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input relationship for forage maize and grass leys on the dairy farm
Agriculture and Environment, 3 (1976) 15--20
15
© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
A COMPARISON OF THE E N E R G Y O U T P U T / I N P U T R E L A T I O N S H I P F O R F O R A G E MAIZE AND GRASS LEYS ON THE DAIRY FARM
R.H. PHIPPS, B.F. PAIN and P.M. MULVANY National Institute for Research in Dairying, Shinfield, Reading RG2 9AT (Great Britain)
(Received 4 March 1976)
ABSTRACT
Phipps, R.H., Pain, B.F. and Mulvany, P.M., 1976. A comparison of the energy output/input relationship for forage maize and grass leys on the dairy farm. Agric. Environm., 3: 15--20. Energy inputs and outputs were calculated for forage maize and compared to a threeyear grass ley grown under similar conditions. Energy ratios of 4.8 and 2.7 were obtained for forage maize and grass respectively. Inputs of energy for maize could be greatly reduced by replacing inorganic fertiliser with cow slurry.
INTRODUCTION The primary energy consumed in agriculture in the U.K. amounts to only 4% o f the national energy budget, with an additional 7% being used in fisheries, f o o d processing and distribution (White, 1975). Energy saved by agriculture can, therefore, do little to improve the national situation. However, with the ever increasing cost of energy and the pressure on profit margins, analysis of the energy o u t p u t / i n p u t relationships for specific crops have far reaching implications on the t y p e of crops and husbandry techniques used for production. The increasing mechanisation and intensification of agriculture in the pursuit o f greater productivity has led to a sharp rise in energy consumption. It has been estimated, for example, that nitrogen fertiliser usage will rise f r o m a p p r o ximately one million tonnes in 1972 to three million tonnes in 1999 (Austin, 1975). At least 64% of nitrogen fertiliser used on major U.K. crops is applied to grass leys, p e r m a n e n t grass and rough grazing, which provide the bulk o f conserved roughage for feeding animals in the winter (Austin, 1975). Forage maize has for a long time been an i m p o r t a n t source of winter roughage in France and Germany, but it is only in the last five years that the area grown in the U.K. has markedly increased (Bunting and Gunn, 1973). At the National Institute for Research in Dairying, forage maize has been grown for silage since 1969. Th e present paper examines the energy o u t p u t / i n p u t relationship for forage maize and compares it with intensive grassland. Some possible ways o f improving the energy o u t p u t / i n p u t ratio are also investigated.
16
ENERGY INPUTS F OR MAIZE AND GRASS
The man hours and tractor fuel used for the establishment and harvesting of both crops are given in Table I. TABLE I Man hours and litres of diesel fuel/ha/year required for the establishment and harvesting of forage maize and grass from a three-year ley cut on average 2.5 times/year Maize Man hrs/ha
Grass Litres fuel/ha
Man hrs/ha
Litres fuel/ha
Ploughing Cultivating Rolling Fertilising Drilling Spraying Rolling Harvesting and ensiling
2.3 2.0 0.5 0.7 1.0 0.5 1.3
21.1 18.0 4.5 2.2 3.4 2.0 6.0
1.5 1.0 0.3 0.3 0.5 0.3 0.3
13.5 9.0 2.2 0.8 1.7 0.9 1.1
14.8
' 78.7
39.5
210.0
Total
23.1
135.9
43.7
239.2
The quantity of diesel fuel was converted to MJ b y taking one litre to be equivalent to 43.3 MJ (Leach, 1975). By agreed convention no charge is made for the energy expended by the labour force at work, or for the support energy required for domestic life, since these are either negligible or of no relevance to food production (I.F.I.A.S., 1974; Leach, 1975). Further inputs are included for the machinery involved in establishment and harvesting. Sixteen tonnes of machinery with an assumed life of 10 years is used for both crops. During one year, 17% and 35% of the working time of this machinery is spent in maize and grass production respectively. The energy equivalent of the machinery was calculated using values given by Pimentel et al. (1973) and include an allowance for repairs and maintenance. Energy inputs from seed and herbicide were 33.2 and 101.0 MJ/kg respectively (Pimentel et al., 1973). For the production of maize 628 kg/ha of a c o m p o u n d fertiliser (22:11:11) with an energy equivalent of 20 MJ/kg were used. The grass ley received an initial seed-bed application of 251 kg/ha of c o m p o u n d fertiliser (9:25:25) with an energy equivalent of 14 MJ/kg, and during each of its three years of productive life 250 kg N, 50 kg P and 50 kg K/ha. M o s t o f the nitrogen is applied as ammonium nitrate and has an energy value of 26.2 MJ/kg. From Table II it is clear that intensive grassland at NIRD requires more energy/ha/year than forage maize, and that in both instances inorganic fertilizer is the main component. The differences in energy requirements would have been even greater if the lower rates of fertiliser application for forage maize
17 TABLE II Energy inputs (MJ/ha/year) for the production of forage maize and intensive grassland Maize Establishment Fuel Fertiliser Harvesting Fuel Fertiliser Seed Herbicide Machinery and repairs Total
Percent of total
Grass
Percent of total
2 477 --
11
1 264 1 171
4 3
3 408 12 560 1 377 341
16 59 6 2
9 093 20150 459 114
26 58 1 <1
1 237
6
2474
7
21 400
34 725
suggested by Phipps and Pain (1975) were used. Energy inputs from t ract or fuel for maize and grass constituted 28% and 30% of the total energy inputs. At NIRD forage maize produces appr oxi m at el y 10 tonnes DM/ha and grass 9 tonnes DM/ha. Low yields o f grass are due to low rainfall and light gravelly soil. It was assumed t hat bot h crops have digestibility values of 68%, and metabolisable energy values of 10.3 MJ/kg DM. This gives an energy o u t p u t of 103 000 and 92 700 MJ/ha/year for maize and grass respectively. The energy ratio (metabolisable energy o u t p u t / e n e r g y input) for maize is therefore 4.8 and for grass 2.7. The figure for grass is in close agreement with Leach (1975). The ratio of 4.8 for maize is appreciably higher than the 2.8 calculated by Pimentel et al. (1973) for grain maize. American workers logically used maize grain yields to c o m p u t e energy o u t p u t / i n p u t ratios because the majority of maize sown in the U.S.A. is harvested for grain rather than for silage, where the whole plant is used. In contrast, over 90% of the crop grown in the U.K. is made into silage. In farming practice ot he r allowances may need to be made, which could affect the calculated energy ratios. Losses of dry matter, for example, occur during ensiling and again between silo and manger. Maize silage contains sufficient protein to achieve satisfactory liveweight gains in y o u n g stock, but protein supplementation is necessary for dairy cows. When considering dairy herds this additional protein should also be included in the energy calculations. METHODS OF REDUCING ENERGY INPUTS The increasing price o f inorganic fertilisers has led to renewed interest in the fertiliser value o f organic manures. On a dairy farm considerable savings can be achieved in cost and energy inputs for maize p r o d u c t i o n by replacing
18 inorganic fertiliser with slurry. A dairy cow produces between 7--8 tonnes of slurry per winter which, if stored through to the spring, contains sufficient nitrogen, phosphorus and potassium to grow the maize required to feed a cow roughage during the following winter (Pain, 1976). This is based on the assumption that maize silage is being fed to dairy cows at the rate of 10 kg DM/cow/day for a 180 day winter feeding period, and that the yield of forage maize was 8.75 tonnes DM/ha. This 1 ha of maize should provide sufficient winter forage for five cows. If the effluent from these five cows is n o t excessively diluted by rainwater, then it will weigh about 40 tonnes and will contain 115 kg N, 53 kg P2Os and 167 kg K20 in an available form. Winter produced slurry recycled in this way n o t only reduces the cost of maize production by 20% but reduces the energy input from 21 400 MJ/ha to 9 744 MJ/ha (see Table III). This reduction in the energy inputs for forage maize improves the energy o u t p u t / i n p u t ratio from 4.8 to 10.6. TABLE III Energy inputs (MJ/ha) for forage maize when inorganic fertiliser is replaced by slurry MJ/ha Establishing and harvesting the crop Seed, herbicide and machinery, etc. Spreading slurry Fuel Extra machinery
5 885 2955
Total
9 744
652 252
Allowances are made for the extra fuel and machinery required to spread slurry instead of fertiliser. No energy inputs for removing slurry from the cowshed and for storage are included because these operations are necessary whether or n o t slurry is used to grow a crop. Using slurry on pasture is more difficult because it is n o t a balanced grassland fertiliser. It contains too much potassium in relation to the nitrogen content which can lead to mineral imbalances in the herbage. The best use is made of slurry on grassland by spreading lighter dressings over a larger area and "topping u p " to recommended fertiliser applications with inorganic nitrogen. This clearly limits the magnitude of energy savings that can be made. In a maize/grass cropping system it is better to use slurry to grow maize and reserve the expensive but more precise inorganic fertiliser for grassland. Part of the grassland nitrogen requirement could be provided by sowing legumes. Recent work at NIRD suggests that using slurry for maize will also reduce the cost and energy inputs for a following crop by raising the potassium and phosphorus levels in the soil sufficiently to grow a winter cereal with only a spring application of nitrogen. Transport of animal wastes from predominantly livestock areas to arable areas could negate the energy saving potential of slurry. Similarly, although the
19 m a n u r e f r o m b a t t e r y h e n s c o n t a i n s 3 - - 4 t i m e s as m u c h n i t r o g e n as c o w slurry, t r a n s p o r t i n g it o n l y 10 miles w o u l d cancel o u t t h e e n e r g y saved b y s p r e a d i n g less p e r u n i t area. T h e e n e r g y f o r t r a c t o r fuel a c c o u n t s f o r 28% o f t o t a l e n e r g y i n p u t so it is w o r t h e x a m i n i n g savings t h a t can be m a d e in this d i r e c t i o n . Direct drilling is a t e c h n i q u e o f t e n e m p l o y e d t o establish m a i z e in t h e U.S.A. and is b e c o m i n g m o r e p o p u l a r in Britain. D i r e c t drilling m a i z e involves o n l y t w o or t h r e e o p e r a t i o n s , d e p e n d i n g o n t h e t y p e o f drill used. T h e residual c r o p is usually s p r a y e d w i t h a h e r b i c i d e a n d t h e m a i z e d i r e c t drilled w i t h a fertiliser a t t a c h m e n t on t h e drill. Since t h e m a j o r i t y o f e n e r g y i n p u t s are c o m m o n t o b o t h c o n v e n t i o n a l a n d d i r e c t drilled m a i z e , t h e t e c h n i q u e gives a saving o f o n l y 10% in t h e t o t a l e n e r g y e x p e n d i t u r e . ( T h u s t h e e n e r g y o u t p u t / i n p u t r a t i o f o r d i r e c t drilled m a i z e is o n l y i m p r o v e d f r o m 4.8 t o 5.3.) E v e n so, t h e e n e r g y e x p e n d e d as diesel fuel is r e d u c e d b y o v e r 30% (see T a b l e IV). TABLE IV Energy input (MJ/ha) from tractor fuel in forage maize production Conventional methods
Direct drilled seed
Establishment Harvesting
2 477 3 408
398 3 408
Total
5 885
3 806
CONCLUSION T a b l e V s u m m a r i s e s the e n e r g y i n p u t s a n d s h o w s t h e e n e r g y o u t p u t / i n p u t ratios f o r t h e t h r e e m e t h o d s discussed f o r g r o w i n g m a i z e a n d c o m p a r e s t h e m TABLE V Energy output/input ratios for forage maize and a three-year grass ley
MAIZE Conventional methods Direct drilled Using slurry as fertiliser GRASS 3-year ley
Energy input (MJ/ha)
M.E. output (MJ/ha)
21 400 19 267
103 000
9 744 34 725
92 700
Energy output/input ratios
M.E. output (MJ/man hour)
4.8 5.3
4 459 6 059
10.8
3 665
2.7
2 121
20
to that of a three-year grass ley. It also shows a labour efficiency ratio expressed in terms of megajoules of metabolisable energy o u t p u t per man hour. Fertiliser and fuel to power machinery are the two major inputs, apart from the sun, in most crop production systems in the developed world. The analysis set out above applies to a particular cropping system on a particular dairy farm, but shows how a re-appraisal of traditional methods such as organic manuring and closer examination of new techniques such as direct drilling can reduce energy inputs and costs of production.
REFERENCES Austin, R.B., 1975. Economy in the use of manufactured fertiliser. Ann. Conf. Inst. Agric. Eng., London, 9 pp. Bunting, E.W. and Gunn, R.E., 1973. Maize in Britain - - a survey of research and breeding. Plant Breeding Institute Cambridge, Annual Report 1973, pp. 32--74. I.F.I.A.S., 1974. Energy analysis. Workshop Report No. 6. International Federation of Institutes for Advanced Study. The Nobel House, Stockholm, Sweden, 89 pp. Leach, G., 1975. Energy and food production. International Institute for Environment and Development, London, 151 pp. Pain, B.F., 1976. Cow slurry for forage maize. Maize Bulletin, 85: 3--6. Pain, B.F. and Phipps, R.H., 1975. The energy to grow maize. New Sci., 66 (949): 394--396. Phipps, R.H. and Pain, B.F., 1975. Levels of fertilizer for forage maize. A.D.A.S.q. Rev., 18: 49--54. Pimentel, D., Hurd, L.E., Belloti, A.C., Forster, M.J., Oaka, I.N., Shoves, O.D. and Whitman, R.J., 1973. F o o d production and the energy crisis. Science, 183: 443--449. White, D.J., 1975. Energy in agricultural systems. Ann. Conf. Inst. Agric. Eng., London, 21 pp.
15
© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
A COMPARISON OF THE E N E R G Y O U T P U T / I N P U T R E L A T I O N S H I P F O R F O R A G E MAIZE AND GRASS LEYS ON THE DAIRY FARM
R.H. PHIPPS, B.F. PAIN and P.M. MULVANY National Institute for Research in Dairying, Shinfield, Reading RG2 9AT (Great Britain)
(Received 4 March 1976)
ABSTRACT
Phipps, R.H., Pain, B.F. and Mulvany, P.M., 1976. A comparison of the energy output/input relationship for forage maize and grass leys on the dairy farm. Agric. Environm., 3: 15--20. Energy inputs and outputs were calculated for forage maize and compared to a threeyear grass ley grown under similar conditions. Energy ratios of 4.8 and 2.7 were obtained for forage maize and grass respectively. Inputs of energy for maize could be greatly reduced by replacing inorganic fertiliser with cow slurry.
INTRODUCTION The primary energy consumed in agriculture in the U.K. amounts to only 4% o f the national energy budget, with an additional 7% being used in fisheries, f o o d processing and distribution (White, 1975). Energy saved by agriculture can, therefore, do little to improve the national situation. However, with the ever increasing cost of energy and the pressure on profit margins, analysis of the energy o u t p u t / i n p u t relationships for specific crops have far reaching implications on the t y p e of crops and husbandry techniques used for production. The increasing mechanisation and intensification of agriculture in the pursuit o f greater productivity has led to a sharp rise in energy consumption. It has been estimated, for example, that nitrogen fertiliser usage will rise f r o m a p p r o ximately one million tonnes in 1972 to three million tonnes in 1999 (Austin, 1975). At least 64% of nitrogen fertiliser used on major U.K. crops is applied to grass leys, p e r m a n e n t grass and rough grazing, which provide the bulk o f conserved roughage for feeding animals in the winter (Austin, 1975). Forage maize has for a long time been an i m p o r t a n t source of winter roughage in France and Germany, but it is only in the last five years that the area grown in the U.K. has markedly increased (Bunting and Gunn, 1973). At the National Institute for Research in Dairying, forage maize has been grown for silage since 1969. Th e present paper examines the energy o u t p u t / i n p u t relationship for forage maize and compares it with intensive grassland. Some possible ways o f improving the energy o u t p u t / i n p u t ratio are also investigated.
16
ENERGY INPUTS F OR MAIZE AND GRASS
The man hours and tractor fuel used for the establishment and harvesting of both crops are given in Table I. TABLE I Man hours and litres of diesel fuel/ha/year required for the establishment and harvesting of forage maize and grass from a three-year ley cut on average 2.5 times/year Maize Man hrs/ha
Grass Litres fuel/ha
Man hrs/ha
Litres fuel/ha
Ploughing Cultivating Rolling Fertilising Drilling Spraying Rolling Harvesting and ensiling
2.3 2.0 0.5 0.7 1.0 0.5 1.3
21.1 18.0 4.5 2.2 3.4 2.0 6.0
1.5 1.0 0.3 0.3 0.5 0.3 0.3
13.5 9.0 2.2 0.8 1.7 0.9 1.1
14.8
' 78.7
39.5
210.0
Total
23.1
135.9
43.7
239.2
The quantity of diesel fuel was converted to MJ b y taking one litre to be equivalent to 43.3 MJ (Leach, 1975). By agreed convention no charge is made for the energy expended by the labour force at work, or for the support energy required for domestic life, since these are either negligible or of no relevance to food production (I.F.I.A.S., 1974; Leach, 1975). Further inputs are included for the machinery involved in establishment and harvesting. Sixteen tonnes of machinery with an assumed life of 10 years is used for both crops. During one year, 17% and 35% of the working time of this machinery is spent in maize and grass production respectively. The energy equivalent of the machinery was calculated using values given by Pimentel et al. (1973) and include an allowance for repairs and maintenance. Energy inputs from seed and herbicide were 33.2 and 101.0 MJ/kg respectively (Pimentel et al., 1973). For the production of maize 628 kg/ha of a c o m p o u n d fertiliser (22:11:11) with an energy equivalent of 20 MJ/kg were used. The grass ley received an initial seed-bed application of 251 kg/ha of c o m p o u n d fertiliser (9:25:25) with an energy equivalent of 14 MJ/kg, and during each of its three years of productive life 250 kg N, 50 kg P and 50 kg K/ha. M o s t o f the nitrogen is applied as ammonium nitrate and has an energy value of 26.2 MJ/kg. From Table II it is clear that intensive grassland at NIRD requires more energy/ha/year than forage maize, and that in both instances inorganic fertilizer is the main component. The differences in energy requirements would have been even greater if the lower rates of fertiliser application for forage maize
17 TABLE II Energy inputs (MJ/ha/year) for the production of forage maize and intensive grassland Maize Establishment Fuel Fertiliser Harvesting Fuel Fertiliser Seed Herbicide Machinery and repairs Total
Percent of total
Grass
Percent of total
2 477 --
11
1 264 1 171
4 3
3 408 12 560 1 377 341
16 59 6 2
9 093 20150 459 114
26 58 1 <1
1 237
6
2474
7
21 400
34 725
suggested by Phipps and Pain (1975) were used. Energy inputs from t ract or fuel for maize and grass constituted 28% and 30% of the total energy inputs. At NIRD forage maize produces appr oxi m at el y 10 tonnes DM/ha and grass 9 tonnes DM/ha. Low yields o f grass are due to low rainfall and light gravelly soil. It was assumed t hat bot h crops have digestibility values of 68%, and metabolisable energy values of 10.3 MJ/kg DM. This gives an energy o u t p u t of 103 000 and 92 700 MJ/ha/year for maize and grass respectively. The energy ratio (metabolisable energy o u t p u t / e n e r g y input) for maize is therefore 4.8 and for grass 2.7. The figure for grass is in close agreement with Leach (1975). The ratio of 4.8 for maize is appreciably higher than the 2.8 calculated by Pimentel et al. (1973) for grain maize. American workers logically used maize grain yields to c o m p u t e energy o u t p u t / i n p u t ratios because the majority of maize sown in the U.S.A. is harvested for grain rather than for silage, where the whole plant is used. In contrast, over 90% of the crop grown in the U.K. is made into silage. In farming practice ot he r allowances may need to be made, which could affect the calculated energy ratios. Losses of dry matter, for example, occur during ensiling and again between silo and manger. Maize silage contains sufficient protein to achieve satisfactory liveweight gains in y o u n g stock, but protein supplementation is necessary for dairy cows. When considering dairy herds this additional protein should also be included in the energy calculations. METHODS OF REDUCING ENERGY INPUTS The increasing price o f inorganic fertilisers has led to renewed interest in the fertiliser value o f organic manures. On a dairy farm considerable savings can be achieved in cost and energy inputs for maize p r o d u c t i o n by replacing
18 inorganic fertiliser with slurry. A dairy cow produces between 7--8 tonnes of slurry per winter which, if stored through to the spring, contains sufficient nitrogen, phosphorus and potassium to grow the maize required to feed a cow roughage during the following winter (Pain, 1976). This is based on the assumption that maize silage is being fed to dairy cows at the rate of 10 kg DM/cow/day for a 180 day winter feeding period, and that the yield of forage maize was 8.75 tonnes DM/ha. This 1 ha of maize should provide sufficient winter forage for five cows. If the effluent from these five cows is n o t excessively diluted by rainwater, then it will weigh about 40 tonnes and will contain 115 kg N, 53 kg P2Os and 167 kg K20 in an available form. Winter produced slurry recycled in this way n o t only reduces the cost of maize production by 20% but reduces the energy input from 21 400 MJ/ha to 9 744 MJ/ha (see Table III). This reduction in the energy inputs for forage maize improves the energy o u t p u t / i n p u t ratio from 4.8 to 10.6. TABLE III Energy inputs (MJ/ha) for forage maize when inorganic fertiliser is replaced by slurry MJ/ha Establishing and harvesting the crop Seed, herbicide and machinery, etc. Spreading slurry Fuel Extra machinery
5 885 2955
Total
9 744
652 252
Allowances are made for the extra fuel and machinery required to spread slurry instead of fertiliser. No energy inputs for removing slurry from the cowshed and for storage are included because these operations are necessary whether or n o t slurry is used to grow a crop. Using slurry on pasture is more difficult because it is n o t a balanced grassland fertiliser. It contains too much potassium in relation to the nitrogen content which can lead to mineral imbalances in the herbage. The best use is made of slurry on grassland by spreading lighter dressings over a larger area and "topping u p " to recommended fertiliser applications with inorganic nitrogen. This clearly limits the magnitude of energy savings that can be made. In a maize/grass cropping system it is better to use slurry to grow maize and reserve the expensive but more precise inorganic fertiliser for grassland. Part of the grassland nitrogen requirement could be provided by sowing legumes. Recent work at NIRD suggests that using slurry for maize will also reduce the cost and energy inputs for a following crop by raising the potassium and phosphorus levels in the soil sufficiently to grow a winter cereal with only a spring application of nitrogen. Transport of animal wastes from predominantly livestock areas to arable areas could negate the energy saving potential of slurry. Similarly, although the
19 m a n u r e f r o m b a t t e r y h e n s c o n t a i n s 3 - - 4 t i m e s as m u c h n i t r o g e n as c o w slurry, t r a n s p o r t i n g it o n l y 10 miles w o u l d cancel o u t t h e e n e r g y saved b y s p r e a d i n g less p e r u n i t area. T h e e n e r g y f o r t r a c t o r fuel a c c o u n t s f o r 28% o f t o t a l e n e r g y i n p u t so it is w o r t h e x a m i n i n g savings t h a t can be m a d e in this d i r e c t i o n . Direct drilling is a t e c h n i q u e o f t e n e m p l o y e d t o establish m a i z e in t h e U.S.A. and is b e c o m i n g m o r e p o p u l a r in Britain. D i r e c t drilling m a i z e involves o n l y t w o or t h r e e o p e r a t i o n s , d e p e n d i n g o n t h e t y p e o f drill used. T h e residual c r o p is usually s p r a y e d w i t h a h e r b i c i d e a n d t h e m a i z e d i r e c t drilled w i t h a fertiliser a t t a c h m e n t on t h e drill. Since t h e m a j o r i t y o f e n e r g y i n p u t s are c o m m o n t o b o t h c o n v e n t i o n a l a n d d i r e c t drilled m a i z e , t h e t e c h n i q u e gives a saving o f o n l y 10% in t h e t o t a l e n e r g y e x p e n d i t u r e . ( T h u s t h e e n e r g y o u t p u t / i n p u t r a t i o f o r d i r e c t drilled m a i z e is o n l y i m p r o v e d f r o m 4.8 t o 5.3.) E v e n so, t h e e n e r g y e x p e n d e d as diesel fuel is r e d u c e d b y o v e r 30% (see T a b l e IV). TABLE IV Energy input (MJ/ha) from tractor fuel in forage maize production Conventional methods
Direct drilled seed
Establishment Harvesting
2 477 3 408
398 3 408
Total
5 885
3 806
CONCLUSION T a b l e V s u m m a r i s e s the e n e r g y i n p u t s a n d s h o w s t h e e n e r g y o u t p u t / i n p u t ratios f o r t h e t h r e e m e t h o d s discussed f o r g r o w i n g m a i z e a n d c o m p a r e s t h e m TABLE V Energy output/input ratios for forage maize and a three-year grass ley
MAIZE Conventional methods Direct drilled Using slurry as fertiliser GRASS 3-year ley
Energy input (MJ/ha)
M.E. output (MJ/ha)
21 400 19 267
103 000
9 744 34 725
92 700
Energy output/input ratios
M.E. output (MJ/man hour)
4.8 5.3
4 459 6 059
10.8
3 665
2.7
2 121
20
to that of a three-year grass ley. It also shows a labour efficiency ratio expressed in terms of megajoules of metabolisable energy o u t p u t per man hour. Fertiliser and fuel to power machinery are the two major inputs, apart from the sun, in most crop production systems in the developed world. The analysis set out above applies to a particular cropping system on a particular dairy farm, but shows how a re-appraisal of traditional methods such as organic manuring and closer examination of new techniques such as direct drilling can reduce energy inputs and costs of production.
REFERENCES Austin, R.B., 1975. Economy in the use of manufactured fertiliser. Ann. Conf. Inst. Agric. Eng., London, 9 pp. Bunting, E.W. and Gunn, R.E., 1973. Maize in Britain - - a survey of research and breeding. Plant Breeding Institute Cambridge, Annual Report 1973, pp. 32--74. I.F.I.A.S., 1974. Energy analysis. Workshop Report No. 6. International Federation of Institutes for Advanced Study. The Nobel House, Stockholm, Sweden, 89 pp. Leach, G., 1975. Energy and food production. International Institute for Environment and Development, London, 151 pp. Pain, B.F., 1976. Cow slurry for forage maize. Maize Bulletin, 85: 3--6. Pain, B.F. and Phipps, R.H., 1975. The energy to grow maize. New Sci., 66 (949): 394--396. Phipps, R.H. and Pain, B.F., 1975. Levels of fertilizer for forage maize. A.D.A.S.q. Rev., 18: 49--54. Pimentel, D., Hurd, L.E., Belloti, A.C., Forster, M.J., Oaka, I.N., Shoves, O.D. and Whitman, R.J., 1973. F o o d production and the energy crisis. Science, 183: 443--449. White, D.J., 1975. Energy in agricultural systems. Ann. Conf. Inst. Agric. Eng., London, 21 pp.