Nitrogen use efficiency in grain production and the estimated nitrogen input/output balance in China agriculture.

BACKGROUND: Understanding the nitrogen (N) use efficiency and N input/output balance in the agricultural system is crucial for best management of N fertilisers in China. RESULTS: In the last 60 years, N fertiliser consumption correlated positively with grain production. During that period the partial factor productivity of N (PFPN ) declined greatly from more than 1000 kg grain kg⁻¹ N in the 1950s to nearly 30 kg grain kg⁻¹ N in 2008. This change in PFPN could be largely explained by the increase in N rate. The average agronomic efficiency of fertiliser N (AEN ) for rice, wheat and maize during 2000-2010 was 12.6, 8.3 and 11.5 kg kg⁻¹ respectively, which was similar to that in the early 1980s but lower than that in the early 1960s. Estimation based on statistical data showed that a total of 49.16 × 106 t of N was input into Chinese agriculture, of which chemical N, organic fertiliser N, biological fixed N and other sources accounted for 58.2, 24.3, 10.5 and 7.0% respectively. Nitrogen was surplus in all regions, the total N surplus being 10.6 × 106 t (60.6 kg ha⁻¹). CONCLUSION: The great challenge is to balance the use of current N fertilisers between regions and crops to improve N use efficiency while maintaining or increasing crop production under the high-intensity agricultural system of China.