Quantifying nitrogen deposition inputs to cropland: A national scale dataset from 1961 to 2020

Nitrogen (N) deposition is one of the major inputs to cropland and
consequently important for the estimation of N Use Efficiency (NUE) for
crop production. However, the estimates for N deposition carry large
uncertainty, and existing assessments of N budgets and NUE on agricultural
land use different estimates of N deposition. To evaluate the
uncertainties in existing methods for national scale N deposition
estimation and assess their impacts on the resulting NUE estimation for
countries around the world, we 1) reviewed existing methods and related
data sources for quantifying N deposition inputs to crop production on a
national scale; 2) identified the most up–to–date data sources and
designed methods to quantify N deposition input to crop production on a
national scale; 3) collected N deposition data from observation sites in
major countries (e.g., UK, US, and China) to validate the estimated N
deposition input; and 4) conducted sensitivity analysis to evaluate how
the uncertainties in N deposition affect crop NUE assessment. As a result,
we established four estimates for N deposition inputs on cropland for 251
countries around the world during 1961–2020 as combinations of two sets of
N deposition maps (ACCMIP1 and Wang et al.2-4) and two sets of cropland
maps (HYDE5 and LUH26). The four products (1. AH: ACCMIP and HYDE, 2. AL:
ACCMIP and LUH2, 3. WH: Wang et al. and HYDE, and 4. WL: Wang et al. and
LUH2) show good agreement in N deposition estimates for the majority of
countries, but have large differences in several Asian countries (e.g.,
China, India, and Pakistan), and the differences are mostly caused by the
use of different N deposition maps. According to the comparison with the
observation records in China, the deposition estimates based on Wang et
al. show a better agreement with the observations. Hence, the
authors recommend using product #4 WL (Wang et al. and LUH2) as the
reference dataset for N deposition in the global assessments of N budgets
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