Management options to reduce nitrous oxide emissions from intensively grazed pastures: A review

Nitrous oxide (N 2 O) emissions from grazed pastures represent a significant source of atmospheric N 2 O. With an improved understanding and quantification of N sources, transformation processes, and soil and climatic conditions controlling N 2 O emissions, a number of management options can be identified to reduce N 2 O emissions from grazed pasture systems. The mitigation options discussed in this paper are: optimum soil management, limiting the amount of N fertiliser or effluent applied when soil is wet; lowering the amount of N excreted in animal urine by using low-N feed supplements as an alternative to fertiliser N-boosted grass; plant and animal selection for increased N use efficiency, using N process inhibitors that inhibit the conversion of urea to ammonium and ammonium to nitrate in soil; use of stand-off/feed pads or housing systems during high risk periods of N loss. The use of single or multiple mitigation options always needs to be evaluated in a whole farm system context and account for total greenhouse gas emissions including methane and carbon dioxide. They should focus on ensuring overall efficiency gains through decreasing N losses per unit of animal production and achieving a tighter N cycle. Whole-system life-cycle-based environmental analysis should also be conducted to assess overall environmental emissions associated the N 2 O mitigation options.