Soil microbial diversity and ecosystem functioning in smallholder African agroecosystems

In this dissertation I assess the effect of fertilizer-based efforts to increase crop yields on smallholder African farms (the African Green Revolution) on the diversity and functional capacity of soil microbial communities and the ecosystem processes they regulate. In the introduction I provide a brief overview of the African Green Revolution and its critiques. In chapter 1, I advocate for the application of a functional trait-based approach to agroecology. I propose a functional trait-based approach to understanding the contribution of biodiversity to ecosystem services in agriculture. In chapter 2, I assess the impact of organic and mineral fertilization on the taxonomic composition and functional capacity of soil microbial communities in western Kenya. In chapter 3, I attempt to link these patterns in taxonomic and functional capacity to ecosystem process rates, specifically denitrification potential and carbon mineralization. Finally, in chapter 4, I measure fast- and slow-cycling organic matter fractions and their relationship to crop production and to the microbial enzymes that drive their turnover. Common to all chapters is the theme that short- and medium-term efforts to improve agricultural production through nutrient addition may feedback on the processes that sustain agriculture. This is in contrast with most research on the impacts of agricultural intensification, which tend to assess environmental impacts per se such as eutrophication and greenhouse gas emissions. I provide a summary and recommendations for future research in the conclusions.