This text presents an authoritative and comprehensive review on soil/plant nitrogen inter-relationships, with special reference to tropical soils and crops in aerobic and anaerobic environments. Use of isotopically labelled nitrogen in experimentation, especially in tropical environments, and recently developed analytical techniques for soil and plant materials are presented. An important aspect is the emphasis placed on the impact of the tropical environment on nitrogen transformations in the soil environment. This book should be a source of information for senior undergraduate and graduate students with interest in soil/plant nitrogen inter-relationships, and for all levels of research workers in these fields.