Can nitrogen input mapping from aerial imagery improve nitrous oxide emissions estimates from grazed grassland?

This is the authors' abstract. We don't add key points for this paper.

Most nitrogen (N) lost to the environment from grazed grassland is produced as a result of N excreted by livestock, released in the form of nitrous oxide (N 2 O) emissions, nitrate leaching and ammonia volatilisation. In addition to the N fertiliser applied, excreta deposited by grazing livestock constitute a heterogeneous excess of N, creating spatial hotspots of N losses. This study presents a yearlong N 2 O emissions map from a typical intensively managed temperate grassland, grazed periodically by a dairy herd. The excreta deposition mapping was undertaken using high-resolution RGB images captured with a remotely piloted aircraft system combined with N 2 O emissions measurements using closed statics chambers. The annual N 2 O emissions were estimated to be 3.36 ± 0.30 kg N 2 O–N ha −1 after a total N applied from fertiliser and excreta of 608 ± 40 kg N ha −1 yr −1 . Emissions of N 2 O were 1.9, 3.6 and 4.4 times lower than that estimated using the default IPCC 2019, 2006 or country-specific emission factors, respectively. The spatial distribution and size of excreta deposits was non-uniform, and in each grazing period, an average of 15.1% of the field was covered by urine patches and 1.0% by dung deposits. Some areas of the field repeatedly received urine deposits, accounting for an estimated total of 2410 kg N ha −1 . The method reported in this study can provide better estimates of how management practices can mitigate N 2 O emissions, to develop more efficient selective approaches to fertiliser application, targeted nitrification inhibitor application and improvements in the current N 2 O inventory estimation.