Improvement of soil fertility is a great benefit of integration of trees in crop fields. Its success depends on efficient use of nutrients in tree biomass. This book addresses this requirement using nitrogen; the most limiting nutrient in the tropics. Efficient N use entails reduction of competition for water and understanding processes and management practices that lead to efficient N use and reduce N losses. Topics covered include biological basis of successful agroforestry systems, control of competition for water; effect of tree pruning on nitrogen contribution in these systems as little is known on how it affects biological nitrogen fixation, BNF; ecological and management factors that influence BNF; a simple nitrogen cycling model, including role of litterfall, the ''albida effect'', the ''safety net phenomenon'', and closed nutrient cycling, and factors that influence decomposition of tree biomass and N contribution, and avenues for N loss; and cardinal management practices that improve efficiency of N contribution from tree biomass. This book is valuable to students of agriculture and forestry, and to professionals involved in advising farmers about agroforestry.