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  • i

    SOIL ORGANIC CARBON SEQUESTRATION

    POTENTIALS IN AGGREGATE FRACTIONS OF

    CULTIVATED AND UNCULTIVATED SOILS OF

    SOUTHEASTERN NIGERIA

    BY:

    OKEBALAMA CHINYERE BLESSING (REG. NO: PG/M.Sc./06/41040)

    A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF

    THE REQUIREMENTS FOR THE AWARD OF THE

    DEGREE OF MASTER OF SCIENCE

    (M.Sc.) IN SOIL SCIENCE

    DEPARTMENT OF SOIL SCIENCE

    UNIVERSITY OF NIGERIA

    NSUKKA

    DECEMBER, 2009

  • ii

    CERTIFICATION

    Okebalama, Chinyere B., a postgraduate student in the Department of Soil Science, with

    the Reg. No: PG/M.Sc./06/41040 has satisfactorily completed the requirements for course and

    research work for the degree of Master of Science (M.Sc.) in Soil Science.

    The work embodied in this dissertation is original and has not been published or

    submitted in part or full for any other diploma or degree of this or any other University.

    ---------------------------------- ----------------------------------

    Prof. C. A. Igwe Prof. C. L. A. Asadu

    Supervisor Head of Department

  • iii

    DEDICATION

    This work is dedicated to Almighty God who in His infinite grace and mercy sustained

    and supported me all through, having endowed me with the intellect to complete it successfully.

    I also dedicate this work to my wonderful parents, Elder and Mrs S.U. Okebalama who

    set the standard I strive to reach.

  • iv

    ACKNOWLEDGEMENT

    My sincere gratitude goes to God Almighty for the knowledge, understanding, sustenance

    and grace granted to me for the successful completion of this research work.

    I am very grateful to my project supervisor, Prof. C.A. Igwe for his intellectual

    inspiration, guidance, encouragement, fatherly advice and provision of valuable materials used in

    the course of this work. Indeed, his intuition is incisive and I am greatly privileged to have been

    mentored by him thus far.

    My special gratitude goes to all members (past and present) of the Department; late Prof.

    J.S.C. Mbagwu of blessed memory, Prof. M.E. Obi, Prof. F.O.R. Akamigbo, Prof. C.L.A. Asadu,

    Prof. N.N. Agbim, Prof. C.C. Mba, Mr M.C. Jidere, Miss I.M. Okpara, Mr S.E. Obalum and all

    the laboratory staff for their directives, advice, suggestions, encouragement and knowledgeable

    contributions in making this work a better one.

    I also appreciate Prof. I.U. Obi, Prof. K.P. Baiyeri, and Dr P.N. Ogbonna whose

    guidance, advice and encouragement were so helpful in the project facilitation. I am thankful to

    Prof. O.A. Opara-Nadi of Abia State University, Uturu who allowed me source for relevant and

    valuable literature from his collections.

    I am particularly grateful to the members of my family, especially my parents whose

    moral and financial assistance made it possible for me to enroll in this programme. Their advice

    has greatly benefited me in my career development.

    Finally, I appreciate all my friends: Mr Funso Fasipe, Gideon Umoh, Darlington Achonu,

    Christopher Nwokocha, Chinyelu Kanemeh, Adaobi Ikeanyi, Mr and Mrs Tayo Ajayi, Emeka

    Muora, Chinedu Okoro, Chimezie Nwaimo, Ozoagu Afamefuna, and Christian Nwosu for all

    their inestimable support and involvement in seeing to the production of this work. May the good

    Lord reward and bless you all exceedingly, Amen.

  • v

    TABLE OF CONTENTS

    PAGE

    TITLE PAGE ........................................................................................................................ i

    CERTIFICATION ................................................................................................................ ii

    DEDICATION ...................................................................................................................... iii

    ACKNOWLEDGEMENT .................................................................................................... iv

    TABLE OF CONTENTS ...................................................................................................... v

    LIST OF TABLES ................................................................................................................ vii

    LIST OF FIGURES .............................................................................................................. viii

    LIST OF APPENDIX........................................................................................................... ix

    ABSTRACT .......................................................................................................................... x

    CHAPTER ONE

    1.0 INTRODUCTION .................................................................................................... 1

    CHAPTER TWO

    2.0 LITERATURE REVIEW ......................................................................................... 4

    2.1 An Overview of Global Carbon ................................................................................ 4

    2.2 Soil Organic Carbon Dynamics ................................................................................ 6

    2.3 Soil Organic Matter and Total Soil Nitrogen in Water Stable Aggregates ............... 10

    2.4 The Concept of Soil Organic Carbon Sequestration ................................................. 12

    2.4.1 Importance of Carbon Sequestration ........................................................................ 14

    2.5 Influence of Soil Carbon and Total Nitrogen on Soil Properties .............................. 15

    2.6 Effects of Land Use Management on Soil Carbon and Nitrogen ............................. 17

    2.7 Factors Affecting Soil Organic Carbon and Total Soil Nitrogen

    Pool in the Tropics ..................................................................................................... 20

    CHAPTER THREE

    3.0 MATERIALS AND METHODS .............................................................................. 26

    3.1 Site Description ......................................................................................................... 26

    3.2 Methods ..................................................................................................................... 27

    3.2.1 Field Study ................................................................................................................. 27

    3.2.2 Laboratory Study ....................................................................................................... 27

    3.2.2.1 Physical Analysis ....................................................................................................... 28

    3.2.2.2 Chemical Analysis ..................................................................................................... 29

    3.3 Statistical Analysis ..................................................................................................... 30

    CHAPTER FOUR

    4.0 RESULTS AND DISCUSSION .................................................................................. 31

    4.1 Results .......................................................................................................................... 31

    4.1.1 Soil Characteristics ...................................................................................................... 31

  • vi

    4.1.2 Microaggregate Stability Indices of the Soils .............................................................. 35

    4.1.3 Water-Stable Aggregates, Mean Weight Diameter and Geometric Mean Weight

    Diameter of the Soils ................................................................................................... 38

    4.1.4 Soil Carbon and Nitrogen Content, and C/N Ratio in the Water-Stable Aggregates .. 40

    4.1.5 Soil Organic Carbon Pool ............................................................................................ 43

    4.1.6 Land Use Effect on Aggregates Size Distribution, C, and N

    Contents of the Soils .................................................................................................... 46

    4.1.7 Soil Texture in Relation to Soil Organic Carbon Pool ................................................ 46

    4.1.8 Relationship between Aggregate Stability Indices and Soil Properties ....................... 56

    4.2 Discussion .................................................................................................................... 64

    CHAPTER FIVE

    5.0 SUMMARY, CONCLUSION AND RECOMMENDATION .................................... 70

    REFERENCES

  • vii

    LIST OF TABLES

    TABLE TITLE PAGE

    1 Global carbon pool and fluxes among them ............................................................. 5

    2 Global soil organic carbon pool ................................................................................ 7

    3 Particle size distribution and textural classification of the soils .............................. 32

    4 Chemical Properties of the soils under cultivated and uncultivated land uses ........ 33

    5 Microaggregate stability indices and water content at field

    capacity (FC) of the soils .......................................................................................... 36

    6 Soil moisture, bulk density, porosity, coefficient of linear extensibility (COLE) and volumetric shrinkage (VS) of the soils ............................ 37

    7 Water stable aggregates (WSA), mean weight diameter (MWD) and geometric mean weight diameter (GMWD) of the soils. ......................................... 39

    8 Carbon and nitrogen content (g kg-1), and C/N ratio in the various water- stable aggregate (WSA) fractions of cultivated and uncultivated soils ................... 41

    9 Soil organic carbon (SOC) pool of cultivated and uncultivated soils

    at the various soil depths. .......................................................................................... 44

    10 Land use effects on water-stable aggregate (WSA) concentration at the various soil depths, and at 0-30 cm depth. ......................................................... 47

    11 Land use effects on soil organic carbon (SOC) content in water-stable aggregates (WSA) at the various soil depths ........................................ 48

    12 Land use effect on total soil nitrogen (TSN) content in water-stable aggregates (WSA) at the various soil depths ............................................................ 49

    13 Land use effect on soil organic carbon (SOC) content in water-stable aggregates (WSA) at 0-30 cm depth .................................................... 50

    14 Land use effects on total soil nitrogen (TSN) content in water-stable aggregates (WSA) at 0-30 cm depth. ....................................................................... 51

    15 Land use effects on C/N ratio of water-stable aggregates (WSA)

    at 0-30 cm depth........................................................................................................ 52

    16 Land use effects on bulk density, > 2.00 mm water stable- aggregate (WSA), mean weight diameter (MWD) and geometric

    mean weight diameter (GMWD) of the soils. .......................................................... 53

    17 Soil texture effects on soil organic carbon (SOC) pool at the various sampling depths ........................................................................................... 54

    18 Correlation coefficient (r) among particles sizes, aggregate indices and some selected properties of the soil under cultivated

    and uncultivated land uses ....................................................................................... 59

    19 Correlation coefficients (r) of the soils chemical properties and soil organic carbon (SOC) pool of cultivated and uncultivated land uses. ....... 62

    20 Relationship between soil organic carbon (X) and structural stability indices (Y) in cultivated and uncultivated land uses (n = 12) ..................... 63

  • viii

    LIST OF FIGURES

    FIGURE TITLE PAGE

    1 Processes affecting soil organic carbon dynamics ................................................... 9

    2 Soil depth effects on soil organic carbon (SOC) pool of cultivated and uncultivated soils ............................................................................................... 45

    3 Soil texture effects on soil organic carbon (SOC) pool at

    the various soil depths .............................................................................................. 55

  • ix

    LIST OF APPENDIX

    APPENDIX TITLE PAGE

    1 Final analysis of variance of a 4 x 2 x 3 factorial experiment in

    CRD showing sources of variation and degree of freedom only ...................... 88

  • x

    ABSTRACT

    A study was carried out on soils sampled at 0-10, 10-20, and 20-30 cm depths from both

    cultivated and uncultivated soils at four different locations (Awgu, Okigwe, Nsukka I, and

    Nsukka II), to evaluate the potentials of various aggregate size fractions of varying soil textures

    and depths to sequester carbon under different land uses. A 4 x 2 x 3 factorial experiment was

    conducted in a completely randomized design (CRD). Factor A was location at four levels, while

    factor B (land use) had two levels. Factor C (soil depth) comprised of three levels. Results

    showed that in both land uses, soil texture varied with depth in each location and included clay,

    loam, clay loam, sandy loam and sandy clay loam. Generally, all the soil properties varied with

    soil depth across the locations and land uses. Land use significantly (P = 0.05) affected pH in

    KCl, Ca2+

    , Al3+

    , CEC, 0.50-1.00 mm water stable aggregates (WSA), total soil nitrogen (TSN) in

    1.00-2.00 mm WSA, and soil organic carbon (SOC) in 1.00-2.00 mm and < 0.25 mm WSA.

    Cultivation at 0-30 cm depth significantly reduced SOC in 1.00-2.00 mm WSA by 19.30 %, and

    TSN in 1.00-2.00 mm WSA by 2.50 %. Land use effects on SOC in WSA at 0-30 cm depth of

    the various locations followed no consistent trend, except that SOC was higher in cultivated than

    in uncultivated soils of Nsukka II location. The SOC pool significantly decreased with soil depth.

    The SOC pool at 0-10 cm, 10-20 cm, and 20-30 cm depths averaged 17.62, 16.40 and 13...

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