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Agriculture and 
Agri-Food Canada 

Agriculture et 
Agroalimentaire Canada 


Direction generale 
de la recherche 


Agriculture Canadian Agriculture Library 

Canada Bibliotheque canadienne de I'agriculture 

Ottawa K1 A 0C5 

Pi5 2 5 1999 


P 1981 

(1999 print) 
c 3 



Digitized by the Internet Archive 

in 2012 with funding from 

Agriculture and Agri-Food Canada - Agriculture et Agroalimentaire Canada 


Toward sustainable agriculture in Canada 

Compiled and edited by 

H.H. Janzen 

R.L. Desjardins 

J.M.R. Asselin 


B. Grace 

Research Branch 

Agriculture and Agri-Food Canada 

©Minister of Public Works and Government Services Canada 1998 

Available from 

Donna Dewan 

Publishing Officer, Strategic Promotion 

Research Branch, Agriculture and Agri-Food Canada 

Sir John Carling Building, Room 777 

Ottawa, Ontario 


Tel. (613)759-7787 

Fax (613) 759-7768 


Electronic version available in May 1999 at 

Publication 1981/E 
Catalog No. A53-1981/1998E 
ISBN 0-662-27 170-X 
Printed 1999 3M:02/99 

Cette publication est disponible en francais sous le titre 

ha sante de Pair que nous respirons: vers line agriculture durable au Canada 

Staff Designer 

Johanne Sylvestre-Drouin 

Strategic Promotion 

Agriculture and Agri-Food Canada 

Production Editors 

Sharon Rudnitski 

Strategic Promotion 

Agriculture and Agri-Food Canada 

Jane T. Buckley 
Gilpen Editing Service 




1 . Introduction i 

Importance of atmospheric health 1 

Our changing atmosphere 1 

Objectives of this report 2 

Scope of this report 2 

Reading this report 3 

2. Canadian agriculture and 
greenhouse gases 5 

A glance at Canadian agriculture 5 

The greenhouse effect 8 

Commitments to reduce emissions 9 

Estimates of emission 10 

Carbon dioxide 10 

Methane 25 

Nitrous oxide 30 

Combined effect of the three greenhouse gases 43 

Uncertainties in current estimates 44 

Techniques to minimize emission of greenhouse gases 45 

Reducing carbon dioxide emissions 46 

Reducing methane emissions 53 

Reducing nitrous oxide emissions 57 

Putting it all together 59 

Other effects of practices that reduce greenhouse gas emissions 60 


3. Ozone 6i 

Source of ground-level ozone 61 

Effect of ozone on plants 62 

Ozone exposure and absorption by crops 63 

Measuring plant response to ozone 65 

Examples of crop response to ozone 66 

Environmental interactions 69 

4. Other links between agriculture 

and the atmosphere 71 

Ammonia 7 1 

Background 7 1 

Agricultural sources of ammonia 72 

Reducing ammonia emissions 74 

Other odors 76 

Nitrogen oxides 77 

Aerosols 77 

Ultraviolet radiation 79 

Background 79 

Effect of ultraviolet radiation on crops 81 

Pesticides 83 

5. Conclusions 85 

Current status 85 

Opportunities to reduce emissions 85 

Future challenges 86 

Remaining questions 88 

6. Bibliography and selected reading 89 
Acknowledgments 93 
Appendix I 95 



It is only in the past four or five 
decades that scientists have 
increasingly understood many of the 
interactions between lands and oceans 
and the atmosphere — and how human 
actions may be modifying these 
exchanges. And it is only in the past 
two decades that the public and 
governments have been confronted 
with clear evidence of the changing 
composition of the global atmosphere 
and its likely effects. In the short space 
of a century, the burning of large 
quantities of fossil fuels stored in the 
ground over millions of years has had 
the largest impact. But the way in 
which we manage the land and 
produce food and fiber is by no means 
negligible. Pollution of the atmosphere 
affects directly all land creatures and 
plants, as well as the climate that 
governs productivity, human activities, 
and occurrence of extreme events such 
as drought, floods, and storms. 

This book comprehensively addresses 
those interactions between land and 
atmosphere that arise because of 
agricultural practices in Canada. Some 
of the atmospheric changes may be 
benign or even beneficial to humans 
and plants. But there is much evidence 
to indicate that adverse effects are 
occurring. These negative effects will 
continue to increase unless changes 
occur in how we manage our energy, 
food, and fiber economies. 

The authors wisely point out that the 
net release of greenhouse gases from 
agriculture "is usually a symptom of 
inefficient use of resources." This is 
also true of other economic sectors 
contributing to atmospheric changes. 
It is not just the case for greenhouse 

gases, but also for problems such as 
emissions of precursors to low-level 
ozone and acid rains. 

Various means of increasing the 
efficiency with which we use our 
resources in agriculture are outlined. 
Also examined is the significant 
potential for restoring organic carbon 
in our soil through conservation tillage 
and other means, thus reducing 
atmospheric carbon dioxide. There are 
many "win-win" opportunities 
demonstrated, where increased soil and 
agricultural productivity go hand-in- 
hand with reducing pollution of the 
atmosphere. This book provides much 
of the scientific information needed to 
develop an effective strategy for 
Canada's agricultural sector. 

Let us hope that this cooperative way 
of approaching the problems 
confronting agriculture and the global 
atmosphere becomes an inspiration for 
other sectors. As in agriculture, there 
are many cost-effective "win-win" 
opportunities for achieving energy 
efficiency to be found in transportation 
and forestry that can improve Canada's 
economic situation and simultaneously 
help protect the life-giving atmosphere 
of our small planet. 

James P. Bruce, O.C, FRSC 
Canadian Climate Program Board 


This book has its roots in two 
international reports: 

• the World Commission on 
Environment and Development, 
Our Common Future, better known 
as the "Brundtland" report 

• the 1990 report of the 
Intergovernmental Panel on 
Climate Change, IPCC. 

In 1987, Our Common Future brought 
world attention to problems such as 
global warming, ozone depletion, 
desertification, reduced biodiversity, 
burgeoning demands of a growing 
population, and the need for a global 
agenda for change that would make 
development sustainable. In short, the 
Commission sought ways to meet 
present needs without compromising 
the ability of future generations to 
meet theirs. 

The IPCC, set up by the World 
Meteorological Organization and the 
United Nations Environment 
Program, produced its first scientific 
assessment in 1990. Several hundred 
scientists from 25 countries helped 
prepare and review the scientific data. 
The IPCC concluded that emissions 
from human activities are increasing 
the concentration of greenhouse gases. 
It warned that this could lead to a 
warming of the Earth's surface. 

These two reports brought climate 
change to the forefront of the world 
environmental agenda. In 1992 nations 
met in Rio de Janeiro to sign the 
Climate Change Convention, an 
agreement to reduce greenhouse gas 
emissions. The IPCC released a 

second scientific assessment in 1995 
stating that "the balance of evidence 
suggests a discernible human influence 
on global climate." A further 
international agreement, signed by 174 
countries in Kyoto, Japan, in 1997, 
agreed to set specific targets for 
greenhouse gas emissions. 

Scientists in Canada, as in other 
countries, now focused more attention 
on issues associated with atmospheric 
pollution, greenhouse gases, and 
climate. Within the Canadian federal 
government, the Atmospheric 
Environment Service (Environment 
Canada) and programs such as the 
Green Plan provided further support. 
Indeed, the four federal, science-based, 
natural resources departments of 
Environment, Fisheries and Oceans, 
Natural Resources, and Agriculture 
and Agri-Food joined forces and 
signed a Memorandum of 
Understanding for Science and 
Technology for Sustainable 
Development in 1995. The goal was to 
enhance cooperative research in areas 
of mutual concern such as climate 

The Research Branch of Agriculture 
and Agri-Food Canada initiated a 
research program in greenhouse gases 
and ground-level ozone in 1992 in 
support of sustainable development. 
The program involved scientists 
working for the federal government, 
universities, provincial agencies, and 
the private sector. After 6 years, we 
now report our findings to the 
Canadian public. 

The Health of Our Air joins The Health 
of Our Soils and the forthcoming The 


Health of Our Water as a series of 
scientific assessments evaluating the 
natural resources upon which 
Canadian agriculture depends. 

This book contains our most recent 
research findings. As the research 
continues, better estimates of 
greenhouse gas emissions will emerge. 
New, more efficient technologies will 
be developed, and we will learn more 
about the relationship between 
agriculture and the health of air. The 
Research Branch of x^griculture and 
Agri-Food Canada is committed to 

research in support of sustainable 
development of the Canadian 
agriculture sector. 

J.B. Moirissey 

Assistant Deputy Minister 

Research Branch 

Agriculture and Agri-Food Canada 

R. Slater 

Senior Assistant Deputy Minister 

Environment Canada 

VI 1 

1. Introduction 

Agriculture is tied tightly to the 
environment. Future food production 
depends on preserving soil, air, and 
water quality; in turn, the way we farm 
influences these resources. As a result, 
we need to assess, from time to time, 
the changes taking place in the 
environment, both to ensure that 
farming can be sustained and to 
measure its effect on other ecosystems. 
An earlier report considered The 
Health of Our Soils; in this companion, 
we focus on The Health of Our Air. 

Unlike soil, which is fixed in place, air 
moves and mixes freely around the 
globe. Air at the earth's surface can 
exchange with air many kilometres up 
within hours, and air currents can 
move around the world in a matter of 
days. Some of the carbon dioxide 
released by fires in Asia may be 
absorbed by orchards in Ontario, and 
some of that released from 
decomposing straw in Saskatchewan is 
taken up by the jungles of South 
America. As a result, we have to view 
the health of our air from a global 

Importance of 
atmospheric health 

Our atmosphere has many essential 
functions. It is a reservoir of gases 
upon which life depends: carbon 
dioxide and nitrogen for plant growth, 
oxygen for us to breathe, water vapor 
for rain that refreshes the land. It 
insulates the planet against 
temperature extremes and filters out 
harmful radiation from the sun. It even 
helps detoxify harmful substances 
released into it, either hastening their 

breakdown or diluting and dispersing 
them. Because living things depend so 
completely and in so many ways on the 
atmosphere, any change in its makeup 
should concern us. 

Our changing 

The air is always being recycled by 
exchange of gases and particles with 
land, water, and living things. The 
rates of gases entering the atmosphere 
are usually balanced by rates of gases 
lost, so that the composition of the 
atmosphere has remained nearly 
constant for many centuries. This 
balance has been disrupted, however, 
by increasing emissions from human 
activity, so that some gases are now 
accumulating, altering the composition 
of the air. 

One of the most noticeable changes, in 
recent years, has been an increase in 
concentrations of some "greenhouse 
gases": carbon dioxide (CO2), methane 
(CH 4 ), nitrous oxide (N 2 0), and 
chlorofluorocarbons (CFCs). These 
gases absorb some of the energy 
radiating from the earth, thereby 
warming the atmosphere. A build-up 
of greenhouse gases, therefore, is 
expected to increase global 
temperature over time. 

Greenhouse gases are not the only 
constituents of air whose 
concentration is changing. The levels 
of other constituents such as nitrogen 
and sulfur gases, ozone (O3), gaseous 
organic compounds, and suspended 
particles are also increasing as a result 
of human activity, including 

agriculture. These changes, like those 
in greenhouse gases, may affect climate 
and the health of the environment. 

Growing concern over the changing 
atmosphere has prompted global 
efforts to reduce emissions. These 
include recent international 
agreements to limit emissions of 
03-depleting chemicals (Montreal 
Protocol) and a Canada-US agreement 
on air-pollution. Perhaps most 
noteworthy is a treaty signed in Kyoto, 
Japan in December 1997 where 174 
countries, including Canada, agreed to 
curb emissions of greenhouse gases. 

Objectives of this 

Agriculture occupies a larger portion 
of global land area (about 35%) than 
any other human activity. Because of 
its scale and intensity, agriculture emits 
a lot of gases into the atmosphere. For 
example, agriculture is a main source 
of greenhouse gases, accounting for 
about 25% of the C0 2 , 50% of the 
CH 4 , and 70% of the N 2 released 
via human activity globally. As well, 
agriculture accounts for more than 
50% of ammonia released into 
the air. 

But because farmlands are managed so 
intensively, farmers can control, at 
least partly, the amounts of gases 
released. Various ways of farming 
produce different emissions; and by 
choosing new practices, it may be 
possible to reduce emissions. For some 
gases, farmlands may, in fact, even be 
made to absorb more than they emit, 
thereby helping to restore air quality. 

In this report, we focus on the effect of 
Canadian agriculture on the 
atmosphere. Specifically, we try to 
answer three questions: 

• How do farming practices affect 
the composition of the 

• What is the amount of 
agriculture's emissions to the air? 

• How can we reduce these 

Scope of this 

The most pronounced change in the 
atmosphere, and the one with greatest 
potential consequence, is the build-up 
of greenhouse gases. Hence, this 
report addresses in detail the amounts 
of greenhouse gas emission and 
possible ways of reducing them. We 
limit our discussions mainly to 
agricultural production itself and, 
except for ethanol, do not consider the 
fate of agricultural products once they 
leave the farm. Many of the findings 
presented were obtained from a 
national research program initiated by 
Agriculture and Agri-Food Canada 
in 1992. 

Besides focusing on greenhouse gases, 
we also consider several other current 
atmospheric issues, though in less 
detail: ground-level O3, ammonia, 
ultraviolet (UV) radiation from the 
sun, aerosols, nitrogen oxides, 
pesticides, and farm-related odors. 
Wherever possible, our discussion is 
based on findings from Canadian 
studies but, where Canadian results are 
only just emerging, we have drawn on 
results from elsewhere. 

Changes to the global environment 
may have pronounced effects on 
Canadian agriculture in the future: 
changing concentrations of CO, may 
affect plant growth; increasing 
temperature may allow greater 
diversity of crops but favor crop pests; 
changing patterns of precipitation may 
favor some areas but induce drought in 
others. Such changes remain hard to 
predict. Because of this uncertainty 
and the constraints of space in this 
report, how agriculture will adapt to 
future changes is only referred to 
indirectly; we await results of ongoing 
research to clarify this issue further. 

Reading this report 

This report is written for students of 
environmental issues, farmers, 
agricultural professionals, decision- 
makers, and others who want to 
understand the links between 
agriculture and air quality. The reader 
does not need a scientific background 
to read the report, though a 
rudimentary knowledge of chemical 
notation will be helpful. For example, 
we refer to various compounds 
containing nitrogen (N), carbon (C), 
oxygen (O), and hydrogen (H), 
elements that are the main 
constituents of greenhouse gases and 
organic matter. For the inquisitive 
reader, we have listed some important 
compounds in the box on this page. 

The information presented is gleaned 
from numerous sources, both 
Canadian and international. To allow 
for easier reading, we have not quoted 
individual sources but have provided a 
general bibliography at the end. More 
detailed information as well as some of 
the original sources may be found 


atmospheric constituents 

Elements and compounds 


Atomic or 

molecular weight 















Methane 1 

CH 4 



NH 3 



N 2 


Nitric oxide 




o 2 


Carbon dioxide 2 



Nitrous oxide 3 

N 2 


Nitrogen dioxide 






1 1 g of CH 4 contains 

0.75 g 


2 1 g of COi contains 

0.27 g 


3 1 g of N 2 contains 

0.64 g 


2. Canadian agriculture and 
greenhouse gases 

Canadian agriculture is diverse, with a 
variety of crops and livestock in a 
range of climates and soils. Emissions 
of greenhouse gases are also highly 
variable, changing with type of 
farming operation and even within 
individual farms. To estimate the 
emission of greenhouse gases from 
Canadian farms, therefore, we have to 
first consider briefly the nature of 
farming in Canada. 

A glance at 



The Canadian landmass has been 
classified into 15 ecological zones 
(ecozones) based on soil and climate. 
Most of Canada's land is forested, and 
only about 5% is suitable for farming, 
mainly in two ecozones — the Prairies 
and the Mixed Wood Plains of the St. 
Lawrence River (Fig. 1). The Prairies 
alone account for about 80% of 
Canada's 68 million hectares of 
farmland. Two-thirds of all farmland is 
used for crops and "improved" 
pastures (those that are seeded, 

Farmland % 

!■ 5.0-10.0 

H 10.1-30.0 
I 30.1-60.0 

I >60.0 
Not rated 

Figure 1 

Farmland as a proportion of land area in various parts of Canada in 1996. (F Wang and D.B. Gleig, AAFC) 

drained, fertilized, or weeded); the rest 
is occupied by "unimproved" pastures 
(largely native grasslands), buildings, 
barnyards, bush, sloughs, and marshes. 
The various types of pasture together 
account for about 30% of farmland 
(Fig. 2). 

The relative areas devoted to annual 
crops and animal husbandry vary 
widely across the country. For 
example, large areas of the Prairies are 
used almost exclusively for cropland 
(Fig. 3), whereas small pockets of 
concentrated livestock production exist 
in areas of British Columbia and the 
southern regions of Alberta, Ontario, 
and Quebec (Fig. 4). 

Although all ecosystems share 
common nutrient pathways, 
agriculture has unique features when 
compared to other land uses such as 

forestry. Farmlands, particularly those 
devoted to annual crops, are 
intensively managed. Moreover, the 
time cycle for agricultural crops is 
short, often annual. As a result, 
agriculture can respond quickly to 
climatic, economic, and policy events 
by changing land use and cropping 
systems, and there can be large shifts 
in just a few years (Table 1). Finally, 
agricultural ecosystems are quite 
"open," involving continual transfer of 
material in (e.g., fuel, fertilizers, and 
pesticides) and material out (e.g., crop 
yields and animal products). Unlike 
forests, which gradually increase their 
store of wood, farmlands rarely 
accumulate vegetation over the long 
term. Because of these unique features, 
studying and estimating greenhouse 
gas emissions from farms differs from 
that in other ecosystems. 

>. 1-15.0 
! 15.1-40.0 
Hi 40.1-60.0 

WM >60.o 

Excluded from analysis 

Figure 2 

(improved and unimproved) as a proportion of farmland in 1996. (F. Wang and D.B. Gleig, AAFC) 

Annual crops % 

■■ <20.0 
J 20.1-40.0 

I 1 40.1-70.0 

I >70.0 
Excluded from analysis 


Figure 3 

Annual crops as a proportion of farmland in 1996. (F. Wang and D.B. Gleig, AAFC) 

Units per ha 

Ml <0.05 

3 0.06-0.15 
□ 0.16-0.30 
■1 0.31-0.60 
■ >0.60 
Excluded from analysis 

Figure 4 

Distribution of livestock in Canada in 1996. One animal unit is the quantity of livestock that produces manure containing 170 
kg of N per year. For example, approximately 2 dairy cows are equivalent to 1 animal unit. (F. Wang and D.B. Gleig, AAFC) 


Table 1 The area of farmland in Canada occupied by annual crops 
(million ha) 





Total farmland 










Summer fallow 





Improved pasture 





Xonimproved pasture 





The "greenhouse effect" 

Short-wavelength radiation emitted from the sun is absorbed by the earth and re- 
radiated at longer wavelengths. Carbon dioxide, CH4, and N 2 account for 90% of 
this "greenhouse effect." In the long term, incoming radiation is balanced by 
outgoing radiation. Because of the greenhouse effect, the average surface temperature 
of the Earth is about 15°C, instead of-18°C. 




Reflected energy 




• Energy trapped 
• by greenhouse gases 

The greenhouse 

The earth is warmed by the sun's 
radiation (including visible light) that 
strikes it. The earth, in turn, radiates 
energy back into outer space, but this 
outgoing radiation differs from that of 
the sun: it has a longer wavelength and 
is invisible to the human eye. 
Furthermore, some of this outgoing, 
long-wave radiation is absorbed by 
various gases in the air, thereby 
warming the atmosphere. This 
warming is referred to as the 
"greenhouse effect" (though the 
warming effect inside glasshouses is 
really quite different!). The warming 
from the greenhouse effect is highly 
beneficial; without it, the average 
temperature on our planet would be 
about 33°C colder, making the earth 

The gases causing the warming of the 
atmosphere are known as "greenhouse 
gases." The most important are water 
vapor, C0 2 , CH 4 , N 2 0, and CFCs. 
Foremost among these is water vapor 
because it is a powerful absorber of 
long-wave radiation and is present in 
relatively high concentration. This gas, 
however, is already present in high 
enough concentration in the lower 
atmosphere that further increases in its 
concentration would have minimal 
effect on temperature. 

Much of the current concern about 
greenhouse gases has arisen from the 
recent recognition that the 
concentration of other greenhouse 
gases— C0 2 , CH 4 , N 2 0, and CFCs- 
has been increasing steadily since the 
industrial revolution, almost certainly 
because of human activity. By 1992, 
C0 2 had increased by 30%, CH 4 by 

145%, and N 2 by 15%. Current 
rates of increase are 0.5% per year for 
CO : , 0.6% for CH 4 , and 0.3% for 
N^O. The CFCs were not even 
present in the atmosphere until a few 
decades ago. If the current rates of 
increase continue, many scientists 
expect significant impact on the 
world's climate. For example, the 
Intergovernmental Panel on Climate 
Change predicts that the doubling of 
the CCS concentration, likely to 
happen in the 21 st century, would 
increase average global temperatures 
by 1 to 3°C — a rate of warming 
unprecedented in the last 10 000 years. 
As well, the enhanced greenhouse 
effect could amplify climate variability. 

In short, greenhouse gases have a 
desirable effect, as they warm the 
atmosphere and create favorable 
conditions for biological activity. 
Further increases in these gases, 
however, may lead to an "enhanced 
greenhouse effect" with uncertain, 
possibly disruptive, consequences. 

Commitments to 
reduce emissions 

Concern about the enhanced 
greenhouse effect has prompted 
international action to reduce 
emissions. A first agreement, intended 
to stabilize emissions at 1990 levels by 
2000, was signed in 1992 at the Earth 
Summit in Rio de Janeiro. A more 
binding agreement was reached at 
Kyoto, Japan in 1997. This protocol 
was aimed at reducing emissions from 
participating countries to at least 5% 
below 1990 levels, by 2008 to 2012. 
This treaty will come into effect, 
however, only when ratified by at least 
55 countries representing 55% of total 

The Intergovernmental Panel on Climate Change 

In 1988, the World Meteorological Organisation and the United Nations 
Environment Programme created the Intergovernmental Panel on Climate Change 
(IPCC). The IPCC evaluates research and policy options and publishes reports on 
climate change and the risk of global warming. 

The latest synthesis report, based on 1995 science, includes the following 

• The balance of evidence from observed changes suggests a discernible human 
influence on global climate 

• Human-induced climate change represents an important additional stress, 
particularly to the many ecological and socioeconomic systems already affected by 
pollution, and nonsustainable management practices 

• Significant reduction in net greenhouse gas emissions are technically possible and 
can be economically feasible ... in all sectors including . . . agriculture 

The assessment report now being planned will provide the major science input to the 
future evolution of the UN Framework Convention on Climate Change and the 
Kyoto protocol. 

The Kyoto protocol 

At Kyoto, developed countries agreed to reduce their combined emissions of 
greenhouse gases by 5.2% from 1990 levels. This target will be realized through 
national reductions of 8% by Switzerland, many Central and East European states, 
and the European Union; reductions of 7% by the United States; and reductions of 
6% by Canada, Hungary, Japan, and Poland. Russia, New Zealand, and Ukraine are 
to stabilize their emissions, while Norway may increase emissions by 1%, Australia 
by up to 8%, and Iceland by 10%. 

The protocol aims to lower overall emissions from a group of six greenhouse gases 
by 2008-2012, calculated as an average over these 5 years. Cuts in the three most 
important gases — CO?, CH4, and N2O-W1II be measured against a base year of f 990. 
Cuts in the three long-lived industrial gases — hydrofluorocarbon, perfluorocarbon, 
and sulfur hexafluoride — will be measured against either a 1990 or a 1995 base year, 
depending on what year is most beneficial. 

Greenhouse gas research methodology 

The sources and patterns of emission of carbon dioxide, methane, and nitrous oxide 
are complex. Laboratory and experimental plot studies are needed to improve our 
understanding of biological processes. Then the emissions must be assessed over 
whole fields and groups of fields, to account for soil, landscape, and management 
variations. Finally, interactions between these three greenhouse gases must be 
considered, regional and climatic variations taken into account, and the global effect 
integrated over complete ecosystems and all of Canada. 

Research Approach 


1) net contributions of greenhouse gas 

2) options for reducing emissions 




temporal/spatial scaling up 
model validation 
interaction of e;ases 

Ecosystem • net balances for 
greenhouse gases 

• feasibility of practices for 
reducing emissions 

Process • identification of 

• characterization of 

greenhouse gas emissions from 
developed countries. 

In the Kyoto protocol, Canada agreed 
to reduce its emissions to 94% of 1990 
levels by 2008 to 2012. But Canada's 
emissions are already well above 1990 
levels. Based on increases from 1990 to 
1997 and assuming a "business as 
usual" scenario thereafter, one estimate 
suggests that Canada will need to 
reduce its emissions by about 21%. 
Consequently, a widespread effort 
involving all sectors of our economy 
will be required to meet Canada's 
i ommitments. 

In 1992, Agriculture and Agri-Food 
Canada initiated a research program to 
estimate emissions of greenhouse gases 
from Canadian agriculture and to 
devise ways of reducing these 
emissions. Findings from this effort, 
some of which are summarized in this 
report, may help Canada meets its 
reduction target. 

Estimates of 

Carbon dioxide 

The global carbon cycle 

There are about 40 000 petagrams 
(Pg) of C in global circulation (Fig. 5). 
Most C is in the oceans but large pools 
also occur in soils, vegetation, and the 
atmosphere. Of these three pools, the 
atmosphere is the smallest but most 
active. The CO2 in the air is 
continually being removed by plants 
through photosynthesis and being 
absorbed into the oceans. At the same 
time, however, CO2 in the air is being 
replenished by release from plants, 
soils, and oceans. Thus, though C is 
always cycling, the concentration of 
atmospheric CO? has remained 
constant from year to year. Analysis of 
air bubbles trapped in old glaciers and 
shells buried in ocean sediments 
reveals that the atmospheric 
concentration of CO? had stayed at 
about 270 parts per million by volume 
(ppmv) for about 10 000 years. 


Soil carbon map of Canada 

The Canadian Soil Organic Carbon Database, consisting of over 1 5 000 soil landscape polygons, contains information describing the 
soil landscape and carbon content of each polygon. The total carbon in the first metre of all Canadian soils is 260 Pg (billion tonnes), 
which represents 13% of the world's total organic carbon. However, most of the carbon is in the northern wetlands and permafrost. 
Only about 10 Pg (billion tonnes) or 4% of the carbon is contained in the soil of agricultural ecosystems. 

Total Soil Organic Carbon Content 


41 - < 70 kg/m 
70 kg/m and over 

(C. Tarnocai, AAFC) 


(Pool size in Pg) 

Figure 5 

A simplified view of the global 
carbon cycle. 

That changed with the advent of the 
Industrial Revolution. Since then, the 
demand for energy has resulted in 
ever-increasing amounts of fossil fuels 
being extracted from deep reserves and 
converted to atmospheric CO2. This 
process, in effect, withdraws C from an 
inactive pool and emits it into the 
atmosphere as COt. Other activities 
have also favored increases in 
atmospheric COt: removal of forests 
has resulted in vegetative C being 
converted to COt, and the cultivation 
of previously undisturbed soils has 
resulted in soil C being converted to 
CO2. Because of these processes, the 
emissions of CO2 into the atmosphere 
now exceed the withdrawals, resulting 
in the gradual buildup of CO2 (Fig. 6) 


E 340 




•• •• 


260 - 


— I — 




Figure 6 

Long-term atmospheric CO? 
concentrations as determined from ice 
core data (before 1950) and 
atmospheric measurements (after 1950). 

In 1995, fossil fuel combustion alone 
released 23.5 Pg (billion tonnes) of 
CO-i into the atmosphere. The natural 
C cycle can absorb some of this 
increased CO2 emission: some is 
absorbed by oceans, some by increased 
photosynthesis in plants. Nevertheless, 
the total amount of C0 2 in the 
atmosphere is still increasing by about 
1 1.7 Pg (billion tonnes) of CO2 every 
year. These increases are readily 
apparent in weekly measurements of 
atmospheric C0 2 at Alert, NWT, 
which, despite seasonal variations 
reflecting plant growth, show a clear, 
undeniable upward trend (Fig. 7). 

Annual average 

Seasonal variations 





-I 1 1 1 1 1 1 1 

88 89 90 91 92 93 94 95 96 97 


Figure 7 

Seasonal variations of C0 2 
concentrations measured at Alert, 
NWT. Most land and, therefore, 
vegetation on the earth is in the 
Northern Hemisphere. This vegetation 
draws heavily on the atmospheric C0 2 
pool in summer but returns the C0 2 as 
the vegetation dies in winter. 

Carbon cycles in 
agricultural ecosystems 

The carbon cycle in cropped land is 
quite simple, at least in principle 
(Fig. 8). Carbon dioxide is absorbed 
from the atmosphere by plant leaves 
and is transformed, via photosynthesis, 


into C-containing compounds such as 
sugars, carbohydrates, cellulose, and 
lignin. Some of this material is used by 
the plant for its own energy and 
converted back to CO2. Of the C 
remaining in the plant, a portion is 
removed during harvest (e.g., in grain) 
and the rest is returned to the soil. 
This residue, including roots, becomes 
part of the soil organic matter. 
Microorganisms in the soil, in turn, 
decompose the soil organic matter, 
releasing CO? back into the 
atmosphere and closing the loop. This 
cycle is essentially the same in all 
cropping systems, but rates vary 
depending on climate, soil, and 
crop type. 

from that in crops grown for human 
food. But the CO2 and wastes from 
human consumption of crops are often 
released far from the farm and therefore 
are not usually thought of as part of the 
agricultural C cycle. 



Soil organic 

Figure 8 

Conceptual C cycle for corn (values are 
estimates of annual flows of C in 

Where present, livestock add another 
component to the carbon cycle (Fig. 9). 
Instead of being exported, much of the 
harvested plant material is fed to 
animals or used as bedding. Some of 
this C is released by the animals to the 
atmosphere as CO?, some is removed as 
animal products, but much is returned 
to the soil as manure. Consequently, 
livestock-based systems often retain 
higher proportions of C on the farms. 
In many ways, this cycle does not differ 

Figure 9 

Conceptual C cycle of a livestock-based 
cropping system. 

In systems that have remained largely 
unchanged for several decades, the 
amount of C entering the soil as plant 
residues is usually balanced by the 
amount of C converted to CO2 by 
microbial activity. Consequently, 
though C is continually added to the 
soil, the amount of C stored in the soil 
may not change measurably. For 
example, in the corn system illustrated 
(see Fig. 8), residue inputs of 4.5 Mg 
(tonne) C per hectare are exactly 
balanced by microbial production of 
CO2 from the soil, so that there is no 
change in the amount of C stored in 
the soil. 

Management effects on 
carbon cycle 

A change in the way land is managed 
can disrupt the C cycle, affecting the 
amount of C stored. Perhaps the most 


drastic example was the initial 
cultivation of soils for farming. This 
event, which happened on many 
Canadian farmlands more than a 
century ago, resulted in high losses of 
soil C: many soils lost about 25% of 
the C originally present in the C-rich 
surface layer, releasing a lot of COi 
into the atmosphere. There are several 
reasons for this loss. First, farming 
involves the harvest of C from the 
fields, and the removal of this C means 
less input of new C. As well, 
cultivation and growing annual crops 
often speed up the conversion of soil C 
to CO2 by soil microbes. After soils 
have been cultivated for a few decades, 
however, losses of C usually slow down 
or cease entirely, and the level of soil 
C is again stable (Fig. 10). 

— ► 















Effect on 

co 2 


Figure 10 

Theoretical changes in soil C as 
influenced by management. 

The effect of the initial cultivation on 
the C cycle is largely past. Today we 
are interested more in how current 
practices or future modifications might 
affect the C cycle. By choosing their 
crops, tillage practices, fertilizer 

treatments, and other options, farmers 
can alter the C cycle, thereby changing 
the amount of C stored in the system. 

Measuring management 
effects on carbon cycle 

How do we determine the influences 
of farming practices on the C cycle? 
One way is to measure all the flows in 
the C cycle in a farm field (see Fig. 8). 
By subtracting the amounts of C 
leaving the field from the amounts 
entering, we can calculate the net 
change in C. Such measurements are 
useful in describing how management 
affects the C cycle, but they are time- 
consuming and are used only at 
selected research sites. 

Another way is to measure the net 
exchange of COi between vegetation 
and the atmosphere above it. Using 
sensors placed on towers, researchers 
can measure CO2 transfer above the 
crop continuously for months or even 
years, allowing them to calculate CCh 
exchange over an entire field. This 
approach, using towers, aircraft, and 
other variations, provides an average of 
net CO2 emissions from larger areas, 
thereby overcoming the natural 
variations that occur across a field. 
The main disadvantage of this method 
is cost and the difficulty of integrating 
over long periods. 

A third method, and that most widely 
used, is to measure the change in the 
amount of stored C after a number of 
years. In farm fields (as opposed to 
forests), virtually all the C is stored in 
the soil organic matter. By measuring 
the amount of soil C once and then 
again several years later, scientists can 
tell whether the field has gained or lost 
C under certain practices (Fig. 1 1). 


A common variation on this approach 
is to measure the change under one 
treatment relative to another. For 
example, if we are interested in the 
effect of tillage on C storage, we can 
maintain two systems side by side — 
one tilled, the other not — and then 
measure the increase in stored C in the 
unfilled plot by comparing it to that in 
the tilled plot. But measuring changes 
in soil C is not easy. Any increase may 
be small, say 3 tonnes C per hectare, 
compared to the amount initially 
there, say 60 tonnes C per hectare. 
This problem is further complicated 
by the natural variability of C in the 
field, which is often much greater than 
the difference we hope to measure. 
Accurate measurement of soil C 
change, therefore, requires careful 
sampling and analysis. Some 
researchers have focused on specific 
forms of soil C or on atomic markers 
(isotopes) to measure soil C changes 
more precisely. 

Tower-based flux measurements 

Tower-based long-term measurements of CCs, water vapor, and energy exchange from 
many ecosystems are now available for North America and Europe. Scientists make 
these measurements to 

• collect critical new information to help 
define the global COi budget 

• improve predictions of future 
concentrations of atmospheric CO? 

• enhance understanding of C0 2 
exchange between atmosphere and 

• determine response of C0 2 fluxes to 
changes in environment and climate 

• provide information on processes 
controlling C0 2 flux and net ecosystem 

• help calibrate and verify data for C0 2 
flux models. 

(S. McGinn and E. Pattey, AAFC) 

Tower-based system for measuring gas 

Conventional tillage 





Time after adoption of no-till (years) 

Figure 11 

Estimating soil C gain after adoption of 

To estimate the effects of management 
on the C cycle over large regions, we 
have to rely on models. These models 
may be simple equations or highly 
complex computer programs that take 
into account many variables such as 

Twin Otter aircraft 

The Twin Otter aircraft (see photo), operated by the Flight Research Laboratory of the 

National Research Council, provides an excellent platform for investigating gas 

exchange near the surface. It is equipped with sophisticated turbulence and trace gas 

sensors. At a flying speed of 60 m/s and at altitudes of 30-100 m, the instruments 

record adnospheric data every 2 m. In 

flight, the measured net fluxes of a 

particular gas, such as C0 2 , water 

vapor, O3, CH4, and N 2 0, can be 

determined as the average product of 

vertical wind and the actual 

concentration of the gas. The flux 

value can be positive (indicating that 

more gas is released by the surface 

than is being absorbed), zero, or 

negative (meaning that more gas is 

being absorbed than is being released). 

0.1. MacPherson, NRC, and 
R.L. Desjardins, AAFC) 


Get a 

feel for 




Other name 


10° gram 


10' grams 



10 6 grams 




10 9 grams 


thousand tonnes 


10 1 - grams 


million tonnes 


lO 1- * grams 


gigatonne or billion tonnes 

P g 

100 mx 100 m = 

1 hectare (ha). 

1 ha = 2.5 acres. 

weather, soil type, and farming 
practices to predict C processes on the 
farm. Whatever their complexity, these 
models need to be checked against 
actual measurements to ensure that 
they are reliable. By using 
measurements from specific locations, 
researchers can verify the models and 
present their predictions for large areas 
with some confidence. 

of this soil, originally cleared from 
forest (Fig. 12). By comparison, soil 
under fallow-wheat showed no 
appreciable gains of C. Within each 
crop rotation, soil receiving fertilizer 
had higher gains of C than unfertilized 
soils, probably because of higher residue 
inputs with fertilization. Manure 
application increased soil C even more 
than fertilizer, because the manure not 
only increased crop yield but also 
provided direct addition of C. 

15 H 


Cereal-forage rotation 








No nutrients 


20 n 




1930 1940 1950 1960 1970 1980 1990 

Examples of management 
effects on carbon cycle 

Scientists have measured the effect of 
management on the C cycle at 
numerous sites across Canada. Rather 
than attempt to summarize all these, 
we offer a few as examples of recent 

Crop rotation in forest soil 

The Breton plots near Edmonton, Alta., 
are among the longest-running research 
sites in Canada. This experiment shows 
that an appropriate crop rotation, 
including legumes and cereal crops, can 
result in large increases in the C content 

Figure 12 

Change in organic C in two cropping 
systems at Breton, Alta., as affected by 
nutrient application. (R.C. Izaurralde, 
University of Alberta) 

Fertilizer application to corn 

Application of fertilizer can increase 
soil C. At a long-term research site in 
Ontario, soil under fertilized corn had 
higher soil C than that under 
unfertilized corn after 32 years 
(Fig. 13). Using C isotopes to 
distinguish between C from corn and 
that from previous organic matter, the 
researchers also showed that the 
increase came entirely from the corn 


residue — fertilization had no effect on 
the organic matter that was there 
before corn was first planted. Adding 
fertilizer to this soil increased yields, 
thereby increasing the amount of 
residues returned to the soil. Where 
there is no yield response to fertilizer, 
there may be no increase in soil C. 

90 -i 



5/2 70 

Original C 

C derived 
from corn 



Figure 13 

Soil C after 32 years of growing corn 
showing the proportion derived from 
corn and that remaining from previous 
organic matter. (E. Gregorich, AAFC) 


Historically, tillage was one of the 
main tools available to farmers for 
controlling weeds and preparing land 
for seeding. But with new herbicides 
and seeding equipment, intensive 
tillage is no longer always necessary. 
Some farmers have opted to eliminate 
tillage entirely, a practice referred to as 
"no-till" farming or "direct seeding." 
This practice can lead to substantial 
increases in soil C. A partial survey of 
studies across Canada shows no-till can 
increase soil C by as much as 10 Mg 
(tonne) per hectare, when compared 

Soil management 

Some of the many techniques used by farmers include 

• Conventional tillage: soils are routinely cultivated to eliminate weeds and prepare 
soil for seeding 

• Reduced, minimum, or conservation tillage: tillage is reduced to keep residues on 
the surface 

• No-till: seeds are planted directly without any prior tillage; weeds are controlled 
by chemicals 

• Summer fallow: no seeding for one season; weeds are controlled by cultivation or 
by chemicals. 

Definitions of tillage practices differ from region to region. 

No-till can have several advantages. It requires less time and machinery. The organic 
residues left on top of the soil help to preserve moisture and protect it against erosion. 

xiii4imk.-: >-i- 

Use of no-till* in Canada 

Area under no-till 









British Columbia 











No-till includes direct seeding into stubble or sod, or tillage of only the ridge of rows. 



Table 2 Examples of the effects of no-till on soil C in selected 
long^-term studies in Canada 





















*C in no-till - C in tilled. 

Tilled treatments and depth of analysis vary among sites. 

(C. Campbell, AAFC; C. Drury, AAFC; T. Vyn, University of Guelph) 

Summer fallow in Canada 

The major development that allowed agriculture in the climatically restricted prairies 
occurred by accident. In the spring of 1885, the farm horses of Indian Head, Sask., 
were conscripted for the army that was suppressing the Rebellion. By the time the 
horses were released, it was too late to plant. However, the land was worked during 
the summer and produced an excellent crop the next year, while drought caused an 
almost complete crop failure everywhere else. Experiments at the Dominion 
Experimental Station at Indian Head, established soon after, led to the system of 
summer fallowing being developed that turned Palliser's Triangle into the bread- 
basket of Canada. (Palliser's Triangle is the dry southwestern area of Alberta and 
Saskatchewan, named after this early explorer.) With modern methods of weed 
control, fertilization, and planting, 
summer fallow is no longer as 
essential as it once was. 

Area of summer fallow 
in Canada 

Fields not cropped for a year still 
require weed control, either 
mechanical or chemical. The bare soil 
is directly exposed to wind and sun, 
enhancing erosion and organic matter 
decomposition. Without a crop, little 
organic residue is returned to the soil. 
Use of summer fallow depends on soil 
moisture and expected crop income. It 
is expected that summer fallowing will 
continue to decrease and stabilize at 
about 4.5 million hectares by 
about 2050. 



1981 1986 

with tilled soil (Table 2). But such 
gains are not automatic. In some cases, 
researchers were not able to detect any 
effect of tillage on soil C. The 
inconsistency of the results is not 
surprising, because the response of soil 
C is affected by climate, soil 
properties, length of time under no- 
till, crop rotation, and many other 
factors. Some of the variability may 
simply reflect the difficulty of 
measuring soil C change precisely. 

Summer fallow 

Summer fallow, the practice of leaving 
land unplanted for a whole year, was 
once widely practiced in western 
Canada because it helped control 
weeds, replenish soil moisture, and 
increase available nutrients in the soil. 
The area of fallow has declined 
recently but still occupies about 6 
million hectares every year. Soils that 
are frequently under summer fallow 
usually have lower C content than 
those that are cropped annually. For 
example, long-term studies in 
Saskatchewan show that, after several 
decades, soil cropped to wheat every 
year have C contents several tonnes 
per hectare higher than those that are 
fallowed every second year (Fig. 14). 
Fallow has two negative effects on soil 
C: it hastens decomposition of soil C, 
and it reduces C inputs into the soil 
during the year when there is no crop. 

Swift Indian Melfort 

Current Head 

(30 years) (40 years) (30 years) 

Figure 14 

Organic C in surface soil of fertilized 

fallow-wheat (FW) and continuous 

wheat (W) in long-term sites in 


(C. Campbell, AAFC) 

Grass on previously cultivated land 

One of the fastest ways to increase soil 
C is to return cultivated land to 
vegetation like that under "native" 
conditions. A study at Lethbridge, 
Alta., compared the C cycle in four 
treatments: native grasses, crested 
wheat grass (a common, introduced 
grass), continuous wheat (wheat 
planted annually), and fallow-wheat 
(wheat planted only every second 
year). These plots were started on land 
that had been under fallow-wheat for 
many decades. Using the C budget 
method described earlier, researchers 
showed that the grass plots were 
gaining large amounts of C (Table 3). 
The fallow-wheat plots, on the other 
hand, were losing C whereas the 
continuous wheat plots were neither 
losing nor gaining C. 

Manure application to silage corn 

Animal manure is widely used as a 
nutrient source for crops. In a study at 
St-Lambert, Que., regular manure 
application increased the amount of C 

stored in the soil after 10 years 
(Table 4). Part of this increase came 
from the direct addition of C in the 
manure. This C represents a recycling 
of the C from plant materials used to 
feed and bed the animals. But the 
manure, by providing plant nutrients 
and improving soil aggregation and 
porosity, also increased crop growth 
and the amount of C returned to the 
soil as residues. Thus, using manure 
not only results in efficient recycling of 
plant C but also promotes soil C gains 
by increasing plant photosynthesis. 

These few examples, along with 
numerous similar studies across 
Canada, show clearly that the choice of 
farming practice can affect the C cycle 
and influence the net exchange of CO2 
from farms. 

Table 3 Carbon balance on plots seeded to grass or wheat 
in Lethbridge 

Crested Native Continuous Wheat- 

wheatgrass grasses wheat fallow 

g/m 2 

Net primary 






Harvested matter 





Carbon input in 

the soils 





Carbon loss from the soils 

(organic matter decay) 





Net soil carbon gain 






(B.H. Ellert, AAFC) 


Table 4 Carbon inputs, soil carbon storage, and soil physical properties of a silty clay loam in Quebec 
following 10 years of biennial applications of solid dairy cattle manure 

Manure application 

C added by 

C added by 

Soil C storage 







(t/ha/2 y) 



(kg /ha) 





































(A. N'Dayegamyie, MAPAQ, Qc and D. Angers, AAFC) 

Energy use 

Most cropping systems depend on 
external energy sources. Much of this 
energy comes from the burning of 
fossil fuels, which releases CO? into 

Table 5 C released as CO2 from manufacturing and 
transporting fertilizers 


kg C per kg of 
nutrient (N,P,K) 

Anhydrous ammonia 


Ammonium nitrate 

Ammonium sulfate 

Urea-ammonium nitrate 

Monoammonium phosphate (N + P) 

Potassium (K 2 0) 


(E. Coxworth, Saskatoon, Sask.) 

the atmosphere. We must consider this 
CO?, which is part of the C cycle on 
farms, if we want to look at the overall 
effect of agriculture on the 

The main use of fuel on Canadian 
farms is to power the machinery for 
tillage, planting, harvesting, and other 
field operations. Additional amounts 
are also used for transportation, 
irrigation, drying of crops, heating of 
buildings, and equipment used in 
livestock operations. 

Aside from that used directly on the 
farms, agriculture also depends on 
energy for the manufacture and 
transport of inputs. For example, 
manufacturing pesticides, buildings, 
and farm machinery uses energy. But 
the largest off-farm use of energy is for 
making and transporting fertilizer, 
notably that containing nitrogen. The 
resulting release of CO? varies 
depending on fertilizer form (Table 5). 
But, on average, producing and 


transporting 1 kg of fertilizer N 
releases about 1 kg of C (or 3.7 kg 
CO?) into the atmosphere. In national 
estimates of emissions, researchers 
usually assign these indirect uses of 
energy to other sectors (e.g., 
manufacturing). But they still relate to 
farming and offer a means of reducing 
CO2 emissions from farms. 

The rate of CO2 emission from energy 
use on Canadian farmland varies 
widely, depending on how intensive 
the farming operation is. For example, 
farms producing livestock on grassland 
may require relatively little external 
energy. By comparison, farms with 
high inputs of fertilizer, intensive 
tillage, and irrigation may generate 
high amounts of CO7 from using 

A typical farming system on cropland 
may release C from energy use at a 
rate of roughly 100 kg C per hectare 
per year. For example, an analysis of 
farming systems at Indian Head, Sask., 
showed that the total C emission from 
direct and indirect use of energy 
ranged from about 100 to 115 kg C 
per hectare per year, depending on 
tillage intensity (Fig. 15). The largest 
sources of this CC»2 were the 
manufacture and transport of fertilizer 
and the on-farm use of fuel. 

The net effect of a farming system on 
atmospheric CO2 is the increase in soil 
C minus the amount of C released 
from energy use. Thus, a farm that 
emits C0 2 from fuel use at a rate of 
1 00 kg C per hectare per year will 
have a net benefit on atmospheric CCh 
only if the rate of soil C gain exceeds 
100 kg C per hectare per year. For 
example, suppose a field gains 4 Mg 
(tonnes) C per hectare over several 
decades in response to better 

management and that soil C then 
stabilizes at that new, higher level. The 
net benefit to the atmosphere will be 
the difference between the soil C gain 
and cumulative CO2 release from 
energy use (Fig. 16). If CO2 from 
energy use is 100 kg C per hectare per 
year, then the CO2 release would be 
equal to the soil C gain after about 40 
years. Thereafter, the field would again 
be a net emitter of CO2, unless some 
further soil C gains are made. 

Machinery I Herbicide 

P fertilizer I N fertilizer 


Conv. till Minimum til] Zero till 

Figure 15 

Sources of CO2 from spring wheat at 
Indian Head, Sask., as affected by 
tillage. (E. Coxworth, Saskatoon, Sask.) 

30 40 50 60 70 

Figure 16 

Conceptual illustration of soil C gain 
and cumulative CO2 from fossil fuels in 
an agroecosystem. 


Modeling soil carbon content 

The site-specific model Century makes use of simplified relationships of the 
soil-plant-climate interactions to describe the dynamics of soil carbon and nitrogen 
in grasslands, crops, forests, and savannas. It accounts for several agricultural 
management practices including planting, applying fertilizer, tilling, grazing, and 
adding organic matter. It simulates above- and below-ground plant production as a 
function of soil temperature and availability of water and nutrients. Century 
predictions of the change in soil carbon in Saskatchewan are shown for two cases: 

A) two soil types and a change from wheat-fallow rotation to continuous barley 
in 1930 

B) one soil type, Dark Brown Chernozem clay loam, but two different rotations 
after 1930. 

Century predictions for different soils and crop rotations 

A B 






11000 -i 
9000 - 
8000 - 
7000 - 

Dark Brown Chernozem, Clay 

- Dark Gray Chernozem, Sandy Loam 

— Wheat-wheat-fallow 
— Wheat-fallow 

wheat- *" — ■ -^ __ 

fallow continuous barley 


— I 1 — 

1930 1950 



1970 1990 1910 1930 


(W. Smith, Ottawa, Ont.) 

Estimates of carbon 
dioxide emissions in 

Scientists calculate the net emissions of 
C0 2 from Canadian agriculture by 
estimating the annual change in stored C 
and adding CO2 release from fossil fuel 
(see Fig. 8). Most of the C stored in 
agroecosystems occurs in soil, so they 
can estimate the change in storage from 
the gain or loss of soil C. 

Estimate of soil C change 

Estimating soil C change for all the 
agricultural area of Canada is difficult, 

because soil properties and 
management practices vary across the 
country 7 . Measuring the change directly 
would require enormous effort, so our 
estimates rely on mathematical models. 

In a recent study, a detailed model 
("Century") was used to predict 
changes in C content of Canadian 
agricultural soils, based on climate and 
soils data from across Canada. 
Information about farming practices 
was taken from recent Statistics 
Canada data. The study considered the 
predominant agricultural systems in 
Canada but did not include all possible 
variations. Some of the factors not 
included were a) biomass burning, a 
practice no longer widely used; b) soil 
erosion, which moves C around the 
landscape; c) manure addition; d) 
minor crops such as potatoes and 
annual legumes; and d) minimum 
tillage, which is intermediate between 
"conventional" and no-till. Future 
analyses may include some of these 

The model predictions agree with 
historical observations: soil C declines 
rapidly after initial cultivation, but the 
rate of decline diminishes gradually 
over time as soils approach a new 
"steady-state" at which they no longer 
lose C (Fig. 17). According to the 
model, current rates of C loss are 
negligible. The model predicts, 
further, that agricultural soils will 
begin regaining some of the lost C in 
the future, as farmers adopt improved 
practices such as no-till and reduced 
summer fallow (Table 6). According to 
the model, the agricultural soils were 
losing C at a rate of about 3 Tg 
(million tonnes) of C per year in 1970 
but could be gaining C at a rate of 0.4 
Tg of C per year by 2010. Predicted 
rates of soil C change differ among 


regions, reflecting variable adoption of 
improved practices and differences in 
soil properties. For example, the model 
suggests that rates of gain are highest 
in Saskatchewan and lowest in Alberta. 
























1 1 1 1 1 

1910 1930 1950 1970 1990 2010 


Figure 17 

Long-term predictions of soil C change 
based on the Century model, assuming 
only a gradual adoption of no-till. 
(W. Smith, Ottawa, Ont.) 

All these predicted rates of change are 
low compared to the total amount of 
stored C. For example, a C gain of 0.4 
Tg/y amounts to a rate of <0.01 Mg 
(tonnes) of C per hectare per year, 
when averaged across all cultivated 
soils in Canada. This value is very 
small compared to the total C content 
of soils, which is commonly about 
60-100 Mg (tonnes) C per hectare. 

The Century model predictions 
represent our current best estimates of 
soil C change across the country. But 
these estimates rely on several 
simplifying assumptions and have not 
yet been fully tested for all conditions 
across Canada. For example, compared 

Rate of change of carbon in Canadian agricultural soils, 1990 

Agriculture's largest store of carbon is in its soils, where dead plants have 
accumulated over the centuries. Cultivating the soil, however, has greatly affected 
this store of carbon, reducing it by about 15-35%. Agriculture and Agri-Food 
Canada's research program confirmed that, in many cases, farmers have been able to 
reduce or even reverse the C loss with good management. 

The Century model (a site-specific computer simulation of the dynamics of soil 
organic matter) was used to estimate the rate of change of carbon in Canadian soils 
for the year 1990. Soil, crop coverage, tillage, and crop rotation data were obtained 
for 1229 soil landscape of Canada polygons. Century runs were carried out on 15% 
of the polygons. For each sampled polygon Century was run for one to five types of 
crop rotations under conventional tillage. It was also run for no-till practices for 
polygons for which no-till represented 5% or more of the agricultural area. 
The map shows carbon change in agricultural soils on the Prairies during 1990. The 
estimated average carbon loss corresponds to about 40 kg/ha/y, which is much 
smaller than the amount that can be measured. 

Rate of change in soil carbon in 1990 (t/ha) 

1 0.040 0.000 


-0.040 -0.080 -0.120 


-0.160 >-0.160 



(W. Smith, Ottawa, Ont.) 


Table 6 Soil organic C change in Canadian crop lands 1 as 
estimated using the Century model 






Average C change (kg/ha/y) 
Total C change (Tg/y) 











Pastures are not included. 

Since 1910, there has been a 24% reduction of soil organic C (1053 Tg C) 

in cultivated soils. Total C in first metre of agricultural soils in Canada is 10 000 Tg. 

(W. Smith, Ottawa, Ont.) 

Table 7 Estimated CO2 emissions from fossil fuel use in Canadian 

1981 1986 1991 1996 

(Tg C0 2 ) 

Direct use 

Fuel used on farm 





Indirect uses 

Fertilizer manufacture, 

transport & application 





Machinery manufacture 

6k repair 





Building construction (steel 

& cement manufacture) 





Pesticide manufacture 





Electricity generation 





Total indirect fossil COi 




(R.L. Desjardins, AAFC; E. Coxworth, Saskatoon, Sask.) 


to some actual data on the change in 
soil carbon under no-till, the predicted 
changes appear to be low by as much 
as 50%. With further research and as 
the reliability of the models improves, 
the estimates may be adjusted. 

Emissions from the use of fossil fuel 

The other major source of C0 2 in 
agriculture, aside from the biological C 
cycle, is burning of fossil fuel. Direct 
fuel use on Canadian farms releases 
about 10 Tg (million tonnes) of C0 2 
annually (Table 7). Indirect sources, 
associated with the production or 
transport of inputs, emit additional 
CO2. Of these, manufacture and 
transport of fertilizer is the most 
important. Emissions from this source 
have increased steadily because of 
increased rates of fertilizer application. 
The manufacture of farm machinery, 
construction of buildings, and 
generation of electricity also emit large 
amounts of C0 2 . Altogether, C0 2 
emissions from indirect sources 
amounted to about 16 Tg (million 
tonnes) of C0 2 in 1996. 

Direct and indirect use of fossil fuels 
on Canadian farms, therefore, 
amounted to about 26 Tg (million 
tonnes) of CO : (7 Tg C) in 1996. In 
calculating national inventories, 
however, researchers count only the 
C0 2 produced from stationary 
combustion (about 3 Tg C0 2 in 1996) 
in estimates for agriculture; the 
remainder they include in emissions 
from manufacturing, construction, and 
transportation sectors. 

Total emissions 

Total emissions of C0 2 from Canadian 
agricultural activity are the sum of net 
soil C loss, emissions from direct use 
of fossil fuel, and emissions from 


indirect uses of fossil fuel (Table 8). 
These estimates suggest that, in 1996, 
agricultural activity released about 28 
Tg of CO2 into the atmosphere, 
slightly less than in 1981. Projections 
to the year 2010 suggest that total 
emissions will not change appreciably 
from those in 1996. Scientists predict 
that emissions from soils are likely to 
decline and become negative (that is, 
soils will gain C) but, at the same time, 
emissions from indirect sources may 
increase, offsetting these benefits. 
These estimates, however, assume a 
"business-as-usual" scenario and do 
not yet take into account any benefits 
that might occur from concerted 
efforts to reduce emissions. 

Table 8 Estimated CO2 emissions from Canadian agriculture from 
direct and indirect sources 



(Tg C0 2 ) 

1991 1996 

Direct emissions 






Fuel used on farm 





Total direct emissions 





Indirect emissions 





Total emissions attributable 

to agriculture 





(R.L. Desjardins, AAFC) 


Methane is perhaps most familiar to us 
as the main component of natural gas. 
Though present in the atmosphere at 
very low concentrations (about 2 
ppmv), it is a comparatively powerful 
greenhouse gas: one kilogram of CH4 
has 2 1 times the warming effect of the 
same amount of CO2, when calculated 
over a 100-year period. This effect 
arises not only from the CH4 itself but 
also from other indirect effects, 
including the COi to which it 
eventually converts. 

The concentration of CH 4 in the 
atmosphere, which had been 
increasing at a rate of 1.1%, is now 
increasing at about 0.6% per year. 
Globally, agriculture is a prominent 
source of CH4, accounting for about 
two-thirds of human-induced 

Most of the CH 4 emitted from 
agriculture is produced by the 
microbial breakdown of plant material. 

Normally, when oxygen supply is 
adequate, most of the C in 
decomposing plant material converts to 
CO2. But, in the absence of oxygen, 
decomposition is incomplete and C is 
released as CH4 instead. In agricultural 
systems, such conditions occur in the 
digestive system of ruminant livestock 
(e.g., cattle) and in water-logged soils 
(e.g., rice paddies). Incomplete burning 
of fuel or organic wastes also produces 
small amounts of CH4. Methane and 
CO2, therefore, are somewhat 
complementary: C not converted to 
CH4 is largely released 
as CO2. 

The CH 4 emitted into the atmosphere 
has a lifetime of, on average, about 12 
years. Chemical reactions in the 
atmosphere convert most CH4 to CO2. 
Microorganisms living in the soil 
convert probably less than 10% of 
CH 4 released into the atmosphere 
to CO?. 


Methane emission by 

All animals produce CH4 when they 
digest feed. But emission is especially 
high from cattle, sheep, goats, and 
other ruminants. These animals have a 
rumen, or "fore-stomach," where 
microbial fermentation partially digests 
feed. Because of this process, 
ruminants can efficiently digest fibrous 
feeds. But, since the fermentation 
occurs under restricted oxygen supply, 
some C in the feed, often about 
5-10%, is released as CH4 rather than 
as COt (Fig. 18). Nonruminant 
animals, such as pigs and poultry, also 
emit some CH4 during digestion, but 
the amounts released are almost 
negligible by comparison (Table 9). 

CH 4 


icrobes ^ Soil organic matter 

Figure 18 

C0 2 and CH 4 flow in a livestock-based 

Measuring methane emission 

We can measure the amount of CH4 
emitted by livestock in a number of 
ways. One method is to place the 
animal in an enclosed chamber and 
measure CH4 accumulating in the 
airspace. This approach permits 
accurate analysis, but estimates may be 
distorted because the animal is 
removed from its normal environment. 
Recently, therefore, researchers have 

Table 9 Estimated CH4 emissions from livestock and manure in 1991 

Number of 

Mass of 


Methane from 




from manure 








Dairy cattle 






Beef cattle 
























Total livestock 






(R.L. Desjardins, AAFC) 


measured CH4 emission from cattle in 
their natural setting. They measured 
the CH4 concentration in air emitted 
from vents in a dairy barn and 
calculated the emission from all cows 
in the barn, including the manure they 
produced. Using this approach, they 
were able to estimate not only the 
average rate of CH 4 production per 
animal (about 550 litres per cow per 
day) but also the daily and seasonal 
fluctuations in emission rates (Figs. 19 
and 20). For example, highest 
emissions usually occurred 
immediatelv after each feeding. 




co 2 

In\ AY \\ 


CH 4 

i t r 




5800 8 

4S00 <3 


0:00 06:00 12:00 18:00 24:00 U 
Time of day 

Figure 19 

Diurnal pattern of C0 2 and CH 4 
emitted by dairy cows. (H. Jackson and 
R. Kinsman, AAFC) 

1000 -i 


| 600 < 

| 400' 

M 200' 

i— I 


1 1 — 

1993 1994 1995 

Figure 20 

Average monthly emission of CH 4 from 
a dairy barn in Ottawa. (H. Jackson and 
R. Kinsman, AAFC) 

Emissions from dairy cows 

A complete barn, with a handling system for liquid manure, was instrumented to 
monitor C0 2 and CI I 4 emissions from 118 dairy cows and their manure. 
Experiments such as this help to determine the amount of greenhouse gases emitted 
from cattle. The rate at which feed energy is converted to CH4 is based on the 
quantity and quality of feed. Dairy cows emit much more CH 4 per year than 
other cattle. 

Cows unknowingly participating in an experiment to measure greenhouse gas at the 
Central Experimental Farm in Ottawa, Ont. 

(H.Jackson and R. Kinsman, AAFC) 

Measuring CH 4 from cattle on 
pastures poses more difficult problems. 
But researchers now have a new 
technique, based on the use of a 
chemical marker, to measure directly 
CH 4 emission from grazing animals. 
This method, used in a grazing study 
in Manitoba, showed that emission 
rates were about 0.7 litre per kilogram 
body weight per day (0.5 g CH 4 per 
kilogram body weight per day). 

Factors affecting methane emission 

Many factors influence the rate of 
CH 4 emission from ruminants. They 
are reasonably well known because 
CH 4 loss represents incomplete use of 


Measuring methane emissions from grazing animals 

Scientists can measure CH4 produced from grazing cuttle by using sulfur 
hexafluoride (SF 6 ) as a tracer gas. Capsules that gradually release SF 6 at a constant 
rate are placed in the animals rumen. Then, by comparing the ratio of the 
concentrations of CH 4 and SF 6 expired by the animal, the researchers can calculate 
the CH 4 produced. 



■ Wt&^'-'Z-I*! 

;jf fV'^'jtTU 


^stwBtt* ~ *-T^#Bi.V : .~? 

Steer equipped to measure CH4 production using a tracer gas. 

(P. McCaughey, AAFC) 

feed energy. As much as 15% of the 
gross energy in feed may be lost 
through CH4 emission. As a result, 
researchers studied the factors 
affecting CH4 emission long before 
the environmental concerns about 
CH4 became prominent. 

One important factor affecting the rate 
of CH4 emission is the quality of the 
feed. In general, diets that increase the 
rate of digestion reduce CH4 
emissions, because the feed does not 
stay in the rumen as long. Thus, 
several characteristics of the feed can 

affect CH 4 emission: the amount of 
roughage in the diet, preservation 
method, growth stage of forage plant, 
degree of chopping or grinding, the 
amount of grain in the diet, and the 
addition of oils. For example, CH4 
emission may be lower from legume 
rather than grass forage, from ensiled 
rather than dried feeds, and from 
highly concentrated rather than high- 
roughage diets. 

Another important factor is the amount 
of feed intake. When intake of feed is 
increased above maintenance levels, the 
amount of CH 4 emitted per animal 
increases, but the efficiency of feed 
usage also increases. Consequently, 
CH4 emission per unit of product (e.g., 
milk or beef) is usually reduced at 
higher levels of feed intake. For this 
reason, it is often better to assess CH4 
emission per unit of product rather 
than per animal or unit of feed. 

For animals on pasture, the CH4 
production may be affected by the 
grazing regime. In a Manitoba study, 
halving the number of beef cattle per 
hectare increased CH4 emission per 
animal but reduced the emission per 
hectare. Overall, CH4 emission per 
kilogram of weight gain (about 150 g 
CH4 per kilogram of gain) was 
unaffected by grazing practice. 

The animal itself — its breed, weight, 
rate of growth, and whether it is 
producing milk — affects CH 4 emission. 
The environment may also affect CH4 
emission. For example, some research 
suggests that emissions may increase at 
lower temperatures. Because of the 
large number of factors that influence 
CH4 release from livestock, it may be 
possible to reduce emissions by 
changing management practices. 


Estimates of methane emission 
from livestock 

Direct emission of CH4 from 
Canadian farm animals can be 
estimated by multiplying the number 
of animals by an average emission rate 
per animal. In 1991, direct emission of 
CH4 from Canadian farm animals was 
about 771 Gg (thousand tonnes) {see 
Table 9). Of this, beef cattle accounted 
for 72% and dairy cattle for 25%. By 
comparison, direct emissions from 
other livestock were almost negligible. 

Emission of methane 
from manure 

Methane is emitted not only from the 
animals themselves but also from the 
C they excrete {see Fig. 18). Manure, 
like other organic materials, is 
decomposed by microorganisms. If the 
decomposition occurs under well- 
aerated conditions, most of the C is 
released as CO->. When oxygen is 
deficient, however, a lot of CH 4 may 
be produced instead. 

The ratio of CO2 to CH4 produced 
depends on how the manure is 
managed. Much of the CH4 from 
manure is produced during storage. 
When manure is stockpiled, 
inadequate aeration inside the pile may 
lead to CH4 production. Even higher 
amounts of CH4 may be released from 
manure stored in liquid form because 
of limited aeration. Thus pig manure, 
commonly stored as a slurry, may emit 
high amounts of CH 4 . Once manure is 
applied to the land, it produces little 
additional CH4 because of adequate 
exposure to air. 

Using estimates of manure produced 
and CH4 emission rates, it is possible 

to estimate the amount of CH4 
emitted from manure in Canada 
{see Table 9). According to this 
calculation, emission from manure 
accounts for about 20% of the total 
CH 4 emitted by livestock (manure + 
direct emission). In particular, these 
estimates point to pig manure as an 
important source of CH4, both 
because of large numbers of animals 
and because of the way the manure 
is stored. 

Methane emission and 
absorption by soils 

Soils can either release CH4 or absorb 
it, depending largely on moisture 
content. When organic materials 
decompose in submerged or water- 
laden soils, the water reduces the 
oxygen supply causing the release of 
large amounts of CH4. Globally, for 
example, rice paddies are an important 
source of atmospheric CH4. In the 
agricultural soils of Canada, however, 
CH4 emission is probably confined to 
localized wetland areas and perhaps to 
brief periods when low-lying soils are 
submerged during snowmelt or after 
high precipitation. Most soils have 
enough aeration that they do not 
produce CH4; in fact, microorganisms 
in the soils convert CH4 to COt so 
that the soils "absorb" CH 4 . The 
amount absorbed depends to some 
extent on management practices. For 
example, CH4 absorption is usually 
higher under grassland than in tilled 
soils and is suppressed by applying N 

Although CH4 absorption by soils is 
an important mechanism in the global 
CH4 cycle, the amounts absorbed by 
Canadian agricultural soils are 
probably small compared to total 


emissions from farms (Table 10). 
Researchers estimate net absorption of 
CH4 by agricultural soils in Canada to 
be about 12 Gg (thousand tonnes) per 
year. Even large increases in amount of 
CH4 absorption by soils would offset 
only a small proportion of current 
emissions from livestock and manure. 

Other sources of 

Fossil fuels used in agriculture release 
small amounts of CH4 by volatilization 
and combustion. This emission 
amounts to about 1 Gg (thousand 
tonnes) of CH4 per year (see Table 10). 
Some CH 4 is emitted from the 
burning of crop residues, but amounts 
are small and will diminish further 
because this practice is becoming 

Table 10 Estimated total CH4 emissions 









Total (Gg CH 4 ) 

Total (Tg C0 2 equivalents) 

























(R.L. Desjardins, AAFC) 

Estimates of net emission 
from all sources 

Virtually all the CH4 emission on 
Canadian farms is from livestock (see 
Table 10). According to current 
estimates, about 1 Tg (million tonnes) 
of CH4 was emitted from Canadian 
farms in 1996. Of this amount, about 
80% came directly from livestock, the 
remainder from livestock manure. 

Changes in emissions from year to 
year reflect differences in livestock 
numbers, which fluctuate depending 
on costs of feeds, market prices for the 
products, and export markets. If 
livestock numbers increase as expected, 
CH4 emissions may further increase 
unless farmers adopt new methods that 
reduce emissions per animal. 

Nitrous oxide 

Nitrous oxide is familiar to us as an 
anesthetic. It occurs naturally in the 
atmosphere at very low concentrations 
(about 0.3 ppmv), but the 
concentration is now increasing at a 
rate of about 0.3% per year. Much of 
this increase comes from agriculture, 
which accounts for up to 70% of the 
N 2 emissions from human activity. 

The increase poses two potential 
threats. First, N->0 is a potent 
greenhouse gas with a long lifetime in 
the atmosphere (about 120 years). Its 
warming potential is about 310 times 
that of CO? over 100 years. Second, 
N 2 released is eventually converted 
in the upper atmosphere to nitric oxide 
(NO), a gas that breaks down O3. 
Ozone in the upper atmosphere filters 
out UV radiation from the sun, so its 
depletion results in higher doses of 
harmful UV radiation reaching the 


earths surface. Higher N 2 C) levels, 
therefore, not only contribute to the 

greenhouse effect but may also 
increase indirectly the intensity of UV 

Most N 2 from agriculture is 
produced in the soil. To understand 
the origins of the N 2 and the factors 
that affect its emission, it is helpful to 
review the overall N cycle on farms. 

Nitrogen cycle 

In terrestrial ecosystems, there are 
three main pools of N — soil, plants, 
and atmosphere (Fig. 21). The largest 
of these is the atmosphere; in the 
column of air above a hectare of land 
there are about 76 million kg of N, 
roughly a million times the amount 
that plants on that hectare use in a 
year. Virtually all this N, however, 
occurs as N 2 , a gas that is almost inert 
and not directly available to plants. 


Figure 21 

Conceptual N cycle in an agroecosystem. 

Despite living in a sea of gaseous N, 
plants obtain most of the N they need 
through their roots, by absorbing 
nitrate (NO3") and ammonium 
(NH 4 + ) dissolved in soil water. When 
the plants later die, the N in the plant 
litter is returned to the soil, where it 

becomes part of die soil organic 
matter. Soil microorganisms, in turn, 
gradually decompose this organic 
matter, releasing NH.| + , which may be 
further converted to NO3". These 
forms are then available again for plant 
uptake, completing the cycle. In 
"natural" systems, this cycle between 
soil and plants can continue almost 
indefinitely, with only very small 
inputs of N from the air via lightning 
or specialized soil bacteria. 

In farmlands the N cycle is more 
complicated, as grain and other 
products remove large amounts of N 
from the field. In fact, cropping 
systems are often designed specifically 
to maximize the amount of N (as 
protein) in the plant parts that farmers 
harvest and remove. In high-yielding 
wheat, for example, harvesting the 
grain removes more than 100 kg N per 
hectare from the field every year. 
Consequently, to continue the cycle 
and to maintain crop growth, inputs 
from outside must replace the lost N. 

The main source of new N is the air. 
There are two ways of converting the 
otherwise inert N 2 into a form 
available to plants. One is the 
industrial approach, which uses energy 
from fossil fuel to convert N7 into 
"chemical" fertilizer. The other is a 
biological approach, which uses 
legumes such as alfalfa, clover, beans, 
and peas to "fix" N 2 . These crops have 
nodules on their roots, containing 
bacteria that convert N 2 into plant- 
available form. The plants absorb this 
N and, when they die and decompose, 
release it back into the soil as NFi4 + . 

The N from fertilizers and legumes 
has allowed large increases in food 
production, but, if they are to feed the 
growing population, producers will 


need even larger amounts of N. 
Already, the global additions of N 
from these sources exceed inputs from 
"natural" sources (mainly fixation by 
lightning and bacteria not associated 
with agricultural crops). Although this 
injection of N sustains food 
production, it exerts pressure on the N 
cycle and often results in losses or 
"leaks" of N into the environment {see 
Fig. 21). Large portions of applied 
N — as much as 50% in extreme 
cases — may leach into the 
groundwater. As well, N enters the air 
in various gaseous forms: ammonia 
(NH 3 ), nitric oxide (NO), N 2 , and 
N2O. Most of these "leaks" occur from 
the pool of plant-available N (NH 4 + , 
NO3"). Consequently, losses are 
highest when producers add these 
forms in amounts greater than the 
plants can use or at a time when plants 
are not growing. 

Table 1 1 Estimates of proportion of N released as N2O from various 
fertilizers as estimated in laboratory studies 

Synthetic fertilizer 

Amount of N fertilizer 

evolved as N 2 



Ammonium sulfate ((NH^tSO^ 

Ammonium nitrate (NH4NO3) 

Anhydrous ammonia 

Nitrogen solution 

Calcium nitrate (Ca(N03) 2 ) 


(Adapted from a review by E.G. Beauchamp and G.W. Thurtell, University ofGuelph) 

Nitrous oxide formation 

Nitrous oxide can originate from two 
places in the N cycle: during 
nitrification (converting NH 4 + to 
NO3"), and during denitrification 
(converting NO}" to gaseous N 2 ). 
Both processes are carried out by 
bacteria living in the soil. 


Most N enters the soil either as NH 4 + 
or in a form that converts to NH^. 
For example, the N in crop residues 
occurs largely in organic forms (like 
protein) which, when decomposed, 
release NH^. Similarly, most of the N 
fertilizers used in Canada contain N as 
NFL)." 1 ", or in a form (like urea), which 
converts to NH 4 + soon after 
application. Most of the N applied to 
soil, therefore, passes through the 
nitrification process. 

During nitrification, most of the N is 
released as nitrate (NO3"), but a small 
proportion of the N (usually less than 
1%) may be emitted as N 2 
(Table 11): 

Organic N 

Fertilizer >. NH 4 + - 


■> NO3- 

In general, the more NH^." 1 " applied, 
the more nitrification occurs, and the 
greater is the potential for N 2 
release. But the proportion of N 
released as N 2 is not fixed; under 
conditions of good aeration and high 
NH4 + , for example, less of the N will 
appear as N 2 than when oxygen or 
NH_|. + concentrations are low. As a 
result, the amount of N 2 released 
from nitrification may not correspond 


directly to the amount of N entering 
the process. 


When movement of oxygen into soil is 
restricted, nitrate (NO3") can be 
converted into nitrogen gas (N 2 ) in the 
process called denitrification. Deprived 
of oxygen in air, some bacteria use 
NO3" instead, thereby releasing N 2 . 
As for nitrification, however, a small 
proportion of the denitrified NO3" 
may be released as N 2 0: 

NO , 

N 2 

► N 2 

Three main factors control the rate of 
denitrification: the supply of oxygen, 
the concentration of NO3", and the 
amount of available C (used by 
bacteria as an energy source). Highest 
rates of denitrification occur when all 
three factors are present: low oxygen, 
high NO3", and high available C. The 
absence of any one of these three may 
reduce denitrification to negligible 
rates. Because it occurs only in the 
absence of oxygen, denitrification is 
most intense in water-logged soils. 
Some denitrification may also occur 
inside the root nodules of legumes. 

The amount of N 2 release, however, 
depends not only on the rate of 
denitrification but also on the ratio of 
N 2 to N 2 produced. This ratio is 
highly variable and tends to be lower 
under conditions favoring high rates of 

Often, we think only of the 
denitrification that occurs on farm 
fields. But N that is lost from the soil 
may also convert to N 2 or N 2 0. For 

example, the NO3" that leaches from 
the soil eventually finds its way into 
the groundwater or into sediments of 
streams and lakes. Once there it can 
undergo denitrification. Consequently, 
the amount of N->0 produced from 
farm practices may be much higher 
than that which is emitted directly 
from the soil. 

Of the two processes, denitrification is 
probably more important than 
nitrification as a source of N 2 in 
Canadian farms. Emissions of N 2 
from denitrification may be several 
times higher than those from 
nitrification, but it is difficult to 
distinguish between the two sources, 
and their relative importance varies 
widely from place to place. 

Management practices 
affecting nitrous oxide 

Because of larger N inputs and 
disrupted N cycling, agricultural soils 
often have higher rates of N 2 
emission than comparable soils under 
"natural" vegetation. For example, a 
fertilized barley field near Quebec City 
had N 2 emissions as high as 7 kg N 
per hectare per year, compared to 
negligible amounts (0.04 kg N per 
hectare) in a nearby forest soil. But the 
rate of N 2 emission is highly 
sensitive to conditions in the soil; 
under many conditions there may be 
no emission; in others there may be 
large bursts of N 2 0. By their effects 
on soil conditions, therefore, farming 
practices can greatly affect N 2 


Form of fertilizer applied 

In Canada, producers use a variety of 
commercial fertilizers to supplement 
soil N (see Table 1 1). Of these, urea 
and anhydrous ammonia (pressurized 
ammonia gas) are the most common, 
together accounting for almost 75% of 
the N applied. Most forms include N 
either as NH4 + or in a form that 
quickly changes to NH4 + after 
application. For example, anhydrous 
ammonia becomes NH 4 + immediately 
upon reacting with water in the soil, 

Fertilizer consumption in Canada 

From 1930 to 1960, the world production of nitrogen, phosphate, and potash was 
about equal. Since 1960, the use of all three nutrients has greatly increased but that 
of nitrogen fertilizers has increased faster than that of phosphate and potash. Canada 
uses about 2% of the world fertilizers. 

Much like the global trend, there has been a large increase in fertilizer use in Canada 
since the 1960s. Most of this increase is in nitrogen fertilizer and occurred in the 
Prairies. In eastern Canada, fertilizer usage has stabilized or even decreased in the 
last decade. Compared to other developed countries, Canada has a low rate of 
fertilizer use per hectare. 

Fertilizer consumption in Canada from 1966 to 1996 


l. "3 


= 1.5 






and urea is converted by soil enzymes 
to NH4 + and C0 2 within days of 
being applied. As a result, most of the 
N in fertilizers passes through the 
nitrification process (conversion to 
NO3") with the potential for some to 
be lost as N 2 0. 

During their initial reactions, 
fertilizers may affect pH, soluble C 
content, and other properties of soil in 
their immediate vicinity. These effects 
vary with fertilizer form so that N 2 
formation during nitrification may 
vary among fertilizers. Indeed, some 
research suggests that there may be 
large differences in N 2 emission 
among fertilizer forms. Highest 
emissions may occur from anhydrous 
ammonia, and lowest from calcium 
nitrate, presumably because the N in 
the latter does not undergo 

Nitrous oxide emissions from various 
fertilizer formulations were compared 
in a study at Elora, Ont. Equivalent 
amounts of N were applied to turfgrass 
in one of several forms: ammonium 
nitrate (NH4NO3), urea (CO(NH 2 ) 2 ), 
and slow-release urea. There was little 
N 2 emission from the slow-release 
urea, probably because its gradual N 
release coincided with plant N uptake, 
preventing the accumulation of NH 4 + 
or NO3". The other two sources 
showed significant N 2 emission, with 
slightly higher values from ammonium 
nitrate than from urea. 

The physical form and placement of 
fertilizers may also influence N 2 
emissions. For example, results of a 
laboratory study suggest that emissions 
may be higher from large granules 
than from fine particles mixed into the 
soil. The finer fertilizer is more widely 
dispersed in the soil and, presumably, 


Selecting the fertilizer 

Selecting a fertilizer is a question of convenience and cost. 
Convenience factors include the following: 

• concentration of nutrient 

• machinery, training, and maintenance requirements 

• safety 

• ease of transportation and application 

• secondary effect on soil acidity 

• possibility of combining with other operations (irrigation, 
spraying, seeding). 

Economic factors include the following: 

• cost relative to other formulations 

• value of the crop 

• efficiency of use by crop. 

Nitrogen requirements of crops 

Nitrogen is the nutrient needed most to ensure growth of nonleguminous crops, such as corn or wheat. Although leguminous crops, 
such as alfalfa and soybeans, derive some nitrogen from the soil, most comes from biological fixation. Other sources of nitrogen 
include synthetic fertilizers and manure. Residues of alfalfa following ploughing or chemical burndown may also supply the 
succeeding crop with significant quantities of nitrogen. 

The optimum rate of application for fertilizer or manure depends on the crop's need for added nitrogen, the anticipated yield, and 

the availability of nitrogen from previous 

manure application or leguminous crop 

residue. Soils differ significantly in their 

ability to furnish nitrogen to crops. Although 

data on historical response to nitrogen are 

generally used to predict the amount of 

nitrogen required, soil tests can also be used. 

Yields of nonleguminous crops may be 
increased by as much as 50% by adding 
manure or nitrogen fertilizer. But the 
amount should not exceed that which will 
return the most profit. Maximum profit 
usually occurs at about 95% of maximum 
yield. When applied at the rate for maximum 
profit, the nitrogen will be used efficiently, 
yet as economically as possible. 

(E. Beauchamp, University of Guelph, 
Guelph, Ont.) 

'.■', ': ■ ■ 


Safe n 




Nitrous oxide emissions measured at Elora (using a tower-based flux- 
measuring system) from a corn field. Bursts of N 2 emissions occur 
just after spring thaw and following fertilizer application. 






100 - 




~l ' 1 r 

60 90 

Calendar day 




(C. Wagner-Riddle and G. Thurtell, University of Guelph, Guelph, Ont.) 

has less effect on the pH immediately 
next to individual particles. Banding 
fertilizer, similarly, concentrates the N 
in localized areas and may therefore 
also affect N2O emission. 

Although these and other data suggest 
that how a ferdlizer is formulated and 
where it is placed may affect N 2 
emission, this effect has not yet been 
fully defined. Because N 2 emissions 
also depend on other factors such as 
rate of application, soil properties, 
timing of precipitation, and crop 
rotation, the effect of fertilizer 
formulation may not always be 
the same. 

Manure management 

Of the N consumed by livestock in 
feed, as much as 78% is excreted in 
urine and feces. In 1 year, for example, 
a dairy cow may excrete as much as 1 00 
kg N or more. Consequently, animal 
manure contains large amounts of N; in 
Canada, the N excreted each year by 
livestock may approach the amount of 
N applied as fertilizer. 

Some N in manures is lost to the 
atmosphere as NH3, either immediately 
or during storage, but most is returned 
to the land. The N content of manures 
varies depending on animal, rations, 
and bedding material but is typically 
about 2 % of dry weight. This N occurs 
largely in two forms: NH4 4 " and organic 
N. The former is immediately available 
to plants and behaves in the soil like 
NH.| + from fertilizer. The organic N, 
however, acts more like a slow-release 
form, gradually being converted to 
Nti^" 1 " by the action of soil 

The N applied in manure is susceptible 
to loss as N->0. Because a large part of 
the N occurs as NH^, some N 2 may 
be formed during nitrification to NO3". 
Denitrification may produce much 
higher amounts, because manure is a 
source not only of N but also of 
available C. Applying high 
concentrations of N and available C 
together favors denitrification. In 
extreme cases, where soils have received 
excessive rates of manure for many 
years in succession, N 2 emissions may 
be as high as 50 kg N per hectare per 
year, though emissions are usually much 

The amount of N 2 emitted from 
manured soils depends on method and 
rate of application, type of manure, and 


soil properties. One study suggests that 
liquid manure applied in hands may 
produce more N 2 than manure 
applied uniformly on the soil surface. 
Placing the manure in hands 
concentrates the N and C, creating 
conditions more favorable for 

Manure management may also have 
indirect effects on N 2 emission. A 
large portion of N excreted from 
livestock, as much as 50%, may be 
released into the atmosphere as 
ammonia (NH3) gas. This NH3 is 
eventually deposited onto soil or water, 
where it reverts to NH4 + and can be 
lost as N 2 like N applied directly. 

Crop residue input and soil 

Crop residues (e.g., straw, roots) and 
other plant materials return much N 
annually to the soil. In many cases, this 
N is merely a recycling of N absorbed 
earlier from the soil. But legumes, 
which can capture N 2 from the air, can 
actually add new N to the soil. 
Sometimes crops grown solely for the 
purpose of capturing N are ploughed 
back into the soil as "green manures." 

The amount of N 2 produced from 
added plant materials depends on the 
rate of N release. Some residues, such 
as wheat straw and corn stover, have a 
low N concentration, commonly less 
than 0.5%. When these materials 
decompose, they release little N; in 
fact, sometimes they even result in the 
withdrawal of NH4 + or NO3" from 
the soil because the microbes need 
extra N to decompose the residue. In 
contrast, N-rich materials such as 
legume residues or green manures can 
quickly release large amounts of NH^ 
(later converted to NO3") during 

decomposition. Like animal manure, 
these materials also provide a ready 
source of available C, favoring the 
release of N 2 from denitrihcation. 
For example, alfalfa residues may 
release 2-4 kg N2O-N per hectare and 
soybean residues 0.3-2 kg N2O-N per 
hectare per year. 

The way in which farmers manage 
crop residues may also influence N 2 
emission. Tillage may be the most 
important tool for managing residues. 
Normally, tillage mixes crop residues 
into the soil, but in no-till or other 
"minimum tillage" systems the 
residues remain on the soil, altering 
decomposition patterns. Some studies 
suggest that no-till techniques may 

Injecting liquid manure 

Injecting liquid manure into the soil prevents rapid loss of nitrogen compounds into 
the air and minimizes release of unpleasant odors. If the soil is loosened-up at the 
same time, deep soil fissures will be broken, and the liquid will not drain directly into 
the drainage tiles. Because manure tankers are very heavy and will compact moist 
soil, such as occurs in early spring, it is often difficult to find appropriate times to 
apply liquid manure. 


Table 12 Comparison of N7O emissions in central Alberta as affected 
by tillage 

1993-94 1994-95 

N (kg/ha) 

Till / with fertilizer 
Till / no fertilizer 
No-till / with fertilizer 
No-till / no fertilizer 

(R. Lemke. University of Alberta) 




increase N 2 emission; others 
conclude that no-till can reduce 
emissions (Table 12). How tillage 
affects N2O emission, it seems, 
depends on soil, cropping system, 
climate, and other factors. Aside from 
their effect on residue placement, 
tillage practices also influence soil 
moisture, temperature, and aeration, 
all of which affect N 2 production. 

Soils, even without recent additions of 
residues or other N, can emit N 2 
from their decomposing organic 
matter. Organic soils, because of their 
rich organic N reserves, may release 
particularly high amounts of N 2 — 
about 5 kg N per hectare per year. 
Similarly, soils that are left unplanted 
for a year (a practice known as summer 
fallow) may emit significant amounts 
of N 2 0. Soil microbes gradually break 
down the organic N in these soils into 
NH^ and NO3", and because there 
are no growing plants to remove this 
N, it accumulates and is highly 
susceptible to loss via denitrification. 

Amount a?id timing of nitrogen 

Often, N 2 emission is assumed to be 
directly proportional to the amount of 
N applied. But a better measure may 
be the amount unused by the crop. 
Matching the NH 4 + or NO3" released 
into the soil precisely to their uptake 
by plants prevents these N forms from 
accumulating in the soil, and N 2 
losses will be minimal. Such ideal 
synchrony, however, rarely occurs. 
Often NH 4 + , and particularly NO 3", 
accumulate in excess of the plants' 
capacity to absorb them, resulting in 
high potential for N loss via leaching 
or denitrification. This situation is 
especially true if the NO3" 
accumulates after harvest, because then 
it is vulnerable over the fall, winter, 
and, especially, the following spring, 
when denitrification is particularly 
intense. Consequently, matching the 
amount and time of N application with 
plant N uptake pattern is an important 
management tool to minimize N 2 

Nature of nitrous oxide 

Nitrous oxide emissions are usually 
sporadic. Unlike C0 2 , which is 
released from soil almost continuously, 
N 2 is often emitted in bursts or 
"flushes." Under Canadian conditions, 
the most important of these flushes 
may occur in early spring, as the snow 
melts. At a site in central Alberta, for 
example, most of the N 2 emitted in 
the entire year occurred during 10 
days at the end of March (Fig. 22). 
These bursts of N 2 emission at 
snowmelt may reflect favorable 
conditions for denitrification and N 2 
formation: high moisture content 


(oxygen deficiency), adequate NO3" 
and available C, and favorable 
temperature. Or the N 2 flush may 
reflect the abrupt release of N 2 that 
was previously trapped under a layer of 
frozen soil or ice. Although the spring 
flush is often the largest, additional 
bursts of N 2 follow heavy rains that 
result in water-logging of soils, 
especially in low-lying areas. As well, 
N2O may erupt immediately after 
fertilizer is applied because of the 
sudden availability of N. 

Emission of N 2 is sporadic not only 
over time but also across space. This 
variability stems, in part, from the 
differences in N and moisture (hence 
oxygen) content across the landscape. 
At any time, there may be minimal 
release of N 2 from most areas in a 
held, but high emissions from small 
"hot spots" where conditions are ideal 
for N 2 production. 

PL, 3 

o % 







146 166 186 
Calendar day 

206 226 

Figure 22 

Seasonal pattern of precipitation and 
N2O emissions from a fertilized wheat 
field at Ellerslie, Alta., 1993. (R. Lemke, 
University of Alberta) 

A further complication is that much of 
the N 2 is often produced in deeper 
soil layers. The release of this N 

Nitrous oxide emissions in the winter 

Eastern Canada, where soils can be covered with snow for up to 5 months, has a 
relatively short growing season. We once thought that N 2 emissions during winter 
were minor and of little importance in the annual N-budget. But we now know that 
significant losses of nitrogen as N 2 occur from under the snow cover. In certain 
cases, soils release substantial amounts of N 2 during the winter. Freeze-thaw cycles 
also affect the N 2 emissions from soils. These cycles induce physical and biological 
changes to the soil; they disrupt soil structure and stimulate denitrification leading to 
more N 2 production. 

(E. van Bochove, AAFC) 

depends on its rate of diffusion to the 
soil surface, which is controlled by soil 
porosity and the presence of ice or 
water at the surface. The trapped N 2 
may also be dissolved in soil water or be 
further converted to N 2 or to NO3" by 
microbes, so that the N 2 formed at 
depth is not all released to the 
atmosphere. Consequently, N 2 
emission from soils depends not only on 
how fast it forms but also on how fast it 
diffuses or converts to other N forms. 

Until recently, we thought little N 2 
would form over winter because of low 


soil temperatures. But this idea may 
not hold true where snow insulates the 
soil. In parts of eastern Canada, for 
example, snow blankets the soil thickly 
for up to 5 months per year, keeping 
soil temperature above or near 
freezing. As a result, N 2 can be 
produced all winter and be released 
through the porous snow. At a site 
near Quebec City, a fertilized barley 
field, ploughed the previous fall, 
released up to 5 kg N per hectare 
during the winter and spring, 
equivalent to 5-10% of the fertilizer N 
applied. The same field released only 
2 kg N during the growing season. 

Because of the sporadic and 
unpredictable pattern of N 2 release, 
estimating amounts of emission is 
difficult. Hence, current estimates of 
N 2 emission are probably less 

Table 13 Estimates of direct and indirect sources of N 2 
emissions from Canadian agriculture in 1996 





Total N 2 





from soils 

from manure 

(GgN 2 Q) 









































(R.L. Desjardins, AAFC) 

reliable than those for the other 
greenhouse gases. 

Estimates of national 
nitrous oxide emission 

Given our limited understanding of 
NtO formation and release, we can 
estimate only tentatively N 2 emissions 
from Canadian farms. Current estimates 
rely on simple equations, developed by 
the International Panel on Climate 
Change (IPCC), that calculate N 2 
release from three sources: direct 
emissions from soils, direct emissions 
from livestock production, and indirect 
emissions from farms. 

Direct emissions from soils include 
N 2 derived from fertilizer, land- 
applied manure, legumes, and crop 
residues. Researchers calculated 
emissions from the total N content of 
these sources, based on national 
statistics, assuming that a specified 
proportion of the N was released as 
N 2 (about 1%, depending on source). 
They also included estimates of N 2 
release from organic soils, though these 
amounts are small. Based on this 
calculation, they estimated direct 
emissions of N 2 from agricultural soils 
in Canada in 1996 to be 70 Gg 
(thousand tonnes) of N 2 (Table 13). 
When averaged over the area of 
cultivated land in Canada, this amount 
equates to about 1 kg N per hectare per 
year. The estimated emission rates, 
however, vary widely among regions 

The scientists calculated direct 
emissions from livestock by estimating 
the amount of N in manure and 
assuming that a specified portion of that 
N was emitted as N 2 0. They assumed 
the fraction of N converted to N->0 to 

be 2% for grazed animals and 0.1-2% 
for odier livestock, depending on waste 
management. Using this approach, they 
estimated direct emissions from 
livestock to be 24.5 Gg (thousand 
tonnes) of N 2 in 1996 
(see Table 13). 

They also calculated indirect emissions 
from estimates of atmospheric N (e.g., 
NH3) deposited on the soil, N leached 
from farm fields, and N produced from 

human sewage. According to these 
calculations, leached N is the most 
important, accounting for more than 
80% of the roughly 38 Gg (thousand 
tonnes) of N7O released from indirect 
sources in 1996 (see Table 13). This 
estimate assumed that 30% of the N 
applied as fertilizer or manure leached 
into the groundwater. 

Based on the IPCC approach, total 
emissions of N 2 from agriculture in 

Figure 23a 

Estimated direct N 2 emissions from agricultural sources in western Canada for 1991. 

Kg N 2 per square kilometre 


- 75 

75 - 150 
150 -225 
225 - 300 
300 - 375 
375 -450 
450 -525 

> 525 
Non Applicable 

■ ■ ■ 



Figure 23b 

Estimated direct N 2 emissions from agricultural sources in eastern Canada in 1991. 



Kg N 2 per square kilometre 

_J - 75 
75 - 150 

i 150 -225 

! 225 -300 

■■ 300 -375 

H 375 -450 

Hi 450 - 525 
■■ > 525 

| | Non Applicable 

Canada in 1996 were about 132 Gg 
(thousand tonnes) of N 2 (see Table 
13). Of this, direct emissions from soils 
accounted for about half. 

The trend in N 2 emissions over time 
may be as important as the total 
amount. Current estimates suggest 
that N 2 emissions have increased 
steadily since 1981, increasing by 20% 
from 1991 to 1996 alone. Much of the 
increase resulted from higher N inputs 

as fertilizers and animal manure. With 
increases in livestock numbers and 
higher crop yields expected in the 
future, N 2 emissions may climb still 
further unless producers make 
improvements in N management. 


Combined effect of 
the three greenhouse 

The three gases (CO2, CH4, and 
N2O) differ in their warming effects. 
To compare their relative effects, 
therefore, their emissions are usually 
expressed as "COi equivalents." One 
kilogram of N2O has the warming 
effect of about 310 kg of COt (when 
considered over 100 years), so it 
represents 310 CO-> equivalents. 
Similarly, 1 kg of CH 4 represents 21 
CO-, equivalents. 

According to best estimates, using the 
approaches described for each gas, 
Canadian agriculture had emissions of 
67 Tg (million tonnes) of COt 
equivalents in 1996 (Table 14). Of this 
amount, about two-thirds was as N2O 
and about one-third as CH4. By 
comparison, net emissions as CO2 
were almost negligible. 

The estimates of CO2 emission, 
however, exclude most of the CO2 
from fossil fuels used to produce 
inputs, power farm machinery, and 
transport products. These sources, 
which are included in inventories for 
transport and manufacturing sectors, 
emitted about 25 Tg (million tonnes) 
ofC0 2 in 1996. 

The emission of greenhouse gases 
from Canadian agriculture are 
increasing, according to current 
estimates (see Table 14). By 2010, 
emissions may be about 9% higher 
than those in 1996, unless producers 
adopt better management practices. 
These projected increases stem largely 
from predicted increases in livestock 
numbers and N inputs as fertilizer and 
manure. Emissions of COt are 
expected to decline, but not nearly fast 

Global warming potential 

Global warming potentials (GWPs) are a simple way to compare the potency of 
various greenhouse gases. They help policy makers compare the effects of reducing 
CO2 emissions relative to another greenhouse gas for a specific time horizon. For 
example, a small reduction in N2O can be just as if not more effective than a larger 
reduction in COi emissions. 

The heat-trapping potential of a gas depends not only on its capacity to absorb and 
re-emit radiation but also on how long the effect lasts. Gas molecules gradually 
dissociate or react with other atmospheric compounds to form new molecules, with 
different radiative properties. For example, CH 4 has an average residence time of 
about 12 years, N 2 C» 120 years, and CG* 2 200 years. Over a 20-year period, CH 4 has 
56 times the radiative impact of C0 2 . However, as time proceeds some of the CH 4 
molecules are broken down into CO? and H 2 0. Therefore, over a 100-year period, 
CH4 has a global warming potential of 21 times that of CO-.. 

Global warming potentials are presented for 20-, 100-, and 500-year time horizons. 
In The Health of Our Air, we use the 100-year GWPs recommended by IPCC. 
Calculations of warming potential are continually refined, so these numbers are 
subject to revision as understanding improves. 

Relative global warming potential 
(CO? equivalents per unit mass of gas) 

Time horizon 


20 y 

100 y 

500 y 

co 2 

CH 4 
N 7 Q 










enough to compensate for predicted 
increases in the other gases. 

Future emissions will depend on 
changes in farming practices that are 
hard to predict. Livestock numbers, 
crops that are grown, fertilization 
patterns, and manure management 
techniques can all change quickly, 
throwing off our current best 


Agri-environmental indicators 

An agri-environmental indicator is a measure 

of change, or the risk of change, in 

environmental resources used or affected 


agriculture. Although the indicators are 

national in scope, regional variations are 

taken into account. Six indicators are being 

developed, each of which has several components as follows: 

Fann resource management: 

used in agriculture and identifies the 

tracks farmers' use of 

areas at risk of contamination. 

environmentally sustainable 

management practices, by measuring 

Agroecosystem greenhouse gas balance: 

soil residue cover and management 

estimates trends in the net emission 

of agricultural land, fertilizers, 

ofCO : , N 2 0, andCH 4 . 

pesticides, and manure. 

Agroecosystem biodiversity change: 

So/7 degradation risk: 

monitors biodiversity in agricultural 

measures progress in reducing the 

ecosystems by measuring changes in 

vulnerability of agricultural soils to 

habitat availability. 

degradation and identifies soils still at 

high risk of erosion, salinization, 

Input use efficiency: 

compaction, or loss of organic 

measures the efficiency of fertilizers, 


energy, and irrigation water used by 
farmers to track possible effects on 

Water contamination risk: 

the environment. 

assesses progress in reducing the risk 

of water contamination by nutrients 

(T. McRae, AAFC) 

Uncertainties in 
current estimates 

Current estimates of greenhouse gas 
emission are not without uncertainty. 
We face many possible pitfalls in 
calculating emissions for ecosystems as 
extensive and diverse as Canada's 
farmlands. We still do not even 
understand all the processes that affect 
emissions. And so we admit that each 
estimate is subject to potential error. 
Of the three gases, N7O has the 
highest degree of uncertainty (Fig. 24). 
Estimates for this gas could be off by 
50% or more. Despite their 
uncertainty, these values are the first 
comprehensive estimates of 
greenhouse gas emission from 
Canadian agriculture and provide a 
reference point for showing trends. 

Though valuable as a first 
approximation, the estimates will likely 
change as we learn more. Ongoing 
research will teach us more about the 
processes leading to emission and allow 

Table 14 Estimates of total greenhouse gas emissions from Canada's agroecosystems 








(Tg CO7 equivalents) 

co 2 






CH 4 








N 2 
















* Predicted using a scenario of medium growth from Canadian Regional Agricultural Model (CRAM) to 2007. All 2010 data follow a best-fit trend 
using data from 1993 to 2007 from the CRAM. All fertilizer data were predicted using a best-fit trend from 1981, 1986, 1991, and 1996 Census data. 
All sheep, chicken, and turkey populations were predicted using a best-fit trend from Census data. 

(R.L. Desjardins, AAFC) 


us to build better models. As well, new 
techniques that simultaneously measure 
all three gases over large areas will allow 
us to evaluate better the models' 
reliability. We can dierefore expect 
more definitive estimates in the future, 
but we need not wait for their arrival 
before dying to reduce actual emissions. 


U 60 

h 40- 

1 20- 

a o- 

W -20 

C0 2 CH 4 N 2 

Figure 24 

Estimates of C0 2 , CH 4 , and N 2 
emissions in C0 2 equivalents from 
Canadian agriculture, showing relative 
uncertainty for each gas. 

Techniques to 
minimize emission of 
greenhouse gases 

Agriculture is a net emitter of 
greenhouse gases. Furthermore, 
current predictions point to increased 
emissions unless some changes are 
made to farming practices. 
Fortunately, farmers can adopt several 
measures to reduce emissions. Some of 
these would be expensive, but some 
can be used with little cost or even at 
higher profit. Widespread use of such 
practices could reduce emissions of all 
three greenhouse gases and, for CO?, 
even make farms net absorbers. 

Population of hogs in Canada 

Future greenhouse gas emissions depend on economic trend. For example, the 
Canadian Regional Agricultural Model (CRAM) estimates that, by 2010, the hog 
population in Canada will be about 14 million. This population is an increase of 36% 
over that recorded in 1990. This increase may cause N 2 and CH 4 emissions from 
manure to greatly increase. Hogs produce the second highest amount of manure per 
1000 kg of live animal per day, which is equivalent to 10 kg CH 4 per animal per year. 
Therefore, the CH 4 emissions from hog manure, in 2010, is expected to be about 
143 Gg (thousand tonnes) of CH 4 , which is 25 Gg higher than 1996 emissions 
from hogs. 

Greenhouse gas emissions from agriculture 

Agriculture contributed about 10% of 
Canadian anthropogenic greenhouse gas 
emissions in 1996. Using the global 
warming potentials, the major sources 
of emissions of all the gases were 
converted into C0 2 equivalents. From 
agriculture, the major sources are 
manure, enteric fermentation, crops, 
and fertilizers. 






(R.L. Desjardins, AAFC) 


A Leasuring greenhouse gases over farms 

Scientists are now looking at ways of 
measuring greenhouse gas emissions from 
entire farms. One way is to use 
instruments mounted on a tethered 
balloon, filled with helium, to measure 
changes in greenhouse gases over time at 
various heights above the farm. 

(E. Pattey, AAFC) 

Conservation tillage 

Conservation tillage prior to potato planting in Prince Edward Island. Minimum 
tillage in corn in Ontario and wheat in Saskatchewan. 

Reducing carbon 
dioxide emissions 

Farming means managing carbon. On 
every hectare of farmland, many 
tonnes (Mg) of C are removed from 
the air every year and changed to 
organic materials through 
photosynthesis (see Figs. 8, 9). At the 
same time, decomposing organic 
matter and the burning of fossil fuels 
releases roughly equivalent amounts of 
CO2 back into the air. By their choice 
of farming practices, farmers can 
manage this cycle, altering it to reduce 
net emissions of CO2. 

There are two main ways of reducing 
emissions: one is to increase the 
amount of C stored in soil; the other is 
to burn less fuel. Several practices are 
already available to achieve each of 

Increasing soil carbon 

In soils that have been managed in the 
same way for many years, the C 
content is reasonably constant. A 
change in management, however, can 
result in losses or gains of C. To 
increase soil C, we can do one of two 
things: increase the amount of C added 
to the soil, or slow the rate at which 
soil C is decomposed (decayed) back to 
C0 2 (see Figs. 8, 9). 

Adding organic matter 

Atmospheric COi enters the soil by 
way of photosynthesis. This process 
traps CO2 in organic forms, a portion 
of which is added to the soil as 
residues (including roots). The only 
direct way to increase C additions, 
therefore, is to use practices that favor 
higher photosynthesis; in other words, 
practices that increase plant yield. 


Farmers can achieve such increases by 
using higher yielding crops and 
varieties, by improving crop nutrition 
(using fertilizers and manures), or by 
reducing water stress (by irrigation, 
water conservation, or drainage). 
Actions that improve soil quality also 
promote higher yields. Perhaps most 
important is to use cropping systems 
that keep actively growing (and 
photosynthesizing) plants on the land 
as long as possible. 

But increased photosynthesis helps 
build soil C only if at least some of the 
additional trapped C is returned to the 
soil. The more of the plant removed 
from the field as grain or other 
products, the less the increase in soil 
C. Thus, using cropping practices that 
keep all residues in the field and 
planting crops (like forage grasses) that 
store much of their C in roots can 
achieve soil C gains. Often, animals 
help recycle the C back into soil. In 
many livestock-based systems, a large 
part of the plant yield is returned to 
the soil as manure, and only a small 
portion is actually exported from the 
field or pasture. 

Reducing decay rate 

The other way to build soil C is to 
slow the rate of organic matter decay 
in the soil. One method of doing that 
is to make conditions less favorable for 
soil microbes. For example, residues 
on the soil surface keep soils cooler, 
slowing decay. Similarly, maintaining 
growing plants on the surface as long 
as possible slows decay, because plants 
dry out the soil and cool it by shading. 

Decay rate can also be slowed by 
shielding the organic matter from soil 
microbes. Soils are usually granulated, 
with organic materials protected inside 

the granules (or aggregates). Breaking 
these aggregates open by intensive 
tillage exposes that organic matter to 
soil microbes. As a result, practices 
that minimize soil disturbance tend to 
preserve soil C. 

Another way to shield organic 
materials is to place them where 
conditions are not favorable for decay. 
For example, they can be kept on the 
surface where they tend to stay dry, or 
placed deep in the profile, where soil is 
cool (although this approach would 
require intensive tillage). 

Practices that increase soil carbon 

Much can now be done to promote 
soil C gain, either by adding more C 
or slowing decay (or both). The 
following methods are often effective, 
though the amount of C gain depends 
on climate and soil type: 

Reduce tillage: Tillage was once 
necessary to control weeds and prepare 
soil for planting. But now weeds can 
be controlled with herbicides, and new 
seeding equipment can place seeds 
directly into unfilled soil. As a result, 
intensive tillage is no longer necessary, 
and a growing number of farmers have 
eliminated tillage entirely, using no-till 
or "direct-seeding" practices. These 
practices protect C inside aggregates 
and keep residues on the surface where 
they decay more slowly and cool the 
soil beneath them. No-till and other 
"reduced tillage" practices also prevent 
erosion, thereby preserving soil quality 
and maintaining future photosynthesis. 
No-till, already used on about 14% of 
cropland in 1996, could be adopted on 
a large proportion of Canada's 

Apply more nutrients: Where soils do 
not have enough nutrients, adding 


Trees on agricultural land as a carbon reservoir 

Farmers have long planted trees as shelterbelts and for other environmental reasons. 
Since "afforestation" — the practice of planting trees on previously untreed land — is 
explicitly recognized as a legitimate carbon offset under the Kyoto protocol, we need to 
know how much C can be stored in such trees and at what rate. 

Prairie Farm Rehabilitation Administration (PFRA) Shelterbelt Centre at Indian Head, 
Sask., has determined the quantities and rates of C stored in prairie shelterbelts. 
Typical shelterbelt trees contained from 162 to 544 kg C, with poplar trees having die 
most. Shrub shelterbelts contained as much as 52 tonnes C per kilometre. 

0- Kort, AAFC) 

fertilizers, animal manure, or green 
manure increases yields, leading to 
higher inputs of C. Manures may also 
improve the physical condition or 
"tilth" of the soil, further increasing 
yields and residue additions. 

Grow more perennial forage crops: 
Perennial crops can trap more C0 2 
than annual crops because they 
continue growing for more months of 
the year. Because they dry out the soil 
more and there is no tillage, decay 
rates may also be slower. Many 
perennial crops, like grasses, have 

extensive root systems that place much 
C below-ground. 

Remove land permanently from 
cultivation: Probably the most effective 
way of increasing soil C is to allow the 
land to revert to its original vegetation, 
whether grasses or trees. Because there 
is little or no removal of C in products, 
virtually all the C trapped by 
photosynthesis is returned to the soil 
or stored in the wood. In theory, such 
"set-aside" lands would eventually 
regain all the C lost since cultivation 
began. However, this option means a 
loss in productivity so it is probably 
only feasible on marginal lands. The 
practice may also be applicable in small 
areas of cultivated land planted to 
shelterbelts or grassed waterways for 
control of wind and water erosion. 

Eliminate summer fallow: Leaving land 
unplanted for a growing season 
(summer fallow) helps control weeds 
and replenish soil moisture. But it 
results in soil C loss because, during 
the fallow year, no new residue is 
added and the soil remains warm and 
moist, which hastens decay. A shift to 
continuous cropping (growing a crop 
every year) therefore favors increases 
in soil C. The area of summer fallow 
has declined in recent years, but it still 
occupies about 6 million hectares every 
year. Eliminating summer fallow r may 
not be practical in very dry regions, 
such as parts of the southern prairies. 

Use cover crops: Where the growing 
season is long enough, a winter cover 
crop can be sown after the main crop 
has been harvested. This practice can 
add more residues to the soil and 
prevent erosion. 

Avoid burning of residues: When 
residues are burned, almost all their C 


is returned to the atmosphere as CO2, 
which reduces the amount of C added 
to the soil. 

Use higher yielding crops or varieties: 
Crops or crop varieties that have more 
efficient photosynthesis often produce 
more residues, which increases soil C. 
But because plant breeders choose 
varieties based on marketable yield 
(e.g., grain yield), residue and root 
yields of new varieties may not 
increase as much as the yield of 
harvested product. 

Improve water management: Water is 
often the limiting factor to crop 
growth. In the dry southern prairies, 
yields can be increased by irrigating or 
by trapping and storing water more 
effectively (e.g., using crop residue or 
windbreaks to trap snow). In parts of 
central and eastern Canada, conversley, 
crop growth may be limited by excess 
water in poorly drained soils. In these 
conditions crop growth and C 
additions to soil can be increased by 

Restore wetlands: Some low-lying areas 
in farmlands have been drained to 
allow crops to grow. Re-submerging 
these soils would cut off oxygen 
supply, preventing decay. These 
restored wetlands or "sloughs" could 
gain a lot of C quickly, though the 
small area of potential wetlands would 
limit CO2 removal. 

Integrate livestock into cropping systems: 
Feeding crops to livestock results in 
effective recycling of C if the manure 
is managed well. Thus, although large 
amounts of C may be removed from 
the field as forage or silage, much of 
this C can be eventually returned as 
manure. The manure also promotes 

crop growth and photosynthesis, 
favoring further soil C inputs. 

Improve grazing management: The way 
a grassland is grazed can affect the C 
cycle in several ways. It influences the 
proportion of the plant "harvested" by 
the animal, the redistribution of C in 
manure, the condition of the soil (via 
hoof action), and the species 
composition. Because of these many 
effects, the relationship between soil C 
and grazing regime is still unclear. 
Overgrazing, however, can result in 
large losses of C via erosion. Reducing 
the number of animals per hectare on 
such lands will likely increase the 
amount of C stored. 

Many studies across Canada have 
shown that these practices can increase 
soil C. The amount of potential gain, 
however, is still unclear and will vary 
depending on the initial soil C content, 
soil properties, climate, and other 
factors. The extent to which farmers 
adopt these practices also influences 
the amount of C gain. That will 
depend on crop prices, costs of 
production, and other factors that 
fluctuate from year to year. 

Despite the uncertainty, some 
estimates suggest that agricultural soils 
in Canada could gain as much as 
several million tonnes of C per year if 
these C-conserving practices were 
widely adopted. Such a gain would 
result in a net removal of CCb from 
the atmosphere. With time, however, 
the rate of C gain would decline 
because it becomes harder to add 
additional C as the C content of soil 
goes up. 


Storing carbon in plant 

Although the soil is the main 
storehouse of C in farm ecosystems, 
plant material can store additional C. 
One way to store more plant C is to 
grow trees on farmland, either as 
shelterbelts (which also control 
erosion) or as woodlots alongside 
farmsteads. The net benefit of this 
practice for atmospheric CO2 depends 
on the area of land devoted to trees, 
their rate of growth, and the fate of 
the wood. If the wood is burned, for 
example, there is little long-term 
benefit unless its use reduces 
dependence on other fuels. 

Another way of storing plant C is to 
convert crop residues into products 
with a long lifetime. One approach is 
to construct fiberboard (wood-like 

Storing carbon in strawboard 

Strawboard made from crop 
residues can store C and may 
help mitigate greenhouse gas 
emissions. At the end of their 
lifetime, the boards could be 
burned in power plants, 
replacing fossil fuel, resulting in 
a true reduction in COt 

One example is the industrial 
Isobord plant in Elie, Man. It 
expects to use 1 80 000 tonnes of 
wheat straw per year, which is 
equivalent to sequestering 
267 000 tonnes of C0 2 per 
year. The plant at Elie has 
already sold 80% of its first 5 
years' production. 

panels) from cereal straws. These 
materials are used for construction 
and, whereas much of the C in straw 
returned to soil would normally decay 
back to CO2, the C in these 
construction materials remains trapped 
for a long time. 

Reducing fossil fuel use 

Farms rely on energy from fossil fuels 
to power machinery, heat buildings, 
dry harvested crops, and transport 
goods. Energy is also used to supply 
materials employed on the farm, such 
as fertilizers, pesticides, machinery, and 
buildings. Most of these emissions are 
not attributed to agriculture in the 
national inventory of greenhouse 
gases. Even so, using less fuel on farms 
would reduce Canada's total COi 

The amount of fuel used on the farm 
and in the supply of farm inputs can be 
reduced in the following ways: 

Reduce til/age: It takes a lot of energy to 
lift and turn soil during tillage. 
Reducing or stopping tillage can, 
therefore, save on fossil fuel use. One 
Ontario study showed diesel fuel use 
reduced from 30 litres per hectare for 
conventional tillage to only 4 litres per 
hectare in a modified no-till system. xA 
study on the Prairies, which 
considered both direct and indirect use 
of fuel, showed that reducing tillage 
decreased emissions from direct fuel 
use by about 40% (see Fig. 15). 
Emissions for pesticide inputs were 
slightly higher under reduced tillage 
and emissions from fertilizer were 
unchanged. When all the direct and 
indirect factors were counted, 
emissions from no-till were 92% of 


those in conventional tillage, and 
emissions from minimum tillage were 

Use fertilizer more efficiently. Making 
and transporting fertilizer is energy- 
intensive. For each kilogram of 
fertilizer N used, about 1 kg of C is 
released into the atmosphere as COj. 
Consequently, methods ot applying 
fertilizer that produce high yields from 
less fertilizer can reduce CO? 
emissions. Possible approaches include 
placing fertilizer more effectively (e.g., 
banding): applying only as much as is 
needed, based on soil tests; and using 
variable rates of application on a field 
to reflect differences in soil fertility 
("precision farming"). 

Grow legumes: Legumes can often get 
much of the N they need from the air. 
When they die and decompose, they 
also release N into the soil. Careful use 
of legumes in cropping systems, 
therefore, can reduce the amount of N 
fertilizer needed, and thereby lower 
CO2 emissions. For example, in a 
study at Melfort, Sask., introducing 
pea into the crop rotation reduced 
CO2 emissions from fossil fuel by 
about 28% (Table 15). 

Use manure more efficiently: Animal 
manure contains many nutrients. 
These nutrients, however, are not 
always used efficiently, in part because 
of the high cost of transporting the 
heavy, bulky manures. Avoiding 
excessive application rates of manure 
in localized areas would not only 
prevent harmful loss of nutrients to the 
environment but also save on fertilizer 
use, thereby reducing CO? emissions. 

Increase energy use efficiency: Additional 
opportunities for reducing energy use 
include drying crops in the field 

Table 1 5 Impact of planting a legume on C emissions in a 
Saskatchewan cropping system 


(legume or no legume) 

Pea-Barley- Wheat 

(E. Coxworth, Saskatoon, Sask.) 

wherever possible, using more efficient 
irrigation systems, and insulating farm 
buildings. As well, many of the energy 
conservation measures advocated for 
urban areas also apply to the farm. 

An entirely different way of reducing 
emissions from fossil fuels is to grow 
crops that provide an alternate energy 
source. This "biofuel" can displace 
fossil use, thereby indirectly reducing 
CO? emission. Instead of extracting C 
from deep within the earth and 
burning it to CO2, biofuel production 
simply recycles the C originally 
removed from the atmosphere by 

The most efficient way of using crop 
materials for fuel is to burn them 
directly. Although this approach is 
used in some parts of the world, it is 
not always practical in Canada, where 
the fuel may have to be transported 
great distances. 

An alternative is to ferment crops, 
producing ethanol and mixing it, at 
proportions of about 10%, with 
gasoline. This mixture can be used in 
most gasoline engines and reduces the 
amount of CO2 produced from fossil 
fuel. The net savings in fossil fuel use, 

CO? emissions 
(kg C/ha/y) 



Ethanol as a fuel 

In 1997, Canadians used about 40 million litres of ethanol and 34 billion litres of 
gasoline, so ethanol represents about 0.1% of total gasoline sales in Canada. Ethanol 
has a lower energy content than gasoline. But when carefully blended at less than 
10%, mileage is not affected. 

Ethanol is a liquid alcohol produced by fermenting either starch materials (corn, 
wheat, barley) or cellulosics (agricultural residues, wood, wood wastes). Much of the 
CO-, released when biomass is converted to ethanol and burned in car engines is 
recaptured when new vegetation is grown, thus offsetting the greenhouse gas effect. 
Net lifecycle CO-i emissions from burning 10% ethanol-blended gasoline have 
shown about 3% reduction when compared to regular unleaded gasoline. Recent 
developments in the ethanol industry are expected to increase Canadian production 
from wheat and corn to about 350 million litres by 2000. 

(M. Stumborg, AAFC) 

however, depend on the amount of fuel 
used to grow the crop in the 
first place. 

The materials most easily converted 
into ethanol are those with high starch 
content. Thus cereal grains, such as 
corn and wheat, are preferred for 
ethanol production. One study 
suggests that, if the CO? emitted in 
crop production are taken into 
account, use of corn-ethanol reduces 

CO2 emissions by about 40%, relative 
to the emissions from the gasoline it 
replaces. If the emissions of other 
greenhouse gases are also taken into 
account, then use of ethanol from corn 
or wheat reduces the global warming 
potential by 25-30%. In Canada, 
about 30 million litres of ethanol are 
currently produced annually from 
wheat and corn, reducing CO? 
emissions by about 3 3 Gg (thousand 
tonnes) per year. If Canadian ethanol 
production reaches the expected 265 
million litres by the end of 1999, 
reductions in net CO2 emission will be 
increased by the same proportion. 

Though ethanol is most easily made 
from high-starch materials, new 
methods now also make it possible to 
make ethanol from fibrous matter, 
such as crop residues, forages, and 
crop wastes. An excess of about 2 Tg 
(million tonnes) of straw and chaff may 
be produced every year, beyond the 
amount needed for animal bedding 
and preventing soil erosion. If all this 
amount were used, it would produce 
about 500 million litres of ethanol and 
replace about 0.5 Tg (million tonnes) 
of fossil fuel CO2 (equivalent to 2% of 
the emissions from fossil fuel used in 
agriculture). The process could also be 
used to produce ethanol from 
perennial grasses grown on 
marginal lands. 

Still another way to reduce reliance on 
fossil fuel is to produce fuel for diesel 
engines ("biodiesel") from oilseed 
crops such as canola, flax, soybean, and 
sunflower. Although technically 
feasible, producing biodiesel is still 
much more expensive than producing 
fossil fuel. 

Current status of 
methods to reduce 
carbon dioxide emissions 

The C cycle is central to farming 
systems. Methods to reduce CO? 
emission rely mainly on managing that 
cycle more efficiently: recycling as 
much organic C as possible, 
minimizing disruption of soil, 
optimizing use of the sun's energy (via 
photosynthesis), and relying less on off- 
farm energy. 

Because they promote efficiency, many 
of these methods also help sustain land 
resources and may even be profitable. 
As a result, they are being adopted for 
reasons quite apart from their benefits 
to atmospheric CO2. For example, 
most farms in Canada now use less 
tillage than a generation ago, and an 
increasing proportion now use no-till 
practices. Similarly, the area of land 
devoted to summer fallow has fallen 
from about 1 1 million hectares in 1971 
to about 6 million hectares in 1996. 
The use of these and other 
C-conserving approaches will likely 
continue to increase in coming 

The two general approaches — storing 
more C and relying less on fossil fuel — 
reduce CO2 emissions over somewhat 
different periods. Storing C in soils has 
highest benefits early, in the first few 
years or decades, but net removal of 
C0 2 declines with time because it gets 
harder and harder to add additional C 
as soil C accumulates. Carbon dioxide 
savings from reduced fossil fuel, on the 
other hand, may seem rather small in 
the short term but can be significant 
when viewed over many decades. The 
net removal of atmospheric CO? from 
soil C gains is finite; that from reduced 
fossil fuel can continue indefinitely. 

Reducing methane 

Methane, like CO?, is part of the C 
cycle in farm ecosystems. It is released 
during decay of organic material when 
a shortage of oxygen prevents organic 
C from being completely converted to 
CO?. Although both CH 4 and C0 2 
are greenhouse gases, CH4 has a much 
higher warming potential, so release of 
C as CO? is preferred. 

Most CH4 from Canada's farms comes 
from the livestock industry, either 
directly from the animals or from the 
manure they produce. A number of 
methods have been proposed to reduce 
emissions from these sources, some of 
which are already in use. 

Reducing methane 
emissions from animals 

Much of the CH4 produced on farms 
is from ruminants — livestock such as 
cattle and sheep that have a rumen for 
digestion of feed. Specific practices 
that can reduce emissions from these 
animals include the following: 

Change rations to reduce digestion time: 
Most CH4 is released from the rumen, 
where feed is fermented in the absence 
of oxygen. The longer the feed 
remains in the rumen, the more C is 
converted to CH4. As a result, any 
practice that speeds the passage of feed 
through the rumen will reduce CH4 
production. One study with steers 
showed that, when scientists increased 
the passage rate of matter through the 
rumen by 63%, CH4 emission fell by 
29%. The passage of feed through the 
rumen can be hastened by 

• using easily digestible feeds grains, 
legumes, and silage 


Effect of feed additives on methane emissions from dairy cows 

Scientists at AAFC measured CH4 emissions from dairy cows in a barn over 3 years 
with an automatic gas sampling system. In one trial, 95 to 100 cows were fed a total 
mixed ration (TMR) consisting of concentrate and ensiled forage (35:65 on a dry 
matter basis) and produced an average of 26.8 kg of milk per cow per day. After a 
control period, monensin was added to the ration. There was an immediate decrease 
in CH4 emissions. At the same time milk production increased and daily feed 
consumption decreased, indicating an increased efficiency in feed usage. The effects 
of feeding monensin lasted 2 months after it was removed from the ration. There 
was, however, indication that rumen bacteria became resistant to monensin when a 
second feeding trial was conducted 5 months later. The use of monensin in dairy 
feeds is under consideration by regulator)' authorities but has not yet been approved. 
This feed additive has been used in beef cattle since 1975. These results show that 
feeding additives can significantly decrease CH4 emissions by dairy cows. However, 
further work is needed to resolve rumen microbial resistance and to develop a 
rotational system of feed additives to overcome this possibility. 



Begin End 

treatment treatment 

TV t \fl\ " ,i-, »£-**«-'. .' i ' 



300—1 1 1 1 1 r 

10 20 30 40 50 60 70 

Day of experiment 





•9 I 

•a e 


— 3 

= C 


(H. Jackson and F. Sauer, AAFC) 

harvesting forages at an earlier, 
more succulent growth stage 

chopping the feed to increase 
surface area 

minimizing use of fibrous grasses 
and hays 

• feeding concentrated supplements 
as required. 

Add edible oils: Adding canola, coconut, 
or other oils to the diet may reduce 
CH 4 production by inhibiting the 
activity of CJTj-producing bacteria. 
Though quite effective, this practice 
may not always be economical. 

Use ionophores: Ionophores are feed 
additives that inhibit the formation of 
CH4 by rumen bacteria. Already 
widely used in beef production, they 
can reduce CH4 emission. However, 
some evidence suggests that rumen 
microbes can adapt to a given 
ionophore, lessening its effect over 
time. For long-term effectiveness, it 
may be necessary to use a rotation of 
different ionophores. 

Alter the type of bacteria in the rumen: In 
the future it may be possible to 
introduce into the rumen genetically 
modified bacteria that produce less 
CH4. Though research efforts are 
promising, such inoculants are not yet 
commercially available. 

Improve production efficiency: Any 
practice that increases the productivity 
per animal will reduce CH4 emissions 
because fewer animals are needed to 
achieve the same output. For example, 
giving animals more feed may increase 
CH4 production per animal but reduce 
the amount of CH4 emitted per litre of 
milk or per kilogram of beef Any 
other practice that promotes efficiency 
will likewise reduce CH4 emission per 
unit of product. 

Many of these practices are already 
practical and economical. When used 
together, they can lower loss of energy 
through CH4 release from about 
5-8% of the gross feed energy to as 


low as 2 or 3 % . Because they increase 
feeding efficiency, these practices also 
often have economic benefits. 
Consequently, they are already widely 
used on many farms, especially in dairy 
herds and beef feedlots. 

Reducing methane 
emissions from manures 

Most of the CH4 from manure is 
produced during storage. When the 
manure is stored as liquid or in poorly 
aerated piles, lack of oxygen prevents 
complete decomposition to COi, 
resulting in the release of CH4. Most 
ways of reducing emission, therefore, 
involve slowing the rate of 
decomposition, providing better 
aeration, or reducing the length of 
storage. Specific methods include the 

Use solid- rather than liquid-manure 
handling syste?ns: Oxygen supply is 
usually better in solid manure, which 
encourages CO? to form rather 
than CH 4 . 

Apply manure to land as soon as possible: 
The longer manure is left in feedlots, in 
stockpiles, or in slurry tanks and 
lagoons, the more CH 4 will be emitted. 
Frequent applications to the land can 
therefore reduce emissions. 
Unfortunately, storing the manure is 
sometimes unavoidable because the land 
is frozen, too wet, or planted to crops. 

Minimize amount of bedding in manure: 
Manure with less bedding, such as 
straw, contains less C that can be 
converted to CH4. 

Keep storage tanks cool: Lowering the 
temperature of tanks, by insulating or 
placing them below-ground, slows 

Cattle management systems 

Producers feed and manage their cattle in different ways during different stages of 
the production cycle. The amount of greenhouse gas emitted depends on the system 
used and the stage in the cycle. Management systems can be compared in terms of 
net emissions; for example, grams of CH4 emitted per kilogram of milk or beef 
produced. Feeding cattle grain instead of forage reduces CH4 emissions. But feed 
type is only one factor to be considered in selecting a management system. For 
example, the use of forages in a feeding system encourages land to be used for 
perennial forage, rather than for annual crop production which results in greater soil 
C losses. Manure management and its greenhouse gas emissions must also be 
considered when determining an optimum management system. 

It .> *» * * 



k'J- ' 

(P. Strankman, Canadian Cattlemen's Association and K. Wittenberg, University of Manitoba) 


Improved manure storage can reduce greenhouse 
gas emissions 

Traditionally, manure is stored during summer and winter and is applied to the field 
in early fall or spring. Summer is usually the season of highest gas production 
because warm temperatures enhance microbial activity in stored manure. Anaerobic 
storage favors CH4 production, whereas aerobic storage produces CO2 and N7O. 

Scientists measured greenhouse gas emissions from beef and dairy manure each 
stored in three ways: compost, slurry, and stockpile. Methane and N->0 emissions, 
expressed in CO? equivalents, were always smaller for compost than for the other 
storage methods. For dairy manure, slurry emitted 1.9 times more greenhouse gas 
than the compost. Stockpiled manure emitted 1.5 times more greenhouse gas than 
the compost. Methane was the dominant gas in both the slurry and the stockpile. 
Nitrous oxide represented most of the compost emissions and a significant portion of 
the stockpile emissions. 

For beef manure, emissions of CH4 and N->0 were much lower than from dairy 
manure. Emissions of CH4 and NtO were 1.3 times higher from stockpiled beef 
manure than from compost and 4-6 times higher from slurry than from compost. 

These results indicate that aerobic storage such as composting may limit the 
greenhouse gas emissions. On the other hand, creating fully anaerobic conditions 
during storage promotes emission of CH4 that could be collected and used as a fuel. 

decomposition, thereby reducing 

Bins in which the manure was stored either as slurry, stockpiled, or for composting. 
A large enclosure was installed over each bin, and the gas emissions were monitored 
for a given time. 

(E. Pattey, AAFC) 

emission of CH4. 

Burn methane as fuel: Methane is a very 
effective fuel; indeed, it is the main 
constituent of natural gas. In some 
countries, CH 4 from stockpiled 
manure is already collected and 
burned. In Canada, this approach may 
not yet be widely practical or 
economical but is receiving growing 
interest. Burning CH4 converts it to 
CO?, which has a much lower 
warming potential. 

Avoid land-fitting manure: Although 
most manure in Canada is applied to 
land, small amounts are still disposed 
of in landfills. Because decomposition 
in landfills is usually oxygen-starved, 
large amounts of CH 4 can be emitted 
from this practice. Furthermore, 
placing it in landfills wastes valuable 
nutrients in the manure. 

Aerate inanure during composting: To 
make it easier to transport, manure is 
sometimes composted before applying 
it to the land. The amount of CH4 
released during composting can be 
reduced by aerating the stockpiled 
manure, either by turning it frequently 
or by providing a ventilation system 
inside the pile. Aeration encourages 
complete decomposition to CO2 
rather than release of C as CH4. 

These methods can reduce, to some 
extent, the CH4 emitted from animal 
manure. Because of high densities of 
livestock in some areas, and the high 
cost of handling and transportation, 
managing manure still remains a 
challenge. Other ways to reduce 
emissions may still be needed. 


Reducing nitrous 
oxide emissions 

Much of the N\() emitted from 
farmland is produced when excess 
NO-," in soil undergoes denitrification, 
either on farmland or after it is leached 
away. Fanners can reduce these 
emissions by preventing build-up of 
NO3" or avoiding soil conditions that 
favor denitrification. Some N^O is also 
emitted when NH4 + is converted to 
NO3" (nitrification). Adding less NH 4 + 
or slowing the rate of nitrification can 
reduce emissions from this source. The 
best way to reduce N->0 losses is to 
manage the N cycle more efficiently, 
thereby avoiding the buildup of 
excessive NH.| + or NO3". 

Specific ways of reducing N2O 
emission vary for farming systems 
across Canada, but examples include 
the following: 

Match fertilizer additions to plant needs: 
The best way to reduce N->0 emission 
may be to apply just enough N so diat 
crops can reach maximum yield without 
leaving behind any available N. A 
perfect match is rarely achievable, but 
the synchrony can often be improved 
by basing fertilizer rates on soil tests 
and estimates of N release from 
residues and organic matter. In fields 
where fertility 7 needs vary, applying N at 
different rates across the landscape 
("precision farming") may also improve 
the match between amount applied and 
the amount taken up by crops. 

Avoid excessive manure application: 
Heavily manured land can emit a lot of 
NiO because the manure adds N and 
available C, both of which promote 
denitrification. Moreover, manure is 
often applied to land as a means of 
disposal, so that rates can be excessive. 

New technology of manure treatment 

Scientists have introduced a new manure treatment process based on the use of 
anaerobic microorganisms in sequencing batch bioreactors (ASBR). Trials performed 
in the laboratory showed that the ASBR technology is very stable and versatile and 
works well at low temperatures (between 10 and 20°C). Furthermore, the bioreactors 
need to be ted only once a week, during regular manure removal. 

The airtight reservoir 
needed to maintain 
anaerobic conditions in 
the bioreactor 
completely eliminates 
any emissions of 
greenhouse gas during 
treatment and storage. 
The biogas can be 
recovered and used for 
energy on the farm. 

The technology also 
has other interesting 
benefits. It deodorizes 
and stabilizes the swine 
manure slurry leading 
to the degradation ot 
most of the 150 odor- 
causing substances in 
the manure. 
Furthermore, this 
technology increases 
the availibility of 
nitrogen and 
phosphorus to crops 
and reduces the need for 
chemical fertilizers. 

(D. Masse and F. Croteau, AAFC) 

Anaerobic sequencing batch bioreactor. 

Applying the manure at rates that just 
supply plant demands can greatly 
reduce N->0 emissions from this source. 

Optimize timing of nitrogen application: 
When the N is applied is as important 
as the rate of addition. Ideally, farmers 
should apply N just prior to the time 
of maximum uptake by the crop. 

Wherever possible, they should avoid 
applying fertilizer and manure in fall. 
Similarly, they should time the plough- 
down of N-rich crops, like legumes, so 
that N release from the residues 
coincides with subsequent crop 

Improve soil aeration: Denitrification, 
and hence N 2 emission, is favored by 
the low oxygen levels that usually 
occur in saturated soil. As a result, 
farmers can reduce emission of N 2 
by managing soil water — draining soils 
prone to water-logging, avoiding over- 
application of irrigation water, and 
using tillage practices that improve soil 

Use improved fertilizer formulations: 
Some research suggests that certain 
forms of fertilizer emit more N 2 
than others. Highest emissions may 
occur from anhydrous ammonia; 
lowest from forms containing NO3". 
This finding suggests that, by selecting 
appropriate fertilizers, farmers could 
reduce N 2 release. However, the 
differences among forms of fertilizer 
have not yet been widely verified in 
Canada. Another option is to use slow- 
release fertilizers, such as sulfur-coated 
urea. These forms release available N 
gradually; they feed the crop yet 
prevent available N from 
accumulating. Though effective in 
reducing N 2 emissions, slow-release 
forms may only be economical for 
high-value crops. 

Use appropriate fertilizer placement: 
Placing fertilizer in close proximity to 
crop roots can improve the efficiency 
of nutrient use, allowing the farmer to 
achieve high yields with lower rates of 
application. On the other hand, 
placing the fertilizer too deep in the 

soil, or concentrating forms like urea 
in bands, may increase N 2 emissions. 

Use nitrification inhibitors: Certain 
chemicals, applied with fertilizers or 
manures, inhibit the formation of 
NO3" from NH^. Their use may 
suppress N 2 formation in several 
ways: it reduces N 2 formation during 
nitrification, it prevents denitrification 
of accumulated NO3", and, because 
NH4 + does not leach easily, it prevents 
loss of N into groundwater where 
denitrification could occur. 

Use cover crops: Where the growing 
season is long enough, farmers can sow 
crops after harvest to extract excess soil 
NO3", which prevents it from leaching 
or converting to N 2 0. 

Lime acid soils: Because it is favored by 
acidity, N 2 emission can be 
suppressed by applying neutralizing 
lime to acid soils. 

Reduce tillage intensity: Though results 
are still inconsistent, some studies in 
Canada suggest that N 2 emission 
may be lower in no-till than in 
conventional tillage. If confirmed, this 
observation may point to no-till as a 
method of reducing emissions, at least 
in some soils. 

These practices can help reduce N 2 
emissions in many settings. Because 
N 2 fluxes are so sporadic, however, 
all these practices cannot yet be 
recommended with confidence across 
Canadian soils and cropping systems. 
But those that improve the efficiency 
of N use are often already justified for 
reasons quite apart from reduced N 2 
emission. Fertilizers account for about 
9% of production costs on farms, and 
any method that reduces N losses has 
economic benefits. 


Putting it all together 

For simplicity, we often discuss 
methods of reducing emissions for 
each gas separately. But the C and N 
cycles are tightly interwoven; a change 
in farming practice that reduces 
emission of one gas almost always 
affects another. Whether or not a new 
practice helps alleviate the greenhouse 
effect depends on the net effect on 
emission of all gases and the relative 
warming potential of each. A few 
examples may help to illustrate some 
of the complex interactions. 

One of the ways to reduce CO2 
emissions is to farm more intensively: 
to eliminate summer fallow, to use 
higher-yielding varieties, and to aim 
for higher productivity. Such practices 
can increase stored C by producing 
higher amounts of residue that become 
soil organic matter. At the same time, 
however, the new, more-intensive 
system may require higher inputs, 
including fertilizers, to maximize 
yields. And those higher inputs of 
fertilizer may increase N 2 emissions. 
The overall effect of the new practice 
must therefore take into account the 
change in soil C, the C0 2 cost of 
making the added inputs, and any 
increase in N 2 emission. Because 
N 2 is such a potent greenhouse gas, 
a small increase in emission rate (say 1 
kg N per hectare per year), will offset a 
comparatively high rate of soil C 
accumulation (-130 kg C per hectare 
per year). 

The evaluation becomes even more 
complex if we include animals. 
Suppose, for example, we opt to 
allocate greater land area to producing 
forages. This effect would have 
pronounced benefits for storing soil C. 
Furthermore, it would reduce fertilizer 

requirements (and N 2 emissions 
from that fertilizer), because nutrients 
are effectively recycled back to the soil 
as manure. On the other hand, much 
of the C in that system would be fed to 
animals, and a portion would be 
released as CH4. Furthermore, some 
CH4 and N 2 would be produced 
from manure. Thus, with one 
management change, we have affected 
emission of all three gases, sometimes 
both negatively and positively. And to 
know the net effect of the practice, we 
must consider all three and their 
relative warming potentials. 

We cannot yet grasp all the 
interactions among gases, nor are our 
models sophisticated enough to predict 
them. At present, however, it may be 
sufficient to recognize that all are part 
of a complex web, and any attempt to 
reduce emissions of one may affect the 
others. Often, the net effect may still 
be overwhelmingly positive; for 
example, it may be that the increased 
soil C from a livestock-based system 
more than offsets any increase in CH4 
emission. Indeed, sometimes the 
effects may even be mutually positive; 
no-till, for example may increase soil 
C, reduce C0 2 from fossil fuel, and 
perhaps even reduce N 2 emissions. 
Similarly, more efficient use of 
manures, can almost certainly reduce 
N 2 and CH4 emissions, while 
reducing C0 2 costs of fertilizer 

A final consideration is that the various 
practices aimed at reducing 
greenhouse gas emissions may work 
over different periods. For example, 
efforts to increase soil C gains may 
show largest response in the short 
term, say one or several decades, but 
rates of C gain may diminish thereafter 
because each new increment of C 


becomes harder and harder to achieve. 
In comparison, efforts to reduce CH4 
emission from ruminants, N 2 
emission from soils, or CO2 emission 
from fossil fuels may have only small 
effects in the short term but achieve 
highest effect over many decades 
because the benefits accrue 

Other effects of 
practices that reduce 
greenhouse gas 

We cannot judge the attractiveness of 
various management practices solely 
on how well they reduce greenhouse 
gas emissions. Other factors that come 
into play include their practical 
feasibility, economic cost, effect on soil 
quality, and influence on the whole 

environment (Table 16). When all 
these factors are considered together, 
many of the proposed practices have 
favorable ratings across the spectrum. 
For example, reducing tillage intensity 
has either favorable or neutral effects 
on all the criteria (though, clearly, 
these tentative ratings will vary for 
different areas of the country). Some 
practices, such as using nitrification 
inhibitors, have numerous benefits but 
their use may be limited by cost. Most 
of the proposed methods of reducing 
greenhouse gas emissions have 
favorable effects on soil quality and 
adjacent environments. 

Many of these other considerations are 
as important as any benefits to the 
atmosphere. The adoption of proposed 
practices will be driven at least as 
much by these factors as by the desire 
to reduce greenhouse gas emissions. 

Table 16 Projected effects of various agricultural practices that affect 
greenhouse gas emissions 


Effect on GHG 

Other considerations 

COt CH4 N2O Feasibility Economics Soil Environment 


Reduced tillage 
intensity ++ 

Reduced summer 
fallow area ++h 

Improved manure 

Improved feeding 

drainage/irrigation + 












+ beneficial no effect - detrimental 

number of + or - signs indicate magnitude of effect 


3. Ozone 

Ozone is a bluish gas, with a sharp, 
irritating odor. It occurs naturally in 
the upper atmosphere ("stratosphere"), 
w here it forms continually from 
reactions promoted by the sun's 
radiation. Unlike the more common 
gas oxygen (O2), O3 is highly unstable, 
reacting with other molecules in the 
atmosphere, so that its lifetime is only 
hours or days. The O3 in the upper 
atmosphere serves a useful function by 
filtering out harmful UV radiation. 
However, pollutants entering the 
upper atmosphere deplete the O3, 
thereby increasing the intensity of UV 
radiation at the earth's surface. 

Ozone also occurs naturally near 
ground level, where it occurs at 
concentrations of 25-40 parts per 
billion by volume (ppbv). Along with 
other pollutants (e.g., nitrogen oxides, 
peroxides, peroxyacetyl nitrate, and 
particulate matter), ground-level O3 
forms smog. The ill effects of smog on 
human health are reasonably well 
known, but its effect on plants has 
received little publicity. Yet, according 
to some estimates, O3 causes tens of 
millions of dollars worth of damage to 
crops in Canada annually, mainly in 
the Fraser Valley of British Columbia, 
the Quebec- Windsor corridor, and the 
southern Atlantic region. 

Thus O3 is unique among atmospheric 
gases: in the upper layer, it is highly 
beneficial; near ground level, it is a 
serious pollutant. Ironically, human 
activity has depleted O3 in the upper 
atmosphere but increased its 
concentration at ground level. In this 
section, we describe the problem of 
ground-level O3; the problems arising 
from depleting O3 in the upper 
atmosphere we discuss later. 

Source of ground- 
level ozone 

Low concentrations of O3 occur 
naturally at ground level, formed in 
the presence of sunlight by reactions 
between nitrogen oxides and volatile 
organic compounds (VOCs) (Fig. 25). 
Natural sources, such as vegetation 
and soils, release these compounds at 
low concentration. But human 
activities have increased the amounts 
released: VOCs from petroleum, 
chemical industries, and transportation 
and nitrogen oxides from combustion 
in power stations and automobiles. 
Consequently, O3 is more 
concentrated and more smog occurs in 
densely populated and industrial 
regions. The health and environmental 
hazards of smog have prompted federal 
and provincial governments to impose 
limits on emissions of nitrogen oxides 
and VOCs into the atmosphere. 

\ ,77 "P 

Ozone concentration measurements 

Ozone concentrations are measured at 
only about 100 locations in Canada as 
part of the air-quality network operated 
by the Atmospheric Environment Service 
of Environment Canada. To see how 
representative these measurements are, 
scientists used low-level flights to 
measure ozone concentrations upwind 
and downwind of the city of Montreal. 












O, concentration (ppbv) 

The ozone concentrations were found to 

be greater downwind than upwind of the 

city at all altitudes. Consequently, ozone concentrations reported by the network may 

have to be adjusted depending on the location of the measurement. 

(J.I. MacPherson, NRC; R.L. Desjardins, AAFC) 


Volatile organic compounds and agriculture 

Volatile organic compounds (VOCs) include natural and artificial chemical 
compounds that contain carhon as a main constituent. Volatile organic compounds 
and nitrogen oxides combine in the presence of sunlight to form ozone at ground 
level. In rural areas, the VOCs are largely contributed by vegetation. Crops that emit 
VOCs include tomatoes, potatoes, soybeans, wheat, lettuce, and rice. Even if artificial 
VOCs were eliminated completely, ozone would still form from VOCs released 
from vegetation. 





Air-quality objectives 

Air-quality objectives are national goals for outdoor air quality that protect human 
health and the environment. These objectives are developed by a working group for 
various atmospheric pollutants under the Canadian Environmental Protection Act. 
The working group reviews the most recent scientific studies. 

The current "maximum acceptable" air-quality objective for ozone is 82 ppbv 
averaged over a 1-hour period. The current ground-level ozone objective was 
established in 1976, based on the best scientific information. It was reaffirmed in 
1989, but a new assessment of the science of ground-level ozone is now nearing 

One aspect of the Harmonization Accord, recently signed by the Canadian Council 
of Ministers of the Environment, identified ground-level ozone as a priority. Work 
currently under way will develop a Canada-wide standard for ambient ozone levels. 

(M. Shepard, Atmospheric Environment Service, Environment Canada) 

Major Canadian cities now experience, 
on several days each year, O3 levels 
above the maximum acceptable air- 
quality level of 82 ppbv for 1 hour. 
Values of 170 ppbv have been recorded 
at several locations in Ontario. Stable air 
conditions during summer and fall 
especially favor the formation of smog. 
In light winds, smog can spread over 
large areas, often affecting regions on 
both sides of the Canada-US border. 
Because it requires sunlight to form, O3 
tends to diminish in concentration at 
night, whereas other smog constituents 
are unaffected. 

Figure 25 

Conceptual diagram showing ground- 
level O3 formation. Volatile organic 
compounds (VOCs), emitted into the 
atmosphere from vegetation and 
artificial sources, react with NO x in the 
presence of sunlight to form O3. 

Effect of ozone on 

Ozone enters plant leaves via stomata, 
tiny valved pores on the leaf surface 
that regulate the exchange of gas 
between plant and air. During the day, 
the stomata are normally open to 
permit entry of C0 2 for 
photosynthesis. Unfortunately, at this 
time O3 levels are highest. 

Once inside the leaf, O3 oxidizes 
molecules in cell membranes, causing 
the membranes to break down. 
Because O3 occurs naturally in the 
atmosphere, plants have evolved some 
protective mechanisms, including 
"antioxidants" like vitamins C and E, 
and specialized proteins (enzymes) that 
repair injury from O3. But at higher 
O3 levels, these protective mechanisms 
are inadequate to prevent injury to 

Ozone can cause direct damage to leaf 
tissue, often visible as flecking, 


bronzing, water-soaked spotting, and 
premature aging of leaves. 
Furthermore, high O3 concentrations 
may cause the stomata to close, which 
cuts the flow of COt and shuts down 
photosynthesis. As a result of the 
direct damage and the reduced 
photosynthesis, yields of some plants 
can be dramatically reduced by long- 
term exposure to elevated O3 levels. 

Although scientists have studied the 
effects of O3 on various crops in 
Canada and elsewhere for more than 
40 years, fluctuations in O3 
concentrations in polluted air pose 
major difficulties in providing reliable 
estimates of the damage caused 
to crops. 

Ozone exposure 
and absorption by 

Air pollution monitoring sites across 
Canada routinely measure ground- 
level O3 concentrations. But 
concentrations alone are insufficient to 
evaluate potential damage to plants. 
Plants are less sensitive at night and 
during periods of slower growth. 
Temperature and moisture conditions 
also affect sensitivity. Consequently, we 
must measure actual O3 absorption to 
assess effects on plants. 

One way of estimating O3 absorption is 
to measure the instantaneous O3 
concentration in downward- and 
upward-moving air, using sensors 
mounted on towers. If the concentration 
is greater in air moving down than in air 
moving up, that indicates O3 
absorption: the greater the difference, 
the higher is the absorption rate. This 
approach allows almost continuous 

Ozone and leaf stomata 

When plants take in CO7 for photosynthesis through their stomata, ozone can also 
enter. The ozone causes the cells surrounding the stomata to decrease in turgidity, 
which reduces the size of the opening. This closing helps to protect the plant from 
further ozone damage. Once inside the leaf, however, ozone is highly reactive and 
can destroy the leaf cells, which can substantially reduce crop yield. 

Diagram of O3 flowing into a leaf via a stomate and causing damage 
by oxidizing cell walls and mesophyl 

co 2 o 

Stomata open in light 

Stomata closed at night 


measurement of O3 flux and provides 
daily and seasonal patterns of 
absorption. In one study, for example, 
the O3 flux above a soybean field 
increased during the day but then 
dropped sharply when the stomata 
began closing (Fig. 26). Because the 
opening and closing of stomata is 
controlled by water stress, there is a 
strong relationship between O3 
absorption and transpiration (the 
amount of water lost from the plants). 

Ozone absorption 








00:00 12:00 

Time (EST) 


Figure 26 

Ozone absorbed and water transpired by 
soybean on a sunny day in August in 
Ottawa. (E. Pattey, AAFC) 

For larger-scale measurements, 
instruments can be mounted on aircraft, 
as described for COi, N7O, and CH4 
measurements. Aerial O3 surveys have 
already been made for many crops, 
weather conditions, and O3 
concentrations. One observation from 
this approach is the strong relationship 
between O3 absorption and the amount 
of green vegetation. 

The scale can be increased still further 
by using satellites. Scientists can 
calculate transpiration from 
environmental conditions and can 
obtain a "greenness" index from satellite 
images. Because of its close relationship 

to transpiration, O3 absorption can then 
be estimated for the entire growing 
season on large areas, using O3 
concentrations from measurement 
networks (e.g., Fig. 27). 

0.1 -0.2 
0.2 - 0.3 
No soybean 



f Quebec 

i j ■ 1 « 



i 'Ottawa 


i •Trenton 

^^71 orortto 
t 'Hamilton 

r ^.onaon 


100 2do a» «o 500 aoo 


T» ■» 900 ton 













l, ji | 'Tre 


"■ 1 oron 
- •Hamilto 








no nok> 

Ozone absorption (flux) [ug/m 2 /s] 

Figure 27 

Estimated O3 absorbed by soybeans in 
the Windsor-Quebec corridor, 1988 
and 1992. (R.L. Desjardins and Y. Guo, 

This approach, however, only estimates 
average absorption over the long term 
and cannot describe the short-term 


fluctuations associated with daily 
changes in moisture stress or plant 
development. Furthermore, it tends to 
"dilute" relatively brief exposures to 
high concentrations that are likely to be 
most harmful to plants. Nevertheless, 
diese estimates provide a useful 
indicator of potential plant damage. 

Measuring plant 
response to ozone 

The simplest way to measure plant 
response to O3 is to grow them inside 
open-top enclosures into which O3 is 
then continually released in 
concentrations that reflect the daily 
variations. This method allows 
researchers to evaluate the effect of 
several concentrations of O3 (typically 
up to three times that in outside air) as 
well as those of other gases or 
pollutants that can be added 

In a less disruptive approach, called the 
"zonal air pollution system" (ZAPS), a 
series of pipes over the crop 
continuously releases O3 into the plant 
canopy at various rates in different 
plots. This method avoids some of the 
artificial conditions inside chambers 
but costs more. As well, the maximum 
enrichment achieved by this technique 
is not high, because of the continual 
mixing with untreated air. 

Open-topped enclosures and ZAPS are 
useful for detailed research studies, but 
they do not provide information on O3 
damage over large areas. Networks of 
instruments that continuously record 
O3 concentrations exist in many 
populated regions but are sparse in 
rural areas. To provide O3 information 
in such areas, scientists use 
"biomonitors" or "passive" monitors. 

Open top enclosures, zonal air pollution system, and biomonitors. 


Biomonitors are plants, like the 
tobacco variety "Bel-W3," that are 
highly sensitive to O3. They are set 
out throughout a region and then 
inspected regularly for flecks of dead- 
tissue, which are symptoms of injury 
from O3. The biomonitors therefore 
provide an estimate of O3 absorption 
by leaves and indicate potential 
damage to other less-sensitive crops, 
even though these may show no visual 
signs of stress. Passive monitors are 
simply filter papers treated with indigo 
dye. When exposed to O3, the dye 
changes color. The degree of color 
change provides an index of the total 
exposure to O3 during the period. 

Observations from biomonitors and 
passive monitors can be related to 
potential crop effects by placing these 
monitors inside a ZAPS along with 
other crop plants. "Flecking" of 
biomonitor leaves or color change in 
passive monitors can then be directly 
related to crop damage. Using these 
relationships, scientists can use 

biomonitors and passive monitors 
placed throughout a region to estimate 
yield effects of O3 absorption 
throughout that area. Researchers have 
used an extensive network of this type 
to monitor O3 effects on yields in the 
Fraser Valley, a highly populated area 
with intensive agriculture (Fig. 28). 

Examples of crop 
response to ozone 

The effect of O3 has already been 
widely studied and some extensive 
reviews are now available. Here we 
present only a few examples to 
illustrate the nature and objectives of 
some recent research. 

Effect of ozone on broccoli 

Broccoli is a high-value crop that is 
harvested about 6-8 weeks after 
transplanting. Rapid leaf growth after 
transplanting feeds the developing 
flower head. Any stress on leaves 

Agricultural land ^f Instrumental monitoring sites O5 utf\ Biomonitor sites 

Figure 28 

Map of the ozone monitoring network in the Fraser Valley, B.C. (P. Bowen, AAFC) 


during this time usually results in 
smaller heads and lower yield. Studies 
using a ZAPS showed that ozone 
injures leaves in two ways: it kills some 
of the tissue directly (Fig. 29a) and 
makes other tissue prone to attack by 
downy mildew, a fungal disease 
(Fig. 29b). Severity of damage was 
directly related to O3 enrichment. 

Ozone enrichment level 







■ '-> 


Ozone enrichment level 

Figure 29 

Response of broccoli to O3: 

a) O3 injury to broccoli leaves; 

b) Leaves infected with downy mildew 
on broccoli exposed to O3. (V.C. 
Runeckles, University of British 
Columbia, Vancouver, B.C.) 

Effect of ozone on orchardgrass 

Orchardgrass is the main feed of dairy 
cows in the Fraser Valley. The grass 
can be harvested for hay up to five 
times a year. Loss in yield at any 
harvest depends on O3 exposures 
received during the preceding growing 
period. One study examined the 
relationship between level of O3 and 
orchardgrass yield in a ZAPS (Fig. 30). 
The data show how yield decreased as 
the exposure increased (reported as the 
number of days during which hourly 
concentrations exceeded 50 ppbv). 
Because orchardgrass is a perennial, its 
early spring growth partly depends 
upon the reserves stored in the roots 
and stems during the previous growing 
season. Studies over successive years 
have shown that exposing plants to O3 
in the fall suppresses yield the next 


10 20 30 40 

Number of days with hourly O3>50 ppbv 

Figure 30 

Dry matter yield of orchardgrass as 
affected by exposure to O3. (V.C. 
Runeckles, University of British 

Effect of ozone on strawberry 

Increased exposure of strawberry 
plants to O3 reduces the number and 
weight of good fruit. A network of 
calibrated passive monitors in the 
Fraser Valley indicated that fruit losses 
can be as high as 15%. 

Effect of ozone on lettuce 

Visual appearance of leaves affects the 
market value of crops like lettuce. In 
ozone exposure studies, lettuce leaves 
showed no visible symptoms. Even at 
the highest exposure levels, the crop 
appeared healthy. Surprisingly, 
however, O3 reduced head size and 
weight, indicating that O3 damage can 
be subtle and detectable only with 
careful scrutiny 

Combined effect of ozone and 
carbon dioxide on alfalfa 

Under high O3 concentrations, alfalfa 
grows more slowly and competes less 
against weeds. Like orchardgrass, 
exposing alfalfa to CL in the fall of one 

year may reduce its yield the year after. 
Its ability to survive cold winters, 
however, does not seem to be affected. 
One study measured the effects of 
increasing both O3 and CO2 
concentration on alfalfa growth. 
Increasing the CCL concentration 
actually increased the tolerance of 
alfalfa to high concentrations of O3 
(Fig. 31), probably because the stomata 
are partially closed at high CCL levels. 
This finding may have important 
implications if, as expected, 
atmospheric CO2 concentration 
doubles some time in the next century. 

Alfalfa varieties 
Wheat varieties 







1 x CO, 2 x CO : 2 x CO, 
3 x + 3 1 x + 0, 3 x + 0. 

Figure 31 

Relative effects of O3 and CO2 on yield 
of alfalfa and wheat. The values in the 
legend indicate concentration relative 
to background. (G. Allard, Universite 


Differences in ozone tolerance 
among varieties 

Plants show a wide range of tolerance 
to O3 in the air, even among varieties of 
the same crop. Comparing two alfalfa 
varieties ("Apica" and "Team") in open- 
topped enclosures for 2 years showed 
that "Apica" was unaffected by low O3 
levels but was strongly affected by 
higher concentrations in both years. 
"Team" was almost unaffected in a cool 
and rainy summer, but was affected 
almost as severely as "Apica" in a warm 

and sunny summer. In a similar study, 
spring wheat varieties "Bluesky" and 
"Opal" were exposed to air with no O3, 
and 1.0, 1.5, and 3.0 times the ambient 
O3 concentration (Fig. 32). "Opal" 
appears more tolerant to O3. The 
pattern of tolerance was different for 
the 2 years tested. This finding suggests 
not only that varieties have different 
tolerances to O3 but also that weather 
conditions affect those tolerances. 

fared worse. One explanation is that 
newer varieties need more CO2 to 
support higher rate of photosynthesis; 
hence, the stomata stay open longer 
and absorb more O3. Another 
explanation is that the improved yield 
of newer varieties results from a higher 
ratio of grain to leaf tissue. With 
relatively less leaf area to absorb C0 2 
for grain production, leaf injury by O3 
may be more pronounced. 

*Sb 4- 



1 6- 

bc 4- 


1 1.5 3 

1 1.5 3 

1 1.5 3 

O3 concentration in multiples 
of ambient concentration 

Figure 32 

Yield response of two wheat cultivars to 
increasing concentration of O3. 
(G. Allard, Universite Laval) 


Unfortunately, crops are rarely 
exposed to only one pollutant. Plants 
growing in high O3 concentrations 
may also suffer injury from sulfur 
dioxide, nitrogen oxides, acid rain, and 
UV radiation. The net effect of 
exposing plants to more than one 
pollutant may be equal to, greater 
than, or less than the sum of their 
individual exposures. The effects are 
further complicated by crop type, time 
of exposure, weather conditions, 
previous exposure, and other 
environmental stresses. Consequently, 
recent studies have only provided some 
knowledge about the potential effects 
of O3 on a few major crops and 

New crop varieties tolerate disease 
better, are better adapted to local 
conditions, and generally produce 
higher yields. Do they also do better 
under higher O3 concentrations? One 
study compared the O3 tolerance of 
wheat varieties released at various 
times, from the 1950s (when O3 
concentrations were generally lower) 
to the early 1990s. Under current O3 
concentrations, the newer varieties 
yielded better, but, at higher O3, they 


4. Other links between agriculture 
and the atmosphere 

Although C0 2 , N 2 0, CH 4 , and 3 
have attracted much attention recently, 
agriculture also releases other 
materials into the air, including 
ammonia, other odors, aerosols, 
nitrogen oxides, and pesticides. As 
well, agriculture may be affected by 
changes to stratospheric O3. Many of 
these issues have not yet been 
thoroughly studied in Canada. Our 
main aim is to identify the potential 
issues and point to some possible 


Current farming practices rely heavily 
on inputs of extra N, most of which 
ultimately derives from atmospheric 
N 2 . These high inputs help sustain 
food production, but they also stress 
the natural N cycle, resulting in 
"leaks" of N into the environment. 
The release of N 2 is one such leak; 
another is the emission of ammonia 


Globally, agriculture is the main 
source of atmospheric NH3 from 
human activity. Much of this NH3 
comes from livestock production. In 
parts of Europe, notably the 
Netherlands, NH3 emissions from 
animal production are so high that 
they warrant strict regulations. In 
Canada, the problem is not yet as 
acute, except perhaps in local areas 
with high livestock numbers. 

Ammonia is a colorless gas, lighter 
than air, with a sharp odor. In remote 

areas, away from sources, it occurs in 
the atmosphere at very low 
concentrations (less than 0.01 ppmv). 
In areas near intensive livestock 
production, however, concentrations 
may be much higher, sometimes well 
above the threshold at which it can be 
detected by smell (~0.6 ppmv). 

Unlike N 2 0, NH3 is highly reactive 
and remains in the atmosphere only a 
short time. It reacts quickly with water, 
forming ammonium (NTTf*"). Thus any 
moist surface — soil, plants, or open 
water — readily removes NH3 from the 
air, as long as the surface is neutral or 
acidic in pH. In the air, NH3 can 
dissolve in precipitation and fall to the 
earth as NH^." 1 ", or it can be oxidized or 
dissociated by sunlight. As well, NH3 
can react with pollutants such as acidic 
sulfates and nitrates, forming tiny 
particles of ammonium nitrate or 
ammonium sulfate. Because NH3 is so 
reactive, its concentrations are 
localized: high near sources and almost 
negligible elsewhere. In an area near 
Lethbridge, Alta., for example, high 
concentrations were found close to 
feedlots, but relatively low values just 1 
km away. 

Ammonia has many undesirable effects 
at high concentrations. Near sources, 
where concentrations are high, it 
produces an unpleasant odor and may 
affect human and animal health. Local 
deposition of emitted NH3 may 
"fertilize" the land, but excessive 
amounts can result in leaching of N 
and contamination of ground- or 
surface-water. Excessive NH3 may 
even be converted to NiO, thus 


indirectly contributing to the 
greenhouse effect. 

Though many of the effects of NH3 
occur locally, it also has long-range 
effects. Ammonium particles, formed 
upon reaction with other N or sulfur 
compounds, can be carried long 
distances by wind before being 
deposited. Because N is often a 
growth-limiting nutrient, the 
deposition of this NH4 + can cause 
undesirable growth in lakes, alter 
forest growth, or disrupt sensitive 
ecosystems. When deposited on native 
grasslands, for example, atmospheric 
NH3 or (NH.| + ) may favor the growth 
of some species at the expense of 
others, causing a shift in the mixture. 
Atmospheric NH3 can also result in 
acidification because it accelerates the 
rate at which sulfur dioxide (SOt) 
converts to sulfuric acid, leading to 
acid rain. The NH3 itself produces 
acid when it undergoes nitrification, 
once deposited on soil as NH 4 + . 

Because of its numerous potential 
effects, both near sources and in 
remote areas, NH3 can be a serious 
pollutant and efforts to reduce its 
emission are warranted. Before 
examining possible ways of reducing 
emissions, however, it may be helpful 
to briefly review the sources of NH3 in 

Agricultural sources 
of ammonia 

The three main sources of NH3 on 
farms are animal wastes, fertilizers, and 
crop residues. The first of these 
accounts for about 80% of agricultural 

Of the N consumed by farm animals in 
feed, only a small proportion (roughly 
one-fifth) is retained by the animal; the 
rest is excreted in feces and urine. 
Some of this N (especially in urine) 
occurs as urea, a form easily converted 
to NH 3 and COi. As a result, a large 
proportion of the N in manure can be 
lost as NH3 soon after excretion. On 
pig farms, for example, 40-95% of the 
nitrogen excreted may be lost before 
the manure is applied to the field. 
Much of that, perhaps 10-40% of the 
N lost, may occur from the barn even 
before storage. Ammonia losses from 
cattle manure are often less than from 
pig manure, probably amounting to 
less than 50% of the total N content. 

Losses of N during storage of manure 
can also be high, depending on 
method of storage. In a US study, 
about 60-80% of N was lost from pig 
manure in lagoons exposed to air, 
compared to losses of only 30-65% 
from that stored in underground pits 
and later spread as liquid. Another 
estimate suggests that the proportion 
of pig manure N lost as NH3 is less 
than 10% for anaerobic storage, 
10-25% for semi-aerobic systems, and 
25-85% during composting. The 
differences reflect the degree of 
exposure to air and the amount of 
water and acid present. 

Some NH3 is also released when 
manure is applied to land, particularly 
if a slurry is sprayed into the air. Most 
loss occurs shortly after application. 
For example, a study of NH3 loss from 
cattle manure showed that about half 
of the total emission occurred within 1 
day (Fig. 33). 
















40 80 120 160 200 240 
Hours after manure application 

Figure 33 

Pattern of NH 3 loss from manure 
applied to the surface of soil. (S. 
McGinn, AAFC) 

Another potential source of NH3 is 
fertilizer. Two forms, both widely used 
in Canada, are especially important: 
anhydrous ammonia (pure NH3) and 
urea. When anhydrous ammonia is 
injected into soil, it normally converts 
immediately to NH^ in soil water and 
then is held tightly by the soil. If the 
soil is extremely dry, however, as much 
as 20% of the NH3 can escape. On the 
other hand, if it is so wet that the soil 
does not close up after injection, as 
much as 50% can be lost. Urea 
fertilizer, like the urea in livestock 
manure, quickly converts to NH3 and 
CO2 after it is applied. If the fertilizer 
is not mixed into the soil, large 
amounts of NH3 can be released to the 

A third possible source of NH3 from 
farms is crop residues. Appreciable 
amounts of NH4 + can be produced 
during the decay of N-rich residues 
like legume green manures. If the 
residues are allowed to decay on the 
soil surface, some of this NH4 + may 
convert to NH3 and be lost to the 

Based on data from 1990, NH 3 
emissions from all sources in Canada 
amount to about 520 Gg (thousand 
tonnes) of N per year. Of this, about 
90% comes from agriculture, largely 
from livestock production (Table 17). 
These estimates, however, are still 

Table 17 Estimated 



from Canadian agriculture 




NH^ emission 



Dairy cattle 

incl. with beef 

Beef cattle 










Total animals 





Ammonium sulfate 
Ammonium nitrate 
Anhydrous ammonia 
Nitrogen solutions 
Ammonium phosphates 
Total fertilizers 

Total agriculture 




Reducing ammonia 

Producers can reduce the emission of 
NH3 from farms in a number of ways. 
In general, these methods rely on 
absorbing NH3 in water or acid, 
preventing excessive N excretion by 
livestock, and minimizing exposure of 
NH3 sources to the air. Specific 
examples of control methods include 
the following: 

Use improved methods of fertilizer 
application: Farmers can reduce 
ammonia loss from fertilizer by 
ensuring good contact between the 
applied fertilizer and moist soil. They 
should place urea either below the soil 
surface or till it into the soil 
immediately after applying it to the 
surface. Injecting anhydrous ammonia 
into moist soil at sufficient depth 
prevents it from diffusing to the 

Minimize nitrogen excretion from 
livestock: The most basic way of 
reducing NH3 emission from animal 
wastes is to produce less manure N in 
the first place. Although animals 
cannot avoid excreting N, farmers can 
reduce the N content of the manure 
by using rations with a better N 
balance, by avoiding excessive N in the 
diet, or, possibly, by adding bacteria 
that help convert uric acid (a 
forerunner of urea) to nitrate. Use of 
these practices could reduce N 
excretion by up to 25% in cattle, pig, 
and broiler poultry operations. Indeed, 
simulation models suggest that, for 
Quebec conditions, better diets could 
reduce the N content of pig manure by 
up to 60%. Nitrogen excretion can 
also be reduced, indirectly, by using 
breeds of livestock, feed formulations, 
or other practices that improve animal 

performance and, hence, the product 
yield per unit of manure N. 

Improve manure handling in the barn: 
Large amounts of NH3 can be emitted 
in the barn when the manure is 
exposed to air. Farmers can minimize 
this exposure by removing manure 
frequently; washing barns with water, 
which absorbs NH3; collecting liquid 
wastes in deep, narrow channels, to 
reduce surface exposure; and, in 
poultry barns, maintaining a deep layer 
of litter. As well, maintaining cool 
temperatures can reduce emission of 
gaseous NH3. In Europe, changes in 
handling procedures (including diet) 
have reduced NH 3 release from pig 
barns by 45%. 

Improve manure storage: Farmers can 
reduce ammonia loss during manure 
storage by minimizing exposure to air 
and lowering temperature. For 
example, applying a cover of mineral 
oil, straw, or peat over lagoons or tanks 
holding pig manure can reduce losses. 
Covers placed on tanks can cut NH 3 
losses by two-thirds, and a thin layer of 
mineral oil on a slurry can reduce 
emissions by more than 30%. As well, 
adding acids to manure or covering 
composting manures with mildly acidic 
peat can minimize NH3 loss. 
Ammonia is readily absorbed and held 
by acid, preventing escape to the 
atmosphere. Farmers can achieve 
reductions of at least 75% by using 
peat moss, sulfuric acid, or phosphoric 
acid during storage. 

Use more effective application procedures: 
Ensuring quick and effective mixing 
with soil can minimize losses of NH3 
during application. For example, 
tillage or irrigation immediately after 
application drastically cuts emissions 
(Fig. 34). Farmers can also reduce 

losses by applying manure before rain, 
injecting slurry directly into soil, or 
using diluted slurry for irrigation. 
Where they must apply slurry to 
grassland, banding it on the surface, 
rather than spraying it, can reduce 
losses. Finally, since rate of gaseous 
loss is related to temperature, applying 
NH3 in cool weather (though not on 
frozen soil) can curtail emission. 


£ 20 




< None Irrigation Tillage 

Incorporation treatment 

Figure 34 

Proportion of manure NH 4 + volatized 
within 8 days of application as affected 
by irrigation or tillage. (S. McGinn, 

This list shows several ways of cutting 
NH3 emissions from agriculture. Not 
all these are practical or even advisable 
in all cases. For example, incorporating 
manure by ploughing is not 
compatible with the no-till systems 
advocated elsewhere. Nevertheless, 
given the number of options available, 
large cuts in emissions are probably 
easier for NH3 than for some of the 
other gases, notably N 2 0. With 
increasing attention to health, 
environmental, and odor issues related 
to NH3, efforts to achieve such 
reductions will likely increase in the 


Gases emitted during composting of organic waste may include CO2, NH3, CH4, 
N>0, and NO. Smaller quantities of reduced sulfur and nitrogen compounds may 
also be produced in anaerobic microsites. The form and quantity of gaseous 
compounds emitted during composting depends on the material being composted 
and the method used. Odor-producing compounds can be virtually eliminated with a 
properly designed aeration system. A biofilter system in enclosed composting 
facilities also ensures odor-free exhaust air. 

iVlethane emission can also be eliminated with adequate aeration. Ammonia emission 
is controlled by the available C:N ratio of the composting material and by the 
aeration system used. When NH3 emission occurs, it is usually early during the 
composting process. Ammonia may be captured using a scrubber. The factors 
influencing N 2 and NO emissions during composting are not well understood. 
Researchers are working toward a better understanding of N?0 emissions during 
composting and strategies to minimize emissions. A well-designed compost facility 
should not negatively affect the health of our air. 

(J. Paul, AAFC) 

The Netherlands has decided that, by 
2000, NH3 emissions must be no more 
than half of those in 1980. There, the 
annual N deposition has reached 85 
kg/ha in parts of the country. Though 
deposition rates in Canada are usually 
much lower, high rates of deposition 
may already occur in local areas of 
intensive livestock production. 


Other odors 

Ammonia is only one of the gases 
released from farms that has an 
unpleasant odor. Many other gases also 
irritate the human nose. Some of these 
are not only unpleasant but also 
dangerous. Perhaps the most 
noteworthy is hydrogen sulfide (H->S), 
a poisonous gas with the smell of 
rotten egg. High concentrations of this 
gas can be released when liquid pig 
manure in tanks is stirred. It can be 
fatal to humans, though only at high 
concentrations produced where 
ventilation is poor. Many other 
compounds, although not known to be 
poisonous, have an objectionable odor; 
more than 150 such compounds have 
been identified in pig manure alone. 

To date, people have perceived farm 
odors only as nuisances, but awareness 
of this problem is now growing. 
Indeed, some countries have already 
established regulations regarding 
allowable odor intensities. 

Odor-causing gases can come from 
many sources. Some of the most 
offensive arise from organic substances 
decaying in the absence of oxygen. 
The decomposing matter may be 
manure, effluent from manure piles, 
silage, plant debris, or a wide range of 
other organic materials. When 
decomposed without an adequate 
oxygen supply, they are not completely 
broken down into CO? and simple 
salts but rather are released as various 
intermediates such as organic acids, 
alcohols, aldehydes, sulfides, and CH4. 
Of these, the compounds with the 
most offensive odors are the volatile 
organic acids. 

Many odor-causing compounds come 
from the same source and therefore 

occur together. For example, volatile 
organic acids are often found with 
NH3 and HtS. Given the many 
compounds involved, odors are not 
easily measured and quantified. 
Indeed, the most sensitive and reliable 
sensor is still the human nose. One 
way to measure odor intensity is to 
count the number of times an air 
sample has to be diluted with fresh air 
before its odor becomes nearly 
imperceptible. A panel of human 
evaluators is used to determine the 
number of "dilutions to the threshold" 
(DT), which may range from to 200 
or more. On this scale, a reading of 
170 DT or higher would be 
considered "unacceptable." The lowest 
value achievable within a feedlot 
operation is about 7 DT. 

A variation on this approach is to 
compare the air sample with known 
concentrations of a reference 
compound, like butanol. With this 
method, the intensity of odor is 
reported in terms of equivalent 
concentrations of butanol. The scale 
normally ranges from to 80 ppmv 
butanol (the highest intensity to which 
the nose is responsive). Most ambient 
odors have a rating of less than 60 
ppmv butanol. 

Researchers have used these 
techniques to evaluate the odor from 
various types of farms. Odors from pig 
farms usually rate "high" to "very 
high," whereas poultry and cattle 
operations normally rate "high," 
comparable to that of paper mills, 
petrochemical plants, and oil 
refineries. Of course, odor intensity 
varies considerably depending on wind 
speed, air stability, humidity, and 
distance from source. 

Producers can reduce the intensity of 
odors from farms in several ways. The 
most obvious, perhaps, is to plan the 
farm layout carefully, placing sources 
of odor, like barns and lagoons, 
downwind and far from dwellings. 
Other methods include cleaning and 
washing barns frequently, aerating 
stored manure (although this action 
may favor NH3 release), injecting 
slurries, and immediately 
incorporating solid manures after they 
are applied. Finally, various chemicals 
and bacterial cultures have been 
proposed for odor control, but their 
cost is often high and their efficacy 
limited. One possible approach is to 
add calcium bentonite, a clay with high 
absorption capacity, to animal diets. 
This additive has even been found to 
enhance weight gain under some 

Nitrogen oxides 

Nitrogen oxides, upon reaction with 
volatile organic carbon (VOC) in the 
presence of sunlight, produces O3, the 
main constituent of smog. Nitrogen 
oxides come mostly from combustion 
of fossil fuel, and are usually linked to 
automobiles and industrial sources. 
But farm machinery also uses a lot of 
fuel; for example, agriculture accounts 
for about 25% of the heavy-duty diesel 
vehicles in Canada. Although the 
importance of farm machinery as a 
source of nitrogen oxides is not 
known, its contribution to smog is 
likely negligible. Even so, energy- 
conserving steps like reduced tillage 
can reduce somewhat the emissions of 
nitrogen oxides. 

Nitric oxide (NO), like N 2 0, is 
sometimes produced in soil as a by- 
product of nitrification and 

denitrification. In rural areas, the 
release of NO from this source can 
rival that of nitrogen oxides from 
industrial sources. Using methods 
similar to those described for N?0 can 
probably reduce the emission of NO 
from agricultural soils. 


Aerosols are solid particles in 
atmosphere, either formed in the air by 
reactions among gases or injected into 
the air by processes on the ground. 
They consist of a variety of materials 
and vary in size from less than 1 
micrometre (urn, one-thousandth of a 
millimetre) to the size of a sand grain. 
The main sources of aerosols are 
natural events like volcanoes, sea spray, 
forest fires, and soil erosion. But some 
aerosols are also produced by human 
activity, like combustion of fossil fuel. 

Particles smaller than 2.5 urn are a 
serious concern for both visibility and 
human health. Aerosols absorb and 
reflect light, producing the haze in 
cities. They can also be breathed in 
and stay in the respiratory system 
causing respiratory illness and even 

Aerosols also have an important effect 
on global climate. They provide the 
nuclei or "seeds" that encourage cloud 
to form. They also reflect solar 
radiation, thereby cooling the earth. In 
some regions, the cooling effect of 
aerosols is now about the same as the 
warming effect of CO2, though it is 
not expected to increase enough to 
offset further increases in CO?. 

The amount of aerosols produced by 
Canadian agriculture has not been 
measured routinely but is probably 


small. Nevertheless, farms do emit 
some aerosols of two types: primary 
particles, which are released intact into 
the air (e.g., field dust, soot, and 
pesticide crystals); and secondary 
particles, which are formed in the air 
from gases emitted by agriculture (e.g., 
NH4" 1 " particles from NH3). Some 
secondary particles were described 
earlier; here we focus only on primary 

The most common aerosol from 
Canadian farms is probably dust from 
soil erosion. When soil is dry, loose, 
and without plant cover, the wind can 
pick up surface particles and carry 
them great distances. The problem was 

Aerosol size distribution and global warming 

The size distribution of an aerosol is closely related to its source. Coarse particles are 
generated mainly from mechanical processes, such as wind, whereas fine particles are 
produced by chemical reactions. Size distribution and chemical contents of aerosols 
are important factors determining global climate change and visibility. Aerosols have 
a cooling effect, which offsets, in part, the warming effect of greenhouse gases. 

Secondary aerosol 

Primary aerosol 




Chemically produced 


Mechanically generated : 

Plant particles (pollen) 
Sea spray 
Volcano emissions 


Fine particles 

1 2 10 

Particle diameter (|im) 

-► M Coarse particles 

(T. Zhu, Ottawa, Ont.) 

most severe in the southern prairies 
during the dirty thirties, when as much 
as several centimetres were lost from 
some fields, obscuring the sky and 
depositing dust everywhere. Although 
conservation measures now prevent 
such large-scale dust storms, 
occasional erosion episodes still occur 

Erosion occurs in two steps. The wind 
first detaches tiny soil grains (0.1-0.5 
mm), which then act as abrasives on 
larger soil particles. The detached 
particles travel in three ways: saltation, 
creep, and suspension. In saltation, 
particles bounce across the surface; in 
soil creep, larger particles (0.5-1.0 
mm) roll and slide after they are hit 
and accelerated by "bouncing" 
particles. These two processes account 
for most erosion. But in fine-textured 
soils, with many particles smaller than 
0.1 mm, soil may be lifted high above 
the surface (suspended), creating dust 
clouds that can travel for hundreds of 
kilometres. Eventually, the suspended 
particles settle out in calm winds or are 
washed out in rain. 

After the bad experience of the 1930s, 
researchers developed many erosion 
control measures. Some of these are 
now commonly used: reduced tillage, 
keeping residues on soil surface, 
shelterbelts, and less-frequent use of 
summer fallow. Consequently, 
although about half of Canada's 
agricultural soil is moderately or 
highly susceptible to wind erosion 
when it is bare, less than 5% of 
cultivated land is now at high risk. 

Although severe and widespread 
erosion has been largely halted, some 
dust from farmland still enters the air 
through localized erosion events or 
during tillage and other farm 

operations. The dust emitted from 
soils is not just inert mineral particles. 
It may also contain seeds, pollen, and 
plant tissue, as well as agrochemicals, 
including pesticides. These materials 
can cause health problems and, in the 
cases of pesticides, contaminate other 

Another agricultural aerosol is smoke 
from burning of weeds or straw. 
Smoke contains soot (particles of 
carbon) that can cause respiratory 
problems. Until recently, burning 
excess straw was commonly practiced 
in areas with high yields, like southern 
Manitoba. Now provincial and 
municipal regulations have almost 
eliminated this practice. Some excess 
straw now goes to industrial uses, like 
"strawboard," which eliminates the 
health hazard and also provides 
additional income. 

Ultraviolet radiation 


The sun produces radiation with a 
wide range of wavelengths. Some 
wavelengths stimulate receptors in 
human eyes, so that we can "see" 
them. Thus, radiation with a 
wavelength of about 390 nm (10~ 9 m) 
to 760 nm is called "visible light." 
Within this range, different 
wavelengths correspond to various 
colors: the shortest wavelengths 
correspond to violet, the longest to 
red. But the sun also produces 
radiation outside the visible range. 
Radiation of wavelength longer than 
red is called infrared radiation; 
radiation of wavelength shorter than 
violet is called ultraviolet radiation. 

The energy of radiation increases as 
the wavelength gets shorter. 
Ultraviolet radiation, therefore, has 
much higher energy than visible light, 
enough to cause severe injury to living 
things. But little of the suns UV 
radiation reaches the earth's surface; 
most is filtered out by O3 in the upper 
atmosphere (the stratosphere). This 
effective screening of UV radiation 
occurs despite the very low 
concentration of O3. If all the O3 were 
placed in a layer at the earth's surface, 
it would be only 3 mm thick. Because 
it protects the earth's surface from 
damaging UV radiation, O3 in the 
upper atmosphere (unlike that at 
ground level) is essential to life. 

Because of its vital function, scientists 
were alarmed to learn, in recent 
decades, that the amount of O3 in the 
upper atmosphere is declining; that is, 
the O3 layer is "thinning." Worldwide, 
O3 concentrations have already 


declined by an average of 3%. But 
much of the depletion has occurred 
near the poles. Average values in 
Canada have declined by about 6% 
since 1980. Decreases near Antarctica 
have been as high as 60%, forming the 
so-called "Antarctic ozone hole." 

The thinning of the O3 layer, scientists 
now believe, is caused by the release of 
various gases from industrial activity. 
Most noteworthy of these are the 
chlorofluorocarbons (CFCs) that are 
used in refrigeration and as a 
propellant in aerosol cans. These 
molecules, which have a very long life, 
migrate into the upper atmosphere 
where they cause O3 to break down 
into O2. Another gas known to break 
down O3 is methyl bromide, used 
throughout the world as a fumigant to 
kill insects and nematodes in farm 
fields, greenhouses, and food storage 
and processing plants. Methyl bromide 

Soybean leaves damage by UV-B radiation 

(M. .Morrison, AAFC) 

accounts for up to 10% of global O3 
losses. Finally, nitric oxide (NO) can 
accelerate O3 breakdown. This gas is 
produced naturally in the atmosphere 
from N2O. Increases in N->0 
emissions, therefore, can also 
indirectly cause O3 breakdown. 

Once they had recognized the cause of 
O3 depletion, the international 
community set up an agreement 
(Montreal Protocol on Substances that 
Deplete the Ozone Layer) to curb 
emissions of gases like CFCs and 
methyl bromide. All developed 
countries have agreed to eliminate the 
use of CFCs by 2000 and the use of 
methyl bromide by 2015. Canada has 
committed to eliminate use of methyl 
bromide by 2001 (with some 
exceptions where no practical 
alternatives are available). Already in 
1995, the use of methyl bromide had 
declined by about 40% relative to that 
in 1990. Promising alternatives to 
methyl bromide include using other 
chemicals, diatomaceous earth (which 
physically damages insects), and 
integrated pest management strategies. 

By adopting strict controls on CFCs 
and other O3 -depleting substances, we 
can probably halt the continued 
depletion of O3 by about 2000. But, 
because of the long life of CFCs 
already in the atmosphere, it may take 
until 2060 before O3 concentration 
returns to its pre- 1980 levels. 
Consequently, we can expect high UV 
intensity for several more decades and 
need to consider some of its effects on 
agricultural production. 

Effect of ultraviolet 
radiation on crops 

Because some UV radiation reaches 
the earth s surface, terrestrial plants 
have evolved protective mechanisms. 
Some produce pigments, similar to sun 
screen, that absorb UV radiation. 
Others, like soybean, have UV- 
absorbing pigments in fine hairs on the 
upper surface of leaves (hence, 
symptoms of UV radiation are often 
more severe on the under surface of 
leaves). As well, most plants have some 
ability to repair cells and DNA 
damaged by excessive UV. 

Despite these defense mechanisms, 
high exposure to UV can injure cell 
membranes and DNA within cells. 
Perhaps its most damaging effect is to 
disrupt the chloroplasts (the 
chlorophyll-containing organs where 
photosynthesis occurs). Damage to the 
chloroplasts reduces photosynthesis, 
which, in turn, can reduce plant 

Many recent studies have evaluated the 
effects of increased UV on plant growth 
using a combination of UV filters and 
UV lamps to produce a range of UV 
intensities. Much of the research has 
focused on UV-B, a band of 
wavelengths from 290 to 3 15 nm. 
Ultraviolet radiation with longer 
wavelengths (UV-A) has less energy and 
is therefore less damaging. Ultraviolet 
radiation with shorter wavelength (UV- 
C) is absorbed so effectively by the 
atmosphere that it never reaches the 
earth's surface. 

Scientists have observed plant growth 
or yield effects from UV-B in numerous 
crops, including timothy, soybean, 
tomato, and canola. The effects of UV- 
B on yield are not always consistent, 

because some varieties yield more with 
increased UV-B than without. Studies 
with some species (e.g., corn) showed 
no damage even at high UV-B levels. 
Furthermore, as observed with canola 
and soybean, the response to UV-B 
seems to vary among varieties of the 
same crop. For example, in a study of 
eight soybean varieties, six had lower 
yield under high UV-B, but two had 
higher yields. Consequently, though 
there is good evidence of potential yield 
loss from increased UV-B intensity, 
there are many factors which 
complicate the results of UV-B studies. 

To evaluate the potential effects of 
increased UV intensity on agriculture, 
researchers measured the growth 
response of 100 varieties from 12 crops 
to an increase in UV corresponding to 
a 20% reduction in 3 . Of these 100 
varieties, 40 showed no effect. A simple 
model, based on these and other data, 
describes the sensitivity of crops to UV- 
B (Table 18). "Tolerant" crops would 
show little yield loss from an increase in 

Table 18 Sensitivity of Canadian crops to UV-B radiation 








Red clover 











Soft fruit 



(M. Morrison, AAFC) 


UV-B radiation as high as 20% increase 
over 1980 levels. Crops with 
"intermediate" sensitivity may have 
yields reduced by 1, 2.5, and 5% with 
increases in UV-B of 5, 10, and 20%, 
respectively; whereas "susceptible 
crops" may have yields reduced by 2, 5, 
and 10% with the same UV-B 
increments. Using these estimates, we 
can predict potential economic losses 
from increases in UV-B. For example, a 
5% increase in UV would result in crop 
yield losses of about $90 million per 
year; a 20% increase in losses of about 
$400 million. 

Ultraviolet radiation may also affect 
crop quality. Exposure may produce 
surface blemishes on vegetables and 
fruits or may affect flavor by causing 
increased pigment production. In one 
study, for example, amounts of UV-B- 
absorbing pigments in broccoli were 
higher with UV-B than without UV-B 
exposure. All these effects can reduce 
the value of the crop. 

There may also be ecological effects of 
UV on plant communities. Under high 
UV-B, species with higher tolerance 
may out-compete susceptible species. 
This effect could be important in 
mixed grasslands or it could alter 
weed-crop competition. Furthermore, 
elevated UV-B can affect seed 
production, because exposed 
reproductive parts may be especially 

Aside from effects on yield, quality, 
and ecology of crops, elevated UV-B 
could also have other implications. For 
example, it could affect animal health, 
plant diseases, pests, and pesticide 
efficacy. These effects have yet to be 

Research into ways of reducing the 
UV-B effect on crops has made little 
progress as yet. Given the differences 
in response among plant species and 
varieties, however, it may be possible 
to limit economic losses by selecting 
UV-B tolerant varieties. 


Most farms in Canada use some 
pesticides to control weeds, insects, 
and diseases. Many of these pesticides 
have at least some toxicity for humans 
or potential adverse effects in the 
environment. Pesticides applied to the 
soil and crops can either drift while 
being applied or volatilize afterwards. 
Once in the air, wind can transport the 
pesticides long distances before 
depositing them on soil or water. 
Pesticides deposited in the Great 
Lakes, for example, have caused 
concern over water quality. 

Some of the earlier concerns about 
pesticides are no longer as valid today 
because older, persistent pesticides 
(like DDT) are no longer used in 
Canada. Farmers now usually use 
newer formulations designed to 
control specific pests and to be easily 
degraded by soil microbes. Further, 
pesticides are now often applied at 
much lower rates, typically at grams 
per hectare rather than kilograms per 
hectare as in the past. 

Despite the improvements in current 
pesticides, however, further 
precautions may be helpful to reduce 
losses to the atmosphere. For example, 
spraying only during calm conditions 
and ensuring that droplets are large 
enough to prevent their suspension in 
the air reduces pesticide drift. In some 
cases, it may be possible to reduce 
rates or frequency of pesticide 
application by relying on other 
methods of pest control. For example, 
biological methods can now control 
some weeds and insects. The use of 
"Integrated Pest Management" (IPM) 
techniques, which rely on optimum 
combinations of chemical, biological, 

and cultural methods, may provide the 
best approach to reducing pesticide 

Pesticides help to produce high yields 
on Canadian farms. Given their 
potential effects on human health and 
the environment, however, farmers 
need to be vigilant to prevent 
pesticides from leaving the target site. 


Agrochemicals, such as insecticides and herbicides, can be released into the 
environment by drift, volatilization, and runoff. For example, some have found their 
way into the Great Lakes. Scientists use a high-volume sampler, installed in an 
aircraft, to measure agrochemicals fluxes on a regional scale. 

(G. St-Amour, AAFC) 


5. Conclusions 

The crops, livestock, and soils that make 
up our farms are immersed in air. They 
give out gases and particles that change 
the air's composition, both locally and 
far afield. At the same time, they take in 
and are affected by air that has been 
altered by industry and other human 
activity 7 . As a result, farms are sensitive 
markers of die health of our air. 

Current status 

One of the main concerns in recent 
years has been the release of 
greenhouse gases into the atmosphere. 
We now know that farms account for 
about 10% of Canada's greenhouse gas 
emissions. About two-thirds of the 
emissions are in the form of N->0 and 
one-third CH 4 . Livestock and manure 
account for about 58% of these 
emissions, cropping practices for 37%. 
At one time, agriculture was also an 
important source of COt, mostly from 
cultivated soils, but these emissions 
have abated to almost negligible levels. 
Some uncertainty remains in these 
emission estimates, particularly for 
NiO, which is released in sporadic 
bursts, making precise estimates 

Agriculture also releases other 
materials into the atmosphere. It is the 
main source of atmospheric NH3 and 
may also release some nitric oxide, 
dust, and pesticides into the air, 
though amounts are usually small. 

Although farms release some gases into 
the air, which affect its composition, 
they are also, in turn, influenced by 
emissions from other sectors of society. 
One example is the ground-level O3 
that causes crop damage in areas of 

high population density 7 . This O3 
affects the yield and quality of produce 
on nearby farms, which, because of 
their proximity to population centres, 
often grow high-value crops. Another 
example is the potential effect of 
increased UV-B radiation, which arises 
when industrial chemicals such as 
CFCs deplete O3 in the upper 
atmosphere. We do not yet know, 
precisely, the effects of the higher UV- 
B on crops and animal health, but 
some damage may occur, particularly if 
intensity of UV-B continues to 
increase, as expected. 

Opportunities to 
reduce emissions 

The net release of gases — N2O, COt, 
CH 4 , and NH3 — is usually a symptom 
of the inefficient use of resources. 
Release of excessive CH4 from 
livestock means a waste of feed; loss of 
N->0 or NH3 reflects inefficient use of 
N in fertilizers, crop residues, or 
manures; and excessive release of CO2 
reflects inefficient use of solar energy, 
stored as fossil fuel or plant C. 
Farmers can reduce emissions, 
therefore, by managing the farm N 
and C cycles more efficiently, to 
prevent gases from leaking into the 
environment. Because of improved 
efficiency, many practices that reduce 
emissions also have other favorable 
effects: reducing production costs, 
conserving soil and water, and 
improving ecosystem health. 

Agriculture will always remain a source 
of some gases: CH4, N2O, and NH3. 
Even the natural ecosystems replaced 
by farms release these gases. But, 


improved efficiency of N and C use 
can minimize the amounts of emission. 
Reductions as high as 20-30% may be 
possible. Improved farming practices 
can actually result in net removal of 

Efficiency improvements 

Market competition makes for more cost-effective production. Energy shortages and 
costs make producers more energy conscious. Similarly, faced with the possibility of 
global climate change, producers may be able to further increase their efficiency in 
using resources, thereby increasing the amount of food produced per unit of 
greenhouse gas emitted. 

Examples of increased productivity in Ontario 




Diesel fuel-equivalent of 
soybean produced (L/t) 
corn produced (t/ha) 







Animals (million) 

Milk (billion L) 

Land area need to produce feed (million ha) 

Manure generated (million t) 












Eggs produced (million dozen) 

Land area need to produce feed (thousand ha) 

Manure generated (kg/dozen eggs) 







Meat produced (million kg) 

Land area need to produce feed (thousand ha) 

Manure generated (kg/kg meat) 





These tables show that productivity has increased considerably in the selected 
periods. Energy per kilogram of soybean has halved in 15 years; and manure per unit 
of milk, eggs, or chicken has halved in 40 years. It may therefore be expected that 
fossil CC»2 and manure N->0 emissions per unit of production have also decreased. 

COt from the atmosphere, by storing 
C in soils. This increased storage could 
even help Canada meet its targets for 
reducing this greenhouse gas. 

Future challenges 

In much of this book, we have focused 
on current farm practices: how they 
affect our air and how, in turn, the 
changing atmosphere affects them. We 
have summarized estimates and 
processes that describe current 
agroecosystems. But we know that 
agricultural systems are always 
evolving; that many of the systems we 
have struggled to understand here may 
be obsolete just years from now. Thus, 
it is important to at least point to some 
impending changes and speculate 
about their possible effects. 

One important factor is the continuing 
drive for higher agricultural 
productivity. As global population 
climbs, demand for farm products 
increases. Moreover, the economic 
survival of farms often depends on 
ever-higher output of products. The 
resulting gains in productivity may 
have some benefits; for example, they 
may help to build soil C by producing 
more crop residue. At the same time, 
however, the higher yield targets may 
require more fertilizers and other 
inputs that could release more 
greenhouse gas. 

Economic factors are another 
consideration. As cost of inputs and 
price of products change, farmers alter 
their farming systems to maintain 
profits. Consequently, the area of land 
devoted to certain crops changes from 
year to year, which affects the release 
of greenhouse gases and other 
emissions. Perhaps the most dramatic 

example is the recent shift toward 
livestock-based systems. This change 
has far-reaching implications. On the 
one hand, higher livestock numbers 
usually mean more land in forages, 
which reduce atmospheric CO2 by 
storing more C in soil. At the same 
time, however, increased livestock 
numbers can lead to more release of 
CH 4 , N 2 0, and NH 3 . If the trend 
toward higher numbers of farm 
animals continues, then many of our 
current emission estimates will need to 
be revised and new measures of 
reducing emissions may be needed. 

But it is not only the farming systems 
that will change. Environmental 
conditions that affect farms will 
themselves change over the next 
decades. Many scientists believe that 
climate will be noticeably altered by 
the greenhouse effect over the next 
decades; even small changes in 
temperature or precipitation would 
affect Canadian farms. Another 
important environmental characteristic 
has already changed measurably: the 
COt concentration, already about 30% 
higher than in pre-industrial times, 
will likely double within the next 
century. Since CO? is the raw material 
for photosynthesis, this increase may 
have important effects on crop yield. 
Some even predict an increase in yields 
through "COt fertilization." Other 
environmental conditions may change 
as well, including concentration of 
ground-level O3 in populated areas, 
and the intensity of UV-B radiation. 
These changes, some of which are not 
easily predictable, may affect the way 
we farm in the next century. As well, 
they will alter the emissions from 
farms, thereby continuing the cycle 
between farms and the atmosphere. 

Carbon dioxide "fertilization effect" 

Higher COt concentration can enhance 

crop yield by increasing photosynthesis 

and allowing more efficient use of 

water. This CO? "fertilization" is more 

pronounced in C^ plants (e.g., wheat, 

soybeans, and most grasses) than in C 4 

(e.g., corn and some grasses). Some 

scientists think that CO? fertilization 

can largely offset yield losses arising 

from climate change. Others suggest 

that the benefits may be overstated, 

because they overlook the interaction 

between increased CO? and other 

environmental conditions. More research on these questions is needed. 


C 4 (e.g., corn) 

400 600 
CO2 (ppmv) 


Organic farming — an alternative approach 

Organic farming minimizes the need for off-farm inputs. It employs systems that 
avoid or largely exclude the use of synthetic fertilizers, pesticides, growth regulators, 
and livestock feed additives. Many believe that greenhouse gas emissions may be less 
for organic systems than for conventional agricultural systems. 

Organic farms attempt to harmonize with natural systems. They rely on renewable 
resources and less input from fossil energy. The holistic view of organic farmers 
follows a natural systems approach to agriculture. Individual growers take daily 
decisions to make a living from the land, based on both economic and ecological 
considerations. With time, agroecosystems reach a steady state, where living and 
nonliving processes are in balance. For many, it is a way of life as much as a way of 
making a living. 

The holistic systems approach requires an intimate knowledge of the 
interrelationships between soil, water, climate, and biology of the agricultural system. 
In addition, these systems also consider off-farm effects such as rural economics and 

Generally, families on organic farms have traditions of environmentalism and are 
careful consumers of all resources. The day-to-day on-farm decisions of organic 
farmers are complex and require an in-depth knowledge of many areas of science. 
Organic farmers believe that their philosophy provides a gentler approach to the 

Both conventional and organic systems of agriculture aim to provide society with 
high-quality food, but some feel that organic farming also attempts to improve 
quality of the on-farm natural resources and to reduce potential environmental 

Q. Dormaar, AAFC) 



The unpredictability of future changes 
in farm ecosystems, along with 
uncertainties about even our current 
estimates of emissions, leave room for 
further study of the ties between our 
farms and the atmosphere. The most 
urgent goals may be the following: 

• To improve further our estimates 
of current gas release, especially 
for N 2 0. We need better ways of 
taking data from local measuring 
points and extending them to 
larger areas, up to the national 

To find ways that will help Canada 
meet its international 
commitments for reduced 
emissions of potentially harmful 

To understand better how C, N, 
and other elements move through 
and among plants, animals, soil, 
water, and air. Such understanding 
will show us how the various gases 

and environmental issues are 
linked together and how they 
interact. As well, it will help us to 
predict better how changing farm 
practices will affect the 

To learn how changes in our 
atmosphere will affect Canadian 
farming in the future. Of 
particular importance may be the 
effects of climate change 
(temperature and precipitation), 
increased CO2 concentration, 
enhanced UV-B intensity, and 
increased ground-level O3. We 
need to know how these will affect 
yields, crop types, animal 
productivity, pests, and production 
costs. As well, we need to 
understand how these changes will 
alter future emissions from 
agriculture to the air. 

6. Bibliography and selected reading 

Acton, D.F. and L.F. Gregorich (eds.). 1995. The health of our soils: toward 
sustainable agriculture in Canada. Centre for Land and Biological Resources, 
Agriculture and Agri-Food Canada. Publication 1906/E, 138 pp. 

Baht, M.C., B.C. English, A.F. Turhollow, and H.O. Nyangito. 1994. 
Energy in synthetic fertilizers and pesticides: revisited. Oak Ridge National 
Laboratory, Tennessee, USA. Report ORNL/Sub/90-99732/2. 

Canadian Council of Ministers of the Environment. 1997. Ground-level ozone 
and its precursors, 1980-1993. Report of the Data Analysis Working Group, 
Canadian Council of Ministers of the Environment. 295 pp. 

Coxworth, E., M.H. Entz, S. Henry, K.C. Bamford, A. Schoofs, RD. Ominski, R 
Leduc, and G. Burton. 1995. Study of the effect of cropping and tillage systems 
on the carbon dioxide released by manufactured inputs to western Canadian 
agriculture: identification of methods to reduce carbon dioxide emissions. Final 
report for Agriculture and Agri-Food Canada. 

Desjardins, R.L. 1998. Agroecosystem greenhouse gas balance indicator: methane 
component. Report no. 21 to Agri-environmental indicator project. Agriculture 
and Agri-Food Canada. 19 pp. 

Dumanski, J., L.J. Gregorich, V. Kirkwood, M.A. Cann, J.L.B. Culley, and D.R. 
Coote. 1994. The status of land management practices on agricultural land in 
Canada. Centre for Land and Biological Resources, Agriculture and Agri-Food 
Canada. Technical Bulletin 1 994-3 E, 46 pp. 

Duxbury, J.M. and A.R. Mosier. 1993. Status and issues concerning agricultural 
emissions of greenhouse gases. Chapter 12 in Agricultural dimensions of global 
climate change, T Drennen and H.M. Kaiser (eds.); St. Lucie Press, Florida. 

ECETOC. 1994. Ammonia emissions to air in Western Europe. European 
Centre for Ecotoxicology and Toxicology of Chemicals. 194 pp. 

Ecological Stratification Working Group. 1995. A national ecological framework 
for Canada. Centre for Land and Biological Resources, Agriculture and Agri- 
Food Canada and Ecozone Analysis Branch, State of the Environment 
Directorate, Environment Canada. 

Environment Canada. 1993. A primer on ozone depletion. The environmental 
citizenship series. Environment Canada. 76 pp. 

Gribbin, John and Mary. 1996. The greenhouse effect. The New Scientist 2037, 
Supplement: Inside Science 92:1-4. 

Houghton, John. 1997. Global warming: the complete briefing. Cambridge 
University Press. 251 pp. 


McAllister, T.A., E.K. Okine, G.W. Mathison, and K.-J. Cheng. 1996. Dietary, 
environmental and microbiological aspects of methane production in ruminants. 
Canadian Journal of Animal Science, 76:231-143. 

Monteverde, C.A., R.L. Desjardins, and E. Pattey. 1998. Agroecosystem 
greenhouse gas balance indicator: nitrous oxide component. Report no. 20 to 
Agri-environmental indicator project; Agriculture and Agri-Food Canada. 29 pp. 

Moss, A.R. 1993. Methane: global warming and production by animals. Chalcome 
Publications, Kingston, UK. 105 pp. 

Policy Branch. Canadian fertilizer consumption, shipments and trade. Annual 
publications of Policy Branch, Agriculture and Agri-Food Canada. Available on 
the internet at 

Shoji S. and H. Kanno. 1994. Use of polyolefin-coated fertilizers for increasing 
fertilizer efficiency and reducing nitrate leaching and nitrous oxide emissions. 
Fertilizer Research 39:147-152. 

Smith, W.N., P. Rochette, C. Monreal, R.L. Desjardins, E. Pattey, and A. Jaques. 
1997. The rate of carbon change in agricultural soils in Canada at the landscape 
level. Canadian Journal of Soil Science, 77:219-229. 

Stumborg, MA. (ed.). 1997. Proceeding of the 1997 ethanol research and 
development workshop. Natural Resources Canada and Agriculture and 
Agri-Food Canada. 

Surgeoner, G.A. 1995. Sustainable agriculture: Heaven on earth? Agri-food 
Research in Ontario. Special edition, July, 29 pp. 

Symbiotics Environmental Research and Consulting. 1996. Inventory of 
technologies to reduce greenhouse gas emissions from agriculture. Report 
prepared for Global Air Issues Branch, Environment Canada and Environment 
Bureau, Agriculture and Agri-Food Canada. 

Symbiotics Environmental Research and Consulting. 1997. Agricultural sources, 
effects and abatement of atmospheric emissions of nitrogen compounds: review of 
Canadian science and technology. Report prepared for Environment Bureau, 
Agriculture and Agri-Food Canada. 

Tenuta, M., E.G. Beauchamp, and G.W. Thurtell. 1995. Studies of nitrous oxide 
production and emission from soil: evaluation of N 2 release with different 
methods and fertilizer sources. Final report to Agriculture and Agri-Food 
Canada's Trace gas initiative project. 

Tollenaar, M. 1996. Corn production, utilisation and environmental assessment — 
a review. Canada's Green plan, Agriculture and Agri-Food Canada. 

Vezina, C. 1997. National ammonia inventory: preliminary emissions. Pollution 
Data Branch, Environment Canada. (Unpublished draft.) 


Wardle, D.I., J.B. Kerr, C.T. McElroy, and D.R. Francis (eds.). 1997. Ozone 
science: a Canadian perspective on the changing ozone layer. Environment 
Canada. 119 pp. 
See also: 

Working Group 1. Climate change 1995: the science of climate change (Chapter 
13: agriculture). Contribution of Working Group 1 to the Second assessment 
report of the Intergovernmental Panel on Climate Change. World Meteorological 



The material presented in The Health of Our Air is derived from the work of many 
scientists who made valuable contributions to the Agriculture and Agri-Food 
Canada research initiatives on greenhouse gases and ground-level ozone. These 
included the principal investigators or team leaders, listed here as contributors, 
along with collaborators, colleagues, postdoctoral fellows, technicians, and 
graduate students. Grateful acknowledgment is made to all. 


Allard, G.; Angers, D.A.; Antoun, H.; Baril, P.; Beauchamp, E.G.; Bordeleau, L.; 
Bowen, P.A.; Buckley, D.; Burton, D.; Campbell, C; Chalifour, F.P.; Chiquette, J.; 
Cho, CM.; Coxworth, E.; Desjardins, R.L.; Dow, D.; Dunfield, P.; Ellert, B.; 
Gleig, D.B.; Grace, B.; Grant, B.; Gregorich, E.; Guo, Y.; Izaurralde, R.C.; 
Jackson, H.A.; Janzen, H.H.; Kaharabata, S.; Kinsman, R.; Knowles, R.; 
Lapierre, C; Lin, M.; Liu, J.; MacDonald, B.; MacLeod, J.; MacPherson, J.I.; 
Masse, D.; Mathison, G.W.; Mathur, S.P.; McAllister, T; McCaughey, W.P.; 
McGinn, S.; McKenny, D.J.; Merrill, C; Monteverde, C; Morrison, M.J.; 
Paul, R.J.; Pattey, E.; Patni, N.; Prevost, D.; Renaud, J. P.; Richards, J.; Riznek, R.; 
Rochette, P.; Runeckles, V.C.; Sabourin, D.; Sauer, E; Schuepp, PH.; Selles, E; 
Smith, W.; St. Amour, G.; Tarnocai, C; Thurtell, G.W.; Topp, E.; 
van Bochove, E.; Van Kessel, C; Wagner-Riddle, C; Wang, E; Zhu, T 

A listing of the principal investigators and their project titles are presented in 
Appendix I for those who wish more detailed information. 


Acknowledgments are also due to the following individuals for their review of this 
manuscript and their helpful comments: T Daynard, Ontario Corn Producers; 
S. Forsyth, National Agriculture Environment Committee; P. Strankman, 
Canadian Cattlemen's Association; K. Whittenberg and D. Burton, University of 
Manitoba; V. Runeckles, University of British Columbia; J. Farrell, Fertilizer 
Institute of Canada; E. Beauchamp, University of Guelph; G. Hamblin, Canadian 
Organic Advisory Board; and E. Gregorich and K. Beauchemin, Agriculture and 
Agri-Food Canada. 

Production team 

The editors wish to thank the following for their valuable technical assistance in 
preparing the manuscript and figures for publication: S. Rudnitski, J. Sylvestre- 
Drouin, R. Riznek, and C. Merrill of Agriculture and Agri-Food Canada, and 
JT. Buckley (Gilpen Editing Service). 

v n 

Program Management 

Acknowledgment is due to J.M.R. Asselin, L. Bordeleau, G. den Hartog, 
R.L. Desjardins, B. Grace, H.H. Janzen, C.W. Lindwall, G.A. Neish, and 
A. St- Yves for their contribution to the management of the AAFC research 
program on greenhouse gases and ozone. We would also like to acknowledge the 
contribution of the Program for Energy Research and Development (PERD), 
managed by Natural Resources Canada. 


Appendix I 

The principal investigators and their project titles are listed here for those who 
wish more detailed information. 

Investigators and projects 

Allard, G. 

Tel.:41 8-656-2 131 x 2706 



Angers, D.A. 

Tel.:41 8-657-7980 x 270 



Antoun, H. 



Baril, P. 


Beauchamp, E.G. 
(see Thurtell) 

Bowen, P.A. 

Tel.:604-796-2221 x225 

Chalifour, F.P 
Tel.:41 8-656-2 131 x2306 

Chiquette, J. 

Tel.:819-565-9171 x 249 



Ozone damage on agricultural species 

Agriculture management effects on carbon 
sequestration in eastern Canada 

Physical, chemical, and biological soil 
factors that affect NiO and CH4 emission 

Development of a plan to reduce 
greenhouse gas emissions from the animal 

Measurement of fluxes of N7O from 
agricultural sites in Ontario 

Ozone impacts to Fraser Valley crops 
grown under field conditions 

Efficiency of N use to limit NtO emission 
in cereal-legume cropping systems 

GHG production from ruminants: a 
system approach 


Cho, CM. 


Coxworth, E. 
Tel.: 3 06- 3 43 -92 81 

Desjardins, R.L. 




Ellert, B. 


Izaurralde, R.C. 




Investigation on stability, persistence, and 
flux of NtO in laboratory and field soil 

Study of the effects of cropping and tillage 
systems on the carbon dioxide released by 
manufactured inputs to western Canadian 

Assessment of ozone uptake by 
agricultural crops in critical areas along 
the Windsor-Quebec corridor 

Contribution of representative prairie 
agroecosystems to greenhouse gas 

Quantification of nitrous oxide, methane, 
and carbon dioxide fluxes over managed 
and natural ecosystems of Alberta 

Jackson, H.A. 
(see Sauer, E) 

Knowles, R. 
Tel.:5 14-398-7890 

Lapierre, C. 




MacDonald, B. 

Tel.:5 19-826-2086 



MacLeod, J. 




Methane and carbon dioxide emissions 
from farm animals and manure 

Methane and nitrogen cycle interactions 
in agriculture systems 

Contribution of liming and tillage to N7O 
and COt emissions in eastern Canada 

Characterization of agroecosystems in 
eastern Ontario for their potential to act 
as sources or sinks of greenhouse gases 

Nitrogen cycling in potato system 

Mathison, G.W. 



McCaughey, W.P. 



McKenny, D.J. 


Strategic approach to quantifying and 
reducing CH4 production by animals 

Morrison, M.J. 

Tel.:61 3-759-1 556 



Paul, R.J. 

Tel.:604-796-2221 x215 

Pattey, E. 

Prevost, D. 




Richards, J. 


Rochette, P. 

Tel.:41 8-657-7980 



Runeckles, V.C. 




Methane production by beef cattle 

Effects of conservation and conventional 
tillage practices with/without 
subirrigation/controlled drainage on 
greenhouse gas emissions from corn 
production systems in southwestern Ontario 

Identification of corn and soybean 
cultivars with tolerance to atmospheric 
ozone pollution 

Nitrous oxide and methane emissions in 
dairy and hog manure management 

Impact of agricultural management on 
greenhouse gas fluxes 

Mechanisms involved during burst of 
N->0 emissions 

Losses of fertilizer and soil N by 
denitrification in podzolic soils 

Contribution of agricultural practices to 
the atmospheric increase of greenhouse 

Ozone impacts to Fraser Valley crops 
grown under field conditions 


Schuepp, P.H. 
Tel.:5 14-389-793 5 

Scaling up of GHG emission models on 
the basis of land-use mapping and 
airborne flux observation 

Selles, F. 


Smith, W. 
Tel.:61 3-256-7093 


Tarnocai, C. 




Thurtell, G.W 

Tel.:5 19-824-2453 



Van Kessel, C. 




Zhu, T. 

Tel.:61 3-759-1889 



Comparison of present and future crop 
management practices on the emission of 
greenhouse gases in the semi-arid prairies 

Modelling C0 2 and N z O fluxes for 
agroecosystems in Canada 

Amount of organic carbon in Canadian soils 

Measurements of fluxes of N 2 from 
agricultural sites in Ontario 

Landscape-scale fluxes of CO* 2 and N 2 
in the Prairies 

Improving flux-measuring technology 
based on the relaxed eddy accumulation 

Grace, B. 

Tel. :2 50-494-77 11 

Program Coordination 




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