There are good, and
frightening, reasons to closely follow the changes in the nitrogen cycle. We
should not be surprised if the effects and costs of disturbing it turn out to
be as dramatic as those for the carbon cycle. In addition, greenhouse gas
emissions from nitrogen fertilizers are around 3% of global emissions, but they
are not visible in greenhouse gas inventories. The abolition or drastic
reduction in the use of chemical fertilizers is a pre-condition for a
sustainable food system.
In farming, the availability of nutrients, particularly of
nitrogen, potash and phosphorus – mostly referred to by their chemical symbols
N, P and K – is a major limiting factor. All traditional farming systems have
had some strategy for replacing nutrients in the soil. One is to rest the soil
and allow a natural re-charge and release of nutrients from the soil and
through atmospheric decomposition. Crop rotations with leguminous crops can fix
nitrogen from the air and the nutritional demands of the various crops can
complement each other. Phosphorous, from deeper layers or bound in the soil,
can be ‘mined’ by some crops making it available to others. Nutrients can also
come from irrigation water (especially sediments in flood waters), animal
manure, human waste, plants, grass and other residues, a plethora of natural
organic fertilizers. Farmers have used oil-cakes, feathers, leathers, bone,
sea weed and fish as fertilizers. There are even reports that human remains
from battlefields and ossuaries have been used as fertilizers. Yet all these
methods have some limitations, and in most cases they require a lot of work or
other efforts.
 | |||
| A farming system dependent on and caused by synthetic fertilizers, Mato Grosso, Brazil Photo: Gunnar Rundgren |
It is therefore no wonder that the farmers of the world took
to artificial fertilizers with enthusiasm. They are easier to transport than
bulky organic materials such as manure, easier to apply and give somewhat
predictable results. Global annual use of nitrogen fertilizers increased from
11 million tons in 1960 to 115 million tons in 2017. Contrary to common belief
most of the fertilizers are not used to replace what is removed by the crop
from the field. The quantities applied mostly surpass this many times. Most
nitrogen is simply wasted through denitrification, leaking, erosion and
volatilization of ammonia.[i]
According to David Montgomery, an American soil scientist, half of the
fertilizer used in the United
States is used to compensate the nutrient
losses caused by erosion. Globally, the nitrogen efficiency in grain production
has deteriorated drastically and rapidly (probably mostly a result of
decreasing marginal return). Around 1960, each ton of chemical fertilizer
resulted in an increase in grain yield of 75 tons, whereas at the end of 1990
this resulted in just 25 tons.[ii]
The greatest single
experiment in global geoengineering ever made
Reflecting on his promotion of chemical fertilizers von
Liebig exclaimed: “I have sinned against the wisdom of the Creator and,
justly, I have been punished. I wanted to improve his work because, in my
blindness, I believed that a link in the astonishing chain of laws that govern
and constantly renew life on the surface of the Earth had been forgotten. It
seemed to me that weak and insignificant man had to redress this oversight.”[iii]
Had von Liebig lived now, he would be even more worried and remorseful.
The quantity of biologically active nitrogen released
annually into the biosphere has increased nine-fold in 100 years and
nitrogenous fertilizers are the main source of this. In one of the most
influential scientific articles of last decade, Planetary boundaries:
Exploring the safe operating space for humanity, professor Johan Rockström
and colleagues identify the nitrogen cycle as one of three areas – together
with climate regulation and biological diversity – where modern civilization
has surpassed a threshold for stable development.
Without knowing it, the average European bears costs of over
€500 per year for farmers’ use of Nitrogen fertilizers. The European
Nitrogen Assessment[iv]
recognizes that synthetic
nitrogen fertilizers have huge advantages but also notes that their use comes with
a huge price tag. The report states that the increased level of biologically
active nitrogen in the biosphere might represent “the greatest single
experiment in global geoengineering ever made”. For a farmer it is profitable
to use nitrogen fertilizer; the return of one Euro invested in nitrogen fertilizer
is estimated at between two and five Euros. But someone else pays a bigger
bill. “Environmental damage related to nitrogen effects from agriculture in the
EU-27 was estimated at €20-€150 billion per year. This can be compared with a
benefit of N-fertilizer for farmers of €10-€100 billion per year, with
considerable uncertainty about long-term N-benefits for crop yield”.[v]
The damage caused by fertilizers includes a wide range of
direct and indirect effects. Increased concentrations of nitrogen and
phosphorus in the biosphere are two of the most important drivers of changes
in ecosystems. Nitrogen plays a role in the formation of tropospheric ozone,
which damages crops and plants.[vi]
Chemical fertilizers have enabled farmers to skip sound crop rotations and to
monocrop, which leads to a reduction of carbon content in soils. Globally, the
discharge of nitrogen to the sea increased by 80% between 1860 and 1990. This
run-off changes species composition and stimulates algal blooms and the
associated dead zones.[vii]
In the United States, the Mississippi, the Columbia,
and the Susquehanna rivers together discharge approximately 1 million tons of
nitrogen (in the form of nitrates) per year to coastal waters – about 10% of
all nitrogen applied in the country.[viii]
Globally, about four hundred coastal areas are now periodically or constantly
oxygen-depleted as a result of fertilizer run-off, sewage discharge and the
combustion of fossil fuels.[ix]
The use of chemical fertilizers has also led to harmful levels of nitrates in
some drinking water.[x]
Huge greenhouse gas
emissions
Counting the emissions in the whole lifecycle, nitrogen
fertilizers is the single biggest source of greenhouse gas emissions in
agriculture. Emissions are caused by the use of fossil fuels, mostly natural
gas, in the production of the fertilizers. There are emissions of carbon
dioxide, laughing gas (nitrous oxide) and methane emitted in the production of
fertilizers. Recent research in the US[xi]
shows that methane leaks from fertilizer factories to a much larger extent than
earlier estimated. There are emissions from the transportation and application
of fertilizers and there are huge emissions of laughing gas from fields where
artificial fertilizers are used; through denitrification, much nitrogen is lost
as nitrogen gas which in essence is harmless, but some is emitted as laughing
gas, a potent greenhouse gas.[xii]
Despite this, there are no figure of the emissions from
nitrogen fertilizers in the IPCC reports or national greenhouse gas
inventories. The emissions are allocated to other categories and therefore they
are invisible. The emissions from the
production is allocated to industrial processes, the emissions from transports
to transport, the emissions from application is under agriculture and the huge
emissions of laughing gas from agriculture land caused by chemical fertilizers
are booked under emissions from agricultural soils. But the total emissions of
global use of nitrogen fertilizers corresponds to 3% of all emissions, roughly equal
to global aviation emissions.
Global emissions from nitrogen fertilizers
Global consumption of N in
fertilizers according to FAO: 115 million ton.
For the production we can
use 6 kg CO2e per kg of N, which was the
European average ten years ago, most likely a bit lower than the current
global average: 115*6 = 690 million ton. Note that these figures don’t include methane
emissions, which according to the new US research might be substantial.
For the use phase: 115 million
ton N * 1 % IPCC:s emission factor * 44/28 (this converts N to laughing gas) *
298 (IPCC factor for conversion of laughing gas to carbon dioxide equivalents):
115*1%*44/28*298 = 538 million ton for the emissions from agriculture soils
caused by N-fertilizers.
Adding rough estimates for
transportation and application we reach somewhere above 1,400 million tons in
total.
Source: own calculations
Can we do without
them?
It is often claimed that nitrogen fertilizers feed half of
the world’s population. There should be no doubt about the importance of
chemical fertilizers, but this figure is based on erroneous assumptions. If you
just cut away fertilizers from the existing systems yields would certainly
plummet, perhaps even by half, but such a scenario is not realistic. In the
same way as farmers have adjusted their production to the availability of cheap
fertilizers, they would make adjustments to deal with a situation without (or
with less) nitrogen fertilizers. That is exactly what organic farmers do and
their yields are rarely that low.
Chemical fertilizers are not (yet) essential for feeding the
world or for human survival, but they are essential for the global model of
commercial agricultural production. They allow farmers – even whole regions or
countries – to specialize in certain crops. They also allow farmers to skip
crop rotations and focus on the commercially most interesting crops. Other
areas develop industrial livestock operations, based on feed bought in from the
specialized crop farm areas. Chemical fertilizers also enable cities to grow
without giving any thought to recycling their waste. Buying fertilizers is also
consistent with the ever increasing commercialization of farming. Because of
the changes in production, monocropping and linear flows, pests and weeds
become more prevalent, which makes farmers dependent on herbicides and biocides.
In this way chemical fertilizers are one of the major building blocks of the
modern food system. And the abolition or drastic reduction in the use of chemical
fertilizers is a pre-condition for a sustainable food system.
It is doable on the farm lever as demonstrated by millions
of farmers in all agro-ecological zones of the world. In all likelihood it is
also doable in the global level. In the report, The future of food and agriculture –
Alternative pathways to 2050, FAO outlines a scenario they call “towards
sustainability” in which chemical fertilizers are no longer used while global food
production is sufficient.
[i] Millenium Ecosystem Assessment 2005 Millennium
Ecosystem Assessment: Ecosystems and human well-being–synthesis World
Resource Institute.
[ii] IAASTD
2009 Agriculture at a Crossroads: Global Report International Assessment
of Agricultural Knowledge, Science and Technology for Development.
[iii] Liebieg,
J. von. 1865 Agrikulturchemie.
[iv] European
Science Foundation 2013 ‘Nitrogen in Europe, Current problems and future
solutions’ part of The European Nitrogen Assessment www.nine-esf.org.
[v] Ibid.
[vi] Millenium
Ecosystem Assessment 2005 Millennium Ecosystem Assessment: Ecosystems and
human well-being–synthesis World Resource Institute.
[vii] Ibid.
[viii] USDA
2013 Fertilizer Use and Price
www.ers.usda.gov.
[ix] UNEP
2010 UNEP Year Book 2010: New science and developments in our changing
environments United Nations
Environment Programme.
[x] Millenium
Ecosystem Assessment 2005 Millennium Ecosystem Assessment: Ecosystems and
human well-being–synthesis World Resource Institute.
[xi] Zhou, X., Passow, F.H., Rudek, J., von Fisher, J.C.,
Hamburg, S.P. and Albertson, J.D., 2019. Estimation of methane emissions from
the U.S. ammonia fertilizer industry using a mobile sensing approach. Elem
Sci Anth, 7(1), p.19. DOI: http://doi.org/10.1525/elementa.358
[xii] Ayres,
R. U. (editor) 1998 Eco-Restucturing: Implications for sustainable
development United Nations University Press.
