50 year trends in nitrogen use efficiency of world cropping systems: the relationship between yield and nitrogen input to cropland

Nitrogen (N) is crucial for crop productivity. However nowadays more than\nhalf of the N added to cropland is lost to the environment, wasting the\nresource, producing threats to air, water, soil and biodiversity, and\ngenerating greenhouse gas emissions. Based on FAO data, we have\nreconstructed the trajectory followed, in the past 50 years, by 124\ncountries in terms of crop yield and total nitrogen inputs to cropland\n(manure, synthetic fertiliser, symbiotic fixation and atmospheric\ndeposition). During the last five decades the response of agricultural\nsystems to increased nitrogen fertilization has evolved differently in the\ndifferent world countries. While some countries have improved their agroenvironmental\nperformances, in others the increased fertilization has\nproduced low agronomical benefits and higher environmental losses. Our\ndata also suggest that, in general, those countries using a higher\nproportion of N inputs from symbiotic N fixation rather than from synthetic\nfertilizer have a better N use efficiency.