Assessing the Impact of Agroforestry Systems on Soil Fertility and Crop Yield

Thesis Abstract

The degradation of soil fertility and declining crop yields represent critical challenges in sustainable agriculture, particularly within smallholder farming systems in tropical regions where traditional practices have often led to soil exhaustion and reduced productivity. Agroforestry systems, which integrate trees with crops and/or livestock, have been recognized as a potential strategy to rehabilitate soil health and enhance crop productivity; however, empirical evidence quantifying their impact remains limited in specific regional contexts. This study aims to assess the influence of different agroforestry practices on soil fertility indicators and crop yield performance, thereby providing evidence-based guidance for sustainable farming interventions. The specific objectives are to (1) evaluate soil nutrient status under various agroforestry systems compared to monoculture farming; (2) determine the effect of agroforestry practices on crop yield; (3) analyze the relationship between soil fertility parameters and crop productivity; and (4) identify the socio-economic factors influencing the adoption and success of agroforestry systems. Framed within the theoretical constructs of the Soil Fertility Restoration Theory and the Sustainable Livelihoods Framework, the study seeks to integrate ecological and socio-economic dimensions in evaluating agroforestry benefits. A quantitative research design employing a cross-sectional survey complemented by field experiments was adopted for this study. The target population comprises smallholder farmers practicing agroforestry or monoculture farming within a defined agro-ecological zone spanning approximately 2,000 square kilometers, with an estimated population of 2,500 farmers. Using Cochran’s formula, a sample size of 350 farmers was determined to ensure statistical representativeness, with stratified random sampling employed to select participants across different agroforestry practice types and farm sizes. Primary data collection involved structured questionnaires, collected through face-to-face interviews, focusing on socio-economic variables, farming practices, and perceptions; and soil sampling from farm plots for laboratory analysis. Soil samples, taken at a depth of 0-30 cm from 15 farms representing each agroforestry system and monoculture controls, were analyzed in accredited laboratories for key fertility indicators, including organic matter, nitrogen, phosphorus, potassium, pH, and cation exchange capacity (CEC). Crop yield data were obtained through direct measurement at harvest from sampled plots. The validity of questionnaire instruments was confirmed via pre-testing and expert review, while reliability was established through Cronbach’s alpha coefficient exceeding 0.8. Data analysis involved descriptive statistics to profile the farming systems and socio-economic factors, and inferential statistics including Analysis of Variance (ANOVA) to compare soil fertility parameters and crop yields across systems. Multiple regression analysis was conducted to examine the relationship between soil fertility variables and crop productivity, controlling for socio-economic factors. Statistical significance was tested at p < 0.05. Qualitative data from open-ended survey responses was thematically analyzed to interpret farmer perceptions and constraints. Expected findings include higher levels of organic matter, nitrogen, phosphorus, and pH stability in soils under agroforestry systems relative to monocultures, as well as significantly increased crop yields. The study anticipates revealing that the diversity and tree-crop combination influence soil restoration processes and productivity gains, substantiated through regression models indicating positive relationships between soil fertility parameters and crop outputs. It is also expected that socio-economic factors such as access to extension services, land tenure security, and market access significantly influence adoption rates and system success. The study contributes to the growing empirical knowledge base on agroforestry’s ecological and economic benefits, with particular emphasis on tropical smallholder contexts. It provides evidence-based recommendations for policymakers, extension agents, and farmers regarding the selection and promotion of agroforestry practices that optimize soil health and crop productivity. Conclusively, the findings support the integration of agroforestry into broader sustainable land management strategies, emphasizing capacity building and socio-economic support to enhance adoption and impact continuity. Future research directions suggested include longitudinal studies to monitor long-term soil and yield dynamics, and participatory approaches to refine agroforestry models in diverse socio-ecological settings.