Nitrogen Dynamics in Grasslands

Nitrogen is a vital nutrient for all living organisms including grasses and legumes. Grasslands/pastures are the largest land users globally, occupying 3.2 billion ha of the 4.9 billion ha of available agricultural land. Grass produces large amount of plant biomass, and when compared to other crops, it also has the ability to regrow after cutting or grazing. However, to increase its productivity, large quantities of fertilizer are used in grasslands many times. When grassland forage is consumed by livestock, only a small portion of the N contained in the forage is retained by the animal and the majority is excreted through dung and urine. These excreta are returned to grasslands directly during animal grazing or in the form of stored organic fertilizers. The N then undergoes some transformation in the soil by leaching, ammonia volatilization, and denitrification. Some of these transformations in the grassland systems are susceptible to the N loss and result in environmental pollution. Keeping this in view, the available information on grassland N is compiled and discussed in this chapter covering different aspects such as transformation of nitrogen in grassland system, nitrogen-uptake in grasses, influence of nitrogen on forage composition, yield and quality, consumption and utilization of forage N in ruminant animals including toxic effects, N budgeting, environmental impacts of nitrogen applied to grasslands, and future research required.