Agroforestry and opportunities for improved nitrogen management

Multi-species systems include herbaceous mixtures (cover cropping, living mulches, intercropping), woody mixtures and herbaceous-woody mixtures, i.e., “agroforestry”. Agroforestry systems have particular potential to improve nitrogen (N) availability to both the tree and herbaceous components, and to increase N-conservation and recycling. This is achieved through the following: (a) deeper and more extensive root distributions, (b) greater root and shoot turnover, (c) N-fixation in either tree or crop roots, (d) facultative mycorrhizal associations, (e) greater interception of light and water resources, (f) improved soil structure and organic matter content, and (g) control of erosion and leaching. Ammonia recapture by tree-foliage from livestock emissions reduces N deposition on nearby sensitive ecosystems, and contributes to reductions in net N2O emissions. Trees, especially if they are not N-fixers, are also likely to reduce soil N2O emissions by drying the soil, increasing soil-aeration, and removing excess nitrate concentrations throughout most of the year. Agroforestry is identified as one of the best options for climate change mitigation and adaptation, but more measurements are required on fluxes of N2O and CH4 from agroforestry systems of different type and age.