Historical global map of NH4+ and NO3- application in synthetic nitrogen fertilizer, link to NetCDF files

This paper provides a method for constructing a new historical global nitrogen fertilizer application map (0.5° × 0.5° resolution) for the period 1961-2010 based on country-specific information from Food and Agriculture Organization statistics (FAOSTAT) and various global datasets. This new map incorporates the fraction of NH+4 (and NONO-3) in N fertilizer inputs by utilizing fertilizer species information in FAOSTAT, in which species can be categorized as NH+4 and/or NO-3-forming N fertilizers. During data processing, we applied a statistical data imputation method for the missing data (19 % of national N fertilizer consumption) in FAOSTAT. The multiple imputation method enabled us to fill gaps in the time-series data using plausible values using covariates information (year, population, GDP, and crop area). After the imputation, we downscaled the national consumption data to a gridded cropland map. Also, we applied the multiple imputation method to the available chemical fertilizer species consumption, allowing for the estimation of the NH+4/NO-3 ratio in national fertilizer consumption. In this study, the synthetic N fertilizer inputs in 2000 showed a general consistency with the existing N fertilizer map (Potter et al., 2010, doi:10.1175/2009EI288.1) in relation to the ranges of N fertilizer inputs. Globally, the estimated N fertilizer inputs based on the sum of filled data increased from 15 Tg-N to 110 Tg-N during 1961-2010. On the other hand, the global NO-3 input started to decline after the late 1980s and the fraction of NO-3 in global N fertilizer decreased consistently from 35 % to 13 % over a 50-year period. NH+4 based fertilizers are dominant in most countries; however, the NH+4/NO-3 ratio in N fertilizer inputs shows clear differences temporally and geographically. This new map can be utilized as an input data to global model studies and bring new insights for the assessment of historical terrestrial N cycling changes.

本研究提出一种构建1961-2010年历史全球氮肥施用图谱（分辨率为0.5°×0.5°）的方法，该方法基于联合国粮食及农业组织统计数据库（Food and Agriculture Organization Statistics, FAOSTAT）的国别信息与多套全球数据集完成构建。该新型图谱通过利用FAOSTAT中的肥料品类信息，纳入了氮肥投入中铵态氮（NH₄⁺）与硝态氮（NO₃⁻）的占比——其中肥料品类可划分为产铵态氮和/或产硝态氮氮肥。数据处理阶段，针对FAOSTAT中缺失的氮肥消费量数据（占全国氮肥消费总量的19%），本研究采用了统计插补方法。多重插补方法借助协变量信息（年份、人口、国内生产总值及作物种植面积）生成合理数值，以此填补时序数据中的空白。插补完成后，本研究将全国消费量数据降尺度至栅格化农田图谱。同时，本研究将多重插补方法应用于已获取的化肥品类消费量数据，以此估算全国氮肥消费中的铵态氮/硝态氮占比。本研究中，2000年的合成氮肥投入量与现有氮肥图谱（Potter等，2010，doi:10.1175/2009EI288.1）在氮肥投入量区间上整体一致。全球范围内，基于补全数据总和估算的氮肥投入总量在1961-2010年间从15 Tg-N升至110 Tg-N。另一方面，全球硝态氮投入量自20世纪80年代末起开始下降，而全球氮肥中硝态氮占比在50年间持续从35%降至13%。多数国家以铵态氮肥为主，但氮肥投入中的铵态氮/硝态氮占比在时间与空间维度上均存在显著差异。该新型图谱可作为全球模型研究的输入数据，为历史陆地氮循环变化评估提供新的研究视角。