Long Term trends in agronomical and environmental performances of world cropping systems: The relationship between yield and nitrogen input to cropland at the country and regional scales

Abstract

Nitrogen (N) is one of the main production factors in agricultural systems and has to be properly managed to sustain crop yields. Nowadays more than half of the N added to cropland is lost to the environment, wasting the resource, producing threats to air, water, soil and biodiversity, and generating greenhouse gas emissions. Based on FAO data of the past ~ 50 years (1961-2009 period), we have reconstructed the trajectory followed by 124 countries in terms of crop yield (expressed in nitrogen) and total nitrogen inputs to cropland (synthetic fertilizer, manure, symbiotic fixation and atmospheric deposition). During the past five decades the response of cropping systems to increased nitrogen fertilization has evolved differently between world countries. While some countries have improved their agro-environmental performances, in others the increased fertilization has produced low agronomical benefits and higher environmental losses. Despite very significant improvements in N use efficiency in several countries, N losses above recommendable levels are still frequently observed. Our data also suggests that, in general, those countries using a higher proportion of N inputs from symbiotic N fixation rather than from synthetic fertilizer have a better N use efficiency. By evidencing the long-term response of N inputs to the soil in terms of production and potential losses to the environment, this chapter provides a summarised and comprehensive diagnosis of the effective changes in agronomical and environmental performances of the cropping systems of 124 countries, as well as of the corresponding aggregated values for 12 macro-regions of the world.