title: A high-resolution assessment on global nitrogen flows in cropland.
abstract: Crop production is the single largest cause of human alteration of the global nitrogen cycle. We present a comprehensive assessment of global nitrogen flows in cropland for the year 2000 with a spatial resolution of 5 arc-minutes. We calculated a total nitrogen input (IN) of 136.60 trillion grams (Tg) of N per year, of which almost half is contributed by mineral nitrogen fertilizers, and a total nitrogen output (OUT) of 148.14 Tg of N per year, of which 55% is uptake by harvested crops and crop residues. We present high-resolution maps quantifying the spatial distribution of nitrogen IN and OUT flows, soil nitrogen balance, and surface nitrogen balance. The high-resolution data are aggregated at the national level on a per capita basis to assess nitrogen stress levels. The results show that almost 80% of African countries are confronted with nitrogen scarcity or nitrogen stress problems, which, along with poverty, cause food insecurity and malnutrition. The assessment also shows a global average nitrogen recovery rate of 59%, indicating that nearly two-fifths of nitrogen inputs are lost in ecosystems. More effective management of nitrogen is essential to reduce the deleterious environmental consequences.
authors.affiliation: School of Nature Conservation, Beijing Forestry University, Beijing 100083, China. water21water@yahoo.com
authors.forename: Junguo
authors.initials: J
authors.lastname: Liu
authors.forename: Liangzhi
authors.initials: L
authors.lastname: You
authors.forename: Manouchehr
authors.initials: M
authors.lastname: Amini
authors.forename: Michael
authors.initials: M
authors.lastname: Obersteiner
authors.forename: Mario
authors.initials: M
authors.lastname: Herrero
authors.forename: Alexander J B
authors.initials: AJ
authors.lastname: Zehnder
authors.forename: Hong
authors.initials: H
authors.lastname: Yang
mesh_terms: D003247:Conservation of Natural Resources / Q000706:statistics & numerical data*; D018556:Crops, Agricultural / Q000378:metabolism*; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D012987:Soil / Q000032:analysis*
chemical_list: D012987:Soil; D009584:Nitrogen
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