This book provides a synthesis of plant-soil-plant interactions in agroforestry, intercropping and grass-legume interactions. It focuses on the process level, which is relevant to many types of multi-species agroecosystem. It also links basic research to practical applications in a wide range of systems with or without trees, and considers effects of global change on below-ground interactions. The contents include soil biodiversity and food webs, phosphorus dynamics and mobilization by plants, and crop and tree root-system dynamics. The book will be of significant interest to researchers in plant, crop and soil sciences as well as agroforestry.