EVALUATION OF PIGEONPEA WHITE YAM ( CAJANUS CAJAN [L] MILLSP DIOSCOREA ROTUNDATA [L] POIR ) CROPPING SYSTEM FOR IMPROVED YAM PRODUCTIVITY AND LIVELIHOOD OF SMALLHOLDER FARMERS By Eric Owusu Danquah A DISSERTATION Submitted to Michigan St ate University in partial fulfillment of the requirements for the degree of Crop and Soil Sciences Doctor of Philosophy 2020 ABSTRACT EVALUATION OF PIGEON PEA WHITE YAM ( CANJANUS CAJAN [L] MILLSP DIOSCOREA ROTUNDATA [L] POIR) CROPPING SYSTEM F OR IMPROVED YAM PRODUCTIVITY AND LIVELIHOOD OF SMALLHOLDER FARMERS By Eric Owusu Danquah Yam ( Dioscorea spp .) production along the West Africa yam belt is a major contributor to deforestation and soil degrada tion resulting from shifting cultivation practi ce in search of fertile land and stakes for yams to climb. This study reports on, field evaluation, simulation evaluation, and economic analysis of integrating pigeonpea into the yam cropping system described as pigeonpea - yam cropping system for improved a nd sustained yam production on continuously cropped fields. The study was conducted in the forest and forest - savannah transition agro - ecological zones of Ghana in 2017, 2018, and 2019 cropping seasons. In 2017 , pigeonpea arrangement options of pigeonpea in an alley (PA), pigeonpea as a border (PB), sole pigeonpea, and no pigeonpea field were laid - out at Fumesua and Ejura in the forest and forest - savannah transition zones respectively. These arrangements conside red the ability to obtain enough pigeonpea biom ass and stakes for the yam production in the 2018 and 2019 cropping seasons. The study used an integrated soil fertility management of pigeonpea biomass and fertilizer for yam production in both locations in t he 2018 and 2019 cropping seasons. The treatmen ts were arranged in a split - plot design in 3 replications with cropping system (yam in PA, Yam in PB and sole yam) and inorganic fertilizer level (No fertilizer, half rate 23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha and full - rate 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) as main plot and subplots respectively. Significantly (P < 0.05) higher sunlight reached the yam leaves above - canopy (AC), mid - canopy (MC), and below - canopy (BC) of the sole yam fields than the leaves of yam in PB and PA. The lower sunlight reaching these various canop y levels resulted in a significant (P < 0.05) suppression of weeds in the PA than PB compared to sole yam fields for both locations and years. The N and other nutrient contributions, moisture conservation from the pigeonpea biomass and maintained bulking m edium (ridges), resulted in a significant (P < 0.05) higher and similar tuber yield per stand and total tuber yield recorded for the pigeonpea - yam fields with a half and full fertilizer rates in both locations and years. Land Equivalent Ratio (LER) indicat ed productivity efficiency with the pigeonpea - yam intercropping systems than sole yam production with about 27 63% and 34 68% more land needed for the sole yam to produce yam as in a pigeonpea - yam intercro p for Fumesua and Ejura respectively across yea rs. The Systems Approach to Land Use Sustainability (SALUS) crop model evaluated the long - term (10 years) implication on Integrated Soil Fertility Management (ISFM) of pigeonpea residue and fertilizer. The res ults revealed, the use of pigeonpea residue, pi geonpea residue in addition to a half and full recommended inorganic fertilizer rate improved the dry tuber yield range to 4.52 - 7.26 t/ha, 5.80 - 8.84 t/ha and 7.0 - 9.99 t/ha, respectively, indicating the influen ce of the pigeonpea residue in sustaining long - term yam tuber yield. Even when a farmer has no access to fertilizer, the use of pigeonpea residue alone presents a better sustainable yam production option than the use of inorganic fertilizer alone for sole yam production. The economic analysis results revealed, planting yam with pigeonpea (PA and PB) without fertilizer had better IER than planting sole yam with full fertilizer rate in both locations. Planting yam with pigeonpea (PA and PB) with half fer tilizer rate presented a slightly lower Net Profit Value (NPV) and Internal Rate of Return (IRR) than planting yam with pigeonpea (PA and PB) with full fertilizer rate; however, the difference in values would only result in marginal income gain. These eval uations thus indicate Integrated Soil Fertility Man agement (ISFM) with pigeonpea in a pigeonpea - yam cropping system would provide stakes for staking the yams, biomass for improving soil and yam productivity, and profit to smallholder farmers. Therefore, pr omoting ion on continuously cropped fields to address the deforestation associated with yam production along the West Africa yam belt. Copyright by ERIC OWUSU DANQUAH 2020 v This thesis is dedicated to my beloved wife (Florence Owusu Danquah) , Kids (Kwadwo Owusu - Fordjour , and Abena Agyeiwaah Owusu - Danquah). Thanks for your prayers, tolerance, support during the study And to all yam farmers in Ghana and along the West Africa yam belt, may the findings of this research contribute to bett er livelihood vi ACKNOWLEDGEMENTS Praise and adoration be unto the Almighty God for his abundant grace and opportunities throughout my life and through this Ph.D. journey. I would not take these blessings and opportunities for granted. My sincere gratitude goes to my major advisor Dr. Cholani Weebad de for her encouragement and support through the program. I am privileged to have her as my advisor and have benefited from her professional network. I have had the opportunity to observe and apply her farmer technology development and transfer. My heartfelt gratitude also goes to my committee members Dr. Sieglinde Snapp (Dept. of Plant, Soil and Microbial Sciences, MS U), Dr. Bruno Basso (Dept. Earth and Environmental Sci ences, MSU) and Dr. Kurt Steinke (Dept. of Plant, Soil and Microbial Sciences, MSU) for their useful advice, time and contributions which have enriched the work. I also wish to thank Prof. Stella Ama En nin (Former director, CSIR CRI) for her continuing e ncouragement and advice towards my research as the In - country advisor. Special thanks go to Dr. S. Snapp again and her lab oratory members for opening up her laboratory facility to me and for sharing the ir experiences in the estimation of biological nitroge n fixation. Of the lab members, special mention goes to Vanessa Thomas and Chiwimbo Gwenambira, for assisting me with processing and packaging of samples sent to the UC Davis laboratory for analysis. I also wish to acknowledge Dr. Lin Liu (Dept. Earth and Environmental Sciences MSU) for her valuable support with the simulation studies using SALUS. The assistance I received from the graduate secretary and the PSM office staff throughout my stay at MSU i s much appreciated. vii This study would not have been possible without the assistance of my colleagues at CSIR Crops Research Institute. Special thanks to Mr. Felix Frimpong, Dr. Stephen Yeboah, Mr. Isaac Tawiah, Mr. Kwame Obeng Dankwa, and the technical staff of the RCM Division for their assistance in the field data collection. I am also thankful to Dr. Enock Bessah for assisting me with the map illustration of the study area. Much appreciation also goes to Farmers and Agriculture Extension officers fro m Ejura municipal, Techiman municipal, and Atebubu - Ama ntin district for sharing their experiences and assisting in the planting and harvesting of yams field at Ejura. I wish to express my profound gratitude to the Borlaug Higher Education for Agricultur al Research and Development (BHEARD) for the scholarsh ip opportunity to pursue a Ph.D. degree at Michigan State University. The BHEARD program allowed me to pursue my passion for addressing food security challenges in the face of climate change in Ghana an d Africa as a researcher with the CSIR Crops Researc h Institute. I am grateful to the Alliance for African Partnerships (AAP), MSU for the financial support to conduct my field research. Sincere gratitude goes to the Co - PIs, Dr. Hashini Galhena Dissan ayake (CANR and James Madison College, MSU), and Dr. P atricia P. Acheampong (CSIR CRI), who assisted me with the economic analysis of my research. I am grateful to Dr. Princess Hayford for sharing her experiences in pigeonpea - sorghum research in Ghana an d Mali, which was very useful for this study. Many tha nks to Ms. Patricia Sutherland for the administrative assistance provided. The AAP also sponsored the Africa R&D Connect platform at MSU, which allowed me to connect with other Africans at MSU and conne ct with faculty members and students working in Africa to widen my professional network. Many thanks to Dr. Isaac Osei - Bonsu, my CSIR CRI colleague and a fellow spartan, who assisted me in viii coordinating the Africa R&D Connect Seminar Series. I appreciate the spiritual nurturing environment the university SD A church provided during my stay in East Lansing. Last but not least, special thanks go to my wife (Florence Owusu Danquah) and my children (Kwadwo and Agyeiwaah) for bearing with my absence during my studies. Many thanks to my parents, siblings, other f amily members, and friends for your continued prayer support and being part of this journey. ix TABLE OF CONTENTS LIST OF TABLES ................................ ................................ ................................ ................. xii LIST OF FIGURES ................................ ................................ ................................ .............. xiv KEY TO ABBREVIAT IONS ................................ ................................ .............................. xvi INTRODUCTION AND RATIONAL E OF RESEARCH ................................ ................... 1 CHAPTER 1 ................................ ................................ ................................ ............................. 4 LITERATURE REVIEW ................................ ................................ ................................ ....... 4 Description of major s pecies of yams in West Africa ................................ .......................... 4 Importance and significance of yam in West Africa and Ghana ................................ ......... 5 Constraints of yam production ................................ ................................ ............................. 6 Soil fertility regeneration ................................ ................................ ................................ 6 Staking ................................ ................................ ................................ ................................ 7 Seedbed preparation ................................ ................................ ................................ ......... 8 General description of pigeonpea ................................ ................................ .......................... 9 Pigeonpea and its role in addressing constraints in yam production ............................... 10 Knowledge of the use of pigeonpea in cropping systems in Ghana ................................ ... 13 Intercropping and crop productivity ................................ ................................ .................... 14 Crop arrangement ................................ ................................ ................................ ............ 15 Evaluation of intercropping systems ................................ ................................ ................ 17 Factors influencing N fixation and dynamics ................................ ................................ ... 18 Nitrogen - fixation in cropping systems ................................ ................................ ............. 20 Methodologies for estimating N fixation in cropping systems ................................ .......... 21 Use of modeling and SALUS in cropping systems ................................ .............................. 25 Use of model in yam production ................................ ................................ ..................... 27 APPENDIX ................................ ................................ ................................ ............................. 29 REFERENCES ................................ ................................ ................................ ....................... 31 CHAPTER 2 ................................ ................................ ................................ ........................... 48 PIGEONPEA ( CAJANUS CAJAN [L] MILLSP .) - YAM ( DIOSCOREA ROTUNDATA ) CROPPING SYSTEM FOR IMPROVED YAM RESOURCE USE AND PRODUCTIVITY ................................ ................................ ................................ .................. 48 ABSTRACT ................................ ................................ ................................ ............................ 48 INTRODUCTION AND RATIONALE ................................ ................................ ............... 50 MATERIALS AND METHOD ................................ ................................ ............................ 53 Site desc ription ................................ ................................ ................................ .................... 53 Experimental design and data collection ................................ ................................ ........... 54 Soil analysis ................................ ................................ ................................ .......................... 57 Access tubes installation for soil moisture monitoring ................................ ...................... 57 Weed biomass determination ................................ ................................ ............................... 58 Determination of Biological N Fixation (BNF) of pigeonpea biomass ............................. 58 Sunlight and relativ e chlorophyll monitoring ................................ ................................ ..... 58 Yam yield and Land Equivalent Ratio determination ................................ ....................... 59 Data collection and statistical analysis ................................ ................................ .............. 60 x R ESULTS ................................ ................................ ................................ .............................. 61 Soil ................................ ................................ ................................ ................................ . 71 Yam stands and establishment ................................ ................................ ............................ 61 N yield and N fixation of applied Leafy biomass ................................ ............................. 62 Above ground competition (Competition for sunlight) ................................ ....................... 64 Stake and ridge height at harvest ................................ ................................ ....................... 64 Relative chlorophyll content of yam leaves ................................ ................................ ......... 65 Below groun d competition (Competition for water) ................................ .......................... 66 Weed pressure in the cropping system ................................ ................................ ............... 67 Resource use and yam productivity ................................ ................................ ..................... 67 DISCUSSION ................................ ................................ ................................ ........................ 72 Yam sprout rate and establishment ................................ ................................ .................... 72 N and other nutrient c ontribution of pigeonpea in the system ................................ ......... 72 Resources use and implication on yam productivity in the cropping system .................... 74 CONCLUSION AND RECOMMENDATIONS ................................ ................................ . 79 APPENDIX ................................ ................................ ................................ ............................. 81 REFERENCES ................................ ................................ ................................ ....................... 90 CHAPTER 3 ................................ ................................ ................................ ........................... 98 EVALUATING LONG - TERM YAM PRODUCTIVITY UNDER INTEGRATED SOIL FERTILITY MANAGEMENT OF PIGEONPEA RESIDUE AND FERTILIZER USING CROP SIMULATION MODEL ................................ ................................ ............ 98 ABSTRACT ................................ ................................ ................................ ............................ 98 INTRODUCTION AND RATIONALE ................................ ................................ ............. 100 MATERIALS AND METHOD ................................ ................................ .......................... 103 Study sit e and field experiment for model validation ................................ ...................... 103 Overview of the Systems Approach to Land Use Sustainability (SALUS) model ........... 105 SALUS model validation ................................ ................................ ................................ .... 107 Simulation experiment ................................ ................................ ................................ ....... 108 Statistical analysis ................................ ................................ ................................ .............. 109 RESULTS ................................ ................................ ................................ ............................ 110 SALUS model evaluation ................................ ................................ ................................ .. 110 Effect of cropping system and inorganic fertilizer on long - term yam tuber yield .......... 110 DISCUSSION ................................ ................................ ................................ ...................... 113 CONCLUSION AND RECOMMENDATIONS ................................ ............................... 116 R E FERENCES ................................ ................................ ................................ ..................... 117 CHAPTER 4 ................................ ................................ ................................ ......................... 123 ECONOMIC ANALYSIS OF A PIGEONPEA - YAM CROPPING SYSTEM OPTIONS ................................ ................................ ................................ ................................ ................ 123 ABSTRACT ................................ ................................ ................................ .......................... 123 INTRODUCTION AND RATIONALE ................................ ................................ ............. 125 METH ODOLOGY ................................ ................................ ................................ .............. 128 Experimental design and treatments ................................ ................................ ................. 128 Income Equivalent Ratio and Cost - Benefit Calculation ................................ .................. 130 Income equivalent rati o ................................ ................................ ................................ .... 131 Cost - Benefit Analysis ................................ ................................ ................................ ......... 132 Data analysis ................................ ................................ ................................ ..................... 134 RESULTS ................................ ................................ ................................ ............................ 135 Income equivalent ratio ................................ ................................ ................................ .... 135 xi Cost of production and Cost - Benefit Analysis ................................ ................................ .. 140 DISCUSSION ................................ ................................ ................................ ...................... 143 Profitability of the pigeonpea - yam cropping system ................................ ........................ 143 Profitability and environmental sustainability ................................ ................................ . 147 CONCLUSION AND RECOMMENDATIONS ................................ ............................... 149 AP PENDIX ................................ ................................ ................................ .......................... 150 REFERENCES ................................ ................................ ................................ .................... 159 CHAPTER 5 ................................ ................................ ................................ ......................... 165 CONCLUSIONS AND FUTURE RESEARCH DIRECTION ................................ ........ 165 Conclusions ................................ ................................ ................................ ....................... 165 Future research directions ................................ ................................ ................................ . 167 xii LIST OF TABLES Table 2.1 : Description of the sites used for the studies . 3 Table 2.2: Po pulation of pigeonpea and yam per plot and per hectare designed for the study . 6 Table 2.3: Total dry matter of pigeonpea biomass applied on ridges in cropping system, N yield and N due to fixation as influenced by c ropping system for 2018 and 2019 cropping season s. 3 Table 2.4: Stake and ridge height at harvest of yam in c ropping systems at Fumesua and Ejura across 2018 and 2019 cropping seasons . . 5 Table 2.5: The l and equivalent ratio of the pigeonpea - yam cropping system at Fumesua and Ejura for 2018 and 2019 cropping season s. . 1 Table 2.6: Pearson correlation of tuber yield components, sunlight intensity and ridge height at F umesua and Ejura across 2018 and 2019 cropping seasons . .. ... ..7 1 Table 2.7: Physico - chemical properties of the soil at planting of pigeonpea, at planting and harvest of yam at Fumesua and Ejura across 2018 and 2019 cropping seasons . .. 2 Table 3.1: Population of pigeonpea, yam and total pigeonpea biomass applied in the study . 4 Table 3.2: Agronomic management evaluated for long - term (10 yrs) yield implication on yam in the study . ... . ..1 09 Table 4.1a: Income Equivalent Ratio (IER) of the pigeonpea - yam cropping system under different inorganic fertilizer levels compared with sole yam with no fertilizer at Fumesua and Ejura for 2018 and 2019 cropping season s . .. .. .. 1 37 Table 4.1b: I ncome Equivalent Ratio (IER) of the pigeonpea - yam cropping system under different inorganic fertilizer levels compares with sole yam with half fertilizer rate (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) at Fumesua and Ejura for 201 8 and 2019 cropping season s . . 38 Table 4.1c: Income Equivalent Ratio (IER) of the pigeonpea - yam cropping system under different inorganic fertilizer levels compares with sole yam with full fertilizer rate (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) at Fumesua and Ejura for 2018 and 2019 cropping season . .. 39 Table 4.2: Revenue effects from yam yield gains for PA and PB intercropping system at Fumesua and Ejura for the 2018 and 2019 cropping seasons . . 0 Table 4.3: Cost - benefit analysis for pigeonpea - yam cropping system with savings deposit rate 7.43% as a discount . .. . . 2 xiii Table 4.3a : Partial budgeting and cost - benefit analysis of pigeonpea - yam cropping system at Fumesua for 2017, 2018 and 2019 cropping season s . . .. 1 Table 4.3 b : Partial budgeting and cost - benefit analysis of pigeonpea - yam cropping system at Ejura for 2017, 2018 and 2019 cropping season s. . . 5 5 xiv LIST OF FIGURES Figure 1.1: Yam production trends in major producing countries of West Africa and the world . 3 0 Figure 2.1a: Rainfall, maximum and minimum temperatures for 2018 and 2019 of the study areas (Fumesua and Ejura) . ... . 5 3 Figure 2.1b: Map showing the study area . ... . 5 4 Figure 2.2: Percentage yam stand, 2 months after planting of yam at Fumesua and Ejura for 2018 and 2019 cropping season s. .. 2 Figure 2.3: Average biwee kly (8 28 weeks after planting) sunlight photon reaching yam leaves in pigeonpea - yam cropping system at Fumesua and Ejura across 2018 and 2019 cropping seasons . ... ................................................................................. . .... ......... ..6 4 Figure 2.4: Average biweekly relative leaf chlorophyll content of yams in pigeonpea - yam cropping system at Fumesua and Ejura across 2018 and 2019 cropping season s. .. ...6 6 Figure 2.5: Weed pressure 8 weeks after planting in th e pi geonpea - yam cropping system at Fumesua and Ejura, for 2018 and 2019 cropping season s. .. ..6 7 Figure 2.6a: Fresh yam tuber yield per plant in a pigeonpea - yam cropping system at Fumesua and Ejura for 2018 and 2019 cropping seasons . . . 69 Figure 2.6b: Fresh yam tuber yield in a pigeonpea - yam cropping system at Fumesua and Ejura for 2018 and 2019 cropping seasons . . .7 0 Figure 2.7: Diagrammatic representation and arrangement of treatments on the f ield . .. 4 Figure 2.8a: Cross - section pictorial view of the yam in ridges and pigeonpea live - staking option designed for the study . . .. .. 5 Figure 2.8b: Cross - section pictorial view of the yam in ridges and cut pigeon pea stem staking option designed for the study . .. 6 Figure 2.8c: Cross - section pictorial view of the yam in ridges and bamboo staking option designed for the study . ... . 7 Figure 2.9a: Per centag e soil moisture along the soil profile of a pigeonpea - yam cropping system at Fumesua and Ejura, 2018 cropping seasons . . 88 Figure 2.9b: Percentage soil moisture along the soil profile of a pigeonpea - yam cropping system at Fumesua and Ej ura, 2019 cropping seasons . ... . . 89 Figure 3.1: Map showing the study area . ... 3 xv Figure 3.2: Overview of the System Approach to Land Use Sustainability (SALUS) . .... .. 6 Figure 3.3: Comparisons between simulate d and observed yam tuber dry matter yield across two cropping systems under three fertilizer rates in 2018 - 2019 at two sites . ... 0 Figure 3.4: Simulated l ong - term (10 yrs) yam yield, dry tuber yield (DM), under two cropping syste ms and three ino rganic fertilizer rates at two sites . . .. 2 Figure 3.5: Cumulative probability of yam tuber yield, dry matter (DM), under two cropping systems and three inorganic fertilizer rates at two sites: (a) Ejura and (b) Fumesua . 2 Figure 5 .1: The future directions of the study . .. 69 xvi KEY TO ABBREVIATIONS BNF Biological Nitrogen Fixation CAADP Comprehensive African Agricultural Development Program T CRI Crops Research Institute CSIR Council for Scientific and Industrial Research ECEC Effective Cation Exchange Capacity EPIC Environmental Policy Integrated Climate FAOSTAT The Food and Agriculture Organization Corporate Statistical Database ICRISAT The International Crops Research Inst itute for the Semi - Arid Tropics ISFM Integrated Soil Fertility Management IER Income Equivalent Ratio LER Land Equivalent Ratio MoFA Ministry of Food and Agriculture, Ghana OC Organic Car bon PA Pigeonpea in Alley PB Pigeonpea as Border pl ant PPMED Policy Planning, Monitoring and Evaluation Division, MoFA, Ghana SALUS System Approach to Land Use Sustainable SOC Soil Organic Carbon SOM Soil Organic Matter 1 INTRODUCTION AND RATIONALE OF RESEARCH In countries of West Africa, whi te yam ( Dioscorea rotundata (L) Poir) is an important food security and a cash crop to smallholder farmers. Yam, one of the two major root crops produced and consumed in Ghana, is currently a major non - traditional export crop bringing in foreign exchange t o the country. Ghana, since 2008 has ranked second in West Africa , Africa , and the worl d yam production , and contribut ing to about 16% to the National Agricultural Gross Domestic Product. Ghana is also the leading exporter of yam in Africa , contributing ab out 94% to exported yam from West Africa ( Anaadumba, 2013 ). However, yam production fa ces constraints with soil fertility sustenance and stakes for staking. Yam is a heavy soil nutrient feeder that needs fertile soils, with a ton of yam extracting a repor ted 3.8 - 4.0kg/ha of N, 0.39 - 1.1kg/ha of P 2 O 5 , and 4.2 - 5.9kg/ha of K 2 O ( Ferguso n and Hay nes 1970; Le Buanec et al ., 1972) . Staking is a significant contributing factor in the cost of yam production ( Asante, 1996 ; Owusu Danquah et al ., 2014). To address thi s constraint , farmers clear new areas yearly in search of fertile lands and stakes, leading to deforestation and soil degradation. The struggle for fertile lands and stakes , coupled with the increasing human population , has led to pressure on cropland and forestlands in the yam growing communities ( Akwag et al ., 2010; Asante , 1996 ) . As a result, the distances to fields farmers would typically want to use for yam production are farther away and more difficult to access, thereby increasing the drudgery associ ated with yam production. As a result, farmers tend to grow yam on non - fallo wed infertile land leading to reduced yields ( Akwag et al ., 2010; Otoo, 2001; Ennin et al ., 2014) . Currently, across all yam varieties, farmers can only achieve just about 20% or 1 0t/ha of the potential yield of 50 t/ha (Frossard, 2017). Therefore, soil fertility maintenance with mineral fertilizer seemed to be a viable means of addressing this issue. The CSIR Crops Research Institute of Ghana has suggested an optimum fertilizer r ate of 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha for 2 yam production on con tinuously cropped fields in the major yam growing areas of the forest - savannah transition zones of Ghana ( Ennin et al ., 2014) . However, as pointed out by Kotschi et al ., (1998), the use of mineral f ertilizer alone has not promoted good soil health Further more, it is becoming increasingly difficult for smallholder farmers who earn less than US $1per day to afford fertilizers. For these reasons, alternative ways of sustaining the soil for yam and othe r crop production is gaining more considerable attention ( Otoo et al ., 2008; Garrity, 2004) . While traditional organic materials such as crop residues and animal manure seemed to be cheap sources for soil amelioration, they are bulky and availability in m ost cases is limited in supply to offer a real alternative ( Kotschi et al ., 1998; Young, 1997; Diby , 2011) . This study evaluates the adoption of leguminous shrub, pigeon pea, in the yam cropping system for sustaining soil fertility for yam production. The p igeonpea would provide readily available biomass for soil fertility improvement and stakes for the staking of the yam. Despite all the positive attributes of pigeonpea, as observed by Pinstrup - Andersen (1982), the adoption of any agricultural intervention depends on their usability and ability to meet the needs. Therefore, we depended on an earlier socio - knowledge and willingness to adopt the pigeonpea - yam cropping system (Acheampong et al ., 2019). This survey guided th e designing and development of a cost - effective pigeonpea - yam cropping system that considers the local context, gender differences, and resource constraints . Working on the hypothesis that yam productivity would improve significantly with the inclusion of p igeonpea in the yam cropping system, the specific objectives of the study were to; i. estimate N contribution from the biomass of the pigeonpea and implications on yam productivity in a pigeonpea - yam cropping system. 3 ii. stimulate long - term yam productivity i n the pigeonpea - yam and implications on sustainable yam production on continuously yam cropped fields. iii. evaluate the profitability of the pigeonpea - yam cropping system. 4 CHAPTER 1 LITERATURE REVIEW Description of major species of yams i n West Africa Yams are a monocot (Monocotyledons) species, related to lilies and grasses. Native to Africa and Asia, yam tubers vary in size from that of potato from small to over 60 kg per tuber. It belongs to the genus Dioscorea, a large genus that contains important species used as food rich in carbohydrates (Mandal, 1993; Mignouna et al ., 2009; Bai et al ., 1998 ). In many parts of the world, and specifically in West Africa and the Pacific islands, Dioscorea is a primary staple food, and a food security crop (Coursey, 1967; Scott et al ., 2000). The most famous and widespread species of yam cultivated and native to Afric a include white or guinea yam ( Dioscorea rotundata ), yellow yam ( Dioscorea cayenesis ), and water yam ( Dioscorea alata ) (Aseidu et al. , 2008; Mignouna et al ., 2007). Dioscorea rotundata (white or guinea yam) is native to Africa and the most cultivated yam in Africa. The name emanates from the color of the fresh tuber, which is firm and white with a roughly cylindrical shape, whiles the skin is smooth and brown (Coursey, 1967; Akoroda, 1983; Demuyakor et al ., 2013; Otoo et al ., 2009). The yell ow yam ( Dioscor ea cayenesis ) is also native to Africa and has yellow flesh resulting from carotenoids (Kay, 1987; Hamon and Toure, 1990). Although most taxonomists now regard D. rotundata and D. cayenesis as the same species, the D. cayenesis has a more ex tended period o f vegetation and a shorter dormancy than white yam (Sartie et al ., 2012; Djeri et al ., 2015; Asiedu et al ., 2008). The growth period of both species is between 7 12 months (Ennin et al ., 2016; Mandal, 1993). Dioscorea alata (water or grea ter yam), anoth er economically important yam, originating from Asia, has the most extensive distribution world - wide of any cultivated yam in Asia, the Pacific islands, Africa, and the West Indies (Mignouna and Dansi, 2003). Even in 5 Africa, the popularity o f water yam is second only to white yam. Compared to white yam, water yam stores longer than white yam, making it a vital role in the food security niche. It is easier to propagate, grows vigorously to suppress weed, and can be grown without stakes (Sartie and Asiedu 201 4; Obiediegwu et al ., 2009; Owusu Danquah et al ., 2014). Also, it has high protein content (7.4), starch (75 - 84%), crude fiber (2%), and vitamin C (13 24.7mg/100) than D. rotundata (Behera et al ., 2009; Oluwole et al ., 2017). Despite these attributes, D. rotundata has more preference and market value than D. alata due to supposedly unattractive food the favorite cohesive and elastic dough in fufu . Also, it is susceptible to pests and diseases, tubers lacking smooth and aest hetics making them unappealing to consumers in the market (Obidiegwu, 2009). Other yam species produced in fewer quantities globally include D. esculenta (Chinese yam) native to China, D. bulbifera (aerial yam) native to both Africa and Asia, and D. du mentorum (Bitter yam) native to West Africa (Kay 1987; Schultz, 1993; Ike and Inoni, 2006; Coursey, 1967; Lebot, 2009). Importance and significance of yam in West Africa and Ghana Yam production in West Africa has food, social, and cultural values (Ege si et al ., 2007; s Nigeria and produces about 92% of the 50 60 million tons of global yam pr oduced annually (FAOSTAT, 2019; Nweke, 2016). Yam is a significant food securit y crop and a major source of income for smallholder farmers (FAOSTAT, 2016; Wanyera et al ., 1996; Nweke, 2016). Currently, Ghana is the second - largest producer of yam in West Af rica after Nigeria, with an estimated production volume of 7m tons since 2013, of yams, exporting over 94% of the total yam exports from West Africa (Anaadumba, 2013). 6 increased from US$ 32.6 million in 2017 to US$ 38 million in 2018 ( Ghana Export Prom o tion Authority (GEPA) report , 201 9 ). Constraints of yam production Among the significant challenges of y am production are soil fertility regeneration, scarcity of stakes for staking, Seedbed preparation, and high cost of seed yam (Akwag et al . , 2010; Ennin et al ., 2014). Soil fertility regeneration Yam is a heavy soil nutrient feeder, and as a result, farm ers move to new lands each year in search of fertile lands and stakes, leading to deforestation. This struggle for fertile land coupled with increasing human population has led to pressure on cropla nd and forestland in the yam growing communities (Ennin et al ., 2014; Asante, 1996; Ekanayake and Asiedu, 2003). The length and quality of fallowed land and available fertile land keeps reducing. The distance to yam fields is increasing and becoming harder to access. As a result, farmers often do not have a choic e except to grow yam on non - fallowed land where pressure on land is intense. For example, in Sekyere - West and Ejura - Sekyedumasi districts of Ghana, major yam growing areas, the forested land before 1983 was 782km 2 , it was predicted to decrease to 78.2km 2 i n a decade whiles the grasslands would increase from 1337km 2 to 2247km 2 in the same period (Akwag et al ., 2000). MoFA report 2017 revealed agricultural lands between 1975 and 2000 increased from 13% to 28% of the total land area cover. As of 2013, agricult ural land has reached 32% and keeps increasing due to agriculture expansion. 7 Staking Staking is an essential practice in yam production; it exposes the leaves and vines to sunlight and helps increase photosynthetic efficiency resulting in high tuber yi elds. Diby et al . , 2011, observed in a study that the higher leaf area index of water yam ( D. alata ), as compared to white yam (Dente) ( D. rotundata ), served as an advantage to capture sunlight to produce more yields. The stakes also lift the leaves and vi nes from the ground to reduce soil - borne diseases (Ndegwe, 1990). Otoo et al . (2008) obse rved a significant increase in tuber yields between 45 56% in staked white yam ( D. rotundata ) varieties compared to their non - staked counterparts. Diseases such as l eaf spot were very severe on the non - staked white yam contributing to the reduction in tu ber yields. A similar study evaluated the various staking options, including no staking, staking practiced by farmers/optimum staking, and trellis staking and a 50% nu mber of stakes on white yam and water yam varieties. The findings indicate that the no - st aking option resulted in a significant reduction of tuber yields of white yam. Also, the mosaic virus significantly affected the no - staked white yam ; thus, accounting partly for the reduction in tuber yields (Owusu Danquah et al ., 2014; Ennin et al ., 2014) . As such, staking is crucial to yam productivity and a significant component of the cost of yam production. Farmers would, therefore, cut trees and shrubs in search o f stakes for their yam production, contributing to deforestation and land degradatio n. In Ghana, the forest - savanna transition and the guinea savanna zones produce the most quantity of yam. In the forest - savannah transition zone, farmers leave selected tre es and shrubs as stakes. Most trees die and get weak upon burning, but farmers conti nue to use them as stakes (Asante, 1996; Wholey and Haynes, 1971). In the guinea savannah, where stakes are scarcer and more difficult to obtain, farmers cannot provide sup port for their yams, thereby affecting yields (Asante, 1996). 8 Seedbed preparation Seedbed preparation is also a significant constraint in yam production. The approach to cultivating yam involves preparing mounds, and this approach of land preparation is labor - intensive and time - consuming, adding to the drudgery associated with cultivati ng yam (Ennin et al . due to the effort required to cultivate the crop. Land clearing and moundin g are done solely by men in almost all yam - growing areas. Women only cut setts and p ut them on the mounds for the men to plant (Nweke et al ., 1991; Baudoin and Lutaladio, 1998). Tetteh and Saakwa (1991) observed mounding to be the highest cost of operation in the production of yam for the savannah and transition zones of Ghana. It is to a ddress this constraint that resulted in the promotion of mechanized ridging as an alternative. On mounds, only about 5,000 to 6,000 plants per hectare are achieved compared to about 9,000 to 10,000 plant s per hectare achieved with ridging (Ennin et al . , 20 14; Anchirinah et al ., 1996). F ertilizer application also significantly increases tuber yields by about 30% on ridges than on mounds. Ridges are more favorable to mounds w hen it comes to other farm operations such as weeding, fertilizer application, and h arvesting (Eninn et al ., 2009; Ennin et al ., 2014). As yam is a heavy nutrient feeder, a recommended fertilizer rate of 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha is optimum to sustain yam production on continuously cropped fields (Ennin et al ., 2014; Ennin et al., 2016). However, for smallholder farmers who earn less than US $1per day, purchasing fertilizer to improve yam yields is not a viable option. Therefore, it is becoming increasingly apparent that farmers need alternative ways of sustaining soil fertility fo r yam and other crop production (Garrity 2004). Besides, the use of mineral fertilizer alone does not promote good soil health (Kotschi et al ., 1998). Although traditional organic material such as crop residue and animal manure are cheap sources for soil a melioration, its availability in most cases is limited in supply to offer a real alternative (Kotschi et al ., 1998; Young, 1997; Diby, 9 2011). It appears increased yam producti on is directly link ed to the area under cultivation. Figures from PPMED (2007), o f the Ministry of Food and Agriculture, Ghana indicate that yam production in Ghana increased by 51.6% with a corresponding increase in area under cultivation of about 53.6% during the same period, suggesting that, a 1% increase in area under yam cultivati on lead to a corresponding 1% increase in yam productivity. While the potential 33.5 % of this potential (MoFA, 2017). These figures call for technologies that w ould address the problem of deforestation associated with yam production by sustaining soil fertility and the provision of stakes, especially on continuously cropped fields. Ge neral description of pigeonpea Pigeonpea [ Cajanus cajan ( L.) Millsp .] belon gs to the family Fabaceae, tribe Phaseoleae subtribe Cajaninae and genus Cajanus (Sharma and Green, 1980; Singh and Oswalt, 1992). The plant is an erect woody shrub with branching. It has a robust taproot system, and harvest duration depends on the variety . Pigeonpea can grow up to a height of about 1 2m, and 3 4m when used as perennials in the cropping system (Singh and Oswalt, 1992; Mula and Saxana. 2010) . The origin of pigeon pea has led to a significant dispute among historians . Plukenet (1692) reported that the plant originated from Barbados, based on its use as animal feed, while oth ers considered the plant to have originated from Eastern Africa since it occurred there in the wild form (Zeven and Zhukovsky, 1975). An extensive review by De (1974) and Vernon Royes (1976) suggest India as the primary center of origin and Africa, the sec ondary center of origin of pigeonpea. At present, several countries in the tropics and subtropics cultivate pigeonpea. Pigeonpea can be cultivated in a broad range of conditions and soil types because it is drought tolerant with an ability to use residu al moisture during the dry season 10 (Phatak et al ., 1993; Mullen et al ., 2003; Cook et al ., 2005; Mula and Saxena, 2010). The only known cultivated food crop of the 32 species that fall under the Cajaninae sub - tribe is pigeonpea. Pigeonpea takes up about 5% of et al ., 2000; FAOSTAT 2019: Young et al ., 2003), with India producing around 70% and East Africa about 18% (FAOSTAT, 2019). Production in Africa is mainly in East Africa, with an average yield of about 718 K g/h a. An increase in production has been observed recently in East Africa, but this is mainly due to expansion in area under cultivation than an increase in productivity (Jones et al ., 2002; Damaris, 2007). Indigenous or wild varieties are highly photoperi od sensitive (McPherson et al ., 1985), and they take about 175 to 280 days to reach maturity. Improvement work mainly by the International Crops Research Institute for the Semi - Arid Tropics (ICRISAT) on pigeonpea resulted in the development of early, mediu m, and long maturing lines. These new lines mature in about 110 - 150 days, 150 - 200 days, and 220 270 days for short, medium, and long duration lines, respectively (Saxena et al ., 2007; Kananji et al ., 2009; Mula and Saxena, 2010). These lines are also r ela tively insensitive to the photoperiod compared to the indigenous or wild accessions (Saxena et al . 2007) . Pigeonpea and its role in addressing constraints in yam production With their ability to fix biological nitrogen, sustainable cropping systems o ften use leguminous crops and shrubs as a significant constituent, an approach that could also benefit yam cultivation (Ennin and Dapaah, 2008; Asafu - Agyei et al ., 1997; Kombiok et al ., 1997; Eze, 2010). The proposed study adopts integrated soil nutrient m anagement with leguminous shrub - pigeonpea ( Cajanus cajan ) for sustainable yam production. The drought - tolerant nature of pigeonpea and its ability to adapt to a wide range of soils suggests its suitability for sustainable farmin g and soil fertility manag ement in Africa (Adjei - Nsiah, 2012; Troedson et al .,1990; Damaris, 2007). Compared to other legumes, the ability to adapt to drought result s 11 from its unique character traits of the deep taproot system of the plant, which allows it to withstand severe droug ht conditions. As such, pigeonpea could give some grain yields under conditions when other legumes such as cowpea and field beans dry up and will not yield (Valenzuela and Smith, 2002; Flower and Ludlow, 1987; Subbarao et al ., 200 0). Pigeonpea can maintai n photosynthetic functions under stress conditions. Its distinct polycarpic and flowering ability enables pigeonpea to protect the reproductive structures and produce yields better than other legumes (Lopez et al ., 1987; Mligo and Craufurd, 2005). Thus, pi geonpea could be a valuable crop that could protect smallholders against total loss and food insecurity (Snapp, 2003; Snapp 1998). Also, the grains of pigeonpea can serve as an additional source of income and nutrition to smallhol der farmers as its grains are nutritionally well balanced and are an excellent source of protein (20 30%), carbohydrates, and high levels of useful in crop produc tion, especially for small holder farmers. Although abundant in the atmosphere, nitrogen is considered the most limiting nutrient in crop production (Vance, 2001). Pigeonpea can fix about 235 kg N/ha and produces more N per unit area from its biomass than o ther legumes (Peoples et a l ., 1995; Giller and Cadisch, 1995). However, differences in the N contribution from pigeonpea grown in different locations have been observed. Through biological nitrogen fixation, pigeonpea contributed 38 117 kg N/ha and 6 7 2 kg N/ha in pigeonpea m aize intercropping systems in Malawi and Tanzania, respectively (Adu - Gyamfi et al ., 2007). Phiri et al ., (2013) using the long term (about eight months maturity duration) and medium - term (about six months maturity duration), pigeo npea as intercrop also obs erved biomass of about 2 2.6 t/ha which contributed about 49.6 50.6 kg/ha N to the soil. Gwenembia (2015), using a medium maturing pigeonpea variety observed an above - ground biomass yield of 11.83 Mg/ha, 6.99 Mg/ha, 5.08 Mg/ha and 3.57 Mg/ha for sole p igeonpea, pigeonpea groundnut intercrop, pigeonpea soybean intercrop and pigeonpea maize 12 intercrop, respectively. The slow initial growth nature of the plant makes it a good companion crop for integration into cropping syste ms (Snapp, 1998). Due to t he extensive root system of especially the late - maturing pigeonpea, it improves the nutrient cycling efficiency for the benefit of the associated crops in the cropping system (Snapp, 1998). It also can form root symbiotic associat ions and secretion of orga nic acids from its roots, improving the uptake of P even from soils with fixed P (Otani et al . , 1996; Vance, 2001). In a study where pigeonpea was used as a preceding crop and plowed into the soil before planting the yam, there wa s a significant increase i n yam tuber yields. When yam followed pigeonpea as a preceding crop, tuber yields were higher, and yields from 3t/ha poultry manure and 15 - 15 - 20 kg/ha N - P 2 0 5 - K 2 0 was similar to the yields when manure and fertilizer were doubled to 6t/ha and 30 - 30 - 40 kg / ha N - P 2 0 5 - K 2 0 ( Ennin et al . , 2013) . Although this unique leguminous shrub can be used in soil fertility management, it has received little research attention, especially in West Africa. e t al ., 2004; Damaris, 2007). Kumar Rao and Dart (1987) and others observed the ability of the long - to medium - maturing varieties of pigeonpea to fix more N and produce more biomass than early maturing varieties. This biomass attribute presents a unique opp ortunity for its use in cropping systems such as white yam, which takes abo ut 8 12 months, depending on the variety to maturity (Ennin et al. , 2016). As such, we believe that the adoption and use of the long and medium maturity varieties of pigeonpea as perennials in a yam cropping system would provide biomass and readily avail able stakes to smallholder farmers for sustainable yam production in Ghana and West Africa. 13 Knowledge of the use of pigeonpea in cropping systems in Ghana ceptions, and importance attached to a crop, tree/shrub, and technologies a re fundamental towards the adoption of agricultural technologies ( Pinstrup Andersen, 1982; Feder and Umali, 1993). Farmers in West Africa are used to intercropping or rotating legu mes such as cowpea, groundnut, and B ambara groundnut with cereals (maize, s orghum, millet and guinea corn). However, the cultivation of a legume such as pigeonpea known to fix more N per unit area is observed to be novel and negligible in Ghana despite its potential for soil fertility improvement and sustainable crop yields (Peop le et al ., 1995; Hayford, 2018; Adjei - Nsiah, 2012). Field research on pigeonpea in Ghana revealed a significant return of biomass to the soil, which resulted in increased soil carb on and yields of associated crops (Hayford, 2018; Agyare et al ., 2002). In a farmer - field demonstration trial using cover crops for improved soil fertility management, farmers selected pigeonpea over mucuna (Adjei - Nsiah et al ., 2007). Acheampong et al . (20 19) observed in a socio - economic survey on pigeonpea - yam cropping system that a majority (75%) of yam farmers had no knowledge of pigeonpea and it s use in cropping systems. However, they were willing to adopt upon alert on its importance for soil fertility and as a source of stakes for staking yams. The major bottleneck indicated by farmers to hinder the adoption of pigeonpea in their cropping system was the marketing of produce, land tenure, and access to high and early yielding varieties. Therefore, bree ding and releasing ns alongside offering participatory farmer demonstrations to showcase the potential of pigeonpea in cropping systems, was identified as the way forward towards adoption (Adjei - Nsiah et al ., 2012; Acheampong et al ., 2019). Thus, farmers, when educated on th e potential benefits of integrating pigeonpea in their cropping systems and are encouraged to adopt it, pigeonpea would play a vital role in soil fertility sustenance and food security. 14 In tercropping and crop productivity In Africa and Asia, intercroppi ng, the practice of growing two or more crops together in the same field at a given time, is common and is more productive than monoculture (Morris and Garrity, 1993; Sakala, 1998). Intercr opping results in increased productivity compared to the sole crop s as a result of complementary use of resources, where the different crop components explore resources at different niches for the benefit of another component crop(s) ( Ofori and Stern, 1987 ; Rao and Singh, 1990; Willey, 1990 ). Thus, interactions between c rop species in a field for both below ground and above ground resources result in competition or facilitation between or among the crops (Vandermeer, 1990; Rao et al ., 1997). When species in a cropping system share the same or similar resources, and a crop interacts negatively or interferes with the growth and development of the other, it is described as competition and reduced productivity. For example, Budelman (199 0) evaluated the effect o f growing three leguminous perennials Leucaena leucocephala , Flemingia macrophylla, and Gliricidia sepium, on the yield of yams. The study found that given the high root density of the L. leucocephala at the upper soil stratum, i t competed with the yam. Simultaneously, the weak insufficiently lignified branches of the F. macrophylla could not support the yam leaves and vines, resulting in reduced tuber yields. However, because G. sepium roots do not compete with the yam and its lignified branches could hold the yam leaves and vines, the study found intercropping G. sepium with yam to improve tuber yield than L. leucocephala and F. macrophylla . Another study by Simpson (1999) found that soybean yield was severely affected when int ercropped with maize, due to shading, small shallow root systems, and inherently low water use efficiency. However, another soybean - maize intercrop study observed that it facilitated a higher photosynthetic active radiation capture by soybean - maize intercr op than their respective sole crop. This higher capture resulted in a significantly (P < 0.05) higher dry matter productivity on the soybean - maize intercrop than their corresponding sole crops (Ennin 15 et al., 2002). The example of G. sepium - yam and soybean - maize intercrop above are examples of facilitative interaction. A facilitative interaction is when one crop in an intercropping system exerts a positive influence on the growth. The positive influence could be providing soil nutrients or a con ducive microclimate. Zhan g and Li (2003) compared yield advantages of a set of cereal - legume cropping systems and observed interspecific facilitation in maize - peanut intercropping, where maize improved the iron nutrition of peanut. The nitrogen and phospho rus uptake by intercroppe d maize was enhanced by faba bean whiles P uptake by associated wheat from phytate - P was facilitated by chickpea. Furthermore, Li et al. (2001) evaluated the yield advantage, N, P, and K uptake by wheat, maize, and soybean in an in tercropping system. They found that the yields and nutrient uptake of intercropped wheat, maize, and soybean were significantly higher than in their sole cropping systems. Crop arrangement Agro - ecological and adaptive management practices are essential for sustainable intensif ication and crop production. The cultivation of woody trees/shrubs in specific intercropping combinations with food crop species enhances resource use efficiency in agro - ec ological systems (Young, 1997; Ong 1991). Strategies for growing crop/s and woody t rees together can be in mixed, strip, and relay to increase resource use efficiency and facilitation in cropping systems to increase crop productivity. In mixed intercropp ing, crops and woody tree species are grown together at the same time in a field wit hout any spatial arrangement. In contrast, in strip intercropping, the crop/s and woody tree species are grown simultaneously in separate but adjacent rows or strips. On th e other hand, relay intercropping involves planting the crop/s and woody species tog ether in a staggered arrangement such that only parts of the life cycle of the crop species overlap (Bybee - Finley and Ryan, 2018: Young, 1997). The improvement in resource use efficiency in 16 intercropping systems result s from the increase in total above and below - ground resource capture (sunlight, water, and nutrients) of the crop/s and the woody trees (Ong, 1991; Young, 1997). The addition of organic inputs from the woody tr ees or crops intercepts and reduces run - off to prevent erosion. Also, the liter fall and root turn - over improve nutrient cycling and retention in the cropping system for the benefit of associated plants (Rao et al ., 1998; Ong, 1996). The use of mineral fe rtilizer only does not promote soil and environmental health and has been observed n ot to be efficient in yam production. Hgaza et al. (2012) observed a maximum recovery of just 30% of N fertilizer in yam tuber, leaving the rest to go waste and to the environment. Therefore, intercropping or rotating yams with legume crops or woody perenn ials have been observed to be the way forward in supplying N, improving nutrient cycling, and increasing yam productivity (Frossard et al ., 2017; Ennin et al. , 2013; Ma liki et al ., 2012a). Intercropping yam with Gliricidia sepium , a woody legume improved biological nitrogen fixation and provided live stakes for the yam vines to climb (Budelman, 1990; et al., 2008). Substitutive and Additive series crop arrang ement s are the most used approach es in Agriculture studies for arranging mixed crop comp onents in intercropping systems (Hamilton, 1994; Geno and Geno, 2001). In the substitutive/replacement approach, proportional populations of each crop component in the polyculture are related to the population of the sole crop. However, the population of t he component crops should always add up to 100%. Whiles in the additive/superimposed approach, the component crops are planted in the same fields using the optimum plan ting density of the sole crops such that the final population of the polyculture is gene rally more than the planting densities of the sole crops. Thus, the constituent monoculture crop population compared to the intercrop population is used in distinguishi ng between the arrangement approach used. For example, if two crop components are involv ed in a substitutive/replacement approach, the bi - culture population of 17 each crop component would be a percentage of the population of the monoculture. Whiles in the ad ditive/superimposed series, the bi - culture has the same population of each crop as in th eir monoculture (Bybee - Finley and Ryan, 2018; Gebru, 2015; Cousens, 1996). The substitutive method is useful for evaluati ng of weed - crop interactions, competition, and yiel d advantage in intercropping (Rodriguez,1997; Firbank and Watkinson, 1990). With the sub stitutive intercropping, the population of each component crop is adjusted down with the intention that if one plant all the component crops with optimum population, co mpetition for above ground (sunlight) and below ground (water and nutrients) resources w ould result in the low overall productivity of the cropping system. However, Sullivan (2003) observed that the challenge would be determining the optimum planting densi ty for each component crop in the mixture. In the additive approach, the challenge will be in dealing with competition for resources and the practicality of combining the component crops at their optimum populations on the same unit area as the sole crops . Evaluation of intercropping systems Several intercropping efficiency indicators exis t, such as the Relative yield total (RYT), Area Time Equivalency Ratio (ATER), Protein production, and Financial Returns. The most widely used indicator of efficiency in intercropping systems is the Land Equivalent Ratio (LER). It is the total area require d under sole cropping to give the yields obtained in the intercrop. That is a summary of ratios of yields of intercrop to the yield of the sole crop. When L ER is greater than one (1), it means there is a yield advantage for using intercrop. LER equal to 1 means no gain or loss in using intercrop whiles less than one means yield loss for using intercrop ( Willey 1985; Ofori and Stern, 1987 ). The LER may overes timate the advantages of intercropping, where one component crop can be harvested early, leaving the other to occupy the whole land as a sole crop. Besides, LER does not compare and account for differences 18 between the yield obtained with the potential yiel d. As such, it does not indicate whether the yield is higher or lower than the potential yield of th e crop/s ( Willey, 1979 ). Fukai and Trenbath (1993) observed that the best productivity from an intercrop could be obtained if the component crops differ sig nificantly in growth duration so that their optimum requirement for growth resources occur at differ ent times. Factors influencing N fixation and dynamics Intercropping of cereals and other crops with legumes is an ancient practice with the potential ben efit of maximizing the use of resources such as sunlight and nutrients. It is a prevalent practice, especially in the tropics, to address soil fertility loss in the face of limited access to inorganic fertilizers (Willey, 1990; Morris and Garrity, 1993). T he leguminous crops and shrubs in cropping systems fix N and improve soil nutrition by incorporating their biomass to benefit the associated crops (Ennin and Dapaah, 2008; Asafu - Agyei et al., 1997; Kombiok et al ., 1997; Budelman, 1990). However, the crop species used (Dakora and Keya, 1997; Eaglesham et al., 1982), agronomic management (People et al ., 19 95), plant species morphology (Wahua and Miller, 1987), and the planting density of legumes in the mixture and competitive ability of the associated c rops (Fujita et al ., 1992; Danso et al., 1987) among others, influence the quantity of nitrogen fixation i n the cropping system. Through the biological nitrogen fixation (BNF), seasonal grain legumes and tree legumes fix about 43 58 kg N/ha and 15 210 kg N/ha respectively for sustainable crop production in Africa (Dakora and Keya, 1997). Eaglesham et al . (1982) observed that although cowpea fixed less N compared to soybean, its residue, left on the soil, contributes more N than soybean. Soybean has a h igh harvest index for N, resulting in loss of more N in the harvested seeds than the N left in the soil an d the residue. Peoples, et al . (1995) observed that sufficient Nitrogen - fixing symbioses between legumes and their N 2 fixing bacteria (rhizobia) is affected by the 19 environmental factors, which is also greatly influenced by management practices. There is a strong influence of soil management practices on the absence and presence of enough effective rhizobia in the soil for N - fixation. Biological Nitro gen Fixation (BNF) is an adaptation strategy used by leguminous crop species to obtain N for growth and de velopment. Increasing soil mineral N through management practices limits the presence of effective rhizobia. As such, there is reduced BNF due to the presence of less nodulation and nitrogenase activity (Peoples et al ., 2009; Wahab et al ., 1996; Herridge e t al ., 1984 ; Purcell and Sinclair, 1990). Wahua and Miller (1978) observed that in sorghum soybean cropping system with a taller sorghum variety, N fixation at the early stage of podding, was reduced by 99% while yields were reduced by 75%. The shading effect from the tall sorghum affected the podding, and yield. Also, the difference in nitrogen - fixing and non - nitrogen - fixing associated crop root mor phology and depth can influence their different abilities to use soil N (Chalk, 1985). Increasing plantin g density of faba beans either as a sole crop or intercropped with barley increased competition for N, which results in an increasing proportion of th e fixed N in the faba beans. The density effect was more pronounced in the intercrop barley field than sol e faba bean fields (Danso et al ., 1987). Fujita et al ., 1992 observed that the intermingling of root systems transfers N through, and therefore, the distance between the cereal and legume root systems is vital for the interaction. However, the most effect ive planting distance varies with the type of legume and cereal. Corre - hellou et al . (2006), using a pea barley intercrop, found that, in the intercro p, barley competed strongly for soil N with competition increasing steadily during the vegetative phase. T his stiff competition from the barley for soil N influenced the N fixation response of the pea and the quantity of N used by the pea. Using an optimum arrangement of plants and pruning of the above - ground structures could address the shading of associated crops in an intercropping system. The pruned biomass, when added to the soil, could further increase soil nutrition. 20 Nitrogen - fixation in cropping sy stems The main aim of intercropping with legumes is to fix N by the legumes for the transfer and benefit of the non - legume associated crops. There are interactions both above and below ground, that aid in the transfer of nutrients in the system. Ong et al . (1991) observed in alley cropping systems of the semi - ari d tropics, that below ground interactions are m ore important than atmospheric or above - ground interactions. Fujita et al . (1990) observed that the inoculation of cowpea seeds used in cowpea maize intercropping system increased nitrogen - fixation of the cowp ea, and the N transferred to the associated mai ze crop. In a soybean sorghum - intercropping system, 32 58% of total N of the sorghum planted at 0.125 X 0.125m was due to the nitrogen - fixation from the soybean. As such, the relative proximity of the legume a nd non - legume crops is vital for e nsuring N transfer between crops in cropping systems. The same study also observed N transfer to be high when other N sources such as the soil are limited. Thus, integration of pigeonpea into the yam cropping systems in Ghana and West Africa where soils a re limited in N and other nutrients (Ennin et al ., 2002) would aid the high transfer of N to yam. Using an isotopic method of 15 N abundance, Snoeck et al . (2000) show that about 30% of the N - fixed in a legume coffee intercropping systems end up in the cof fee. Nutrients included in a system are in the continuous dynamic transfer. Plants return their nutrients to the soil either through natural litterfall or deliberate pruning in agroforestry systems (Nair et a l ., 1995; Nair et al ., 1998). The pigeonpea use d in a pigeonpea yam cropping system needs pruning to avoid a closed canopy. The biomass from pruning can be incorporated into the soil to contribute N to the system. The above and below ground interactions be tween the species and the associated crop are a significant determinant of crop yields, especially for root and tuber crops. 21 Methodologies for estimating N fixation in cropping systems There are four main approaches used in the estimation of Biological Nitrogen Fixation (BNF) in the intercropping sy stem. These are a) Total Nitrogen Difference (TND) b) Acetylene Reduction Assay (ARA) c) Ureide Xylem Sap technique, and d) 15 N labeling technique ( Unkovich et al ., 2008; Danso 1995 ). The Total Nitrogen Difference (TND) technique is the oldest approach us ed in BNF estimation. It estimates BNF as the difference between the total N fixed by a nitrogen - fixing plant and a non - nitrogen - fixing reference plant. This approach assumes that both the nitrog en - fixing plant and the non - nitrogen - fixing reference plant a bsorbs equal quantities of soil N for growth and development. This assumption requires that the physiological attributes, maturity period, root morphology, and root depth operations of the nitrog en - fixing plant and the non - nitrogen - fixing plants should be similar, but this is not always the case, hence a significant weakness of this approach (Danso et al ., 1992; Rennie and Rennie, 1983). Despite this weakness, estimations using this approach compa red with the more sophisticated and expensive methods reveale d similar results (Hardarson et al ., 1988; Hardy, 1973). Thus, the approach is simple and inexpensive when compared to others. However, because BNF is higher in soils and systems with low N, this approach is observed to give a more reliable result when pla nts are grown on soils with low initial N (Rennie, 1984; Patterson and LaRue, 1983). Also, the choice of reference crop affects the estimation of BNF, therefore a mutant non nodulating version o f a legume and more than one reference non - legume crops would help improve on the reliability of the results (Unkovich et al ., 2008; Kermah et al ., 2018). The Acetylene Reduction Assay (ARA) is an indirect approach in estimating BNF pioneered by Hardy et al ., (1968). The ARA focuses on the nitrogenase enzyme that c atalyzes the reduction of acetylene to ethylene (Dilworth, 1966). Nitrogenase is the enzyme involved in N 2 22 no dules, or detached nodules is incubated in a gas - tight chambe r containing 0.03 to 0.1% (v/v) acetylene for a period. After the period, the gas from the gas - tight chamber is injected into a gas chromatograph fitted with a P column and assayed for ethylene p roduction. The quantity of ethylene produced is converted to a total amount of N - fixed by multiplying by a conversion factor of 3 ( Unkovich et al ., 2008) number of analyses per day to make it advan tageous. However, the ARA technique measures BNF over a short duration whiles BNF in plants occurs over a very long duration. T he method uses extrapolations to cover a more extended period, including periods where measurements are not taken but does not account for seasonal and other variations in BNF (Zapata et al . , 1987a; Zapata et al ., 1987b; Rainbird, 1983). Also, it is chall enging to assess the active nodules of the plants, limiting field application of the technique resulting in variations in sampling and results (Vessey, 1994; Witty and Minchin, 1988). Due to these limitations, many researchers shy away from using this tech nique. Herridge and Peoples pioneered the Ureide Xylem Sap approach on the assumption that an abundance of ureides relative to other N solutes provides an indirect measure of nitrogen - fixati on (Herridge 1978; Peoples et al ., 1989). The soil N absorbed by t he plant is transported through the xylem to the shoot either as amides (asparagine and glutamine) or as ureides (allantoin and allantoic acid) (Peoples et al ., 1989). The Ureide Xylem Sap a pproach determines the amount of N flowing through the xylem sap o f the shoot or the N composition et al . (2008) suggested the analysis of the extracted xylem sap for Ureides or Amides and calibrated based on the plant type. This approach is less complicated and straight forward in compari son to the 15 N labeled approach . However, only a small proportion of nitrogen - fixing plants uses export ureides in their xylem, hindering the use of this approach in BNF estimations in most nitrogen - fixing plants (Danso, 1995; Unkovich et al ., 2008). 23 The use of 15 N labeling approach explores the fact that the soils or medium in which nitrogen - fixing plants are grown have measurably different 15 N: 14 N ratio from that of the almost con stant 15 N: 14 N ratio of 0.3663% in the atmosphere. Also, nitrogen - fixation and use by a plant will result in a different 15 N: 14 N ratio in the plant tissue than the soil or medium in which it is grown (Danso 1993; Unkovich et al ., 2008) . This approach has e volved with three main methods, namely, the use of 15 N labeling gas, A value, and 15 N Isotope techniques. Over, the years the of use 15 N labeling gas, A value techniques were proved to be impractical and associated with too many errors as compared to the 15 N i sotope technique, resulting in the extensive use of the 15 N isotope technique in the estimation of BNF (Fried et al ., 1983; Danso et al ., 1993). The 15 N isotope approach consists of the 15 N natural abundance and 15 N isotope dilution techniques . Both techniques use similar principles, where nitrogen - fixing and non - nitrogen - fixing reference plants are grown in either enriched or regular soil or medium and total soil 15 N analyzed, and the percentage of the atmospheric 15 N resulting from the atmosp here is estimated. The 15 N isotope dilution technique uses N enrichment of the soil or planting medium, whiles there is no enrichment of the soil or planting medium in the 15 N natural abundance approach. The 15 N isotope dilutio n technique was popular in th e 1970 1990s before improving the use of mass spectrometry. Since the discovery and use of high precision mass spectrometry analysis, the 15 N natural abundance technique has been widely used in BNF estimations. However, w here a high - precision mass sp ectrometer facility is not available, the recommended method is the isotope dilution technique (Peoples et al ., 1991; Unkovich et al ., 2008 ). The 15 N natural abundance technique considers that a non - nitrogen - fixing plant depend s on the soil N when planted in soil medium. Therefore, the isotopic composition ( 15 N value) for a non - nitrogen - fixing plant would be similar to that of the soil N. In contrast, a nitrogen - fixing - plant could depend on the nitrogen available in the soil, an d the atmospheric nitrogen fi xed by the 24 plant. Therefore, for a nitrogen - fixing plant, the isotopic composition ( 15 N value) of the plant tissue would reflect contributions from the atmospheric N 2 and the soil N. The exploitation of the differences in isotopic composition ( 15 N value) b etween a nitrogen - fixing plant and a referenced non - nitrogen - fixing plant with the equation below (Eqn. 1.1), provides an estimation of BNF (Unkovich et al ., 2008). Where %Ndfa the percentage of N due to Biological Nitrogen Fixation (BNF); the nat ural abundance of reference crop or legume (pigeonpea); B - The smallest weighted value of reference crop ( Unkovich et al ., 2002). The 15 N natural abundance technique is more applicable in the field and observed to be less prone to severe errors from th e reference plants than other approaches. Also, aside from the BNF estimation, other useful agronomic details such as the N use efficiency of the refe rence plant, and the N transfer between plant components in a cropping system can be obtained at no extra cost. 25 Use of modeling and SALUS in cropping systems The conventional approach of crop production functions in statistical analyses without reference to underlying biological and physical principles has contributed to the progress of studies of cro pping systems and agricultural science. However, information obtained from this type of analysis is rather site - specific. Therefore, there i s a limit to applying these functions to sites other than those with similar climate, soil, and crop management para meters to where the data and information are obtained (Oteng - Darko et al ., 2013; Jones et al ., 2017). It is common knowledge that even soils within a small area of land are heterogeneous ( Farley and Fitter, 1999 ). Also, with climate variability and weather extremes, long - term (more than ten years) field data is required to develop statistical relationships that are useful in making agricultura l decisions (James and Cutforth, 1996: Jones 1993; Jones et al ., 2017). Field experimentation requires large amounts of resources and may not be able to provide enough information in space and time to make an appropriate and effective decision on managemen t practices ( Penning e t al ., 1992 ). Therefore, there is a need for adopting approaches that quantitatively combine the plant, soil, and climatic systems to make a more accurate prediction of growth and yields in crop production systems. Thus the use of modeling in crop product ion enables the development of sustainable land management options across diverse agro - ecological and socio - econo mic conditions ( Penning et al ., 1992 ; Jones 2017). Crop models serve two primary purposes; for scientific understanding and decision/policy support (Van Itters um et al ., 2003; Ri t chie, 1991). The crop models for scientific understanding tends to be more mechanistic and based on known physical, chemical, and biological hypotheses in an agricultural system. The model helps increase the scientific bases of agricult ural systems, their interactions, and their responses. Examples of these models include the use of AgMIP for simulating maize and wheat yields (Van Ittersum et al ., 1998; Jones et al ., 2017; Asseng et al ., 2013). The models for decision/policy support, on the other 26 hand, desc response to the policy or decision under consideration. Thus, results from model help guide public policy processes, and the possible outcomes, should a particular decision be made (Van Ittersum et 1998; Thornton and Herrero, 2001; Basso et al ., 2016). The most widely used crop models at present include; Decision Support System for Agrotechnology Transfer (DSSAT), The Agricultural Production Systems sIMul ator (APSIM), The En vironmental Policy Integration Climate (EPIC), The Agricultural Production System (CropSyst), Simulateur Multidisciplinaire pour les Cultures Standard (STICS), Root Water Quality (RZWQM), and System Approach to Land Use Sustainab ility ( SALUS), (Asseng et a l ., 2014; Jones et al ., 2003; Jones et al ., 2016; FAO, 2015; Keating et al ., 2003). These crop models used in agricultural systems guide field management decisions such as nitrogen application rate, response to N by crops, loss of the N to the environment (Asseng et al ., 2001; Basso et al ., 2016; Van Delden et al ., 2003 ). Sowing decisions on best timing, cultivar to use, planting density to maximize yields and profit can be made with models (Asseng et al ., 2008; Batchelor et al. , 2002; R itchie, 1991). Crop models can also guide decision making on nutrient use and dynamics, component interactions in rotation, and intercropping systems (Corre - Hellou et al ., 2009; Adiku et al ., 1998). The Systems Approach to Land Use Sustainability (SALUS) model, u sed in this study, was developed by the Michigan State University (MSU). The model contains crop growth modules, SOM and nutrient cycling modules, and soil water balance and temperature modules. It simulates not only the effects of climate and mana gement o n the water balance, SOM, and N and P dynamics, but also heat balance, plant growth, and plant development. (Basso et al . 2006, Basso et al ., 2010; Basso and Ritchie 2015). It operates on the principle that; potential crop growth is influenced by i ntercept ed sunlight by using solar radiation data and Leaf Area Index (LAI) and account for limitations resulting from nitrogen and water. In crop growth 27 simulations, the genetic coefficients and climate data (daily solar radiation, precipitation, and air temperat ure) are the primary external inputs required. Though the SALUS is similar to the DSSAT family of models, it simulates not only crop yields in cropping systems, but also water, nutrient dynamics, and soil as influenced by management strategies over the yea rs. In a simulation, the SALUS model considers the effect of rotation, tillage practice, planting date, planting density, irrigation, and fertilizer applications. Therefore, the use of SALUS modeling would enable the simulation of management scenar ios of u sing pigeonpea biomass and other soil amendments in yam production. Also, in making the right decisions for sustainable yam production, the long - term effect of integrated amendments on soil and implications on yam production can be simulated to ser ve as a guide. Use of model in yam production While research on yam using crop models is limited, modeling approaches in studying the physiology and yield in yams ( Dioscorea spp. ), would enable a greater understanding of the influence of various ecologic al and biotic factors on the production of yam. The model would also permit the prediction of yield under various conditions to serve as a tool in the evaluation of soil amendment options in sustaining yam production (Onwueme and Haverkort, 1991). Srivasta va (2010) modeled the effect of fertilizer and fallow land availability for water yam ( Dioscorea alata ) and white yam ( Dioscorea rotundata ) production in the bush savannah of the republic of Benin using Environmental Policy Integrated Climate (EPIC ) model. At the time, the best scenario under the prevalent cropping patterns for tuber yields was the assumption that 50% bush savannah was available as a fallow. Since population increase has put pressure on the land and therefore the 50% of bush savanna h as a f allow is not feasible, the study recommended using mineral fertilizer as an essential option for sustaining yam production. However, because of the high cost of mineral fertilizers, farmers are not able to 28 afford them. Therefore, fertilizer subsidy from th e government and integration of legumes into yam cropping systems was suggested as the way forward. In another study evaluating the effect of climate variability and CO 2 on the productivity water yam ( Dioscorea alata ) on three soil types in the sav annah zo nes of West Africa, Srivastava (2012) observed a decline of about 33% in tuber yields of yam upon increasing the ambient CO 2 concentration to 350 ppmv. Raw mine 33%, respectively, in a decade. The study concluded with a strong recommendation of including management options in the evaluation of the climatic variables. Using a mod el propo sed for modeling the growth of potatoes on yam, Marcos et al ., (2009 & 2011) showed the relationship between sink and source in yam and its influence on tuber bulking. The leaf area and level of radiative use efficiency control sink and source in y am and i ts influence on tuber bulking. Thus, both photoperiod and temperature affect the development and yields of water yam ( Dioscorea alata ), especially between the emergence and tuber initiation stage. The study, therefore, recommended using modeling in yam gro wth and predicting yam yields to serve as a guide for management options. To assist researchers and other stakeholders in the physiology study of yam, Cornet et al . (2015), using the allometric model, has suggested a more acceptable and accurate ap proach f or predicting leaf area and leaf biomass of Dioscorea alata and D. rotundata in different environments. A stochastic frontier production function studies on yam in Nigeria revealed that labor for land preparation and maintenance, distance to farm, and farm ing experience are significant factors influencing and reducing yam output. It was, therefore, recommended improvement in these factors would improve on yam productivity and income of smallholder farmers (Ojo, 2004). 29 APPENDIX 30 APPENDIX Figure 1.1: Yam production trends in major producing countries of West Africa and the world. Source: Drawn by Author with data from FAOSTAT, 2019. http://www.fao.org/faostat/en/#data/QC 31 REFERENCES 32 REFERENCES Acheampong, P. P., Owusu Danquah, E., Dissanayake, H. G., Hayford, P and Weebadde, C. (2019). A socioeconomic study of transition zone yam farmers; Addressing constr aints and exploring opportunities for integrating pigeonpea into yam cropping systems. Sust ainability 11 (3): 717. Adiku, S. G. K., Rose, C. W., Gabric, A., Braddock, R. D., Carberry, P. S., & McCown, R. L. (1998). 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London, UK: Oxford University. Zhang, F., & Li, L. (2003). Using competitive and facilitative interactions in intercropping systems enhances crop productivity and nutr ient - use efficiency. Plant and Soil . 2003, Vol. 248, Iss. 1 2 , pp 305 312 48 CHAPTER 2 PIGEONPEA ( CAJA NUS CAJAN [L] MILLSP .) - YAM ( DIOSCOREA ROTUNDATA ) CROPPING SYSTEM FOR IMPROVED YAM RESOURCE USE AND PRODUCTIVITY ABSTRACT Increasing and sustaining food crop productivity per unit area on the limited land resources is imperative for the world population projected to increase from 7. 8 billion to 9 billion by 2050. The objective of this study was to evaluate resource use in pigeonpea - yam cropping systems and implications on yam productivity. Research activities were conducted at Fumesua and Ejura in the for est and forest - savannah trans ition agroecological zones of Ghana, respectively, through 2017, 2018, and 2019 cropping seasons. The establishment of the pigeonpea either in an alley or as a border was done in the 2017 cropping season. The 2018 and 2019 crop ping seasons were used as two seasons to cultivat e yam with pigeopea in both locations. A split - plot design with three replications with cropping system (yam planted in alleys of pigeonpea PA; yam planted in pigeonpea as a border PB and Sole yam) and f ertilizer (0 - 0 - 0; 23 - 23 - 30; 4 5 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) was used to arrange the main - plot and subplot treatments respectively. When the competition for sunlight reaching the yam leaves were considered, results revealed that the cropping system had a signifi cant (P < 0.05) influence on the sunlight reaching the yam leaves on the canopy. Sunlight reaching the mid - canopy (MC) of PB and sole yam fields appeared higher than the sunlight reaching the yam leaves above the canopy (AC) of PA whiles sunlight at the b elow canopies (BC) of PB, and sole yam was higher than the sunlight reaching the mid - canopy of PA. As such, the PA field resulted in a significant (P < 0.05) suppression of weeds for both locations and years. The presence of the pigeonpea biomass resulted in a reduction in ridge erosi on, improved moisture conservation, improved soil ECEC resulting in a significantly (P < 0.05) higher and similar tuber yields for the yam planted in pigeonpea with half (23 - 23 - 30 kg/ha N - P 2 O 5 - K 2 0) and full 49 (45 - 45 - 60 kg/ha N - P 2 O 5 - K 2 0) fertilizer rates than the sole yam in both locations and years. As a result of significantly (P < 0.05) higher pigeonpea biomass produced by PA than PB, corresponding significantly (P < 0.05) higher tuber yields were observed irrespective of the lo cation and year. The Land Equivalent Ratio indicates about 27 - 63%, and 34 - 68% more land area would be needed by the sole yam field to produce similar yam yields as the pigeonpea - yam cropping system at Fumesua and Ejura respectively across the two growing s easons. The refore, the st udy, showed that the use of pigeonpea - yam cropping system could sustain soil fertility, improve sprouting of yam, and provide stakes to address the constraint of deforestation and land degradation associated with yam production. Ho wever, to encourage the a doption of the pigeonpea - yam cropping system, smallholder farmers with limited access to land would need an alternative livelihood during the 8 12 months lag phase associated with pigeonpea to mature. Also, breeding and improvement on pigeonpea for traits such as erectness, moderate branching, high biomass, and ability to withstand pruning could help produce pigeonpea accessions more suitable for the pigeonpea - yam cropping system. Keywords: Sustainable yam production, Pigeonpea, Smallholder farmers, Reso urce use, cropping system 50 INTRODUCTION AND RATIONALE The world population is expected to increase from 7.8 billion to 9 billion by 2050 (Roberts, 2011) . To keep pace with feeding the growing population, in creasing and sustaining food production per unit area on the limited land resources is imperative. The challenge of limited access to resources, soil fertility maintenance, and drought as a result of er ratic rainfall, are the main factors contributing to l ow agricultural productivity in Sub - Saharan Africa (McCann, 2005). Ajayi et al ., 2007, observed that agriculture innovative technologies accessible and affordable to smallholder farmers especially would be the way forward. A lthough known for its vital role in rural households, yam production, also serves as food supply and income generation through the consumption and marketing of ware yams. However, yam production faces the challenge of soil fertility m aintenance and scarcity of stakes for yams to climb on for sunlight (Ennin et al ., 2014; Owusu Danquah et al ., 2014). The cultivation of yam requires nutrient - rich soils. The harvest of a ton of yam from the field is estimated to export N of 3.8 - 4.0kg N/ha , 0.39 - 1.1kg P 2 O 5 /ha, 4.2 - 5.9 K 2 O kg/ha (Le Buanec et al ., 1972; Ferguson and Haynes , 1970). To cope with the fertile soil demands of the yams, farmers move to new lands every year in search of fertile fields and stakes for yams to climb, resulting in land degradation and deforestation. This shifting cultivat ion practice, coupled with the increasing human population , has led to pressure on arable lands and forest in the yam growing communities (Ennin et al ., 2014; Ekanayake and Asiedu, 2003; Asante, 1996). Fallow period and available fertile lands keep reducin g whiles distances to yam fields are getting farther and more difficult to access. The Ministry of Food and Agriculture, Ghana (MoFA) report attributed the total loss of about 25% of all forest classes in Ghana to the traditional slash - and - burn method of c ultivation, logging, and wildfires (MoFA, 2017). Soil improvement with fertilizer and manure have been suggested to address th is situation. However, increasing and high cost of fertilizers are making it difficult for resource - poor farmers to access and use 51 fertilizers on their farms. Also, the use of fertilizer alone has been observed not to promote good soil health (Garrity, 200 4; Kotschi et al ., 1998). The use of traditional organic materials such as crop residue and animal manure has been a cheaper sourc e of nutrition for crop production. However, they are bulky, and availability at reasonable quantities in most cases is also l imited to offer a real alternative (Kotschi et al ., 1998; Young, 1997; Diby et al ., 2011). The option of Integrated soi l fertility management (ISFM), which combines mineral fertilizer and organic matter for sustainable crop production, is being promoted for intensification of food production (Vanlauwe et al ., 2010; Giller, 2001). The use of legume crops and shrubs has been identified as a major constituent in sustainable cropping systems due to their Biological Nitrogen Fixation (BNF) and therefo re could be adopted in yam production (Ennin and Dapaah, 2008; Asafu - Agyei et al ., 1997; Kombiok et al ., 1997; Eze and Orkwor 2010 ). This study proposes adopting integrated soil nutrient management with the legume shrub pigeonpea ( Cajanus cajan [L] Mills p. ) for sustainable yam production. Pigeonpea ( Cajanus cajan [L] Millsp. ) is an important grain legume in the semi - arid tropics an d an important income source in countries like Tanzania, Malawi, and Myanmar as they export the grain to India (Walker et al ., 2015; Odeny, 2007). Smallholder farmers in low input, rain - fed systems, generally cultivate the crop as a sole, mixed, intercrop or ratoon crop. In West Africa, pigeonpea is a novel crop species, and it has features that include multipurpose production of biomass above and belowground. This species has shown promise as a means to improve soil aggregation, organic matter, and soil nu trient status (Adu - Gyamfi et al ., 2007; Snapp et al ., 2003). Several studies in the semi - arid and sub - humid tropics of East Af rica report multiple ecosystem services of pigeonpea including biomass production, replenishing soil fertility, efficient water us e, and reduced soil erosion, in addition to the long - term sustainability from diversifying cropping systems with pigeonpea (Ki maro et al ., 2009; Mafongoya et al ., 2006; Snapp et al ., 2002). It fixes more N per unit area from its biomass than other major le gumes 52 used in cropping systems (Peoples et al ., 1995; Giller and Cadisch, 1995). Cropping systems involving pigeonpea in West Africa are rare, even though pigeonpea is found in some home gardens. Few studies have evaluated crop rotation or intercropping of pigeonpea with maize, cowpea, and cassava ( Manihot esculenta ) in Ghana. These have found that pigeonpea returns large qu antities of crop residue to the soil, increases yield of subsequent maize crop, and minimizes soil carbon loss (Adiku et al ., 2009; Adj ei - Nsiah et al ., 2007; Agyare et al ., 2002). In a farmer - managed trial in Ghana, farmers selected the use of pigeonpea as a soil fertility improvement crop over mucuna ( Mucuna pruriens ) and also because pigeonpea provided immediate benefits both a s a food and a cash crop (Adjei - Nsiah et al ., 2007). Thus, pigeonpea could play a positive role in food security. The grains of pi geonpea can serve as an additional source of income and nutrition to smallholder farmers. The grains are nutritionally well balanced an d are an excellent source of protein (20 30%), carbohydrates, and high levels of vitamins A and C (Snapp et al ., 2003). I t can also be used as a cheaper source of fodder for livestock (Saxena et al ., 2002). However, before introduc ing pigeonpea into yam pr oduction systems in Ghana, it is nec essary to evaluate the above and belowground competition that exists between the two plants so appropriate measures can be used to improve productivity. This field study aimed at assisting yam farmers in integrating pig eonpea into yam production in Ghana to improve soil fertility, income, and livelihoods. The specific objectives are to as sess the resource use and implication on yam productivity in the pigeonpea - yam cropping system. 53 MATERIALS AND METHOD Site descrip tion The study was conducted on a 13 15 year continuously cropped field with maize and cowpea in rotation at Fumesua (6 o o o o and forest - savannah transition zones of Ghana respectively. Fumesua soi ls are Ferric Acrisols; Asua n si series with greyish brown sandy clay loam topsoil whiles Ejura soils are Ferric Lixisol; Ejura series with a thick top layer of fine sandy loam (Table 2.1, Figure s 2.1a & 2.1b). Table 2.1: Description of the sites used for the s tudies . Characteristics Location Fumesua (6 o o Ejura (7 o o Agro - ecological zone Humid Forest Forest - Savannah Transition Soil type Ferric Acrisol; Asuasi series upper topsoil consisted of 5cm greyish brown sandy lo am topsoil of dark brown gritty clay loam Ferric Lixisol; Ejura series with a 20 - 30cm thick top layer of loam soils. Soils are dark brown to brown fine sandy loam Temperature (Min - Max. o C) 2017 - 2019 22 - 31 21 - 34 Wet season Bimodal rainfall pattern Bimo dal rainfall pattern Major March mid August March mid - August Minor Sept - Nov; peak in Oct September - Nov; peak in Oct Total annual rainfall (mm) 2017 - 2019 1127 - 1602 averaging 1442mm/yr 1171 - 1574; averaging 1311mm/yr Adopted from Adu, 1992 and Ennin et al ., 2009 Figure 2.1a : Rainfall, maximum and minimum temperatures for 2018 and 2019 of the study areas (Fumesua and Ejura) . Source: Data from the Ghana Meteo ro logical Agency (GMA), 2019 54 Figure 2.1b : Map showing the study area. Source: C ourtesy of: Enock Bessah with data from the geological survey department, Ghana, 2019. Experimental design and data collection The treatment was arranged in a split - plot design with three replications. Pigeonpea - yam cropping system (yam in an alley of pigeonpea (PA), yam in pigeonpea as a border (PB), and No pigeonpea/sole yam) was the main - plot. The subplot of fertilizer levels consisted of full - rate 45 - 45 - 60 kg/ha N - P 2 0 5 - K 2 0; half - rate 23 - 23 - 30 N - P 2 05 K 2 0 kg/ha and no fertilizer as recommended by CSIR CRI yam (Ennin e t al ., 2016). Also, a sole pigeonpea/ no yam field established adjacent to each replicate to enable a comparison of the productivity of the systems. The combination of the pigeonpea and yams on the plots followed the replacement/subs titutive approach with a ro w/ridges for yams substituted for pigeonpea either within the yam ridges or around the border of the field for pigeopea in alley and pigeonpea as border plant fields respectively. A total pigeonpea population of 5,931 plants per ha (about 27% of the sole 55 p igeonpea population) planted at one per stand was used on each of the pigeonpea in alley and pigeonpea as border field. The pigeonpea used was a late - maturing (after 8months) whiles Dioscorea rotundata local acc ession, was used. Yam sett was treated with 120g Conti - an insecticide in 15l of water (Ennin et al ., 2016). The fields were tractor plowed, and pigeonpea was planted in the first and second weeks of May 20 17 at Fumesua and Ejura, respectively. The yams were planted on ridges in both locations for the pigeonpea in alley and pigeonpea as border/live fence and sole yam (No pigeonpea) during the 2018 and 2019 cropping seasons during t he last week of April and f irst week of May for Fumesua and Ejura respectively. On the pigeonpea in alley fields, pigeonpea was planted at 3.6m and 0.5m inter and intra - row respectively to enable two rows/ridges of yams to be planted within the two rows of the pigeonpea. Two rows/ri dges of yams were then planted at 1.2m and 0.8m inter and intra - row respectively to achieve a population of 7,177/ha yam stands within the alleys of pigeonpea with a population of 5,931/ha ( Appendix F igure s 2.7 & 2.8a ; Table 2.2) . Pigeonpea biomass was app lied on the ridges for each cropping system overtime at both locations and years. The pigeonpea alleys served as live - stakes for yams to climb for sunlight with stake height ranging between 2 2.4m. On the pigeonpea as border fi eld, two rows of pigeonpea were planted at three sides of the field at 1.2m and 0.5m inter and intra - row respectively to achieve a population of 5,931 plants per ha. Ridges were constructed in the space within the pigeonpea fence, and yams planted 1.2m and 0.8 inter and intra - row, r espectively to achieve a population of 7,177/ha. Stakes were cut from the thick stems of the pigeonpea from the border for staking the yams. Stake height ranged between 0.8 1.2m (Appendix F igure s 2.7 & 2.8b; Table 2.2) . On the sole yam field, yams were p lanted on ridges at 1.2m X 0.8m inter and intra - rows respectively to achieve a population of 10,416/ha whiles the sole pigeonpea field had pigeonpea planted in rows at 0.9m and 0.5m inter and intra - row to achieve a population of 22,222/ha. Stakes were 56 purc hased and transported to the no pigeonpea/sole yam fields for staking. Stake height ranged between 2 2.5m (Appendix F igure s 2.7 & 2.8c; Table 2.2) . Ridges were about 40 45 cm high at planting for all treatments. Eight weeks a fter p lanting, yam stands w ere refilled for all treatments to ensure the optimum population. The subplot treatment of fertilizer was formulated from 15 - 15 - 15 N - P 2 05 K 2 0 (popular fertilizer on the market) with a 15% mur i ate of potash (MOP) top - up to obtain the 60% K 2 O needed. It was split applied using band placement (5 X 5 cm) per yam plant on the ridges at 5 - 6 and 12 weeks after planting in both locations and years. 2.31 with 105 days to maturity was planted two times in th e year adj acent to each replication as a reference crop for N - fixation determination. Table 2.2: Population of pigeonpea and yam per plot and per hectare designed for the study . Treatment Size of plot (m 2 ) Number of pigeonpea/plot/ hectare Number of yam/ plot/ hectare Yam in PA 200.64 119 / (5,931) 144 / (7,177) Yam in PB 200.64 119 / (5,931) 144 / (7,177) Sole yam 200.64 -- 209 / (10,416) Sole pigeonpea 200.64 446 / (22,222) -- PA Pigeonpea in alley; PB - Pigeonpea as a border 57 Soil analysis Com posite soil samples (9 subsamples) were sampled at the planting of pigeonpea, planting of yam, and harvesting of yam at random on the ridges for all cropping seasons. Soil analysis was conducted at the CSIR Soil Research Institute, Kumasi, for total nitr ogen, pH, organic carbon, phosphorus, and potassium measured at 0 - 20 cm and 20 - 40 cm on the ridges. Total N was determined using the Kjeldahl method, and soil pH w as measured using a pH meter (1:2.5, Soil: H 2 O), organic carbon (OC) using the Walkley and Bl ack method (Walkley and Black 1934). Soil available P was determined using the Bray method 1 (Bray and Kurtz, 1945) and available K using flame photometry (Toth and Prince, 1949). Exchangeable cations and Cation Exchange Capacity (CEC) were determined usin g the ammonium acetate method. Access tubes installation for soil moisture monitoring The soil moisture of each cropping system was measured and monitored on a bi - weekly bas i s using a Time Dorman Reflectometry (TDR) approach with a PR2/6 soil profile pro be device from Delta - T Devices (Dalton, 1992; Delta - T Devices Ltd, Cambridge, UK). The soil probe (PR2/6) allowed monitoring of the soil profile to a depth of 1m with six separat e rings enabling soil moisture monitoring at 0 - 100mm, 100 - 200mm, 200 - 300mm, 30 0 - 400mm, 400 - 600mm, and 600 - 1000mm. The probe upon inserting into the tubes emits electromagnetic field around each measuring ring, which penetrates the soil to record moisture r eadings for each depth (Delta - T Devices Ltd, Cambridge, UK; Dalton, 1992). Two access tubes were inserted at random on ridges of each treatment. The access tubes for each treatment were open, and the PR2/6 probe was inserted on a bi - weekly basis to record the percentage of moisture for the six depths for each cropping system. The so il moisture data were used to evaluate the belowground competition for water and nutrients in each treatment. 58 Weed biomass determination A quadrant of 1.2 X 1m was placed at rand om three times on each field 8 - 9 weeks after planting yam, and the weeds wit hin the area were carefully removed, and fresh weight was taken. Fresh weed samples were then dried in an oven at 75 o C until a constant weight was obtained for dry weight determi nation. Fresh weed weights were converted from the sub - sample fresh weights to dry weights using fresh to dry weight conversion factor. Determination of Biological N Fixation (BNF) of pigeonpea biomass Dried leafy biomass of the pigeonpea and maize refere nce was subsampled and weighed into capsules and sent to the stable isotope fa cility at UC Davis for determination of 15 N determination. Maize served as the non - N - fixing reference plant. The BNF was calculated using the natural abundance method by Unkovich et al . (2008) with the equation 2.1 shown below. Where %Ndfa the percentage of N due to Biological Nitrogen Fixation (BNF); natural abundance of reference crop or legume (pigeonpea) biomass; B - The smallest weighted value of reference crop ( Unkovich et al ., 200 8 ). Sunlight and relative chlorophyll monitoring A photosyn Q multispeQ device V1.0 (Kuhlgert et al ., 2016) was used to monitor photosynthetic related parameters such as light intensity and leaf relative chlorophyll content on a bi - weekly basis on the yam leaves. After the establishment of yam on the stak es (9 - 10 WAP), fresh and fully developed young ya m leaves on the central rows of each treatment were selected bi - weekly on three strata of the stakes (above canopy - AC, mid - canopy - MC and below canopy - BC) for monitoring. The stake height of the yams ranged b etween 0.8 1.2m, 2 2.4m, and 2 2.5m for pig eonpea as a border, pigeonpea in an alley, and sole yam fields respectively. 59 These stake heights influenced the position of the mid - canopy (MC) on the stakes used for the monitoring. For the above canopy lev el, young and fully developed apical yam leaves a t the top of the stakes were used. Young and fully developed yam leaves at an average height of 1.1m, 1.2m, and 0.7m were monitored at mid - canopy for pigeonpea in an alley, sole yam, and pigeonpea as border respectively. Young and fully developed yam leave s on the ridges of all the treatments were used for monitoring light, reaching the below canopy. The device also recorded leaf relative chlorophyll content alongside the light intensity. The leaf relative ch lorophyll content indicates the health of the pla nt and N usage in the soil. Yam yield and Land Equivalent Ratio determination Yam tuber yields were determined by harvesting the central row of each treatment (8m X 3.6m = 28.8m 2 ), and adjacent stands were harvested as a replacement in case of loss of sta nd with - in the central row ( Appendix F igure 2.7). For each treatment, both total and sub - sample fresh weights were taken in the field. The fresh tuber sub - samples were oven - dried at 75 o C to a constant weight to determine the dry weight. T he fresh tuber wei ghts were converted from the sub - sample fresh weights to dry weights , using fresh to dry weight conversion factor. The Land Equivalent ratio was determined following the approach of Willey (1979), equations (2.2, 2.2a and 2.2b) shown below; 60 Data collection and statistical analysis An analysis of variance at 5% significant level (P < 0.05) of the SAS, 9.4 version was used to analyze the data collected on sunlight intensity on yam leaves, percentage soi l moisture along the soil profile, yam stand e stablishment, pruned pigeonpea biomass applied on ridges, and the yam yield components. PROC MIXED of Cropping system and Fertilizer level as fixed effects with block, location, and year as random effects were used (SAS inc, 2013). The effect of the Croppi ng system, location, and year was tested on total pigeonpea pruned biomass, biomass N yield, N - fixation, yam stand establishment, sunlight intensity on yam leaves and weed pressure in a three - way ANOVA. Using t he cropping system, fertilizer level as fixed factors and the location, and year as random factors, a four - way ANOVA was used to test the effect on yam yield components and yam leaf chlorophyll content. Where treatment means differ significantly, the Stand ard Error of the difference between means (SED ) at 5% significant level was used in the separation of means. 61 RESULTS Soil Irrespective of the timing of soil sampling, the soils at Ejura showed better indications of fertility (pH and Effect ive Cation Exchange Capacity (ECEC)) than Fumesua soils ( Appendix T able 2.7). Fumesua soils were generally very strongly acidic (pH 4.4 - 5.2) whiles Ejura soils were closer to neutral (pH 6.6 7.9). Eju ra soils are lixisols known to be less weathered, have deeper topsoil, and are more fertile than the acidic acrisols found in Fumesua (Lal, 1976). The introduction of the pigeonpea and application of its biomass on the ridges did improv e ECEC in the soil o f both locations and years. Also, P was high at harves t on Fumesua soils than Ejura soils ( Appendix T able 2.7 ). Yam stands and establishment Yam stands, and the establishment was significantly (P < 0.05) influenced by the cropping system in both locations and years. Irrespective of the location, yam plante d in PA (pigeonpea in an alley) had significantly (P < 0.05) higher number of stand and establishment at the field for both locations and years. Generally, sole yam fields (No pigeonpea field) re corded the worst field establishment in both locations and ye ars (Figure 2.2). 62 Figure 2.2: Percentage yam stand, two months after planting yam at Fumesua and Ejura for 2018 and 2019 cropping season s . PA Pigeonpea in alley; PB Pigeonpea as border. Error bars represent SED of cropping system means N yield a nd N fixation of applied Leafy biomass The interactions between location, year, and cropping system and their two - way interactions did not significantly (P < 0.05) influence the N yield and fixation of the applied biomass. However, the cropping system s ignificantly (P < 0.05) influenced the leafy biomass production of pigeonpea in both locations and years. Pigeonpea stand s at harvest was similar for the cropping systems in 2018 but significantly reduced for all the cropping systems in the 2019 cropping s eason. PA produced significantly (P < 0.05) higher leafy biomass in 2018 than 2019 cropping seasons irrespective of the cropping system and location. Leafy biomass applied on the PA f ield resulted in an N yield of 51.10 kg/ha and 76.45 kg/ha at Fumesua and Ejura, respectively, for the 2018 cropping season. In 2019, on PA fields, the N yield reduced significantly (P < 0.05) to 25.44 kg/ha and 30.05 kg/ha for Fumesua and Ejura, respectiv ely. Similar trends were observed on the PB fields with the applied bioma ss N yield of 36.08 kg/ha and 65.72 kg/ha at Fumesua and Ejura respectively for the 2018 cropping season compared to N yield of 20.10 kg/ha and 22.86 kg/ha in Fumesua and Ejura respec tively for the 2019 cropping season. High N due to fixation of 27.06 kg/h a (52.95%) and 49.2 kg/ha (62.35%) 63 were observed for Fumesua and Ejura respectively in PA whiles PB had N fixation of 17.99 kg/ha (49.86%) and 34.05 (51.81%) at Fumesua and Ejura resp ectively in the 2018 cropping season. N due to fixation reduced to 16.30 kg/ha (64.07%) and 19.25 (64.06%) for PA and 10.34 kg/ha (51.44%) and 11.69 kg/ha (51.14%) for PB at Fumesua and Ejura respectively for the 2019 cropping season (Table 2.3). Table 2 .3: Total dry matter of pigeonpea biomass applied on ridges in the croppi ng system, N yield and N due to fixation as influenced by cropping system for 2018 and 2019 cropping season s. Location Pigeonpea - yam cropping system Population density at harvest /ha Total leafy biomass added (t/ha) N content of biomass (kg/ha) N due to f ixation (kg/ha) 2018 2019 2018 2019 2018 2019 2018 2019 Fumesua Yam in PA 5,910 a 4,712 b 2.41 c 1.06 c 51.10 c 25.44 c 27.06 c 16.30 c Yam inPB 5,871 a 4,613 b 2.13 d 0.91 d 36.08 d 20.10 d 17.99 d 10.34 d Ejura Yam in PA 5,914 a 4,837 a 3.57 a 1.25 a 76.45 a 30.05 a 49 .20 a 19.25 a Yam in PB 5,881 a 4,638 b 3.19 b 1.04 b 65.72 b 22.86 b 34.05 b 11.69 b SED (5%) 118 0.053 10.61 6.02 Mean 5,297 1.94 40.98 23.24 Location (Loc) 0.5192 0.0042 0.1508 0.0811 Year (Yr) <.0001 <.0001 0.0088 0.0093 Cropping system (CS) 0.0018 <.0001 0.0006 0.0005 Loc*Yr 0.0195 <.0001 0.1574 0.0548 Loc*CS 0.3032 0.0046 0.7356 0.6519 Yr*CS 0.6842 <.0001 0.0945 0.0852 Loc*Yr*CS 0.2446 0.4402 0.4039 0.9647 PA Pigeonpea in alley; PB Pigeonpea as border. Means followed by the same alphabet in each year does not significantly differ from each other 64 Above ground competition ( C ompetition for sunlight) There was no significant (P < 0.05) interaction between location, cropping system, and year and their two - way interactions. Cropping system significant ly (P < 0.05) influenced the light intensity on the yam leaves in both locations and years. Generally, the light intensity observed on yam le aves at mid - canopy (MC) of PB and sole yam was similar to the light intensity on the yam leaves of PA in both locat ions across the years. Also, the light intensity on yam leaves below the canopy of PB and sole yam were significantly (P < 0.05) higher than the light intensity on yam leaves at mid - canopy (MC) of PA fields (Figure 2.3). Figure 2.3: Average biweekly ( 8 28 weeks after planting) sunlight photon reaching yam leaves in pigeonpea - yam cropping system at Fumesua and Ejura across 2018 and 2019 c ropping seasons. PA - Pigeonpea in alley; PB Pigeonpea as border. Error bars represent SED of sunlight reachi n g a canopy level across seasons. Stake and ridge height at harvest Interaction between location and cropping system significantly (P < 0.05) influenced the stake height and the ridge height at harvest (Table 2. 4 ). The bamboos used in the sole yam field at b oth locations and years had an average height of 2.33m and 2.63m in line with the optimum stake height of 2.5m recommended by Rao and Newton (1991), for yam production. The stake height in PA depended on the height of the pigeonpea. Thus, a live - stake pige onpea 65 with an average height of 2.17m and 2.31m was used at Fumesua and Ejura, respectively. The stake height of the PB field was lowest as a result of shorter pigeonpea stem cuttings used as stakes from the borders with an average height of 0.98m and 1.12m at Fumesua and Ejura, respectively (Table 2.4). Table 2.4: Stake and ridge height at harvest of yam in cropping systems at Fumesua and Ejura across 2018 and 2019 cropping seasons . Location Cropping system Stake heigh t at harvest (m) Ridge height at harves t (m) Fumesua Yam in PA 2.17 b 0.34 a Yam in PB 0.98 c 0.27 b Sole Yam 2.33 a 0.20 c Ejura Yam in PA 2.31 b 0.38 a Yam in PB 1.12 c 0.32 b Sole Yam 2.63 a 0.23 c SED (5%) 0.09 0.01 Mean 1.92 0.29 Location (Loc) 0.0248 0.1465 Cropping system (Cs) <.0001 <.0001 Loc*Cs 0.0252 0.0005 PA Pigeonpea in alley; PB Pigeonpea as border. Means followed by the same alphabet in each location does not significantly differ from each other Relative chlorophyll content of yam leaves Significant (P < 0.0 5) interaction was observed between pigeonpea - yam cropping system and fertilizer rate on the relative chlorophyll content of yam leaves in both locations and years. The average leaf relative c hlorophyll content was significantly (P < 0.05) higher at Ejura than Fumesua. Generally, at no fertilizer and half fertilizer rate (23 - 23 - 30 N - P 2 O 5 - K 2 0 kg/ha) leaf chlorophyll content followed the order of PA>PB> sole yam whiles at full rate (45 - 45 - 60 N - P 2 O 5 - K 2 0 kg/ha) it followed an order of PA=PB>sole yam. T he yam le af chlorophyll content was also similar to the use of half and full fertilizer rate on PA fields (Figure 2.4). 66 Figure 2.4: Average biweekly relative leaf chlorophyll content of yams in pigeonpea - yam cropping system at Fumesua and Ejura across the 2018 and 2019 cropping season s . PA pigeonpea in alley; PB Pigeonpea as border. Error bars represent SED of the Cropping system m ean across seasons. Below ground competition (Competition for water) The presence of the pigeonpea and biomass on the field i nfluenced the moisture on the ridges (0 - 40cm). Pigeonpea in alley fields generally had the highest moisture content followed by pigeonpea as a border as a treatment, and the lowest in the sole yam field in both locations and years. Sole yam field had a hig h percentage of the soil moisture below 400cm as compared to yam planted in PA and PB fields in both locations and years ( Figur e s 2. 9 a & 2. 9 b). Thus, soil moisture was available in the ridges for the growth and development of yam during the growing season on PA, followed by PB with worse soil moisture availability on the ridges of the sole yam field for both years and locations. 67 Weed pressure in the cropping system Weed pressure was significantly (P < 0.05) influenced by the pigeonpea - yam croppi ng system. Weed was significantly (P < 0.05) suppressed (72 73%) in yam planted in PA fields, followed by yam in PB field s (20 28%) than sole yam field in both locations and years. Generally, weed pressure was high for all the cropping systems in 2019 than the 2018 cropping season and higher at Ejura than Fumesua for both cropping seasons (Figure 2.5). Figure 2.5: Weed pressure 8 weeks after planting in the pigeonpea - yam cropping system at Fumesua and Ejura, for 2018 and 2019 cropping season s . PA pigeonpea in alley , PB Pigeonpea as border . Error bars represent SED of means of the cropping system. Resource us e and yam productivity Significant (P < 0.05) interactions between location, year, cropping system, and fertilizer was observed on the y am tuber per plant and total tuber yields. Generally, yam productivity was higher at Ejura than Fumesua and in 2018 cropping season than the 2019 cropping seas on. Also, fertilizer application generally improved yield except in sole yam fields in the 2019 c ropping season, where similar yield was observed for no fertilized and half fertilized fields in both locations (Figure s 2.6a & 2.6b). Significantly (P < 0.05) lower per plant yield was observed for the sole yam field irrespective of the fertilizer rate, l ocation, and 68 cropping season (Figure 2. 6 a). Generally, across locations and years, tuber yields per plant were similar for yam in PA and PB with half fertilize r rate (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) and full fertilizer rate (45 - 45 - 60 P 2 O 5 - K 2 O kg/ha) than tuber yield per plant on sole yam fields. Also, significantly (P < 0.05) higher and similar yields were observed for tuber yields of yam in PA with half fertilizer r ate (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) and full fertilizer rate (45 - 45 - 60 P 2 O 5 - K 2 O kg/ha) at both locati ons and years (Figure 2.6b). The Land Equivalent Ratio (LER) was influenced significantly (P < 0.05) by the cropping system in both locations and years. The re lative yield of yam in all the cropping system s was more than one (1) , while that of the pigeonpe a w as less than 1 for both locations and years. More than 1 LER were recorded for all the intercrop system with yam in PA, recording the highest LER than yam in PB for both locations and years (Table 2.5). The Pearson correlation indicates the factors tha t exp lain the increase in yam tuber components. Total pigeonpea biomass applied and ridge height significantly (P < 0.05) and directly contributed about R2=77%; R2=53% and R2=66%; R2=54% to yam tuber yield per plant at Fumesua and Ejura respectively across the two cropping seasons. The relative leaf chlorophyll content explains 61% and 30% of the tuber yield per plant at Fumesua and Ejura, respectively. However, a significant (P < 0.05) inverse relationship was observed between the yam yield components and the t otal sunlight reaching the yam leaves in both locations across the two seasons (Table 2.6). 69 Figure 2.6a: Fresh yam tuber yield per plant in a pigeonpea - yam cropping system at Fumesua and Ejura for 2018 and 2019 cropping seasons. PA and PB are p igeonpea in alley and pigeonpea as border respectively. Error bars represent the SED of cropping systems . 70 Figure 2.6b: Fresh yam tuber yield in a pigeonpea - yam cropping system at Fumesua and Ejura for 2018 and 2019 cropping seasons. PA and PB a re pigeonpea in alley and pigeonpea as border , respectively. Error bars represent the SED of cropping systems . 71 Table 2.5: The l and e quivalent r atio (LER) of the pigeonpea - yam cropping system at Fumesua and Ejura for 2018 and 2019 cropping season s . Location Cropping System Relative yield LER Pigeonpea Yam 2018 2019 2018 2019 2018 2019 Fumesua Yam in PA 0.30 a 0.15 a 1.32 a 1.24 a 1.62 a 1.39 a Yam in PB 0.27 b 0.14 b 1.14 b 1.13 b 1.41 b 1.27 b Ejura Yam in PA 0.38 a 0.17 a 1.31 a 1.29 a 1.69 a 1.46 a Yam in PB 0.33 b 0.14 b 1.11 b 1.21 b 1.44 b 1.35 b SED (5%) 0.024 0.059 0.059 Mean 0.24 1.22 1.46 Location (Loc) 0.1938 0.5319 0.176 Year (Yr) <.0001 0.8691 0.0023 Cropping system (CS) <.0001 <.0001 <.0001 Loc*Yr 0.0028 0.1637 0.4981 Loc*Cs 0.0004 0.6407 0.4928 Yr*Cs 0.1625 0.0030 0.0038 Loc*Cs*Yr 0.4837 0.3432 0.4759 LER Land Equivalent ratio; PA Pigeonpea in alley; PB pigeonpea as border. Means with the same alphabets within a location indicate no significant ( ) differences among treatments. Table 2.6: Pearson correlation of tuber yield components, sunl ight intensity and ridge height at Fumesua and Ejura across 2018 and 2019 cropping seasons . **correlation is significant at the 0.01 level (2 - tail ed) *correlation is significant at the 0.05 level (2 - tailed) Fumesua Fresh tuber yield/ ha Fresh tuber yield/ stand Av g. ridge height Total sunlight on yam leaf Rel. leaf chlorophyll content Applied pigeonpea biomass Fresh tuber yield/ ha 1 Fresh tuber yield/ stand .891** 1 Average ridge height .617** .812** 1 Total sunlight on yam leaf - .605** - .72 2** - .893** 1 Relative leaf chlorophyll .930** .783** .476** - .430** 1 Applied pigeonpea biomass .648** .880** .853** - .721** .558** 1 Ejura Fresh tuber yield/ ha 1 Fresh tuber yield/ stand .911** 1 Average ridge height .469** .727** 1 Total sunlight on yam leaf - .421** - .541** - .677** 1 Relative leaf chlorophyll .701** .647** .459** - .359** 1 Applied pigeonpea biomass .508** .729** .799** - .593** .624** 1 72 DISCUSSION Yam sprout rate and establishment The observed significantly (P < 0.05) higher stand establishment for planting yam in the PA at Funesua and Ejura for both cropping seasons could be attributed to the shade provided by the pigeonpea and its biomass during the sprouting of the yams. Even in the 2019 cropping season, when pigeonpea biomass reduced significantly for both locations, yam sprouting, and es tablishment were significantly (P < 0.05) better on PA and PB fields than the sole yam fields in both locations (Figure 2 .2 ). Thus, shade provided by the pigeonpea canopy and biomass on the ridges resulting in reduced direct heat from the sun and moisture loss from the ridges creating a suit able medium for the yam sprouting and yields. Agbede et al ., 2013 observed that mulching in yam is essential for the growth and development of yams. Soil nutritional improvement as a result of mulch and the ability of th e mulch to control the soil temperat ure and moisture for the benefit of the yam was demonstrated using Tithonia and Chromoleana mulch. The use of plant biomass for mulching yam resulted in the reduction of soil temperature between 5 7% at 5 10 cm depth of the soil for the benefit of the yam (Adeoye 1984). These suggest, to reduce soil temperature and conserve soil moisture, especially in the tropics to prevent seed yam rot and loss after planting, shading, and biomass from the pruning of shrubs such as pigeonpea would play a vital role in yam production. N and other nutrient contribution of pigeonpea in the system The generally high pigeonpea biomass production in Ejura than Fumesua, irrespective of the similar stands, could be attributed to the lixiso ls found at Ejura, which are less we athered and more fertile than the acidic acrisols found at Fumesua (Lal, 1976). Thus, the Ejura fertile soil supported more growth and pigeonpea biomass production at Ejura than Fumesua (Table 2.3). A s imilar pigeonpea population density w as observed for PA and PB in 2018 whiles PA 73 had a higher population density in 2019 and produced significantly (P < 0.05) higher biomass compared to the PB fields (Table 2.3). This observation could be attributed to the less space and high intra - specific competition for res ources by the pigeonpea of the PB field. PB fields had all pigeonpea population crowded at three borders of the field planted at 1.2 X 0.5m, whiles the pigeonpea in an alley field had pigeonpea planted 3.6m X 0.5m. Th e planting distances imply whiles the i ntra - specific competition for above ground (Sunlight) and below ground (soil nutrients and water) resources were high among the pigeonpea stands in PB fields, the intra - specific stand competition was minimal in the PA field. As such, the PA would have had almost all resources for growth and accumulation of biomass. Several studies have made similar observations. Kaur and Saini (2018), observed that planting determinate pigeonpea at a wider row spacing of 0.6 m resulted in a significantly high yield attribut e than planting at a row spacing of 0.5m and 0.45m. Also, planting pigeonpea at 0.6 X 0.1m resulted in a high yield attribute than planting at 0.45 X 0.1m (Tigga et al ., 2017). High leafy biomass of the PA field than PB fields contributed to the significan tly (P < 0.05) higher N yield and N - fixation for both locations and years. Significant (P < 0.05) reduction in the number of stands and leafy biomass in both locations for the 2019 cropping season resulted in signific antly lower N yield and N - fixation (Tab le 2.3). N - fixation depends significantly on the total biomass yield and total N yield of the biomass (Giller, 2001; Peoples et al ., 2009). Mhango et al . (2017) observed that high biomass production of pigeonpea, espe cially in good rainfall years, resulted in high N - fixation. The significant (P < 0.05) reduction in the number of stands, leafy biomass, N yield, and N - fixation by PA and PB in both locations in 2019 cropping season might be due to pruning effect from the 2018 cropping season (Table 2.3). Sever ely pruning of pigeonpea to a height of 25cm significantly reduced the survival and yield of pigeonpea in a pigeonpea - pepper cropping system, although it significantly (P < 0.05) increased the fruit yield of the assoc iated pepper (Fabunmi et at., 2010). Ag yare et al . (2002) in managing pigeonpea as a short fallow observed 74 pruning affected biomass production. As such, the control of no pruning treatment recorded significantly (P < 0.05) higher biomass and seed yields. T hus, the need to further pay attention to the pruning and management of the pigeonpea in the pigeonpea - yam cropping system to ensure sustainable biomass production. Pigeonpea can produce root exudates, enabl ing it to efficiently take up P from the soil int o its biomass for the benefit of associ ated crops (Ae et al ., 1990). This observation is in line with the general improvement in phosphorus (P) and cation exchange capacity on the ridges upon appl ying pigeonpea biomass ( Appendix T able 2.7). Dabin, (1980) a nd Friesen, et al . (1997) has indicated high P fixation in tropical soils. Thus, inclu ding pigeonpea in the cropping system, especially in the tropics, would be a strategic option for efficient P cycling for the benefit of associated crops. Resources use and implication on yam productivit y in the cropping system Leaf relative chlorophyll content and tuber yield of yam were influenced significantly (P < 0.05) by the interaction between cropping system and fertilizer in both locations and years . The generally high leaf relative chlorophyll c ontent and tuber yields at Ejura as compared to Fumesua could be accounted for by the more fertile lixisols at Ejura, which supported plant growth and development than the acidic acrisols found at Fumesua (La l, 1976) ( Figure s 2.4 , 2.6a & 2.6b). Shiwachi et al . (2004) observed that a soil with a pH between 6 and 7, such as in Ejura are suitable for yam production. ECEC improved whiles P reduced at harvest in Ejura soils than Fumesua soils suggesting better upta ke of nutrients and P in Ejura soils (pH 6.4 6 .8) than strongly acidic soils of Fumesua (4.4 5.3) ( Appendix T able 2.7 ). The presence of the pigeonpea, especially in yam planted in PA fields, did shade the yam leaves resulting in significantly (P < 0.05) lower sunlight photons reaching the yam leaves in both locations and years (Figure 2.5) , s uggest ing reduced sunlight on yam leaves as a result of the pigeonpea in the pigeonpea - yam cropping system. However, the shading from the pig eonpea positively 75 resulted in soil moisture conservation, reduced ridge erosion, and reduction in weed pressure (Table 2.4; Appendix F igures 2. 9 a & 2. 9 b ; Figure s 2.6 a & 2.6b ). Thus, the generally significantly (P < 0.05) higher tuber yields recorded in 201 8 than 2019 cropping season could be attributed to the corresponding hi gh pigeonpea biomass, produced in the 2018 cropping season than 2019 cropping season (Figures 2 . 6 a & 2 . 6 b). Yam in PB fields received similar sunlight photons as the sole yam fields res ulting in generally similar sunlight reaching the leaves at various lev els of the canopy as compared to sole yam in both locations and years (Figure 2.5). The shading effect of the pigeonpea on the yam in PA, however, did not reduce yam productivity but in stead enhanced the yam yields (Figure s 2.4 , 2.6a & 2.6b; Table 2.6). Si gnificantly (P < 0.05) higher tuber yields recorded for the yam planted in PA than PB and sole yam in both locations and years indicates the positive effect of the shade and biomass pro vided by the pigeonpea. Yam as a climber and C3 plant species upon rece iving 50% of require light intensity becomes saturated, making yams tolerant to shade and operate under full photosynthetic potential in the moderate shade by increasing their leaf size and chlorophyll content as an ad a pt at ion strategy (Coursey and Haynes, 1970; Johnston and Onwueme, 1998). Also, environmental conditions such as high - temperature results in increased oxygenation reaction along the photorespiratory pathway causing about 25 30% losses in carbon fixation especially in C3 plants (Raines, 2011 ; Sage and Kubien, 2007). Thus, the moderate shading provided by the pigeonpea in the alley might have reduced temperature and improved photosynthetic efficiency resulting in hig h productivity of yams in PA fields than yam in PB fields and sole yam fields. Improvement in nutrient assimilation and productivity of cocoa under moderate shade have been observed by Isaac et al . (2007) and Asare et al . (2017) and are in line with this s tudy. Arrangement of agroforestry tree, Flemingia macrophylla in alleys and in tercropped with maize a C4 plant, resulted in similar radiative use efficiency of maize in an alley and sole maize cropping system. The similar radiative use efficiency suggest s 76 that shading from the tree component did not significantly affect the qualit y of photons needed for the maize grain yield (Friday and Fowes, 2002). Stakes for the yam vines to climb are very important for yam productivity (Ennin et al ., 2014; Owusu Danqu ah et al ., 2014). Yam planted in PA and PB had 2.1 2.3m live - stake and 0.9 1.1m cut stakes respectively from the pigeonpea to climb for enough sunlight (Table 2.4 ). Pigeonpea has deep root system (Nene and Sheila, 1990 and Akinnifesi et al ., 2004) and an ability to improve the availability of soil nutrients especially N and P fo r the benefit of the associated cropping system (Valenzuela and Smith, 2002; Sinclair and Vadez, 2012; Ae et al ., 1990). These attributes of pigeonpea created a beneficial microe nvironment facilitating the use of resources to benefit the yam in the pigeonp ea - yam cropping system. Similar relative chlorophyll content of the yams and corresponding similar yam tuber yields for especially yam in PA fields with half fertilizer (23 - 23 - 30 kg/ha N - P 2 O 5 - K 2 O) and full (45 - 45 - 60 kg/ha N - P 2 O 5 - K 2 O) fertilizer rates were observed for both locations and years. These results suggest that the half fertilizer rate was able to meet the nutrient requirement of the yam in the presence of the pigeonpea l eafy biomass. Even where no fertilizer was applied, yam yields were relatively better with the presence of the pigeonpea biomass on either yam in PA or PB than sole yam fields (Table 2.6). Ennin et al . (2013), made a similar observation in a pigeonpea prec eding yam cropping system. When pigeonpea preceded yam, tuber yields were high er for 3 t/ha poultry manure and 15 - 15 - 20 kg/ha - N - P 2 O 5 - K 2 O and similar to when poultry manure and fertilizer were doubled to 6 t/ha and 30 - 30 - 40 kg/ha N - P 2 O 5 - K 2 O. The major contributing factor for the significantly (P < 0.05) higher total tuber yield on t he yam pigeonpea intercropped fields (PA and PB) is as a result of the corresponding significantly (P < 0.05) higher yield per plant compared to the sole yam fields ( Figure 2 .6 a & 2.6b ; Table 2. 6 ). Several studies have observed that the availability of mo isture is not only crucial for sprouting and establishment during the early stages of the roots and tuber crops but also vital 77 for bulking larger tubers (Eruola et al ., 2012; Sunitha et al ., 2013; Bhattacharjee et al . 2011; Ennin et al ., 2016). U nlike cass ava, yam does not penetrate its roots in the soil before bulking, and as such, the tuber expansion, size, shape, and quality are depende nt on the soil medium. Mignouna et al . (2009) observed that the presence of organic matter on yams would prevent erosion of the medium in which the yam is bulking, increase infiltration and water conservation, and improved microbial activity to enhance yam tuber bulking and yield. Kang and Wil son (1981) found that the size of the bulking medium has a more pronounced influen ce on yam tuber yield than fertilizer application with significantly higher yields recorded for unfertilized yams on larger size (about 0.30m high) mounds (11.30t/ha) than fe rtilized yams planted on flat (7.30t/ha) ground. Although reshaping of the ridges was conducted one and two times for PB and sole yam fields respectively, for this study, no reshaping was needed in the PA fields. The PA fields had a ridge height of 0.34 0.38m whiles the PB fields had a ridge height of 0.26 0.32m at the time of harv est in comparison to a ridge height of 0.19 0.23m in the sole yam fields in both locations and years (Table 2.5). These results suggest that the pigeonpea and biomass on th e PA fields protected the ridges from eroding. The significant influence of applie d pigeonpea biomass and ridge height on yam tuber yield component (Table 2.3; Figure s 2. 6 a & 2. 6 b) indicates the vital role pigeonpea could play in a pigeonpea - yam cropping s ystem. Thus, the presence of the pigeonpea would provide shade, reduced erosion of ridges, improve infiltration, conserve moisture, reduce weed pressure, and improve soil nutrition on the ridges resulting in improved yam tuber yield per stand of the associ ated yam crop. Yam production along the West African yam belt is far below poten tial yield, achieving just about 10t/ha yields compared to a potential of about 50t/ha across all yam varieties and increase in yam production are mainly as a result of an in crease in the area under yam cultivation (Frossard et al ., 2017). The Ministry of Food and Agriculture (MoFA), Ghana, had 78 also reported that between 2011 2016, when yam production decreased by 6.90%, a correspondent decrease of 5.22% was observed in the area under yam cultivation within the same period (MoFA, 2017). Thus, yam producti on increase or decrease in Ghana is directly related to increasing the area under yam cultivation. These observations suggest yam would continue to contribute to land degradation and deforestation if improved technologies are not employed to sustain its pr oduction on continuously cropped fields, which farmers under normal circumstances would not prefer for yam production. Integrated soil fertility management, along with farmer options and preferences, has been observed to be the way forward (Frossard et al . , 2017). This study demonstrate s that the integration of pigeonpea into the yam cropping system would reduce ridge erosion, improve soil nutrien ts, and moisture conservation to sustain the productivity of yam even on the continuously cropped fields. 79 CONCLUSION AND RECOMMENDATIONS Integrated soil fertility management with pigeonpea biomass and fertilizer is a possible option for sustainable yam production to address the constraint of staking acquisition and soil fertility sustenance resulting in deforestation and land degradation associated with yam production. Apart from the provision of reliable cut - stakes or live - stakes, the pi geonpea biomass and shade reduce ridges erosion, conserves soil moisture, improve yam sprouting, and suppresses wee ds. These attributes of the pigeonpea on yam resulted in the facilitation of resources used in the cropping system and enhanced the productiv ity of yam. Growing yam in an alley of pigeonpea with half fertilizer rate (23 - 23 - 30 kg/ha N - P 2 O 5 - K 2 O) resulted in sustained soil fertility, provided live - stake for yam vines and improved yam productivity. Besides, the cultivation of yam with pigeonpea at the borders (equivalent to using about a third of the field for growing pigeonpea) as a reliable source of cut - stak es with half fertilizer rate (23 - 23 - 30 kg/ha N - P 2 O 5 - K 2 O) also presents an option better than the sole yam cultivation. Therefore, integrated soil fertility management of planting yam with pigeonpea with half the recommended fertilizer rate (23 - 23 - 30 kg/ha N - P 2 O 5 - K 2 O) has been observed as a way forward for sustainable yam production on continuously cropped fields. However, there would be a need for further studies on the fertilizer rate to ascertain if the half - rate (23 - 23 - 30 kg/ha N - P 2 O 5 - K 2 O) can be furthe r reduced without affecting the productivity and returns on the yam. Economic analysis of the pigeonpea - yam cropping system options would be needed to ascertain the profitability of each cropping system option. Further research work on pruned height and frequency of pruning of the pigeonpea to ensure a sustainable supply of biomass would be needed. Breeding and selecti ng a more erect, less br anching, high biomass, and grain yield would present an ideal pigeonpea accession for the pigeonpea - yam cropping sy stem. The pigeonpea would need about 8 12 months to accumulate enough biomass to provide these positive attributes to compliment yam produc tion. 80 This waiting period may discourage farmers, especially smallholder farmers, with limited access to land to ad d - approach of cultivating legumes such as cowpea and groundnut (peanut) d uring this lag phase (8 - 12 months) should be pursued for an informed decision on options to make the integrated soi l fertility management using pigeonpea - yam for sustainable yam production attractive especially to smallholders. 81 APPENDIX 82 APPENDIX Table 2.7: Physico - chemical properties of the soil at planting of pigeonpea, at planting and harvest of yam at Fumesua and Ejura across 2018 and 2019 cropping seasons. % Sand % Clay % Silt Texture pH 1:2.5 %Total N ECEC me/100g Brad P (ppm) Location Crop ping syste m Fertillizer N - P 2 O 5 - K 2 0 kg/ha 0 - 20c m 20 - 40c m 0 - 20c m 20 - 40c m 0 - 20 cm 20 - 40c m 0 - 20c m 20 - 40c m 0 - 20c m 20 - 40c m 0 - 20c m 20 - 40c m 0 - 20cm 20 - 40c m 0 - 20c m 20 - 40c m At planting of pigeonpea, May, 2017 Fumesua -- 62 58 8 8 30 34 SCL SCL 4.79 4.43 0.07 0.04 4.05 3.15 38.9 16.0 Ejura -- 76 70 10 10 14 20 SL SL 7.76 7.88 0.06 0.03 7.24 5.9 3 36.7 19.9 At planting of yam, May, 2018 & 2019 Fumesua YAP -- 64 66 14 12 22 22 SCL SCL 5.08 5.09 0.10 0.09 4.80 4.94 260 253 YPB -- 69 72 10 8 21 20 SCL SL 4.74 4.88 0.15 0.08 4.87 4.57 235 212 SY -- 60 66 10 10 30 24 SCL SCL 4.81 4.86 0.08 0.0 8 4.21 4.02 163 113 Ejura YAP -- 74 76 18 17 10 13 SL SL 6.39 6.39 0.09 0.10 8.12 8.38 264 232 YPB -- 72 70 18 17 10 13 SL SL 6.22 6.24 0.09 0.08 6.64 6.34 275 258 SY -- 74 74 16 15 10 11 SL SL 6.31 6.08 0.10 0.05 6.38 6.16 228 151 At harvest of y am, December, 2018 & 2019 Fumesua Yam in AP 0 - 0 - 0 68 71 10 9 22 20 SCL SCL 5.12 4.64 0.12 0.13 4.96 3.74 302 337 23 - 23 - 30 72 72 10 10 18 18 SL SL 4.68 4.52 0.11 0.11 4.32 6.71 268 270 45 - 45 - 60 70 70 9 9 21 21 SCL SCL 4.44 4.49 0.11 0.10 3.68 4.06 80.1 85.3 Yam in PB 0 - 0 - 0 69 70 10 9 21 21 SCL SCL 5.05 5.14 0.11 0.11 5.24 5.44 314 342 23 - 23 - 60 73 70 9 9 18 21 SL SCL 5.26 4.69 0.11 0.44 5.72 4.35 199 133 45 - 45 - 60 69 72 10 9 21 19 SCL SL 5.16 5.16 0.13 0.12 4.98 5.16 309 304 83 Table 2.7 ( c ont d) SCL Sandy Clay Loam; SL Sandy Loam; CS Cropping System; Y Yam, S Sole, PA Pigeonpea in alley, PB Pigeonpea as border Sole Yam 0 - 0 - 0 74 72 8 7 18 21 SL SL 5.38 5.34 0.10 0.09 5.11 5.28 352 298 23 - 23 - 30 73 78 9 6 18 16 SL SL 4.87 5.04 0.10 0.11 4.35 4.06 281 329 45 - 45 - 60 72 74 7 10 21 16 SCL SL 5.34 5.75 0.09 0.09 6.38 6.09 119 241 Ejura Yam in PA 0 - 0 - 0 77 74 14 19 9 9 SL SL 6.68 6.61 0.11 0.11 8.09 7.66 28.3 23.4 23 - 23 - 30 81 80 12 13 7 7 SL SL 6.73 6.87 0.10 0.07 9.17 8.31 82.5 57.9 45 - 45 - 60 73 75 16 19 11 6 SL SL 6.66 6.67 0.13 0.46 8.44 8.62 71.6 69 Yam in PB 0 - 0 - 0 79 76 13 15 8 9 SL SL 6.44 6 .56 0.09 0.09 6.04 6.59 26.8 35.6 23 - 23 - 30 79 78 14 15 7 7 SL SL 6.46 6.55 0.11 0.09 6.17 6.59 159 32.7 45 - 45 - 60 79 78 12 13 9 9 SL SL 6.57 6.45 0.10 0.08 7.08 7.03 20.9 20.5 Sole Yam 0 - 0 - 0 75 78 15 10 10 12 SL SL 6.79 6.84 0.10 0.12 7.51 7.15 33. 6 20.3 23 - 23 - 30 81 81 12 12 7 7 SL SL 6.50 6.49 0.10 0.24 5.97 5.59 44.5 39.5 45 - 45 - 60 79 77 12 12 9 11 SL SL 6.43 6.64 0.10 0.08 7.68 7.46 58.0 46.3 84 Figure 2 . 7: Diagrammatic representation and arrang ement of treatments on the field 85 Figure 2. 8 a: Cross - section pictorial view of the yam in ridges and pigeonpea live - staking option designed for the study. PA Pigeonpea in alley . 86 Figure 2. 8 b: Cross - section pict orial view of the yam in ridges and cut pigeonpea stem staking option designed for the study. PB Pigeonpea as a border plant . 87 Figure 2. 8 c : Cross - section pictorial view of the yam in ridges and bamboo staking option designed for the study. 88 Figure 2.9a: Percentage soil moisture along the soil profile of a pigeonpea - yam cropping system at Fumesua and Ejura 2018 cropping seasons . 89 Figure 2.9b: Percentage soil moisture along the soil profile of a pigeonpea - yam cropping system at Fumesua and Ejura, 2019 cropping seasons . 90 REFERENCES 91 REFERENCES Adeoye, K. B. (1984). Influence of grass mulch on soil temperature, soil moisture and yield of maize and gero millet in a savanna zone soil. Samaru Journal of Agricultural Researc h (Nigeria). Adiku, S. G. K., Jones, J. W., Kumaga, F. K., & Tonyigah, A. (2009). 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Field Crop Abstracts, 32(1), 1 10. Young, A. (1997). Agroforestry for Soil Management. 2 nd edition. CAB International & International Centre for Research in Agroforestry, Wallingford/Nai robi 98 CHAPTER 3 EVALUATING LONG - TERM YAM PRODUCTIVITY UNDER INTEGRATED SOIL FERTILITY MANAGEMENT OF PIGEONPEA RESIDUE AND FERTILIZER USING CROP SIMULATION MODEL ABSTRACT Integrated Soil Fertility Management (ISFM) for the intensification and sustainable yam production on continuously cropped fields holds the key to addressing deforestation and land degradation associated with yam production along the West African yam belt. The objective of this study was to evaluate the long - term (10 years) implication o f integrated soil fertility management of pigeonpea residue and fertilizer on yam tuber yield using the Systems Approach to Land Use Sustainability (SALUS) crop model. The m odel was calibrated and validated with agronomic data from a three - year pigeonpea - y am evaluation study conducted in the forest and forest - savannah transition zones of Ghana. Six soil fertility management scenarios consisting of factorial of two pigeonpea r esidue options (yam with pigeonpea residue and sole yam) and three inorganic fertil izer rates (0 - 0 - 0; 23 - 23 - 30; 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) were simulated for their long - term implications on yam tuber yields. The model simulation of the long - term yam yield agreed with the observed results across the two cropping systems, three fertilizati on rates , and two locations. The root mean square of deviation between the simulated and the observed tuber yield was 0.73 t/ha, mean absolute percentage error was 10.7%, an d the coefficient of determination (r 2 ) was 0.72. Increasing inorganic fertilizer r ate from no fertilizer (farmer practice) to half (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) and full (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) rate on sole yam field in both locations resulted in a dry yam tuber yield range of 1.73 - 3.15 t/ha, 3.59 - 4.43 t/ha and 4.83 - 5.84 t/ha respecti vely indicating enhanced long - term yam tuber yield with the use of inorganic fertilizer. The use of pigeonpea residue, pigeonpea residue in addition to a half and full recom mended 99 inorganic fertilizer rate further increased the range to 4.52 - 7.26 t/ha, 5.8 0 - 8.84 t/ha and 7.0 - 9.99 t/ha respectively indicating the influence of the pigeonpea biomass in sustaining long - term yam tuber yield. A better probability of long - term yam y ield was observed with cultivating yam with only pigeonpea residue (4.52 - 7.26 t/ha) than planting sole yam with the full recommended fertilizer rate (4.83 - 5.84 t/ha). These suggest that integrated soil fertility management with pigeonpea residue could be m ore sustainable than the use of only inorganic fertilizer at any rate for sole yam cultivation. Thus, the use of inorganic fertilizer alone in soil fertility management for ya m would not sustain yam production, and at best, would stagnate yam productivity on continuously cropped fields. The study has shown, integrated soil fertility mana gement with legumes such as pigeonpea residue and inorganic fertilizer could sustain soil fert ility and yam productivity to address deforestation and land degradation associated with yam production. Keywords: Modelling, Food Security, Simulation, Sustain ability and Deforestation 100 INTRODUCTION AND RATIONALE Yam is an essential staple food and food security crop serving as food and income generation to about 60 million people in Ghana and along the West African yam belt (Asiedu and Sartie, 2010; Andr es et al ., 2017). Despite this importance of yam, its production has been dwindling due to many challenges, including declining soil fertility, pests and diseases, and low - quality planting material and thus threatening food security, income, and rural live lihoods (Frossard et al ., 2017). In Ghana, yam is normally cultivated under monoculture with shifting cultivation in search of fertile land and stakes for yam to climb on (Ennin et al ., 2014; Owusu Danquah et al ., 2014). Because yam is a heavy soil nutrie nt feeder and access to land by smallholder farmers is limiting, it results in continuou s cultivation on soils containing less than 1% carbon, which is inadequate to sustain productivity ( Benneh et al., 1990; NSFMAP, 1998). Thus, improving soil fertility w ould increase and sustain yields for smallholder farmers (Diby et al et al ., 2008). The use of biomass and residue of legumes in rotation or intercrop results in increased protection of the soil against erosion, increase soil organic mat ter, nutrients, and soil water holding capacity (Hayford, 2018; Thierfelder et al ., 2012 ; Snapp et al ., 1998). Pigeonpea ( Cajanus cajan L ) is a legume shrub identified with high potential of improving N and P cycling for the benefit of associated crops on smallholder farms in the tropics for improved and sustainable crop production ( Giller et al ., 2009; Snapp et al ., 2010; Ennin et al ., 2013; Hayford, 2018). Long - term field research involving legumes such as pigeonpea for soil fertility management and prod uctivity of root and tuber crops such as yam is limiting. Also, it takes a longe r period to evaluate and monitor productivity and sustainability in cropping systems. Given that, this field study was just for three seasons, and the effect of applied pigeonp ea residue on soil fertility and 101 yam productivity may take a longer period than three seasons adds to the multiple questions to be addressed. Can the pigeonpea be managed to play its role of biomass for soil fertility and stakes provision for yams to climb ? How much yam productivity improvement could be anticipated in the long - term (1 0 years) with the use of pigeonpea - yam cropping system s ? These questions call for multiple factor field studies over a long period with a major resource commitment. Instead, a process - based cropping system model has been used to offer an efficient and effe ctive option in addressing these research questions within a reasonable time and resource use (Jones et al ., 2003; Keating, 2003 ) . Process - based crop simulation models such as APSIM, SALUS, and CERES - Maize have been used to explore cropping systems questio ns resulting in the understanding of the dynamics of crop - soil - climate - management interactions in cropping systems in Africa. These explorations have mostly been conducted for legume - cereal cropping systems (Adiku, 1995; Carberry et al ., 1996; Whitbread et al ., 2010; Liu and Basso, 2017; Ollenburger and Snapp, 2014). Not much has been done on the productivity of root & tuber cropping systems with a legume, especially for white yam. This current study explores how integrated soil fertility with pigeonpea bi omass residue and fertilizer would sustain yam production on continuously cropped fields using SALUS (System Approach to Land Use Sustainability) model. The SALUS model stimula tes and models continuous crop, soil, water, and nutrient conditions under diffe rent management approaches for multiple years. The agricultural land use management approaches simulated by SALUS include crop rotations, planting dates, plant populations, ir rigation and fertilizer applications, and tillage systems (Basso and Ritchie, 20 15). Therefore, using the SALUS, we explore research questions such as: How do integrated soil fertility management impact long - term (10 yrs) yam tuber yields? Are the yam tube r yields on continuously cropped fields sustainable for Long - term (10 yrs)? The specific objective was to evaluate long - term (10 yrs) yam 102 tuber yield under pigeonpea - yam cropping system management. The specific pigeonpea - yam cropping system op tions simulated for evaluation include; (a) yam with pigeonpea residue (2t/ha) a nd full recommended fertilizer rate (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) (b) yam with pigeonpea residue (2t/ha) and half recommended fertilizer rate (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) (c) yam with pigeonpea residue (2t/ha) and no fertilizer (d) sole yam with full recommen ded fertilizer rate (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) (e) sole yam with half recommended fertilizer rate (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) (f) sole yam with no fertilizer. These management approaches were taken to reflect the current yam production practices and the p roposed integrated soil fertility management approach for adoption. The sole yam with no fertilizer would represent the baseline scenario and the current practice where farmers with limited access to land do continuous cropping on the same land year after year. The sole yam with full fertilizer option was an intervention approach released to farmers by the CSIR Crops Research Institute of Ghana (Ennin et al . 2016). The integra ted soil fertility management options of cultivating yam with pigeonpea residue are being tested as an Integrated Soil Fertility Management (ISFM) option for release to farmers. 103 MATERIALS AND METHOD Study site and field experiment for model validati on The field study was conducted on - station at the CSIR Crops Research Institute at Fumesua (6 o o o o - savannah transition zones of Ghana respectively (Figure 3.1) from 2017 through 2018 an d 2 019 cropping seasons. The fields were about 13 15 years continuously cropped fields with a rotation of maize and cowpea/groundnut. Ejura soils are Ferric Lixisol; Ejura series with a thick top layer of fine sandy loam whiles Fumesua soils are Ferric A cri sols; Asuasi series with a greyish brown sandy clay loam topsoil ( Adu, 1992; MoFA, 2017) . Both locations have a bimodal rainfall pattern with rainfall between March mid - August, and September November as the major and minor rainfalls, respectively. M ini mum and maximum temperatures range between 22 31 o C and 21 34 o C at Fumesua and Ejura, respectively, as shown in chapter 2 (Figure 3.1). Figure 3.1: Map showing the study area. Source: Drawn by the author with data from the geological survey depart men t, Ghana, 2019 104 The treatments were arranged in a split - plot with three replications. The two main plots were yam in pigeonpea as a border (PB) and No pigeonpea/sole yam. The subplot treatments were variations in fertilizer levels as recommended by CSIR Crops Research Institute of Ghana for yam production as full - rate 45 - 45 - 60 kg/ha N - P 2 0 5 - K 2 0; half - rate 23 - 23 - 30 N - P 2 0 5 K 2 0 kg/ha and no fertilizer (Ennin et al ., 2016). The pigeonpea and yams on the plots followed the replacement/substitutive approac h with a row/ridges for yams substituted for pigeonpea around the border of the field for pigeonpea as a border plant. I n all locations and years, pigeonpea biomass was prune d and applied on the ridges whiles stems were cut and used as stakes for the yams to climb (Table 3.1). Pigeonpea were planted in 2017 cropping season while the yams were planted, and fertilizer applied in the 2018 and 2019 cropping seasons in both locatio ns. Yam in PB had stakes cut from the border whiles bamboo stakes were procured an d transported to the sole yam field for staking. Table 3.1: Population of pigeonpea, yam and total pigeonpea biomass applied in the study . Cropping system Size of the plot (m 2 ) Number of pigeonpea/ ha Number of yam/ ha Dry biomass kg/ha applied Fumes ua Ejura Yam in PB 200.64 5,931 7,177 1521.44 2113.06 Sole yam 200.64 -- 10,416 -- -- NB - PB had two rows of PP & yam planted at inter and intra - row of 1.2X 0.5m along three sides of the field and 1.2X 0.8m, respectively. Whiles sole yam had 1.2 X 0.8m of the only yam. PB Pigeonpea as a border plant Dioscorea rotundata ) were used. Ridges were constructed manually on all treatments . A fter being treated with a fungicide and insecticides, yam sets were planted in April and May at Fumesua and Ejura respectively for both seasons . The fertilizer was split applied at 5 - 6 and 12 weeks after planting in both locations and years. Weeds were controlled manually 4 and 5 times on the PB and sole yam fields respectively in both locations and years. Re - shaping of ridges took place one and two times for PB and sole 105 yam fields. Yam tubers were harvested in December in all locations and years. Soil sampling was conducted at planting and harvesting on the ridges at 0 - 20cm and 20 40cm for all treatments, locations, and years. Overview of t he Systems Approach to Land Use Sustainability (SALUS) model SALUS model is a process - based cropping system model that simulates the interaction between climate - soil - c rop - management and their implications on soil water & nutrient cycling and crop growth & development (Figure 3.2). The SALUS model was derived from th e Crop Environment Resource Synthesis (CERES) with improved modifications to soil nutrient, and water - cycl e growth cycle (Basso and Ritchie, 2015; Basso et al ., 2016). SALUS runs on a daily time step for multiple years using a minimum input dataset of dail y weather data, the soil at each layer, crop genetics parameters, and field management data. The daily wea ther data consist of minimum and maximum temperatures, precipitation, and solar radiation . T he soil layer data consist of layer depth, drained upper l imit, lower limit, bulk density, and organic carbon. The field management data includes details of plantin g date, fertilizer use and rate, and date of harvesting. It uses two main approaches; simple and complex, in the analysis of the development and growt h of crops. The simple approach is based on the generic crop - specific curve of leaf area index (LAI), to t he thermal time for crop development (crop durations) and potential biomass accumulation (harvest index) in the face of the prevailing stresses such a s temperature, water, N on the plant development in the season (Liu and Basso, 2017; Dzotsi et al ., 2013). The complex approach is similar to CERES, where genetic coefficients are used. Leaf area, ability to use radiation efficiently, and the ability of th e crop to grow in the presence of nutrient and water stresses are vital for biomass accumulation. The SALU S soil nutrient cycling model was adapted from the 106 century (Parton et al ., 1988) with temperature, clay, and water functions modified. Soil organic m atter (SOM) goes through the process of decomposition, mineralization of N, N immobilization, and transfor mation into gaseous N. The model uses three pools of phosphorus and three soil organic carbon pools; active, slow and passive. Also, turnover rate and C: N ratio are factored in the model for the simulation SOM, N mineralization, and immobilization. Fresh crop residue such as pigeonpea biomass is split into two pools of structural and metabolic using their N and lignin content. SOC goes through a dynami c process starting with residue and root decomposition, mineralization in the soil, immobilization, and lo ss to the atmosphere in gaseous form. The SOC initialization process follows the method used by Basso et al ., 2011, and an example of the SOC decompos ition process shown by Senthilkumar et al . (2009). The water balance followed the method used by Ritchie for simulating infiltration, drainage, evapotranspiration, runoff, and water redistribution (Basso and Ritchie 2012; Suleiman and Ritchie 2003). K cy cle was not considered in the model. SALUS, however, does not simulate weed, pests, and diseases. Figure 3.2: Overview of the System Approach to Land Use Sustainability (SALUS) . Source: Basso et al., 2006) 107 SALUS model validation SALUS has been tested for simulation of cropping systems under different climates. Simulated cereal gain yields match observed yi elds in Italy with a Mediterranean climate (Basso et al ., 2011; Pezzuolo et al ., 2014), in Argentina with a humid subtropical c limate (Albarenque et al ., 2016) and in the warm, humid climate of the US (Basso and Ritchie, 2015). It has been used successful ly to simulate spatial variability in maize - pigeonpea cropping system in the humid subtropical and tropical sava nnah climates of Malawi (Liu and Basso, 2017). Also, grain yield, evapotranspiration, drainage and SOC dynamics in cropping syste ms under various management has been tested and simulated (Basso and Ritchie, 2015; Basso et al ., 2015; Basso et al ., 2006; Sen thilkumar et al ., 2009; Basso and Ritchie, 2012). In this study, the SALUS model was parameterized to represent the growth and d evelopment of the white yam ( Dioscorea rotundata eld under two cropping systems (sole yam and yam in pigeonpea as border plant) with three fertilizer application levels (0 - 0 - 0, 2 3 - 23 - 30 and 45 - 45 - 60 N - P 2 0 5 K 2 0 kg/ha) for two years (2018 - 2019) in two locations, Fumesua and Ejura (Chapter 2). The soil and management input for model validation was collected during field experiments, discussed in Chapter 2. The weather input for SALUS validation was derived from two sources. Daily rainfall, minimum and maximum temperatures were obtained from weather stations near the two study sites, provided by the Ghana Meteorological Agency . The daily solar radiation was obtained from the grided, Pr ediction Of Worldwide Energy Resources (POWER) Agroclimatology dataset ( https://pow er.larc.nasa.gov ). The accuracy of the model was assessed using Root Mean Square of Deviation (RMSD), the Mean Absolute Percenta ge Error (MAPE) between simulated and observed tuber yield, and the Coefficient of Determination (r 2 ) of a linear regression mo del with simulated yam tuber yield 108 as the independent variable and observed yam tuber yield as the dependent variable (Figure 3.4 ). The Root Mean Square of Deviation (RMSD) (Eqn. 3.1) indicates the magnitude of the mean difference between observed and sim ulated results (P ineiro et al ., 2008 ). The mean absolute percentage error (MAPE) (Eqn. 3.2) indicates the percentage of the relat ive difference between simulated and observed data (Chipanshi et al ., 2015; Kumar et al ., 2013). When MAPE < 10%, 10% < MAPE > 20%, and MAPE > 20%, it means the performance of the model is highly accurate, good accuracy, and low accuracy prediction, respec tively ( Ramasamy et al ., 2015). The Coefficient of Determination (r 2 ) indicates the str ength of correlation between the observed and simulated yields. The r 2 ranges from 0 and 1. r 2 of 1 indicates a perfect correlation between observed and simulated yield , and r 2 of 0 means no correlation between the two yields ( Chipanshi et al ., 2015 ; John son, 2014). Where n is the number of observations where n is the number of observations, Simulation e xperiment We used the validated SALUS model to evaluate th e effect of integrated soil fertility management of pigeonpea biomass and fertilizer on long - term (10 years) yam tuber yield. Two cropping systems consisted of yam in pigeonpea as the border (Yam in PB) and s ole yam cultivation. Each cropping system was sp lit into three, where the recommended fertilizer rate of full rate - 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha, half rate 23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha and no fertilizer were applied (Table 3.2). Simulations were carried out for 2010 - 2019. The long - term weather record was der ived from NASA POWER. In simulations, 2 t/ha of dried pigeonpea leafy biomass 109 (average leafy biomass produced in the experiments for two years) was added annually for the PB cropping system. Table 3.2: Agron omic management evaluated for long - term (10 yrs) yield implication on yam in the study . Cropping system Fertilizer (N - P 2 O 5 - K 2 O kg/ha) Agronomic management description Sole yam No fertilizer Yam cultivated continuously in 2010 - 2019 on ridges with no fertilizer. On ly yam tubers harvested and exported from the field. 23 - 23 - 30 Yam cultivated continuously in 2010 - 2019 on ridges with half recommended fertilizer rate. Only yam tubers harvested and exported from the field. 45 - 45 - 60 Yam cultivated continuously in 2010 - 2019 on ridges with full recommended fertilizer rate. Only yam tubers harvested and exported from the field Yam in PB No fertilizer Yam cultivated continuously in 2010 - 2019 on ridges with pigeonpea as the border plant. Average dry pigeonpea residue of 2t/ha with no fertilizer applied on ridges. Only yam tubers harvested and exported from the field. 23 - 23 - 30 Yam cultivated continuously in 2010 - 2019 on ridges with pigeonpea as the border plant. Average dry pigeonpea residue of 2t/ha and h alf recommended fertilizer rate applied on ridges. Only yam tubers harvested and exported from the field. 45 - 45 - 60 Yam cultivated continuously in 2010 - 2019 on ridges with pigeonpea as the border plant. Average dry pigeonpea residue of 2t/ha and full r ecommended fertilizer rate applied on ridges. Only yam tubers harvested and exported from the field. Statistical analysis To compare the integrated soil fertility management treatment options, the dry tuber yields for all the ten years (2010 2019) of each treatment were presented in line and empirical cumulative distribution function graphs. 110 RESULTS SA LUS model evaluation SALUS model was able to reproduce yam cultivation in Ghana with good accuracy. The root means square of deviation (RMSD), and th e mean absolute percentage error (MAPE) between the simulated and observed yam tuber yield was 0.73t/ha an d 10.73%, respectively. Overall, the simulated tuber yield matched with the observed yield, with a coefficient of determination (r 2 ) of 0.72 (Figure 3 .3). Figure 3.3: Comparisons between simulated and observed yam tuber dry matter yield across two cropping systems under three fertilizer rates in 2018 - 2019 at two sites. DM Dry Matter; No fertilizer, H alf rate, and F ull rate are 0 - 0 - 0, 23 - 23 - 30, and 4 5 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha, respectively. Effect of cropping system and inorganic fertilizer on long - term yam tuber yield For c ultivating sole yam without fertilizer input on continuously cropped fields (farmers practice) for ten (10) years, the dry tuber yield ranged from 2.31 to 2.92 t/ha and 1.73 to 3.15 t/ha at Fumsua and Ejura respectively. The probability of exceeding 2.5 t/ha is 50% and 40% at Funesua and Ejura respectively (Figures 3.4 & 3.5). When sole yam was fertilized with half and recommended full 111 fertilizer rat e, yam tuber yield improved to 3.59 - 4.43 t/ha and 4.83 - 5.65 t/ha , respectively , at Fumesua. At Ejura, the use of half and full fertilizer rates on the sole yam field resulted in an improved yam tuber yield range of 3.73 - 4.16 t/ha and 5.0 3 - 5.84 t/ha respect ively. At Fumesua, yam tuber yield would not exceed 4.0 t/ha and 5.4 t/ha under half and full fertilizer rate , respectively , when given a 70% probability. Given 60% probability, yam tuber yield would not exceed 4.0 t/ha and 5.4 t/ha unde r half - rate and ful l - rate fertilizer input, respectively at Ejura. (Figures 3.4 & 3.5). Incorporation of pigeonpea leaf residue further enhanced yam tuber yields in both locations. At Fumesua, cultivating yam with pigeonpea residue alone, pigeonpea residue with half fertiliz er rate, and pigeonpea with full fertilizer rate resulted in yam tuber yield range of 4.52 - 6.02 t/ha, 5.80 - 7.74 t/ha and 7.0 - 8.38 t/ha respectively. At Ejura, pigeonpea residue alone, pigeonpea residue with half fertilizer rate, and pige onpea residue with full fertilizer rate resulted in a yield range of 5.81 - 7.26 t/ha, 6.92 - 8.84 t/ha and 7.91 - 9.99 t/ha respectively (Figure 3.4). There is a 30% and 100% chance of exceeding 5t/ha tuber yield at Fumesua and Ejura respectively, upon using pi geonpea residue wit hout fertilizer. The use of half recommended fertilizer rate in addition to the pigeonpea residue improved the chances of exceeding 6 t/ha to 70% and 100% at Fumesua and Ejura respectively. Yam tuber yield is further enhanced exceeding 7 .5 t/ha at a probab ility of 30% and 100% for Fumesua and Ejura respectively when full recommended fertilizer rate is used in addition to pigeonpea residue (Figure 3.5). The range and chance of improving yam tuber yield were better when yam was cultivated with only pigeonpea residue than when sole yam was cultivated with full fertilizer rate (Figure s 3.4 & 3.5). 112 Figure 3.4: Simulated long - term (10 yrs ) yam yield, dry tuber yield (DM), under two cropping systems, and three inorganic fertilizer rates at tw o sites. DM Dry Matter; No fertilizer, Half rate, and Full rate are 0 - 0 - 0, 23 - 23 - 30, and 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha, respectively. Figure 3.5: Cu mulative probability of yam tuber yield, dry matter (DM), under two cropping systems and three inorganic fertilizer rates at two sites: (a) Ejura and (b) Fumesua . No fertilizer, Half rate, and Full rate are 0 - 0 - 0, 23 - 23 - 30, and 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha, r espectively. 113 DISCUSSION Models are simplified, formal representations of relationships between defined q uantities or qualities in physical and mechanical terms developed to assist in making informed decisions in the management of agricultural systems (Jef fers, 1982: Basso and Ritchie, 2015; Oteng - Darko et al ., 2013). SALUS evaluated ISFM of pigeonpea and ino rganic fertilizer implication on the long - term (10 yrs) yam tuber yield on the continuously cropped field s . The generally better yield range and the chance of improving long - term tuber yields recorded at Ejura than the Fumesua could be attributed to the mo re fertile soil (Lixisols) with almost neutral pH (6.6 7.9) at Ejura than acidic acrisols with very stro ng acid pH (4.4 - 5.2) at Fumesua (Chapter 2; Lal, 1976). This soil condition favored yam growth and yield at Ejura than Fumesua. The better chance of s ustaining long - term yields on the PB field than the use of sole yam irrespectively of the tested fertilize r rates and location (Figure 3.4 & 3.5) indicates the impact of the pigeonpea residue on soil fertility and yam yield on continuously cropped fields. The pigeonpea residue improved nitrogen (N), phosphorus, and the exchangeable cation capacity (ECEC) of th e soil. Also, the presence of the pigeonpea residue improved soil moisture and reduced erosion of the ridges favoring bulking and tuber yield (Chapter 2). Several studies have noted the integration of leguminous shrub such as pigeonpea ( Cajanus cajan ), gl iricidia sepium into yam cropping system did improve on soil N, nutrient cycling and yam tuber yields (Ennin et al ., 2013; Maliki et al ., 2012a; Malik i et al ., 2012b; Liu et al ., under review). The better chance of sustaining long - term yam yields upon plan ting yam with pigeonpea residue without fertilizer than planting yam as a sole crop with any inorganic fertilizer rate (Figures 3.4 & 3.5), indicates that the use of only inorganic fertilizer in soil fertility management on continuously cropped fields is n ot sustainable. This is in line with the observation that the use of 114 only inorganic fertilizer for long - term resulted in a faster loss of soil organic matter on yam producing fields across Ghana than integrating with pigeonpea (Liu et al ., under review). T he reduced or no fallow periods, slash and burn land preparation and intensive soil preparation medium (mound) for yam cultivation, has resulted in a loss of soil organic matter and soil microbial communities. This loss has resulted in yam producing areas of W est Africa having low soil organic matter (about 1%) (Nwaga et al ., 2010; Tchabi et al ., 2008 & 2009). The low soil organic matter leads to low so il moisture infiltration, retention, and increased erosion of the bulking medium (mound) (Frossard 2017; c hapter 2). As a result of these soil conditions, O'Sullivan et al . (2008) noted that yam yields did not respond to N, P and K application on some soil s whiles Hgaza et al ., (2012) observed a maximum of just 30% N recovery in yam tuber indicating more loss of N to the environment. These conditions, alongside limited land resources and climate change in sub - Saharan Africa, are hampering yam and other food crop production (FAO, 2017; Montanarella et al ., 2016). The use of leguminous shrubs in sustaining soil f ertility, especially at the yam producing belt of West Africa, is imperative for sustainable yam production and food security. Using the EPIC (Environ mental Policy Integrated Climate) crop growth simulation model, Srivastava et al . (2012) evaluated the imp act of climate change on yam ( Dioscorea alata ) yield in Benin. The study projected a 27 48 % reduction in yam yields resulting from weather variabil ity, especially temperature and rainfall. Also, Cornet et al . (2016), using the Bayesian network model, fo und that, the emergence date of the yam sett was the major direct cause of plant yield variability in both white ( D. rotundata) and water yam (D. alat a ). The study recommended agronomic practices, which improve early and uniform sprouting, to be very impor tant in improving yam yields in W est Africa. Thus, plant biomass residue, especially from the leguminous shrub, is vital in addressing soil fertility challenges and climate change impact mitigation. However, producing reasonable 115 quantities of leguminous sh rub biomass for an ISFM for crop production is a major challenge for soil fertility maintenance and yam production (Frossard et al ., 2017). Planting y am with pigeonpea as a border plant has shown to be an option in addressing this challenge in yam producti on. Three border sides or a third of the field, when used for growing and provision of pigeonpea residue and stakes, could sustain the yam on the two - thirds of the remaining field. Even when farmers have no access to inorganic fertilizer, the use of pigeon pea residue alone result s in a better chance of long - term tuber yield than the use of full (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) fertilizer rates on sole yam fi elds (Figure s 3.4 & 3.5). This indicates, integration of pigeonpea into yam cropping systems by planting y am in alleys of pigeonpea, or planting yam with pigeonpea as border plants described here as pigeonpea - yam cropping system, presents options for susta inable yam production on continuously cropped fields. 116 CONCLUSION AND RECOMMENDATIONS The study has indicated that the provision of pigeonpea residue for ISFM with inorganic fertilizer for sustainable yam production on continuously cropped fields i s possible with the pigeonpea - yam cropping system. The chances of sustaining l ong - term (10yrs) yam tuber yields improved significantly on pigeonpea residue treated fields than sole yam fields. When a farmer has no access to inorganic fertilizer, planting y am with pigeonpea residue alone resulted in an improved chance of sustaining l ong - term tuber yields than sole yam cultivation with full (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) recommended inorganic fertilizer rate. Thus, suggesting ISFM of pigeonpea residue and inorg anic fertilizer could improve and sustain yam yield on continuously cropped fi elds than using only inorganic fertilizer. However, further simulation of the long - term changes in soil carbon, N, P, and other nutrients resulting from the pigeonpea residue and their correlation with yam productivity in the pigeonpea - yam cropping system would be needed. Also, simulation for long - term pigeonpea residue production in a pigeonpea - yam cropping system, and implications on yam productivity should be pursued. These wo uld provide a guide on ISFM of pigeonpea residue and fertilizer for sustainabl e yam production on continuously cropped fields to address the search for fertile lands yearly, resulting in deforestation in the yam producing areas of West Africa. 117 REFERENCES 118 REFERENCES Adiku, S. G. K, Carberry, P. S, Rose, C. W, McCown, R. L, & Braddock, R. (1995). A maize ( Zea mays ) - cowpea ( Vigna unguiculata ) intercrop model. 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Eu ropean Journal of Agronomy 32, 51 - 58. 123 CHAPTER 4 ECONOMIC ANALYSIS OF A PIGEONPEA - YAM CROPPING SYSTEM OPTIONS ABSTRACT Economic analysis is a vital process for determining the benefits a nd attractiveness of technologies and the costs associated with those interventions to inform better decision - making on adoption. An i nvestigation into the cashflows and profitability was conducted as part of a larger study to compare the effects of integr ating pigeonpea into yam cropping system with different fertilizer rates to sole yam (SY) with different fertilizer rates replicating the farmer practice. The integration of pigeonpea into yam described as a pigeonpea - yam cropping system consists of; yam p lanted with pigeonpea in all eys (PA) and as a border (PB ). PA, PB, and SY plots are further divided into sub - plots, which are subjected to three treatments of N - P 2 O 5 - K 2 O in kg/ha at 0 - 0 - 0, 23 - 23 - 30, 45 - 45 - 60 as no, half and full fertilizer rate respectivel y. The study was conducted in Fumesua and Ejura in the F orest and Forest - Savannah transition zones, during the 2018 2019 cropping seasons. The income advantage of each cropping system and fertilizer combination was estimated using Income Equivalent Ratio (IER) and Cost - Benefit Analysis (CBA) to complement the agronomic trials. The IER was evaluated under three farmer - practiced scenarios of 1) when a farmer has no access to fertilizer; 2) when a farmer can apply half the recommended fertilizer rate; 3) whe n a farmer can apply the full recommended fertilizer rat e. A significant interaction was observed between the pigeonpea - yam cropping system and the fertilizer rate. Planting yam in PA with half and full fertilizer rates resulted in a significantly (P < 0.0 5) higher and similar IER than sole yam for all three sc enarios in both locations and seasons. Also, planting yam with pigeonpea (PA and PB) without fertilizer was observed to have better IER than planting sole yam with full fertilizer rate in both locatio ns. The total cost of production (TCP) was higher for so le yam across 124 fertilizer rates in both locations, mainly due to the cost of stakes and labor costs for staking. The total cost of implementing a PA cropping system with no fertilizer was the cheapest option for farmers in the two locations. The cash inflow s and outflows discounted at 7.43% were based on the social opportunity cost of capital observed ; planting yam in pigeonpea (PA and PB) with half fertilizer rate w as only slightly lower than the use o f full fertilizer rate. A maximum Internal Rate of Retur n (IRR) ranging from 6.38% 6.36% and 6.12% 6.11% for planting yam in PA with full and half fertilizer rates respectively were observed between the two locations. Interestingly, planting yam in PA with half and full fertilizer rates resulted in similar Benefit - Cost Ratio (BCR) of 2.14 and 2.13 respectively for Fumesua whiles the same treatments recorded 2.38 and 2.36 for Ejura suggesting that estimated benefits from adopting the proposed technologie s will be more when yams were planted without fertilizer, the presence of the pigeonpea (PA and PB) resulted in a better IER, IRR, and BCR than when half and full fertilizer rates were used for sole yam in both loc ations. With these results and in consideration of the e nvironmental pollution caused by excessive and unregulated fertilizer usage, doubling the fertilizer rate would result in marginal income gains and not worth the environmental and cost implications. P igeonpea - yam cropping system can be promoted as a viable option for soil fertility management and a source of readily available stakes for sustainable yam production. Adoption by farmers would address deforestation and land degradation issues associated wi th yam production whiles improving productivity and inco me of smallholder yam farmers. Keywords: Benefit - cost Ratio; Income Equivalent Ratio; Cost of Stakes; Present Net Value, Internal Rate of Return; Cost of Production 125 INTRODUCTION AND RATIONALE Agricu lture has a critical role in improving the income and livelihoods of smallholder farmers of the African continent since the bulk of the labor force is employed by the agriculture sector (Hawkins et al ., 2009). The situation is similar in Ghana, where the a griculture sector is the largest source of employment (Darfour and Rosentrater, 2016). The Medium - Term Agricultural Sector Investment Plan (METASIP) and the Comprehensive African Agricultural Development Program (CAADP) program targeting 6% annual agricult ural growth were thus introduced to promote agricultural development for improved income and food security (Ministry of Food and Agriculture (MoFA), 2010; National Development Planning Commission (NDPC), 2010). Despite the importance of agriculture and the programs introduced, the agriculture secto r is still challenged with low productivity and inadequate processing and storage facilities , resulting in the decline of product quality (NDPC, 2010). This fact has reduced the contribution of the agriculture sec tor to Gross Domestic Product (GDP) and has risen poverty amongst smallholder farmers (NDPC, 2010; Ghana Statistical Services (GSS), 2014). One of the primary reasons for this outcome is the low adoption of improved technologies for sustainable crop produc tion (MoFA, 2010). New and improved techno logies are critical to boost agricultural productivity to meet the growing demand , enhance food security and stimulate economic growth (Fuglie et al ., 2019). According to Jain et al . (2009), "improved techniques a nd practices which affect the growth of agr icultural output" are referred to as agricultural technologies. As such, better soil and fertility management and input reduction techniques fall under new or improved technologies. They help boost yields and redu ces the average cost of production while re ducing the negative impacts on the environment leading to substantial productivity and socioeconomic gains by farmers. Pinstrup - Andersen (1982) observed that the adoption of agricultural technology is driven by th eir usability 126 and ability to meet the farme rs' needs, which in the case of smallholder farmers, mainly includes food and income. Moreover, the adoption of technologies and delivering technical assistance will be more effective when there is a better unders tanding of the farmers' social and cultural background (Crane, 2014). Other attributes, such as affordability, accessibility, safety, and scale neutrality, also play a pivotal role in technology uptake (Fischer, 2016). Despite the best intentions to assist smallholders and resource - poor farmers, so cioeconomic, and environmental benefits from new agricultural technologies do not benefit these groups (Loevinsohn et al. , 2012). Yam is an essential staple food and cash crop produced and consumed along the yam belt of West Africa. In Ghana, yam is one o f the most important root and tuber crops cultivated for food and income generation predominantly by smallholder farmers (Babaleye, 2005). It contributes about 16% to the National Agricultural Gross Domestic Produ ct (Anaadumba, 2013). As the second - largest global producer, and the leading exporter of yams, Ghana exported about US$ 33 million worth of yam in 2017 (Ghana Export Promotion Authority (GEPA), 2018). Despite this importance of yam, its production is chall enged with the regeneration of soil fertili ty and scarcity of stakes for staking ( Akwag et al ., 20 0 0 ; Ennin et al ., 2014; Owusu Danquah et al ., 2014). Yam is an input - intensive crop that is a heavy nutrient feeder. Farmers are constantly pressed to source or maintain fertile fields and move to a new field each year. As a result, farmers clear forest areas in search of new fertile lands and stakes, leading to deforestation and other detrimental environmental impacts (Owusu Danquah et al. , 2014; Ennin et al ., 2014). Despite these efforts, the yam yi elds are still low, and farmers cannot maximize productivity and profitability. Given that Ghana is a top exporter of yam, cost - effective and sustainable cultivation of yam would help sustain the livelihoods for tho usands of smallholder farmers and generat e export revenues. Thus, technologies that can improve soil fertility and minimize the need for stakes can 127 address two major constraints faced by farmers (Acheampong et al ., 2019). Research shows that intercropping nutrient - intensive crops with leguminous plants have agronomic (Ege and Idoko, 2009; Ngwira et al. 2012; Chapter 2) and economic benefits (Egbe et al. , 2012; Mutegi and Zingore, 2014) for farmers in Africa. Intercropping with pigeon p e a is particularly suit ed for drought - prone areas with degraded soils (Egbe et al. , 200 9 ; Kiwia et al ., 2019). A multipurpose and drought - tolerant leguminous shrub such as pigeonpea ( Cajanus cajan ) is well suited for the climate in Ghana . It can help address the soil fertility a nd staking problems and provide several other benefits. Pigeonpea adds Nitrogen to the soil, and its biomass, when incorporated into the soil, can increase soil organic matter and conserves moisture. A mature pigeonpea tree trunk provides a sturdy and dura ble stake for the yam vines to climb on, eliminating the need to procure and install stakes (Chapter 2). Seran and Brintha (2010) noted complimentary benefits such as input use efficiencies, weed control, pest and dise ase management, erosion control, and g rain yield when pigeonpea was intercropped with maize. 128 METHODOLOGY Experimental design and treatments The fieldwork to evaluate the performance of the pigeonpea - yam cropping system was conducted in Fumesua and E jura during the 2018 and 2019 cropping season. Fumesua and Ejura are in the forest and forest - savannah transition agroecological zones of Ghana, respectively. Fumesua has a mean temperature range of 22 - 31 o C , mean temperature ranges from 21 to 34 o C. Both agroecological zones have a bimodal rainfall pattern with the major rainy season starting from March and continue through to August and the minor rainy season starting from September and continues through to N ovember. Annual rainfall ranges between 1027 - 1322mm for Fumesua and 1171 - 1574mm for Ejura (Adu, 1992). As described in a previous chapter, the field study was conducted in a split - plot design with three replications. The main plot was divided into three co nsisting of 1) sole yam (SY); 2) yam with pigeonpea in alleys (PA); 3) ya m with pigeonpea as a boarder (PB). The SY plot replicated the farmer scenario. The three subdivided plots were further divided into sub - plots with three N - P 2 O 5 - K 2 O kg/ha fertilizer t reatments - no fertilizer (0 - 0 - 0); half fertilizer rate (23 - 23 - 30); and f ull fertilizer rate (45 - 45 - 60). The fertilizer rate recommended for yam production by the Council for Scientific and Industrial Research Crop Research Institute (CSIR - CRI) in Ghana was used as the full fertilizer rate for this research (Ennin et al ., 201 6). The pigeonpea variety used was a long duration (6 - 8 months) accession sourced locally and planted a year ahead (May 2017) in both locations before planting the yam in April - May 20 18. " Pona ," a premium white yam ( Dioscorea rotundata ) variety was used in the study. The fertilizer rates were split applied at 5 - 6 weeks after planting (WAP), and 12WAP on the yam stands on the ridges for all treatments. The combination of the pigeonpea a nd the yams on the PA and PB field followed the substitutive/replacement approach. In the PA field, pigeonpea 129 was planted 3.6m apart between rows and 0.5m apart within a row to enable planting two ridges/rows yams in - between 1.2m apart and 0.8m apart withi n a ridge (described with diagrams in Chapter 2). A total plant populatio n of 5,931 pigeonpea plants/ha and 7,177 yam plants/ha with one plant per stand were achieved for pigeonpea and yam in fields at both locations. In PB fields, two rows of pigeonpea we re planted in the margins on three sides of the field 1.2m apart and 0.5m intra - row. Yam was planted in the middle at a recommended spacing of (1.2m X 0.8m) (Ennin et al ., 2016). With this spacing, a population of 5,931 pigeonpea plants/ha and 7,177 yam pl ants/ha was achieved . The SY field had yams planted on ridges at 1.2m X 0 .8m inter and intra - rows respectively to achieve a population of 10,416 plants/ha. Biomass was pruned from the pigeonpea and applied on ridges as green manure to add nutrients to the soil to benefit the yams crop. The woody trunks of pigeonpea grown in all eys served as live stakes in the PA treatments and stakes cut from the surrounding pigeonpea was used as stakes in the PB treatments. In the case of SY fields, stakes were purchased a nd transported to the field for staking. Data from two cropping seasons r eveal that the integration of pigeonpea into the yam production system helped improve and sustain soil fertility through the fixing of atmospheric nitrogen and provide readily availab le stakes for yam production. There were substantial productivity gains w hen yam was intercropped with pigeonpea compared to sole yam with different fertilizer rates in both locations (Chapter 2, figure 2.6b). It would be useful to estimate the potential c osts and/or benefits to producers associated with each technology to make more informed recommendations to farmers . This study aims to quantify several economic measures used to determine the profitability of the pigeonpea - yam cropping systems. The combine d economic impacts of each cropping system and fertilizer combination wil l complement the agronomic data and aid in decision making. Access to this information will enable research in the technology dissemination process and empower farmers 130 with evidence t o make more rational decisions. The analysis was conducted using yam and pigeonpea productivity data from field evaluation of pigeonpea - yam and SY from Fumesua and Ejura during the 2018 and 2019 cropping seasons (Chapter 2). Income Equivalent Ratio and Cost - Benefit Calculation The profitability of the cropping systems was es timated using Income Equivalent Ratio (IER). To better understand the implications of the various cost components of yam in PA, PB, and sole yam cropping systems, a Cost - Benefit Analysis (CBA) was conducted, taking into account variation in fertilizer rate . Discounted cash inflows and outflows were used to calculate the Net Present Value (NPV), Internal Rate of Return (IRR), and Benefit - Cost Ratio (BCR). When calculating these dif ferent parameters, three possible scenarios that could apply in the farmers' c ontext of continuous crop production were considered: scenario 1: when there is no access to fertilizer; scenario 2: when a farmer can apply half recommended fertilizer rate (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha); and scenario 3: when a farmer can apply full recommen ded fertilizer rate 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha). All parameters were computed on a per hectare basis. The costs were classified into fixed costs (FC) and variable costs (VC). Cost s reported under FC included expenses incurred during the production process t hat did not change with the volume of output and initial investments made towards establish ing the pigeonpea - yam cropping system. The costs of land preparation and pigeonpea esta blishment were classified as FC since these costs were investments made only i n 2017. Variable costs (VC) included recurring costs that varied with production. The costs of various inputs such as seed yam, fertilizer, labor costs (for ridging, fertilizer a pplication, weeding, and harvesting), cost of stakes , were categorized under V C. Total Cost of Production (TCP) is the sum of FC and VC. It was assumed that in the case of SY, the land is undergoing a 131 fallow period in year 1. In the case of the PA and PB f ields, yam cultivation did not begin until the second year because the pigeonp ea plants needed to reach a certain level of maturity before they can be used as stakes in PB or replace the stakes in PA. Therefore, no harvesting of pigeonpea or yam was done during year 1. The revenue generation begins in year 2 with the 1 st season of yam and pigeonpea harvesting. The amount of yam and pigeonpea harvested was adjusted by 10% to account for post - harvest losses. This adjusted value was adopted from Ennin et al . (2014) to account for extrapolation from smaller plots to a hectare . Total rev enue was estimated for SY and intercropped systems based on the average market price of yam and pigeonpea for years 2018 and 2019, assuming the sale of the total adjusted harvest of yam and pigeonpea is possible. Income equivalent ratio The Income Equi valent Ratio (IER) is a concept similar to the Land Equivalent Ratio (LER), which uses gross income instead of yields. In this case, gross income from sole yam and pigeonp ea systems was used to calculate IER to compar e the income for the three cropping sys tems (PA, PB, and SY) factored in the partial IER for sole pigeonpea. The IERs for the three scenarios described earlier were calculated following the approach used by Gha ffarzadeh (1997). Equation 4.1 was modified to reflect the different scenarios and fe rtilizer rates on the sole yam fields. Equations 4.1a and 4.1b were used to calculate the IER for scenario 1, and equations 4.1c and 4.1d were used to calculate IER for sc enario 2. Equations 4.1e and 4.1f were used for calculating the IER of scenario 3. 132 Scenario 1: Farmer has no access to fertilizer (sole yam without fertilizer) Scenario 2: Farmer has access to half fertilizer rate (sole yam with half rec. fertilizer rate) rec. recommended; fert - fertilizer Scenario 3: Farmer has access to fu ll fertilizer rate (sole yam with full rec. fertilizer rate) rec. recommended; fert fertilizer Cost - Benefit Analysis The approach proposed by Gittinger (1982) was used for the Cost - Benefit Analysis (CBA). It was assumed that the smallholders would receive an incremental net benefit from their investment in the SY and pigeonpea - yam cropping systems. This analysis attempts to identify and estimate the net present value (NPV) of stream discounted cash inflows (benefits) and outflows (costs) resulting from the crop production operations under three types of cropping systems (SY, PA, and PB) with alternative fertilizer rates. It enables the comparison of net cashflows with the adoption of PA or PB to SY, represent ing the typical production system execute d by the smallholder yam farmers in Ghana. The CBA conducted here entails several steps involving NPV (equation 4.3), IRR (equ ation 4.4), and BCR (equation 4.5). First, farm budgets were developed 133 for each location, taking into account the cropping systems and the three levels of fertilizer treatments. A discount rate ( i ) of 7.43% was used to convert all benefits (gross revenues) and costs into their present value (equation 4.2). The discount rate used in this analysis was based on the opportunity cost of c apital, considering the next best option for the farmer is to invest his/her money in a savings account. The average savings i nterest rate published by the current Bank of Ghana formed the basis for selecti ng this value (Bank of Ghana (BoG), 2020). Next, t he NPV was calculated using equation 4.3 to estimat e of the net incremental benefit from implementing the various cropping sys tems. An NPV higher than zero is considered to be a good investment (Gittenger, 1982). The IRR is the discount rate at which the p resent value of total benefit equals the present value of total cost (equation 4.4) or when NPV equals zero. Thus, IRR represe nts the maximum interest that a cropping system could yield based on the resources used if the cropping system recuperate s its inv estment and operating costs and still break s even (Vawda et al ., 2001). The IRR will facilitate the ranking of the cropping sy stems evaluated in this research based on its return rate. The cropping systems with IRR greater than or equal to the savings inte rest rate will be most attractive. BCR is calculated by dividing the present value of benefit by the present value of cost (eq uation 4.5). A BCR ratio of one (1) indicates costs and benefits breakeven, a ratio of greater than one (1) indicates a profitable venture where returns accrued is more than the costs incurred, and a ratio of less than one (1) indicates non - profitable vent ure as costs outweigh the benefits (Vawda et al ., 2001). In this evaluation of multiple cropping systems with different fertilizer rates, the cropping system with the highest NPV, IRR, and BCR would be selected. All these different profitability analysis a pproaches provide potential investors ; in this case, farmers with feasible options to make informed decisions on profit - maximizing cropping systems. 134 Where FV = future value of cash flows; discount rate; and t Where: C t = cost in year t ; B t = benefits in year t ; discount rate; t = number of years (1, 2, 3, INV is the initial inv estment. Where: C t = cost in year t ; B t = benefits in year t ; discount rate; and t = number of years (1, 2, Where: C t = cost in year t ; B t = benefits in year t ; discount rate; and t = number of years (1, 2, Data analysis Data a nalysis for this study was subjected to analysis of variance (ANOVA) at a 5% significance level using statistical analysis software (SAS) version 9.4. With the cropping system and f ertilizer level as fixed factors and block, location, and year as ran dom fa ctors, a four - way ANOVA was used to test the effect of the c ropping system , and fertilizer on IER under the three scenarios described earlier. T he Standard Error of the difference between means (SED) at 5% significant level was used in the separation of me ans, where treatment means differed significantly. Microsoft Excel and Simple descriptive statistics were also used to estimat e various economic measures and results presented in tables. 135 RESULTS Income equivalent ratio The IER of all the three scenario < 0.05) influenced by the interaction between cropping system, fertilizer rate, location, and year. Generally, planting yam in PA and PB with half fertilizer or no fertilizer rates present a better IER than plant ing yam in PA and PB with full fertilizer rates in both locations and seasons. Also, sole yam presented the worse IER under all three scenarios (Table s 4.1a, 4.1b & 4.1c). When a farmer has no access to fertilizer (Scenario 1), planting yam in PA presents a significantly higher (P < 0.05) IER for both 2018 (1.81) and 2019 (1.46) seasons at Fumesua. For Ejura, planting yam in PA resulted in similar IER values compared to plating yam in PB (1.55 and 1.57 respectively) for the 2018 cropping season . However, PA presented the best option for the 2019 cropping season with IER values of 1.53 for PA and 1.36 for PB (Table 4.1a). When a farmer has access to half the recommended fertilizer rate (Scenario 2), planting yam in PA was still the best option at Fumesua for both seasons. However, at Ejura planting yam in PA was observed as the best option in 2018 and similar to planting yam in PB in 2019 (Table 4.1b). In Ejura, when a farmer has access to full fertilizer rate planting yam in PA rec orded the best IER for the 2 018 cropping season while a similar IER was observed for plating yam in PA and PB for the 2019 cropping season (Table 4.1c). Across cropping seasons (2018 2019), planting yam in PA with no, half, and full fertilizer rate resu lted in an average IER of 1. 54, 1.88, and 1.39, respectively, at Ejura. However, planting yam in PA with no, half, and full fertilizer rates resulted in an average IER of 1.64, 1.59, and 1.36 at Fumesua across seasons. Thus, whiles planting yam in PA with half fertilizer rate improve s IER at Ejura, planting yam in PA with half fertilizer rate resulted in a decreased IER at Fumesua (Table s 4.1a, 4.1b, and 4.1c). Planting yam in PB with no, half, and full fertilizer rate resulted in an average 136 IER across seas ons of 1.38, 1.42, and 1.26, respectively, at Fumesua. Whiles, an average across seasons IER of 1.47, 1.55, and 1.26, were recorded for planting yam in PB with no, half, and full fertilizer rate respectively at Ejura (Table s 4.1a, 4.1b & 4.1c). Although pl anting yam in PB did result in a significantly (P < 0.05) higher IER than planting yam in PA for both locations and seasons, it presented a similar IER as planting yam in PA in Ejura during 2018 and 2019 cropping seasons when a farmer has no access, half a ccess and full access to fer tilizer respectively. At Fumesua, similar IER was observed for planting yam in PB and PA for the 2019 cropping seasons when a farmer had access to full fertilizer rate (Table s 4.1a, 4.1b, and 4.1c). The largest average income ad vantage (2018 2019) for Fu mesua was between the SY and PA without fertilizer amounting to 63.5% more income (Table 4.1a) and for Ejura between SY and PA with half the fertilizer rate increasing income by 87.5% (Table 4.1b). If all the produced yams from 2018 and 2019 are marketable , the maximum potential average gross income from just the sale of yams harvested from the intercropping system where pigeonpea is grown in all eys tilizer rate (Table 4.2). 137 Table 4.1a: Income Equivalent Ratio (IER) of the pigeonpea - yam cropping system under different inorganic fertilizer levels compared with so le yam with no fertilizer at Fumesua and Ejura for the 2018 and 2019 cropping season s . Location Cropping system Partial Income Equivalent Ratio IER Yam Pigeonpea 2018 2019 2018 2019 2018 2019 Fumesua Sole Crop 1.00 c 1.00 b 0.00 b 0.00 b 1.00 c 1.00 c Yam in PA 1.51 a 1.31 a 0.30 a 0.15 a 1.81 a 1.46 a Yam in PB 1.28 b 1.07 b 0.27 a 0.14 a 1.55 b 1.20 b SED (5%) 0.02 0.06 0.03 0.01 0.02 0.06 Ejura Sole Crop 1.00 c 1.00 c 0.00 c 0.00 c 1.00 b 1.00 c Yam in PA 1.16 b 1.36 a 0.38 a 0.17 a 1.55 a 1.53 a Yam in PB 1.24 a 1.22 b 0.33 b 0.14 b 1.57 a 1.36 b SED (5%) 0.01 0.07 0.02 0.01 0.02 0.06 Location (Loc) 0.2093 0.0264 0.8533 Year (Yr) 0.0879 <.0001 0.0008 Cropping System (CS) <.0001 <.0001 <.0001 Loc*Yr 0.0043 0.0142 0.0082 Loc*CS <.0001 0.0011 0.0001 Yr*CS 0.0031 < .0001 <.0001 Loc*Yr*CS <.0001 0.0321 0.0002 PA Pigeonpea in an alley; PB pigeonpea as a border. Means with the same alphabets within a . 138 Table 4.1b: Income Equivalent Ratio (IER) of the pigeonpea - yam cropping system under different inorganic fertilizer levels compares with s ole yam with half fertilizer rate (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) at Fumesua and Ejura for the 2018 and 2019 cropping season s . Locati on Cropping system Partial Income Equivalent Ratio IER Yam Pigeonpea 2018 2019 2018 2019 2018 2019 Fumesua Sole Crop 1.00 c 1.00 c 0.00 c 0.00 c 1.00 c 1.00 b Yam in PA 1.35 a 1.38 a 0.30 a 0.15 a 1.65 a 1.53 a Yam in PB 1.15 b 1.28 b 0.27 b 0.14 b 1.42 b 1.42 a SED (5%) 0.09 0.07 0.02 0.007 0.011 0.07 Ejura Sole Crop 1.00 c 1.00 b 0.00 c 0.00 c 1.00 c 1.00 b Yam in PA 1.72 a 1.48 a 0.38 a 0.17 a 2.10 a 1.65 a Yam in PB 1.23 b 1.39 a 0.33 b 0.14 b 1.56 b 1.53 a SED (5%) 0.08 0.13 0.02 0.01 0.10 0.15 Location (Loc) 0.0440 0.0215 0.0373 Year (Yr) 0.6062 <.0001 0.0213 Cropping System (CS) <.0001 <0.001 <.0001 Loc*Yr 0.1691 0.0099 0.0974 Loc*C S 0.0036 0.0004 0.0022 Yr*CS 0.0022 <.0001 0.0009 Loc*Yr*CS 0.0392 0.0169 0.0501 PA Pigeonpea in an alley; PB pigeonpea as a border. Means with the same alphabets within a . 139 Table 4.1c: Income Equivalent Ratio (IER) of the pigeonpea - yam cropping system under different inorganic fertilizer levels compares with s ole yam with full fertilizer rate (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) at Fumesua and Ejura for the 2018 and 2019 cropping season s . Locati on Cropping system Partial Income Equivalent Ratio IER Yam Pigeonpea 2018 2019 2018 2019 2018 2019 Fumesua Sole Crop 1.00 b 1.00 b 0.00 b 0.00 b 1.00 c 1.00 b Yam in PA 1.17 a 1.09 a 0.30 a 0.15 a 1.47 a 1.24 a Yam in PB 1.03 b 1.07 ab 0.27 a 0.14 a 1.30 b 1.21 a SED (5%) 0.10 0.08 0.03 0.01 0.13 0.09 Ejura Sole Crop 1.00 c 1.00 c 0.00 c 0.00 c 1.00 c 1.00 b Yam in PA 1.12 a 1.10 a 0.38 a 0.17 a 1.50 a 1.27 a Yam in PB 0.97 b 1.08 a 0.33 b 0.13 b 1.30 b 1.22 a SED (5%) 0.05 0.05 0.02 0.01 0.06 0.10 Location (Loc) 0.5398 0.0264 0.6570 Year (Yr) 0.7047 <.0001 0.0126 Cropping System (CS) 0.0007 <.0001 <.0001 Loc*Yr 0.3494 0.0143 0.9187 Loc*CS 0.8710 0.0011 0.8533 Yr*CS 0.0702 <.0001 0.0055 Loc*Yr*CS 0.7555 0.0321 0.9948 PA Pigeonpea in an alley; PB pigeonpea as a border. Means with the same alphabets within a . 140 Table 4.2: Revenue effects from yam yield gains for PA and PB intercropping system at Fumesua and Ejura for the 2018 and 2019 cropping seasons . Location Cropping system Fertilizer (N - P 2 O 5 - K 2 0 kg/ha) Gross revenue gain Avg. gross rev. gain ( 2018 2019 Fumesua Yam in PA 0 - 0 - 0 13.50 7.56 10,530 23 - 23 - 30 12.75 10.53 11,640 45 - 45 - 60 7.25 3.24 5,245 Yam in PB 0 - 0 - 0 7.50 1. 62 4,560 23 - 23 - 30 5.50 7.83 6,665 45 - 45 - 60 1.50 2.43 1,965 Ejura Yam in PA 0 - 0 - 0 4.56 8.42 6,488 23 - 23 - 30 24.72 14.03 19,373 45 - 45 - 60 6.72 4.08 5,400 Yam in PB 0 - 0 - 0 6.72 5.36 6,038 23 - 23 - 30 7.92 11.22 9,570 45 - 45 - 60 - 1.68 3.06 690 PA Pigeonpea in an alley; PB pigeonpea as a border. Cost of production and Cost - Benefit Analysis The results of the CBA provided a more comprehensive understanding of costs and benefits. The TCP in 2017 was mainly associated with the establishment an d maintenance of pigeonpea for subsequent yam cultivation in the 2018 and 2019 cropping season. Generally, the TCP was higher on the sole yam fields followed by yam planted in PB and yam planted in PA fields for both seasons and locations. The use of half or full fertilizer rate on each cropping system further increased production cost for both locations and ye ars with SY with a full fertilizer costing the most. High net income was recorded for planting yam in PA, followed by yam in PB with sole yam being t he least profitable for both locations and cropping seasons. Generally, planting yam in PA with half recomm ended fertilizer rate (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) resulted in closer Net income to planting yam in PA with a full fertilizer rate (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) (Table s 4.4a and 4.4b). The NPV and IRR of planting yam in PA with half fertilizer rate were only slightly 141 lower than planting yam in PA with a full fertilizer rate. The NPV values further reinforce that the integration of pigeonpea is beneficial not only for yam productivity and soil health but also to increase the profitability of yam cultivation by 0.1 to nearly five folds in Ejura and 0.42 to 23 folds in Fumesua under different fertilizer rates. Planting yam in PA with half and full fertilizer rates resulted i n a maximum IRR of 5.67 and 5.90 respectively at Fumesua and 5.66 and 5.88 respectively at Ejura Generally, higher benefit - cost ratios (BCR) were observed for all cropping systems at Ejura than Fumesua. Compared to all cropping systems, pla nting yam in PA with half fertilizer rate resulted in a higher and similar BCR in both locations and seasons (Table 4.3). Thus, doubling the fertilizer to 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha in pigeonpea - yam cropping system had marginal effects on income for both lo cations. Even wh en yams were planted without fertilizer, the presence of the pigeonpea resulted in better profit and BCR than when half and full fertilizer rates were used on sole yam fields for both locations (Tables 4.3). 142 Table 4 .3 : Cost - benefit analysis for pigeonpea - yam cropping system with savings deposit rate 7.43% as a discount . Fumesua Ejura Cropping System Fertilizer rate (N - P 2 O 5 - K 2 O kg/ha) Net Present Value (NPV) Internal Rate of Return (IRR) Benefit - Cost Ratio (BC R) Net Present Value (NPV) Internal Rate of Return (IRR) Benefit - Cost Ratio (BCR) Yam in PA 0 - 0 - 0 25.49 4.21 1.87 17.73 1.96 1.57 23 - 23 - 30 35.13 5.67 2.14 44.62 5.66 2.38 45 - 45 - 60 36.08 5.90 2.13 46.23 5.88 2.36 Yam in PB 0 - 0 - 0 13.12 2.46 1.40 13 .93 1.69 1.41 23 - 23 - 30 24.14 3.86 1.70 26.23 2.84 1.73 45 - 45 - 60 27.63 4.42 1.78 35.68 4.18 1.96 Sole yam 0 - 0 - 0 1.05 * 1.03 3.09 * 1.09 23 - 23 - 30 9.13 * 1.23 9.95 * 1.26 45 - 45 - 60 19.65 * 1.49 32.81 * 1.84 * - IRR was not able to be calculated du e t o no cash flow on the 1 st year of the project . 143 DISCUSSION Profitability of the pigeonpea - yam cropping system Several studies have used IER as a basis for estimating the gross returns from the cropping system in comparison to sole cropping (Ba ntie, 2014; Tetteh, 2019; Yang et al ., 2018; Dudha d e et al ., 2009; Yus u f et al ., 2016). Further, the CBA helps quantify the monetary value of costs and benefits of inputs and outputs to guide decision making. Thus, it indicates the long - term profitability of the cropping system when the fixed cost is accounted for (Vawda et al ., 2001). These two analyses were used to evaluate the economic aspects of the PPY cropping system and were used to make decision s and recommendations. Across t he cropping seasons (2018 - 2019), the average partial IER of the yam in the pigeonpea fields (PA and PB) in both locations for all the scenarios were better than the pigeonpea, indicating high returns on the yams in the inter crop than the pigeonpea. The pa rtial IER of the pigeonpea would mean an additional income to farmers if they chose to integrate pigeonpea into the yam cropping system (Table s 4.1a, 4.1b & 4.1c). The generally better IER on yam production in Ejura than Fume sua could be attributed to the more fertile lixisols at Ejura, which supported yam growth and tuber yields than the acid acrisols found in Fumesua (Lal, 1976; Ennin et al ., 2009). Also , the higher IER in PA and PB systems in 2018 compared to 2019 cropping season could be attributed to t he high quantity of pigeonpea biomass productivity and the resulting N fixation in 2018 than 2019 (Chapter 2). The observed improved and reduced IER fo r planting yam with half fertilizer rate at Ejura and Fumesua, respectively, could be attributed to the soil conditions at both locations (Tables 4.1a, 4.1b). Ejura soils were slightly alkaline (pH 7.76 7.88) whiles Fumesua soils were very strongly acidi c (4.43 4.79). The slightly alkaline soil at Ejura might have resulted in better nutrient use efficie ncy than the strongly acidic soil at Fumesua, resulting in higher productivity and returns 144 capable of offsetting the half fertilizer cost introduced at E jura. At Fumesua, due to the very strongly acidic soil condition, the improved productivity was not cap able of offsetting the half fertilizer cost introduced, resulting in low IER. The significantly (P < 0.05) higher IER in PA than SY and similar values be tween half and full fertilizer rates further suggests that a higher fertilizer application does not sub stantially increase yam productivity and farmers' income (Tables 4.1a, 4.1b & 4.1c). This finding reinforces that even with limited access to inputs, far mers will have the potential to improve their income with the presence of pigeonpea than by proportiona tely increasing fertilizer use leading to detrimental environmental and health outcomes. For continuously cropped fields, this provides a more sustainabl e and economical option that helps enhance livelihoods and help produce safe food with a reduced impact on the environment. The comparison of average IER from planting yam in PA without fertilizer, which amounted to 1.64 and 1.54 at Fumesua and Ejura, resp ectively, implies better revenues for farmers than applying full fertilizer rate for 1.36 and 1.39 at F umesua and Ejura. Planting yam in PB with no fertilizer also resulted in higher IER of 1.38 and 1.47 at Fumesua and Ejura compared to an IER of 1.26 for both locations for planting yam in PB with full fertilizer rate (Tables 4.1a, 4.1b & 4.1c). The general ly low IER and gross profit of yam on sole yam fields irrespective of fertilizer rate for both locations and seasons could mainly be attributed to the lo w yam tuber yields, the cost of stakes, and the labor cost for staking on sole yam fields. The cost of stakes was eliminated by planting yam with pigeonpea in PA and PB fields, where live - stake and cut trunks of the pigeonpea replaced purchased stakes. Als o , the incorporation of pigeonpea biomass helped to improve and sustain soil fertility and productivity . Several studies highlight ed staking to be a major issue influencing productivity and profitability of yam production and suggested reduced or live sta king as an alternative to farmers' 145 practice (Obiazi, 1995; Owusu Danquah et al ., 2014; Ekanayake and As iedu, 2003; Behera et al ., 2010). The pigeonpea - yam cropping system proposed in this study help address this major constraint in yam production. The obse rvations by Otu and Agboola (1991) showed that the use of Gliricidia sepium live - stake resulted in a 16 % increase in yam productivity than when yam is cultivated with bamboo stakes. With pigeonpea, yam productivity gains of 51% for Fumesua, and 50% for Eju ra without fertilizer, are in line with this study. Also, Bantie, (2014) observed a significantly highe r IER of 1.91 when potatoes were intercropped with maize in a ratio of 1:1 than when produced as sole potatoes or sole maize. Thus, intercropping, especi ally with legumes such as pigeonpea, would sustain and increase yam productivity and income while lesse ning the burden on smallholder farmers by reducing the need to search for fertile lands to improve yam yields periodically . This outcome enhances food an d income security and lowers the cost of production , freeing up revenues for family use or invest ing in other income generation activities. The NPV values for Ejura and Fumesua revealed that the net cash flows for SY were very low unless treated with a ful l dose of fertilizer. Also, the generally less IRR for the cropping systems than the opportunity cost o f capital observed at both locations indicates the real situation of smallholder farming in many contexts resulting in low returns. Planting yam in PA wi th half fertilizer rate resulted in a better NPV than SY with different fertilizer levels but a similar NPV and BCR as with a full fertilizer rate in both locations and seasons. Planting yam in PA with half and full fertilizer rate resulted in a similar BCR of 2.14 and 2.13 , respectively , at Fumesua whiles the same treatments had 2.38 and 2.36 , respectively , at Ejura (Table 4.3). That is if yam is planted in PA 1. 00 invested in both locations. Even when a farmer has no fertilizer access, the returns with the use of 146 pigeonpea in an alley or as a border plant would be better than cultivating yam as a monocrop with fertilizer (Table 4.2). Thus, the economic analysis with IER and CBA suggests the integration of pigeonpea into yam cropping systems would improve and sustain yam production. Howeve r, planting yam in alleys of pigeonpea (PA) with half fertilizer rate resulted in the highest returns and profit in both locati ons and years. This result is because N, P, and other nutrient contributions, and moisture conservation of the pigeonpea in the y am cropping systems resulted in the use of the half - recommended fertilizer rate enough for the yam (Chapter 2). Similar profits recorded for half and full fertilizer rates with pigeonpea biomass in PA fields for both locations implies the use of full ferti lizer rate with pigeonpea biomass has little to no economic benefit . It only increases production cost without a correspond ing increase in yam productivity and profit. Even with the initial investment and the loss of a cropping year to establish pigeonpea, the farmers have NPV greater than zero with pigeonpea - yam systems. This results is in line with the observation by Ennin et al . (2013), that it is more profitable to precede yam with pigeonpea and thus would require half recommended poultry manure rate (3 t/ha) and a third (15 - 15 - 20 N - P 2 O 5 - K 2 O kg/ha) recommended fertilizer rate for sustainable yam production. As a result of a sear ch for fertile land and stakes for staking, yam production contributes to deforestation and land degradation (Akwag et al ., 2000; Otoo et al ., 2008; Owusu Danquah et al ., 2014; Ennin et al ., 2014). The study has indicated that the integration of pigeonpea into the yam cropping system would address the constraint of stake acquisition and high labor cost for staking on the field. In addition to this, the moisture conservation and soil fertility amelioration provided by the pigeonpea biomass would fu rther enhance the yields and the profit margin than planting yam as a sole crop. 147 Profitability and environmental sustainability Evaluat ion of long (10 years) term yields of yam using crop model SALUS, indicated that yam yields could be sustained in the long - term with integrated soil fertility management (ISFM) of pigeonpea biomass with recommended fertilizer rate than with just the use of fertilizer application for yam production (Chapter 3). The SALUS results suggest that both yam produ ctivity and profitability can be sustained in the long - term. As such, the smallholder farmers can continue to reap benefits from the integration of pigeonp ea into yam cultivation in West Africa. It also incentivizes and motivates farmers to invest in land and yam production activities. Given that yam farmers are vulnerable to various uncertainties from finding land to timely rainfalls to market fluctuation, this system offers more stability to farming activities and a reliable flow of income over time. As n oted earlier, planting yam with pigeonpea (PA and PB) with full fertilizer (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) rate presented a slightly higher NPV and IRR than pl anting yam with pigeonpea (PA and PB) with half fertilizer rate, the difference in values were very c lose (Tables 4. 3 ). In the face of global calls for reducing environmental and ecosystem pollution as a result of increased agricultural input use, such as fertilizer use and application, a balance between environmental and productivity sustainability is r equired (Zhang et al ., 2018; Abler and Shortle, 1995). Basso et al . (2016) , using the SALUS crop model , observed that, instead of a blanket uniform applica tion, applying variable N in response to variability in soil and landscape of a field would result in higher profit and less nitrate leaching to the environment. Thus, planting yam with pigeonpea and half fertilizer rate would be more environmentally frien dly and profitable than doubling the fertilizer at the expense of the environment. One limitation of this study is that the profitability indicators used in this study (IER and CBA) all measure the cost a nd benefit of the 148 various yam production systems wit h explicit monetary values. It does not take into account the costs and benefits resulting from social and environmental variables (Senkondo, 2004). Thus, in this study, environmental services/benefits s uch as carbon sequestration rendered by the pigeonpe a and the implications of reducing fertilizer rate to half instead of full were not factored into the CBA. Quantification and inclusion of these environmental services/benefits of integrating pigeonpea wo uld provide a more precise estimate of the economic returns from the pigeonpea - yam cropping system against the sole yam cropping system. 149 CONCLUSION AND RECOMMENDATIONS The study has demonstrated, integrated soil fertility management (ISFM) for sustainable yam production with half recommended fertilizer and pigeonpea would provide live - stakes or readily available stakes for yam in the cropping system. Even if a farmer has no access to fertilizer, planting yam with pigeonpea (PA and PB) presents a better option in terms of profitability , and env ironmentally beneficial than the use of full recommended fertilizer for yam production. Thus, the soil moisture conservation, soil fertility maintenance, and provision of stakes from th e pigeonpea make s it a profi table option on continuously cropped fields than the current practice of yam production. Sensitivity analysis of changes in crop produce price and interest rates over time would be needed to provide a short and long - term guide to yam farmers interested in investing in yam production using the pige onpea - yam cropping system. One valuable lesson learned from this research is that it is important to carr y out the pruning of the pigeonpea at appropriate timing and intensity to ensure a continuous and sustainable supply of pigeonpea green manure each yea r while ensuring the health of pigeonpea trees. A further study on this would be pursed and made an integ ral component of this technology dissemination to farmers. Further studies would also be needed to quantify the environmental returns/benefit associate d with pigeonpea (As carbon sink, N, and other nutrients added to the soil) in the yam cropping system. B reeding and Introducing farmers to pigeonpea with improved biomass, erect stems, and high grain yield would make the pigeonpea - yam cropping system attr active for adoption by farmers. These findings give researchers, farmers, and stakeholders more insights and data to guide and support decisions on the use of pigeonpea - yam cropping systems for profitable and sustainable yam production. 150 APPEND IX 151 APPENDIX Table 4.3a : Partial budgeting and cost - benefit analysis of pigeonpea - yam cropping system at Fumesua for 2017, 2018 and 2019 cropping season s. CS Yam in PA Yam in PB Sole yam Yr 2017 2018 2019 2017 2018 2019 2018 2019 Fertilizer level NF ½ rate FR NF ½ rate FR NF ½ rate FR NF ½ rate FR NF ½ rate FR NF ½ rate FR Yam yld. (t/ha) 0.0 16 20 20 12 14 15 0.0 14 17 18 10 13 14 11 14 17 9.0 10 13 Adj yam yld. (t/ha) 0.0 15 18 18 11 13 13 0.0 12 15 16 8.6 12 13 9.6 13 16 8.1 9.4 12 Ya m GI (in 000) 0.0 36 44 46 29 35 35 0.0 31 37 41 23 32 35 24 32 39 22 25 32 PP yld. (t/ha) 0.0 0.3 0.3 0. 3 0.1 0.1 0.1 0.0 0.2 0.2 0.2 0.1 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.0 Adj. PP yld (t/ha) 0.0 0.2 0.2 0.2 0.1 0.1 0.1 0.0 0.2 0.2 0.2 0.1 0.1 0.1 0 .0 0.0 0.0 0.0 0.0 0.0 PP GI (in 000) 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.0 0.1 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 TRCS (in 000) 0.0 36 44 46 29 35 35 0.0 31 37 41 23 32 35 24 32 39 22 25 32 152 Table 4.3a ( c ont LC (in 000) 1.8 0.4 0.4 0.4 0.4 0.4 0.4 1.8 0.4 0.4 0.4 0.4 0.4 0.4 1.8 1.8 1.8 0.5 0.5 0.5 Cost of PP Est. (in 000) 1.5 0.0 0.0 0.0 0.0 0.0 0.0 1.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 TFC (in 000) 3.3 0.4 0.4 0.4 0.4 0.4 0.4 3.3 0.4 0.4 0.4 0.4 0.4 0.4 1.8 1.8 1 .8 0.5 0.5 0.5 CPPH (in 000) 0.0 0.6 0.6 0.6 0.7 0.7 0.7 0.0 0.6 0.6 0.6 0.7 0.7 0.7 0.0 0.0 0.0 0.0 0.0 0.0 PP biom. spread 000) 0.0 0.7 0.7 0.7 0.7 0.7 0.7 0.0 0.8 0.8 0.8 0.9 0.9 0.9 0.0 0.0 0.0 0.0 0.0 0.0 FC (in 000) 0.0 0.0 0.6 1.2 0.0 0.6 1.2 0.0 0.0 0.6 1.2 0.0 0.6 1.2 0.0 0.6 1.2 0.0 0.6 1.2 FAC (in 000) 0.0 0.0 0.5 0.5 0.0 0.6 0.6 0.0 0.0 0.5 0.5 0.0 0.6 0.6 0.0 0.5 0.5 0.0 0.6 0.6 CRC (in 000) 0.0 1.6 1.6 1.6 1.7 1.7 1.7 0.0 1.6 1.6 1.6 1.7 1.7 1.7 2.0 2 .0 2.0 2.2 2.2 2.2 153 Table 4.3a ( c ont CSY 000) 0.0 6.1 6.1 6.1 6.3 6.3 6.3 0.0 6.1 6.1 6.1 6.3 6.3 6.3 6.7 6.7 6.7 7.0 7.0 7.0 CPY (in 000) 0.0 1.8 1.8 1.8 1.9 1.9 1.9 0.0 1.8 1.8 1.8 1.9 1.9 1.9 2.2 2.2 2.2 2.3 2.3 2.3 CRY ( in 000) 0.0 0.5 0.5 0.5 0.5 0.5 0.5 0.0 0.7 0.7 0.7 0.9 0.9 0.9 1.6 1.6 1.6 1.8 1.8 1.8 CSY (in 000) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.5 1.5 1.5 1.6 1.6 1.6 LCS (in 000) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.5 0. 6 0.6 0.6 1.0 1.0 1.0 1.1 1.1 1.1 WCPP (in 000) 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 WCY (in 000) 0.0 1.5 1.5 1.5 1.6 1.6 1.6 0.0 2.0 2.0 2.0 2.1 2.1 2.1 2.5 2.5 2.5 2.6 2.6 2.6 CRR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.5 0.6 0.6 0.6 1.2 1.2 1.2 1.3 1.3 1.3 CYH (in 000) 0.0 1.5 1.5 1.5 1.6 1.6 1.6 0.0 1.5 1.5 1.5 1.6 1.6 1.6 2.0 2.0 2.0 2.0 2.0 2.0 154 Table 4.3a ( c ont NB: *Average yield adjusted 10%; NF (No fertilizer), ½ rate and (FR) full fertilizer rates are 0 - 0 - 0, 23 - 23 - 30 and 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha, respectively, Far m - gate price s per kg of white yam tubers (Pona) in 2018 and 2019 were Gh cedis 2.5 and Gh cedis 2.7, respectively. Farm - gate price per kg of pigeonpea grains in 2018 and 2019 were Gh cedis 0.48 and Gh cedis 0.49 , respectively. Weeds were controlled 3, 4 , a nd 5 times in yam planted in PA, PB and sole yam, respective ly. Re - shaping of mounds was done 0, 1, 2 times for PA, PB, and sole yam, respectively. PA yam planted in pigeonpea in an alley; PB yam planted in pigeonpea as a border; Est. Establishment; PP Pigeonpea, CS Cropping System; Yr Year; yid Yield ; LC Land clearing; TFC Total Fixed Cost; TCP Total Cost of Production, FC Fertilizer Cost; FAC Fertilizer Application Cost; CSY Cost of Seed Yam; CPY Cost of Planting Yam; CRC Cos t of Ridges Construction; CRR Cost of Reshaping of Ridges; WCY Weeding Cost in Yam; WCPP Weeding Cost in PP; CSY Cost of Staking Yam; LCS Labor Cost for Staking; CYH Cost of Yam Harvest; Cost of PP Harvest; GI Gross Income; NI Net Income; G P Gross Profit; TVC Total Variable Cost. TVC (in000) 0.7 14 15 16 15 16 17 0.7 16 17 18 17 18 19 21 22 22 22 23 24 TCP (in000) 4.0 15 16 16 16 17 17 4.0 17 18 18 18 19 19 23 24 24 22 23 24 GP (in000) - 1 22 29 30 14 19 19 - 1 15 20 23 6.0 14 16 3.4 11 17 0.1 2.4 8.8 NI (in000) - 4 22 28 29 13 18 18 - 4 14 20 22 5.7 14 15 1.6 8.8 15.0 - 0.4 1.9 8.3 155 Table 4.3 b : Partial budgeting and cost - benefit analysis of pigeonpea - yam cropping system at Ejura for 2017, 2018 and 2019 cropping season s. CS Yam in PA Yam in PB Sole yam Yr 2017 2018 2019 201 7 2018 2019 2018 2019 Fertilizer level NF ½ rate FR NF ½ rate FR NF ½ rate FR NF ½ rate FR NF ½ rate FR NF ½ rate FR Yam yld. (t/ha) 0.0 14 25 26 13 17 17 0.0 14 18 22 11 16 17 12 14 23 9.3 11 16 Adj yam yld. (t/ha) 0.0 12 22 23 11 15 16 0.0 13 16 20 10 14 15 10 13 20 8.4 10 14 Yam GI 000) 0.0 2 9 53 55 29 39 40 0.0 31 38 48 26 36 39 25 31 49 21 26 36 PP yld. (t/ha) 0.0 0.3 0.3 0.3 0.1 0.1 0.1 0.0 0.3 0.3 0.3 0.1 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.0 Adj. PP yld (t/ha) 0.0 0.3 0.3 0.3 0.1 0.1 0.1 0.0 0.2 0.2 0.2 0.1 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.0 PP GI 000) 0.0 0.1 0.1 0. 1 0.1 0.1 0.1 0.0 0.1 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 TRCS 000) 0.0 29 53 55 29 39 40 0.0 31 38 48 26 36 39 25 31 49 21 26 36 156 Table 4.3b ( c ont LC (in 000) 1.7 0.4 0.4 0.4 0.0 0. 0 0.0 1.8 0. 4 0.4 0.4 0.0 0.0 0.0 1.7 1.7 1.7 0.0 0.0 0.0 Cost of PP Est. (in 000) 1.4 0.0 0.0 0.0 0.0 0.0 0.0 1.5 0. 0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 TFC (in 000) 3.1 0.4 0.4 0.4 0.0 0.0 0.0 3.3 0. 4 0.4 0.4 0.0 0.0 0.0 1.7 1.7 1.7 0.0 0.0 0.0 CPPH (in 000) 0.6 0.5 0.5 0.5 0.6 0.6 0.6 0.6 0. 5 0.5 0.5 0.6 0.6 0.6 0.0 0.0 0.0 0.0 0.0 0.0 PP biom spread (in 000) 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0. 8 0.8 0.8 0.8 0.8 0.8 0.0 0.0 0.0 0.0 0.0 0.0 FC (in 000) 0.0 0. 0 0.6 1.2 0.0 0.6 1.2 0.0 0. 0 0.6 1.2 0.0 0.6 1.2 0.0 0.6 1.2 0.0 0.6 1.2 FAC (in 000) 0.0 0.0 0.5 0.5 0.0 0.6 0.6 0.0 0. 0 0.5 0.5 0.0 0.6 0.6 0.0 0.6 0.6 0.0 0.7 0.7 157 Table 4.3b ( c ont CRC (in 000) 0.0 1.5 1.5 1.5 1.6 1.6 1.6 0.0 1.5 1.5 1.5 1.6 1.6 1.6 2 .0 2.0 2.0 2.0 2.0 2.0 (in 000) 0.0 5.9 5.9 5.9 6.1 6.1 6.1 0.0 5.9 5.9 5.9 6.1 6.1 6.1 6.5 6.5 6.5 6.9 6.9 6.9 CYP (in 000) 0.0 1.8 1.8 1.8 1.9 1.9 1.9 0.0 1.8 1.8 1.8 1.9 1.9 1.9 2.2 2.2 2.2 2.3 2.3 2.3 CRR (in 000) 0.0 0.5 0.5 0 .5 0.5 0.5 0.5 0.0 0.7 0.7 0.7 0.8 0.8 0.8 1.6 1.6 1.6 1.7 1.7 1.7 CSY (in 000) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.5 1.5 1.5 1.8 1.8 1.8 LCS (in 000) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.5 0.5 0.5 0.5 1.0 1.0 1.0 1.2 1.2 1.2 WCPP (in 000) 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 WCY (in 000) 0.0 1.4 1.4 1.4 1.4 1.4 1.4 0.0 1.8 1.8 1.8 1.9 1.9 1.9 2.3 2.3 2.3 2.3 2.3 2.3 CRR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.5 0.5 0.5 0.5 1.0 1.0 1.0 1.1 1.1 1.1 CYH (in 000) 0.0 1.4 1.4 1.4 1.5 1.5 1.5 0.0 1.4 1.4 1.4 1.5 1.5 1.5 2.0 2.0 2.0 2.1 2.1 2.1 158 Ta ble 4.3b ( c ont NB: *Average yield adjusted 10%; NF (No fertilizer), ½ rate and (FR) full fertilizer rates are 0 - 0 - 0, 23 - 23 - 30 and 45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha, respectively, Farm - gate price s per kg of white yam tubers (Pona) in 2018 and 2019 were Gh ced is 2.4 , and Gh cedis 2.55, respectively. Farm - gate price per kg of pigeonpea grains in 2018 and 2019 were Gh cedis 0.48 and Gh cedis 0.49 , respectively. Weeds were controlled 3, 4 and 5 times in yam planted in PA, PB , and sole yam, respectively. Re - shaping of mounds was done 0, 1, 2 times for PA, PB, and sole yam, respectively. PA yam planted in pigeonpea in an alley; PB yam planted in pigeonpea as a border; Est . Establishment; PP Pigeonpea, CS Cropping System; Yr Year; yid Yield; LC Land cl earing; TFC Total Fixed Cost; TCP Total Cost of Production, FC Fertilizer Cost; FAC Fertilizer Application Cost; CSY Cost of Seed Yam; CPY Cost of Plan ting Yam; CRC Cost of Ridges Construction; CRR Cost of Reshaping of Ridges; WCY Weeding Cost in Yam; WCPP Weeding Cost in PP; CSY Cost of Staking Yam; LCS Labour Cost for Staking; CYH Cost of Yam Harvest; Cost of PP Harvest; GI Gross Income ; NI Net Income; GP Gross Profit; TVC Total Variable Cost. 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Economic analysis of sorghum/soyabean intercrop systems by par tial budget in the guinea savannah of Nigeria. Continent al Journal of Agricultural Economics , 2016, 8 (1), pp.9 - 12. 164 Zhang, L., Yan, C., Guo, Q., Zhang, J. & Ruiz - Menjivar, J. (2018). The impact of agricultural chemical inputs on environment: global evide nce from informetrics analysis and visualization. Inte rnational Journal of low - Carbon technologies , 13(4), pp.338 - 352. 165 CHAPTER 5 CONCLUSIONS AND FUTURE RESEARCH DIRECTION Conclusions This present research was conducted to provide some answers towards addressing dwindling yam productivity , land degradation, and deforestation resulting from shifting cultivation and search for stakes that characterized smallholder yam production in West A frica. The general objective was to evaluate the effect of pigeonpea - yam cropping system on yam productiv ity on continuously cropped fields. The study was built on an earlier socio - e conomic survey that identified yam farmers' perception and knowledge of pigeonpea in the major yam growing areas of Ghana. A farmer participatory on - station study was implement ed on continuously cropped fields at Fumesua (Forest Zone) and Ejura (Forest - Sa vannah transition zone) in Ghana during the 2017, 2018 , and 2019 cropping season for the field evaluation. An integrated soil fertility management of pigeonpea biomass and ferti lizer were laid out for the study with yam planted in all eys of pigeonpea (PA), yam planted with pigeonpea as a border (PB) and sole yam as cropping systems and further divided into three where no, half (23 - 23 - 30 N - P 2 O 5 - K 2 O kg/ha) and full (45 - 45 - 60 N - P 2 O 5 - K 2 O kg/ha) recommended fertilizer rate for yam production were applied. Planting yam in PA with half fertilizer rate resulted in similar tuber yield as planting yam in PA with a full fertilizer rate. Also, planting yam with pigeonpea (Yam in PA and PB) w ith out fertilizer presents a better yam tuber yield than cultivating sole yam with fertilizer on a continuously cropped field. 166 To evaluate the long - term yam yield sustainability, the field study data were used in the calibration and validation of the SA LUS crop model for simulation studies. The results indicated long (10 years) term yields of yam could be sustained with integrated soil fertility management (ISFM) of pigeonpea biomass with recommended inorganic fertilizer rate than with just the use of in org anic fertilizer for yam production on continuously cropped fields. To ascertain the pigeonpea - yam cropping system's profitability, an economic analysis with three scenarios of a farmer having no access to inorganic fertilizer, a farmer with access to ha lf inorganic fertilizer rate, and a farmer with access to full inorganic fertilizer rate was conducted. The results indicated, planting yam in PA with half and full inorganic fertilizer rates resulted in a similar Income Equivalent Ratio (IER) for all thre e s cenarios in both locations and seasons. Planting yam with pigeonpea (PA and PB) without inorganic fertilizer had better IER than planting sole yam with full inorganic fertilizer rate in both locations. Also, planting yam with pigeonpea (PA and PB) with hal f inorganic fertilizer rate presented a slightly lower Net Profit Value (NPV) and Internal Rate of Return (IRR) than planting yam with pigeonpea (PA and PB) with full inorganic fertilizer rate, the difference in values were very close, resulting in marg ina l income gain. Given the above results, the use of pigeonpea with half inorganic fertilizer rate would sustain yam production and income on continuously cropped fields for smallholder farmers. This is in line with the global call for reducing environme nta l and ecosystem pollution due to increasing agricultural input use. Also, deforestation and land degradation resulting from shifting cultivation in search of fertile land and stakes can be addressed with the pigeonpea - yam cropping system. 167 Future resear ch directions Figure 5.1 gives the future direction of this study. For the present study to benefit yam farmers, there would be the need to scale up the pigeonpea - yam technology to other yam growing areas of Ghana and the rest of the countries along the W est Africa yam belt (Nigeria, Togo, Ivory C oast , and Benin). As a Scientist with the CISR Crops Research Institute (CRI) , a national research institution, my collaborations with the International Institute of Tropical Agriculture (IITA), a CGIAR institut ion gives me the opportunity to scale up this technology to other countries. The CSIR CRI has collaborated with IITA on major yam projects such as Yam Improvement for Incomes and Food Security in West Africa (YIIFSWA) and Community Action in Improving Fa rme r - Saved See Yam (CAYSEED). This study would contribute by offering smallholder farmers options that would sustain yam productivity on continuously cropped fields to achieve improved yam productivity, income, and food security. To ensure cost - effectiv e a nd rapid scale - up of the pigeonpea - yam cropping system to other yam producing countries, I would continue my collaboration with to explore using SALUS and other crop models to simulate and link the long term improveme nt in soil fertility and yam productivity resulting from ISFM of pigeonpea biomass and fertilizer along the West Africa yam belt. To encourage adoption, there is the need to make farmers productive during the 8 - 12 - month lag phase for the maturity of th e p doubled - approach where legumes such as cowpea, groundnut, and soybean are cultivated with the pigeonpea may be a way forward. This has been pioneered in East Africa (Malawi and Tanzania) by the Global Change Learning Lab in 168 Sub - Saharan Africa under the leadership of Dr. Sieglinde Snapp of MSU. I will collaborate with this lab and explore how this approach could be used to mak e farmers productive during th e 8 - 12 months maturity period of the pigeonpea. To be able to present to smallholder farmers, a pigeonpea genotype with improved biomass and grain yield, erect stems , and tolerant to pruning , suitable for the pigeonpea - yam c ropping system. I will continu e my collaboration with Dr. Cholani Weebadde of MSU, my major advisor, and other breeders of CSIR CRI on pigeonpea breeding and improvement research to meet this objective. Quantification of environmental benefits suc h as carbon sink, N, and other nutri ents added to the soil associated with the pigeonpea would be needed to enable a comprehensive economic analysis of the pigeonpea - yam cropping system. This would be achieved through collaborations with agriculture and en vironmental economists. These future research directions would give researchers, farmers, and all stakeholders more insights to guide and support decisions on the pigeonpea - yam cropping system for sustainable and profitable yam production . 169 Figure 5.1: The future directions of the study. The a ccomplishment of the current study relevant in achieving the overall goal indicated by dotted boxes. Achieved to some extent by the current study are indicated in thick line boxes. Future directions of the current study ar e indicated by thin li ne boxes. PP Pigeonpea, PPY Pigeonpea - Yam, CCF continuously cropped field, WAYB West Africa Yam Belt. Efforts at i m proving yam productivity in Ghana and along the W est Africa Improving and sustaining productivity on CCF Improving and sustaining soil fertility on CCF Simulation evaluation with crop models Sc aling - up of PPY technology to the WAYB Profitability analysis of the PPY PPY technology for yam production on CCF Farmer and participation/ farmer field days Collaborations between NARS , CGIAR and Universities (eg. IITA , MSU) Improved and sustained yam productivity along the west Africa yam belt Breeding and improvement research on PP Piloting f ield evaluation of ISFM of PP and Fertilizer