account for 40 ~ of the production costs (Sheard, 1976). The problem for the engineer or physicist seeking ways to conserve energy in the greenhouse is that the structure is primarily designed for maximum light transmission. As a direct result the structure is very inefficient for the conservation of energy, but it is difficult to devise improvements which are not counter-productive through reduction of light transmission (Bailey et al., 1976). The use of insulating blinds during the night, to reduce heat losses without affecting light transmission and hence yields, is being developed. Such a thermal screen reduces the heat transferred to the glasshouse roof by convection, the transfer of latent heat and radiation. Table 13 shows the percentage reduction in thermal transmittance obtained with screens of various materials at a given wind speed. An apportionment TABLE 13 REDUCTIONIN THERMALTRANSMITTANCEOBTAINEDWITHSCREENSATGIVENWIND SPEED (~/o)

Cover material 0 Black polyethylene Clear polyethylene Aircap C Silver Polyto Aluminised polyester

32 33 34 28 43

Wind speeds (re~s) 2 4 37 41 42 40 50

41 46 47 47 56

44 50 51 53 60

Source: Bailey et al. (1976).

of heat transfer in a heated, unventilated house has been calculated by Morris & Winspear (1967). Of the total heat transfer from crop zone to glass cladding, 42 ~o was by convection, with radiation and evapo-transpiration accounting for 33 ~o and 25 ~o respectively. However there are still questions to be answered about the effect of shadow caused by the screen when withdrawn during the day and about the effect of the screen on relative humidity and thus on the incidence of fungal diseases (Winspear et al., 1970). The Building Research Establishment (1975) has evaluated a discounted cashflow method to assess cost-effectiveness and to make a comparison with competing investments. Using this procedure, Winspear (1976) has shown that thermal screens give an internal rate of return of 42 ~o. Indeed such a screen made of aluminised polyester gave an average reduction in the heat loss of 55 ~o, which is equivalent to a 38-44 ~o reduction in annual fuel consumption (Bailey, 1975; Winspear, 1976). Inflated plastic houses with good insulation and light transmission properties are reportedly able to reduce fuel consumption by 20 ~o under typical UK night-time conditions (Leach, 1976). Good environmental control by means of accurate instrumentation can have a markedly beneficial effect; thus the maintenance of

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temperature only l°C nearer to the optimum can result in a saving of oil consumption of about 60t/ha per year (JCO, 1974).

WASTE HEAT UTILISATION

There is the possibility of building glasshouses close to power stations, so that the waste heat from the latter could provide much of the required heat and save up to 6 ~o of the total input to UK agriculture. Within the CEGB, fish farming in warm water from power stations has been successfully conducted on an experimental basis (Aston & Brown, 1974). Eels (Anguilla anguilla L) maintained in warm condenser water (mean temperature 25.5 °C) grew more rapidly than eels in water from cooling tower ponds (mean temperature 18-8°C) and river water (mean temperature 15.5°C). Other workers have studied the practical aspects of horticultural use of reject heat (Gillham et al., 1974; Leggeat, 1974). The former authors, however, noted that there are considerable difficulties in utilising the waste heat to maximise crop yields at a commercially acceptable price. Experiments at Eggborough Power Station in Yorkshire (Statham, 1975; Masterson, 1976; Owens, 1976) have evaluated the problem. Statham (1975), in a preliminary survey, noted that although the utilisation of reject heat gave comparable results with conventional greenhouse practice, no single heating scheme could be considered outstanding in comparison with the other systems. Glasshouse complexes already exist in association with power stations in Eastern Europe (Fukala, 1961; Korolkov and Karpenko, 1970) and France (White, 1977).

EXPLOITATION OF WIND POWER

The UK is well placed for the exploitation of wind power. Although about 2 ~o of the solar energy received is converted into wind, only a small proportion is exploitable, partly because of site limitations and because of engineering problems in constructing large machines. The winds are strongest around the west coast of Ireland, Scotland and Wales (7.8 m/s), fairly strong around the other coasts (5.6 to 6.7 m/s) and lighter in most coastal inland regions (around 4.4 m/s average wind speed) (Swift-Hook, 1976). Golding (1955) suggested that the economic generation of electrical power becomes feasible where the average wind speed is more than 8.9 m/s. Wind power can be used in several ways--(a) fluctuating use; (b) the 'gain' principle, viz., energy injected into an existing system to save fuel; (c) a standby source of power; and (d) energy storage. Heat storage is available economically wherever low-grade heat (below 100°C) is the main end use of energy (Shapiro, 1975). It would appear that wind power plants can be provided on a commercially

65

ENERGY USAGE IN BRITISH A G R I C U L T U R E - - F U T U R E PROSPECTS

viable basis mainly for the supply of low-grade heat for horticultural and domestic purposes. W o r k in this former area is being conducted at the M A F F Efford Experimental Horticultural Station, although not without difficulty (Clements, personal communication, 1978). When this is fully operational it is hoped to produce 200,000 kWh of heat/year which is equivalent to 5500 gallons of fuel oil. However, at any particular site the amount of energy which can be extracted is proportional to the swept area. Economically, windmills with rotor diameters of 30-60 m are best. However a 45 m diameter rotor at an average wind speed of 5.2 m/s could produce energy equivalent to 33,000 gallons of oil a year, but its cost is estimated at £70,000. In addition a short term heat store would be necessary to cover periods of low wind (Bailey, 1976).

CULTIVATIONS AND TRACTORS

The reduction of ploughing and other field cultivations through greater use of herbicides to control weeds can make a contribution to energy conservation. Due to reasons unrelated to increasing fuel costs, notably to avoid damage to soils by heavy machinery during the wet weather, ploughless farming or direct drilling can cut the energy input to cereal cultivation by about 10~o (Rutherford, 1974). This is illustrated in Table 14. White (1976b) produced similar figures although fertiliser energy values and the energy factors given for drying and storage differ quite markedly from those of Rutherford. Patterson (1976) showed that only one ninth of the fuel normally required in a conventional cultivation system involving ploughing

TABLE 14 PRIMARY ENERGY INPUTS FOR CEREAL GROWING SYSTEMS( M J/ha)

Operation Conrentional

Plough Secondary cultivation Prepare seed bed Drill and harrow Roll Spray Combine Bale Bale handling Stubble cultivation Fertilisers Drying and storage Total Source: Rutherford (1974).

System Reduced cultiration

Direct drilling

738 243 150 150 48 45 552 60 150 195 6630 5760

390 6630 5760

6630 5760

14721

13803

13215

150 183 48 90 552

--183 90 552 -

66

P . N . WILSON, T. D. A. BRIGSTOCKE TABLE 15

COMPARATIVE ENERGY CONSUMPTION AND LABOUR REQUIREMENTS OF VARIOUS PRIMARY CULTIVATION IMPLEMENTS (AVERAGE VALUES 1 9 7 1 - 7 4 )

Energy per unit area ( MJ/ha)

Specific energy Labour requirements consumption (man hours~ha) (k Jim 3) Heary soil Light soil HeazT soil Light soil Heavy soil Light soil Mouldboard plough (20 cm) Shallow plough (11 cm) Chisel plough (12 cm) Rotary digger (rotor 10, tines 20)

275

160

131

77

2.47

1.58

114 120

68 98

105 123

74 105

0.95 0.99

0.70 0.80

120

122

120

84

0.83

0.77

Source: Matthews (1975).

was needed in a direct drilling system. White (1976a) noted that a direct drilling system uses about 11 ~o less energy than a conventional one. Matthews (1975) reviewed the subject of the inefficient use of tractors. He concluded that, although no revolutionary changes were envisaged in the short term future, energy and operating costs could be reduced significantly by research and more informed operation of machinery. Table 15 sets out the comparative energy consumption and labour requirements of various cultivation implements. The extremely high variations in the performance of these implements when working in light or heavy soil should be noted.

CROP CONSERVATION

Crop conservation is a further area in which economies could well be made. Hightemperature grass drying requires a much greater energy input than does an ensiling process. Weston (1978) noted in a survey of 15 grass drying plants that thermal TABLE 16 EFFECT OF CROP MOISTURE CONTENT (MC) ON FUEL CONSUMPTION

Fresh crop (MC %) 85 82 80 75 70

Water evaporated to produce It dried grass at 10 °/o MC kg MJ/kg evaporated 5000 4000 3500 2600 2000

t 1 litre oil is equivalent to 41-1 MJ. Source: Manby & Shepperson (1975).

3.108 3.192 3.275 3.360 3-444

Oil consumption~ litre/t dried grass

Energy input M J × 10~/t dried grass

367 310 279 212 168

! 5.1 12-8 11-5 8.7 6.8

ENERGY USAGE IN BRITISH A G R I C U L T U R E - - F U T U R E PROSPECTS

67

efficiency is obviously reduced as the crop moisture content is lowered (Table 16). Furthermore some 70 ~ of the heat in exhaust gases is present as latent heat in vapour. Waste heat recovery could be used for pre-drying. Manby & Shepperson (1975) outlined a strategy for increasing the efficiency of grass conservation. Work is now in progress at the National Institute of Agricultural Engineering to design mowing machinery which will enhance the rate of crop-drying in the field (Klinner, 1975). Bailey (1975) reviewed the case for using solar grain driers. He concluded that the biggest problem is the need for a large quantity of fanned air which leads to a thermally inefficient and uneconomic process. This problem is still to be resolved.

ALTERNATIVE ANIMAL PRODUCTION SYSTEMS

Although the biological efficiency of food energy production by animals is low, the high economic cost of the energy inputs, including support energy, can always be met if a sufficiently high demand results in a high premium price for the resultant animal products (Wilson & Brigstocke, 1977). Nevertheless, within the different systems of animal production there would still be an economic incentive to reduce high cost energy inputs wherever possible. Thus beef and lamb are more likely to be produced from uncroppable land, while poultry and pigmeat might be fed on higher proportions of waste or by-products of arable farming or from extraction processes based on very high yielding forage (see British Grassland Society, 1977). In this way the reliance of livestock on high cost cereals as the main source of feed energy can be reduced(Wilson & Brigstocke, 1978). However, as Spedding (1976) noted, one of the features which will influence future animal production is the tolerance of the community to the animal production methods employed. Two major categories of animal species that appear to have been under-exploited agriculturally are mammals with high reproductive rates, such as rabbits and other rodents, and cold-blooded animals, notably fish, shell-fish and insects (Spedding et al., 1976). These species could provide a more efficient use of resources, although they might form only one link in the food chain. They are more likely to be used as feed for other farm animals rather than food for direct consumption by man.

CONCLUSION

This paper has indicated that the future for energy usage in agriculture is full of interesting and potentially useful developments, all of which need continuing inputs of R & D. However, it may well take another 'energy crisis' for farmers and growers to respond to changes in the energetic balance of British agriculture and to modify their production systems accordingly. Nevertheless, investment in new energy forms must come from governments because of the high capital costs and attendant risks,

68

P.N. WILSON, T. D. A. BRIGSTOCKE

a n d this c o u l d slow d o w n research effort into alternative energy sources. W i n d , wave a n d tidal p o w e r c o u l d m a k e c o n t r i b u t i o n s as 'new' energy forms, a l t h o u g h the possibility o f these sources p r o v i d i n g direct m e c h a n i c a l p o w e r has not yet been fully exploited. It m a y well be t h a t the e c o n o m i s t s ' view o f the cost-effectiveness o f a system is n o t a p p r o p r i a t e as it is largely b a s e d on s h o r t - t e r m c o n s i d e r a t i o n s . P e r h a p s a b r o a d e r c o n s i d e r a t i o n o f n a t i o n a l a n d indeed w o r l d resources is necessary. U l t i m a t e l y , as Blaxter (1974) n o t e d , b y the end o f the c e n t u r y the harnessing o f nuclear fusion will p r o v i d e an entirely new p o w e r base for agriculture a n d o t h e r industries. This c o u l d well have m a j o r consequences for o u r p a t t e r n o f lifestyle as well as the w a y in which energy is used in British agriculture. In the long term the s t a t e m e n t t h a t ' m a n does n o t eat food, he eats oil' m a y no longer be true. The a d v a n c e d technologies o f the future m a y well be as energetically efficient as were some o f the m o r e primitive technologies o f the past.

REFERENCES ASAE (American Society of Agricultural Engineers) (1974). The Cast Report, Agric. Engr., 55(3), 19-22. ARMSTEAD,H. C. H. (1977). Geothermal energy development, Proc. Energy Combus. Sci., 2, 181-238. ASTON,R. J. & BROWN,D. J. A. (1974). The growth of eels (Anguilla anguilla L.) in power station cooling water, Central Electricity Research Laboratories, RD/L/N119/74, August 1974. BAILEY, B. J. (1975). Reducing glasshouse heat losses by internal blinds of different materials, DN/G/617/2105, Natn. Inst. Agric. Engng, Silsoe (unpublished). BAILEY,B. J. (1976). Shape of things to come, Hort. Ind. June, pp. 452, 454, 456. BAILEY,B. J., BOWMAN,G. E. & COX,S. W. R. (1976). Energy saving in greenhouses, Proc. Int. Conf. on Physics in Industry (eds. E. O'Mongain and C. P. O'Toole), Dublin, Pergamon Press, pp. 501-8. BAILEY,P. H. (1975). Written communication, Agric. Engr., 30(3), 84-5. BARnlER,E. & FANELLI,M. (1977). Non-electrical uses of geothermal energy, Proc. Energy Combus. Sci., 3, 73-103. BARTLETT,E. T. & CLAWSON,W. J. (1978). Profit, meat production or efficientuse of energy in ranching, J. Anim. Sci., 46, 812-18. BAUMAN,B. F., FINNER,M. F. & SHOVE,G. C. (1975). Low temperature gram drying with supplemental solar heat from an adjacent metal building, Am. Soc. Agric. Engrs., Winter Meet., Paper No. 753514. BLACK,J. N. (1971). Energy relations in crop production, Ann. Appl. Biol., 67, 272-7. BLAXTER,K. L. (1974). The limits to agricultural improvement, New Scientist, 61, 400-3. BLAXT~R,K. L. (1975). The energetics of British agriculture, The Biologist, 22(I), 14-18. BLAXT~R,K. L. (1978). Energy use in farming and its cost, Paper presented at the Oxford Farming Conf., January 1978, Grass, 21, pp. 4, 6, 8. Summer issue. BOWMAN,G. E. (1975). Energy sources, Agric. Engr., 30(3), 59-61. BRINKWORTH,B. J. (1976). Solar energy. In: Aspects of energy conversion (eds. I. M. Blair, B. D. Jones and A. J. Van Horn), Pergamon Press, pp. 431-48. Oxford, BRITISHGRASSLANDSOCIETY(1977). Green crop fractionation, Proc. Syrup. organised by BGS and BSA P. Occasional Symp. No. 9 (ed. R. J. Wilkins). BRODY,S. (1945). Bioenergetics and growth with special reference to the efficiency complex in domestic animals, New York, Harrier Publ. Co., 1964 edition, p. 954. BUILDINGRESEARCHESTABLISHMENT(1975). Energy conservation: A study of energy consumption in buildings and possible means of saving energy in housing, Current paper 56/75, June 1975. BUILTENVIRONMENTRESEARCHGROUP(1977). Storing collected solar energy in agriculture, horticulture andfishculture, Report No. 7, The Polytechnic of Central London. CHAPMAN,D. (1973). An end to chemical farming, Environment (St Louis), 15(2), 12-17. CooK, E. (1971). The flow of energy in an industrial society, Sci. Amer., 225(3), 135-44.

ENERGY USAGE IN BRITISH AGRICULTURE--FUTURE PROSPECTS

69

COOKE,G. W. (1971). Fertilisers and society, Proc. Fertil. Soc., No. 121. COOPER, J. P. (1970). Potential production and energy conversion in temperate and tropical grasses, Herb. Abstr., 400), 1-15. DEPARTMENTOF ENERGY(1976). Energy R & D in the UK, Dept. of Energy Paper No. II, London, HMSO. DEPARTMENTOFENERGY(1977). The prospects for solar energy in the UK, Dept. of Energy Paper No. 16, London, HMSO. DEPARTMENTOF ENERGY(1978). Energy policy. A consultative document, Cmnd. 710 I. London, H M SO. DIGESTOF UNITEDKINGDOMENERGYSTATISTICS(1974). London, HMSO. DUCKHAM,A. N. (1974). Biological effciency in crop and livestock production, Chem. Ind., 23, 934-7. FUKALA, E. (1961). Ved. Prace. Vyzk Ust Zelin, C Z A Z V v Olmouci 1961, 1, 229-51 (in Czech). GARNISH, J. D. (1976). Geothermal energy: The case for research in the UK, Energy Paper No. 9, London, HMSO. GARNISH,J. D. (1978). Geothermal energy and the UK, Phys. Educ., 13, 372-9. GIFFORD,R. M. (1973). Energy,foodandagriculture, Annual Report of the Division of Plant Industries, CSIRO, pp. 19-24. GIFFORD, R. M. & MILLINGTON,R. J. (1973). Energetics of agriculture and food prodaction with special emphasis on the Australian situation, Adelaide, UNESCO Symposium on Energy and How We Live. GILLHAM,E. W. F., SIMPSON,O. T. 8/. MARTIN,A. (1974). The utilisation oJpower station waste heat in agriculture, CEGB Midlands Region SSD/MID/R41/74, June, 1974. GOLDING, E. W. (1955). Electrical energy from the wind, Proc. I.E.E., 102, 677. GRAHAM,R. W. (1975). Fuels from crops: Renewable and clean, Mech. Engng, 97, May, 27-31. GRAY,J. A. (1976). Energy and the Gas Industry. In: Aspects of energy conversion (eds. I. M. Blair, B. D. Jones and A. J. Van Horn), Oxford, Pergamon Press, pp. 217-37. GREENHALGH,J. F. D. (1976). The dilemma of animal feeds and nutrition, Anita. FeedSci. Technol., 1, 1-17. HESLOP-HARRlSON,J. (1975). Crops, commodities and energy capture, The Biologist, 22,(2), 60-7. HIRST, E. (1974). Food-related energy requirements, Science, New York, 184, 134-8. HOLMES, W. (1970). Animals for food, Proc. Nutr. Soc., 29, 237-44. HOLMES,W. (1975). Assessment of alternative nutrient sources. Proc. 21st Easter School in Agric. Sci.-"Meat" (eds. D. J. A. Cole and R. A. Lawrie). Univ. of Notts., 1974, pp. 535-53. JACQUES,J. K. & BLAXTER,K. L. (1978). The use of support energy in the meat processing industry, J. Sci. Fd. Agric., 29, 172-81. JCO (Joint Consultative Organisation for Research and Development in Agriculture and Food) (1974). The report of the energy working party, Report No. 1, UK, ARC, DAFS and MAFF. KENWARD, M. E. (1976). Potential energy, London, Cambridge Univ. Press. KLINNER,W. E. (1975). Mechanical and chemical field treatment of grass for conservation, Report No. 21, Natn. Inst. Agric. Engng, Silsoe, July 1976. KOROLKOV,E. D. & KARPENKO,B. JA. (1970). The use of low temperature thermal waste from power stations in vegetable growing. Izv timirjazev sel'-hoz Akad, 2, 168-75 (in Russian with English summary). LEACH,G. (1974). The energy costs of food production. In: The man-foodequation (eds. F. Steele and A. Bourne), London, Academic Press. pp. 139-63. LEACH, G. (1976). Energy and food production, Guildford, IPC Science and Technology Press. LEGGEAT,A. (1974). Waste heat utilisation, CEGB Midlands Region Memo SSD/MID/M61/74, October 1974. MAFF (Ministry of Agriculture, Fisheries and Food) (1968). A century of agricultural statistics, GB 1866-1966, London, HMSO. MAFF (Ministry of Agriculture, Fisheries and Food) (1974). Output andutilisation offarmproduce in the UK 1967-68/1972-73, London, HMSO. MANBY,T. C. D. & SHEPPERSON,G. (1975). Increasing the efficiency of grass conservation, Agric. Engr., 30(3), 77-83. MASTERSON,H. G. (1976). The use of reject heat in grass drying plants, Bristol, Br. Assoc. Green Crop Driers Conv. MATTHEWS,J. (1975). Effcient use of tractors, Agric. Engr., 30(3), 66-9, 76. MELLANBY,K. (1975). Can Britain feed itself?., London, Merlin Press. MOr~TEITH,J. L. (1972). Solar radiation and productivity in tropical ecosystems, J. Appl. Ecol., 9, 747-66. MORRIS, L. G. & WINSPEAR,K. W. (1967). The control of temperature and humidity in glasshouses by heating and ventilation. In: Proc. Agric. Engng Syrup. Silsoe 1967, lnstn. Agric. Engrs.

70

P . N . WILSON, T. D. A. BRIGSTOCKE

ODUM,H. T. (1971). Environment, power and society, New York, Wiley-lnterscience. OSBOURN, D. F. (1976). Forage conservation and support energy use. In: Energy use and British agriculture (eds. D. M. Bather and H. I. Day), Reading Univ. Agricultural Club, pp. 29-34. OWENS, P. M. (1976). Reject heat for horticulture. In: Growingenergy, Inst. Fuel Conf., Southampton. PATTERSON,D. E. (1976). Equipment for reduced cultivation systems, Agricultural Research Council Working Group on Direct Drilling and Reduced Cultivation, Paper No. 15/76. PIMENTEL,D., HURD, L. E., BELLOTTI,A. C., FORSTER,M. J., OKA, I. N., SHOLES,O. D. & WHITMAN, R. J. (1973). Food production and the energy crisis, Science, New York, 182, 443-9. PIMENTEL,D., DRITSCHILO,W., KRUMMEL,J. & KUTZMAN,J. (1975). Energy and land constraints in food protein production, Science, New York, 190, 754-61. RUTHERFORD,I. (1974). Communication to the Energy Working Party. Reference quoted by the Joint Consultative Organisation for Research and Development in Agriculture and Food (1974). The report oJ the Energy Working Party, Report No. l, UK, ARC, DAFS and MAFF. SHAPIRO,J. S. (1975). Written contribution, Agric. Engr., 30(3), 84. SHEARD,G. F. (1976). Energy relations in protected cultivation. In: Growing Energy, Inst. Fuel Conf., Southampton. SHORT, T. H., ROLLER,W. L. & BADGER,P. C. (1976). A solar pond for heating greenhouses and rural reSidences--a preliminary report, Am. Soc. Agric. Engrs., Annual Meet., Paper No. 76-4012. SLESSER,M. (1973). Energy subsidy as a criterion in food policy planning, J. Sci. Fd. Agric., 24, 1! 93-207. SPEDDING,C. R. W. (1973). The meaning of biological efficiency. In: The biological efficiency of protein production (ed. J. G. W. Jones), Cambridge, Camb. Univ. Press, pp. 13-26. SI'EDDING,C. R. W. (1976). Can human energy needs be met ? In: Conservationof resources. London, The Chemical Society, pp. 83-95. SPEDDING,C. R. W. & WALSINGHAM,J. M. (1975). Energy use in agricultural systems, Span, 18(0, 7-9. SI'EDDING,C. R. W., WALSINGHAM,J. M. & BATHER,D. M. (1976). Alternative animal species for more efficient farming. In: Energy use and British agriculture (eds. D. M. Bather and H. I. Day), Reading Univ. Agricultural Club, pp. 23-9. STANSFIELD,J. R. et al. (1974). Fuel in British agricuhure,INIAE Report No. 13. STATHAM,J. (1975). A preliminary review of the problem of heating glasshouses utilising cooling water from power stations, CEGB Report SSD/NE/R307. SWIFT-HOOK, D. T. (1976), The atmosphere and the oceans as energy sources. In: Aspects of energy conversion (eds. 1. M. Blair, B. D. Jones and A. J. Van Horn), Oxford, Pergamon Press, pp. 405-30. TABOR, H. (1963). Large area solar collectors for power production. Solar Energy, 7, 189-94. VAUGHAN,D. H., BELL, E. S. & HUGHES,H. A. (1976). Solar energy collection with lagoon storagefor heat pumps, Am. Soc. Agric. Engrs., Annual Meet., Paper No. 76-4053. VLITOS,A. J. (1978). Creative botany--opportunities for thefuture, Paper presented at the British Assoc. for the Advancement of Science Meeting, Bath Univ., September 1978. WEDIN, W. F., HODGSON,H. J. & JACOBSO~,N. L. (1975). Utilising plant and animal resources in producing human food, J. Anita. Sci., 41,667-85. WESTON, H. B. (1978). Further aspects of energy conservation. Preliminary report of energy efficiency survey, Grass, 21, 9. Summer issue. WHITE, D. J. (1975). Energy in agricultural systems. Agric. Engr., 30(3), 52-8. WHITE, D. J. (1976a). Energy use in agriculture. In: Aspects of energy conversion (eds. I. M. Blair, B. D. Jones and A. J. Van Horn), Oxford, Pergamon Press, pp. 141-76. WHITE, D. J. (1976b). Energy accounting in agricultureandJood. Paper presented at Instn. Mechn. Engrs. Conf. on Energy Accountancy, London, 1976. WHITE, D. J. (1977). Prospects for greater efficiency in the use of different energy sources, Phil. Trans. R. Soc. Lond. B, 281, 261-75. WILSON, P. N. (1976). Introductory address. In: Energy use and British agriculture (eds. D. M. Bather and H. I. Day), Reading Univ. Agricultural Club, pp. 1-5. WILSON,P. N. & BRIGSTOCKE,T. (1977). Energy and UK agriculture, Long Range Planning, 10(5), 64-71. WILSON, P. N. & BRIGSTOCKE,T. (1978). Animal nutrition over 20 years, Span, 21(2), 66-8. WINSPEAR, K. W. (1976). Thermal screens for glasshouse fuel saving. In: Proc. of subject day on greenhouse engineering, Natn. Inst. Agric. Engng, Silsoe, Report No. 23, Nov. 1976. WINSPEAR,K. '~., POSTLETHWAITE,J. D. & COTTON,R. F. (1970). The restriction of Cladosporiumfulvum and Botrytis cinerea attacking glasshouse tomatoes, by automatic humidity control, Ann. Appl. Biol., 65, 75-84.