Nitrogen cycling in intensively grazed pastures and practices to reduce whole‐farm nitrogen losses

摘要

1.A large proportion of the N ( ＞ 70% ) consumed by grazing animals is excreted and this excreta is the main source of N losses from grazed pastures by ammonia (NH3 ) volatilisation, nitrous oxide (N2 O) emission and nitrate (NO-3 ) leaching.2.Management strategies and practices that can reduce N losses in grazing systems include optimising N inputs, manipulating soil N cycling processes, selecting for plants and animals that maximise N utilisation and altering grazing and feeding management.3.Using stand‐off/feed pads or housing systems for removing grazing animals off pasture during greatest risk periods of N loss can reduce excreta deposition to soil at these times, thereby reducing N leaching and N2 O emissions.However, NH3 losses as a result of.N pollution swapping" need to be controlled.4.Mitigation strategies and practices always need to be evaluated in a whole farm system context to ensure overall efficiency gains through decreasing N losses per unit of animal production and to achieve a tighter N cycle.