Exploring the Trends in Nitrogen Input and Nitrogen Use Efficiency for Agricultural Sustainability

Crop production is threatened by the increased nitrogen (N) input and declining N use efficiency (NUE). Information on total N input from planted seeds/tubers, atmospheric deposition, irrigation water, crop residues, animal manure, biological N fixation, and synthetic N fertilizer and NUE based on these N inputs in China’s crop production is limited. We calculated the amount of various N inputs and NUE based on 117 primary crops from 1961 to 2012 in China. The total N input increased from 8.0 Mt in 1961 to 60.8 Mt in 2012. The substantial shift in the types of N input was observed from animal manure and biological N fixation toward synthetic N fertilizer. Animal manure plus biological N fixation and synthetic N fertilizer accounted for 70.9% and 6.8% of total N input in 1961, respectively, and these values were changed to 15.7% and 74.0% in 2012. Partial factor productivity of applied synthetic N and crop’s recovery efficiency of total N input declined substantially during the study period. These results suggest that it is essential to reduce synthetic N input and increase NUE with improved crop management practices and N-efficient crop varieties to achieve the sustainability of crop production in China.