Recent assessments have indicated that most grain cropping systems of Australia (Figure 1-1) are in negative nitrogen (N) balance (Norton and van der Mark 2016, Angus and Grace 2017); that is, more nitrogen is being exported off farm in products than is being applied as fertiliser or through biological dinitrogen (N2) fixation. Therefore, soil N fertility in Australian farms is likely to be declining. While N fertiliser use in Australia has been increasing, it is unlikely to have matched the decline in area under N2-fixing legume-based pastures and the associated increase in cropping in many areas. Nitrogen management is therefore coming into sharp focus.