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Research
Results
The Glenlea
Long-Term Rotation Study was established in 1992 to determine the interaction
of crop rotation and crop inputs (fertilizer and herbicide). Crop rotation
ranged from simple annual systems to more complex forage based systems.
The present study reports on results from the first 12 years of this
study. The results focus on the base plots in Plot
Plan 1 before modifications have occurred. For information on how
the experiment is designed see Experiment
Description.
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Flax
is grown as a test crop at the end of all rotation systems. Flax is
an important organic crop in the Northern Great Plains currently receiving
high prices. Flax was chosen as the test crop in this experiment due
to its poor competitive ability with all weed types. The influence of
crop rotation and crop inputs on yield should, therefore, be evident.
Yield of this flax test crop is discussed below.
Flax is used as a "test"
crop at the end of each 4-year rotation cycle. Flax yields in bu/ac
for 1995, 1999 and 2003 in the three main rotations are shown below.
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| Rotation |
Inputs |
1995 |
1999 |
2003 |
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| Annual |
F+H+ |
30 |
22 |
27 |
| wheat-pea-wheat-flax |
F+H- |
16 |
10 |
1.3 |
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F-H+ |
21 |
17 |
15 |
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F-H- |
15 |
10 |
4 |
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| Green
Manure |
F+H+ |
29 |
29 |
10 |
| wheat-clover-wheat-flax |
F+H- |
20 |
18 |
1.2 |
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F-H+ |
18 |
25 |
8 |
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F-H- |
16 |
16 |
3 |
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| Alfalfa |
F+H+ |
27 |
23 |
21 |
| wheat-alfalfa-alfalfa-flax |
F+H- |
21 |
16 |
1.5 |
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F-H+ |
25 |
24 |
20 |
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F-H- |
22 |
22 |
8 |
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| Crop
rotation effect: |
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The
beneficial effects of alfalfa and clover green manure appeared to
be stronger in the first and second rotation cycle (1995 and 1999)
than in the third rotation cycle (2003). |
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After two or three cycles of the crop rotation, when
weed pressure was much higher, green manure and forage did not offer
weed suppression benefits to the following flax crop. |
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A two-year stand of alfalfa had a greater effect on
subsequent grain yield than did a clover green manure. |
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By 2003, organic flax yields were low in all three
rotations, however. Alfalfa yields began to suffer possibly due
to low soil P and S (see Soil
Nutrient Status). This may have reduced alfalfa's ability to
suppress weeds. |
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| Input
effect: |
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There was a greater yield loss when herbicide was
removed (F+H-) from the system than when fertilizer was removed
(F-H+) suggesting that weeds have a greater limiting impact on crop
production than nitrogen fertility. |
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Flax yield was very low in systems that used fertilizer
but no herbicide (F+H-) because weeds took better advantage of the
added N fertilizer than the crop. |
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| Interaction
of crop rotation and inputs: |
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In both low input systems (F+H- and F-H+), flax yields
were lowest in the annual crop rotation vs the sweetclover and alfalfa-containing
rotations. |
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Under organic production conditions (F-H-), flax in
the alfalfa-containing rotation had the highest grain yield, followed
by flax in the sweetclover rotation, followed by flax in the annual
crop rotation. |
Why
is this important?
Crop
rotation is important to farming with fewer chemicals. In this study,
when alfalfa or green manure were included in the rotation organic flax
yield was better than when only annual crops were in the rotation. Even
when these legumes were included in the rotation, by the end of the
third cycle of the rotation, organic yields were low. Soil P and S may
be a big limiting factor to the success of alfalfa as a weed clean-up
crop. In the fourth rotation cycle, treatments will be further subdivided
to include manured treatments and early and late seeding dates.
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Weed dry
matter (DM) was measured at harvest time in each of the flax test crop
years to determine the effect of crop rotation and input management
on weed production.
Crop
rotation effect:
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Crop
rotation only had a significant effect on weed production in 1995
when weed DM was significantly less in the rotations that included
green manure or forage (Figure 1, below). The biggest increase in
weed DM production between 1995 and 2003 occurred in the forage
rotation. This most likely can be attributed to the additional nitrogen
that the alfalfa in that rotation provides to the weeds. |
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Weed
DM for the annual rotation was comprised of predominantly green
foxtail (millet), wild oat, lady's thumb (green smartweed) and Canada
thistle (data not shown). Stinkweed (field pennycress), a winter
annual weed, wild buckwheat and Canada thistle were associated with
the green manure rotation. Volunteer alfalfa, dandelion and wild
mustard were associated with the forage rotation. |
Figure 1. The effect of crop rotation on weed
dry matter (kg/ha) at flax harvest at Glenlea.
Input
effect:
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Crop
input management had a strong influence on weed DM production in
all three test crop years (Figure 2, below). As expected, weed DM
production was consistently lower where herbicide was used (f+h+
and f-h+). In all years of the study, weed DM was greater for the
fertilizer only treatment (f+h-) than for the organic treatment
(f-h-). In this situation, the weeds were taking better advantge
of the added fertilizer than the crop. |
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The
management of crop inputs influenced the weed spectrum (data not
shown). Briefly, hemp nettle was most abundant when fertilizer and
herbicide were used (f+h+). This may be due to the fact that herbicides
effectively controlled all other weeds thus allowing this species
to occupy available niches. Wild mustard, wild buckwheat, wild oat,
and stinkweed were in greatest abundance in the fertilizer only
system (f+h-). When no inputs were used (f-h-) Canada thistle was
more abundant than when fertilizer was used but no herbicide (f+h-).
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Figure 2. The effect of crop input management
on weed dry matter (kg/ha) at flax harvest at Glenlea.
Interaction
of crop rotation and inputs:
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During
the first rotation cycle, there was an interaction between crop
rotation and input management for weed DM. In 1995, when herbicide
was removed but fertilizer remained (f+h-), weed DM was greater
in the annual crop and green manure rotations than in the forage
rotation (Figure 3, below). Therefore, the presence of alfalfa in
the rotation suppressed weeds during the first rotation cycle. |
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After
three rotation cycles, the decrease in yield when herbicide (f+h-)
was removed from the system was similar for all rotations (2003).
Thus, by the third cycle of the rotation, herbicide was necessary
to decrease weed DM regardless of the crop rotation. This suggests
that even when a crop known to be competitive with weeds is consistently
in the crop rotation (i.e. alfalfa hay), herbicide may be necessary
to control weeds. |
Figure 3. The interaction of crop rotation
and crop input management on weed dry matter production (kg/ha) at flax
harvest in 1995 at Glenlea.
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The maintenance
of maximum biological diversity within a cropping system is important
as biodiversity is an index of the health of the cropping system. Bioindicators
are organisms within an ecosystem which are sensitive to changes in
the environment, and their populations are affected by disturbance.
Ground beetles are excellent bioindicators. Ground
beetles have often been considered a beneficial insect as some species
eat weed seeds and other eat pest insects. Therefore, the ability to
maintain or enhace ground beetle populations could lead to less reliance
on therapeutic pest control measures.
Methods
In this
study, pitfall traps were used to trap insects from 1992 to 1999. Traps
were placed in each sub-plot (i.e. F+H+, F+H-, F-H+, F-H-). Insects
caught in the traps were identified, separated and counted.
Results
indicate:
Why
is this important?
The
association of Harpalus and Amara the weediest subplots
(F+H-) suggests that these ground beetles may be used to sustainably
manage weed populations through seed predation. Other studies have indicated
that 50 to 80% of weed seeds in the soil may be consumed by insect seed
predators. In this study, however, the abundance of weeds in the no
herbicide plots (F+H- and F-H-) was too high for the beetles to reduce
weed seeds significantly. Ground beetles may be more effective in an
Integrated Pest Management (IPM) system where some herbicide is used
to keep weed densities at levels lower than in the present study. In
a system that depends entirely on herbicide for weed control, populations
of ground beetles remains small and never have the opportunity to build
to beneficial levels.
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Reducing
non-renewable energy use and carbon dioxide (CO2) production,
and increasing energy efficiency can make cropping systems more sustainable.
Nitrogen benefits of legumes to succeeding non-leguminous crops are
well documented, while organic cropping systems have reduced levels
of crop inputs. The long-term effects of perennial forage legumes
and organic cropping practices on energy use, CO2 production,
and energy efficiency of crop production were examined at Glenlea.
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The
first objective of the current study was to examine the effectiveness
of perennial forage legume crops in reducing energy use and CO2
production, and improving energy efficiency of cropping systems,
by replacing a portion of the nitrogen fertilizer required for
crop production with nitrogen fixed by the alfalfa. |
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The
second objective of this study was to examine the effectiveness
of organic crop production in reducing energy use and CO2
production, and improving energy efficiency of cropping systems,
by eliminating fertilizer and pesticide inputs. |
Methods
Data
collected included levels of all crop inputs, such as seed, fertilizers,
pesticides, and fuel and machinery needed for all field operations,
and crop yields from each treatment. This information was then converted
to energy values (MJ/ha) using energy coefficients assigned for each
crop input, field operation, and crop harvested.
Rotational
ENERGY USE was calculated by adding the energy coefficients of all
the field operations and crop inputs. Rotational ENERGY PRODUCTION
was calculated using energy output coefficients assigned to the different
crops through laboratory bomb calorimeter tests. ENERGY EFFICIENCY
was calculated for each treatment by dividing rotational energy production
by rotational energy use. Rotational CO2 production was
calculated by multiplying total rotational energy use by CO2
coefficients used by Gulden and Entz (1996).
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Total rotational energy consumption (MJ/ha)
at the Glenlea long-term cropping systems study, 1992-2003 |
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| Rotation |
Inputs |
Total
Energy
Consumption |
Seed
Energy |
Fuel
and Lube Energy |
Machinery
Energy |
Pesticide
Energy |
Fertilizer
Energy |
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| WPWF |
F+H+ |
68498 |
7902 |
16133 |
2367 |
7116 |
34980 |
| WPWF |
F-H- |
24233 |
7902 |
14229 |
2102 |
0 |
0 |
| WAAF |
F+H+ |
49255 |
3657 |
18184 |
2515 |
3499 |
21400 |
| WAAF |
F-H- |
22181 |
3657 |
16213 |
2311 |
0 |
0 |
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WPWF
= wheat-pea-wheat-flax; WAAF = wheat-alfalfa-alfalfa-flax
| Results
indicate: |
| Energy
Use and CO2 Production |
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When
comparing the same treatments between rotations, the organic and
conventional wheat-pea-wheat-flax (annual) systems used 9% and
39% more energy than the organic and conventional wheat-alfalfa-alfalfa-flax
(forage) systems, respectively. |
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When
comparing the conventional and organic systems within rotations,
the conventional forage system produced approximately 2 times
as much CO2 as the organic forage system, while the
conventional annual system produced approximately 2.5 times as
much CO2 as the organic annual system. |
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When
comparing the conventional and organic systems within rotations,
the conventional forage system consumed approximately 2.2 times
as much non-renewable energy as the organic forage system, while
the conventional annual system consumed approximately 2.8 times
as much energy as the organic annual system. |
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When
comparing the same treatments between rotation, the organic and
conventional annual systems produced 6% and 34% more CO2
than the organic and conventional forage systems, respectively.
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The
reductions in energy use and CO2 production for the
forage system were primarily through reductions in nitrogen fertilizer
requirements. |
| Energy
Production |
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Within
the annual rotation, rotational energy production was 85% higher
in the conventional system, while rotation energy production in
the forage rotation was approximately 26% higher in the conventional
system. |
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The forage systems had levels of rotational energy production
that were approximately two- and three times higher than the organic
and conventional systems in the annual rotation, respectively.
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The
apparent benefits of including alfalfa in the rotation becomes
more and more evident, the more years that the rotation was in
existence, as the systems in the annual rotation appear to have
energy production that is dropping more than in the forage rotation. |
| Energy
Efficiency |
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It
was found that energy efficiency in cropping systems containing
perennial forage legumes was up to 222% greater than in the conventional
cropping systems, as a result of decreases in energy use and increases
in energy production. |
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Within
each rotation, the organic system was more efficient than the
conventional system. This was primarily due to substantially higher
levels of input energy in the conventional systems, where energy
use was more than twice as great as in the organic systems. While
output energy for both of the conventional systems was higher
than in the organic systems, it was not enough to negate the higher
amounts of input energy consumed, in terms of rotational energy
efficiency. |
Why
is this important?
The
findings of this study point to the importance of including legumes
in cropping systems in order to improve energy efficiency. The vast
majority of energy used in crop production is in the form of fossil
fuels. When burned, these fossil fuels release carbon dioxide, a greenhouse
gas, into the atmosphere. With ever-increasing concern over global
warming as a result of greenhouse gases, any steps taken to improve
the energy efficiency of agriculture should be welcome steps indeed.
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Soil samples
were collected from the three main rotations in the fall of 2003. Only
the full input (F+H+) and no-input (F-H-) systems were tested. Samples
were taken in six locations per subplot in all three replicates. The
replicate samples were bulked prior to lab analysis.
Results
show both a strong crop input and a strong crop rotation effect for
many of the nutrients (see Table below). Nitrogen levels were affected
by both fertilization and crop rotation. The alfalfa-containing rotation
had the highest level of N, followed by the sweetclover-containing system.
Soil
nutrient status in three different crop rotations after 12 years of
cropping. Rotation 1, wheat-pea-wheat-flax; rotation 2, wheat-sweet
clover green manure-wheat-flax; rotation 3, wheat-alfalfa-alfalfa-flax.
Values in kg available nutrients per hectare.
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Rotation
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Input
Level
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N
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P
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K
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S
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| wheat-pea-wheat-flax |
F+H+ |
32 |
46 |
1316 |
141 |
| wheat-pea-wheat-flax |
F-H- |
22 |
33 |
1312 |
86 |
| wheat-sclover-wheat-flax
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F+H+ |
29 |
24 |
1169 |
87 |
| wheat-sclover-wheat-flax |
F-H- |
31 |
37 |
1116 |
76 |
| wheat-alfalfa-alfalfa-flax |
F+H+ |
81 |
24 |
1140 |
63 |
| wheat-alfalfa-alfalfa-flax |
F-H- |
37 |
11 |
1073 |
26 |
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Phosphorous
levels were adequate for all systems except the unfertilized alfalfa
rotation (see Table). The phosphorous mining effect of alfalfa forage
crops is well documented. It is important to note that these values
only reflect the available P levels, yet about 50% of soil P is in the
organic form (which these soil tests do not measure). Soil potassium
and sulfur levels were also lowest in the unfertilized alfalfa-containing
rotation (see Table).
Why
is this important?
Results
of the present study show no evidence of serious nutrient deficiencies
in organic systems for the annual or sweetclover-containing rotations
(see Table). Only in the organic alfalfa-containing rotation did signs
of nutrient deficiencies occur (see Table). In a survey of commercial
organic farms in the eastern prairies, Entz et al. (2001) reported that
long-term organically farmed soils had extremely low levels of inorganic
phosphorous.
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Economic
analysis of 8 years of the Glenlea Rotation Study The following table
shows the cost of production and net income for the 8 years (1992-1999)
of rotations 1 and 3 at Glenlea. Costs are in "1996 Canadian dollars"
while commodity prices are in 1996 dollars (minus 20%). Values are averaged
over the entire 8 year rotation and are shown in mean annual dollars/acre.
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Crop Rotation |
F+H+
Full inputs |
F+H-
Low input |
F-H+
Low input |
F-H-
Organic system |
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| wheat-pea-wheat-flax |
Input cost 104.14
Net return 27.87 |
Input cost 77.17
Net return 30.87 |
Input cost 71.36
Net return 26.67 |
Input cost 43.44
Net return 40.23 |
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| wheat-alfalfa-alfalfa-flax |
Input cost 71.68
Net return 77.83 |
Input cost 51.92
Net return 93.42 |
Input cost 55.92
Net return 73.73 |
Input cost 36.08
Net return 93.77 |
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Results
indicate:
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With
full inputs, input costs were lower and net returns were higher
in the alfalfa-containing vs the annual crop rotation. |
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In
the annual rotation, removing either fertilizers or herbicides did
not seriously reduce the net return, but did reduce input costs
(equal reduction in input costs). |
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In
the alfalfa-containing rotation, removing inputs increased net return
in a number of cases compared with the full inputs treatment. |
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The
organic systems had the lowest cost of production and the highest
net returns over the 8 year period in both the annual grain and
alfalfa-based rotations. |
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Organic
flax production appears to be very economically attractive when
included in an alfalfa-based crop rotation.
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