Excess N application on agricultural land greatly impacts the environment in multiple ways, driven by population growth and improving quality of human diets. Therefore, it is essential to quantify the sources of the emissions of N compounds and their determinants (e.g. biological N fixation (BNF), mineral fertilizer, manure N and N deposition) to develop adequate mitigation measures. Here we aim at comprehensively mapping and quantifying N fluxes on agricultural land to analyze these sources on different scales. As underlying grazing land maps used for such calculations are fairly different in terms of methodology and definition and thus spatial extent and pattern, we investigate how this diversity in grazing land maps affects quantification of N indicators. We compared three different global grazing land maps and analyzed the propagation of differences to discrepancies in N indicators calculated from them. We discovered that (i) area differences propagated to high discrepancies in N surplus mostly in Asia, and to a minor extent also in Europe and Northern Africa. (ii) BNF constitutes an important translator for differences on grazing land to N indicators, while also being a source of further uncertainty, which warrants further scrutiny. (iii) A more inclusive definition of grazing land results in overall less N surplus given the larger areas included but allows to provide a more comprehensive estimate of the influence of human activity on the N cycle. This study is the first to provide an in-depth analysis of the effect of grazing land and agricultural land area differences on various N budget terms and N indicator calculation, highlighting opportunities for further research, and the importance of a comprehensive accounting of N surplus when using an inclusive definition of grazing land.

在人口增长和人类饮食质量提高的推动下，农业用地过量施氮会对环境产生多种影响。因此，必须量化氮化合物的排放源及其决定因素（例如生物固氮（BNF）、矿物肥料、粪肥氮和氮沉积），以制定适当的缓解措施。在这里，我们旨在全面绘制和量化农业用地的 N 通量，以在不同尺度上分析这些来源。由于用于此类计算的基本放牧地图在方法和定义以及空间范围和模式方面相当不同，我们研究了放牧地图的这种多样性如何影响 N 指标的量化。我们比较了三种不同的全球放牧地图，并分析了差异与 N 指标差异的传播情况。我们发现 (i) 面积差异主要在亚洲传播到 N 盈余的高差异，在欧洲和北非也有小部分。(ii) BNF 是将牧场差异转化为 N 指标的重要转换器，同时也是进一步不确定性的来源，需要进一步审查。(iii) 考虑到包含的面积更大，对放牧地的更具包容性的定义会导致总体氮盈余减少，但允许对人类活动对氮循环的影响提供更全面的估计。