Energy Use and Carbon Release by Manufactured Inputs in Crop Production
A Comparison of Two Manitoba Farms with Contrasting Tillage Systems
By Robert H. Gulden and Martin H. Entz
Results of small plot research have shown that the energy use and carbon emissions in a zero tillage system are lower than those of a conventional tillage system when similar annual crops are considered (Entz, 1995). The purpose of this study was to compare the energy use and carbon emissions of a zero tillage and a conventional tillage farming system using two case study farming operations with similar crop rotations.
The energy use and carbon emissions release by manufactured inputs varies among cropping systems. Machinery and fuel costs tend to be lower in a zero tillage cropping system compared to a conventional tillage cropping system (Henry, 1995). Conversely, the energy use and carbon emissions of herbicides tend to be higher in a zero tillage cropping system compared to a conventional tillage cropping system (Henry, 1995) resulting from the necessary shift from mechanical to chemical weed control. Most previous research has indicated that the total energy use and carbon emissions of manufactured inputs are lower in zero tillage cropping systems compared to conventional tillage cropping systems (Townsend, 1977; Henry, 1995, Entz, 1995).
Adding leguminous perennial forages to the rotation reduces the long term energy inputs and carbon emissions compared to farming systems solely dependent on annual grain crops (including grain legumes). Other benefits of alfalfa in rotation with annual grain crops include nitrogen contributions to subsequent crops (Kelner, 1994), as well as weed suppression (Ominski and Entz, 1994). To date, energy use and carbon emission studies have been conducted primarily on small scale research plots and results have been extrapolated to farming operations of various sizes. Limited research in this area has been conducted using case study farms.
This research included two 650 ha commercial farms located in Manitoba. Data was collected for one field (approx. 160 acres) for a period of eight years (1988-1995) and extrapolated over the entire acreage of the farm. The conventional cropping system operation had the following crop rotation:
canola/alfalfa (flax /alfalfa) - alfalfa - alfalfa - wheat - canola - wheat - pea - flax (barley)
The deviations in the zero tillage farming system are indicated in parentheses. The rotations were very similar with the exception that the zero tillage system had one more cereal crop than the conventional tillage rotation over the eight year duration. The first year of each crop rotation was the establishment year for the forage crop (alfalfa). The forage was kept in the rotation for two years following establishment. An equal acreage of each crop was assumed for the calculations on a whole farm basis.
The equipment life-span and energy coefficients were derived from Coxworth et al. (1994) and adjusted for the forage in rotation. When energy coefficients were not available, the formula given by Coxworth et al. was used to calculate the energy coefficients. Energy use coefficients for the baler, fertilizer spreader and truck and auger as well as energy coefficients and carbon emissions of fuel and machinery use were obtained from Entz (1995). Coefficients for fertilizers and herbicides were obtained from Stout (1990), Coxworth et al. (1994), and Henry (1995). In the rare event that coefficients were not available for a particular herbicide, conversions from average values given by Coxworth et al. (1994) were used to determine the carbon emission coefficients from the energy use coefficient. When neither energy use nor carbon emission coefficients were available, the average values presented by Coxworth et al. (1994) were substituted. Crop energy coefficients were derived from Southwell and Rothwell (1977), Henry (1995), and Pimentel (1980).
The energy required per tonne crop produced and energy output/input ratios were calculated using the producers actual yields as well as the provincial averages to eliminate climatic and other location specific differences.
Conventional Tillage Farm
The energy inputs and carbon emissions were highest for the annual non-leguminous grain crops, ranging from 6214.97 to 9914.05 MJ/ha and 101.08 to 156.24 kg C/ha, respectively. The energy use and carbon emissions were intermediate for the pea crop (5397.37 MJ/ha and 86.97 kg C/ha, respectively) and lowest for the alfalfa crop, ranging from 685.27 to 2491.61 MJ/ha and 13.18 to 43.61 kg C/ha, respectively. The primary reason for the observed differences between the legume and non-legume crops was the higher N fertilizer requirement for the non-legume crops. Less important, but still significant were the lower fuel energy use and carbon emissions in the forage alfalfa compared to the annual crops.
Zero Tillage Farm
Once again, non-leguminous annual crops were highest in energy use and carbon emissions (5735.83 to 9315.65 MJ/ha and 92.37 to 137.82 kg C/ha), peas were intermediate (2479.80 MJ/ha, 44.83 kg C/ha) and alfalfa was lowest (414.85 to 1803.96 MJ/ha, 7.98 to 29.69 kg C/ha). The reasons for these trends are similar to those observed in the conventional tillage farming operation.
Comparing the Tillage Systems
Average energy use and carbon emissions in the zero tillage system were approximately 86.4 % that of the conventional tillage system (Table 1). This was similar to previous reports in the literature (Townsend, 1977; Henry, 1995; Entz, 1995). The reduced machinery and fuel use contributed most to the observed savings with the zero tillage system, at 67.1 and 63.7 % of the energy use and 67.1 and 64.6 % of the carbon emissions of the conventional tillage system, respectively. Lower machinery costs under zero tillage were expected since fewer machine passes over each field is one of the main advantages of a zero tillage farming system.
Table 1. Comparison of energy use and carbon emissions in zero-till and conventional-till systems.
|Zero-till expressed as % of Conventional till|
|Conv Till||Zero Till||Conv Till||Zero Till||NRG Use||C Emission|
The fertilizer energy use and carbon emissions of the zero tillage farming system were also lower compared to the conventional tillage farming system (Table 1). This may be a result of the location differences of the two case study farming operations, as the conventional tillage farming system is located in a more intensive farming area. However, the herbicide energy use and carbon emissions of the zero tillage farming system were 136.9 and 129.8 % of the conventional tillage farming system, respectively. This was not unexpected as under zero tillage, a shift from mechanical to chemical weed control is necessary to maintain productivity. Despite the large increase in herbicide use in the zero tillage system, the proportion of the total energy use and carbon emissions contributed by herbicides is relatively small.
The results showed that the non-legume annual crops had the highest energy input per tonne crop produced (1964.8 - 7483.2 MJ/t). The energy cost of pea production was intermediate in the conventional tillage farming system (2673.2 MJ/t) and comparable to the energy inputs per tonne of alfalfa produced in the zero tillage system (736.9 MJ/t). The energy required to produce each tonne of crop tended to be lower under zero tillage compared to conventional tillage. However, the two case study farming operations are located in different farming regions of the province. In addition to differences in soil type, the conventional tillage farming system experienced excessive moisture conditions for a number of years during the study period which decreased the potential yield.
To compare these two farming systems at the same crop yield levels, the provincial average yields were substituted for each crop (Bourgeois, 1995). This step reduced the differences in the amount of energy required to produce a tonne of each crop when comparing the two tillage systems. When provincial average yields were used, the production costs per tonne crop produced were similar between farms, although costs were somewhat lower under zero tillage.
The energy ratio of output/input was calculated for all annual grain crops in both tillage systems using the actual yield data obtained and the provincial yield averages. These ratios were quite variable for both farming systems when the actual yield data was used (1.87 - 19.00 MJout/MJin). The ratios were lower and the variation was reduced dramatically when the provincial yield averages were substituted for the actual yields (1.62 - 9.27 MJout/MJin). Wheat after alfalfa and peas tended to have the highest output/input energy ratios (4.26 - 9.27 MJout/MJin) which was attributed to the reduced nitrogen fertilizer inputs. Flax grown alone had the lowest output/input energy ratio (1.62 MJout/MJin) and the ratios of wheat, canola and barley were intermediate and similar (2.79 - 4.16 MJout/MJin).
Results of this study indicate that a simple method of decreasing the energy use and carbon emissions in the conventional tillage farming system is a shift to a minimum tillage system. Decreasing the amount of harrow passes would reduce the amount of energy use and carbon emissions by 1 to 2 % per pass, depending on the annual crop grown. However, a reduction in the cultivation passes per field would require a different means of managing crop residue. It should be noted that the energy saving from shifting from a conventional to a minimum tillage system are not as large as the energy savings attainable from the switch from a minimum to a zero tillage system (Entz, 1995). The inclusion of more annual legume crops and/or increasing the alfalfa stand length would also reduce the energy use and carbon emissions in the conventional tillage system. Not only would annual legume crops reduce the nitrogen fertilizer inputs, but also reduce the number of cultivation and harrow passes required resulting from the lower amounts of residue produced by these crops.
Fewer options to reduce energy use and carbon emissions are available to the zero tillage farming system. One suggestion might be to include more annual legume crops or extend the duration of the alfalfa stand in the rotation, reducing the amount of nitrogen fertilizer required.
Energy use - carbon emissions - conventional tillage - zero tillage - alfalfa
1. Bourgeois, L. 1995. Part 1: Analysis of crop distribution, crop yield trends, and crop management practices in Manitoba. Report prepared for Special Problems in Plant Science I. Crops 39.735 course. Dept. Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2.
2. Coxworth, E., Hultgreen, G., Leduc, P. 1994. Net carbon balance effects of low disturbance seeding systems on fuel, fertilizer, herbicide and machinery usage in western Canadian agriculture. Report prepared for TransAlta Utilities Corp., Calgary, AB.
3. Entz, M. H., Henry, S., Bamford, K. C., Schoofs, A., Ominski, P. D. 1995. Carbon released by manufactured inputs in prairie agriculture: Impact of forage crops and tillage systems.
4. Henry, S. The energetics of cropping systems: A study of two crop rotations utilizing conventional and zero tillage production methods. Report prepared for Advanced Crop Production course. Dept. Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2.
5. Kelner, D. J. 1994. Benefits of alfalfa related to nitrogen. MSc. Thesis. Dept. Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2.
6. Ominski, P. D. & Entz, M. H. 1994. Suppression of annual and perennial weeds using short-term alfalfa stands. Agron. Abs. 90.
7. Pimentel, D. 1980. Handbook of energy utilization in agriculture.
8. Southwell, P. M. & Rothwell, R. M. 1977. Analysis of output/input energy ratios of food production in Ontario. Report to engineering research service, Agriculture Canada, Ottawa, Ont.
9. Stout, B. A. 1990. Handbook of energy for world agriculture. Elsevier Applied Sciences.
10. Townsend, J. S. 1977. Energy efficiency of farm equipment and zero tillage systems. Manitoba - North Dakota Zero Tillage Workshop. Jan. 1979. Table 1. Average Energy Use and Carbon Emissions from two Case Study Farming Operations using different Tillage Systems.
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