Nitrogen is a key element in the grassland ecosystem, because of its capacity to limit primary and secondary production. Dormaar et al. determined the effects of grazing on the composition and quantity of nitrogen in the Ah horizon of the rough fescue (Festuca scabrella) grasslands that were stocked at either light (0.8 ha/AUM) or very heavy (0.2 ha/AUM) fixed rates for 38 years and in exclosures located within each field for an equal period of time. Grazing resulted in more NH4+-N and NO3--N in both fields at the time of sampling and each was greater at the higher stocking rate. Although soil N was less mineralizable, it was more acid-hydrolyzable at the higher stocking rate. Time and extent of availability are essential parameters for optimal plant growth.
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