Soil Organic Carbon Content and Stability, and Greenhouse Gas Emissions in Three Agroforestry ...

257 Pages·2016·3.86 MB·English

by  Carlyle, Cameron

Soil Organic Carbon Content and Stability, and Greenhouse Gas Emissions in Three
Agroforestry Systems in Central Alberta, Canada

by
Mark Baah-Acheamfour

A thesis submitted to the Faculty of Graduate Studies and Research
in partial fulfillment of the requirements for the degree of

Doctor of Philosophy

in
Soil Science

Department of Renewable Resources
University of Alberta

© Mark Baah-Acheamfour
Abstract

Western Canada’s prairie region is extensively cultivated for agricultural production, which is a
large source of greenhouse gas (GHG) emissions. Agroforestry systems are common land uses
across Canada, which integrate trees into the agricultural landscape and could play a substantial
role in sequestering carbon (C) and mitigating increases in atmospheric GHG concentrations.
This thesis research quantified soil C storage and stability, and CO , CH , and N O emissions in
2 4 2
forest and herbland (areas without trees) components of three agroforestry systems (hedgerow,
shelterbelt, and silvopasture) over two growing seasons (May through September in 2013 and
2014). The study evaluated 36 sites (12 hedgerows, 12 shelterbelts, and 12 silvopastures) in
central Alberta, Canada, distributed along a soil/climate gradient of increasing moisture
availability. Within each agroforestry system, the areas under forest consistently had greater total
soil organic C (SOC) and SOC in most soil fractions separated by particle-size (up to 10 cm) and
density (up to 30 cm) fractionation than in herbland areas. The C stored in this forest cover is
more stable, so less of it is expected to be lost as CO when the climate warms in the future. Soil
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CO emission and temperature (r2= 0.53, p < 0.01) and CH uptake and soil water content (r2 =
2 4
0.38, p < 0.01) were significantly related in the studied land uses. Soil temperature and water
content are dominant controls on N O emissions, and together explained 71% of the variation in
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N O emissions. Over the two seasons, forest soils had 3.4% greater CO emission, 36% higher
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CH uptake, and 66% lower N O emission than adjacent herbland soils. As a result, forested
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areas had a smaller global warming potential (129) than their herbland counterpart (157 kg CO
2
ha-1) based on all three GHGs. Autotrophic respiration contributed more to total respiration in the
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forest than in herbland (p < 0.01), that, in turn, may be responsible for the high CO emissions in
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the forest.
The SOC stock in the bulk soil (up to 30 cm) was greater in the silvopasture (201) than in
either the hedgerow (178) or shelterbelt system (162 Mg C ha-1). Across particle-size fractions,
SOC in the more stable fine fraction was in the order of: hedgerow >shelterbelt > silvopasture
system. Similarly, the largest pool of SOC in the more stable heavy density fraction of both the
0-10 and 10-30 cm depth classes was in the shelterbelt (33 and 35 Mg ha-1, respectively), while
the least SOC was in the silvopasture system (26 and 20 Mg ha-1, respectively). While ranked
emissions of CO were silvopasture > hedgerow > shelterbelt, soils in the silvopasture system
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had 15% greater CH uptake and 44% lower N O emission rates compared with the other two
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agroforestry systems. Silvopasture system can provide greater potential to induce soil C
sequestration because it leads to a larger reduction in heterotrophic respiration (p = 0.03) than the
hedgerow and shelterbelt systems. Overall, opportunities appear to exist for enhancing soil C
storage and stability, while reducing GHG emissions by retaining and establishing perennial
vegetation, both forest and grassland, within agricultural landscapes.

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Preface

This thesis is an original work by Mark Baah-Acheamfour. Chapter 3, 4 & 5 of this thesis has
been published as Baah-Acheamfour, M., Carlyle, C.N., Bork, E.W., Chang, S.X. "Trees
increase soil carbon and its stability in three agroforestry systems in central Alberta, Canada,"
Forest Ecology & Management, vol. 328, 131-139 (2014), Baah-Acheamfour, M., Chang, S. X.,
Carlyle, C. N., Bork, E. W. "Carbon pool size and stability are affected by trees and grassland
cover types within agroforestry systems of western Canada," Agriculture, Ecosystem, &
Environment, vol. 213, 105-113 (2015), and Baah-Acheamfour, M., Carlyle, C. N., Lim, S.S.,
Bork, E. W., Chang, S. X. "Forest and grassland cover types reduce net greenhouse gas
emissions from agricultural soils," Science of the Total Environment, doi:10.1016/j.scitotenv.
2016.07.106 (2016), respectively. I was responsible for the data collection, analysis as well as
manuscripts writing. Lim, S.S. assisted with data collection and contributed to manuscript edits.
Chang, S.X., Bork, E. W., and Carlyle, C. N. were the supervisory authors and contributed to the
editorial corrections of manuscripts.

M.B.-A.

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Acknowledgements

My deepest gratitude goes to my supervisors, Dr. Scott X. Chang and Dr. Edward Bork. This
work would not have been possible without their very active involvement. In addition to the
scientific guidance, their advice, and comments in the structuring of this dissertation have been
extremely helpful. I would also like to thank my advisory committee members: Drs. Cameron
Carlyle, Phil Comeau, and Guillermo Hernandez Ramirez, for taking the time to read my thesis,
as well as providing important editorial corrections.
During the field work, I received tremendous support and cooperation from landowners,
county officers, and other collaborators. I recognize and express my sincere gratitude to the
numerous landowners in central Alberta, Canada, who allowed me access to their farmland to
conduct this study. Thank you to Dr. Samiran Banerjee, Dr. Farrah Fatemi, Dr. Sang-Sun Lim,
Ghulam Murtaza Jamro, Dr. Jin-Hyeob Kwak, Qiting Chen, Agathe Hery, and Isabel Fodor, for
their assistance with fieldwork, and Shujie Ren and Shirin Zahraei for their help with laboratory
analysis of soil samples.
I am grateful for the financial support from Agriculture and Agri-Food Canada (AAFC),
funded under the Agricultural Greenhouse Gases Program (AGGP) Program. Finally, special
thanks are due to the Faculty of Graduate Studies and Research and Graduate Students’
Association of the University of Alberta for providing me funding for attending conferences.

M.B.-A.

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Table of Contents

CHAPTER 1 General introduction.................................................................................................1
Research background.......................................................................................................................1
2 Research objectives................................................................................................................ .......4
3 Thesis structure..............................................................................................................................5
References………………………………………………………………..........................................8

CHAPTER 2 Agroforestry enhance C storage and mitigation GHG emissions in Canada’s
agricultural landscapes ………………………………………………………………...………...13
1 Review of C sequestration and GHG emissions in agroforestry systems.........................13
2 Carbon stored in vegetation in agroforestry systems.........................................................15
3 Soil C stored in agroforestry systems..................................................................................20
4 Potential for reduction of CO , CH , and N O emissions…..............................................24
2 4 2
5 Challenges, constraints and future research needs............................................................29
6 Conclusions…………………………………………............................................................32
References.................................................................................................................................37

CHAPTER 3 Forest and grassland cover types increase soil carbon and its stability in
agroforestry systems in western Canada ………….....................................................................49
1 Introduction...........................................................................................................................49
2 Materials and Methods…….................................................................................................52
2.1 Site description...............................................................................................................52
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2.2 Sampling design.............................................................................................................54
2.3 Soil physical and chemical characterization………………...........................................55
2.4 SOC fractionation.................................... .....................................................................55
2.5 Statistical analysis…………………………………………..........................................56
3 Results.....................................................................................................................................57
3.1 Soil properties.................................................................................................................57
3.2 SOC and N in whole soil................................................................................................58
3.3 SOC and N in fractionated soil……………………………...........................................58
4 Discussion…………………………………………...............................................................60
5 Conclusions…………………………………………............................................................66
References..................................................................................................................................74

CHAPTER 4 Forest and grassland cover types increase carbon pool size and stability in
agroforestry systems: evidence from density fractionation........................................................82
1 Introduction…………………………………………………………...……………………..82
2 Materials and Methods…….................................................................................................84
2.1 Site description...............................................................................................................85
2.2 Sampling design..............................................................................................................86
2.3 Soil physical and chemical analyses……………….......................................................87
2.4 Soil density fractionation.................................... ...........................................................88
2.5 Statistical analysis…………………………………………...........................................89
3 Results.....................................................................................................................................90
3.1 Soil properties................................................................................................................90
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3.2 Percent mass distribution of soil density fractions.........................................................91
3.3 SOC and N stocks in soil density fractions and bulk soil…..........................................92
4 Discussion…………………………………………..............................................................93
5 Conclusions…………………………………………............................................................98
References...............................................................................................................................105

CHAPTER 5 Forest and grassland cover types reduce net greenhouse gas emissions from
agricultural soils .........................................115
.........................................................................................................................
1 Introduction.........................................................................................................................115
2 Materials and Methods……...............................................................................................118
2.1 Site description.............................................................................................................119
2.2 Sampling design............................................................................................................120
2.3 Measurements of total CO ,CH , and N O emissions…..............................................121
2 4 2
2.4 Determining heterotrophic CO emission rate..............................................................122
2
2.5 Soil temperature and water content measurements......................................................123
2.6 Calculations…..............................................................................................................123
2.7 Statistical analysis…………………………………………........................................125
3 Results..................................................................................................................................126
3.1 Soil temperature and water content............................................................................136
3.2 Soil CO emissions....................................................................................................127
2
3.3 Soil CH uptake..........................................................................................................128
4
3.4 Soil N O emissions....................................................................................................128
2
3.5 Global warming potential of microbe-mediated soil GHG emission (GWP )..........129
m
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3.6 Environmental controls of GHG emissions...............................................................130
4 Discussion…………………………………………...........................................................130
4.1. Total CO emission from soils...................................................................................130
2
4.2. Soil CH uptake..........................................................................................................133
4
4.3. Soil N O emission......................................................................................................134
2
4.4. Global warming potential of microbe-mediated soil GHG emission (GWP )..........136
m
5 Conclusions…………………………………………..........................................................136
References...............................................................................................................................149

CHAPTER 6 Forest and grassland cover types increase CO emissions from agricultural
2
soils by enhancing autotrophic but not heterotrophic respiration..........................................161
1 Introduction.........................................................................................................................161
2 Materials and Methods……...............................................................................................163
2.1 Site description.............................................................................................................163
2.2 Partitioning of autotrophic and heterotrophic components..........................................165
2.3 Calculations………………………………….…………….........................................166
2.4 Statistical analysis………………………………........................................................167
3 Results..................................................................................................................................168
3.1 Total CO effluxes measured with a Li-Cor 8100A and the static chamber method...168
2
3.2 Land cover effects on autotrophic and heterotrophic respiration.................................168
3.3 Response of soil respiration components to temperature changes……………....…....170
4 Discussion…………………………………………..........................................................170
5 Conclusions…………………………………………........................................................175
References.............................................................................................................................183
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CHAPTER 7 Conclusions and future research ……………………………………................189
1 Overview of the study objectives.......................................................................................189
2 Summary of the research results and management implications……….......................193
3 Recommendations and future research needs ………………………….........................193
4 References……….................……………............................................................................195
Bibliography ………………………….........................................................................................199
Appendix..................................................................................................................................234
Appendix 2-1 Soil carbon storage potential under agroforestry systems in different
locations in Canada…………………………………………………………………...…...237

Appendix 5-1 Variability of soil temperature and moisture content across study sites in central
Alberta, Canada. Values represent the mean from mid-May through September, during each of 2013
and 2014..............……………………………………………………………………..........239

Appendix 5-2 Soil carbon storage potential under agroforestry systems in different
locations in Canada…………………………………………………………………….....240

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