The face of farming has been transformed by the industrial production of nitrogen-based fertiliser. But scientists estimate that almost half of the nitrogen spread onto fields is not taken up by crops, and instead washes away.
In this article, Nicola Nosengo reports on the impact this is having on the world's forests. A significant amount of reactive nitrogen ends up in the air as ammonia and nitrogen oxide gases. When the latter dissolves in water vapour it produces nitric acid, which falls to the ground as acid rain.
The effects on forests can already be seen: trees are dying and the relative abundance of different plant species in some woods has started to change. Scientists are planning to propose a protocol to address the issue of nitrogen at a global level at the 3rd International Nitrogen Conference to be held next year in Nanjing, China.
Reference: Nature 425, 894 (2003)