Protecting soil and water from pollution may mean releasing more greenhouse gas.
It was gratifying to see the range of well-argued responses in Correspondence (Nature 427, 99; 200410.1038/427099b) to your News Feature “Fertilized to death” (Nature 425, 894–895; 2003). All the correspondents put forward valid points regarding the pros and cons of nitrogen fertilizer use. However, a key issue was overlooked, that of ‘pollution swapping’.
Pollution of our ground and surface waters by nitrogen fertilizers poses a host of potential environmental problems, including toxic algal blooms and fish kills. Preventing nitrogen fertilizer from leaching into drainage waters, as may be achieved by no-till practices, would therefore seem to be an obvious goal.
Here, though, we run into a real danger of what has become known as ‘pollution swapping’. If the added nitrogen fertilizer is neither taken up by plants nor lost via leaching, then more of it is likely to end up as the powerful greenhouse gas nitrous oxide (A. Mosier et al. Nutr. Cyc. Agroecosyst. 52, 225–248; 1998), through the process of denitrification.
By limiting the pollution of water by nitrogen fertilizers, using so-called ‘buffer strips’ or strategies such as no-till farming, we may simply be swapping a relatively local pollution problem for the global problem of climate change (M. Hefting et al. J. Environ. Qual. 32, 1194–1203; 2003).
Which of these is the more important problem depends on your perspective, and there may be other land-use strategies through which we can limit nitrogen leaching without bumping up emissions of nitrous oxide.
In the end, though, the answer for much of the developed world is likely to be a familiar one — use less fertilizer, but more efficiently.
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