Spatial trends in the nitrogen budget of the African agro-food system over the past five decades

Low nitrogen (N) fertilization is a dominant cause of malnutrition in Africa, but the spatial and temporal variability of N cycling patterns in Africa remain unclear. This study is the first to perform a detailed analysis of the N cycling patterns of 52 African countries from 1961 to 2016. We calculated the N use efficiency (NUE) in crop production, country-specific N fertilization trends, and the impacts of N fertilization on human protein demand and the environment. Over the past five decades, total N input to African croplands increased from 20 to 35 kg N ha(-1) yr(-1), while the application of synthetic N fertilizers (SNF) increased from 4.0 to 15 kg N ha(-1) yr(-1). N contributions from animal manure and biological N fixation remained lower than 10 kg N ha(-1) yr(-1) and 20 kg N ha(-1) yr(-1), respectively. The totalNcrop production increased from 15 to 22 kg N ha(-1) yr(-1) from 1961 to 2016. Total N surplus in Africa increased from 5 to 13 kg N ha(-1) yr(-1), while estimated gaseous losses increased from 4.0 to 11 kg N ha(-1) yr(-1). However, NUEdeclined from 74% to 63% during the past five decades, and protein consumption increased from 2.99 to 3.78 kg N capita(-1) yr(-1). These results suggest that Africa suffers from extremely lowNinput and thatNloss is increasing in agricultural land. Werecommend the implementation of an effectiveNmanagement strategy incorporating the use of locally available organic material along with the balanced application of SNF. Such measures will require effective policy development and cooperation between all stakeholders.