FACTORS INFLUENCING MAIZE YIELD GAPS ON SMALLHOLDER FARMS IN VIHIGA AND KAKAMEGA COUNTIES OF WESTERN KENYA MUNIALO SUSSY A80/51206/2016 RESEARCH THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF DOCTOR OF PHILOSOPHY IN AGRICULTURAL RESOURCE MANAGEMENT DEPARTMENT OF PLANT SCIENCE AND CROP PROTECTION FACULTY OF AGRICULTURE, UNIVERSITY OF NAIROBI JULY 2020 DECLARATION This thesis is my original work and has not been presented for a degree in any other University Signature …………………………………….Date…………August 3rd 2020…………… Munialo Sussy APPROVAL: This thesis has been submitted for examination with approval as University supervisors Prof. Cecilia Moraa Onyango, Department of Plant Science and Crop Protection, University of Nairobi. Signature ……… ………….Date……August 6th 2020…… Prof. Willis Oluoch Kosura, Department of Agricultural Economics, University of Nairobi. Signature … …Date……August 5, 2020………………………………… Prof. Ingrid Öborn, Department of Crop Production Ecology, Swedish University of Agricultural Sciences. Signature Date……4 August 2020 Prof Sigrun Dahlin, Department of Soil and Environment, Swedish University of Agricultural Sciences. Signature Date…...4 August 2020 ii DEDICATION I dedicate this work to my mother and my siblings for their ever continuous support through prayer and encouragement throughout the journey. iii ACKNOWLEDGEMENT I would like to express my sincere gratitude to my supervisors; Prof. Cecilia Moraa Onyango, Prof. Willis Oluoch Kosura, Prof. Ingrid Öborn and Prof Sigrun Dahlin for their tireless efforts and immense assistance throughout the research period. Despite their busy schedules, they were available for consultations physically, through emails and through telephone communication. My appreciation to the Swedish Research Councils Formas (220-2014-646) and VR for financial support. Special appreciation to smallholder farms in Mukuyu and Shikomoli who willingly donated portions of their farms for field activities. I wish to thank extension officers and field guides in Mukuyu and Shikomoli for their guidance during the field activities. Appreciation to the Crop and Nutrition Services Laboratory in Nairobi for soil analysis, the Research methods and Geoscience Laboratory staff at ICRAF for providing guidance in data collection and analysis. Many thanks to University of Nairobi research assistants; Shadrack Nyawade, Rodgers Rogito and Getrude Kabochi for their assistance in soil sampling and field work activities. I am also grateful to the Yield gap project team members: Prof. Hakan Marstop from Swedish University of Agricultural Science; Dr. Ola Hall, Prof Goran Djurfeldt, and Prof. Magnus Jirstrom from Lund University; Dr. Fred Dzanku University of Ghana, Prof. Stephen Wambugu of Chuka University and Dr. Robert Wayumba of Technical University of Kenya for their invaluable advice and support. I would like to thank World Agroforestry (ICRAF) for providing a PhD Fellowship to support my study. I also appreciate ICRAF Systems theme, Anne Omollo and Mary-Jude Kariuki, the Capacity Development Unit, Imelda Igumba, as well as the Finance, CT and Knowledge Management units for their administrative and logistical support. I wish to also thank Ibrahim Wahab; Lund University whom we jointly collaborated in overseeing the research activities. I can’t forget my colleagues; Penina Mueni, Raphael Ibanda, Tarirai Muoni, Mercy Mbugua, Samuel Omondi, Muhati, friends; Mercy Onyango, Dorcas Jalang’o, Dennis Olumeh, Joseph Nzioki and iv my family members for their support and motivation. Above all, I am so grateful to the Almighty God for inner strength, patience and health throughout the study period. v Table of contents DECLARATION OF ORIGINALITY ............................................................................................ i DECLARATION ............................................................................................................................ ii DEDICATION ............................................................................................................................... iii ACKNOWLEDGEMENT ............................................................................................................. iv Table of contents ............................................................................................................................ vi List of tables .................................................................................................................................... x Table of figures ............................................................................................................................. xii List of appendices ........................................................................................................................ xiv GENERAL ABSTRACT ............................................................................................................. xvi CHAPTER ONE ............................................................................................................................. 1 INTRODUCTION .......................................................................................................................... 1 1.1 Background ........................................................................................................................... 1 1.2 Statement of the problem ...................................................................................................... 3 1.3 Justification for the study ...................................................................................................... 3 1.4 Objectives of the Study ......................................................................................................... 4 CHAPTER TWO ............................................................................................................................ 6 LITERATURE REVIEW ............................................................................................................... 6 2.1 The yield gap concept ........................................................................................................... 6 2.2 Relevance of yield gaps analysis ........................................................................................... 7 2.3 Methods for analyzing yield gaps analysis ........................................................................... 8 2.3.1 Comparison of statistical analysis methods used in yield gap studies ......................... 11 2.4 Multi-disciplinary assessment of factors influencing yield gaps ........................................ 13 2.5 Assessing yield gaps at a local level ................................................................................... 16 CHAPTER THREE ...................................................................................................................... 17 SOIL AND MANAGEMENT-RELATED FACTORS CONTRIBUTING TO MAIZE YIELD GAPS IN WESTERN KENYA .................................................................................................... 17 Abstract ..................................................................................................................................... 17 3.1 Introduction ......................................................................................................................... 19 3.2 Materials and method .......................................................................................................... 23 3.2.1 Description of the study sites........................................................................................ 23 vi 3.2.2 Identifying and geo-referencing of maize plots ............................................................ 25 3.2.3 Measuring crop performance and weed pressure ......................................................... 26 3.2.4 Soil measurements, sampling, and analysis.................................................................. 27 3.2.5 Quantifying maize yield gaps ....................................................................................... 29 3.2.6 Data analysis ................................................................................................................. 30 3.3 Results ................................................................................................................................. 31 3.3.1 Crop performance and weed pressure at key maize development stages ..................... 31 3.3.2 Characterization of soil physical and chemical properties ........................................... 32 3.3.3 Maize yields and yield gaps in Mukuyu and Shikomoli .............................................. 34 3.3.4 Soil and Management-related Factors contributing to yield gaps in Mukuyu ............. 36 3.3.5 Factors contributing to maize yield gaps in Shikomoli ................................................ 39 3.4 Discussion ........................................................................................................................... 43 3.4.1 Consistent factors influencing maize yield gaps regardless of agroecology ................ 43 3.4.2 Agroecology-specific factors influencing maize yield gaps ......................................... 46 3.4.3 Methodological applicability and relevance in yield gap studies ................................. 48 3.5 Conclusion and Recommendation ....................................................................................... 49 CHAPTER FOUR ........................................................................................................................