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Worldwide increases in nitrogen (N) inputs to croplands have been and will continue to be an important contributor to growing more food. But a substantial portion of N inputs to croplands are not captured in harvested products and leave the field, contributing to air and water pollution. Whether the proportion of N inputs captured in harvest grows, shrinks, or remains unchanged will have important impacts on both food production and N pollution. We created a new global N input database (fertilizer, manure, fixation, deposition, and residues) that enables evaluation of trends in nitrogen use and recovery by country and by crop from the 1960s through 2007. These data show that despite growth in yields and increased N fertilization, differences in efficiency of N use between Organisation for Economic Co‐operation and Development (OECD; http://www.oecd.org ) and other countries have persisted over nearly 50 years and exhibit no sign of convergence. The high yield, high nitrogen input systems characteristic of rich countries have released large amounts of reactive N to the environment but have operated with greater efficiency—recovering a greater portion of added N in crops. Aggregate yields in OECD countries are 70% greater than in non‐OECD countries on N input rates just 54% greater. Variation in recovery efficiency between countries suggests that there is scope for improvements through enhanced N delivery and capture in the world's low‐yielding croplands and that increasing efficiency of N use is an important component of meeting food demand in the future.
Conant et al. (Sat,) studied this question.