Nitrogen in Soils - Cycle

Nitrogen (N) is the element most often limiting plant nutrition in terrestrial ecosystems. The greatest source of available N is atmospheric dinitrogen (N 2), which is relatively inert and can only be used by symbiotic and free-living prokaryotic bacteria with the capacity for N 2 fixation ( Table 1 ). For other plants and soil organisms, the slow release of N from rocks and minerals and cycling between organic and inorganic forms in soil is crucial to life. Unfortunately, some aspects of N cycling can be problematic. Nitrogen can be readily lost from terrestrial soils, leading to reduced fertility and surface- or groundwater contamination, and several transformations give rise to intermediate or final products that can have negative environmental consequences.