|
Robert H. Gulden and Martin H. Entz
Problem 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. Literature Review 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. Study Description 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.
Major Findings 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. 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). Industry Impact 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. Keywords Energy use - carbon emissions - conventional tillage - zero tillage -
alfalfa References 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.
Energy Use Carbon Emission Zero Till expressed as MJ/ha/year
kg C/ha/year % of Conv Till
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||