THE IMPACT OF CONSERVATION TILLAGE ON SOIL ...

THE IMPACT OF CONSERVATION TILLAGE ON SOIL QUALITY AND POTENTIAL FOR CLIMATE CHANGE MITIGATION

Shamsudheen Mangalassery, M.Sc. (Agri.)

Thesis submitted to the University of Nottingham for the degree of Doctor of Philosophy 2013

Abstract Conservation tillage is generally considered as an important component of sustainable agriculture. The benefits of conservation tillage have been presented as reducing runoff, enhancing water retention and preventing soil erosion. There is also general agreement that it can be used to conserve and enhance soil organic carbon levels to some extent. However, its applicability in mitigating climate change has been extensively debated, especially when the whole profile of carbon in soil is considered along with a reported risk of enhanced N2O emissions under conservation tillage. The suitability of conservation tillage in mitigating climate change and enhancing carbon sequestration is addressed in this research in an integrated approach combining characterisation of the soil porous architecture and other chemical and biological properties. Novel analytical tools such as X-ray Computed Tomography were used to characterise the 3-D soil pore network under conservation tillage for the first time. The study indicated zero tilled soils had a lower net emission of greenhouse gases on a CO2 equivalent basis indicating potentially zero tillage can be used to mitigate climate change. The net global warming potential under conventional tillage was 20% higher than zero tilled soil. A model developed to predict the greenhouse gas emissions from soil found that soil pore characteristics such as porosity played a significant role in the emission of greenhouse gases such as CO2 and CH4 among other factors such as microbial biomass carbon, bulk density and shear strength. Soil porosity alone accounted for 39.7% of the total variation for CO2 flux which was larger than any other parameter including microbial biomass carbon and soil carbon. Soil pore characteristics were revealed as one of the important determinant in aiding the GHG flux in soil. However N2O emission from soil

I

was mainly dependent on soil moisture, microbial biomass carbon and microbial biomass nitrogen. It was also found that zero tilled soils contained 9% more soil carbon and 30% higher microbial biomass carbon than the tilled soil. It was found that tillage mediated aggregate changes could bring changes in carbon storage in soil depending on texture of soil. Increased microbial activity was evident at zero tilled soils as observed from the increased activities of hydrolysing and oxidising enzymes. The preservation of aromatic structures during

residue

decomposition

might

have

contributed

to

enhanced

sequestration of carbon under zero tilled soils as revealed by the FTIR data. The study indicates that soil management practices strongly influence other properties and by making a suitable choice of the tillage system, a comparative reduction in greenhouse gas emissions could be achieved at the same time enhancing sequestration of carbon.

II

Publications from this work Peer reviewed publications included in the thesis Mangalassery S, Sjögersten S, Sparkes DL, Sturrock CJ, Mooney SJ (2013) The effect of soil aggregate size on pore structure and its consequence on emission of greenhouse gases. Soil and Tillage Research, 132, 3946. Mangalassery S, Sjögersten S, Sparkes DL, Sturrock CJ, Craigon J, Mooney SJ (2013) To what extent can zero tillage lead to a reduction in greenhouse gas emissions?

Abstract of papers presented in seminars (not included in this thesis) Mangalassery S, Sjogersten S, Sparkes DL, Sturrock C, Mooney SJ (2012a) In 4th International Congress of European Confederation of Soil Science Societies (Eurosoil 2012)-Soil Science for the benefit of mankind and environment Bari, Italy. Mangalassery S, Sjogersten S, Sparkes DL, Sturrock C, Mooney SJ (2012b) In British Society of Soil Science Annual Meeting 2012. University of Nottingham, Sutton Bonington Campus, Sutton Bonington, Leicestershire.

III

Acknowledgements I wish to express my deep sense of gratitude and indebtedness to Prof. Sacha Mooney, Dr. Sofie Sjogersten and Dr. Debbie Sparkes for their excellent guidance and constant encouragement throughout the period of my PhD and the training they have given to develop professional academic skills. It was indeed great pleasure and privilege studying under their guidance. I am grateful to all technical staff that helped me to complete this work in time; John Corrie and Darren Hepworth for their support for laboratory work, purchase, training and administrative help, John Alcock and William Donger for sampling help at Sutton Bonington and Julietta Marquez and Neil Saunders. I am extremely thankful to Emma Hooley for the excellent administrative support rendered. All the staff members and colleagues were always helpful and friendly to me and many thanks for that. The help I received for field sampling from Boris Lazarevic and Aveen Khalil is thankfully acknowledged. I am overwhelmed with sincere feelings of indebtedness to my beloved, parents, brothers, sisters, brother-in-laws and sister-in-laws for their abundant love and affection showered on me, which inspired me in completing my studies. I heartily express my special thanks to Dr. Craig Sturrock for his help and cooperation throughout my PhD study especially for training with X-ray CT, Dr. Brian Atkinson for training to use gas chromatography and Dr. Sarah Martin for helping with Biolog ecoplating. I am grateful to the Indian Council of Agricultural Research, New Delhi for providing financial assistance in the form of International Fellowship and to the University of Nottingham for providing International Research Excellence Scholarship without which it could not have been possible to pursue my PhD at this prestigious University and also to the British Society of Soil Science for providing travel grants to attend conferences. I express my sincere gratitude to the Director, Central Arid Zone Research Institute, Jodhpur for granting me permission to pursue PhD studies. I am extremely thankful to my lovely wife Sanu and cute daughters Munny and Minu for their love and support throughout my studies. Any omission in this brief acknowledgement does not mean lack of gratitude.

AUGUST, 2013

(SHAMSUDHEEN M)

IV

CONTENTS Abstract

I

Publications from this work

III

Acknowledgements

IV

Abbreviations and acronyms

X

List of tables

XII

List of figures

XIV

Dedication

XXII

1.

CHAPTER 1: GENERAL INTRODUCTION

1

1.1

Rationale

1

1.2

Literature Review

3

1.2.1

Introduction

5

1.2.2

Materials and methods

8

1.2.3

Conservation tillage and soil properties

10

1.2.4

Climate change and greenhouse gases

11

1.2.5

Sequestration of carbon under conservation tillage

12

1.2.6

Greenhouse gas emission under conservation tillage

25

1.2.7

Soil quality and yield responses under conservation tillage

30

1.3

Research aim and objectives

35

1.4

Thesis structure

36

CHAPTER 2: THE EFFECT OF SOIL TEXTURE AND 48 MANAGEMENT ON SOIL BIOPHYSICAL AND CHEMICAL BEHAVIOUR

2.

2.1

Introduction

48 V

2.2

Materials and methods

49

2.2.1

Field site and sampling

49

2.2.2

X-ray Computed Tomography

50

2.2.3

Carbon dioxide emissions from soil

57

2.2.4

Soil organic matter and microbial biomass carbon

57

2.2.5

Soil physical properties

57

2.2.6

Statistical analysis

57

2.3

Results

58

2.3.1

Soil pH

58

2.3.2

Soil organic matter

58

2.3.3

Soil organic carbon and carbon stock

59

2.3.4

Microbial biomass carbon and nitrogen

60

2.3.5

Hydraulic conductivity, shear strength and ponding limit

62

2.3.6

Bulk density

64

2.3.7

Carbon dioxide emissions

65

2.3.8

Soil structural analysis

66

2.3.9

Relationship between different soil properties

69

2.4

Discussions

70

2.5

Conclusions

73

CHAPTER 3: THE EFFECT OF SOIL AGGREGATE 74 SIZE ON PORE STRUCTURE AND ITS CONSEQUENCE ON EMISSION OF GREENHOUSE GASES

3.

3.1

Introduction

76

3.2

Materials and methods

77

VI

3.2.1

Sample preparation

77

3.2.2

Greenhouse gas emission and soil carbon

77

3.2.3

X-ray Computed Tomography (CT)

77

3.2.4

Statistical analysis

78

3.3

Results

78

3.3.1

Saturated hydraulic conductivity

78

3.3.2

Soil organic matter

78

3.3.3

Greenhouse gas release

78

3.3.4

Soil pore characteristics

80

3.3.5

Relationship between fluxes of greenhouse gases and soil physical properties

81

3.4

Discussion

81

3.5

Conclusions

82

CHAPTER 4: TO WHAT EXTENT CAN ZERO 84 TILLAGE LEAD TO A REDUCTION IN GREENHOUSE GAS EMISSIONS?

4.

4.1

Introduction

87

4.2

Materials and methods

89

4.2.1

Site selection and sample collection

89

4.2.2

Soil physical properties

93

4.2.3

X-ray Computed Tomography (CT)

93

4.2.4

Soil chemical and biological properties

95

4.2.5

Fluxes of greenhouse gases

95

4.2.6

Statistical analysis

95

4.3

Results 4.3.1

Soil physical properties

96 96

VII

4.3.2

Soil pore characteristics

98

4.3.3

Soil chemical and biological properties

99

4.3.4

Fluxes of greenhouse gases

100

4.3.5

Relationship between greenhouse gas fluxes and soil properties

103

4.4

Discussion

105

CHAPTER 5: MICROBIAL MECHANISMS 113 GOVERNING SOIL CARBON SEQUESTRATION UNDER CONSERVATION TILLAGE IN TEMPERATE SOILS

5.

5.1

Introduction

115

5.2

Materials and methods

118

5.2.1

Sample preparation

118

5.2.2

Soil chemical properties

119

5.2.3

Soil biological properties

119

5.2.4

Statistical analysis

120

5.3

Results

121

5.3.1

Soil chemical properties

121

5.3.2

Soil biological properties

124

5.3.3

Factors affecting carbon content in soil

128

5.4

Discussion

129

5.5

Conclusions

135

6.

CHAPTER 6: CONCLUSIONS

GENERAL

DISCUSSION

AND 141

6.1

Introduction

141

6.2

Effect of tillage/zero tillage on physico-chemical properties

141

VIII

6.3

Physical and microbial basis of carbon sequestration in soil

143

6.4

Climate change mitigation under zero tillage

144

6.5

Zero tillage on soil biological properties

146

6.6

Conclusions

148

6.7

Future work

150

6.7.1

Studies on soil pore characteristics on micro scale

150

6.7.2

Insitu studies in the field involving crop component

150

6.7.3

Effect of conservation tillage on crop yields vis a vis climate change mitigation

151

6.7.4

Carbon sequestration

151

7.

REFERENCES

152

8.

APPENDIX

175

IX

Abbreviations and acronyms µ

Micro

µA

Micro ampere

AWCD

Average well colour development

CH4

Methane

CO2

Carbon dioxide

CT

Computed Tomography

FTIR

Fourier Transform Infrared spectroscopy

g

Gram

GC

Gas chromatography

GE

Glucose equivalents

GHG

Greenhouse gas

GWP

Global warming potential

h

Hour

IPCC

Intergovernmental Panel on Climate Change

kg

kilogram

kPa

kilo Pascal

kV

Kilo volt

L-DOPA

L-3,4-dihydroxy phenylalanine

LSD

Least significant difference

M

Molar

mg

Milligram

min

Minute

mL

Millilitre

X

mM

Milli molar

mM

milli molar

N2O

Nitrous oxide

ng

Nanogram

nm

Nanometre

NMR

Nuclear Magnetic Resonance spectroscopy

PCA

Principal component analysis

PVC

Ploy Vinyl Chloride

s

Seconds

SOC

Soil organic carbon

SOM

Soil organic matter

TPF

Triphenyl formazan

VG

Volume graphics

W

watt

XI

List of Tables Table

Title

number

Page number

Chapter 1 1.1

Area under conservation tillage in different countries

38

1.2

Carbon stock reported under conventional and zero-

39

tillage around the globe 1.3

Reported yields under various crops in no-till and

44

conventional tillage systems 1.4

Soil carbon sequestration rates under conservation 47 tillage

Chapter 2 2.1

Soil organic carbon stock (Mg ha-1) in different soils in 60 Sutton Bonington and Bedford

2.2

CT measured average soil porosity (%), and average 66 pore size (mm2) under different treatments

Chapter 4 4.1

Selected soil and management characteristics of the 110 experimental sites.

4.2

Statistical output from linear mixed modelling (texture,

111

tillage, duration, depth) for the physico-chemical characteristics of soils under zero tillage and conventional tillage (F statistic) 4.3

Selected chemical properties of soils under zero tillage

112

and conventional tillage Chapter 5 5.1

Microbial biomass C (MBC), microbial biomass N 138 (MBN) and total C and N at surface (0-10 cm) and subsurface (10-20 cm) layers under zero tilled and tilled soils

5.2

F statistic from analysis of variance for the absorbance 139 at different wave numbers XII

5.3

CO2 flux, CH4 flux, N2O flux and net global warming 140 potential at surface (0-10 cm) and subsurface (10-20 cm) layers under zero tilled and tilled soils

Appendix A.1

Carbon Sources in Biolog GN2 microtitre plates

186

XIII

List of Figures Figure

Title

Page

number

number

Chapter 1 1.1

Net

sequestration

of

carbon

(Mg

ha-1)

under 14

conservation tillage in comparison to conventional tillage as affected by duration under conservation tillage in tropical and temperate soils. (F1,55 = 1.42, NS overall, F1,16 = 4.40, P