Since the industrial revolution, the need to serial and meat has increased along with the increase in the global population. This resulted in the cropland expansion.

While the use of nitrogen fertilizers significantly increased serial harvest and met the need of residents, it has negative side effects- pollutions in water and atmosphere. Excess nitrogen fertilizer is washed into rivers and lakes resulting in eutrophication. Gaseous ammonia is important precursor of PM2.5, the major particles in smog.

However, the gaseous N₂ released from farmland dos not have any negative effect.

Prof Bai E, assistant WANG Chao and others in the research group of Bio-Geo Chemistry, IAE, cooperated with Prof Benjamin Houlton from UCDAVIS University of California, analyzed nitrogen input and output routs and compared the difference between pre-industrial period (1860) and modern time (2000) on a global scale using N-isotope model and IAMGE model. The results show that from 1860 to 2000, N input in global farmland increased 9 times. The N fertilization increased from 0 Tg N yr-1 to 70Tg N yr-1. The active form N NH₃, N₂O, NO and leached N increased 2.7, 20, and 10 times. The release of inert gas-N₂ increased 13 times. N₂ is only 20% of the whole amount of nitrogen released from cropland, cannot offset the negative effect of released active nitrogen species.

The work was supported by 973 project and  NNSFC Youth Project.

The results were published entitled as Growth in the global N2 sink attributed to N fertilizer inputs over 1860to 2000 in Science of The Total Environment.