The authors used both a "top-down" (from an atmospheric model) and "bottom-up" (e.g. scaling-up local flux measurements) approaches, and come to remarkably similar agreements in the total N2O emissions between 2007 and 2016: 16.9 Tg N for the former and 17.0 for Tg N the latter.
The authors also looked at how N2O emissions vary geographically. They found that while Africa and South America have seen the largest increases in N2O emissions over the past decade, there still is work to be done sourcing N2O from these regions as their different modelling methods showed less agreement. Currently, it is suspected that N2O emissions in these regions are largely from tropical forest soils, livestock, and manure compared to synthetic N fertilizer applications in East Asia, North America, and Europe.