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A high-resolution assessment on global nitrogen flows in cropland
- Liu, Junguo, You, Liangzhi, Amini, Manouchehr, Obersteiner, Michael, Herrero, Mario, Zehnder, Alexander J.B., Yang, Hong
- Proceedings of the National Academy of Sciences of the United States of America 2010 v.107 no.17 pp. 8035-8040
- agricultural land, agricultural soils, nitrogen, biogeochemical cycles, biogeochemistry, soil nutrient dynamics, nitrogen fertilizers, losses from soil, soil nutrient balance, soil fertility, nutrient offtake, harvesting, crops
- 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.