Content uploaded by Peter Tyedmers
Author content
All content in this area was uploaded by Peter Tyedmers
Content may be subject to copyright.
Content uploaded by Peter Tyedmers
Author content
All content in this area was uploaded by Peter Tyedmers
Content may be subject to copyright.
Scenario Modeling Potential Eco-Efficiency Gains from
a Transition to Organic Agriculture: Life Cycle Perspectives
on Canadian Canola, Corn, Soy, and Wheat Production
N. Pelletier Æ N. Arsenault Æ P. Tyedmers
Received: 4 May 2007 / Accepted: 12 May 2008
Springer Science+Business Media, LLC 2008
Abstract We used Life Cycle Assessment to scenario
model the potential reductions in cumulative energy
demand (both fossil and renewable) and global warming,
acidifying, and ozone-depleting emissions associated with
a hypothetical national transition from conventional to
organic production of four major field crops [canola
(Brassica rapa), corn (Zea mays), soy (Glycine max), and
wheat (Triticum aestivum)] in Canada. Models of these
systems were constructed using a combination of census
data, published values, and the requirements for organic
production described in the Canadian National Organic
Standards in order to be broadly representative of the
similarities and differences that characterize these disparate
production technologies. Our results indicate that organic
crop production would consume, on average, 39% as much
energy and generate 77% of the global warming emissions,
17% of the ozone-depleting emissions, and 96% of the
acidifying emissions associated with current national
production of these crops. These differences were almost
exclusively due to the differences in fertilizers used in
conventional and organic farming and were most strongly
influenced by the higher cumulative energy demand and
emissions associated with producing conventional nitrogen
fertilizers compared to the green manure production used
for biological nitrogen fixation in organic agriculture.
Overall, we estimate that a total transition to organic
production of these crops in Canada would reduce
national energy consumption by 0.8%, global warming
emissions by 0.6%, and acidifying emissions by 1.0% but
have a negligible influence on reducing ozone-depleting
emissions.
Keywords Life cycle assessment Organic
Conventional Efficiency Nitrogen Green manure
Agriculture
Introduction
Modern agriculture largely owes it successes to an abun-
dant supply of inexpensive fossil fuels, which are
prerequisite to synthetic fertilizer production, suppressing
insect damage and weed competition through pesticide/
herbicide production and application and supplying
mechanical advantage in the form of farm machinery and
irrigation (Pimentel and others 2005). However, energy-
intensive agriculture has been implicated in a broad range
of proximate, ecological impacts, including water pollution
(Carpenter and others 1998), soil erosion (Gerhardt 1997),
pesticide toxicity (Carvalho 2006), and selection for pest
resistance (Carvalho 2006; Fournier 1999). Moreover, the
finite nature of fossil fuel reserves as well as the macro-
scale environmental impacts of extracting and consuming
the fossil energy that underpins intensive agriculture are of
increasing concern (Pimentel and others 2005) and merit
closer attention.
Organic agriculture has been promoted as a means to
reduce many of the negative impacts associated with con-
ventional food production (Pimentel and others 2005;
Stolze and others 2000). In a broad sense, organic farmers
strive to sustain agricultural production while minimizing
external inputs (synthetic fertilizers and pesticides in par-
ticular) in favor of resources found on or near the farm.
These resources generally include biologically fixed
N. Pelletier (&) N. Arsenault P. Tyedmers
School for Resource and Environmental Studies, Dalhousie
University, Kenneth C. Rowe Management Building, 6100
University Avenue, Suite 5010, Halifax, NS, Canada B3H 3J5
e-mail: nathanpelletier@dal.ca
123
Environmental Management
DOI 10.1007/s00267-008-9155-x
nitrogen, mineral-bearing rocks, and biological pest con-
trol. Fallowing, intercropping, use of buffer zones, and
integrated production of both plants and animals are
common as well (El-Hage Scialabba and Hattam 2002).
Organic production practices have also been criticized as
inefficient relative to conventional production technologies
due to lower yields (Offerman and Nieberg 2000), although
some large-scale reviews examining comparative yields in
conventional and organic agriculture strongly challenge
this critique (Badgley and others 2007; Stanhill 1990).
Improving the sustainability of agricultural production
systems requires the promotion of farm practices that
provide high-quality, affordable food in sufficient quantity
while ensuring appropriate economic returns and mini-
mizing negative environmental effects. Although numerous
researchers have described the local-scale ecological ben-
efits of organic versus conventional farming as well as
reduced fossil energy dependency (as summarized in
Stolze and others 2000), many of the broader, macroscale
environmental implications of these alternative production
technologies, including their comparative emission inten-
sities of globally problematic compounds, have historically
received considerably less attention. However, rising
awareness of energy security issues and broad-scale
anthropogenic perturbations of biogeochemical cycles such
as ozone depletion, acid precipitation, and climate change
has spurred interest in understanding the comparative eco-
efficiency (i.e., the resource and emissions intensity per
unit service) of conventional and organic food production
strategies, and research in this area is increasing.
In a 12-year study of energy use, energy output, and
energy-use efficiency in conventional and organic crop
rotations and crop production systems in Canada, Hoeppner
and others (2006) found that energy use was 50% lower with
organic compared to conventional management. Although
energy output was 30% lower per hectare with organic
management, overall energy efficiency (output energy/input
energy) was highest in the organic rotations. Similarly, Pi-
mentel and others (2005) found that industrial energy use in
organic cropping systems was 28–32% less than in con-
ventional rotations for a 25-year trial in the United States.
Smolik and others (1995) compared the relative sustain-
ability of alternative (organic), conventional, and reduced-
till farming systems in South Dakota. Productivity relative to
total energy consumption (including fuel, fertilizers, and
pesticides) was two to six times higher in the alternative
systems than in the conventional and reduced-till systems.
Whereas energy use is often a good proxy for fuel
combustion-related emissions intensity, other accounting
methodologies are available to accurately describe a wider
suite of the macroscale environmental dimensions of
industrial activity. This is particularly valuable in the
context of crop production, where field-level greenhouse
gas and acidifying emissions related to nitrogen fertilizers
typically exceed those associated with crop input produc-
tion (i.e., fertilizers, seed, and pesticides) and fuel use
(Williams and others 2006).
Life Cycle Assessment (LCA) is an ISO-standardized
biophysical accounting framework used to inventory the
material and energy inputs and emissions associated with
each stage of a product life cycle and to express these in
terms of their quantitative contributions to a specified suite
of environmental impact categories (Guinee and others
2001). Such analyses facilitate the identification of life-
cycle stages that contribute disproportionately to specific
areas of environmental concern, as well as comparisons of
environmental performance between competing production
technologies. Because LCA impact assessment methods
require discrete, quantifiable relationships between the
inputs and emissions of product/service systems and their
environmental impact potentials, the tool is not well suited
to accounting for contributions to local-scale environmen-
tal degradation (e.g., biodiversity loss) that results from
multiple, synergistic influences or context-specific bio-
geochemical conditions (Pelletier and others 2007). Rather,
it is best suited to evaluating how product/service systems
contribute to broader-scale environmental change through
resource appropriation and globally problematic chemical
emissions.
Several researchers have used LCA to compare con-
ventional and organic food production technologies. In an
LCA of intensive, extensive, and organic grassland farming
in southern Germany, Haas and others (2001) found that
organic farms consumed less energy and generated lower
greenhouse gas emissions. This was primarily due to
foregoing the use of nitrogen fertilizer. The organic farms
also scored better in terms of lower contributions to acid-
ification and eutrophication. Mattsson (1999) reported
trade-offs in environmental impacts between organic and
conventional carrot production systems in Sweden.
Organic production created higher acidification and eutro-
phication impacts due to the use of manure as fertilizer and
it required more arable land. However, energy use was
higher in the conventional system due to the production of
pesticides and fertilizers, both of which also contributed to
greater toxicity impacts. Similar analyses include com-
parisons of conventional and organic milk production in
the Netherlands (Thomassen and others 2008), a hybrid
input/out-LCA study of conventional and organic farming
in Australia (Wood and others 2006), and an analysis of
feed production systems for conventional and organic
aquaculture (Pelletier and Tyedmers 2007).
Conventional canola, corn, soy, and wheat together
accounted for 75% of both seeded area and production for
all field crops (excluding hay) produced in Canada in 2005
and occupied 24.2 million hectares of the Canadian
Environmental Management
123
agricultural landscape (Statistics Canada 2007). Given this
scale of production, changes in production technologies
that influence eco-efficiency might have non-trivial impli-
cations in terms of total resource use and emissions at the
national level. This study used LCA to quantify the cumu-
lative energy demand (both fossil and renewable) and
greenhouse gas, ozone-depleting, and acidifying emissions
associated with generic models of conventional and organic
canola, corn, soy, and wheat production in Canada. The
information derived subsequently informed an assessment
of how the specific production strategies characteristic of
conventional and organic farming differentially affect eco-
efficiency and the magnitude of energy savings and emis-
sions reductions potentially associated with a national
transition to organic production of these crops.
Methods
Goal Definition and Scoping
The goal of this research was to generate generic life-cycle
models of contemporary conventional and organic canola,
corn, soy, and wheat production systems in Canada in order
to predict the cradle-to-farm gate cumulative energy
demand (both fossil and renewable) and greenhouse gas,
ozone-depleting, and acidifying emissions associated with
these distinct production technologies, as well as to assess
the magnitude of energy use and emission reductions that
might be achievable through a nationwide transition to
organic production practices for these crops. The system
boundaries encompassed all direct inputs and emissions
associated with the use of farm machinery (i.e., fuel for
field operations and crop drying), the production of fertil-
izers/soil amendments, seed, and pesticides, as well as
field-level nitrous oxide and ammonia emissions from
fertilizers and crop residues. Inputs and emissions associ-
ated with the production and maintenance of farm
machinery and infrastructure as well as transportation of
inputs were not included, nor were anticipated differences
in soil carbon sequestration or methane production.
Although each crop was modeled and analyzed indepen-
dently, for the sake of calculating and assigning input costs
of green manure nitrogen provision in the organic systems,
corn–soy and wheat–canola rotations with green manure
intercrops or cover crops were assumed. The functional
unit was 1 kg of each crop produced, at the farm gate.
Life Cycle Inventory
The life cycle inventory (LCI) stage of an LCA involves
collecting relevant data regarding the material and
energetic inputs and emissions associated with each stage
of the product life cycle. Data for material inputs (fertilizer,
fuel, seed, pesticides, etc.) and yields for the conventional
production systems were derived from Canadian GHGe-
nius reports (Levelton Engineering and (S&T)
2
1999;
(S&T)
2
2003, 2005) and represent average contemporary
Canadian conditions. Specific fertilizer mixes for N, P
2
O
5
,
and K
2
O were based on average fertilizer use in the major
production regions for each crop (corn and soy in Ontario,
canola and wheat in the western Prairies/Alberta) as
reported in Korol (2002). Field-level nitrogen emissions
and CO
2
emissions from urea fertilizers were calculated
following IPCC Tier 1 Guidelines (IPCC 2006).
Comparable, broadly representative data were not
available for organic agriculture in Canada. Hypothetical
organic models were therefore designed to maximize
comparability with the conventional systems while
reflecting key similarities to and differences from con-
ventional production technologies based on the Canadian
Organic Production Systems Permitted Substances list
(Canadian General Standards Board 2006) and broad trends
identified through a literature review of comparative inputs
and emissions in conventional and organic crop production.
Key aspects of the modeled organic systems included the
following:
• Fertilizer Inputs: Quantities of fertilizers (N, P
2
O
5
,
K
2
O) required in the organic systems were assumed to
be equivalent to fertilizer inputs in the conventional
systems on a per-hectare basis. Nitrogen inputs were
assumed to be derived from the cultivation of sweet
clover green manure intercrops or cover crops.
Reported estimates of the fertilizer replacement value
of sweet clover vary widely, with a high of 450 kg/ha, a
more typical range of 40–225 kg/ha and an apparent
mode of roughly 100–120 kg/ha, depending on seeding
density, biomass yield, and seasonal factors (e.g., see
Killpack and Buchholz 1993; Leikem and others 2007;
Rehm and others 2002; Shelley 2004; State and Posner
1995). Given that nitrogen inputs to the conventional
systems were 140 kg/ha for corn and 59, 7.9, and
65.6 kg/ha for canola, soy, and wheat, respectively, we
assumed that a single sweet clover green manure
intercrop or cover crop that did not displace productive
land use was cultivated to satisfy nitrogen requirements
for each corn–soy rotation, and similarly for each
canola–wheat rotation. Individual crops were assigned
the energy and seed input costs of green manure
production weighted for their total share of nitrogen
demand in the rotation. Input data for green manure
production were 16.1 L of diesel and 45 kg of seed/ha
based on long-term field trial data collected at Agri-
culture Canada research stations (Zentner, personal
Environmental Management
123
communnication). Finally, phosphate rock was
assumed to replace conventional concentrated phos-
phorus fertilizers in the organic systems, and potash
was assumed to supply potassium.
• Machinery use differs between conventional and
organic systems, with conventional producers employ-
ing machinery more frequently for fertilizer and
pesticide application and organic producers relying on
increased tillage for weed control as well as green
manure production. Consistent with field trial data
reported in Hoeppner (2001), which were derived from
long-term multiple-replicate trials at Agriculture Can-
ada research stations, fuel inputs/hectare were assumed
to be similar for organic and conventional production
but were adjusted per unit mass produced to account for
anticipated yield differences.
• Based on a global review of datasets examining
comparative yields in established conventional and
organic crop production systems (Badgley and others
2007), yield rates for organic canola, corn, soy, and
wheat were assumed to be 90%, 95%, 100%, and 90%
of conventional yields, respectively.
• Considerable uncertainty exists regarding comparative
field-level nitrous oxide and ammonia emissions from
nitrogen fertilizers in conventional and organic agri-
culture. Stolze and others (2000) reviewed existing
literature and concluded that no significant differences
can be identified. We therefore assumed identical
emissions between organic and conventional systems
on a per-hectare basis, but we adjusted per unit mass
produced to account for yield differences.
• The organic systems did not employ pesticides.
Life Cycle Impact Assessment
Impact assessment, which is the third stage of an LCA,
involves calculating the potential environmental burdens
associated with specific life-cycle activities by quantita-
tively expressing all inputs and emissions tabulated in the
LCI according to their contributions to a suite of specified
environmental impact categories (Pennington and others
2004). Numerous environmental impact categories have
been developed for use in LCA (Pelletier and others 2007)
and should be chosen according to the specific goals of the
study at hand. Because the purpose of the present study was
to compare contributions to macroscale environmental
concerns between conventional and organic production
systems, the impact categories considered were cumulative
energy demand (in MJ), global warming potential (as CO
2
equiv.), ozone-depletion potential (as CFC-11 equiv.), and
acidification potential (as SO
2
equiv.). Cumulative energy
demand (including both fossil and renewable sources) was
quantified following the Cumulative Energy Demand
method v 1.03 (VDI 1997). Global warming, acidification,
and ozone-depletion potentials were calculated according
to the CML 2 Baseline 2000 method (CML 2001). All
impact assessment calculations were carried out using the
SimaPro 7.0 LCA software package from PRe
´
Consultants
(PRe
´
2006). Proximate ecological impacts such as eco-
toxicity effects from pesticide use and potential
eutrophication impacts were not addressed.
In order to identify life-cycle ‘‘hot spots,’’ relative
contributions to each impact category associated with fuel
inputs to machinery, fertilizer production, nutrient emis-
sions, and other inputs (pesticides, seed, sulfur) were
evaluated for each crop system, as were the proportional
contributions of nitrogen, phosphorus, and potassium
inputs to overall impacts for each crop. The impacts
associated with the production of 1 kg of average con-
ventional nitrogen, phosphorus, and potassium fertilizers
[based on Canadian fertilizer mixes as per Korol (2002)] as
well as phosphate rock and potash were also calculated
using average European process models from the EcoIn-
vent database (EcoInvent 2007) that were modified to
reflect the Canadian electricity mix. The impacts of green
manure nitrogen production were calculated assuming a
conservative yield of 110 kg N/ha. Finally, 2005 Canadian
national crop production statistics for canola, corn, soy, and
wheat (Statistics Canada 2007) were used to estimate the
total potential energy savings and emission reductions
associated with a hypothetical nationwide transition from
conventional to organic production of these crops in Can-
ada. In light of the conflicting claims regarding yield
potentials in conventional and organic crop production, a
sensitivity analysis was carried out to determine the yield
levels for the organic crops at which contributions to the
impact categories considered would be equivalent to those
of conventional crops.
Results
Life Cycle Inventory Results
Table 1 reports the LCI data and data sources that informed
our generic models of the inputs and emissions associated
with the cradle-to-farm gate production of conventional
and organic canola, corn, soy, and wheat in Canada.
Life Cycle Impact Assessment Results
Table 2 reports total cradle-to-farm gate life-cycle impact
assessment results for the cumulative energy demand and
global warming, ozone-depleting, and acidifying emissions
associated with the production of 1 kg of conventional and
organic canola, corn, soy, and wheat in Canada. Due to the
Environmental Management
123
assumed lower yield rates for canola (90% of conventional
yields), corn (95%) and wheat (90%) in the organic crop
models (soy yields were assumed to be equivalent), with
inputs and emissions per hectare held constant, the pre-
dicted impacts associated with fuel inputs to machinery and
field-level emissions from nitrogen fertilizers were corre-
spondingly slightly higher per kilogram of crop produced
for organic compared to conventional production (Fig. 1).
Specifically, fuel-related impacts were, on average, 8%
higher for organic production of canola, corn, and wheat
across impact categories, whereas fertilizer-related field
emissions were 7% higher (only applies to global warming
and acidifying emissions). Conversely, averaged across the
three crops and all impact categories, impacts related to
both fertilizer and seed/pesticide production (Other) for the
conventional systems were 845% and 380% of those for
Table 1 Cradle-to-farm gate LCI data for the production of 1 kg of conventional and organic canola, corn, soy, and wheat in Canada
Canola Corn Soy Wheat
Con.
a
Org. Con.
b
Org. Con.
c
Org. Con.
d
Org.
Inputs
N
e
(g) 46.1 19.5 3.3 24.4
P
2
O
5
f
(g) 50.4 56.0 6.3 6.6 30.7 30.7 28.1 31.2
K
2
O
g
(g) 12.0 13.4 3.8 4.0 53.5 53.5
Sulfur (g) 8.0 8.9 1.7 1.7
Pesticides
h
(g) 1.4 0.4 0.5 1.6
Diesel (mL) 35.2 39.1 6.6 7.0 14.2 14.2 10.8 12.0
Diesel for GM
i
(mL) 6.6 2.2 0.4 3.5
Gasoline (mL) 4.5 4.5
Natural gas (cm
3
) 181.7 191.3 6.3 6.3
LPG (mL) 1.4 1.4
Electricity
j
(kJ) 7.0 7.0
Seed
k
(g) 5.2 5.8 2.6 2.7 45.0 45.0 46.0 51.1
Seed for GM
l
(g) 18.4 6.2 1.0 9.8
Fertilizer emissions
m
N
2
O (g) 1.2 1.3 0.6 0.6 0.3 0.3 0.7 0.8
NH
3
(g) 9.7 10.8 3.0 3.2 2.9 2.9 4.9 5.4
NO
x
(g) 0.9 1.0 0.4 0.4 0.1 0.1 0.5 0.6
CO
2
from urea (g) 15.6 8.7 1.5 8.2
Yield (kg/ha) 1288 1159 7180 6821 2380 2380 2690 2421
a
Data from (S&T)
2
Consultants (2005)
b
Data from Levelton Engineering and (S&T)
2
Consultants (1999)
c
Data from (S&T)
2
Consultants (2005)
d
Data from (S&T)
2
Consultants (2003)
e
For conventional, assumes any manure N is ultimately derived from synthetic N and is modeled based on a regional fertilizer mix for dominant
production region of each crop (Korol 2002)
f
For conventional, modeled based on P
2
O
5
content of regional P fertilizer mix for dominant production region of each crop (Korol 2002); for
organic, modeled based on P
2
O
5
content of phosphate rock
g
For conventional, modeled based on K
2
O content of regional K mix for dominant production region of each crop (Korol 2002); for organic,
modeled on K
2
O content of potash (IFIA 2007)
h
Active ingredients
i
Diesel for green manure calculated based on average fuel inputs of 16.1 l/ha as per data collected at Agriculture Canada research stations
(Zentner, personal communication) and is apportioned to each crop based on its share of nitrogen demand in the assumed corn–soy and canola–
wheat rotations
j
Based on electricity mix in dominant production region for each crop
k
Modeled as if derived from same production system
l
Seed input for sweet clover green manure is 45 kg/ha, based on data collected at Agriculture Canada research stations (Zentner, personal
communication.) and is apportioned to each crop based on its share of nitrogen demand in the assumed corn–soy and canola–wheat rotations
m
Calculated following IPCC Tier 1 Guidelines employing all default values as listed and assuming a 90%/10% NH
3
/NO
x
split for volatization
(IPCC 2006)
Environmental Management
123
the organic systems (Fig. 1). For soy production, where
yields were equivalent, only fertilizer- and seed/pesticides/
sulfur (Other)-related impacts differed, with the organic
crop generating, on average, 37% and 53% of the impacts
of the conventional crop for these respective inputs.
The production of fertilizer was the dominant contrib-
utor to cumulative energy demand for conventionally
produced crops (average of 62% across all crops), with fuel
inputs contributing 30% and seed, pesticides, and sulfur
(Other) contributing only 8% (Fig. 1). In contrast, fuel
inputs were most important to cumulative energy demand
for organic production (average of 66% across all crops),
with fertilizer production contributing 32%. The produc-
tion of seed and sulfur (Other) contributed a nominal 2% in
organic production, suggesting that avoidance of pesticide
use resulted in a small but nontrivial energy savings. Fer-
tilizer production was the dominant contributor to ozone-
depleting emissions for both conventional (78%) and
organic (57%) crops. A notable exception was the case of
corn production, for which the use of natural gas for crop
drying increased the contribution from fuel inputs to 39%
and 93% of ozone-depleting emissions for conventional
Table 2 Cradle-to-farm gate life-cycle impact assessment data for the cumulative energy demand and global warming, ozone-depleting, and
acidifying emissions associated with the production of 1 kg of conventional and organic canola, corn, soy, and wheat in Canada
Canola Corn Soy Wheat Ave. D in
Org./Conv.
Con. Org. Con. Org. Con. Org. Con. Org.
Cumulative energy
demand (MJ/kg)
5.2. 2.2 (42%) 2.4. 1.3 (54%) 2.3. 1.5 (65%) 2.7. 0.8 (30%) 48%
Global warming potential
(g CO
2
equiv./kg)
696.3. 541.0 (78%) 330.1. 256.3 (78%) 247.6. 190.3 (77%) 382.2 290.6 (76%) 77%
Ozone-depletion potential
(lg CFC-11 equiv./kg)
27.6 4.3 (16%) 15.1 6.6 (44%) 10.4. 5.0 (48%) 15.2. 0.8 (5%) 28%
Acidification potential
(g SO
2
equiv./kg)
20.2. 19.8 (98%) 5.6. 5.4 (96%) 7.2. 5.7 (79%) 10.2. 9.7 (95%) 92%
Ave. D in Org./Conv. 59% 68% 67% 52%
Note: Values in parentheses are the relative magnitudes of impacts in organic systems relative to conventional systems
0.0
1.0
2.0
3.0
4.0
5.0
Canola
Canola
Corn
Corn
Soy
Soy
Wheat
Wheat
0
200
400
600
800
0
10
20
30
0
5
10
15
20
25
Fertilizers (N,P,K) FuelEmissions Other
A) Cumulative Energy Demand
B) Global Warming Potential
C) Ozone Depletion Potential D) Acidification Potential
MJ/kg
CFC-11 equiv. (µg/kg)
SO2 equiv. (g/kg)
CO2 equiv. (g/kg)
6.0
Organic Organic Organic Organic
Canola
Canola
Corn
Corn
Soy
Soy
Wheat
Wheat
Organic
Organic Organic Organic
Canola
Canola
Corn
Corn
Soy
Soy
Wheat
Wheat
Organic
Organic Organic Organic
Canola
Canola
Corn
Corn
Soy
Soy
Wheat
Wheat
Organic Organic Organic Organic
Fig. 1 Cradle-to-farm gate cumulative energy demand and global
warming, ozone-depleting, and acidifying emissions associated with
the production of 1 kg of conventional and organic canola, corn, soy,
and wheat in Canada. ‘‘Fertilizers’’ refers to the production of N, P,
and K inputs. ‘‘Emissions’’ refers to field-level emissions of N
compounds and CO
2
associated with fertilizer use. ‘‘Fuel’’ refers to all
energy inputs to farm machinery and crop drying. ‘‘Other’’ refers to
production of all other field level inputs (seed, pesticides, sulfur)
Environmental Management
123
and organic production, respectively. Field-level emissions
associated with fertilizer use contributed the majority of
global warming and acidifying emissions for all conven-
tional and organic crops. Specifically, this accounted for
(on average) 50% of global warming and 76% of acidifying
emissions in the conventional systems and 66% of global
warming and 88% of acidifying emissions in the organic
systems. Fertilizer production was the second most
important contributor to these impact categories for con-
ventional production (31% and 15% of global warming and
acidifying emissions, respectively), whereas fuel use was
the second largest contributor to these impact categories in
the organic systems (22% and 6%, respectively) (Fig. 1).
Overall, however, the organic crop production models
generated consistently lower contributions to all impact
categories considered (Table 2, Fig. 1). Averaged over the
four crops, cumulative energy demand for organic pro-
duction was 48% of that for conventional crop production,
whereas global warming potential for the organic crops
was 77%, ozone depletion potential was 28%, and acidi-
fication potential was 92% relative to the conventional
crops (Table 2). Differences were greatest for canola and
least for soy, which have the highest and lowest nitrogen
requirements, respectively.
These differences were almost exclusively due to the
varied life-cycle impacts associated with the production of
the fertilizers particular to conventional and organic
farming. More specifically, they were most heavily influ-
ence by the different nitrogen procurement strategies
characteristic of conventional (using synthetic nitrogen
fertilizers) and organic (using green manure cultivation)
crop production, although differences in phosphorus fer-
tilizer production for conventional and organic systems
was the most important factor for acidifying emissions
(Fig. 2).
For all conventionally produced crops other than soy (a
legume requiring nominal nitrogen inputs), nitrogen fer-
tilizer production was the dominant contributor to
fertilizer-related cumulative energy demand (on average,
75% for canola, corn, and wheat production), global
warming (72%), and ozone-depleting emissions (78%).
Green manure nitrogen production was proportionally less
important for these impact categories in the organic sys-
tems, contributing, on average, 52% to fertilizer-related
cumulative energy demand for organic canola, corn, and
wheat production, 64% to global warming, and 1% to
ozone-depleting emissions. In contrast, green manure
nitrogen production accounted for 78% of fertilizer-related
acidifying emissions for these crops (Fig. 2). Phosphorus
fertilizer was the major contributor to fertilizer-related
acidifying emissions in the conventional production sys-
tems (average of 76% for all crops). In the organic systems,
0
1
2
3
4
0
50
100
150
200
250
0
5
10
15
20
25
0
0.5
1
1.5
2
2.5
3
Nitrogen
Phosphorous Potassium
A)
Cumulative Energy Demand
B)
Global Warming Potential
C)
Ozone Depletion Potential
D)
Acidification Potential
MJ/kg
CFC-11 equiv. (µg/kg)
SO2 equiv. (g/kg) CO2 equiv. (g/kg)
Canola
Canola
Corn
Corn
Soy
Soy
Wheat
Wheat
Organic Organic Organic Organic
Canola
Canola
Corn
Corn
Soy
Soy
Wheat
Wheat
Organic Organic Organic Organic
Canola
Canola
Corn
Corn
Soy
Soy
Wheat
Wheat
Organic
Organic Organic Organic
Canola
Canola
Corn
Corn
Soy
Soy
Wheat
Wheat
Organic
Organic Organic Organic
Fig. 2 Cumulative energy demand (A), global warming (B), ozone-
depleting (C), and acidifying emissions (D) associated with fertilizer
provision for the production of 1 kg of conventional (using average
N, P
2
O
5
, and K
2
O fertilizers) and organic (using green manure N,
rock phosphate, and potash) canola, corn, soy, and wheat in Canada
Environmental Management
123
the use of phosphate rock contributed, on average, only
19% to acidifying emissions. The contributions from
potassium fertilizer to fertilizer-related impacts were small
for all impact categories for both conventional and organic
production of all crops other than soy, for which potassium
inputs were relatively high (Fig. 2). Overall, cumulative
energy demand associated with fertilizer production in the
organic systems was 25% of that in the conventional sys-
tems, whereas global warming, ozone-depleting, and
acidifying emissions were 22%, 17%, and 14%, respec-
tively (Fig. 2).
The large differences in the contributions of specific
fertilizers to the life-cycle impacts of crop production were
partially attributable to the varied application rates modeled
for nitrogen, phosphorus, and potassium for each crop
(Table 1). For example, canola receives high levels of
nitrogen, whereas soy receives very little. However, the
actual magnitude of impacts associated with the production
of specific fertilizers played a still more important role
(Table 4). For conventional fertilizers, the magnitude of
cumulative energy demand as well as global warming and
ozone-depleting emissions for nitrogen production was two
to three times that of phosphorus production on a per-
kilogram basis and approximately six times that of potas-
sium production. In contrast, phosphorus production
generated much higher acidifying emissions than either
nitrogen (4 times higher) or potassium production (17 times
higher), largely due to the production and use of sulfuric
acid to concentrate the phosphates derived from phosphate
rock (Table 4). These differences were more variable and of
consistently lesser scale among the fertilizers used in
organic production.
More interesting in the context of this study, however, is
the difference in impacts associated with the specific fer-
tilizers used to supply nitrogen, phosphorus, and potassium
in the conventional and organic production systems,
respectively. On a per-kilogram basis, the impacts associ-
ated with the modeled production of the average synthetic
nitrogen fertilizer mix employed in Canada were
approximately five times higher than those of producing an
equivalent amount of nitrogen through green manure cul-
tivation. Similarly, the impacts of producing the typical
Canadian conventional phosphorus fertilizer were, on
average, six times higher than those associated with pro-
ducing the phosphate rock used in organic agriculture. In
contrast, the differences between the conventional potas-
sium mix and the potash used for organic production were
much smaller (Table 3). This is attributable to the fact that
potash makes up the majority of the conventional potas-
sium fertilizer mix used in Canada.
Given the large differences in cumulative energy demand
and global warming, ozone-depleting, and acidifying emis-
sions among conventional and organic corn, canola, soy, and
wheat production in Canada, most of which are attributable
to the fertilizer-related impacts characteristic of these dif-
ferent production technologies, it is worth considering the
magnitude of energy savings and emissions reductions
potentially achievable through a nationwide transition from
conventional to organic production of these crops. Based on
the differences in contributions to each impact category for
conventional and organic production as predicted by our
models (Table 2) and total 2005 Canadian production vol-
umes for each of these crops (CANSIM 2007), we estimate
that a complete transition to organic production would
reduce cumulative energy demand by over 90 billion
megajoules (Table 4) which is equivalent to the combustion
energy of approximately 2.5 billion liters of diesel fuel and
equals roughly 0.8% of Canada’s total energy consumption
in 2004 (Environment Canada 2006). Such a transition
would similarly reduce greenhouse gas emissions by
4.8 million tonnes (Table 4)-approximately 0.6% of Can-
ada’s total greenhouse gas emissions and 8.7% of
greenhouse gas emissions from agriculture in 2004 (Envi-
ronment Canada 2006). The most recent estimate of
Canadian emissions of ozone-depleting substances was 2000
tonnes of CFC-11 equiv. per year (Canadian Council of
Ministers 2001), suggesting that a transition to organic crop
production would have negligible impact in reducing
Table 3 Cumulative energy demand and global warming, ozone-depleting, and acidifying emissions associated with the production of 1 kg of
N, P
2
O
5
,orK
2
O in fertilizers used in conventional (average nitrogen, phosphorus, and potassium fertilizer mixes) and organic (green manure
nitrogen, phosphate rock, and potash) crop production in Canada
Inputs/emissions Con. N
fertilizer
Green
manure (N)
a
Con. P
fertilizer
Phosphate
rock
Con. K
fertilizer
Potash
(K
2
O)
Cumulative energy demand (MJ/kg) 52.7 6.7 (13%) 20.0 4.9 (25%) 9.6 9.2 (96%)
Global warming (kg CO
2
equiv./kg) 3.2 0.5 (16%) 1.4 0.2 (14%) 0.5 0.5 (0%)
Ozone-depletion (lg CFC-11 equiv./kg) 374.0 0.4 (.1%) 121.0 24.4 (20%) 66.0 63.1 (96%)
Acidification (g SO
2
equiv./kg) 10.3 5.8 (56%) 43.2 1.3 (3%) 2.6 1.7 (65%)
Note: Values in parentheses are the perecentages of impacts generated by organic fertilizer relative to conventional fertilizer
a
Inputs and emissions for Green Manure (N) based on the fuel, nutrient and seed requirements for the cultivation of the 90.9 m
2
of sweet clover
required to yield 1 kg of N, assuming a fertilizer replacement value of 110 kg N/ha
Environmental Management
123
national emissions. Acidifying emissions would be reduced
by 24.5 thousand tonnes of SO
2
equivalents (Table 4)-
approximately 1% of Canada’s estimated emissions in 2000
(Environment Canada 2007).
Due to the sensitivity of the reported results to
assumptions regarding comparative yields between the
conventional and organic systems, a sensitivity analysis
was conducted to determine the yield levels for the organic
crops at which the estimated impacts would be equivalent
per unit yield to those predicted for the conventional sys-
tems (Table 5). To consume equivalent amounts of energy
per unit yield, organic crop yields would have to drop to
between 27% (wheat) and 65% (soy) of conventional
yields. Similarly yields would have to range from 68%
(wheat) to 77% (soy) to produce equivalent greenhouse gas
emissions per unit yield and from 5% (wheat) to 48% (soy)
for equivalent ozone-depleting emissions. In contrast, due
to the much smaller difference in acidifying emissions
between the conventional and organic systems, yields
would only need to dip from 79% (soy) to 91% (corn).
Discussion
To produce food crops at rates greater than those afforded
by unmanaged ecosystems, intensive modern agriculture
replaces or augments ecosystem goods and services with
industrial inputs such as fossil fuels, pesticides, and syn-
thetic fertilizers. However, it is clear that such increases in
material and energy throughput result in both benefits
(higher yields) and costs (local and nonlocal environmental
impacts). It is thus of value to understand the environ-
mental trade-offs associated with alternative production
technologies that are characterized by variable resource
and emissions intensities. More specifically, in an energy-
constrained world increasingly compromised by anthro-
pogenic perturbations of biogeochemical cycles directly
attributable to unsustainable levels of material and energy
consumption and waste production, the identification and
promotion of more ecologically efficient production tech-
nologies must be prioritized (Hall and Klitgaard 2006;
MEA 2005).
The results of this study suggest that organic crop
production systems for canola, corn, soy, and wheat con-
sume considerably less energy and produce lower
greenhouse gas, ozone-depleting, and acidifying emissions
relative to conventional systems. This result is driven
almost exclusively by differences in the fertilizers char-
acteristic of conventional and organic crop production and,
in particular, the much lower impacts of green manure
Table 5 Estimated yield levels relative to yields achieved in con-
ventional crop production at which organic production of canola,
corn, soy, and wheat in Canada would generate equivalent impacts
per kilogram of crop produced to those associated with conventional
crop production
Canola
(%)
Corn
(%)
Soy
(%)
Wheat
(%)
Cumulative energy demand 38 51 65 27
Global warming potential 70 74 77 68
Ozone-depletion potential 14 42 48 5
Acidification potential 88 91 79 86
Table 4 Projected reductions in cradle-to-farm gate cumulative energy demand and global warming, ozone-depleting, and acidifying emissions
associated with a total transition of Canadian canola, corn, soy, and wheat production from conventional to organic methods [based on total
national production data for each crop in 2005 (CANSIM 2007) and differences in energy inputs and emissions for each crop as calculated in this
study (Table 2)]
Production (tonnes) Canola Corn Soy Wheat Total %D
9.11 9 10
6
9.27 9 10
6
3.53 9 10
6
2.73 9 10
7
4.92 9 10
7
CED (MJ) Con. 4.74 9 10
10
2.22 9 10
10
8.12 9 10
9
7.37 9 10
10
1.51 9 10
11
39
Org. 2.00 9 10
10
1.21 9 10
10
5.29 9 10
9
2.18 9 10
10
5.92 9 10
10
D 2.74 9 10
10
1.01 9 10
10
2.83 9 10
9
5.19 9 10
10
9.18 9 10
10
GWP (tonnes CO
2
equiv.) Con. 6.34 9 10
6
3.06 9 10
6
8.74 9 10
5
1.04 9 10
7
2.07 9 10
7
77
Org. 4.93 9 10
6
2.37 9 10
6
6.72 9 10
5
7.93 9 10
6
1.59 9 10
7
D 1.41 9 10
6
6.90 9 10
5
2.02 9 10
5
2.47 9 10
6
4.80 9 10
6
ODP (tonnes CFC-11 equiv.) Con. 2.51 9 10
-1
1.40 9 10
-1
3.67 9 10
-2
4.15 9 10
-1
8.43 9 10
-1
17
Org. 3.92 9 10
-2
6.12 9 10
-2
1.76 9 10
-2
2.18 9 10
-2
1.40 9 10
-1
D 2.12 9 10
-1
7.88 9 10
-2
1.91 9 10
-2
3.93 9 10
-1
7.03 9 10
-1
AP (tonnes SO
2
equiv.) Con. 1.84 9 10
5
5.19 9 10
4
2.54 9 10
4
2.78 9 10
5
5.39 9 10
5
96
Org. 1.80 9 10
5
5.01 9 10
4
2.01 9 10
4
2.65 9 10
5
5.15 9 10
5
D 4.00 9 10
3
1.80 9 10
3
5.30 9 10
3
1.30 9 10
4
2.40 9 10
4
CED: cumulative energy demand; GWP: global warming potential; ODP: ozone-depletion potential; AP: acidification potential
Environmental Management
123
nitrogen production in organic farming compared to con-
ventional synthetic nitrogen fertilizer production. These
findings are consistent with other LCA research, as well as
numerous energy analyses of conventional and organic
crop production (Ess and others 1994; Haas and others
2001; Mattsson 1999; Pimentel and others 2005; Smolik
and others 1995).
This conclusion is not surprising considering that
nitrogen fixation via plant/bacteria symbiosis is solar dri-
ven and, hence, essentially free, whereas the production of
nitrogen fertilizer is a highly energy-intensive process
(Bhat and others 1994). Moreover, the policy relevance of
this distinction should not be overlooked. According to
Smil (2001), 40% of the human population is at present
fundamentally dependent on synthetic nitrogen use in
agriculture, and Crews and Peoples (2004) questioned the
life history strategy of a species that has become funda-
mentally dependent on the abundant and inexpensive
availability of nonrenewable energy sources for the pro-
curement of food. This issue is especially pertinent for
developing nations, for which synthetic nitrogen fertilizers
might become unaffordable due to rising energy costs and,
more generally, for nations lacking in the natural gas
reserves necessary for synthetic nitrogen production. It
would appear that organic crop production offers sub-
stantial eco-efficiency gains with respect to energy use.
Although important, comparative energy intensity in
agriculture must be considered in tandem with other eco-
efficiency measures. Our analysis indicates that fertilizer
production strongly influences the comparative eco-effi-
ciency of conventional and organic crop production in all
impact categories considered, with organic fertilizer pro-
curement strategies resulting in consistently lower
emission intensities per unit yield. However, we also found
that field-level emissions related to nitrogen fertilizer use
were the dominant contributor to overall greenhouse gas
and acidifying emissions for both conventional and organic
production. For this reason, despite the fact that fertilizer
production for the organic systems had substantially lower
associated emissions, much of this gain was overshadowed
by the much larger field-level emissions from nitrogen
fertilizer use, which, consistent with available literature (as
reviewed by Stolze and others 2000), our models assumed
were comparable between conventional and organic crops
on a per-hectare basis. This is in agreement with Williams
and others (2006), who described the importance of con-
sidering the nitrous oxide footprint of agriculture over the
greenhouse gas emissions associated with fertilizer pro-
duction and on-farm fuel use.
Given that field-level emissions are central to green-
house gas and acidifying emission intensities in crop
production and that they are notoriously variable within
and between production systems because they are
influenced by a wide variety of factors, including climate,
season, soil, fertilizer type, and management practices
(Dobbie and others 1999), comparisons of these dimen-
sions of eco-efficiency in conventional and organic
production systems must therefore be approached with
caution. Moreover, other factors such as soil carbon
sequestration, which we did not consider in our analysis,
might also have a strong influence on comparative green-
house gas intensities. For example, Robertson and others
(2000) compared the total greenhouse gas emissions
associated with legume and fertilizer-based cropping sys-
tems and found that the global warming potential of
conventional systems was almost three times higher than
that of legume-based systems. However, conventional no-
till systems were less emissions-intensive than were the
legume-based systems due to greater soil carbon seques-
tration. Further research in this area should be prioritized,
as this consideration might be a critical determinant of
comparative greenhouse gas emissions in conventional and
organic systems.
One of the most common arguments against organic
farming is that reduced yields per hectare and the necessity
of devoting land to green manure rotations would require
the cultivation of additional land at the expense of wild
ecosystems. Given that 670 million hectares of land were
dedicated to cereal production in 2000, each 10% decrease
in yield would require an additional 6.7 million hectares of
land to maintain productivity (MEA 2005). That said, any
net loss in caloric production could easily be mitigated by
allocating greater shares of crop production for direct
human consumption rather than animal husbandry. More-
over, as evidenced by this study and others, the production
and use of fertilizers and pesticides on conventionally
managed croplands also have clear environmental costs.
Weighing the relative merits of highly intensive, land-
efficient production technologies versus lower intensity but
less land-efficient practices demands a complex calculus
indeed.
Several extensive published literature reviews suggest
that for most crops, organic yields are very close to,
equivalent to, or greater than yields of conventionally
managed crops (Badgley and others 2007; Lockeretz and
others 1980
; Stanhill 1990). In a comparison of 26 com-
mercial mixed-grain and livestock farms covering a range
of soil types in the western Corn Belt, the mean yield for
corn was 8.5% higher on conventional fields compared to
fields grown without pesticides and conventional fertiliz-
ers, although the difference was not statistically significant.
Yields tended to be higher for conventional fields under
favorable conditions but lower under adverse conditions
(Lockeretz and others 1980). Stanhill (1990) compared the
productivity of organic and conventional systems in a wide
range of environments, including the eastern US Corn Belt,
Environmental Management
123
Switzerland, Germany, Finland, Sweden, Israel, and Aus-
tralia. On average, yields in organic systems were within
10% of yields obtained in conventional systems. More
recently, Badgley and others (2007) compared yields of
organic versus conventional food production using a global
dataset of 293 examples and estimated the average
organic:conventional yield ratio of different food catego-
ries for the developed and the developing world.
Generally, the average yield ratio was slightly \1.0 for
studies in the developed world and [1.0 for studies in the
developing world. These findings suggest that the pre-
dicted yields and associated energy use/emissions for
conventional and organic crops employed in the present
study are realistic. Moreover, as evidenced by our sensi-
tivity analysis, yields in organic crop production would
have to be substantially lower before cumulative energy
demand and emissions intensity per unit yield would be
equivalent to that predicted for conventionally produced
crops.
Although our analysis suggests large differences in
energy use and emissions intensity between conventional
and organic crop production and despite the fact that the
four crops considered account for three-quarters of field
crop production (excluding hay) in Canada (Statistics
Canada 2007), it would appear that a nationwide transition
to organic production of these crops would have a rela-
tively small influence on total energy use and emissions of
greenhouse gases, ozone-depleting, and acidifying com-
pounds at the national level. As a policy instrument for
improving national eco-efficiency in terms of the impact
categories considered in this study, there are therefore
likely more effective leverage points than a wholesale
transition to organic cropping practices. However, these
gains must be considered in concert with other measures of
socioeconomic and ecological integrity—an exercise far
beyond the scope of this article.
Several important simplifying assumptions in our anal-
ysis should also be noted. For example, only industrial
fertilizers and green manure were modeled as potential
nutrient sources. In reality, manure might be an important
nutrient source in both conventional and organic systems.
However, because manure is simply a conduit for nutrients
originally derived from either industrial sources or bio-
logical nitrogen fixation, we do not consider its exclusion
from our analysis to be problematic. It could also be argued
that inputs and emissions related to crop production are
context dependent, regardless of whether the system is
conventional or organic. For this reason, we believe that
modeling average systems based on national production
data provides a realistic and useful comparison of the
tradeoffs associated with these competing production
technologies.
Certainly, there are many more trade-offs associated with
a conversion from conventional to organic agriculture than
have been addressed in this study. However, ample literature
is presently available regarding the numerous proximate
environmental interactions characteristic of conventional
versus organic farming technologies (Stolze and others
2000). What is clear from our work is that, given the
important role of nutrient provision in the environmental
performance of crop production and the varied life-cycle
impacts associated with the production and use of different
fertilizers (Brentrup and others 2001), the identification and
promotion of least-environmental-cost nutrient sources and
efficient fertilizer use should be a research priority. It might
be that combining elements of conventional and organic
production (e.g., using pesticides to maintain high yields but
relying on green manure as a nitrogen source) would actually
optimize environmental performance according to the
impact categories considered in this study, although a con-
sideration of additional trade-offs such as toxicological
impacts might again shift the balance in favor of organic
production technologies. However, rather than a simple
transition from conventional to organic nutrient procure-
ments strategies, it should also be considered that the goal of
achieving sustainable food production systems might be
much better served by a transition away from many annual
crops such as corn and soybeans, which are used predomi-
nately for animal fodder, toward perennial cropping systems
and crops for direct human consumption. Cox and others
(2006) and Jordan and others (2007) suggested that such a
transition would reduce problems frequently associated with
annual crop production, including water degradation due to
sedimentation and nutrient/pesticide runoff, groundwater
depletion, soil erosion, and higher greenhouse gas emissions,
while increasing biodiversity value and soil organic carbon
sequestration.
Conclusions
Global grain production is expected to double by 2050
(Alexandratos 1999; Cassman 1999) to satisfy the demands
of a growing population consuming increasing volumes of
grain-fed meat and biofuels. How to achieve this objective
as well as respond to the pressing needs of the estimated
3.7 billion currently malnourished people (Pimentel and
Pimentel 2006) without further compromising the ecolog-
ical integrity of agroecosystems and biogeochemical cycles
is among the most pressing challenges of the 21st century.
A transition to organic crop production practices might be
instrumental in meeting this goal, although insufficient in
isolation to substantially mitigate human-induced envi-
ronmental perturbations.
Environmental Management
123
Food is a fundamental human requirement. Although
much of the material and energy throughput of contem-
porary society is nonessential and can be pared away as
resource constraints require, we cannot change the basic
human physiological requirement for a minimum amount
and quality of food energy. What we can change is the
efficiency of our food production systems, such that we
satisfy human needs in ways that minimize environmental
harms. Such considerations must necessarily be central to
the development of a sustainable human society.
Our analysis underscores the importance of considering
the broader, macroscale implications of conventional and
organic crop production (and industrial activities gener-
ally), with particular reference to present and future
constraints on fossil fuel availability and contributions to
climate change, acid precipitation, ozone depletion, and
other concerns. Certainly, ignoring the contributions of
industrial agriculture to the disruption of the biogeochem-
ical cycles that cumulatively provide the implicate order
for biological productivity is, at best, a serious oversight.
Acknowledgments This work was generously supported by the
Social Science and Humanities Research Council of Canada, the
Killam Trust, and the Natural Science and Engineering Research
Council of Canada. We also acknowledge the thoughtful and con-
structive input of three reviewers. Any errors are, of course, the sole
responsibility of the authors.
References
Alexandratos N (1999) World food and agriculture: outlook for the
medium and longer term. Proceedings of the National Academy
of Science 96:5908–5914
Badgley C, Moghtader J, Quintero E et al (2007) Organic agriculture
and the global food supply. Renewable Agriculture and Food
Systems 22:86–108
Bhat M, English B, Turhollow A et al (1994) Energy in synthetic
fertilizers and pesticides: revisited. NRNL/Sub/90-99732/2.
National Technical Information Service, Springfield, VA
Brentrup F, Kusters J, Kuhlman H et al (2001) Application of the Life
Cycle Assessment methodology to agricultural production: An
example of sugar beet production with different forms of
nitrogen fertilizers. European Journal of Agronomy 14:221–233
Canadian General Standards Board (2006) Canada organic production
systems permitted substances lists. Retrieved May, 2006, from
http://www.pwgsc.gc.ca/cgsb/on_the_net/organic/032_0311_20
06-e.pdf
Canadian Council of Ministers (2001) National action plan for the
environmental control of ozone-depleting substances and their
halocarbon alternatives: May 2001 update. Retrieved January,
2007, from http://www.ccme.ca/assets/pdf/nap_update_e.pdf
CANSIM (2007) Average yield of principal field crops in Canada.
Retrieved January, 2007, from http://cansim2.statcan.ca/
Carpenter S, Caraco N, Correl D et al (1998) Non-point pollution of
surface waters with phosphorus and nitrogen. Ecological Appli-
cations 8(3):559–568
Carvalho F (2006) Agriculture, pesticides, food security and food
safety. Environmental Science and Policy 9(7–8):685–692
Cassman K (1999) Ecological intensification of cereal production
systems: yield potential, soil quality, and precision agriculture.
Proceedings of the National Academy of ScienceUSA 96:5952–
5959
CML (2001) CML 2 Baseline Method 2000. Centre for Environmen-
tal Studies, University of Leiden, Netherlands
Cox T, Glover J, Van Tassel D et al (2006) Prospects for developing
perennial grain crops. BioScience 56(8):649–659
Crews T, Peoples M (2004) Legume versus fertilizer sources of
nitrogen: ecological tradeoffs and human needs. Agriculture,
Ecosystems and Environment 102:279–297
Dobbie K, McTaggart I, Smith K (1999) Nitrous oxide emissions
from intensive agricultural systems: variations between crops
and seasons, key driving variables, and mean emission factors.
Journal of Geophysical Research: Atmospheres 105(21):26891–
26899
EcoInvent (2007) Swiss centre for life cycle inventories. Available at
http://www.ecoinvent.ch/
El-Hage Scialabba N, Hattam C (eds) (2002) Organic agriculture,
environment and food security. Environment and Natural
Resources Service Sustainable Development Department, UN-
FAO, Rome. Retrieved September, 2005, from http://www.fao.
org/DOCREP/005/Y4137E/y4137e01.htm#P0_0
Environment Canada (2006) National Inventory Report 1990–2004:
greenhouse gas sources and sinks in Canada. Retrieved January,
2007, from http://www.ec.gc.ca/pdb/ghg/inventory_report/2004_
report/2004_report_e.pdf
Environment Canada (2007) Acid rain and the facts. Retrieved
January, 2007, from http://www.ec.gc.ca/acidrain/acidfact.html
Ess D, Vaughan D, Luna J et al (1994) Energy and economic savings
from the use of legume cover crops in Virginia corn production.
American Journal of Alternative Agriculture 9(4):178–185
Fournier J (1999) Pesticides: are they pests or blessing? Actualite
Chimique 11:34–39
Gerhardt R (1997) A comparative analysis of the effects of organic
and conventional farming systems on soil structure. Biological
Agriculture and Horticulture 14:139–157
Guinee J, Gorree M, Heijungs R et al (2001) Life cycle assessment:
an operational guide to the ISO Standards Part 2. Ministry of
Housing, Spatial Planning and Environment, The Hague, Neth-
erlands. Retrieved January, 2006, from http://www.leidenuniv.
nl/cml/ssp/projects/lca2/part1.pdf
Hall C, Klitgaard K (2006) The need for a new, biophysical-based
paradigm in economics for the second half of the age of oil.
International Journal of Transdisciplinary Research 1(1):4–22
Haas G, Wetterich F, Ko
¨
pke U (2001) Comparing intensive,
extensified and organic grassland farming in southern Germany
by process life cycle assessment. Agriculture, Ecosystems and
Environment 83:43–53
Hoeppner J (2001) The effects of legume green manures, perennial
forages, and cover crops on non-renewable energy use in western
Canadian cropping systems. Master’s thesis, Department of Plant
Science, University of Winnipeg, Canada
Hoeppner J, Entz M, McConkey B et al (2006) Energy use and
efficiency in two Canadian organic and conventional crop
production systems. Renewable Agriculture and Food Systems
21:60–67
IPCC (2006) Guidelines for national greenhouse gas inventories.
Intergovernmental panel on climate change. Retrieved Septem-
ber, 2006, from http://www.ipcc-nggip.iges.or.jp/public/2006gl/
index.htm
Jordan N, Boody G, Broussard W et al (2007) Environment:
sustainable development of the agricultural bio-economy. Sci-
ence 316(5831):1570–1571
Killpack S, Buchholz D (1993) Nitrogen replacement value of
legumes. University of Missouri Extension. Retrieved
Environmental Management
123
September, 2006, from http://www.extension.missouri.edu/
explore/envqual/wq0277.htm
Korol M (2002) Canadian fertilizer consumption shipments and trade
2001/2002. Agriculture and Agri-food Canada. Retrieved Janu-
ary, 2006, from http://www.agr.gc.ca/pol/pub/canfert/pdf/canfert
01_02_e.pdf
Leikem D, Lamond R, Bonczkowski L et al (2007) Using legumes in
crop rotations. Kansas State University. Retrieved January, 2008,
from http://www.oznet.ksu.edu/library/crpsl2/l778.pdf
Levelton Engineering Ltd., (S&T)
2
Consultants Inc (1999)Assessmentof
net emissions of greenhouse gases from ethanol-gasoline blends in
southern Ontario. Agriculture and Agri-Food Canada, Policy
Branch, Ottawa. Retrieved January, 2006, from http://www.oregon.
gov/ENERGY/RENEW/Biomass/docs/FORUM/GHG_Eth.PDF
Lockeretz W, Shearer G, Sweeney S et al (1980) Maize yields and
soil nutrient levels with and without pesticides and standards
commercial fertilizers. Agronomy Journal 72:65–72
Mattsson B (1999) LCA of carrot puree: case studies of organic and
integrated production. Swedish Institute for Food and Biotech-
nology Report No. 653, Gothenburg, Sweden
MEA (2005) Ecosystems and human well-being. Volume 1. Current
state and trends. Findings of the Conditions and Trends Working
Group. Millennium Ecosystem Assessment, Island Press,
Washington, DC
Offerman F, Nieberg H (2000) Economic performance of organic
farms in Europe. Organic Farming In Europe: Economics and
Policy 5, University of Hohenheim, Germany
Pelletier N, Tyedmers P (2007) Feeding farmed salmon: is organic
better? Aquaculture 272:399–416
Pelletier N, Ayer N, Tyedmers P et al (2007) Impact categories for
life cycle assessment research of seafood production: review and
prospectus. International Journal of Life Cycle Assessment
12(6):414–421
Pennington D, Potting J, Finnveden G et al (2004) Life cycle
assessment part 2: current impact assessment practice. Environ-
ment International 30:721–739
Pimentel D, Pimentel M (2006) Global environmental resources
versus world population growth. Ecological Economics 59:195–
198
Pimentel D, Hepperly P, Hanson J et al (2005) Environmental,
energetic and economics comparisons of organic and conven-
tional farming systems. Bioscience 55(7):573–582
PRe
´
(2006) SimaPro 7.0. PRe consultants, Netherlands. Retrieved
January, 2006, from http://www.pre.nl
Rhem G, Schmitt M, Eliason R (2002) Fertilizer recommendations for
edible beans in Minnesota. University of Minnesota Extension.
Retrieved September, 2006, from http://www.134.84.92.126/
distribution/cropsystems/DC6572.html
Robertson G, Paul E, Harwood R (2000) Greenhouse gases in
intensive agriculture: contributions of individual gases to
radiative forcing of the atmosphere. Science 289:1922–1925
Shelley K (2004) Nitrogen fertilizer rates and application timing for
winter wheat in Wisconsin—What are the economic optimums?
University of Wisconsin Extension Services. Retrieved Septem-
ber, 2006, from http://www.soils.wisc.edu/extension/FAPM/
2004proceedings/Shelley.pdf
Smil V (2001) Feeding the world. MIT Press, Cambridge, MA
Smolik J, Dobbs T, Rickerl D (1995) The relative sustainability of
alternative, conventional, and reduced-till farming systems.
American Journal of Alternative Agriculture 10(1):25–35
Stanhill G (1990) The comparative productivity of organic agricul-
ture. Agriculture, Ecosystems and Environment 30:1–26
State J, Posner J (1995) Legume cover crops as a nitrogen source for
corn in an oat–corn rotation. Journal of Production Agriculture
8(3):385–390
Statistics Canada (2007) Seeded area of field and speciality crops in
Canada. Retrieved January, 2007, from http://www40.statcan.ca/
l01/cst01/prim11a.htm
Stolze M, Priorr A, Haring A et al (2000) The environmental impacts
of organic farming in Europe. Organic farming in Europe:
economics and policy 6. University of Hohenheim, Germany.
Retrieved February, 2006, from http://www.uni-hohenheim.de/
i410a/ofeurope/organicfarmingineurope-vol6.pdf
(S&T)
2
Consultants Inc (2003) The addition of ethanol from wheat to
GHGenius. Natural Resources Canada, Office of Energy Effi-
ciency, Ottawa. Retrieved February, 2006, from http://www.gov.
mb.ca/est/energy/ethanol/wheat-ethanolreport.pdf
(S&T)
2
Consultants Inc (2005) Biodiesel GHG emissions using
GHGenius: An update. Natural Resources Canada, Office of
Energy Efficiency, Ottawa. Retrieved January, 2006, from http://
www.studio255.com/crfa/pdf/res/20050311_NRCan_Biodiesel_
GHG_Emissions.pdf
Thomassen M, van Calker K, Smits M et al (2008) Life cycle
assessment of conventional and organic milk production in the
Netherlands. Agricultural Systems 96:95–107
VDI (1997) Cumulative energy demand: terms, definitions, methods
of calculation. VDI-Richtlinien (4600) Verein Deutscher Ingeni-
eure, Du
¨
sseldorf
Williams A, Audsley E, Sandars D (2006) Determining the environ-
mental burdens and resource use in the production of agricultural
and horticultural commodities. Main Report. DEFRA Research
Project IS0205, Cranfield University. Retrieved January, 2007
from www.silsoe.cranfield.ac.uk
Wood R, Lenzen M, Lundie S (2006) A comparative study of some
environmental impacts of conventional and organic farming in
Australia. Agricultural Systems 89:324–348
Environmental Management
123
