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Fertilizer and irrigation management for energy conservation in crop production
Energy Vol. 20, No. 8, pp. 771-776, 1995
Pergamon
0360-5442(95)00011-9
Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0360-5442/95 $9.50+0.00
FERTILIZER AND IRRIGATION MANAGEMENT FOR ENERGY CONSERVATION IN CROP PRODUCTION G. C. AGGARWAL Department of Soils, Punjab Agricultural University, Ludhiana, India-141 004 (Received 10 August 1994; receivedfor publication 17 January 1995) Abstract--Fertilizers and irrigation water are the two major energy inputs in Indian agriculture. Energy returns from energy inputs in fertilizers and irrigation water have been evaluated. An increase in either of these two inputs increased the crop yield but decreased the energy-use efficiency. Judicious use of fertilizers and irrigation water reduced the energy cost of irrigation plus fertilizers by 20-50%. Optimum use of limited energy was in irrigation.
INTRODUCTION Indian agriculture has become energy-intensive since the early 1960s, the advent of the green revolution. Consumption of fertilizers in India has increased from 10 kg/ha in 1968 to 67 kg/ha in 1989 and the irrigated area has increased from 30 million hectare in 1970 to 42.8 million hectare in 1988. A previous study revealed that accelerating the growth rate of agricultural production through adoption of modern inputs and technology would result in a more than proportionate acceleration in the total energy demand for the agricultural sector.1 Energy availability and its cost, however, are becoming important constraints, especially in India and other Third-World, oil-importing countries, 2"3 which necessitates judicious use of non-renewable energy in agriculture. Evaluation of use rates of fertilizers and irrigation is required since about 70% of the commercial energy input in Indian agriculture occurs in this manner? The effects of using organic manures, 3.4 weeding, 5 tillage, and planting methods 6 on energy-use efficiency (ratio of energy output to input) have been reported. The objectives of this study were (i) to study the effects of fertilizer and irrigation use on the energy-use efficiency of crops, (ii) to evaluate especially the energy-use efficiency of N (nitrogenous) fertilizers, and (iii) to study the effects of changes in energy costs for N fertilizer and irrigation water on the energy-use efficiency. METHODOLOGY This analysis is based on four field studies conducted by us on deep, non-saline sandy loam and loamy sand soils at Punjab Agricultural University, Ludhiana (30 ° 50'N, 75 ° 52'E), India. Pertinent details about these experiments are summarized below. Nitrogen, phosphorous and irrigation effects in wheat The main and interactive effects of nitrogen, phosphorous and irrigation on wheat yield were studied for two years. 7 The treatments comprised three rates of nitrogen (40, 80 and 120 kg/ha), three rates of phosphorous (0, 13.1 and 26.2 kg/ha) and four numbers (1--4) of irrigation based on IW/PAN-E ratios, s Fertilizer-irrigation interaction in wheat Fertilizer-irrigation interaction in wheat was evaluated for 2 years. The fertilizer treatments consisted of 0, 33, 67, 100, and 133% of the optimum fertilizer NPK dose based on soil-test values and planned number of irrigations based on IW/PAN-E ratios varied from 0 (no irrigation) to 5. However, due to frequent rains, only two irrigations were actually applied. Nitrogen and irrigation effects on cowpea and maize fodders The responses of maize and cowpea fodder as monocultures and as a 1:1 mixture to applied irrigation and nitrogen were studied for 2 years. 9 Treatments involved three irrigation schedules based on IW/PAN-E ratios of 0.6, 0.9 and 1.2 and four nitrogen rates 0, 40, 80, and 120 kg/ha. 771
772
G.C. Aggarwal Table 1. Energy requirements for various field operations and recommendedagricultural inputs for the cultivation of wheat, based on data from Refs. 6 and I 1.
Parameter Seedbed preparation Sowing Seed Fertilizers 120 kg N/ha 26 kg P/ha 50 kg K/ha Weeding Irrigation water (30 ha-cm) Harvesting and threshing Total energy input Grain-energy output Energy-use efficiency
Energy input (MJ/ha) 325 102 2045 7272 666 402 76 648 445 11,982 63,386 5.3
Fertilizer and periodic moisture stress effects on rice The stresses of fertilizers and periodic soil moisture on rice were studied. ~° The treatments included combinations of two soil-moisture regimes, viz., continuous submergence and a periodic moisture stress imposed 50, 75 and 95 days after transplanting by withholding irrigation for four to five days after infiltration of ponded water and five fertilizer treatments, i.e. (i) No Po, (ii) N6o Po, (iii) Ni2 o Po, (iv) N6o PI3, and (v) Ni2 o P26- Subscripts indicate the use rates (kg/ha) of nitrogen and phosphorous, respectively. Continuous submergence was maintained for 1 month. Energy requirements for different field operations and recommended inputs for wheat, rice and maize fodder are given in Tables 1-3. The costs of seedbed preparation and other cultural practices depend on soil, mechanization level and other factors. The energy costs for insecticides and fungicides, which were sometimes applied, have not been included. The energy output was computed by taking the energy value of wheat and rice grain to be 14.7 MJ/kg 6 and that of dry fodder to be 18.0 MJ/kg. 6 The energy-use efficiency (EUE) or the energy output-input ratio is the ratio of the grain energy output to the energy input) The energy-use efficiencies of irrigation (EUEI), of fertilizers (EUEF), of nitrogen (EUEN), and of phosphorous (EUEP) were computed by performing cost-benefit analyses using a partial budgeting method.~2 Benefits were calculated only for the yield increases due to irrigation
Table 2. Energy requirements for various field operations and recommended inputs for the cultivation of rice, based on data from Refs. 6 and 11.
Parameters Nursery raising Seedbed preparation Seed Transplanting Fertilizers 120 kg N/ha 26 kg P/ha Weeding Irrigation water (323 ha-cm) Harvesting and threshing Total energy input Grain-energy output Energy-use efficiency
Energy input (MJ/ha) 129 318 304 70 7272 666 2l 6975 623 16,378 109,074 6.7
Energy conservationin crop production
773
Table 3. Energy requirements for various field operations and recommended inputs for the cultivation of maize fodder, based on data from Refs. 6 and 11. Energy input (MJ/ha)
Parameter Seedbed preparation Sowing Seed Fertilizers 120 kg N/ha 26 kg P/ha 25 kg K/ha Weeding Irrigation water (30 ha-cm) Harvesting Total energy input Energy output Energy-use efficiency
362 117 1029 7272 666 201 62 648 90 10,447 154,800 14.8
Table 4. Energyconservationwithjudicious managementof fertilizers and irrigation in wheat. Equivalent yield (kg/ha)
1920 1900 1890 2630 2650 3210 3220 3260 3800 3790 3830
Feailizer
Irrigation number
Nt Pt (kg/ha) 40 40 40 80 40 120 80 80 120 120 120
26.2 0 0 0 13.1 13.1 26.2 0 26.2 13.1 0
1 2 1 2 4 1 2 4 2 3 4
Energy saved (%)
Ref.:~ 10.6 8.1 Ref. 21.6 Ref. 18.0 21.1 Ref. 1.5 3.0
Energyuse efficiency
4.5 4.9 5.0 4.7 4.9 4.4 5.3 5.6 5.0 5.0 5.2
tN and P indicate nitrogen and phosphorous, respectively. SRef. indicatestreatment with respect to which energy is conserved.
or fertilizers above the lowest input level (RL) and the costs were taken as the additional energy costs of irrigation or of fertilizers. RESULTS AND DISCUSSION The similar wheat yields obtained in experiment No. 1 with different energy inputs of fertilizers and irrigation (Table 4) indicated that with proper management, the energy input in crop production could be reduced. An energy input of 8994 MJ or 10,590 MJ resulted in the similar yields, thus effecting 16% saving in the energy input. A wheat yield of 2200 kg/ha and 1980 kg/ha with the fertilizer plus irrigation energy input of 6075 MJ/ha and 6246 MJ/ha, respectively indicated considerable scope for energy saving. Variations (from 4.3 to 6.1 ) in the energy-use efficiency (EUE) with different combinations of irrigations and use rates of fertilizers also suggested that the energy output from a given energy input increased with proper management. The energy use efficiency in wheat increased with an increase in the energy input through irrigation (Table 5), decreased with an increase in the energy input through nitrogen but was unaffected by the phosphorous level. The energy output from unit energy input in irrigation (EUEI), phosphorous (EUEP), EGY 20-BoE
774
G.C. Aggarwai Table 5. Energy use efficiency as affected by irrigation, nitrogen and phosphorous in wheat. Treatment Irrigation (number 1 2 3 4 Phosphorous (kg/ha) 0 13.1 26.2 Nitrogen (kg/ha) 40 80 120 Mean
EUE
EUEI
EUEN
EUEP
4.7 5.0 5.2 5.6
RLt 22.4 18.6 21.3
4.4 5.2 4.4 4.8
6.9 15.9 10.6 6.3
5.0 5.3 5.1
14.9 26.5 21.0
4.0 4.7 5.5
RL 11.9 7.8
5.3 5.3 4.9 5. I
17.0 22.8 22.6 20.8
RL 5.1 4.3 4.7
5.0 12.1 12.6 9.9
tRL is the lowest input level of irrigation, nitrogen, and phosphorous.
Table 6. Effect of irrigation and nitrogen on energy use efficiency in intercropped fodder. Treatment IW/PAN-E 0.6 0.9 1.2 Nitrogen (kg/ha) 0 40 80 120 Mean
EUE
EUEI
EUEN
20.1 20.6 19.1
RLt 71.7 10.2
8.2 8.9 11.2
27.8 21.1 16.8 14.1 19.9
4.9 43.1 23.6 92.3 41.0
RL 1!.6 9.0 7.7 9.5
tRL is the lowest input level of irrigation and nitrogen.
and nitrogen (EUEN) varied from 14.9 to 26.0, 5.0 to 15.9, and 4.0 to 5.5, respectively (Table 5). Mean energy outputs of 20.8, 9.9 and 4.7 per unit energy input through irrigation, phosphorous and nitrogen, respectively, show that the most efficient use of limited energy was through irrigation. Analyses of the data obtained from experiment No. 2 showed that the EUE in wheat decreased from 13.5 when no fertilizer was used to 6.5 when the use rate of fertilizers was 133% of the recommended dose. The changes in the EUE due to increased energy input through irrigation were, however, small. The mean EUEI was nearly four times the mean EUEF. These results are consistent with those of experiment No. 1. Analyses of the data reported by Gajri et al '3 also indicated that nearly 25% energy in wheat production could be saved by efficient management of nitrogen and irrigation in loamy sand and sandy loam soils. Furthermore, the energy output from a given energy input changed with soil, the mean EUE on a sandy loam soil being higher than that on a loamy sand soil. In the intercropped fodders (experiment No. 3), an increase in the use rate of nitrogen decreased the EUE but an increase in energy input through irrigation did not decrease the EUE (Table 6). The similar yields obtained with energy inputs of 8230 and 10,567 MJ show that with proper management, energy costs of fodder production could be reduced by 20%. The mean EUEI was more than five times the mean EUEN. Thus, the highest energy could be harvested from the limited energy input through irrigation of
Energy conservationin crop production
775
Table 7. Effectof periodic moisturestress and fertilizers on energy use efficiencyin rice. Treatment
EUE
Fertilizers No P~t N6o Po Nr~ P~3 NI2o Po N~2oP26 Irrigation Periodic stress No stress Mean
E U E I EUEF
9.9 8.9 9.0 7.0 6.7
17.1 15.3 5.9 3.8 5.9
RL:[: 6.8 7.1 3.9 3.5
8.2 8.4 8.3
RL 9.6 9.6
4.6 6.1 5.3
tSubscripts indicate the use rates (kg/ha) of nitrogen and phosphorous. SRL is the lowest input level of irrigationand fertilizer.
Table 8. Effect of changes in total hydraulichead and energy cost of N fertilizeron energy use efficiencyof irrigation(EUEI) and of nitrogen (EUEN) in wheat. EUEI
EUEN
Total hydraulic head (m)
Energy cost of 1 kg N (MJ)
Treatment
Irrigation (number) 1 2 3 4 Nitrogen (kg/ha) 40 80 120 Mean
10
20
30
60.6
48.0
41.1
RLt 28.1 23.3 26.8
RL 13.2 11.0 12.6
RL 8.1 6.7 7.7
4.4 5.2 4.4 4.8
5.6 6.5 5.6 6.1
6.5 7.6 6.5 7.1
21.3 28.6 28.4 26.1
10.0 13.4 13.3 12.3
6.1 8.2 8. I 7.5
RL 5.1 4.3 4.7
RL 6.5 5.4 6.0
RL 7.6 6.3 7.0
tRL is the lowest input level of irrigationand nitrogen.
the fodder crops. Analyses of the data on sorghum fodder reported by Sandhu et a114 also suggested that judicious use of fertilizers and irrigation reduced the energy input through fertilizers and irrigation by 50%. The values of EUE, EUEN and EUEI at different use rates of nitrogen and irrigation again indicate that the optimum use of limited energy was in irrigation. Periodic moisture stress (experiment No. 4) did not decrease the EUE (Table 7) although it significantly decreased the rice yield. The energy-use efficiency (EUE) and the EUEF decreased with an increase in the use rate of fertilizers. The mean EUE! was about 1.8 times that of the mean EUEF. These results also indicate that if energy is limited, it should be used for irrigation. The present study demonstrates that energy input through fertilizers and irrigation could be considerably reduced without lowering the crop yields by judicious management of fertilizers and irrigation. An increase in the use rate of fertilizers improved the crop yields but the energy output per unit energy input through fertilizers decreased. The energy output from increased energy input through irrigation, however, did not decrease. This shows that the most efficient use of limited energy was through irrigation. The energy cost of pumping ground water increases with an increase in the depth of ground water. Since the water table is receding in many areas due to over exploitation of ground water, this factor
776
G.C. Aggarwal
alone will lower the EUEI even if all inputs and the crop yields remain constant. Moreover, the energy cost of N fertilizer is decreasing with improvements in fertilizer manufacturing technology. 15 This will result in increased EUEN. Consequently, the effect of an increase in water-table depth (total hydraulic heads of 10, 20 and 30 m) and reduction in energy cost of N fertilizer (48.0 and 41.1 MJ/kg) ~5 on EUE, EUEN and EUEI in wheat (experiment No. 1) was evaluated. In some situations, the energy returns from a given energy input through N fertilizer were comparable with returns from input of the same energy through irrigation (Table 8). These results highlight the need for an energy audit of irrigation and use rates of fertilizers in different regions and situations on different soils for maximizing energy-use efficiency in crop production. REFERENCES 1. T. K. Moulik, B. H. Dholakia, and P. R. Shukla, Energy Demand For Agriculture in India in the Year 2000, Oxford & IBH Publishing, New Delhi, India (1991). 2. D. Pimentel, in Food, Climate and Man, p. 73, M. R. Biswas and A. K. Biswas eds., Wiley, New York, NY (1979). 3. G. C. Aggarwal and N. T. Singh, in Energy Conservation and Use of Renewable Energies in the Bio-lndustries, Vol. 2, p. 2, F. Vogt ed., Pergamon, Oxford, England (1983). 4. G. C. Aggarwal, Energy--The International Journal 14, 349 (1989). 5. G. C. Aggarwal, D. Pimentel, and M. Giampietro, Agric. Ecosystems Environ. 39, 235 (1992). 6. S. Singh, R. Bakhshi, and M. P. Singh, "Research Digest on Energy Requirements in the Agricultural Sector in the State of Punjab," p. 145, Punjab Agricultural University, Ludhiana, India (1988). 7. A. S. Sidhu and G. C. Aggarwal, Indian J. EcoL 19, 20 (1992). 8. S. S. Prihar, P. R. Gajri, and R. S. Narang, Indian J. Agric. Sci. 44, 567 (1974). 9. G. C. Aggarwal and A. S. Sidhu, Field Crops Res. 18, 177 (1988). 10. G. C. Aggarwal, A. S. Sidhu, and N. T. Singh, J. Indian Soc. Soil Sci. 35~ 280 (1987). 11. B. S. Sandhu and S. S. Prihar, "Scheduling Irrigation to Crops in Punjab," p. 41, Punjab Agricultural Univ., Ludhiana, India (1983). 12. M. D. J. Islam and M. K. Mandal, Agric. Water Mgmt 22, 335 (1992). 13. P. R. Gajri, S. S. Prihar, and V. K. Arora, Field Crops Res. 31, 71 (1993). 14. B. S. Sandhu, Baldev Singh, and T. S. Aujla, J. Indian Soc. Soil Sci. 35, 603 (1987). 15. E. Worrell and K. Blok, Energy--The International Journal 19, 195 (1994).
Pergamon
0360-5442(95)00011-9
Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0360-5442/95 $9.50+0.00
FERTILIZER AND IRRIGATION MANAGEMENT FOR ENERGY CONSERVATION IN CROP PRODUCTION G. C. AGGARWAL Department of Soils, Punjab Agricultural University, Ludhiana, India-141 004 (Received 10 August 1994; receivedfor publication 17 January 1995) Abstract--Fertilizers and irrigation water are the two major energy inputs in Indian agriculture. Energy returns from energy inputs in fertilizers and irrigation water have been evaluated. An increase in either of these two inputs increased the crop yield but decreased the energy-use efficiency. Judicious use of fertilizers and irrigation water reduced the energy cost of irrigation plus fertilizers by 20-50%. Optimum use of limited energy was in irrigation.
INTRODUCTION Indian agriculture has become energy-intensive since the early 1960s, the advent of the green revolution. Consumption of fertilizers in India has increased from 10 kg/ha in 1968 to 67 kg/ha in 1989 and the irrigated area has increased from 30 million hectare in 1970 to 42.8 million hectare in 1988. A previous study revealed that accelerating the growth rate of agricultural production through adoption of modern inputs and technology would result in a more than proportionate acceleration in the total energy demand for the agricultural sector.1 Energy availability and its cost, however, are becoming important constraints, especially in India and other Third-World, oil-importing countries, 2"3 which necessitates judicious use of non-renewable energy in agriculture. Evaluation of use rates of fertilizers and irrigation is required since about 70% of the commercial energy input in Indian agriculture occurs in this manner? The effects of using organic manures, 3.4 weeding, 5 tillage, and planting methods 6 on energy-use efficiency (ratio of energy output to input) have been reported. The objectives of this study were (i) to study the effects of fertilizer and irrigation use on the energy-use efficiency of crops, (ii) to evaluate especially the energy-use efficiency of N (nitrogenous) fertilizers, and (iii) to study the effects of changes in energy costs for N fertilizer and irrigation water on the energy-use efficiency. METHODOLOGY This analysis is based on four field studies conducted by us on deep, non-saline sandy loam and loamy sand soils at Punjab Agricultural University, Ludhiana (30 ° 50'N, 75 ° 52'E), India. Pertinent details about these experiments are summarized below. Nitrogen, phosphorous and irrigation effects in wheat The main and interactive effects of nitrogen, phosphorous and irrigation on wheat yield were studied for two years. 7 The treatments comprised three rates of nitrogen (40, 80 and 120 kg/ha), three rates of phosphorous (0, 13.1 and 26.2 kg/ha) and four numbers (1--4) of irrigation based on IW/PAN-E ratios, s Fertilizer-irrigation interaction in wheat Fertilizer-irrigation interaction in wheat was evaluated for 2 years. The fertilizer treatments consisted of 0, 33, 67, 100, and 133% of the optimum fertilizer NPK dose based on soil-test values and planned number of irrigations based on IW/PAN-E ratios varied from 0 (no irrigation) to 5. However, due to frequent rains, only two irrigations were actually applied. Nitrogen and irrigation effects on cowpea and maize fodders The responses of maize and cowpea fodder as monocultures and as a 1:1 mixture to applied irrigation and nitrogen were studied for 2 years. 9 Treatments involved three irrigation schedules based on IW/PAN-E ratios of 0.6, 0.9 and 1.2 and four nitrogen rates 0, 40, 80, and 120 kg/ha. 771
772
G.C. Aggarwal Table 1. Energy requirements for various field operations and recommendedagricultural inputs for the cultivation of wheat, based on data from Refs. 6 and I 1.
Parameter Seedbed preparation Sowing Seed Fertilizers 120 kg N/ha 26 kg P/ha 50 kg K/ha Weeding Irrigation water (30 ha-cm) Harvesting and threshing Total energy input Grain-energy output Energy-use efficiency
Energy input (MJ/ha) 325 102 2045 7272 666 402 76 648 445 11,982 63,386 5.3
Fertilizer and periodic moisture stress effects on rice The stresses of fertilizers and periodic soil moisture on rice were studied. ~° The treatments included combinations of two soil-moisture regimes, viz., continuous submergence and a periodic moisture stress imposed 50, 75 and 95 days after transplanting by withholding irrigation for four to five days after infiltration of ponded water and five fertilizer treatments, i.e. (i) No Po, (ii) N6o Po, (iii) Ni2 o Po, (iv) N6o PI3, and (v) Ni2 o P26- Subscripts indicate the use rates (kg/ha) of nitrogen and phosphorous, respectively. Continuous submergence was maintained for 1 month. Energy requirements for different field operations and recommended inputs for wheat, rice and maize fodder are given in Tables 1-3. The costs of seedbed preparation and other cultural practices depend on soil, mechanization level and other factors. The energy costs for insecticides and fungicides, which were sometimes applied, have not been included. The energy output was computed by taking the energy value of wheat and rice grain to be 14.7 MJ/kg 6 and that of dry fodder to be 18.0 MJ/kg. 6 The energy-use efficiency (EUE) or the energy output-input ratio is the ratio of the grain energy output to the energy input) The energy-use efficiencies of irrigation (EUEI), of fertilizers (EUEF), of nitrogen (EUEN), and of phosphorous (EUEP) were computed by performing cost-benefit analyses using a partial budgeting method.~2 Benefits were calculated only for the yield increases due to irrigation
Table 2. Energy requirements for various field operations and recommended inputs for the cultivation of rice, based on data from Refs. 6 and 11.
Parameters Nursery raising Seedbed preparation Seed Transplanting Fertilizers 120 kg N/ha 26 kg P/ha Weeding Irrigation water (323 ha-cm) Harvesting and threshing Total energy input Grain-energy output Energy-use efficiency
Energy input (MJ/ha) 129 318 304 70 7272 666 2l 6975 623 16,378 109,074 6.7
Energy conservationin crop production
773
Table 3. Energy requirements for various field operations and recommended inputs for the cultivation of maize fodder, based on data from Refs. 6 and 11. Energy input (MJ/ha)
Parameter Seedbed preparation Sowing Seed Fertilizers 120 kg N/ha 26 kg P/ha 25 kg K/ha Weeding Irrigation water (30 ha-cm) Harvesting Total energy input Energy output Energy-use efficiency
362 117 1029 7272 666 201 62 648 90 10,447 154,800 14.8
Table 4. Energyconservationwithjudicious managementof fertilizers and irrigation in wheat. Equivalent yield (kg/ha)
1920 1900 1890 2630 2650 3210 3220 3260 3800 3790 3830
Feailizer
Irrigation number
Nt Pt (kg/ha) 40 40 40 80 40 120 80 80 120 120 120
26.2 0 0 0 13.1 13.1 26.2 0 26.2 13.1 0
1 2 1 2 4 1 2 4 2 3 4
Energy saved (%)
Ref.:~ 10.6 8.1 Ref. 21.6 Ref. 18.0 21.1 Ref. 1.5 3.0
Energyuse efficiency
4.5 4.9 5.0 4.7 4.9 4.4 5.3 5.6 5.0 5.0 5.2
tN and P indicate nitrogen and phosphorous, respectively. SRef. indicatestreatment with respect to which energy is conserved.
or fertilizers above the lowest input level (RL) and the costs were taken as the additional energy costs of irrigation or of fertilizers. RESULTS AND DISCUSSION The similar wheat yields obtained in experiment No. 1 with different energy inputs of fertilizers and irrigation (Table 4) indicated that with proper management, the energy input in crop production could be reduced. An energy input of 8994 MJ or 10,590 MJ resulted in the similar yields, thus effecting 16% saving in the energy input. A wheat yield of 2200 kg/ha and 1980 kg/ha with the fertilizer plus irrigation energy input of 6075 MJ/ha and 6246 MJ/ha, respectively indicated considerable scope for energy saving. Variations (from 4.3 to 6.1 ) in the energy-use efficiency (EUE) with different combinations of irrigations and use rates of fertilizers also suggested that the energy output from a given energy input increased with proper management. The energy use efficiency in wheat increased with an increase in the energy input through irrigation (Table 5), decreased with an increase in the energy input through nitrogen but was unaffected by the phosphorous level. The energy output from unit energy input in irrigation (EUEI), phosphorous (EUEP), EGY 20-BoE
774
G.C. Aggarwai Table 5. Energy use efficiency as affected by irrigation, nitrogen and phosphorous in wheat. Treatment Irrigation (number 1 2 3 4 Phosphorous (kg/ha) 0 13.1 26.2 Nitrogen (kg/ha) 40 80 120 Mean
EUE
EUEI
EUEN
EUEP
4.7 5.0 5.2 5.6
RLt 22.4 18.6 21.3
4.4 5.2 4.4 4.8
6.9 15.9 10.6 6.3
5.0 5.3 5.1
14.9 26.5 21.0
4.0 4.7 5.5
RL 11.9 7.8
5.3 5.3 4.9 5. I
17.0 22.8 22.6 20.8
RL 5.1 4.3 4.7
5.0 12.1 12.6 9.9
tRL is the lowest input level of irrigation, nitrogen, and phosphorous.
Table 6. Effect of irrigation and nitrogen on energy use efficiency in intercropped fodder. Treatment IW/PAN-E 0.6 0.9 1.2 Nitrogen (kg/ha) 0 40 80 120 Mean
EUE
EUEI
EUEN
20.1 20.6 19.1
RLt 71.7 10.2
8.2 8.9 11.2
27.8 21.1 16.8 14.1 19.9
4.9 43.1 23.6 92.3 41.0
RL 1!.6 9.0 7.7 9.5
tRL is the lowest input level of irrigation and nitrogen.
and nitrogen (EUEN) varied from 14.9 to 26.0, 5.0 to 15.9, and 4.0 to 5.5, respectively (Table 5). Mean energy outputs of 20.8, 9.9 and 4.7 per unit energy input through irrigation, phosphorous and nitrogen, respectively, show that the most efficient use of limited energy was through irrigation. Analyses of the data obtained from experiment No. 2 showed that the EUE in wheat decreased from 13.5 when no fertilizer was used to 6.5 when the use rate of fertilizers was 133% of the recommended dose. The changes in the EUE due to increased energy input through irrigation were, however, small. The mean EUEI was nearly four times the mean EUEF. These results are consistent with those of experiment No. 1. Analyses of the data reported by Gajri et al '3 also indicated that nearly 25% energy in wheat production could be saved by efficient management of nitrogen and irrigation in loamy sand and sandy loam soils. Furthermore, the energy output from a given energy input changed with soil, the mean EUE on a sandy loam soil being higher than that on a loamy sand soil. In the intercropped fodders (experiment No. 3), an increase in the use rate of nitrogen decreased the EUE but an increase in energy input through irrigation did not decrease the EUE (Table 6). The similar yields obtained with energy inputs of 8230 and 10,567 MJ show that with proper management, energy costs of fodder production could be reduced by 20%. The mean EUEI was more than five times the mean EUEN. Thus, the highest energy could be harvested from the limited energy input through irrigation of
Energy conservationin crop production
775
Table 7. Effectof periodic moisturestress and fertilizers on energy use efficiencyin rice. Treatment
EUE
Fertilizers No P~t N6o Po Nr~ P~3 NI2o Po N~2oP26 Irrigation Periodic stress No stress Mean
E U E I EUEF
9.9 8.9 9.0 7.0 6.7
17.1 15.3 5.9 3.8 5.9
RL:[: 6.8 7.1 3.9 3.5
8.2 8.4 8.3
RL 9.6 9.6
4.6 6.1 5.3
tSubscripts indicate the use rates (kg/ha) of nitrogen and phosphorous. SRL is the lowest input level of irrigationand fertilizer.
Table 8. Effect of changes in total hydraulichead and energy cost of N fertilizeron energy use efficiencyof irrigation(EUEI) and of nitrogen (EUEN) in wheat. EUEI
EUEN
Total hydraulic head (m)
Energy cost of 1 kg N (MJ)
Treatment
Irrigation (number) 1 2 3 4 Nitrogen (kg/ha) 40 80 120 Mean
10
20
30
60.6
48.0
41.1
RLt 28.1 23.3 26.8
RL 13.2 11.0 12.6
RL 8.1 6.7 7.7
4.4 5.2 4.4 4.8
5.6 6.5 5.6 6.1
6.5 7.6 6.5 7.1
21.3 28.6 28.4 26.1
10.0 13.4 13.3 12.3
6.1 8.2 8. I 7.5
RL 5.1 4.3 4.7
RL 6.5 5.4 6.0
RL 7.6 6.3 7.0
tRL is the lowest input level of irrigationand nitrogen.
the fodder crops. Analyses of the data on sorghum fodder reported by Sandhu et a114 also suggested that judicious use of fertilizers and irrigation reduced the energy input through fertilizers and irrigation by 50%. The values of EUE, EUEN and EUEI at different use rates of nitrogen and irrigation again indicate that the optimum use of limited energy was in irrigation. Periodic moisture stress (experiment No. 4) did not decrease the EUE (Table 7) although it significantly decreased the rice yield. The energy-use efficiency (EUE) and the EUEF decreased with an increase in the use rate of fertilizers. The mean EUE! was about 1.8 times that of the mean EUEF. These results also indicate that if energy is limited, it should be used for irrigation. The present study demonstrates that energy input through fertilizers and irrigation could be considerably reduced without lowering the crop yields by judicious management of fertilizers and irrigation. An increase in the use rate of fertilizers improved the crop yields but the energy output per unit energy input through fertilizers decreased. The energy output from increased energy input through irrigation, however, did not decrease. This shows that the most efficient use of limited energy was through irrigation. The energy cost of pumping ground water increases with an increase in the depth of ground water. Since the water table is receding in many areas due to over exploitation of ground water, this factor
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alone will lower the EUEI even if all inputs and the crop yields remain constant. Moreover, the energy cost of N fertilizer is decreasing with improvements in fertilizer manufacturing technology. 15 This will result in increased EUEN. Consequently, the effect of an increase in water-table depth (total hydraulic heads of 10, 20 and 30 m) and reduction in energy cost of N fertilizer (48.0 and 41.1 MJ/kg) ~5 on EUE, EUEN and EUEI in wheat (experiment No. 1) was evaluated. In some situations, the energy returns from a given energy input through N fertilizer were comparable with returns from input of the same energy through irrigation (Table 8). These results highlight the need for an energy audit of irrigation and use rates of fertilizers in different regions and situations on different soils for maximizing energy-use efficiency in crop production. REFERENCES 1. T. K. Moulik, B. H. Dholakia, and P. R. Shukla, Energy Demand For Agriculture in India in the Year 2000, Oxford & IBH Publishing, New Delhi, India (1991). 2. D. Pimentel, in Food, Climate and Man, p. 73, M. R. Biswas and A. K. Biswas eds., Wiley, New York, NY (1979). 3. G. C. Aggarwal and N. T. Singh, in Energy Conservation and Use of Renewable Energies in the Bio-lndustries, Vol. 2, p. 2, F. Vogt ed., Pergamon, Oxford, England (1983). 4. G. C. Aggarwal, Energy--The International Journal 14, 349 (1989). 5. G. C. Aggarwal, D. Pimentel, and M. Giampietro, Agric. Ecosystems Environ. 39, 235 (1992). 6. S. Singh, R. Bakhshi, and M. P. Singh, "Research Digest on Energy Requirements in the Agricultural Sector in the State of Punjab," p. 145, Punjab Agricultural University, Ludhiana, India (1988). 7. A. S. Sidhu and G. C. Aggarwal, Indian J. EcoL 19, 20 (1992). 8. S. S. Prihar, P. R. Gajri, and R. S. Narang, Indian J. Agric. Sci. 44, 567 (1974). 9. G. C. Aggarwal and A. S. Sidhu, Field Crops Res. 18, 177 (1988). 10. G. C. Aggarwal, A. S. Sidhu, and N. T. Singh, J. Indian Soc. Soil Sci. 35~ 280 (1987). 11. B. S. Sandhu and S. S. Prihar, "Scheduling Irrigation to Crops in Punjab," p. 41, Punjab Agricultural Univ., Ludhiana, India (1983). 12. M. D. J. Islam and M. K. Mandal, Agric. Water Mgmt 22, 335 (1992). 13. P. R. Gajri, S. S. Prihar, and V. K. Arora, Field Crops Res. 31, 71 (1993). 14. B. S. Sandhu, Baldev Singh, and T. S. Aujla, J. Indian Soc. Soil Sci. 35, 603 (1987). 15. E. Worrell and K. Blok, Energy--The International Journal 19, 195 (1994).