GHG emissions from agriculture (such as
N2O and CH4) are some of the most difficult
to reduce. In the energy sector, humanity
needs to perform one action: Stop burning
fossil fuels. And, at least in principle, there
are clean-energy alternatives. In agriculture,
many different actions are required. There is
no alternative to eating.
Nevertheless, we can begin to structure
our thinking about solutions for the sector
in a way that mirrors the fuel-switching solutions for other GHG sources—a rule of thumb
that everyone from policy-makers to farmers,
communities, and even children can comprehend and help put into practice.
Among policy-makers and researchers in-
terested in decarbonization, there is a rough
but useful slogan: “Clean up the grid and
electrify everything.” The slogan is not per-
fect. There are industrial processes, such as
steel and cement production, where fossil-
fuel use is not the main GHG culprit. But as
a heuristic, the slogan works well. A similar
heuristic is used in nitrogen management: ni-
trogen use efficiency (NUE), which tradition-
ally refers to product produced per unit of
nitrogen fertilizer or manure. It makes sense
to focus on increasing NUE as more than 60%
of coastal nitrogen pollution globally comes
from nitrogen losses from crop and livestock
production (4). The NUE of U.S. maize pro-
duction at the national scale and of Asian rice
at plot scale have been improved by 36% and
30%, respectively (5, 6). Agriculture-intensive
Denmark has halved nitrogen loss to the
aquatic environment without decreasing ag-
ricultural output (7). But in such places, the
lowest-hanging fruit has been picked; further
reductions require greater expense and tech-
The NUE concept is now being extended
to the entire nitrogen budget, including cutting food waste and increasing recovery of nitrogen from compost, effluents, and sewage
for reuse. Many exciting prospects are still
on the lab bench, but real breakthroughs are
likely in coming years. However, technical,
commercialization, and public acceptance
hurdles remain. For example, the genetic
modification of cereals such that they can
“fix” nitrogen gas into biochemically useful
forms, thus reducing the need for fertilizer
use, remains a substantial challenge (8). Genetically modified organisms also often face
resistance from civil society.
In sewage treatment facilities, potentially
useful nitrogen compounds (such as ammonia and nitrate) are either discharged to
the environment or converted to nitrogen
gas and thus lost to the air. Instead, these
compounds could be converted to protein
by microbes, which could then be harvested
and recycled for animal feed or food (9),
thus reducing nitrogen fertilizer use, eutrophication, and N2O production. This
short-circuiting of the nitrogen cycle is already used to produce feed in aquaculture,
but wide use will need to overcome public
reluctance regarding the use of bacteria to
produce food from sewage.
Livestock and their feed production are
responsible not only for a large portion of
coastal nitrogen loading but also for 18%
of GHGs worldwide (37% of methane emis-
sions, 65% of N2O emissions) (10). “Cultured”
meat produced in the laboratory may help to
reduce these emissions; however, such meat
may be a decade or two away from commer-
cial viability. Moritz et al. have produced lab-
grown hamburgers and claim that the world’s
current 1.5 billion heads of cattle could be
reduced to 30,000, a herd of donor animals
from which stem cells are extracted (11, 12).
Public perceptions must be carefully man-
aged to overcome fears of “frankenfoods.”
Minimizing coastal eutrophication while
increasing global food production and de-
creasing GHG emissions will require efficient
nitrogen management in agriculture, maxi-
mizing nitrogen recycling and reuse, changes
in diet (13), and development and adoption
of new technologies. The global nature of the
challenge requires sharing of best practices
and technology, with a more direct interface
between scientists and policy-makers. The
International Nitrogen Initiative (INI) (14)
aims to provide such an interface. INI has
developed an international community of sci-
entists and representatives from farmers, in-
dustry, and governments to share knowledge
toward optimizing nitrogen use in food and
energy production and minimizing conse-
quent harm to humans and the environment.
Linked to INI is the newly formed Interna-
tional Nitrogen Management System (15), a
structured process of science support for pol-
icy and practice development with a goal to
improve economy-wide NUE while reducing
nitrogen pollution. One of their first regional
demonstrations is in South Asia.
Although the challenges are great, successful commercialization of technologies
currently in development and increased nitrogen efficiency in agriculture could help to
reduce the pressures on coastal ecosystems
and to reduce GHG emissions while permitting increased production to feed a growing
population. There is potentially an exciting
optimistic story to be told about global nitrogen stewardship in the Anthropocene. j
REFERENCES AND NOTES
1. The Ocean Conference, United Nations, New York, 5 to 9
June 2017; https://oceanconference.un.org.
2. E.Sinha,A.M.Michalak, V.Balaji, Science 357, 405(2017).
3. O. Edenhofer et al., Climate Change 2014: Mitigation of
Climate Change. Contribution of Working Group III to the
Fifth Assessment Report of the Intergovernmental Panel on
Climate Change (IPCC, Cambridge Univ. Press, 2014).
4. S.P.Seitzinger et al., Global Biogeochem. Cycles 24,
5. K.G.Cassman, A.Dobermann,D. T. Walters, Ambio 31,132
6. A. Dobermann et al ., Field Crops Res. 74, 37 (2002).
7. N. J. Hutchings et al ., Environ. Res. Lett.9, 115012 (2014).
8. E. Stokstad, Science 353, 1225 (2016).
9. S.Matassa, D.J.Batstone, T.Hülsen, J.Schnoor,
W. Verstraete, Environ. Sci. Technol. 49, 5247 (2015).
10. Food and Agriculture Organization, Livestock’s Long
Shadow (FAO, Rome, 2006); www.fao.org/docrep/010/
11. M. S. M. Moritz, S. E. L. Verbruggen, M. J. Post, J. Integr.
Agric. 14, 208 (2015).
12. “Meet the new meat” (2016); https://youtu.be/
13. L. Lassaletta et al ., Environ. Res. Lett. 11, 095007 (2016).
14. International Nitrogen Initiative; www.initrogen.org.
15. International Nitrogen Management System; www.inms.
From 2008 until 2015, S.P.S. was the director of the International
Geosphere-Biosphere Program (IGBP), which cosponsored the
INI. As director of IGBP, she approved the appointment of the
28 JULY 2017 • VOL 357 ISSUE 6349 351 SCIENCE sciencemag.org
A massive algal bloom caused by nitrogen
pollution spreads through the James River in
Pacific Institute for Climate Solutions, University of Victoria,
Victoria, BC, Canada. Email: email@example.com