ABSTRACT
Nitrogen (N) management is the most critical component for most agronomic systems. Biological N fixation, ammonification, nitrification, and denitrification are all important components of the soil N cycle which regulate the status of N in terrestrial ecosystems. Rather than relying purely on applications of N fertilizer, alternative N sources are needed to help develop more sustainable farming systems. Nodule-forming legumes have the potential to fulfill this requirement due to the ability of their nodules to fix N biologically from the atmosphere, benefiting not only the legumes themselves but also intercropped plants or subsequent crops. Plants employ various mechanisms in competition to acquire N such as enhanced root growth to enlarge the surface area for uptake, sequestration of N in constituents of the plant, adaptations to minimize N needs and maximize N use efficiency, and, in legumes and a few other plant types, to reduce N with the aid of symbiotic bacteria.
